Fats and Fatty Foods

8 Fats and Fatty Foods INTRODUCTION World production of fats and oils has continued to increase in recent years (Table 8.1). Soya-bean oil remains the leading oil but sunflower-seed, palm and rapeseed oils have increased markedly. Increased acreages planted with soya beans, sunflowers and oilseed rape have contributed to the increased production of oils from these plants, but the increase in production of palm oil is largely due to improved yield resulting from modern plant breeding techniques. The development and propagation of higher yielding oil palms has played a major role in increased oil production by Malaysia. Rapeseed oil low in antinutritional components has gained acceptance as an edible oil and there have been big increases in the acreage of oilseed rape in Europe and Canada. Genetic modification of other plants has led to modifications in oil composition including the development of high oleic sunflower oil and high oleic linseed oil. Table 8.1 World production of major vegetable and animal oils Thousands of metric tonnes (of oil or fat) Soya-bean Cottonseed Groundnut Sunfiowerseed Rape Olive Coconut Palm Palm kernel oil Other vegetable oils Butterfat Lard Tallow and grease 1985/86 1987/88 1989/90 14236 3700 3324 6894 6426 1870 3334 7924 992 2754 6493 5092 6488 15530 3593 3489 7557 7842 2198 2937 8575 1152 2965 5386 5386 6773 16123 3588 3787 7767 8025 1736 3187 10917 1421 2995 5344 5344 6559 From Oils and Fats International Directory, 1991, International Trade Publications, Redhill, UK. Dietary advice from many quarters continues to recommend that the total fat content of Western diets should be reduced and this has led to large M. D. Ranken et al. (eds.), Food Industries Manual © Springer Science+Business Media New York 1993 increases in the production and sales of low-fat foods including low-fat spreads and low-fat cheese. ACETOGLYCERIDES Acetoglycerides are fatty acid glycerides in which at least one of the hydroxyl groups of the glyceride molecule is esterified with acetic acid. Thus, acetostearin, acetopalmitin and aceto-olein are names used to describe acetoglyceride mixtures in which the predominant acid present in addition to acetic acid is stearic, palmitic or oleic acid, respectively. Acetoglycerides are manufactured either by direct acetylation of partially esterified glycerides with acetic acid, or by interesterification of appropriate oils and fats with triacetin. Acetoglycerides possess unusual physical properties which are valuable in food products. They are non-greasy, waxy, translucent solids which are highly flexible and can be formed into films that will bend without cracking. This is due to the existence of acetoglycerides in a stable ex-polymorphic form, which contrasts with that of most other fats. Acetoglycerides are low-melting and are generally stable to heat and oxidation. Because of their physical nature they are suitable as edible coatings for food products. They can be applied by dipping and are preferred to paraffin wax for two reasons. On one hand, they are less brittle and, on the other hand, they have an enhanced consumer appeal over that of paraffin wax, which is criticized by some customers who doubt the wisdom of using mineral hydrocarbons in foods. Acetoglycerides can be blended with hard fats and so they have been used to coat cheese, nuts, chocolate pieces, meat, and poultry. When blended with hard fats, acetoglycerides form eutectics with other glycerides in much the same way as oleic acid glycerides. In fact, the acetic acid chain appears to influence the interaction of acetoglycerides in FATS AND FATTY FOODS determining eutectic or solid solution behaviour in much the same way as an oleic chain in the corresponding oleic glyceride. Acetoglycerides are useful constituents of shortenings and increase the plastic range of the shortening; that is, they reduce the tendency of the shortening to be too hard at low temperatures and too soft at high temperatures. They are also said to confer improved spreadability in margarine, perhaps due to their eutectic forming behaviour. Their use as salad oils and mayonnaise substitutes has also been suggested. Confectionery uses of acetoglycerides include use as an enrobing fat for chocolate, as slab dressings and mould release agents and as a substitute for chicle. In baking they can be used as pan release agents. The physiological properties of acetoglycerides appear to be similar to those of the conventional long-chain triglycerides, while digestibility compares favourably with that of a commercial shortening. Acetoglycerides are permitted food additives in the EC, USA, Canada and New Zealand. AFLATOXINS In the early 1960s a large number of turkey poults died of liver damage due to feeding with a meal derived from mould-infested groundnuts. The mould, Aspergillus flavus, had produced a toxin, subsequently named aflatoxin, in the groundnut kernels, and this had remained in the groundnut kernels during oil extraction and finally appeared in the meal fed to the turkey poults. It was subsequently realized that this is a more general problem, and toxic materials produced by the growth of mould on foods are now known as mycotoxins. They are seldom a problem in refined oils and fats, as the neutralization, bleaching, and deodorization steps fully remove any mycotoxins present. However, it is possible for unprocessed groundnut oil, favoured in some parts of the world for its nutty flavour, to be contaminated with aflatoxins; peanuts eaten whole might also be contaminated. Legislation varies in different parts of the world on the level of mycotoxins permitted in foodstuffs intended for human consumption and for animal feedingstuffs, the amounts permitted being generally in the range 5 to 30 parts per billion. An excellent review of this topic is given by Diener and Davis (1983). 289 ANALYSIS OF OILS AND FATS: COMPOSITION AND IDENTITY Acetyl value The acetyl value is defined as the number of mg of potassium hydroxide required to neutralize the acetic acid formed when 1 g of acetylated fat is saponified. The hydroxyl value is defined as the number of mg of potassium hydroxide required to neutralize the acetic acid capable of combining by acetylation with 1 g of an oil or fat. Both values are thus measures of the hydroxyl groups present in a fat; they are effectively the same for values of less than 2.0. Hydroxyl groups may occur in a fat as a result of the presence of mono- or diglyceride emulsifiers, or they may be present in a fatty acid combined with glycerol in a triglyceride, a typical example being ricinoleic acid, the main fatty acid of castor oil. The preferred forms of the test are specified in British Standard 684, Section 2.9: 1977 (as amended by amendment slip 2653, July 1978). In this, the fat is acetylated with a measured quantity of acetic anhydride in pyridine; the excess acetic anhydride is decomposed by boiling water and the acetic acid formed is titrated with sodium hydroxide solution in ethanol. A control test with acetic acid in pyridine, but without the fat, is carried out to determine the amount of acetic anhydride available for acetylation and a similar test is carried out with fat, but omitting the acetic acid, to determine the free fatty acids present. Because of the lengthy nature of this test the determination is not often carried out as a routine. Ash As oils and fats are organic substances, they should burn completely and leave no residues. Measurement of the inorganic residue after ignition is therefore a useful test for the determination of inorganic impurities. In the test a weighed amount of about 10 g of fat is heated in a crucible to the ignition of the fat and left to burn. When the burning ceases, the crucible is heated to a dull red heat until no more change is observed. The ash content is calculated from the initial weight of sample, and the difference in weights of the empty crucible and the crucible together with the ash. The method in British Standard 684: Section 2.2 may be contrasted with the IUPAC procedure, which is claimed to avoid loss of relatively volatile alkaline compounds. 290 FOOD INDUSTRIES MANUAL Density Moisture and volatile matter The relative density or specific gravity of an oil (at to j20°C) is defined as the ratio of the apparent mass, determined by weight in air, of a given volume of the oil at tOC to that of a same volume of water at 20°C; whereas the apparent density (at t°C) is the apparent mass in grams, determined by weighing in air, of 1 ml of fat at tOC. The method commonly used in the UK is that in British Standard 684: Section 1.1. The density of an oil should always be determined at a temperature of at least 10° above its melting point but preferably below 65°C. The main value of a density determination is in the calculation of the weights of oil in large tanks. The volume of the oil in the tank can be readily determined by calibration, and its temperature can be measured. Careful measurement of the density of the oil at that temperature can then be used to calculate the weight of oil. A term normally used for oil densities at the dock side is 'litre weight in air', a form in which density may be expressed in commercial contracts. The amount of water in a fat may be determined by several methods. The titrimetric Karl Fischer method described in BS 684: Section 2.1 is very useful for the determination of water in fats or fatty foods having a water content in the range of 0.5-1 %. Three rapid, and more frequently applied, methods to determine moisture and other volatile matter by drying are described in BS 684: Section 1.10. These are a method using a sand bath or hot plate, which is applicable to all oils and fats; a method using a drying oven, which is applicable only to non-drying fats and to oils with an acid value of less than 4; and a method using a stream of nitrogen to protect the oil from oxidation during the test, which is particularly applicable to drying oils such as linseed oil. The determination of the moisture content can be particularly important in commercial transactions of large quantities of oils and fats. Iodine value The refractive index (RI) is a property closely related to those of density and molecular weight, and to the constitution of oils. It is helpful in the identification of oils. It can be determined either by means of the Zeiss refractometer, which reads on an arbitrary scale, or by means of the Abbe refractometer, which gives the true refractive index. Monochromatic light is used in the measurement of RI, and when this is the sodium D line the RI measured in the refractometer is given the abbreviation nb, where t is the temperature of measurement. As RI is temperature-dependent, the instrument and the oil sample must be thermostatted during the measurement. This is normally achieved by circulating water from a thermostatically controlled bath. RI has been used to follow the course of hydrogenation, but in this case the temperature of measurement must be sufficiently high to ensure fluidity throughout the whole course of the hydrogenation. The RIs of a number of oils and fats are given in Table 8.2. The iodine value (IV) of a fat is a measure of its unsaturation and is a useful criterion of purity or identity. The measurement is based on the fact that halogen addition occurs to unsaturated bonds until these are completely saturated. Because substitution reactions, as well as addition, can occur it is important to carry out the determination under carefully controlled and standardized conditions. Not all unsaturated bonds are alike in reactivity, and those near a carbonyl group hardly absorb iodine. These acids are, however, rare. When the double bonds are conjugated, they react more slowly than non-conjugated double bonds. Several methods are available, those in common use being the tests of Wijs, Hanus and RosenmundKuhnhenn. The original Wijs method is now adopted almost universally and is described in British Standard 684: Section 2.13: 1981 (ISO 3961-1979). The main differences between the methods cited are in the halogenating agents, Wijs' method using iodine monochloride, the Hanus method using iodine monobromide, and the RosenmundKuhnhenn employing the milder pyridinesulphate-bromide reagent. All of the methods give similar results when applied to the majority of ordinary oils and fats, but differences can arise when large amounts of sterols or other unsaponifiable matter are present. Iodine values of common oils are given in Table 8.2. Refractive index Uosapooifiable matter 'Non-saponifiable' and 'unsaponifiable' are synonymous terms and are used to refer to that material present in oils and fats which, after reaction of the oil or fat with caustic alkali, remains insoluble in the aqueous alkali and non-volatile during drying. The amount of unsaponifiable matter in a fat is determined according to BS 684: Section 2.7. The unsaponifiable matter of a fat contains Table 8.2 Analytical properties of some oils and fats Refractive Index n1f Titre eC) Melting point eC) Saponification value' Unsaponifiable matter Iodine value Babassu Borneo tallow (Illipe) Castor-bean Cocoa butter Coconut Com (maize) Cottonseed Groundnut Kapok Kokum Linseed Mustard-seed Olive Palm Palm-kernel Rapeseed (high erucic) Rapeseed (low erucic) Rice bran Safflower Sal fat Sesame-seed Shea nut Soya-bean Sunflower-seed Walnut 1.448-1.455 1.456-1.457 1.466-1.473 1.456-1.459 1.448-1.449 1.465-1.468 1.464-1.468 1.460-1.465 1.460-1.466 1.456 1.474-1.475 1.461-1.469 1.460-1.463 1.449-1.456a 1.449-1.452 1.465-1.469 1.465-1.467 1.466-1.471 1.467-1.469 1.456-1.457 1.465-1.469 1.463-1.467 1.467-1.470 1.466-1.469 1.469-1.471 22-23 51-53 245-256 190-205 176-187 188-189 248-265 187-193 189-198 187-196 189-195 192 188-196 170-184 182-196 190-207 230-254 168-181 188-193 179-195 186-198 186-194 187-195 178-190 188-195 188-194 189-198 0.2-0.9 0.7-2.0 14-18 45-50 20-24 14-20 30-37 26-32 27-32 60 19-21 6-8 17-26 40-47 20-28 11-15 20-22 25 15-18 51 20-25 49-54 20-21 16-20 14-16 24-26 37-39 -12 to -10 31-35 23-26 -12 to -10 -2 to 2 -2 30 40-42 -20 -16 -3 to 0 33-40 24-26 -9 -20 0-8 -18 to -13 33-39 -4-0 37-42 -23 to -20 -18 to -16 -16to-12 0.1-0.2 0-0.5 0.5-2.8 0.2-1.5 0.2-0.8 0.5-1.0 c.2.3 0.1-1.7 0.7-1.5 0.7-1.1 b 0.3-1.2 0.2-0.8 0.2-2.0 0.2-1.8 33-42 7.5-10 103-128 99-115 84-105 Butter (cow's) Beef tallow Lard Mutton tallow Cod liver Herring Menhaden Whale 1.452-1.457 1.457-1.459 1.458-1.461 1.455-1.458 1.470-1.475 1.465-1.467 1.472-1.475 1.465-1.472 33-38 40-47 32-43 43-48 28-35 40-48 33-46 44-51 233-240 190-202 192-203 192-197 180-190 179-194 189-193 185-194 Oil or fat a b At 50°C Pressed oil; extracted oil up to 2.5 23-27 31-33 22-24 155-205 106-113 80-88 50-54 16-19 97-110 106-126 135-150 0.3-1.3 0.9-2.0 4-8 0.5-1.6 0.3-1.3 0.5-1.0 0-1.0 0-0.8 0-1.0 0-1.5 1.2-2.0 104-120 125-136 85 25-42 45-57 59-70 35-46 110-135 FOOD INDUSTRIES MANUAL 292 sterols, higher alcohols, hydrocarbons, pigments and in some cases (e.g. fish liver oils) vitamin A. Crude fats contain varying amounts, of up to 8% in the case of shea oil, while refined oils contain lower amounts of unsaponifiable matter. Halibut liver oil contains a high level (7-20%) of unsaponifiable matter, most of which is vitamin A. Determination of the unsaponifiable matter content can be useful if contamination of the oil with a mineral oil or other non-triglyceride contaminant is suspected. Unsaponifiable matter contents of several oils are given in Table 8.2. Tests for identity or adulteration Crude sesame oil gives a deep pink colour when it is reacted with ethanol and ammonia and then with acidified sucrose solution. The test is known as the Baudouin test and is described in Section 2.30 of British Standard 684. The test enables detection of small amounts of sesame oil in any other product. In Italy, all oils other than olive oil are treated with crude sesame oil to enable Government officials to detect adulteration of olive oil. In India the test may be used to detect adulteration of ghee. (i) Baudouin test. The presence of cottonseed oil in vegetable or animal fats or oils can be detected by the Halphen test. The fat is heated with a solution of sulphur in carbon disulphide in the presence of amyl alcohol. The presence of cottonseed oil is shown by the appearance of a red colour due to reaction of the constituent cyclopropenoid acids. Some oils, such as kapok-seed oil, also contain these cyclopropenoid acids and can therefore confuse the interpretation of the test. Hydrogenation removes the cyclopropenoid acids from cottonseed oil, and hydrogenated cottonseed oil therefore gives a negative result. (ii) Halphen test. (iii) Reichert-Meissl, Polenske and Kirschner values. All three values are measures of the shorter-chain fatty acids which are present in some oils, especially dairy butter, coconut and palm-kernel oils. The Reichert-Meissl value is a measure of the watersoluble volatile acids, while the Polenske value is a measure of the water-insoluble volatile fatty acids. The Kirschner value is a measure of the watersoluble fatty acids not heavier than butyric acid. The determinations are carried out according to the procedure in BS 684: Section 2.11, but they have fallen into disuse in recent years in favour of the accurate determination of fatty acid composition by gc. (SV) is defined as the number of mg of potassium hydroxide required to neutralize the fatty acids liberated on the complete hydrolysis or saponification of I g of the fat or oil. It is determined by refluxing 2 g of the oil with 25 ml of O.1M alcoholic potash for 1 h, on a water bath, then back-titrating the excess alkali. The value obtained is subtracted from the value for a blank carried out simultaneously. The esters of low molecular weight fatty acids require the most alkali for saponification, so that the saponification value is inversely proportional to the mean molecular weight of the fatty acids in the glycerides present. Because many oils have similar saponification values, the test is not universally useful in establishing identity or indicating adulteration, and should always be considered along with the iodine value (q.v.) for these purposes. Fats with relatively high proportions of the lower fatty acids include coconut oil (SV 255), palm kernel oil (SV 247) and butter fat (SV 225) and their presence may frequently be detected in this way. Paraffin has of course a negligible SV and can therefore be detected and estimated. The SV of some oils and fats are given in Table 8.2. With the widespread application of gas chromatography (gc) has come the possibility of rapid and convenient estimation of all the component fatty acids in the glycerides present in an oil or a mixture, and this is now a powerful tool for establishing the identity or purity of any oil or fat. In the International standard method (ISO 5508: 1990) the glycerides are first hydrolysed to the component fatty acids with sodium hydroxide and neutralized, then the fatty acids converted to their methyl esters with methanol under suitable conditions and extracted into heptane or hexane for gc analysis. A portion of the solution is passed through the gas chromatograph with a suitable detector. Successive peaks corresponding to the individual fatty acids are noted by the chart recorder and from their relative areas the proportions of the fatty acids are calculated. In addition to the chemical diagnostic value, a simplified version of the fatty acid profile, showing the totals of the saturated, mono-unsaturated and poly-unsaturated fatty acids, gives very useful nutritional information. (For fatty acid profiles of a number of fats and oils see Tables 8.4, 8.5 and 8.6.) (v) Fatty acid profile. (vi) Titre. (iv) Saponification value. The saponification value FATS.) (See below under TEXTURE OF OILS AND FATS AND FATTY FOODS ANALYSIS OF OILS AND FATS: TESTS OF QUALITY C:olour moeasuremoent The colour of an oil is of considerable commercial importance. Pale, bright colours are desired in refined oils, as this is regarded as the criterion of quality and purity, and also facilitates production of finished foods with a desired colour shade. Colour removal is generally effected by BLEACHING. Oil colours are measured in the Lovibond system by comparing the colour of the cell containing the oil with that of coloured glasses, the glasses being adjusted until a good match is obtained. Normally, only red and yellow colour units are quoted, although blue and neutral glasses may also be provided. There are a number of different Lovibond systems, and care must be taken to specify which system is being used, and the size of cell used, when comparing the colour ratings of different oils. In the UK, British Standard 684: Section 1.14 is normally used for colour measurement. Staff making such colour measurements should of course be tested for colour blindness, an aspect sometimes overlooked. Automatic versions of the Lovibond Colorimeter are now available, but it is generally accepted that these may not always be suitable for measurement of colours in crude oils. Free fatty acids The presence offree fatty acids (FFAs) in an oil or fat is an indication of previous lipase activity, other hydrolytic action or oxidation. The FF A content as commonly determined is a measure of the uptake of caustic alkali during the titration. The values may be quoted as acidity, or as a percentage by weight of a specified fatty acid in the oil. In the UK acidity and FF A content are determined by the method in the British Standard 684: Section 2.10. Peroxide value Oxidation of an unsaturated oil or fat takes place via the formation of hydroperoxides. The hydroperoxides subsequently decompose into secondary oxidation products, the majority of which have unpleasant odours or flavours. Although hydroperoxides themselves have no off-flavours, they are an important aspect of rancidity development. The method used for the determination of peroxide value in the UK is that described in British Standard 684: Section 2.14: 1976. In this test a solution of the fat in a mixture of acetic acid and 293 chloroform is treated with a solution of potassium iodide. The peroxide oxygen liberates iodine from the potassium iodide, and the liberated iodine is then titrated with a solution of sodium thiosulphate. Specific extinction in ultraviolet light Oxidation of an unsaturated fat leads to the formation of conjugated dienes which have characteristic ultraviolet absorption spectra. Different absorption spectra are associated with conjugated trienes which may be generated during earth bleaching of unsaturated oils at high temperatures. The specific extinction in uv light is determined by British Standard 684: Section 1.15. Swift Test; Rancimoat; Active Oxygen Method The Swift Test is a method of measuring the resistance of a fat to oxidation. It is sometimes called the 'Active Oxygen Method' or 'AOM'. In this test the oil is heated to 100°C and air is then bubbled through it. Samples of the oil are periodically taken and the peroxide value determined. The increase in peroxide value is plotted against time, and a sharp break in the curve is noticed when the natural resistance to oxidation is exhausted and oxidation proceeds at a progressively increasing speed. The time during which the oil exhibited resistance to oxidation is called the Induction Period (IP), or Swift Test life. There are various methods of interpreting the results from this test, that used in the UK being described in BS 684: Section 2.25. In recent years the automated Rancimat apparatus has appeared in which the effiuent gases are led into distilled water and the electrical conductivity of the water automatically measured (Allen and Hamilton, 1989). The time at which the conductivity rapidly increases is taken as the end of the Induction Period. Thiobarbituric acid (TBA) value The TBA value is a guide to the oxidation or deterioration of fats. TBA, it is believed, reacts with malonaldehyde formed during the oxidative decomposition of polyunsaturated fats to form a coloured product. One attraction of the test is that it can be carried out on whole foods, and may pick up oxidation damage to materials other than the triglyceride fats themselves. ANTIOXIDANTS When fats are exposed to atmospheric oxygen they gradually become oxidized. Some fats oxidize more 294 FOOD INDUSTRIES MANUAL readily than others and develop off-flavours. This is known as oxidative rancidity, and it may also give rise to deleterious nutritional effects, for example, destruction of essential fatty acids and vitamins. Any substance which retards the oxidative deterioration of fats may be referred to as an antioxidant. Tocopherols, which occur naturally in vegetable oils, have good antioxidant properties and may provide effective protection. Animal fats are deficient in natural protection and may need added antioxidants; so may fats required to have long shelf life, such as certain baking fats, or oils used for frying. In the latter case, oxidation can occur on the fried product which may have a high fat content and a large surface area. The addition of artificial antioxidants is controlled by law and only those substances which have been rigorously tested toxicologically are permitted. In the UK permitted synthetic antioxidants include n-propyl, n-octyl and n-decyl gallate, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). Adverse reports were made about the physiological effects of BHT in the early 1960s but these have not been substantiated. Combinations of the antioxidants, with one another or with citric acid, may be beneficial. Although citric acid would not normally be classed as an antioxidant it complexes with any trace transition metal catalyst present, neutralizing its catalytic effects on oxidation (see SYNERGISM). Tocopherols, particularly 'Y-tocopherol, possess good 'carry-through' properties. 'Carry-through' refers to the ability of certain components to escape destruction on baking or frying. BHA and BHT also possess good carry-through properties during baking, but their volatility gives them reduced effectiveness during frying operations, BHA being less volatile than BHT. Antioxidants function in two ways. They may act as oxygen scavengers, removing oxygen from the oil, or by virtue of their ability to inhibit autoxidation by capturing free radicals (see PEROXIDE VALUE). General reviews of oil rancidity and antioxidant effect are given by Allen and Hamilton (1989). ANTI-SPATTERING AGENTS When margarine is used for frying (a frequent practice in continental Europe, rare in the UK), bubbles of water vapour escape and burst, causing hot fat to fly. This unpleasant effect is known as 'spattering'. Some emulsifiers reduce the effect if incorporated in margarine and these materials are called anti-spattering agents. Egg yolk was formerly widely used, but this has been replaced by citric acid esters of mono- and diglycerides, and blends of these with lecithin. Polyglycerol esters of fatty acids, polydimethylsiloxane, and monostearin sodium sulphoacetate are also effective. Salted margarines spatter less than salt-free margarines. BLEACHING Bleaching is one of the operations in the refining of oils and fats. It normally follows the neutralizingwashing-drying procedures. After bleaching, oils and fats may either be deodorized for immediate use or they may be hydrogenated. If the oil or fat is hydrogenated, a second bleaching treatment is usually carried out on the hydrogenated product before it is deodorized, mainly in order to remove traces of hydrogenation catalyst. Bleaching removes colouring matter such as carotenoids and chlorophyll, and also other minor constituents such as protein degradation products or traces of transition metals from the oils or fats. Some of these minor constituents are hydrogenation catalyst poisons, and it is therefore essential to bleach an oil thoroughly before hydrogenation. Transition metals, especially iron and copper, are pro-oxidants, and their removal therefore improves the oxidative stability of the oil. Bleaching is achieved by stirring the oil under vacuum with 0.1-2% of activated fuller's earth. Temperatures of treatment range from 90° to 130°C, whilst times range from 10 to 60 minutes. The bleaching takes place in vertical vessels made of mild steel, which hold up to 25 tons of oil. Each vessel is fitted with a mechanical stirrer, a means of heating and cooling, valves, sight glass, a vacuum gauge and a thermometer. The earth is sucked into the oil under vacuum at 60-80°C. After treatment, the earth is removed by filtration, usually in a plateand-frame filter press. Considerable interest has also developed in continuous bleaching. Other methods include the use of mixed adsorbents (e.g. mixtures of fuller's earth and carbon); the possibility of bleaching oil miscelh (i.e. treating the oil plus solvent mixture obtained in oil extraction plants before recovery of the oil); use of high temperatures during deodorization to effect thermal breakdown of colour material; and hydrogenation. Chemical bleaches are not suitable for use with food fats, as these usually oxidize the oil, causing an increase in peroxide value and subsequent ofl'flavour development. 295 FATS AND FATTY FOODS CAKE MARGARINE content of cakes is about 20%. The amount of sugar that can be incorporated into a cake depends on the amount of moisture and eggs present. As the percentage of water can be increased in a cake when using a margarine containing an emulsifier, the percentage of sugar can also be increased. The manufacture of cake margarine is similar to that of ordinary TABLE MARGARINE. The book by Schwitzer (1956) is a useful reference on this topic. Although ordinary table margarine is suitable for cake-making, industrial bakeries use special cake margarines with a wide plastic range, high creaming powder and an ability to impart shortness to certain classes of baked goods. To achieve these aims, cake margarines are made by blending high-melting point fats with a fair amount of liquid oil. A typical fat blend might consist therefore of a mixture of palm oil with hydrogenated fish oil. The moisture content of cake margarines is lower than that of domestic table margarines. The most desirable quality of margarine in cakemaking is its creaming power, i.e. its ability to take up air in the form of finely divided bubbles. The volume and cellular structure of a cake, its lightness, and to a large extent its palatability, depend on this creaming power. During baking, the entrapped air, saturated with water vapour, expands because of the increased pressure of the water vapour. Creaming power and the ability to take up a high percentage of moisture are improved by incorporating into the margarine emulsifiers such as glyceryl monostearate. Work carried out at the Leatherhead Food Research Association, and since substantiated by others, showed that fats modification which crystallize in a ~-polymrhic comprise micro-crystals and have improved creaming properties. Margarines intended for use in short pastry do not contain emulsifiers (see SHORTENINGS). The main difference between a cake and a short pastry is that the latter is essentially dry. It contains only about 4% of moisture and there is no need for volume and cellular structure. The moisture CAROTENE The chemical identity of the colour components in oils and fats is not fully understood, but the characteristic yellow-red of many natural fats is due to the presence of polyene-carotenoid pigments. These pigments derive their colour from the presence in their structure of a sequence of multiple conjugated double bonds which absorb light in the region of 440-450 nm. Of the vegetable oils widely used, palm oil has the highest concentration of carotenoids, usually about 0.03-0.15% (m/m) in the crude, unbleached oil. Figure 8.1 shows the relationto vitamin A. ship of ~-caroten CATALYST A catalyst is a material which, when added in minute amounts to a mixture of substances capable of reacting with each other, greatly increases the rate of the reaction. CH3 CH3 (a) ~ ~ ~ CH3 ~ ~ ~ ~ ~ ~ CH3 CH3 CH3 (b) Figure 8.1 The relationship of (a) ~caroten to (b) vitamin A. CH3 CH3 296 FOOD INDUSTRIES MANUAL Hydrogenation catalysts In the oils and fats industry, hydrogenation catalysts are the most important. Nickel is the usual hydrogenation catalyst, although patents have been issued for the use of many other noble metal catalysts. Nickel catalyst was at one time prepared by the dry reduction of nickel carbonate, the wet reduction of nickel formate or from Raney alloy. With the increased costs of nickel, supported nickel catalysts are now preferred, however. In the production of a supported nickel catalyst, the support material is stirred into an aqueous solution of a nickel salt such as sulphate. The solution is gradually rendered more alkaline, e.g. by the addition of sodium carbonate, whereupon basic nickel carbonate is precipitated on to the surface of the support. The mixture is filtered, washed free of sulphate ions, dried, and reduced with hydrogen. The size of the nickel crystallites on the surface of the support, and the size of the pores left in the surface of the nickel, determine the activity and selectivity of the resulting catalyst. Catalysts prepared on this basis normally contain between 15-25% nickel. As they are pyrophoric, the fresh catalyst is normally suspended in a fully hydrogenated oil, which is allowed to crystallize and is converted into flakes. A review of hydrogenation with non-poisoned nickel catalysts is given in 'Hydrogenation-symposium papers' (American Oil Chemists Society, 1970). In some cases special attributes are imparted to the catalyst by the addition of promoters such as zirconium, or of poisons such as sulphur. Sulphured nickel catalysts are especially useful in converting cis double bonds in a fat to the trans form, a process which gives a steep melting fat suitable for uses in the confectionery industry. The amount of catalyst used in hydrogenation is usually about 0.1 % of nickel on the weight of the oil for a fresh catalyst but rising to 1-2% for a poisoned or spent catalyst. Catalysts can normally be re-used for a number of batches, artificially poisoned or sulphured catalysts lasting much longer than fresh catalysts, as in the latter case impurities in the oil gradually poison the catalyst and lower its activity. After hydrogenation, the catalyst must be removed from the hardened fat by filtration, to give a clear oil. In the USA and Canada this is often accomplished by adding bleaching earth to the oil and filtering off the combined catalyst and bleaching earth slurry. In such an operation it is not economic to recover the nickel from the filter cake. In Europe, however, it is more common to filter off the bulk of the catalyst separately and then subject the oil to an additional earth filtration to remove the last traces of nickel catalyst. Incomplete removal of the nickel catalyst may be criticized from a nutritional point of view, and it can also give the oil a greenish or greyish appearance. Inter-esterification catalyst A second use of catalysts in the oils and fats industry is for INTER-ESTERIFICATION. In the process of inter-esterification, the fatty acids in the triglyceride molecules are rearranged until they are completely random with regard to their distribution among the triglyceride molecules and their position on the glycerol backbone of the triglycerides. This may be achieved by heating neutral, dry oil at a temperature of 100°C under a vacuum in the presence of an inter-esterification catalyst such as sodium methoxide. In a continuous version of this process, hot oil is pumped through a reaction tube, into which an alloy of sodium and potassium metals is dosed. In the conventional view of the reaction, sodium ions momentarily liberate fatty acids from the triglyceride molecules and on recombination a randomization is effected. Inter-esterified oils have different properties from the original oil, and are frequently useful in tailormaking fatty products for specific uses. CHOCOLATE Chocolate is prepared by combining ground cocoa beans with cocoa butter and sugar. The cocoa bean itself contains about 52% fat, which is not sufficient to permit the addition of the desired quantity of sugar and maintain the necessary fat content of about 30%. Fat is therefore expelled from cocoa beans to give Pure Prime Pressed (PPP) cocoa butter, which is then used to augment the fat in the recipe. The initial blend contains several astringent flavours, which are moderated by stirring in open vessels, called conches, for a period of hours or days, depending on the recipe and desired characteristics. In the UK milk chocolates are usually preferred, and in these cases part of the cocoa and sugar is replaced by full-cream milk powder. A variation on the production of milk chocolate is the use of milk crumb, which is prepared by evaporating milk to a low moisture content, and then combining it with ground cocoa beans (i.e. cocoa mass) and sugar. Milk crumb is a fully dried and kibbled product. The original attraction of this process was that it conferred the good keeping properties of cocoa upon milk powder, which could therefore be stored with greater reliability. FATS AND FATTY FOODS However, the flavour attributes of milk crumb were found to be attractive in the United Kingdom, where the majority of milk chocolate now contains a fair proportion of this component. The use of milk crumb in other parts of the world is less popular. A comprehensive review of chocolate production is given by Minifie (1980); see also Beckett (1988). COATINGS 'Coatings' is a term applied to substitute chocolate compositions used primarily for coating cakes, wafers or biscuits. These compositions are inferior to, and cheaper than, real chocolate, but fulfil a useful purpose in many food applications. In the majority of countries, legislation prohibits the description of such product as 'chocolate'. COCOA BUTTER Cocoa butter is obtained by pressing ground, roasted, decorticated cocoa beans and is derived almost entirely from the nib or kernel of the cocoa bean. Cocoa butter is used extensively in the making of chocolate and in other confectionery products, and to a limited extent in the pharmaceutical industry. It is particularly suitable for these purposes because it has a low, but sharp, melting point; it is brittle and fractures readily, and whilst it is not greasy to the touch it melts completely in the mouth. These properties are a reflection of its triglyceride composition. The principal triglycerides present are mono-unsaturated, disaturated glycerides, predominantly 2-0Ieopalmitostearin. In all of the triglycerides present in cocoa butter, the 2- or central hydroxyl group on the glycerol backbone of the triglyceride molecule is esterified with an unsaturated acid. The price of fats has varied considerably over the years, but cocoa butter is normally one of the most expensive. The high and variable cost has stimulated an extensive search for cocoa butter replacement fats (see below). COCOA BUTTER REPLACEMENT FATS Cocoa butter replacement fats are used in the confectionery trade in chocolate COATINGS or for the partial replacement of cocoa butter in the manufacture of chocolate. The earliest cocoa butter substitutes were prepared by fractionation of palm-kernel oil, the higher melting components of the fat being separated. These palm-kernel stearins melt at 297 approximately the same temperature as cocoa butter, but as they contain different triglycerides they are not compatible with cocoa butter and form eutectics with it. As a result, the melting point of a blend of cocoa butter and palm-kernel stearin is lower than that of either of the components, which makes it unsuitable for use in chocolate. Another class of cocoa butter substitute is manufactured by a combination of hydrogenation and fractionation of cheaper vegetable oils such as soya-bean oil or palm oil. These fats have high trans values, and have moderate compatibility with cocoa butter. Nevertheless, they are far from ideal, and coatings made with such fats often have a waxy palate response. The most sophisticated cocoa butter replacement fats, commonly known as cocoa butter equivalents (CBEs), are prepared by blending carefully selected natural fat fractions. Commercially successful CBEs are manufactured on a large scale by blending a middle melting fraction from palm oil with naturally occurring (Borneo) illipe butter, the upper melting fraction (i.e. stearin) of shea oil, and sal stearin. Each of these triglyceride fractions provides a concentrate of triglycerides normally present in cocoa butter, giving a final blend with almost identical physical characteristics to those of cocoa butter itself. The use of cocoa butter replacement fats in products labelled 'chocolate' is strictly controlled, the legislation varying from country to country. Various analytical methods must be brought to bear in order to detect their presence. Fats such as palm-kernel stearin may be detected by their high lauric acid content, whilst products based on hydrogenation and fractionation may be detected by the increased trans value imparted to the mixture. Cocoa butter equivalents are more difficult to detect, and sophisticated methods must be brought to bear. COLOUR Colour may be added to a fat to improve the appearance of a food product. For example, colour is normally added to margarine to give it an attractive yellow appearance. The tendency to avoid the use of synthetic dyestuffs in food has concentrated attention on the use of natural colours, such as carotene and annatto. ~-Caroten is the natural colouring matter of butter and is thus an obvious choice for addition to margarine. Often it is used in the form of a dilute solution in palm oil. Crude palm oil contains about 0.1 % of a mixture of carotenes and, if refined carefully, can be used to colour margarine (see CAROTENE). 298 FOOD INDUSTRIES MANUAL Annatto seed is the seed of Bixa orellana, the main compound responsible for the colour being the carotenoid bixin. The colouring matter is found in the seed coat and may be extracted into a vegetable oil such as soya-bean oil. Other food colours may be used in the preparation of pastel icing, ice-creams and cream fillings of biscuits. Local legislation varies with regard to colouring materials permitted. product is thereby obtained. There is also a possibility that some of the free fatty acids originally present combine with partial glycerides, to form triglycerides, thus increasing the yield further. Deacidification may be carried out in batch, semi-continuous or fully continuous plant. Some heat bleaching also takes place. DEGUMMING (DESLIMING) COLOUR OF OILS Most oils when extracted from oilseeds are green or orange in colour due to the presence of chlorophyll or carotene. Only virgin olive oil is sold as a green coloured oil; the colour of most oils is removed by the BLEACHING stage of the refining process. This leaves the oil as a pale yellow colour. COMA REPORT See Chapter 17. CRUDE OIL The term 'crude oil' is applied to the unprocessed oil directly after it has been extracted from the vegetable or animal raw material. Crude oils normally need refining to render them fit for human consumption. Separate stages of BLEACHING, NEUTRALIZATION or DE-ACIDIFICATION, and DEODORIZATION are normally applied to crude oils before they reach the consumer. In some cases a crude oil may be of adequate quality and does not need any further processing, for instance, olive oil produced by the first pressing of olives. Such oils are often termed 'virgin oils'. Crude oils often contain non-glyceride substances, either dissolved or in suspension. These impurities consist of carbohydrates, proteins, phospholipids, resins, etc. Oils such as groundnut and soya bean are rich in these impurities, whilst others such as coconut or palm-kernel oils are relatively free of them. The simplest method to remove these impurities is to heat the oil to just below lOO°C and add 3-5% of hot water or a weak salt or alkali solution. The oil is then stirred and the impurities become hydrated and flocculate to form an oil-insoluble gum or mucilage. The gum may be allowed to settle and run off, or may be separated from the oil by centrifuging. Various organic and inorganic acids may be used to improve the efficiency of the process. Aqueous citric and phosphoric acids are often used. In some cases, the phospholipids may react in the seed, or in the oil, to form calcium salts, or possibly other substances which do not readily hydrate and which remain dissolved in the oil. If left behind, they interfere with subsequent processes such as high-temperature deacidification. One of the advantages of phosphoric or citric acid degumming is that these non-hydratable salts are rendered hydratable and can be removed with other phospholipids. The gum separated from phosphatide-rich oils such as soya-bean and rapeseed oil is often used as a commercial source of vegetable LECITHIN. DE-ACIDIFICATION DEODORIZATION De-acidification, as distinct from neutralization, consists of the removal of free fatty acids from an oil by steam distillation. The oil is first treated with hot water and optionally phosphoric or citric acid to remove phosphatides in a process known as DEGUMMING. The oil is then subjected to a light bleach and charged into the deodorization vessel. The oil is heated to a temperature of up to 270°C under vacuum and live steam is injected. Fatty acids are thereby volatilized and drawn off. This process avoids the loss of some of the neutral oil, as occurs in alkali neutralization, and a higher yield of final Deodorization is the final processing step in the preparation of an oil for edible purposes, such as a salad oil or cooking fat, or in the preparation of an oil stock for margarine. Deodorization removes from the oil volatile impurities, among which are many of the foreign odours and off-flavours which would render the oil unsatisfactory. Hardened fats are always deodorized after hydrogenation to remove characteristic off-flavours formed during the hydrogenation process. Deodorization is essentially a steam distillation FATS AND FATTY FOODS under low pressure. The oil is heated at a temperature of between 180°C and 240°C, at pressures ranging from 2-25 Torr, and live steam is injected. The time of treatment varies, according to the design of plant and the temperature used, from 5 h in low temperature batch processes to as little as 15 minutes in some continuous systems. Batch deodorization vessels consist of vertical steel tanks holding up to 25 tons of oil. A large vapour space is maintained above the liquid level to contain the oil during the violent agitation caused by steam injection. Provision for reducing the entrainment of oil in the escaping steam is made at the top of the deodorizer, where it connects with the vacuum line. The heating of the oil to deodorization temperature, and its subsequent cooling, are carried out under vacuum since it is important that the hot oil should not come into contact with atmospheric oxygen, which would lead to the production of new off-flavours. The deodorized oil is often filtered after deodorization, a process known as 'polishing'. DIGESTmILITY The digestibility of a fat is the percentage of total ingested fat which is absorbed. Vegetable and animal fats melting below 50°C are almost completely absorbed by man, but those having higher melting points are less easily digested. There has been some suggestion that digestibility may depend on chain length, and patients suffering from tropical sprue are advised to eat mediumchain-length (MCT) fats. These are fats \n which the fatty acids are predominantly those with 6, 8 and lO carbon atoms. EMULSIFICATION Emulsification is the dispersion of one liquid phase, in the form of fine globules, in another liquid phase with which it is incompletely miscible. In the food industry the two phases most commonly emulsified are oil (0) and water (W), thus forming either oil-inwater (O/W) or water-in-oil (W /0) emulsions. Emulsifiers are usually added to one of the phases to promote ease of formation or stability of the emulsion. The emulsifier reduces the interfacial tension between the two phases and makes possible the formation of the greatly enlarged interfacial area with a much reduced energy input via mechanical agitation. In addition, the emulsifier can stabilize the formed emulsion, e.g. by formation of a semirigid interfacial film, by its relative partial solubility 299 in the two phases, or by its contribution to the formation at the interface of an electrical double layer of charge which inhibits coagulation. The particle size of an emulsion is generally decreased by more vigorous agitation during its preparation, by arranging for the viscosities of the two phases to be more nearly equal, and by use of the correct emulsifier. The main factors in the choice of emulsifying equipment are the apparent viscosity in all stages of manufacture, the amount of mechanical energy input required, the type of agitation and the heat exchange requirements. Thus the planetary stirrer, in which the axis about which the paddle rotates itself follows a circular orbit, is used at fairly slow speeds for the intimate mixing of very viscous emulsions, e.g. heavy batters, and at higher speed for the aeration of low-viscosity emulsions. A mixer consisting of one or more propellers mounted on a common shaft is widely used for preparing low- and medium-viscosity emulsions. In recent years, there has been an almost universal adoption of the continuous Votator system for the manufacture of margarine, which is a W/0 emulsion produced by blending about 16% water and 4% of other substances with 80% of fat. In this system the oil phase (containing 0.1-0.5% of an emulsifier, such as lecithin or a monoglyceride) and the aqueous phase are fed continuously by separate proportioning pumps through externally refrigerated cylinders equipped with rapidly revolving coaxial shafts bearing scraper blades. Centrifugal force and the resistance to rotation offered by the mixture cause the scraper blades to bear lightly against the cylinder walls, thus giving a very high rate of heat transfer. The emulsification process is considerably promoted by this efficient cooling, since a proportion of the globules are solidified at the lowest temperatures. The whole system is enclosed, thus giving complete protection from atmospheric contamination. The margarine emerging from the cylinders is ready for sizing, packing, etc. Whereas a fine distribution of water globules in margarine is essential, the water droplets must not be too small as the product would then give a sticky, fatty sensation to the palate. In a good margarine, some 95% of the 4% of 5-lO globules have a diameter of 1-5 ~m, ~m and 1% of 10-20 ~m. There are 10000 to 20000 million water globules per gram of margarine. Emulsification has many other applications in the food industry apart from margarine, for example in the manufacture of ice-cream, cakes, and mayonnaise. Other means of agitation used include turbine agitators, colloid mills, homogenizers and ultrasonic oscillators. A useful review of emulsification is given by Becher (1965). 300 FOOD INDUSTRIES MANUAL EMULSIFIERS Emulsifiers play an important role, as the manufacture of many foodstuffs involves the formation and stability of emulsions of two basically immiscible phases, usually oil (0) and water (W). The use of an emulsifier increases the ease of formation and promotes the stability of an emulsion (see EMULSIFICATION). The concept of hydrophilic-lipophilic balance (HLB) (Griffin, 1949) is now widely used in the selection of emulsifiers for a particular purpose. Each emulsifier is assigned an HLB value, which is a number expressing the balance of the number and strength of its polar as compared to its non-polar groups, and this serves as an indication of the emulsifying action it will perform. Whereas the HLB system has proved quite adequate in applications in which only water and oil are involved, the selection of a proper emulsifier for food applications is often considerably complicated by the fact that the emulsions concerned are so complex that the determination of their 'required HLB' is extremely difficult. Nevertheless, the HLB system can be very useful in narrowing the selection from the very many emulsifiers available. In addition to the HLB of an emulsifier, attention may have to be given to its physical nature, which may be dictated by the form of the complete product, and to its chemical composition, minor differences in which can cause vast differences in performance. The method of preparation of an emulsion can also be important; for example, a homogenizer or a heat exchanger may give either an OjW or a WjO emulsion, from the same two phases. In some cases, such as in ice-cream, bread and cake, emulsifiers exert important influences on the product by means of their effect on other ingredients like starch and protein, their unique crystallization characteristics or their indirect induction of interactions lowering the interfacial tension between the two phases. Blends of emulsifiers usually give better results than a single compound, and techniques such as response surface methodology have been used to determine the optimum levels and proportions of several emulsifiers for a blend designed for a specific application, for example in cake-mix shortenings. Some of the most common applications of emulsifiers in foodstuffs are: (i) Bread: at 0.1-0.5% (of the flour), emulsifiers improve the loaf volume, crumb structure, and tenderness of the bread and markedly decrease its rate of staling. Di-acetyl tartaric acid (DATA) esters are used together with a small proportion of hard fat in bread improvers. (ii) Cakes: at 1-4% level (of the fat), emulsifiers improve the cake volume, crumb softness, texture, moisture retention, and keeping quality of the cake. (iii) Ice-cream: at 0.1-0.5% level (of the mix), emulsifiers improve the aerating properties (overrun), dryness, texture, body and apparent richness of the ice cream. (iv) Margarine: at 0.5% level (of the fat), emulsifiers improve the stability, texture and spreadibility of the margarine and some reduce its spattering when used for frying (see ANTI-SPATTERING AGENT). (v) Whippedjillings: at 2% level (of the fat), emulsifiers improve the whipping characteristics, appearance, volume and stability of the fillings, toppings and icings. (vi) Chocolate: the main advantage of adding emulsifiers to chocolate is to reduce the chocolate viscosity, and thus reduce the fat requirement. Lecithin is the most widely used emulsifier, the optimum level of utilization being about 0.4% of the total mix. Other emulsifiers, such as phosphorylated monoglycerides (both ammonium and sodium salts), polyglycerol polyricinoleate, and sucrose dioleate, are useful in the reduction of chocolate viscosity. Sucrose dioleate is not at present permitted in the UK for use in chocolate. Sorbitol tristearate and other sorbitol esters are sometimes used to reduce bloom tendency, and enhance texture, gloss, keeping qualities and melt-down on the palate. However, these emulsifiers are found to have more effect in coatings than in real chocolate. Emulsifiers used in foods may be present in some of the basic ingredients, for example lecithin in egg yolks and casein in milk, or they may be added at a given stage in the process. The added emulsifiers may have been obtained from natural sources, for example, lecithin extracted from soya-bean oil is widely used as an emulsifier in bakery fats, margarine, confectionery and pan release agents. However, while these natural emulsifiers have proved very useful, they are somewhat limited in their application to the great variety of technological problems currently facing the food industry. Thus in recent years a whole range of synthetic products has been developed, some of which have been specifically designed for particular applications. These synthetic compounds have all been subjected to rigorous toxicological examination before they are permitted for use as food additives. The following classes of synthetic emulsifiers are currently permitted in the UK. FATS AND FATTY FOODS Stearyl tartrate This is used as a bread improver, sometimes in combination with tartaric or diacetyl tartaric acid esters (see below). Partial glycerol esters The partial esters include any compound formed by incomplete esterification of the hydroxyl groups of glycerol with: (i) Any single fatty acid or mixture of fatty acids. This class comprises the well-known monoglycerides, diglycerides and their mixtures, which were the first synthetic emulsifiers to be used in the food industry. Because of their great diversity of application, stability and relative cheapness, they are still by far the most widely used emulsifiers in foodstuffs. They are used in the preparation of bread, cakes, margarine, ice-cream, whipped toppings, confectionery, cereal products, starch products and frozen and dehydrated foods. Saturated monoglycerides inhibit oiling out of peanut butter. (ii) Any mixture of fatty acids with one of a series of organic acids. These are modified mono and diglycerides and are generally more hydrophilic than the parent compounds. The permitted organic acids are: (i) Acetic acid. The acetoglycerides, which are exceptionally stable in the ex-polymorphic form, are particularly effective emulsifiers in high-ratio cakes and in cake mixes designed for single-stage preparation. They are also used in edible protective coatings, enrobing fats, spreads, salad oils, pan release agents and lubricants for machinery used to process foods. (ii) Lactic acid. The lactoglycerides, such as glycerolactopalmitate, tend to be stable in the expolymorphic form and are widely used as emulsifiers in shortenings, both for conventional and high-ratio cakes, and in cake mixes. They are particularly effective aerating agents when incorporated in liquid shortenings for cakes and are also used as whipping agents in topping creams. Their other applications include ice-cream mixes, baked goods, bread and confectionery coatings. (iii) Citric acid. These esters are not widely used, their main application being as anti-spattering agents in margarine. They exert a mildly 301 anti-oxidative effect when incorporated into oils and fats. (iv) Tartaric or diacetyltartaric acid. These esters improve bread, cakes and other baked goods. They also improve confectionery, margarine and whipped toppings. The diacetyl tartaric (DATA) esters are permitted in the UK and are widely used, but the simple tartaric acid esters are not allowed. (v) Phosphoric acid. These esters are not widely used, their main application being as viscosity reducers in molten CHOCOLATE. Partial esters of polyglycerols Polyglycerol mixtures, which are made by the alkalicatalysed thermal dehydration of glycerol, consist of chains of glycerol molecules joined together by ether linkages. The remaining free hydroxyl groups are incompletely esterified with: (i) Any single fatty acid or mixture of fatty acids. (ii) Dimerized fatty acids of soya-bean oil. (iii) Interesterified fatty acids of castor oil. Since the length of the polyglycerol chain, the degree of esterification and the nature of the fatty acids can all be varied independently of each other, a very wide range of esters, covering the HLB range, can be prepared. This versatile class of emulsifiers has found application in margarine, peanut butter, ice-cream, confectionery, chocolate, cakes, baked goods, low-calorie spreads, toppings and bakery release agents. They retard crystal formation in salad oils. The esters tend to be hydrophilic in character and are therefore particularly effective in synthetic creams and high-ratio shortenings. Propylene glycol esters Propylene glycol may be completely or partially esterified with: (i) Any single fatty acid or mixture of fatty acids. These esters tend to crystallize in the ex-polymorphic form and are very effective emulsifiers in cake mixes and in plastic and liquid shortenings for cakes. They impart excellent whip stability to dessert toppings, ice-cream and icings made from prepared dry mixes. They are also used in confectionery products. When a molten equimolar mixture of glycerol monostearate and propylene glycol monostearate is cooled, mixed crystals are formed in which the majority of glycerol ester is in the normally unstable ex-polymorphic form. These crystals disperse readily 302 FOOD INDUSTRIES MANUAL in water and this property is retained for over one year. The aqueous dispersions foam when shaken and, due to this unique property, the mixed crystals exhibit enhanced effectiveness in bread, cake mixes, sponges, whipped sauces, purees, toppings and confectionery. (ii) Any mixture of fatty acids and lactic acid. Mixtures obtained by the reaction of lactic acid with mixed fatty acid esters by propylene glycol and glycerol are particularly effective as emulsifiers in cake mixes. (iii) Alginic acid. Propylene glycol alginate is used as an emulsifier in baked goods, brewery products, canned goods, soft drinks, sauces and margarines containing highly unsaturated oils. It is also used as a thickening agent in a wide variety of foods. Fatty acid esters of sorbitan and their polyoxyetbylene derivatives The sorbitan esters, prepared by the reaction of sorbitol with fatty acids, are more hydrophilic than monoglycerides and their hydrophilicity can be still further increased by condensing them with ethylene oxide. The esters cover a wide HLB range and have found applications in baked goods, whipped toppings, ice-cream, confectionery COATINGS and beverages. A blend of sorbitan ester and a polyoxyethylene derivative usually gives better results than a single ester. Monostearin sodium acetate This is an effective anti-spattering agent for margarine, but is not permitted in the UK or the USA. Miscellaneous emulsifiers Other compounds, such as cellulose ethers, sodium carboxymethyl cellulose and brominated vegetable oils, are stabilizers rather than emulsifiers, and are used in baked goods, frozen foods, sauces, soft drinks, soups, jellies, etc. Brominated vegetable oils were removed from the permitted list in the UK in 1970. The fatty acid esters of sucrose comprise a very versatile class of emulsifiers which, when pure, are entirely non-toxic. Until recently, however, great difficulty was experienced in completely removing the toxic solvents, usually dimethylformamide, used in their manufacture and for this reason they are not permitted in some countries. However, methods of manufacture which do not involve toxic solvents have now been found and the esters are gaining wider acceptance. They have proved to be effective emulsifiers in cakes, biscuits, confectionery, chocolate, bread, margarine, shortenings, and salad oil. The compounds calcium stearoyl lactylic acid and sodium stearyl fumarate, which have been gaining wider acceptance, are effective improvers for bread and other baked goods. Table 8.3 shows the acceptable daily intake (ADI) figures recommended by the FAO/WHO Expert Table 8.3 Food emulsifier status (1986) Chemical name Lecithin Mono-diglycerides Acetic acid esters of mono-diglycerides Lactic acid esters of mono-diglycerides Citric acid esters of mono-diglycerides Diacetyl tartaric acid esters of mono-diglycerides Succinic acid esters of mono-diglycerides Salts of fatty acids (Na, K, Ca) Polyglycerol esters of fatty acids Propylene glycol esters of fatty acids Sodium stearoyl-Iactylate Calcium stearoyl-Iactate Sucrose esters of fatty acids Sorbitan monostearate Polysorbate 60 Polysorbate 65 Polysorbate 80 Notes: (I) EC Council Directive (74/329/EEC) (2) US Code of Federal Regulations (3) Calculated as polyglycerol esters of palmitic acid (4) Calculated as propylene glycol (5) Calculated as total sorbitan esters Abbreviation MG AMG LMG CMG DATA SMG PGE PGMS SSL CSL SMS PS 60 PS 65 PS 80 ADI value ECno.! USA FDA 21 CFR2 Not limited Not limited Not limited Not limited Not limited 0-50 E 322 E 471 E472a E472b E 472c E 472e Not limited 0-25 3 0-254 0-20 0-20 0-10 0-25 5 0-25 6 0-25 6 0-25 6 E 470 E 475 E477 E 481 E 482 E 473 E 491 E 491 E 436 E 433 SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS SS (6) (7) (8) (9) (10) 184.14007 182.45057 172.828 8 172.852 172.8329 182.4101 7, 172.830 172.863\0 172.854 172.856 172.846 172.844 172.859 172.842 172.836 172.838 172.840 Calculated as total polyoxyethlene (20) sorbitan esters Generally Regarded as Safe (GRAS) Relates to mono glycerides only Relates to mono-oleate citric acid ester Specifies salts of Na, K, Ca, Mg and AI. FATS AND FATTY FOODS Codex Committee on Food Additives, together with the current status in the EC and the USA. The UK position is equivalent to the EC status and is controlled by the Emulsifiers and Stabilisers in Food Regulations (1980), Statutory Instrument (1980) No. 1833, amended by SI (1982) No. 16 and SI (1983) No. 1810. FATTY ACIDS The types and proportions of the fatty acids present in the triglycerides of an oil have a major influence on the physical, chemical and nutritional properties of the oil. The fatty acid composition of an oil is therefore its most important chemical characteristic. In view of the recent dietary concern over the composition of oils and fats, it has become customary to group various categories of fatty acids according to their degree and type of unsaturation. The following groups are commonly used. Saturated acids (saturates) These are acids such as myristic, lauric, stearic, etc., the hydrocarbon chain of which has no double bonds (but note that in the COMA report, 1984, the description 'saturated*' includes the trans unsaturated acids). Some experts recommend that only C12, C14 and C16 saturated acids should be counted for dietary purposes. The individual members of this group are described below. (i) Butyric acid (C4) occurs in butter and is responsible for the characteristic 'butyric' note of rancid butter. (ii) Caproic acid (C6) occurs to a small extent in butter and coconut oils. (iii) Caprylic (C8) and capric (CIO) acids are present in babassu, coconut and palm-kernel oils and to a slight extent in butter. (iv) Lauric acid (CI2) is the major fatty acid constituent in babassu, coconut and palm-kernel oils; these oils are, therefore, collectively known as the lauric oils. The acid also occurs to a small extent in butter. (v) Myristic acid (CI4) occurs in babassu, coconut and palm-kernel oils and to a trace extent in cottonseed and palm oils, as well as in a number of animal fats such as butter, lard, tallow, and fish oils. (vi) Palmitic acid (CI6) is an acid of wide occurrence found in practically all oils and fats. It is the major constituent of palm oil, from which it derives its name. 303 (vii) Stearic acid (CI8) is found in almost all naturally occurring animal, marine and vegetable oils. (viii) Arachidic acid (C20) is present to a small extent in groundnut (Arachis) oil, from which it derives its name. It also occurs in trace amounts in other oils, e.g. soya-bean oil, cocoa butter, and sal fat. (ix) Behenic (C22) and lignoceric (C24) acids occur to a small extent in groundnut oil. Unsaturated acids (unsaturates) (1 ) Mono-unsaturated acids. These have a single double bond in the hydrocarbon chain. Trans mono-unsaturates such as elaidic acid are classed as 'saturated*' in the COMA report, 1984. The individual members of this group are described below. (i) Myristoleic acid (CI4: I-cis) occurs to a small extent in butter, tallow and fish oils. (ii) Palmitoleic acid (CI6: I-cis) is present in relatively large amounts in many fish oils, menhaden oil, for instance, containing up to 15%. It is also present in small amounts in palm oil, cottonseed oil, butter, and lard. (iii) Oleic acid (CI8: I-cis) is the most commonly occurring fatty acid. It is present in almost all vegetable and animal fats, in particular olive, palm, low erucic rapeseed, groundnut, teaseed, almond, and fish oils. (iv) Elaidic acid (CI8: I-trans), the isomer of oleic acid, is present to a small extent in animal fats and mammalian butters, and also in partially hydrogenated oils and fats. (v) Ricinoleic acid (CI8: I-cis) contains one hydroxy group and occurs as the principal acid in castor oil. (vi) Erucic acid (C22: I-cis) is present in many of the oils from brassica seed, such as mustard and Sinapis arvensis. It was formerly present in most rapeseed oil, and rapeseed oil grown in the Third World is still mostly of the high erucic acid form. In view of evidence that erucic acid may cause cardiac lipidosis, new varieties of rapeseed have been introduced which are free of erucic acid. The use of high erucic acid rapeseed oil in foods is subject to legislation (Statutory Instrument No 691, 1977-The Erucic Acid in Foods Regulations 1977). Where necessary, the erucic acid content of the oil must be diluted before use to a level of less than 5%, by blending. (vii) Cetoleic acid (C22: I-cis) is an isomer of 304 FOOD INDUSTRIES MANUAL erucic acid and occurs in fish oils; it has not been implicated as a health hazard, and does not come within the scope of the legislation on erucic acid in foods. oils. PUFAs with trans double bonds are sometimes given names such as 'linolelaidic', but these names lack specificity and are not often used. The trans isomers of some of the above acids have trivial names, e.g. myristelaidic (C14: I-trans), palmitelaidic (C16: I-trans), and brassidic (C22: 1- (3) Trans acids. The trans index is most easily measured by infrared, using IUPAC Method 2.207. However, this may give inaccurate results when cis-trans or trans-trans dienes are present. The cis-trans diene absorbs infrared at 85% of the absorption of the trans-mono-, and the trans-trans diene at 166% (instead of the 200% expected). These influences compensate to some extent in oils containing both cis-trans and trans-trans dienes. In nutritional calculations a trans-mono-, a cistrans diene, and a trans-trans diene each contribute one fatty acid to those classed as trans, and are grouped with the saturated acids in the COMA report. Some individual trans acids, such as elaidic, have been discussed above. trans). (2) Polyunsaturated acids (polyunsaturates, or PUFA). These have more than one double bond in the hydrocarbon chain. In natural vegetable oils and unhydrogenated fish oils these are in the cis-cisI,4-diene structure (all cis-) and these are the EF As. Hydrogenated oils may contain polyunsaturates in which double bond migration or isomerization has taken place, so that not all the bonds are cis-cis, or 1,4-. Identification of the proportion of polyunsaturates which are still cis-cis-I,4- may be carried out by the lipoxidase technique (lUPAC method 2.312). But this is of low accuracy with less than about 15% EF A. Capillary column gc may be used, but here there may be a problem in separating the peaks of positional isomers. The individual members of this group are described below. (i) Linoleic acid (CI8:2-all cis) is the principal acid in saftlower, soya-bean, sunflower and corn oils. It also occurs in smaller amounts in other vegetable, animal and marine oils. It is regarded as the most significant EF A in the diet. (ii) Linolenic acid (CI8:3-all cis) occurs as the principal acid in linseed oil, from which it derives its name. It is also present in smaller amounts in soya-bean and rapeseed oils. The common variety is the ex-isomer. The less common variety, y-linolenic acid (GLA), is a mammalian metabolite of linoleic acid which also occurs in a few vegetable oils, the best known being evening-primrose seed, blackcurrant pip and borage seed oils. Oils containing GLA are said to have enhanced dietary value. Eleostearic acid is the cis-9, trans-II, trans-I3 isomer of linolenic acid found in tung oil, useful in the paint and varnish industry. (iii) Arachidonic acid (C20:4-all cis) is a major constituent of unhydrogenated fish oils. (iv) Eicosapentaenoic acid (C20:5-all cis)-EPA -is a constituent of unhydrogenated fish oils. Other PUF As with chain lengths of up to 26 carbons and up to 6 double bonds occur in fish Essential fatty acids Certain polyunsaturated fatty acids (PUF A) are essential in the diet of animals if proper growth is to be maintained, and these acids are known as essential fatty acids (EFA). Three fatty acids which are effective in curing EFA deficiency syndromes are linoleic, y-linolenic, and arachidonic. Arachidonic acid is the most effective and can be synthesized from linoleic acid in the body by mammals. Considerable importance has been attached to this topic during the last decade, as it has been maintained that essential fatty acids may be effective in preventing coronary heart disease and other vascular problems (F AO, 1980; Holman, 1981). Mammalian biosynthesis converts arachidonic acid into prostaglandins metabolites which have far-reaching effects in the body. The richest common source of linoleic acid is saftlower-seed oil, but as this is expensive, sunflower-seed oil is far more widely used. Soya-bean oil, corn oil and cottonseed oil are also rich sources of linoleic acid. In recent years margarines rich in linoleic acid have been marketed. The immediate metabolite of linoleic acid is y-linolenic acid (GLA). This differs from the normally occurring ex-linolenic acid in the position of its double bonds. The position of the double bonds in unsaturated fatty acids has considerable dietary importance, and in order to emphasize the relationships of classes of compounds metabolized from dietary fatty acids, the position of the double bond is often counted from the methyl end of the fatty acid chain. This is called the 'n-' nomenclature. FATS AND FATTY FOODS II-Linolenic acid is in the n-3 series, whilst GLA is in the n-6 series as is naturally-occurring linoleic acid. GLA is found in very few natural oils, the best known being evening-primrose seed, blackcurrant pip, and borage seed oils. Eicosapentaenoic acid (EPA), a natural component of many fish oils, is a mammalian metabolite of II-linolenic acid. In has been claimed that GLA is more effective in curing essential fatty acid deficiency and other related medical problems. EPA is also said to have beneficial properties, especially for the nervous system and brain formation. Fatty acid composition The fatty acids comprise about 9S% of most oils and the fatty acid composition is the most important chemical characteristic of an oil. The fatty acid compositional ranges for a number of oils are shown in Tables 8.4, 8.S and 8.6. FAT SUBSTITUTES 'Fat substitutes' have been defined as synthetic or natural substances whose molecules closely resemble fat molecules and can replace fats in all applications, even frying. 'Fat mimetics' (or fat imitators) is a name given to substances which imitate the food textural effects of fat, including mouthfeel, but not all of the other properties. The term 'fat replacers' is also used, to cover either type of material. Fat has a number of functions in food which need to be considered when reducing fat levels. It is a high energy nutrient, which in many modern cases is a major reason for wishing to reduce its amount. It contributes characteristically, depending on the extent to which it is emulsified, to the texture, mouthfeel and 'richness' of food. It is a carrier of flavours, whose perception in the mouth may also be influenced by the degree of emulsification. It may influence the appearance of the product before or after cooking. With such a complex of properties and effects it is not surprising that there are few true fat substitutes. Jojoba oil, used for centuries for frying by some American Indian tribes, is coming into increasing use. It is not a triglyceride oil but a wax, therefore is likely to be only poorly metabolized by humans. However it contains a significant proportion (3%) of erucic acid which, if it were liberated in the gut, might have detrimental side-effects; there is therefore some resistance to its widespread use without further testing. Other substances with roughly similar molecular structures to the fats include medium-chain and 30S very-long-chain triglycerides (e.g. caprenin), glyceryl ethers, glycoside fatty acid esters and other polyesters (e.g. sucrose polyester, 'Olestra'). Most attempts at fat substitution tend to avoid applications where all or most of the characteristic properties of fat are essential (such as frying), concentrating instead on products where only some of the effects are required and might be copied using different ingredients. A wide range of such products, carbohydrate-based, protein-based and other, is now available for the enterprising product development department to test. A good list of currently available materials in all the above classes is given in the publication 'Fat Substitutes-an Update' (Food Focus Series, November 1991; Leatherhead Food RA, Leatherhead, UK). FLASH, FIRE AND SMOKE POINTS These three tests are a guide to the content of volatile inflammable organic materials in an oil. They all involve observation of the surface of a fat as it is heated. The smoke point is defined as the temperature at which the sample begins to smoke when tested under the specified conditions of the test; the flash point is the temperature at which combustible products are volatilized in sufficient quantity to allow instantaneous ignition, and the fire point is the temperature at which evolution of volatiles proceeds with sufficient speed to support continuous combustion. The smoke point is of most benefit in assessing the quality of a frying oil, when it is mainly the FF As produced in the frying operation which contribute to the smoke haze. The flash point is of most value with regard to the safety during storage or transport of an oil; the contracts issued by FOSF A International for oils traded in bulk specify that the flash point should be above 121°C (2S0°F). There are two methods for the determination of flash point, namely those of the open, or closed, flash tests. The two methods give different results. FLAVOUR The flavour of a properly refined and deodorized oil is mild and bland. Off-flavours can develop on storage, and these are variously defined as rancidity, hydrogenation off-flavours, or reversion flavours. The food chemist is often concerned in preventing the development of these off-flavours in his processed oils. Table 8.4 Ranges of fatty acid composition of commercially important vegetable oils (%mjm) Fatty acid Oils analysed Palm-kernel Coconut C6 NO-0.8 0.4-0.6 C8 2.5-4.7 6.9-9.4 CI0 2.8-4.5 6.2-7.8 C12 43.6-51.4 C14 C16 High erucic rapeseed Low erucic rapeseed Safllowerseed 0.8-1.3 tr-O.l 0.1 tr-0.2 tr-0.2 9.2-13.9 43.1-46.3 5.6-7.4 2.8-5.1 3.4-6.0 5.3-8.0 tr-O.4 tr-O.l tr-0.3 tr-O.I 0.2-0.5 0.2-0.6 tr-0.2 Soya-bean Maize 45.9-50.3 tr-O.l tr tr-0.3 15.3-17.2 16.8-19.0 0.7-1.0 tr-0.2 tr-0.3 tr-O.I 7.2-10.0 7.7-9.7 21.4-26.4 9.9-12.2 10.7-13.6 0.3-1.1 tr-0.2 C16:1 C18 Sunflower-seed Cottonseeda Groundnut Palm NO-0.2 1.9-3.0 2.3-3.2 2.3-3.2 3.6-5.4 1.8-3.3 2.2-4.4 4.0-5.5 3.0-6.3 0.7-1.3 1.1-2.5 2.1-2.9 C18:1 11.9-18.5 5.4-7.4 14.7-21.4 17.7-25.5 24.6-42.2 36.6-65.3 36.7-40.8 14.0-34.0 9.8-49.8 52.0-65.7 8.4-21.3 C18:2 1.4-3.3 1.3-2.1 46.7-57.7 50.5-56.8 39.4-60.4 15.6-40.7 9.4-11.9 55.5-73.9 13.0-22.9 16.9-24.8 67.7-83.2 C18:3 tr-0.7 tr-0.2 0.1-0.2 5.5-9.5 0.7-1.3 tr-O.l 0.1-0.4 tr-O.l 7.0-10.3 6.5-14.1 tr-O.l 0.1-0.3 tr-0.2 0.2-0.4 0.2-0.6 0.3-0.6 1.1-1.7 0.1-0.4 0.2-0.3 0.2-1.0 0.2-0.8 0.2-0.4 NO-O.5 tr-0.2 0.1 0.2-0.3 0.2-0.4 0.8-1.7 NO-0.3 0.1-0.2 2.6-9.4 1.2-3.4 0.1-0.2 0.2 0.3-0.7 0.1-0.5 2.1-4.4 0.6-1.0 0.3-0.9 0.1-0.5 0.2-0.8 tr-0.3 NO-0.2 5.0-51.6 tr-5.0 tr-l.0 1.2-2.2 0.2-0.3 C20 C20:1 C22 C22:1 C24 NO-O.3 0.1 NO-0.4 0.1-0.4 C24:1 NO = not detected tr = trace Where single values are shown, all samples had same concentration within experimental error. Cottonseed oil also contains small amounts of cyc1opropenoid fatty acids. These normally decompose during conventional gIc of the methyl esters. a 0.1-0.3 0.1-0.2 0.1 0.3-1.1 0.1-0.4 0.1-0.2 Table 8.5 Fatty acid compositions of miscellaneous animal fats (ranges and typical values, % m/m) Fatty acid Chicken fat Pig fats Mutton (lamb) fats Beef fats Brisket Cod Flank Suet Breast Body Shoulder Back Belly Flare Head Cl2 C14 C14:1 0.2 2-4 2-2.5 0.2 1-1.5 0.2 3-5 1-2 0.2 3-4 0.5-1 0.5-1 3.5-5 0.5-1 0.5-1 2.5-4.5 tr-O.5 0.5-1 3-4 tr-l 0.2 1.3 tr 0.2 1.6 tr 0.2 1.7 tr 0.2 1.5 tr 0.2 1.2 0.2 C16 C16:1 21-24 8-9 25.5-29 3.5-4 25-27 4-5 26-28 2-3 20-21 1-2 20-21 1-1.5 19-21 1-1.5 23.8 3.2 25-28.5 2.5-3.5 28-31 1.5-2.5 23-26 3-3.5 23.2 6.5 C18 C18:1 C18:2 C18:3 7-9 45-48 1-2 0.5 17-19.5 35-38 0.5-1.5 0.5 14-18 38-43 1-2 0.5 23-27 30-35 1-1.5 0-1 16-20 36-38 tr-2.5 tr-2 22-26 33-37 2-2.5 tr-1.5 23-27 33-37 2-2.5 tr-1.5 11.7 45.3 9.1 0.8 14-17 37-42 tr-13 0.5-1.5 18-24 30-38 7-12 0.5-1 11-15 41-45 8-13 0.5-1.5 6.4 41.6 18.9 1.3 C20 C20:1 C22 C22:1 C24 C24:1 Others tr-O.l 1-2 tr-O.l tr tr 0.1 0.5-1 tr-O.l tr-0.5 0.5-1 tr tr-0.5 tr-l tr-O.l tr-1.5 2-3 tr-O.l tr-2 1.5-2.5 tr-O.l tr-2 1.5-2 tr tr-O.l tr-O.l tr 5-8 6-8 0.2 1.0 0.3 0.1 0.4 0.3 1-3 0.2 1.0 0.2 0.1 0.3 0.3 1-4 0.3 1 0.2 0.1 0.3 0.3 1-2 0.2 0.5-1.5 0.3 0.1 0.5 0.5 1-2 0.4 -- tr 4-6 4-8 - 1-2 - 1-2 _.- - _ .. - 1-2 -_.- -_.- = trace. Table 8.6 Approximate content of principal fatty acids typical of fish oils (%) C14:0 C16:0 C16:1 C18:1 C20:1 C22:1 C20:5 C22:6 Iodine value Capelin Herring Sprat Norway pout Mackerel Sandeel Menhaden Sardine/ pilchard Horse mackerel Anchoy 7 10 10 14 17 14 8 6 100/140 7 16 6 13 13 20 5 6 110/140 NO 16 7 16 10 14 6 9 125/150 6 13 5 14 11 12 8 13 140 8 14 7 13 12 15 7 8 135/160 7 15 8 9 15 16 9 9 140/175 9 20 12 11 1 0.2 14 8 150/175 8 17 9 12 3 3 17 9 140/200 6 24 7 13 2 2 11 16 180/195 9 19 9 138 5b 2 17 9 170/200 a = contains element of C16:4 content b = C20:1 and C18:4 combined NO = no data 308 FOOD INDUSTRIES MANUAL Flavours are often added to an oil, or to the food recipe, when these are not provided by the other ingredients. In the case of margarine, the flavours are added to give the margarine a flavour approaching that of butter. Early work on butter showed that the lower fatty acids and diacetyl were important flavour constituents. Addition of these compounds to margarine gives an approximation to the flavour of the butter. A comprehensive examination of the trace components of butterfat has shown the C8C14 lactones of hydroxy fatty acids, particularly rand o-lactones, to be important. Other flavour components of butter were identified as acetylmethylcarbinol and the lower-chain fatty acids. Over 80 flavouring materials were identified. Much of this information is available in the patent literature, and clearly many flavour blends are possible, each contributing its own specific taste to a fatty product. Mono- and diglycerides and the nature of the free and combined fatty acids also playa role in flavour, and the addition of specific manufactured mixtures of such compounds is also practised. Heated fat generally has its own flavour and this is very marked when butter is used for frying or other similar purposes such as baking. Margarines or shortenings which develop the appropriate flavour attributes during cooking are said to have 'carry-through flavour'. The texture of a fat can also influence the flavour, in that it influences the release of fat-soluble flavour components. Liquid oils clearly release the components very quickly, whilst solid fats which do not melt on the palate are unlikely to release any flavour at all. Hard fats which melt quickly on the palate, such as cocoa butter, release their flavours quickly giving a sudden flavour impact, whilst fats such as suet, or some types of cocoa butter substitute, melt progressively and give a progressive release of fat-soluble flavours. In this case, the senses become dulled by the initial moderate impact of the flavour, and do not respond to the slow release of additional flavour as the fat slowly melts. It is partly as a result of this that some chocolate coatings appear to have inferior flavours. FRACTIONATION Fractionation is a process applied to semi-solid fats such as palm oil. It involves a physical separation of higher and lower melting triglycerides and results in a semi-solid fat being split into a low-melting oil (olein fraction) and a solid fat (stearin fraction). There are three types of fractionation, namely dry, solvent and detergent fractionation. In dry fractionation, the fat is melted completely and then cooled with agitation until the higher melting fraction crystallizes. The crystals of the stearin fraction are then removed by filtration. In solvent fractionation, the fat is dissolved in a solvent such as acetone or hexane. The warm solution is cooled with agitation until the stearin fraction precipitates and can be removed by filtration. Solvent fractionation gives a more efficient separation than dry fractionation but the costs involved in using organic solvents limit the application of the process. Solvent fractionation is commonly applied in the preparation of palm midfraction which is commonly included in cocoa butter equivalent fats for use in chocolate. Detergent or Lanza fractionation involves the use of an aqueous detergent solution to reduce entrainment of the liquid fraction in the solid crystals in a dry fractionation process. Although the separation efficiency of the dry fractionation is improved, the problems of the eflluent have limited the application of this process. FRYING OILS Frying oils can be considered under two headings: (i) for industrial consumption and (ii) for domestic consumption. The larger market is in the industrial area, where enormous quantities are used for frying fish fingers, pre-cooked chips, crisps, and various snack foods. In the domestic market the appearance on the supermarket shelf is of considerable importance, and oils which will remain clear and bright, without the deposition of solid fat crystals, are in greatest demand. Vegetable oils rich in polyunsaturated acids are satisfactory in this respect, but can oxidize quickly during use in the kitchen, developing off-flavours. This problem is particularly severe with soya-bean and rapeseed oils, as these contain up to 10% of linolenic acid (CI8:3), the triple unsaturation of which renders the oil easily oxidized. This problem can be alleviated by selective hydrogenation of the oil to reduce the linolenic acid to a low level. Hydrogenation also produces high-melting triglycerides, but these may be removed in a dry fractionation process. In a wellcontrolled plant, a yield of 70% of clear liquid oil with a very low linolenic acid content can be obtained from soya or rape oils by this means. Commercial frying oils must also meet strict quality requirements, and here again fluidity at low temperatures can be important. This is especially the case, if, for instance, the oil is stored outside in bulk storage tanks, from where it is piped to the frying installation. It has been known for frying oils to set up in these pipes in cold weather FATS AND FATTY FOODS or overnight, leading to considerable production difficulties. It is also important with snack foods that are eaten cold that the frying medium should give no waxy palate response. Industrial frying oils are also used to produce fried foods which must have a long shelf life, a problem seldom encountered with domestic frying oils. Measures are therefore taken to preserve the quality of the frying oil, and thus ensure adequate shelf life of the fried food. The addition of suitable antioxidants, and of methyl polysiloxane anti-foam agent, are often recommended, as is the continuous filtration of the frying oil in a recirculatory system. The fried food normally absorbs a proportion of oil, which is made good by 'topping up' with fresh oil. In a well-organized system the amount of 'top up' is sufficient to maintain the oil in adequate condition, so that there is no need to reject frying oil on the basis of deterioration in quality. In both domestic and industrial frying operations, smoke haze can be a problem. Smoke arises from the volatilization of breakdown products in the oil, in particular free fatty acids. Lauric oils are unsatisfactory frying oils since the constituent fatty acids are more volatile than with the other oils. In the frying process, the oil acts as a medium for heat transfer from the fryer to the product. The industrial fryer can be heated directly, often with gas jets under the base of the fryer, or can be heated by internal coils or by external heat exchangers. Many modem industrial frying operations now have external heat exchangers through which the oil is pumped, in conjunction with a filtration system. GHEE, VANASPATI See Chapter 3. HYDROGENATION Hydrogenation, or hardening, causes an increase in the melting point of fats through classical addition of hydrogen to some, if not all, of the double bonds present in the fatty acids of the triglycerides. It also stabilizes the fat toward oxidation, and often has a bleaching effect. Hydrogenation has great commercial significance in the edible fat industry, as many of the raw materials are liquid oils at room temperature and are liable to oxidative deterioration. Many of the cooking fats and margarines available today contain a proportion of hydrogenated fat blended with natural oils. Fish oil is an exception among food oils in that it is very seldom used in the unhardened condition, as off-flavours very quickly develop in the unhydrogenated oil. 309 The increase of melting point (mp) with decreasing unsaturation, and double bond geometry, can be demonstrated in the series of eighteen carbon fatty acids as follows: linolenic acid, 3 cis double bonds, mp - IISC; linoleic acid 2 cis double bonds, mp -6°C; oleic acid, I cis double bond, mp 16.2°C; elaidic acid, I trans double bond, mp 42°C; stearic acid, 0 double bonds, mp n°e. The difference between cis and trans double bonds lies in the positions of the other carbon groups attached to the carbons linked by the double bonds. In the cis form these both lie on the same side of the double bond, whereas in trans isomers they lie on opposite sides. The cis form occurs almost exclusively in natural fats. This has led to some criticism of hydrogenated fats containing high levels of trans double bonds. In the preparation of edible fats, the majority of oils are only partially hydrogenated, the double bonds which remain may be in the cis or the trans form, and there may be either one or two double bonds per fatty acid molecule. Hydrogenation conditions, and CATALYSTS are carefully selected in order to regulate the ratio of cis to trans double bonds, and the proportions of saturated, mono- and polyunsaturated acids. It is the balance of these different factors which governs the physical properties of the product and suits it for a frying oil, a soft tub margarine, a harder block margarine, a fat for cream fillings in biscuits, a dough fat or a coating. Hydrogenation is generally carried out in special pressure vessels, with an operating pressure of from 20 psi to up to 100 psi, and a temperature of 100180°e. After the catalyst is added, hydrogen is pumped into the oil, which is vigorously stirred. Hydrogenation is an exothermic reaction with fresh nickel catalysts, but not so with poisoned catalysts, and the heating requirements must therefore be balanced depending on the catalyst. Normally, hydrogenation is a batch process, but efforts are being made to devise continuous processes in which the catalyst is supported in heated columns. The hydrogenation process can be controlled by measuring the refractive index, iodine value, or melting point of samples withdrawn at intervals. Hydrogenated fats are filtered to remove the hydrogenation catalyst, subjected to a light earth bleach and deodorized before they can be used for edible purposes. In some countries such as the USA and Canada, the earth bleach and catalyst removal are sometimes combined into a single operation, but in these cases the nickel catalyst cannot be recovered. Patterson (1983) gives an excellent review of hydrogenation. 310 FOOD INDUSTRIES MANUAL ICE-CREAM See Chapter 3. number of triglycerides generated becomes extremely high, leading to complex eutectic and intersolubility interactions between the different triglyceride groups. IDENTIFICATION AGENTS ISO-ACIDS In some countries the addition of identification agents to most food fats is compulsory by law. The process is intended to make adulteration of noble fats such as olive oils easily detected. Development of modem analytical techniques should make such additions unnecessary, however. Up to 5% sesame oil may be added to a fat blend, after which it can be detected by the BAUDOUIN TEST. An alternative is 0.2% starch, which can be detected by the blue colour developed on addition of iodine. In the EC, butter is sometimes sold at a subsidized price in an effort to reduce the butter 'mountain'. This cheap butter, known as 'intervention butter', may only be used for specified purposes. In order to control its use and detect fraudulent use in nonpermitted outlets, various identification agents are added. These are stigmasterol, ethyl butyrate, vanillin, enanthic acid (C7:0) and carotene, in various combinations. During hydrogenation, double-bond isomerization and migration take place. The resulting positional and geometric fatty acid isomers are sometimes termed iso-acids. This term is less often used nowadays, trans-isomers being specifically referred to as such. LECITHIN Lecithin is a phospholipid, known chemically also as phosphatidyl choline. The lecithin molecule contains glycerol and fatty acids, as do the simple glycerides, but also contains phosphoric acid and choline residues. An (X-lecithin is represented by the formula shown in Figure 8.2. ~-Lecithn contains the phosphoric acid and choline moieties on the centre carbon atom of the glycerol. Lecithins are widely distributed in body cells and are found particularly in egg yolk and liver. INTER-ESTERIFICATION Triglycerides consist of three fatty acids esterified with the three free hydroxyl groups of the original glycerol molecule. The physical and chemical properties of the resulting triglyceride vary depending upon the nature and positions of the fatty acid residues in the triglyceride molecule. In many natural oils and fats the positions of the individual fatty acids are controlled during biosynthesis. The physical properties of an oil can be modified by rearrangement of the fatty acids in the triglyceride molecules. To achieve this, the oil or fat is heated to a temperature of about 100°C together with an inter-esterification catalyst (see CATALYST). Under these conditions the fatty acids are momentarily liberated but almost immediately recombined with different hydroxyl groups in a random manner. Inter-esterified fats are therefore often referred to as 'randomized'. This feature can be especially attractive when two different oils are first blended and then inter-esterified. Inter-esterified oils have different properties from those of the original oil, and are frequently used in tailor-making fatty products for specific uses. However, it is almost impossible to predict the properties of an inter-esterified oil, or oil blend, without recourse to experimental information, as the Figure 8.2 Structure of ex-lecithin. R, R' = fatty acids. The most important source of commercial lecithin is soya-bean oil. The commercial product contains other phospholipids (cephalin, phosphatidyl serine and inositol). Soya-bean lecithin is separated by heating the crude oil with water and centrifuging. The water is evaporated, and the crude residual lecithin may be bleached with peroxide. However, where the product is needed for food, unbleached crude soya lecithin should be obtained, as the bleached lecithin contains fatty acid peroxides which can lead to off-flavours in the finished food. Soya lecithin contains 60-75% phospholipid and up to 40% oil. Lecithin has marked surface-activity properties and is widely used in the food industry, FATS AND FATTY FOODS for example as an antispattering agent in margarine, and for viscosity reduction in chocolate. A review of lecithin production and properties is given in symposium papers (American Oil Chemists Society, 1980). LIPASES Lipases, or glycerol ester hydrolases, are enzymes which catalyse the breakdown of oils and fats. They are concerned in the digestion of fat, splitting triglycerides into fatty acids, diglycerides, monoglycerides and glycerol. Resynthesis of triglycerides may take place partly in the intestinal lumen, where pancreatic lipase has synthetic as well as hydrolytic functions. Lipases may originate from plant, animal or microbiological sources. Controlled action of these enzymes is useful in the development of desirable flavours in cheeses and ~ther fermented dairy products. Qualitatively, hpases release fatty acids from fat-based products, but variations exist in the kinds or quantities of specific fatty acids released, depending upon the nature and source of the lipase. Lipases are usually destroyed by common pasteurization treatment, but those of microbiological origin may be heat-stable and may be destroyed only by autoclaving treatment. Lipase is generally assayed by the indoxyl acetate test. The selectivity of pancreatic lipase in partial hydrolysis of triglycerides has been used as a biochemical method of analysis in establishing the configuration of some natural fats. Acyl groups attached to the 1- and 3-positions of the glycerol moiety are hydrolysed preferentially, allowing the residual 2-monoglycerides to be separated and subjected to independent fatty acid analysis. This has enabled theories of fatty acid distribution in triglycerides to be developed, the application of which often allow the calculation of triglyceride composition from simple fatty acid data. However, confusions can arise through misapplication of the theory. The technique may be used as a criterion of purity. More recently, specific lipases have been used to carry out microbiological modification of oils and fats by i~cubaton of triglycerides with carefully chosen mixtures of fatty acids, or fatty acid methyl esters, and lipase enzymes. These techniques may be particularly useful in manufacturing fats with properties similar to those of cocoa butter. LOW-FAT SPREADS See under MARGARINE. 311 MARGARINE Margarine is a fatty food closely resembling butter. The fat of margarine is not derived from milk fat however, or, at most, only to a minor extent: Margarine was invented in the 19th century by a Frenchman, Mege Mouries, who patented his original process in 1869. Mouries won a competition organized by the French Government for a butter substitute, cheaper and less perishable than butter, needed to alleviate the shortage of fats among poorer parts of the population and the armed forces. The process was taken up in Holland by Jurgens of Oss and in a number of other countries. ' The term 'margarine' is derived from the Greek word margarites, meaning pearl, and refers to the pearly lustre of the fat then known as margaric acid and subsequently shown to be a mixture of stearic and palmitic acids. It should be pronounced with a hard 'g', but it is often mispronounced. The basic method margarine consists, as it did in Mege Mouries' day, of emulsifying a purified oil blend with skim milk, chilling the mixture to solidify it, and working it to improve the texture. Margarine is subject to statutory regulations which vary throughout the world. In the UK i~ must not contain more than 16% moisture, nor less than 80% fat, the balance being salt, protein, colouring matter, emulsifiers, antioxidants and vitamins, ingredients which are also subject to regulations. World production World production rose from a mere hundred thousand tons in 1875 to one million tons in 1925 two million in 1950, three million in 1954, fou; million in 1959, and was just reaching five million tons in the late 1960s. These increases in production were reflected in UK manufacture also. This was 300000 tons in 1920, fell to 140000 in 1925, but ~as since risen to 211000 tons in 1938, 380000 m 1950, and to a peak of 453000 tons in 1951. Production then fell gradually to just over 300000 tons in 1965, after which it rose steadily to a total of 380000 tons in 1980. At the time of writing, sales of margarine have overtaken those of butter but the market for non-butter yellow fat spreads i~ now split between regular margarine and LOW-FAT SPREADS. There are also products in which cows' butter is with polyunsaturated vegetable oils to give a dietary product with a high essential fatty acid (EF A) content. These may have a little less than the 80% fat content of margarines and butters, and may not therefore be described as such. ble~d 312 FOOD INDUSTRIES MANUAL Raw materials (i) Oil. The selection of oils for margarine is made by the manufacturer with regard to cost, quality, and desired properties in the margarine. The stability, consistency, plastic range, and EFA level must all be considered. In selecting a blend, information about the ratio of solid and liquid glycerides present at various temperatures is important. The pattern of usage of oils for margarine manufacture has changed considerably in recent years. Thus, in 1960, 56% of the oils used for margarine manufacture in the UK were vegetable oils, whilst in 1965 this figure had dropped to 37% due to the increased availability of fish oils, which almost completely replaced whale oil. Lard has also been used when it has been available cheaply, notably from 1962 to 1965. In recent years, rapeseed, soya-bean, palm and sunflower-seed have been the most important vegetable oils used, partly in view of their availability, but also in the case of soya-bean and sunflower-seed oils as a result of their high EF A contents. Of course the pattern of raw material usage will vary in different parts of the world, and the increasing quantities of rapeseed oil currently grown within the EC has been reflected in the increasing use of rapeseed oil in European margarines. Speciality margarines may of course contain a preponderance of a particular component, and in this respect it should be noted that the dietary margarines high in essential fatty acids are normally based on sunflower-seed oil, while margarines said to have a very close resemblance to butter are often based on fractions derived from beef tallow. (ii) The aqueous phase. About 16-18% of margarine consists of an aqueous milk preparation, except in certain special products such as pastry and kosher margarines, when just water may be used. In the production of the aqueous phase pasteurized fresh milk or reconstituted dry milk is subjected to a ripening process. During this process diacetyl and other aroma-giving substances are developed. To induce the ripening process, carefully selected strains of Streptococcus cremoris and S. citrovorus are added to milk held in ripening vats at 20° to 22°C and at a pH of 5.3 to 6.3. pumps may be used. The fat blend may contain natural crude fats, or processed fats such as fractionated, hydrogenated or interesterified mixtures. It is first refined and deodorized and then emulsified with the aqueous phase, emulsifiers being generally added at this point. Other ingredients such as vitamins, dyes, flavours, etc., are usually incorporated just before emulsification. If emulsification is to take place in a VOTATOR, the fat and aqueous phases can be fed separately by proportioning pumps and emulsification carried out in the chilling tubes. Packing Margarine is moulded and packed directly from the production unit. Rectangular half-pound or 250 g blocks are a common unit while the softer margarines are packed directly into plastic tubs. Modem automatic packaging machines, such as those manufactured by Forgrove Machinery Co., Benz and Hilgers, and Kunster Fn!res, operate at very high speeds of over 150 packets per minute. It is now common to use a mechanical case packer. Whipped margarines Margarines containing a relatively large volume of finely dispersed gas (air or nitrogen) and hence of high volume in relation to weight, are sold in the UK. These products are claimed to spread easily, to mix more readily in cake making and to be better as cooking fats. Refrigerator margarines Margarines usually have a fat blend which is so designed that the product will spread well at normal room temperatures. Use of refrigerators for storing margarines has led to the introduction of margarines that will spread well immediately after removal from the refrigerator as well as at normal room temperature. These margarines normally contain a high proportion of liquid oil and of solid fats which melt quickly in the mouth, although they must give sufficient body to the margarine over the desired temperature range. Low-fat spreads Production methods The first step in the production of margarine is the preparation of the fat blend. A weighing tank is often used for measuring out the fat ingredients; this may be done automatically, or metering In the last decade a number of low-fat spreads have appeared on the market. As these contain less than the statutory amount of fat, it is not legally possible to call them margarines, although they are often referred to as such by the public. These spreads FATS AND FATTY FOODS contain a higher proportion of water and may be useful to people who need to reduce the fat content of their diets. A blend of stabilizers and emulsifiers is necessary to retain the plasticity range of these products. The terms 'halverine' or 'minarine' are sometimes used to describe these low-calorie spreadable table fats. MAYONNAISE Mayonnaise is an emulsion of vegetable oil, egg yolk or whole egg, vinegar, lemon juice and salt, mustard or other seasoning. Usually, mayonnaise contains 70-85% of oil, and it is difficult to produce a product having a sufficiently stiff body with a proportion of less than 70% oil. A typical formulation is: oil 75%, vinegar (4.5% acetic acid) 10.8%, egg yolk 9%, sugar 2.5%, salt l.5%, mustard 1% and white pepper 0.2%. The oil forms an internal discontinuous phase dispersed in an external aqueous phase of vinegar, egg yolk and other ingredients. In a good mayonnaise the largest droplets are not more than 8 11m in size and many particles are in the size range of 2-4 11m. The temperature of mixing is important; too thin a product may result if mixing is carried out above 16-21°C. Thicker emulsions can be made by mixing at 4°C, but it is usually inconvenient to work at this temperature. In making mayonnaise the egg yolks, sugar, seasonings and part of the vinegar are mixed, the oil is gradually beaten in and the emulsion is thinned by addition of the remainder of the vinegar. During the mixing, about 10-20% of air is usually incorporated. A coarsely emulsified product can be further treated in a colloid mill. It is essential to use best quality oils, corn oil, sunflower-seed oil, or winterized cottonseed oil being suitable. Oils which throw down a deposit, or crystallize, at refrigerator temperatures are generally unsatisfactory, as crystallization of the oil breaks the emulsion and can cause separation of the phases when the mayonnaise warms to room temperature. MEDIUM-CHAIN TRIGLYCERIDES Medium-chain triglycerides (MCT) are triglycerides based on fatty acids with 8-10 carbon atoms. Fats containing high levels of these triglycerides are beneficial to patients suffering from digestive illnesses such as tropical sprue and idiopathic steatorrhoea, who are unable to assimilate normal triglycerides because they lack the necessary enzymes. 313 MIS CELLA The solution of oil in solvent obtained during solvent extraction of oilseeds. MONOGLYCERIDES Monoglycerides are partial esters of fatty acids with glycerol in which only one hydroxyl group is esterified, while the other two remain free. Commercial monoglycerides are made by reacting triglycerides of fatty acids with glycerol at an elevated temperature. The product is an equilibrium mixture of glycerol, free fatty acid, and mono-, di- and triglycerides. The economic equilibrium mixture contains 35-40% of monoglyceride. A second type of product contains over 90% monoglyceride, and is made by molecular distillation of the 35-40% product. Monoglycerides are excellent emulsifiers and have been widely used in the food industry (see EMULSIFIERS) in bread, cakes, margarines, icecreams, etc. MYCOTOXINS See AFLATOXINS. NEUTRALIZATION The neutralization of crude oils to remove free fatty acids (FFAs) as distinct from other methods of deacidification, consists of treating the crude oil with aqueous alkali, usually caustic soda or sodium carbonate (soda ash). The oil is heated to between 75-95°C, and aqueous alkali added as a fine spray from above (sparging). The fine droplets of aqueous alkali fall through the oil, reacting with the FF As to form soaps which are soluble in the hot water. The aqueous soap solution is then separated from the oil either by settling or by centrifuging. In the former case, the soap solution, or soap stock, is run off and the oil is then washed with several doses of hot water, which remove any residual soap from the oil. The wash waters are then separated from the bulk oil by settling or centrifuging as before. The oil is dried under vacuum before treatment with earth in a bleaching process. Variations of the techniques are employed, particularly with regard to the quantity and strength of alkali, stirring speeds, use of salt solution, etc. These variations are designed primarily to prevent 314 FOOD INDUSTRIES MANUAL emulsification of the water and oil, and to minimize occlusion of neutral oil in the soap stock. Variations may also be introduced in order to assist removal of non-triglyceride impurities present in the original oil, depending on the crude oil quality. The traditional plant for neutralization consists of mild steel vessels holding up to 25 tons of crude oil. The vessels have conical bottoms, mechanical stirrers, heating coils, and means for spraying alkali into the oil. Often, but not always, the bleaching process is carried out in the same vessel, which is therefore capable of being closed and evacuated for drying and bleaching. However, continuous plant is also employed, based usually on continuous alkali and wash water addition, in conjunction with centrifugal separation. In continuous neutralization the time of contact of the oil with alkali is considerably shorter than is the case with batch processing. Among companies providing continuous processing plants are the Alfa-Laval Co., Sharples Corp., Clayton and Refining Inc., and Simon Rosedowns Ltd. Other neutralizing methods include the use of ammonium hydroxide instead of conventional alkali and neutralization of oil in a solvent or in the miscella, methods designed to further decrease the loss of neutral oil. OILS AND FATS The production of edible oils and fats has increased progressively in recent time. This has been mainly effected by rapid increases in the production of soya-bean oil, palm oil, and sunflower-seed oil, whilst in the EC and Canada the production of rapeseed oil has increased considerably in the last 5 to 10 years. Table 8.1 shows the world production of edible oils since 1985, while properties of many oils and fats are given in Tables 8.2 to 8.6. Properties and features of the most important oils are reviewed below. Babassu oil Babassu palms (Orhignya rnatiana or O. oleiferae) grow only in Brazil, mainly in the remoter parts, as a wild crop. The output of oil varies considerably from year to year. Potentially, they are a tremendous source of edible babassu oil, but expansion of production is limited by the technical difficulty of cracking the very hard thick shell of the nut. The oil features to only a very minor extent in international trade. Its composition and properties are similar to those of coconut and palm kernel oils. Blackcurrant oil This oil, extracted from the seeds of the blackcurrant plant, has generated interest recently because it is a good source of y-linolenic acid. Borage oil The oil extracted from borage is higher in y-linolenic acid than evening primrose oil and consequently is of interest as a nutritional supplement. Coconut oil Coconut oil is extracted from copra, which is dried pieces of coconut kernel. Coconuts are fruit of the coconut palm (Cocos nucifera), which is cultivated in tropical coastal areas. Dried copra contains 6065% oil, and in this respect it is the oiliest of the commercial oilseed crops. World production is about 2640000 tons (Table 8.1), about half of which is traded internationally. The main producing area is the Philippines; other producing areas, such as West Malaysia and Sri Lanka, produce only about 20% of that harvested in the Philippines. Coconut oil, formerly used in margarine and cooking fats, is now less common in view of its high price. However, it is still used in the manufacture of cream fillings for biscuits and in other confectionery applications. Coconut oil is a lauric oil similar in composition to palm kernel and babassu oils. The high content of lauric acid imparts a plastic consistency to the fat at room temperature, but this melts rapidly at body temperature, explaining the popularity of the fat in confectionery products. Cottonseed oil The production of cottonseed oil varies with the cotton fibre industry. In 1984/85, 3770000 tons of cottonseed oil were produced (Table 8.1), the bulk being used in the main producing countries of the USA, Brazil, mainland China, the USSR, India, and Pakistan. Egypt and. countries in the Middle East formerly featured as main cottonseed producers and exporters, but are not so prominent now in this industry. Cottonseed has an oil content of 15-25%, but the extraction rate is often only about 16%. The kernel contains 30-38% of oil, but industrially processed seeds invariably have adherent linters. Cottonseed oil has a strong flavour, and has a dark red colour due to the presence of gums and FATS AND FATTY FOODS gossypol. Cottonseed oil can be refined to give a pale yellow oil, however, but it requires thorough refining. Oil produced in the USA is generally considered to be of the best quality. Cottonseed oil is used in production of margarine, shortenings, and as a cooking fat. Winterized cottonseed oil is used as a salad oil. Cottonseed oil may be detected by the HALPHEN REACTION. The fatty acid composition is shown in Table 8.4 other properties being given in Table 8.2. Corn oil (maize-germ oil) The main producer of corn oil is the USA, the annual production being almost twice that of South Africa, its nearest competitor. In Europe, France is a significant producer with about 12000 tons per annum. World production is rising slowly. Corn oil is used mainly as a salad or frying oil, but health margarines based on corn oil have been marketed. The low cloud point makes it a useful edible oil. The kernel of the corn plant, Zea mays, contains only 3-7% oil, the oil being concentrated in the germ or embryo. The germ is separated from the kernel in the milling process, and is crushed to obtain the oil. The composition and properties of the oil are given in Tables 8.2 and 8.4. Corn oil contains a higher level of sterols (up to 2%) than most other liquid vegetable oils. Evening primrose oil This expensive oil is a rich source of y-linolenic acid (see ESSENTIAL FATTY ACIDS), an EF A said by some to have potent properties. Fish oils Fish oils are obtained by the extraction of oil from the whole fish. They are highly unsaturated, containing a proportion of penta- and hexaenoic acids, as shown in Table 8.6. This renders them particularly susceptible to oxidation. They must, therefore, be carefully hydrogenated and refined before they can be used in foods. Since the 1960s there has been a great upsurge in the amount of fish oil available throughout the world. In the early 1960s an exceptional growth in production of fish oil from anchoveta took place in Peru, reaching 151000 tons in 1962. However, production of Peruvian fish oil has since diminished, due to a combination of overfishing and a change in the Humboldt ocean currents off the coast of Peru. In the mid-1960s there were also substantial 315 increases in the amounts of Norwegian and Icelandic herring and American menhaden oils. Consequently, the amount of fish oil used in the western world for margarines and shortenings has increased. In the UK, fish oils are now a major edible oil, accounting for 20-30% of UK consumption, ranking second to rapeseed oil. The demand for fish oils has stimulated production elsewhere, and sardine and oils are now produced from mackerel, in Japan from menhaden in the USA, capelin in Norway and Iceland, sand eel and Norway pout in Denmark, and pilchard and horse mackerel in Chile. Grapeseed oil Grapeseed oil is derived from the seeds of grapes (Vilis vinifera Linnaeus) as a by-product of the wine industry, mainly in Argentina and Italy. The oil content varies from about 6% for black grapes to 20% for white grapes. The oil is high in polyunsaturated fatty acids, mainly linoleic acid. It is used as a substitute for linseed oil in the manufacture of paints but may also be used for edible purposes after refining. Groundnut oil (arachis or peanut oil) Although production of groundnut oil has varied over the years (Table 8.1) the amount traded internationally has stayed fairly static. In 1938, 800000 tons of groundnut oil were exported by the producing countries. This fell to 700000 tons in 1954, rose to 900000 tons in 1977/78, but fell again to 650000 tons in 1980/81. The fact that much of the oil is consumed in the country of origin is illustrated by the fact that about 3 195000 tons of oil are produced throughout the world at the present time. India is currently the largest producer of groundnuts, having produced 5 000 000 tons in 1980/81 and 6000000 tons in 1981/82. However, none of this is exported. Mainland China both produces and exports groundnuts for oil production, while the USA produces groundnuts mainly for the edible groundnut trade. The groundnut consists of a shell, a thin red skin and a kernel. Shelling is usually carried out at the point of harvesting. The kernels contain 40-50% of oil, which is obtained by a combination of pressing and solvent extraction. The residual meal is a valuable animal feedingstuff because of its high protein content. The oil is pale yellow and has the characteristic flavour of groundnuts when fresh and produced from good-quality kernels. This aromatic 316 FOOD INDUSTRIES MANUAL oil is prized in some parts of the world, but in general the oil is refined and deodorized. The oil is widely used on the continent as a frying and salad oil. Groundnuts infected with Aspergillus flavus mould contain aflatoxin, and while this is removed from the oil during normal refining, it remains in the oilseed meal or cake. This has resulted in a dramatic fall in the use of groundnut meal in animal feedingstuffs, and must in time rebound on the price and availability of groundnut oil. Hard butters Hard butters are vegetable fats which melt over a narrow temperature range. They are often used in the manufacture of cocoa butter replacement fats. The most common are COCOA BUTTER and illipe, sal and shea butters. (i) Illipe butter (Borneo tallow). This fat is derived from the seeds of jungle trees such as Shorea stenoptera, which grow wild in Sarawak and other parts of northern Borneo. The composition of the fat resembles that of cocoa butter and its main use is as a cocoa butter equivalent per se, or as a component of cocoa butter equivalent (CBE) blends. The trees crop erratically, and the nuts are harvested by the local population on a sporadic basis. This has in the past led to rumours that a crop is available once every seven years. An unfortunate confusion has arisen in botanical circles with nuts from the Bassia species, which grows in India, and is sometimes referred to as 'true illipe'. Fat from the seeds of Bassia species is of little value in chocolate or CBE production, and is seldom harvested or traded. (ii) Sal fat. Sal fat is one of the newest additions to the range of hard butters available for CBE formulation. Sal trees grow in remote areas of India, bearing nuts about the size of European acorns. The nuts fall to the ground shortly before the onset of the seasonal monsoon, leading to considerable difficulties in harvesting and collection. Nevertheless, the Indian authorities have made considerable advances in the collection of sal seeds. The nut contains only about 14% oil, which must therefore be removed by solvent extraction. The oil often has a very intense green colour, but this can be alleviated by a fractionation process, most of the colour remaining with the softer, or olein, fraction. The harder, stearin, fraction may be slightly modified by a very mild hydrogenation, after which it is bleached and deodorized for use in chocolate and CBE manufacture. Sal fat is now exported to many parts of the world, and is becoming an important source of foreign currency for the Indian Government. (iii) Shea butter. Shea nuts are obtained from a tree (Butyrospermum parkiz) which grows wild in West Africa, Upper Volta and Uganda. The nut contains 40-55% of a hard edible fat, which has up to 10% of unsaponifiable matter. Shea butter therefore has one of the highest unsaponifiable matter contents of any natural vegetable oil. The unsaponifiable matter comprises a mixture of terpenoid hydrocarbons. Shea butter can be processed to remove the un saponifiable matter, and solvent-fractionated to give hard and soft fats. The hard stearin fraction can be used as a constituent in chocolate, or as a component in a CBE formulation. Trade in shea nuts and shea butter varies sporadically with varying climatic and harvesting conditions in West Africa, where prices offered by Government agencies sometimes lead to smuggling. Hazelnut oil Hazelnut oil is a liquid oil, often sold in health food shops as a salad oil. It is rich in mono-saturated fatty acids and has an attractive nutty flavour. The kernels contain 50-68% oil, usually extracted by cold pressing. Jojoba oil Jojoba oil is derived from the seeds of the jojoba shrub (Simmondsia chinensis), and is the subject of growing interest as a replacement for sperm whale oil. As the shrub grows in arid regions such as Arizona, Mexico, the Negev desert, Northern Australia, the Sahel region of Nigeria, etc., it is seen as a means of bringing agricultural industry to these areas. Chemically the oil is a liquid wax, comprising esters of the long-chain eicosenoic and decosenoic (erucic) acids with eicosanol and docosanol alcohols. Its main applications are in the industrial sector and in cosmetics, but several food applications, including use as a coating agent for dried fruits, are foreseen. Lard The most useful form of lard is obtained by wet rendering of pig fat, and this is known as prime steam lard. Refined lard of commerce is usually FATS AND FATTY FOODS prime steam lard which has been dried, clarified and solidified. Lard is also obtained by a dry rendering process and, when made this way, tends to be darker and to be more strongly flavoured. A further type is 'continuously rendered lard', which is continuously comminuted, heated and then centrifuged. The composition of lard varies considerably (Tables 8.2 and 8.5) with the animal from which it is obtained, the part of the animal, and the diet on which the animal has been fed. The fat from an individual animal becomes increasingly unsaturated as one goes from the internal organs outwards toward the back. Lard from the USA tends to have a higher iodine value than European lard. Lard has a relatively low resistance to oxidation, due to a deficiency of natural antioxidants. Because of this, lard is often treated with synthetic antioxidants before sale. Lard is also important as a shortening and has been used for many years for this purpose. However, its creaming properties are not good and it possesses a decided flavour, which may be a disadvantage. The properties of lard can, however, be modified by interesterification, and the consistency and performance in cake making are thereby improved. World production of lard is shown in Table 8.1. Linseed oil Linseed oil is extracted from the seed of the flax plant (Linum usitatissimum Linnaeus) which contains 35-45% oil. The main producers include Argentina, India, Canada and states of the former Soviet Union. Linseed oil is mainly used as a drying oil for the oleochemicals industry particularly for paints, varnish and linoleum. The high ex-linolenic acid content (57%) makes it suitable for these applications. However, the oil is also used for edible purposes. In India about 35-40% of the oil is consumed as cooking and frying oil. Hydrogenation of the oil or blending with other oils are often needed to give the oil sufficient stability for use as a cooking oil. However, recent nutritional interest in n-3 fatty acids which include ex-linolenic acid has led to cold-pressed linseed oil and ground flaxseed products being sold in health-food shops. The world production of the oil in 1990-1991 was 2.7 million tonnes. Olive oil Olive oil is derived from the fruit of Olea europaea, the olive tree, which grows extensively in countries 317 with a Mediterranean climate. The yield of olive oil varies considerably from year to year according to the conditions, leading to price variations. Because of this, most olive oil producing countries fix a guaranteed minimum price for the oil. They may reserve stocks of the oil from a good year to tide them over a bad year. Olive oil is considered to be the best of the liquid edible oils for salad and culinary purposes, and the finest quality 'virgin' olive oil is used without refining. It has a fine flavour and a very good shelf life. Refined olive oils are also obtained from crude olive oils of inferior organoleptic properties, or oils obtained by solvent extraction. The olive also contains a kernel, the oil from which has a similar composition. Refined olive oil may at times contain small amounts of olive kernel oil. The high esteem in which olive oil is held in some Mediterranean countries can lead to political and other problems. The SPANISH OIL SICKNESS was caused by unscrupulous dealers selling contaminated rapeseed oil as a substitute for olive oil, or in blends with it. In the EC olive oil has a guaranteed price, and at the time of writing there is confusion about the future of the olive oil market as the Common Agricultural Policy of the EC is extended to Spanish and Greek olive oil production. World production is shown in Table 8.1. Palm kernel oil Palm-kernel oil (PKO) is extracted from the kernel of the oil palm (see Palm oil, below). It is a lauric oil, very similar in appearance and constitution to coconut oil, containing 83% saturated fatty acids, mainly lauric (Table 8.4). PKO was formerly extensively used in margarine manufacture but it is seldom used now as technological advances have enabled the use of other, cheaper oils. PKO is also used as a confectioners' hard fat in the production of chocolate-type coatings for baked products. The oil may be fractionated, to produce a hard fat stearin which is very useful as a cocoa butter substitute. However, palm-kernel stearins are not compatible with cocoa butter and cannot therefore be used in the formation of CBEs. Palm-kernel oil is also widely used as a component in the filling creams in cream biscuits and in coffee whiteners for vending machines and domestic use. West Malaysia is the main exporter of PKO, exporting 200000 tonnes in 1979/80. Nigeria is also a major producer, having exported 81 000 tonnes in the same period. World production is shown in Table 8.1. 318 FOOD INDUSTRIES MANUAL Palm oil The oil palm (Elaeis guineensis) is native to West Africa but is also cultivated in southeast Asia, especially Malaysia. The fruit consists of mesocarp, or outer pulp, endocarp or shell, and the palm kernel itself. The mesocarp contains 25-55% of palm oil, whilst the kernel contains 45-55% PKO. Although both oils are derived from the same fruit, they differ markedly in composition (Table 8.2) and the palm kernels are therefore carefully separated from the pulp during processing. Palm oil must be extracted at the point of harvesting, as enzymes present in the fruit would otherwise cause hydrolysis and deterioration of the oil. The extraction units are therefore located in the centre of plantations. As the trees bear fruit all year round, and as transportation to the processing plant is so short, the palm oil plantation and processing plant is the most productive source of vegetable oil in the world. As the fruit is a tree crop, the harvest cannot be altered on a short-term basis by planting schedules. World exports of palm oil have risen considerably in recent times. In 1938 400000 tonnes were traded internationally in export markets. This rose to 1 000 000 tonnes in 1971/72, 2 000 000 tonnes in 1976/77, and was 6720000 tonnes in 1984/85 (Table 8.1). These dramatic production increases are expected to continue in the future, as selected palm tree strains are now being cultivated by cloning. Pollination of the flowers in Malaysian plantations is now being assisted by the Elaeidobius species of weevil, which will probably have a farreaching effect on the production of palm and palm kernel oils in Malaysia. Palm oil is a semi-solid fat, and as such it needs no hydrogenation prior to use in food applications. It is often used as a component in margarine, biscuit fat blends, etc. Palm oil may be fractionated into several components. In Malaysia, it is often fractionated by dry or detergent fractionation processes into a hard stearin fraction and an almost liquid olein. This olein is much used in warmer countries as a frying oil, but has less attraction in Europe for this purpose as it tends to throw down a deposit of intermediate melting triglycerides in temperate climates. Palm oil may also be solvent fractionated to give a more liquid olein, a middle melting point fraction and a very hard stearin or upper fraction. The middle melting fraction contains large quantities of the triglyceride 'POP', a major component of cocoa butter. Palm mid-fraction is for this reason an important CBE component. As it is usually the cheapest component in the blend, and may be the only component not subject to political and/or climatic pressure on its availability (see Hard butters, above), much effort has been spent on obtaining palm mid-fractions of the very best quality. The composition and properties of palm oil are given in Tables 8.2 and 8.4. Premier jus Premier jus ('first juice') is an old-established name applied to carefully rendered fresh beef suet (see Tallow, below). Rapeseed oil Rapeseed oil is grown in temperate and warm temperate zones, both summer and winter varieties being sown. Several varieties of Brassica give rise to rapeseed, including Brassica napus and B. campestris. The oil is known as colza oil in some parts of Europe. In the early 1950s rapeseed oil contained a high level of erucic acid, and this was implicated in certain dietary and health problems. Canadian researchers were able to breed a new variety of rapeseed in which the oil was free of erucic acid. This oil is now known as low erucic acid rape (LEAR). As it is a temperate-climate crop, its cultivation has been encouraged in Canada and in the EC, where it now forms a major agricultural item. UK production in 1984/5 reached 923000 tonnes, a considerable amount bearing in mind that production was negligible about 20 years ago. There are now many cultivated strains of rapeseed available in Europe, each having particular features related to agricultural yield, value of the meal as a feedingstuff, or oil quality. The strain most often grown in the UK is Jet Neuf, the seed of which contains 4045% oil. World production in 1984/5 reached 5 500000 tonnes of oil, most of which was used in the producing countries, notably India and China, the main exporting countries being Canada and France. Rapeseed oil is a liquid oil with a dark amber or green colour. This can usually be removed on bleaching or deodorization, but difficulties can arise if the seed is harvested in an unripe condition or allowed to sprout during storage. Unripe seeds contain more chlorophyll, which leads to darkcoloured green oils, and this can give rise to problems during refining. In recent years, extraction of oil from decorticated seed has been attempted. In view of its high level of unsaturation, the oil is frequently hydrogenated prior to use in food products. In the hydrogenated form, it is used in FATS AND FATTY FOODS 319 Rice bran is a product of rice milling, and although little oil is produced from this source at present, it has enormous potential. The main difficulty in the production of rice bran oil is that enzymes present in the bran degrade the oil if it is not quickly extracted. As rice bran is produced predominantly in the Third World, much effort is being spent in overcoming problems of rice bran collection and oil extraction. notably in North and South America, where the climate is suitably warm and damp. Soya beans provide a useful source of protein as well as of edible oil, the residual cake from soyabean extraction being a valuable feedingstuff in considerable demand. It is only comparatively recently that soya bean has been primarily produced as an oilseed crop. In most eastern countries most of the crop is still eaten directly by farm animals. Crude soya-bean oil is usually obtained by solvent extraction of the beans, which contain from 17-20% oil. The crude oil contains a high proportion of phospholipids, which are removed during processing. This is a valuable source of LECITHIN, an emulsifying agent widely used in food products. Crude soya-bean oil has an objectionable 'beany' flavour, which is removed by the refining process. However, similar flavours can return during storage of refined or hydrogenated and refined soya-bean oil. These new off-flavours are called reversion or hydrogenation flavours. Soya-bean oil is used in the manufacture of margarine compound cooking fat and as a salad oil. For the latter application it is frequently given a mild hydrogenation, after which the harder components are removed by fractionation. The major producing areas are the USA, Brazil, Argentina and China. The properties of soya-bean oil are listed in Tables 8.2 and 8.4. Safltower-seed oil Sunflower-seed oil Safllower is an annual plant, a member of the Compositae. The major producer is the USA, but safllower is also grown in India, North Africa, Mexico and Canada. The production of safHowerseed oil in 1984/5 was 265000 tonnes. The oil content of the seed is 25-45%. The oil is semidrying, but it is widely used for edible purposes, having recently gained popularity for dietary use in view of its high EFA content. It has the highest linoleic acid content of any commercially available oil. Its composition is listed in Table 8.2. In the late 1960s a high oleic acid variety of safllower-seed oil was introduced. This may be used for dietary purposes, such as baby milk. Sunflower-seed oil is an important oil seed crop, production of which reached a record 6 165 000 tonnes in 1984/5. The major production areas are the former USSR, the USA, Argentina and China. In Europe, France is a significant producer. The popularity of sunflower-seed oil in recent years is attributable to its good flavour stability, coupled with its high linoleic content (Table 8.4). This has made it useful for the manufacture of margarines and other foods high in EFA. the production of margarine, in fats used for the production of milk powders, and in dough fats. Oil which is lightly hydrogenated and then fractionated to remove harder components may also be used as an industrial frying oil. Oil high in erucic acid is still grown in China, in India, in Eastern Europe, and in parts of Scandinavia. The use of this oil in the UK falls under the Erucic Acid in Food Regulations, which limit the amount of erucic acid in human foods to 5%. The high erucic acid varieties of rapeseed oil can, however, be used if suitably blended with other oils of low erucic content. High erucic acid rapeseed oils are also used for specific industrial purposes, particularly in the production of lubricant additives for jet engines. The properties and composition of rapeseed oil are listed in Tables 8.2 and 8.4. Rice bran oil Soya-bean oil Soya-bean oil is the most important single edible oil, world production having reached 14.7 million tonnes in 1984/5 (Table 8.1). The soya bean is the seed of a leguminous plant. Although it is native of Asia, it is extensively cultivated in other areas, Tallow The better-quality edible tallow is derived from beef. The composition of tallow varies with the animal's diet and, as with the pig, the more unsaturated fat is found nearest the skin (Table 8.5). The degree of unsaturation therefore depends to some extent on the technique used on cutting and rendering. Tallow is likely to go rancid quickly, as with lard, due to the absence of natural antioxidants. 320 FOOD INDUSTRIES MANUAL Premier jus, or oleostock, is a high grade of tallow made by wet rendering of fresh beef fat at low temperatures. This material is light yellow and of good flavour. It can be fractionated to give a hard material, oleo stearin, which contains all the fully saturated glycerides. It may be used as a hard fat in pastry margarines. The soft fraction known as oleo oil is used in newer varieties of margarine, said to have texture and flavour properties closely related to those of butter. Beef oleo oil is also used in the preparation of baby foods. Tallow intended for non-edible use is graded according to the scheme in British Standard 3919. World production of tallow in 1984/5 was just over 6200000 tonnes (Table 8.1). PASTRY MARGARINE Whale oil POLAR COMPOUNDS IN HEATED OILS Before 1960 whale oil was a common component of margarine and other fatty foods. However, whale oil declined in importance as a result of its decreased availability. The whale oil industry passed completely out of British hands and became concentrated mainly between Japan and the USSR. Continued hunting of whales led to a fall in their numbers, and as a result restrictions were imposed on the whaling industry. This failed to halt the decline, and many species of whales are now classed as endangered. The sperm whale was formerly one of the most important. Its oil has an unusual composition in that it comprises a high proportion of fatty acids esterified with long-chain fatty alcohols. These compounds are commonly known as wax esters. The high proportion of wax esters gives sperm whale oil attractive properties in some fields, especially mechanical lubrication. Efforts have been made to find vegetable oil alternatives for sperm whale oil in these specialist applications. One of the most attractive of these vegetable oil alternatives is jojoba oil (see above). Used frying oils deteriorate through oxidative polymerization of the unsaturated fatty acids. This leads to increases in viscosity, darkening of colour and decrease in the nutritional quality of the oil. The polar compounds formed during frying can be determined by a column chromatographic separation followed by weighing of the separated polar liquids. It is recommended to discard the oil if the level of polar compounds reaches 27%. Pastry margarine is used for making flaky or puff pastry. The margarine must have a smooth texture and a tough consistency because it should form thin coherent layers in the pastry. It must stand up to heavy mechanical working and rolling which occur when it is rolled into thin layers. The margarine has to be relatively dry and free from occluded air, because the puff effect of the pastry is obtained by expansion of the dough between the fat layers. The composition of pastry margarine is usually made up of a high melting fat and a proportion of liquid oil. PHYSICAL REFINING Physical refining is a term often used for the deacidification of oils by high-temperature steam stripping (see DEACIDIFICATION). PROSTAGLANDINS See ESSENTIAL FATTY ACIDS. RANCIDITY PIS RATIO The ratio of polyunsaturated fatty acids to saturated fatty acids is called the PIS ratio. In the COMA Report (DHSS, 1984) and elsewhere, P, the 'polyunsaturated' acids, are taken to include only those with a cis, cis-I,4-diene structure, i.e. the essential fatty acids, whereas S, the 'saturated acids', mayor may not include the mono- or polyunsaturated acids with one or more trans double bonds. It is to be recommended that the terms used should be clarified in any case where confusion might occur. Freshly deodorized oils and fats have bland flavours, but off-flavours develop on storage, some oils being more resistant to the development of offflavours than others. When an oil has developed offflavours it is known as a rancid oil. The phenomenon is called rancidity. There are several forms of rancidity, the two most common being hydrolytic rancidity and oxidative rancidity. In hydrolytic rancidity a catalyst such as a residue of alkaline soap, an enzyme, or an active mould or yeast, together with moisture, cause hydrolysis of the constituent triglycerides. This leads to the liberation of 321 FATS AND FATTY FOODS free fatty acids (FF As). In most oils a low level of FF As is no problem, but in the lauric oils (palm kernel and coconut) the liberated acids have a distinctive soapy taste and the phenomenon is therefore also known as 'soapy rancidity'. Oxidative rancidity is, as the name implies, caused by oxidation of the fat. This type of rancidity may be alleviated by adequate provision of ANTIOXIDANTS (see also FLAVOUR). RANCIMAT TEST See SWIFT TEST. non-representative sample is of less value than an imperfect analysis on a fully representative sample. The importance of starting with a fully representative sample cannot be over-emphasized, and International Standard ISO 5555 therefore lays down procedures for taking samples from bulk lots in a variety of circumstances. One of the most important factors is that the oil or fat should be sufficiently warm to be fully fluid, as otherwise higher-melting components will crystallize and settle to the bottom of the container or adhere to its sides. On the other hand, it is important not to damage the cargo by overheating. Table 8.7 gives the recommended temperature limits for sampling. Table 8.7 Temperature limits for sampling REFINING Fat or oil Crude oils and fats, especially vegetable oils, contain various kinds of extraneous matter such as gums, phospholipids, carbohydrates, pigments, flavouring substances, moisture and free fatty acids. To remove these and to achieve a pleasing colour and bland flavour, oils are refined. Refining involves the processes of DE·GUMMING, BLEACHING, DE·ACIDIFICATION OR NEUTRALIZATION, and DEODORIZATION. In the USA, the term 'refining' refers to the degumming, neutralization, washing and drying stages only. Olive, maize, rape, safflower, Sesame, soya, sunflower, linseed Groundnut (arachis), tung Cottonseed Castor Whale, fish oils Sperm Coconut Palm kernel Shea nut butter Greases Lard, palm oil Tallow Palm stearin SALAD OIL Salad oils are vegetable oils which remain liquid when kept in a refrigerator at about 5°C, and are used for salad dressings, for the preparation of mayonnaise etc. The total consumption in the UK is small compared with that in Mediterranean countries where large quantities are consumed for cooking purposes. Salad oils may be naturally flavoured oils such as virgin olive oil, or refined deodorized oils which are preferred in the UK and the USA. Winterized cottonseed oil is often used in North America, as it does not become turbid on keeping. SAMPLING When the properties or composition of a bulk consignment of oil or fat are in question, a sample is taken and submitted to the laboratory for examination. However, the value of the analytical results is only as good as the sample-a perfect analysis on a Temperature °C Min. Max. 15 20 20 25 25 30 25 30 35 35 40 35 35 40 45 45 50 50 55 45 45 50 55 55 60 70 Solid fats are best melted and rendered completely homogeneous, e.g. by stirring, before any sample is taken. Sometimes this is not feasible, however, and in these cases a metal fat trier, with a C-shaped cross-section, is used. It is pushed into the fat, rotated and withdrawn with a plug or core of the fat. SELECTIVITY Selectivity is a term applied to catalytic hydrogenation, and refers to the ability of a catalyst to promote the preferential hydrogenation of polyunsaturated acids. Various forms of selectivity are recognized, depending on whether the manufacturer wishes to hydrogenate the linolenic acid but not the linoleic acid, or if he wishes to hydrogenate both linolenic and linoleic, but not the oleic. These selectivities are called selectivity 2 and selectivity 1, respectively. Selective catalysts are usually less active than non-selective catalysts, and are more likely to promote a higher degree of trans bond formation. (See CATALYSTS.) 322 FOOD INDUSTRIES MANUAL SHORTENING The term shortening arises from the use of this type of fat to impart shortness in the preparation of flour confectionery, such as shortbread, short pastry or cakes. The main domestic use is for pastrymaking, frying and cake-making. The term 'shortening' is of US origin and the product was originally developed as an outlet for cottonseed oil available as a by-product of the cotton-growing industry. Shortenings contain no moisture and consist entirely of fat. They frequently have glyceride compositions resembling those of margarine fat blends. The traditional shortening in Europe is lard and this is still used extensively. The consistency and plasticity of shortenings are important; too soft a shortening will mix poorly with flour and cause problems in baking, whilst too hard a product gives a tough shortbread which does not aerate properly. Shortenings are improved by aeration and domestic shortenings generally fall into one of two categories, moulded products containing up to 10% air and liquid-filled products containing 10-30% air. Moulded products are usually parchment-wrapped and aim to be competitive with lard and to have better flavour and better cake-making properties. Liquid-filled, highly aerated products are more expensive, but offer advantages in ease of use. High-ratio shortenings High-ratio shortenings allow a greater proportion of sugar to fat in cake recipes, due to a higher dough strength, which is dependent upon the emulsifying properties of mono- and diglycerides in the shortenings (see EMULSIFIERS). Because such shortenings contain a higher proportion of combined glycerol in the form of mono- or diglycerides, they are referred to as 'superglycerinated' shortenings in the USA. are delivered to customers at temperatures of 2325°C, a temperature which must be maintained in the tanker. Procter and Gamble hold a number of patents covering the preparation of pumpable shortenings. Liquid shortenings have also been developed, and these offer the convenience of being pourable from a bottle. The base material is a liquid oil, such as cottonseed oil, containing a finely dispersed emulsifier. SINGLE-CELL OIL Single-cell oil is the term applied to triglyceride fats generated by microbial means on non-fat substrate. Mould fermentations were first used to generate proteinaceous material for animal feeding stuffs, and it was subsequently realized that a similar technology could be used to produce oils or fats of specified properties. At the time of writing no single-cell oil has yet been successfully produced on a fully commercial basis, but the most likely candidate is an alternative to evening primrose oil, a rich source of the EFA y-linolenic acid (see ESSENTIAL FArry ACIDS). SLIP POINT See MELTING POINT. SMOKE, FIRE AND FLASHPOINTS See FLASH POINT. SOLID FAT INDEX (SFI) See under TEXTURE OF OILS AND FATS. Pumpable shortening Pump able shortening was developed in response to a trend in the flour confectionery industry for bulk delivery of raw materials. Flour, sugar and liquid were all delivered in bulk and a desire therefore developed for a pumpable shortening which could also be delivered in bulk. Pumpable shortenings are delivered in bulk road tankers and pumped to holding vessels from which they can be easily pumped to any point of a factory, as required. Pumpable shortenings are tempered in bulk, usually in 6- to 12-ton vessels into which they are fed directly from a Votator processing unit. They SPANISH OLIVE OIL SICKNESS In early 1981 some industrial rapeseed oil, denatured with aniline, and which therefore attracted a low rate of duty, was imported into Spain. This oil was apparently processed to remove the aniline. It was then blended with olive oil and sold in street markets in the working-class areas of Madrid. Unfortunately, the treatment with aniline and the subsequent processing had apparently generated highly toxic components in the oil, and people using the oil subsequently became seriously ill. FATS AND FATTY FOODS Over 500 people died, while 10 000 or more required hospital treatment. The exact cause of the illness is still not known, as the reported symptoms do not correspond to those known for aniline or anilide poisoning. A paper by Noriega (1982) describes the symptoms of this sickness, while a World Health Organisation monograph reviews all aspects of the catastrophe (WHO, 1984). STEAM REFINING See DE-ACIDIFICATION. STEROLS Plant sterols (phytosterols) occur in the unsaponifiable matter of vegetable oils. Cholesterol (a zoosterol) occurs in animal fats and fish oils, but in only trace quantities in vegetable oils, and was once considered to be absent from these. The sterols may be characterized and identified by a combination of thin-layer chromatography and gas-liquid chromatography according to the International Standard method (ISO 6799). Sterol compositions have been used to prove purity, contamination or adulteration of fats and oils, as each oil type has its own sterol composition. The level of sterols in an oil can be reduced or modified by processing, however, and skilful interpretation of the results is therefore needed. SUPERCOATINGS The term 'supercoatings' is applied to compositions which are not entitled to the description 'chocolate', containing whole cocoa mass, sugar, cocoa butter equivalent (CBE), and optionally additional cocoa and milk products. In supercoatings the fat phase may contain 50% or 60% of CBE, the balance being cocoa butter derived from the cocoa mass and dairy milk fat (see COATINGS). TEXTURE OF OILS AND FATS Solid/liquid ratio The ratio of solid fat to liquid oil is the most important physical property of an oil/fat mixture, as it will govern the physical properties of any fatty food into which it is incorporated. The proportion of solid fat changes with temperature and at ambient can vary from zero in a liquid frying oil, 323 to 20-30% in margarines, around 50% in shortenings and 80% or more in fats intended for chocolate or coatings. The ratio of solid fat to liquid oil was formerly measured by dilatometry, but more recently nuclear magnetic resonance (nmr) has been used. As the ratio of liquid oil to solid fat varies with temperature it is important to control the temperature carefully during the determinations and to report the temperature along with the results. This is normally carried out by reporting the dilatation at 20°C as D20, or the actual solid content as determined by nmr at 20°C as N20. Fats have complicated polymorphic and crystallization hehaviour and it is therefore necessary to temper and stabilize the fats carefully at the measuring temperature prior to the solid/liquid ratio measurement. This is particularly the case with fats of the cocoa butter type, which crystallize Standard procedures for in the ~-modifcatn. tempering and stabilization of fats prior to solidi liquid fat determinations have therefore been established. The procedure used in British Standard 684: Section 1.12 (Dilatation) is also used in the IUPAC methods for dilatometry and solid fat content by nmr. The largest source of error with both techniques is the time and temperature of stabilization, an aspect often overlooked, as duplicate determinations are often conducted in the same thermostatic bath. Cooling curve The cooling curve of a fat is a measure of its crystallization properties. It is particularly useful in the assessment of cocoa butter and cocoa butter replacement fats, as it can form a guide to the tempering behaviour of the chocolate. Two different methods are used, namely the Schukov cooling curve and the Jensen cooling curve. The latter is described in British Standard 684: Section 1.13. Dilatometry Dilatometry is a term applied to the measurement of the temperature/volume relationships of a fat over the range of temperature during which it changes from solid to liquid. The isothermal expansion on melting of the fat is measured, which provides information about the ratio of solid fat to liquid oil in the fat over the temperature range used. These measurements have great practical value in providing an assessment of the suitability of a fat, or fat blend, for use in any particular food product. Dilatations were widely used in manufacturing industry for 324 FOOD INDUSTRIES MANUAL selecting fat blends for margarines, cocoa butter replacement fats, etc. The method used in Europe is described in British Standard 684: Section 1.12, and gives dilatation units measured in mm 3 per 25 g of fat. In the BSI system, fats may have dilatation values of up to 2500. The American Oil Chemists Society (AOCS) method (Cd 10-57) gives the dilatation values in ml per kg of fat. These values are, therefore, about one twenty-fifth of those obtained in the BSI method. This conversion factor is not accurate, however, as the tempering procedures in the two methods differ. The fact that the AOCS method gives values ranging from 0 to about 100 has led to the mistaken impression that the AOCS dilatation, also known as the solid fat index (SFI), is a true measure of the proportion of solid fat present. Dilatometry is at present rapidly being replaced, however, by wide-line, continuous-wave and pulse NUCLEAR MAGNETIC RESONANCE measurements of the solid fat to liquid oil ratio. Hardness Measurements It has for a long time been customary to describe the hardness of fats by reference to their melting points, or solid fat contents. This method gives a rough and ready idea of hardness, but in more recent years direct measurement of hardness by use of a penetrometer has become established. Melting point Natural fats are complex mixtures of glycerides and have no sharp melting point. Fats also exhibit polymorphism (i.e. solidification in more than one crystalline form, each one possessing a different melting point). Melting points of the constituent fatty acids can, however, be accurately determined. This property of the liberated fatty acids of a fat is called the titre, and is described in British Standard 684: Section 1.6. Melting points and titres of several fats are given in Table 8.2. To obtain reliable results for the melting point of whole fats, it is necessary to follow carefully a standardized procedure. The melting point method most commonly used in the UK is the slip melting point, described in British Standard 684: Section 1.3. This is the temperature at which a column of fat of specified length rises in an open capillary tube suspended in a water bath of gradually increasing temperature. Stabilization of the fat prior to measurement of the slip melting point is extremely important, different procedures of stabilization being necessary for fats with pronounced polymorphic behaviour, such as cocoa butter. It is also important to ensure that the capillary tubes used in the melting point determination have parallel sides with no tendency to taper toward one end. Nuclear magnetic resonance Nuclear magnetic resonance (nmr) spectroscopy can distinguish between the protons of liquid oil and solid fat. It can therefore be used to measure the liquid/solid ratio in fats and oils and also to measure the oil content of oilseeds or other products. As the protons in water also give a signal, samples should be dried before evaluation. Two forms of nmr instrument are on the market, namely continuous wave wide-line nmr and pulsed nmr. In the former, the instrument is adjusted to respond only to the signal from the proton in the liquid oil phase. The intensity of this signal is measured and related to the amount of sample used. As the signal varies with temperature, a correction factor must be derived from measurements on an oil which is fully liquid at all temperatures of measurement. Olive and soya-bean oils are frequently used for this purpose. A similar measurement enables the determination of oil content in fatty foods or oilseeds. This technique has now become established as the standard IUPAC method 2.323. The method has been shown by collaborative test to be highly reproducible between different laboratories. However, in the present author's view it has not been adequately shown that the method gives exactly the same answer as solvent extraction methods for the determination of oil content of oilseeds. Pulse nmr is used primarily for the determination of solid fat content. Instruments based on two techniques have been developed. In one of these the liquid signal only is measured, the procedure therefore relating closely to that of the wide-line instrument. In a second version of this technique, the one most favoured in Europe, solid and liquid signals are measured, and distinguished by the rapidity with which the excited protons relax in the liquid and solid phases. Separate signals from the liquid and solid phases are obtained, and converted into a digital readout showing the actual percent of solid fat on an illuminated display. A general review of the subject is given by Waddington (1986). Plasticity Margarine, cooking fat and other semi-solid food fats consist of discrete crystalline particles embedded in a considerable proportion of liquid oil. There is some loose adhesion between the crystals, which breaks down rapidly when the fat FATS AND FATTY FOODS is subjected to working and a shearing stress is applied; this characteristic is known as plasticity. The plasticity of a food fat is of great practical importance. It determines, for instance, the spreadability of margarine, the shortening properties of baking fats and the creaming power of cake margarine. It can be controlled during manufacture, important factors being: (i) Content of solids (ii) Size and shape of crystals (iii) Persistence of crystal nuclei during heat treatment (iv) The mechanical working of the fat etc. Plasticity per se is difficult to measure and instead the consistency of a fat at different temperatures is measured. Penetrometers are often used for this purpose. Titre The titre is the value of the maximum of a temporary temperature rise during the crystallization of a fat's constituent acids. If the latent heat is not sufficient to cause a rise in temperature, the temporary interruption of the cooling process is considered as the titre. The titre is determined according to BS 684: Section 1.6. Titres of several fats are given in Table 8.2. Thermal analysis Thermal analysis of fats may be by differential thermal analysis (dta) or differential scanning calorimetry (dsc). In both techniques a small quantity of fat is slowly heated and compared with a reference sample. In dta the temperature of the fat is compared with a reference, whilst in dsc the temperature of the fat is kept the same as that of the control, the heat necessary to do this being measured. Thermal transitions, such as melting, are displayed by a fall in temperature of the sample relative to the control, or a necessity for the supply of extra heat. Cooling runs can also be carried out, in which case the crystallization phenomena are followed. It has been claimed that the solid-to-liquid ratio of fats may be determined by these techniques, but the author is sceptical about this approach as it is impossible to obtain continuous baselines before and after melting or crystallization, because the specific heat of a solid is always different from that of its liquid. Thermal analysis can also be used to study polymorphism, but as the thermal history of the fat has a pronounced influence on the shape of the thermograms, the results of thermal analysis can be very difficult to interpret. Some heating rates can give rise to spurious peaks, which again hinder interpretation. Tocopherols Tocopherols are naturally occurring antioxidants. They occur in nearly all vegetable fats, there being several related compounds. (Figure 8.3). Tocotrienols also occur, especially in palm oil, while soya-bean oil contains I)-tocopherol. The determination of tocopherol content in vegetable oil used to be difficult, as the tocopherols were liable to oxidation during the analytical procedure. In recent years, however, the introduction of hplc methods, coupled with fluorescence detection, has enabled much more accurate determinations. (b) (a) (c) 325 (d) Figure 8.3 Structure of the tocopherols: (a) alpha; (b) beta; (c) gamma; and (d) delta. 326 FOOD INDUSTRIES MANUAL TRANS FATTY ACIDS Natural unsaturated vegetable oils contain double bonds in the cis configuration. This is thermodynamically less stable than the trans form, in which the carbon-carbon chains are diametrically opposite to one another. During hydrogenation and other processing procedures, some cis double bonds therefore transform into trans double bonds, the equilibrium mixture containing about three times more trans bonds than cis bonds. The proportion of trans bonds in a fat can be estimated by infrared spectroscopy according to the IUPAC method 2.207. The nutritional value of fats containing trans bonds has been subject to some criticism (DHSS, 1984). TRIGLYCERIDES Structurally most oils and fats are esters of glycerol, which has three alcoholic hydroxyl groups, with three fatty acids. These fatty acids may be the same as one another or different. Figure 8.4 illustrates the structure of POS, the major triglyceride in cocoa butter. In natural fats, mixed triglycerides strongly predominate, but it is now accepted that in the vast majority of vegetable fats the central, or 2-, position is esterified with an unsaturated fatty acid, as shown in Figure 8.4 The physical properties of a fat or oil are of course dependent upon the physical properties of the constituent triglycerides, and the interactions between these triglycerides. A redistribution of fatty acids amongst the triglycerides, for instance by INTER-ESTERIFICATION, can therefore change the physical properties of the fat. In some cases, for instance with cocoa butter, this can lead to a serious deterioration in performance. VITAMINS Vitamins are accessory food factors which cannot be synthesized in the human body and have to be supplied in the diet, albeit in small quantities. The lipid-soluble vitamins are coded A, D, E and K. Vitamins A and D are present in butter and it is compulsory to add them to margarine in the United Kingdom. In the USA it is compulsory to add vitamin A, optional to add vitamin D. ~­ Carotene (Figure 8.1) is a natural source of vitamin A, and occurs in high quantities in palm oil. Tocopherols (Figure 8.3), a naturally occurring source of vitamin E, occur in most vegetable oils. Vitamin D is a sterol and is essential for bone formation. VOTATOR 'Votator' is the proprietary name of the Girdler Corporation of the USA for their continuous, totally enclosed, scraped-surface heat exchanger used in the manufacture of shortenings, cooking fats, margarine and other fat products. There is a family of related scraped-surface heat exchangers available on the market, differing slightly from one another in design but effectively functioning in the same manner. Minor modifications may be built into the machine and its ancillary equipment, depending upon customers' individual requirements. WEEVIL Palm trees growing in Malaysia were found to be suffering from incomplete flower fertilization, leading to a sub-optimum fruit yield. Considerable research with insects pollinating flowers in Cameroun and other parts of West Africa led to the identification of the weevil Elaidobius kamarunicus. This species was therefore introduced to the oil palm plantations of Malaysia, where it has bred extensively. Much better flower fertilization resulted, and this led to a dramatic increase in fruit production. A consequence of this appears to be a smaller yield of palm oil in each individual Palmitic Acid Residue MpW H 01 eic Acid { CIS:I (6. 9-cis) R eSI'd ue MO" CIS:I (n-9 cis) Stearic Acid Residue MS" Figure 8.4 The triglyceride POS, a major constituent of cocoa butter. FATS AND FATTY FOODS fruit, whilst the yield of palm-kernel oil remains more constant. The overall yield, plantation-wide, of palm kernel has therefore increased more dramatically than that of palm oil following the introduction of the weevil. WINTERIZING Winterizing is a process of fractional crystallization of oils in which the higher-melting glycerides are removed, giving the oil a clear, bright appearance even after refrigerator storage. The name is derived from the original method of carrying out the process, by allowing the oil to stand in outdoor tanks during the winter. Winterization is now carried out in chilled brine tanks under carefully controlled conditions. Alternatively, other forms of fat fractionation may be applied; the resulting clear oil is nevertheless termed 'winterized' oil. Winterization is most often applied to cottonseed oil, which is grown extensively in the USA and tends to throw down a deposit during refrigerator storage. On the other hand it has a better flavour stability than soya-bean oil which does not need winterization. In the American market, winterized cottonseed oil is therefore often considered optimum for a salad or table oil. YUSHO DISEASE Modern physical refining systems operate at very high temperatures, up to 270°C, and it is not always convenient to transfer heat from the boiler to the plant with high-temperature steam. Instead, inert mobile fluids of low volatility are used as heat transfer fluids, a popular one being a mixture of diphenyl and diphenyl oxide. In a Japanese accident in 1968, a plant on the island of Kyushu developed a leak, contaminating the edible oil with the fluid, which was one based on polychlorinated biphenyls. About 1300 people became ill through eating the contaminated oil, and in the eleven years following exposure eleven people died from the so-called 'Yusho disease'. This type of heat transfer medium has since been withdrawn and most new plants are now being built with highpressure steam installations. 327 FURTHER READING Allen, J.e. and Hamilton, RJ. (eds) (1989) Rancidity in Foods, 2nd edn, Elsevier-Applied Science, London. American Oil Chemists Society (1980) Lecithin-papers from a symposium at the AOCS Annual Meeting in New York City, April 28 1980. J. Amer. Oil Chem. Soc., 58, 885-916. Becher, P. (ed) (1965) Emulsions, Theory and Practice 2nd edn, Reinhold, New York. Beckett, S.T., (1988) Industrial Chocolate Mamifacture and Use Blackie, Glasgow and London. Department of Health and Social Security (1984), Diet and Cardiovascular Disease, DHSS Report on Health and Social Subjects No 28, HMSO, London (so-called COMA report by the Committee on Medical Aspects of Food Policy-Report of the Panel on Diet in Relation to Cardiovascular Disease). Diener, V.L. and Davis, N.D. (1983) Aflatoxins in com, in Xenobiotics in Food and Feeds, (eds J.W. Finely and D.E. Schwass), American Chemical Society, Washington DC. Food and Agriculture Organization (1980) Dietary Fats and Oils in Human Nutrition-Report of an Expert Commission, Food and Agriculture Organization of the United Nations, Rome. Griffin, W.C. (1949) Classification of surface-active agents by HLB. J. Soc. Cosmetic Chem., 1, 311-326. Hamilton, R.J. and Rossell, B.J. (eds) (1983). Analysis of Oils and Fats, Elsevier-Applied Science, London. Hoffmann, G. (1989) The Chemistry of Edible Oils and Fats and their High Fat Products, Elsevier-Applied Science, London. Holman, R.T. (1981) Essential fatty acids and prostaglandins. Prog. Lipid Research, 907. Laning, S.J. (1991) Fats, Oils, Fatty Acids and Oilseed Crops, in (eds I. Goldberg and R. Williams) Biotechnology and Food Ingredients, Van Nostrand Reinhold, New York. Minifie, B.W. (1980) Chocolate, Cocoa and Confectionery; Science and Technology, 2nd edn, AVI, Westport, Connecticut. Noriega, A.R. (1982) Toxic epidemic syndrome, Spain 1981. Lancet, 697-702. Patterson, H.B.W. (1983) Hydrogenation of Fats and Oils, Applied Science Publishers, London. Pomeranz, Y. (1985) Additives II-food emulsifiers, in Functional Properties of Food Components (ed. Y. Pomeranz), Academic Press, London, pp. 329-464. Rossell, J.B. and Pritchard, J.L.R. (eds) (1991) Analysis of Oilseeds, Fats and Fatty Foods, Elsevier-Applied Science, London. Salunkhe, D.K., Chavan, J.K., Adsule, R.N. and Kadam, S.S. (1992) World ai/seeds-Chemistry, Technology and Utilization, Van Nostrand Reinhold, New York. Schwitzer, M.K. (ed) (1956) Margarine and Other Food Fats, Leonard Hill (Blackie), London. Stuyenberg, J.H. van (1969) Margarine, Liverpool University Press. Waddington, D. (1986) Applications of wide-line NMR in the oils and fats industry, in Analysis of Oils and Fats (eds R.J. Hamilton and J.B. Rossell), Elsevier-Applied Science, London,pp.341-4oo. World Health Organization (1984) Toxic Oil Syndrome-Mass Food Poisoning in Spain. WHO Regional Office for Europe, Copenhagen (92 pp.).