The “Hurdles” Technology in Food Processing

INTERNATIONAL FOOD CONGRESS NOVEL APPROACHES IN FOOD INDUSTRY ABSTRACT BOOK MAY 26-29 2014 KUŞADASI- TURKEY EDITED BY ŞEBNEM TAVMAN SEMİH ÖTLEŞ TANER BAYSAL YEKTA GÖKSUNGUR DUYGU KIŞLA ÖZGÜL ÖZDESTAN GÜLTEN GÜNDÜZ NAFI 2014 International Food Congress 26-29 May 2014 Kuşadası TURKEY The “Hurdles” Technology in Food Processing Stylianos Anestis, Athanasios Labropoulos Technological Educational Institute of Athens, Kallithea 17674 Greece anestis@essolutions.eu, athanlab@teiath.gr Abstract Hurdle technology is a method of ensuring that pathogens in food products can be eliminated or controlled in order firstly to be safe for consumption and secondly to extend their shelf life. Hurdle technology usually works by combining more than one processing approach. Such approaches can be thought of as "hurdles". The right combination of “hurdles” can ensure that all pathogens are eliminated or rendered harmless in the final products. Foods are preserved by heating, chilling, drying, salting, conserving, acidification, oxygen-removal, fermentation, adding various preservatives, and others. Often these methods are applied in combinations. The parameters of these traditional methods have been defined as F, t, aw, pH, Eh, competitive flora, etc. Effective limits of these factors for microbial growth, survival, and death were established. Food preservation and also food quality depends in most cases on the empirical and now more often on the deliberate and intelligent application of combined preservative methodologies/processes called “hurdles” technologies. It is, also, obvious that future food preservation methodologies such as high hydrostatic pressure, high-intensity pulsed electric fields, high-intensity pulsed light, oscillating magnetic fields as well as food irradiation are more effective in combination. Thus, “hurdles” technology may be the key to food preservation in the future. Furthermore, basic aspects of “hurdles” technology including, e.g. homeostasis, metabolic exhaustion, and stress reactions of microorganisms, have been recognized to be of significant important and are increasingly studied. Keywords: Hurdle technology, food safety, food preservation 138 1 THE “HURDLES” TECHNOLOGY IN FOOD PROCESSING 2 S. Anestis1 and A. Labropoulos2 3 athanlab@teiath.gr , sanestis@teiath.gr 4 2 1 Abstract 5 Hurdle technology is a method of ensuring that pathogens in food products can be eliminated or 6 controlled in order firstly to be safe for consumption and secondly to extend their shelf life. Hurdle 7 technology usually works by combining more than one processing approach. Such approaches can be 8 thought of as "hurdles". The right combination of “hurdles” can ensure that all pathogens are eliminated or 9 rendered harmless in the final products. 10 Foods are preserved by heating, chilling, drying, salting, conserving, acidification, oxygen-removal, 11 fermentation, adding various preservatives, and others. Often these methods are applied in combinations. 12 The parameters of these traditional methods have been defined as F, t, aw, pH, Eh, competitive flora, etc. 13 Effective limits of these factors for microbial growth, survival, and death were established. Food 14 preservation and also food quality depends in most cases on the empirical and now more often on the 15 deliberate and intelligent application of combined preservative methodologies/processes called “hurdles” 16 technologies. It is, also, obvious that future food preservation methodologies such as high hydrostatic 17 pressure, high-intensity pulsed electric fields, high-intensity pulsed light, oscillating magnetic fields as well 18 as food irradiation are more effective in combination. Thus, “hurdles” technology may be the key to food 19 preservation in the future. Furthermore, basic aspects of “hurdles” technology including, e.g. homeostasis, 20 metabolic exhaustion, and stress reactions of microorganisms, have been recognized to be of significant 21 important and are increasingly studied. 22 23 Keywords: Hurdle technology, food safety, food preservation 24 25 1.Introduction 26 For centuries, food preservation has been necessary to supply food between harvest and time of 27 need. Many preservation methods, such as heating, chilling, freezing, drying, salting, sugar addition, 28 acidification, fermentation, removal of oxygen, and addition of preservatives have emerged over the 29 centuries. However, a quantitative approach has been introduced that expresses heating in F values, 30 chilling in t values, drying in aw values, acidity in pH values, removal of oxygen in Eh values, etc. 31 Food safety, as well as the sensory and nutritional quality of most preserved foods, is based on a 32 combination of several empirically applied preservative factors (hurdles), and more recently on 33 knowingly employed hurdle technology. However, various expressions for the same concept in different 34 languages are now used: Hürden-Technologie in German, hurdle technology in English, technologie des 35 barrières in French, barjernaja technologija in Russian, technologia degli ostacoli in Italian, technologia de 36 obstaculos in Spanish, shogai gijutsu in Japanese, and zanglangishu in Chinese. Therefore, hurdle 37 technology is a contribution to global sustainable food product development. 1 38 The hurdle technology (homeostasis, metabolic exhaustion, stress reactions of micro-organisms, 39 etc.) has also advanced in recent years for the preservation of foods. However, hurdle technology was 40 developed several years ago as a new concept for the production of safe, stable, nutritious, tasty and 41 economical foods. It advocates the intelligent use of combinations of different preservation factors or 42 techniques ('hurdles') in order to achieve reliable preservation effects in applications identified in many 43 food areas. The present study briefly introduces the concept of hurdle technology, presents potential 44 applications and gives information details on recently concluded studies concerned with this topic. 45 Today, consumer demand for more natural and fresh foods, urges food manufacturers to use only 46 mild preservation techniques such as refrigeration, modified-atmosphere packaging, bio-conservation, 47 etc. Thus, for the benefit of food manufacturers there is a strong need for new or improved mild 48 preservation methods that allow the production of fresh, stable and safe foods (Aguilera and Parada, 49 1992; Aguilera et al., 1990). Hurdle technology include combined methods, combined processes, 50 combination of preservations, combination techniques and others advocating the deliberate combination 51 of existing and novel preservation techniques in order to establish a series of preservative factors 52 (hurdles) that any microbial present should be controlled. These hurdles may be temperature (F or C), 53 water activity (aw), pH, redox potential preservatives, etc. Some hurdles, like pasteurization, can be high 54 for a large number of different types of microorganisms, whereas others, like salt content, have a less 55 strong effect in limiting the range of types of microorganisms. 56 Stiebing and Rodel (1992) introduced the surface water activity of fermented sausages 57 (determined by temperature measurement just beneath the surface of the sausage during ripening) 58 as the leading criterion for an optimization and automation of the ripening process. Further 59 developments also occurred in relation to defining 'hygiene hurdles,' which are important for the 60 aseptic packaging of cooked meats in 'clean-rooms' or, on the other hand, for the production of 61 fermented meats in 'bio-rooms' (Leistner, 1990). Finally, an update was presented on meat 62 preservation by combined methods (hurdle technology) and the concept was introduced (Leistner, 63 1992a). 64 The combination of preservative factors influences the microbial stability and safety of foods has 65 been known for many centuries, while the concept is more or less unconsciously used in many traditional 66 foods. The concept is now ready to be introduced for use with a much wider range of food products 67 including fruits and vegetables, bakery products, dairy products, fish, and so on with many novel 68 preservative factors such as gas packaging, bio conservation, bacteriocins, ultrahigh pressure treatment, 69 etc. Finally, we can say that “hurdle technology” is a crucial concept for the mild preservation of foods, as 70 the hurdles in a stable product concertedly control microbial spoilage and food poisoning, leaving desired 71 fermentation processes unaffected (Chirife et al., 1991; El-Khateib et al., 1987; Gould, 1988). 72 73 2.Case Studies 74 A food product is microbiologically stable and safe because of the presence of a set of hurdles 75 that is specific for the particular product, in terms of the nature and strength of their effect. Together, 76 these hurdles keep spoilage or pathogenic microorganisms under control. Examples of sets of hurdles are 77 illustrated by Figs 1a-e. 2 78 The example shown in Fig. 1a represents a food containing six hurdles: high temperature during 79 processing (F value), low temperature during storage (t value), low water activity (aw), acidity (pH) and 80 low redox potential (Eh), as well as preservatives (pres) in the product. Some of the micro- organisms 81 present can overcome a number of hurdles but none can jump over all the hurdles used together. Thus 82 the food is stable and safe. This example is only a theoretical case, because all hurdles are depicted as 83 having the same intensity, which is rarely the case in practice. More likely, hurdles are of different 84 intensity, as in the second example (see Fig. 1b), where aw and preservatives are the main hurdles and 85 storage temperature, pH and Eh are minor hurdles. If there are only a few microorganisms present at the 86 start (see Fig. 1c), fewer different hurdles or hurdles of lower intensity may achieve microbiological 87 stability. On the other hand, if high numbers of microorganisms are present owing to poor hygienic 88 conditions, the usual set of hurdles may not suffice to prevent spoilage or food poisoning (see Fig. 1d). 89 The example shown in Fig. 1e is a food rich in nutrients and vitamins, which may allow for short-term, 90 strong growth of the microorganisms, and as a result their initial number is increased sharply ('booster 91 effect'). However, in the examples shown in Figs 1d and 1e, additional or higher hurdles are needed to 92 assure product stability. 93 94 Case 1: Examples of a hurdle-preserved food 95 Salami-type fermented sausages can be produced that are stable at ambient temperature for 96 extended periods of time using hurdle technology. The microbial stability can be achieved by the use of a 97 combination of hurdles that are important in different stages of the ripening process. Important hurdles 98 in the stage of the ripening process of salami are the preservatives salt and nitrite, which inhibit many of 99 the bacteria present in the meat batter. However, other bacteria multiply, use up oxygen and thereby 100 cause a drop in Eh, which inhibits aerobic organisms and favors the selection of lactic acid bacteria. The 101 Iactic acid bacteria then flourish, causing acidification of the product and a decrease in pH. The various 102 hurdles gradually become lower during long ripening of the salami due to the fact that nitrite is depleted, 103 the number of lactic acid bacteria decreases, Eh and pH increase. On the other hand, aw decreases with 104 time, and thus becomes the main hurdle in long-ripened sausage. Similar combinations of hurdles in 105 other types of fermented foods such as cheese and vegetables are responsible for the stability and 106 quality of the products. 107 108 Case 2. Example of non-fermented foods 109 A hurdle technology approach has also been established for use with non-fermented foods, for 110 instance in the production of tortellini, an Italian pasta product. In this case, reduced aw, and mild heating 111 are the principal hurdles employed during processing, in addition to a modified atmosphere or ethanol 112 vapor in the package mild chilling of the product during storage can be effective. However, ethanol was 113 found to be very effective in inhibiting microbial growth, especially moulds and micrococci. 114 115 Case 3. Other examples of food products 116 A recent survey of foods traditionally preserved using hurdle technology. It conducted in 10 Latin 117 American countries in which identified some 260 different food items derived from fruit, vegetables, fish, 3 118 dairy products, meat and cereals. They often had a high aw (as high as 0.97) and that were stable at 119 ambient temperature (25-35°C) for several months (. Based on the increased knowledge of the principles 120 underlying hurdle technology, the Latin American scientists involved in this study are now applying the 121 concept to design shelf-stable, innovative food preparations based on tropical and subtropical fruits such 122 as peach, pineapple. mango, papaya, etc. (Leistner, 1978 and 1985). 123 An overview of combinations of hurdles that have either been studied or already employed, to 124 date in a range of food products is given in Leistner, (1995). In a number of recently developed food 125 products an almost infinite shelf life can be obtained. An example of this is canned peas marketed in the 126 UK, in which the heat-stable bacteriocins nisin is used as an extra hurdle, (Normally, heating and pH 127 reduction are the only two hurdles employed, but these do not suppress the growth of surviving acid- 128 tolerant, spore-forming clostridia, where are completely inhibited by nisin). 129 130 131 Homeostasis 132 An important phenomenon that is crucial with regard to hurdle technology is the so-called 133 “homeostasis” of microorganisms. Homeostasis is the constant tendency of microorganisms to maintain 134 the stability and balance (uniformity) of their internal environment. Although the pH values in different 135 foods may be quite variable, the microorganisms living in them expend considerable effort keeping their 136 internal pH values within very narrow limits. In an acid food, for example they will actively expel protons 137 against the pressure of a passive proton influx. Another important homeostatic mechanism regulates the 138 internal osmotic pressure (osmohomeostasis). The osmotic strength, which is inversely related to the aw, 139 of a food is a crucial physical property, which has a great effect on the ability of organisms to proliferate. 140 Cells have to maintain a positive turgor (pressure) by keeping the osmolarity of the cytoplasm higher 141 than that of the environment, and they often achieve this using so-called osmoprotective compounds 142 such as proline and betaine. 143 Preservative factors (hurdles) may disturb several or just one of the homeostatic mechanisms of 144 microorganisms, and as a result the microorganisms will not multiply but instead remain inactive and/or 145 die. Food preservation is achieved by disturbing the homeostasis of microorganisms in foods either 146 temporarily or permanently. This means that any hurdles included in a food should act positively against 147 the undesired micro-organisms by affecting the cell membrane, DNA, enzymes, pH, Eh and aw 148 homeostasis systems. This approach is often more effective than single-targeting but might act 149 synergistically and enables the use of hurdles of lowers intensity, and thereby has less of an effect on 150 product quality. Also, it is possible that different hurdles in a food will not just have an additive effect on 151 stability. In practical terms this could mean that it is more effective to use a combination of different 152 preservative factors with low intensities that affect different microbial systems or act synergistically than 153 to use a single preservative factor with a high intensity. Moreover, in the hurdle technology concept, the 154 objective is to inhibit the growth and proliferation of undesired organisms rather than to actually kill 155 them, thus allowing for the use of hurdles that are not too extreme. 156 Another phenomenon of practical relevance is referred to as the auto sterilization of stable, 157 hurdle preserved foods. In some ambient-temperature-stable meat products containing clostridia and 4 158 bacilli spores that had survived the heat treatment applied during processing, it has been observed that 159 some of these spores are able to germinate to form vegetative cells, but that these appear not to be 160 viable and therefore die off. The viable spore count thus shows a gradual decrease during storage, [5, 161 16]. The same phenomenon has been observed for several bacteria, yeasts and moulds in hurdle 162 preserved fruit products stored without refrigeration. A general explanation for the phenomenon might 163 be that, because of the elevated temperature, which favors and probably triggers microbial growth, 164 vegetative cells strain every possible repair mechanism to overcome the various hurdles present. In doing 165 so, they become metabolically exhausted; they completely use up their energy sources and die. Thus, 166 because of such auto sterilization hurdle-preserved foods that are microbiologically stable become even 167 safer during storage, especially at ambient temperatures. 168 169 Potential of hurdle technology 170 The most important hurdles commonly used in food preservation are temperature (high or low), 171 water activity (aw) (see Colligative Properties), acidity (pH), redox potential (Eh), preservatives (nitrite, 172 sorbate, sulfite, etc.), and competitive micro-organisms (e.g., lactic acid bacteria). More than 60 potential 173 hurdles for foods of animal or plant origin, which improve the microbial stability and/or the sensory 174 quality of these products, have been already described. At present, physical, non-thermal processes (high 175 hydrostatic pressure, oscillating magnetic fields, pulsed electric fields, light pulses, etc.) receive 176 considerable attention (see Nonthermal Processing), since in combination with other conventional 177 hurdles they are of potential use for the microbial stabilization of fresh-like food products. Another group 178 of hurdles, of special interest in industrialized and developing countries at present, would be ‘natural 179 preservatives’ (spices and their extracts, lysozyme, chitosan, pectine hydrolysate, etc.). In most countries, 180 these ‘green preservatives’ are preferred because they are not synthetic chemicals, but in some 181 developing countries. 182 The critical values of many preservative factors for the death, survival, or growth of micro- 183 organisms in foods have been determined in recent decades and are now the basis of food preservation. 184 However, the critical value of a particular parameter changes if additional preservative factors are present 185 in the food. For example, the heat resistance of bacteria increases at low aw and decreases at low pH or in 186 the presence of preservatives, while low Eh increases the inhibition of micro-organisms due to reduced aw. 187 The simultaneous effect of different preservative factors (hurdles) could be additive or even synergistic in 188 food preservation, which is illustrated by the hurdle effect. 189 190 Hurdle Effect 191 For every microbiologically stable and safe food, a certain set of hurdles is inherent. It differs in 192 quality and intensity depended on the particular product but In any case, the hurdles must keep the 193 ‘normal’ population of micro-organisms in the food under control. The micro-organisms present in a food 194 should not be able to overcome the hurdles inherent in this food. This is illustrated by the so-called 195 hurdle effect, which is of fundamental importance for the preservation of foods. The hurdles effect 196 controls microbial spoilage and food poisoning as well as desired fermentation processes. Some 197 examples will facilitate the understanding of the hurdle effect, which is presented in Figure 1. 5 198 Example 1. It represents a food containing six hurdles: (i) high temperature during processing (F value); 199 (ii) low temperature during storage (t value); (iii) water activity (aw); (iv) acidity (pH); (v) redox 200 potential (Eh); and (vi) preservatives (pres.). The micro-organisms present cannot overcome these 201 hurdles, and thus the food is microbiologically stable and safe. However, example 1 is only a 202 theoretical case, because all of the hurdles are of the same height (intensity), which rarely occurs. 203 Example 2. A more likely situation is presented in Example 2. The microbial stability of this product is 204 based on hurdles of different intensity where the main hurdles are aw and preservatives and other less 205 important hurdles are storage temperature, pH, and redox potential. These five hurdles are sufficient to 206 inhibit the usual types and numbers of micro-organisms associated with such a product. 207 Example 3. If only a few micro-organisms are present at the start, a few or low number of hurdles will be 208 sufficient for the stability of the product. 209 Example 4. If due to bad hygienic conditions, too many undesirable micro-organisms are initially present, 210 even the usual hurdles inherent to a product may be unable to prevent spoilage or food poisoning. 211 Example 5. A food rich in nutrients and vitamins, which could foster the growth of micro-organisms 212 called the booster or trampoline effect, must enhance the hurdles of such a product or otherwise be 213 overcome. 214 Example 6. It illustrates the behavior of sub-lethally damaged organisms in food. If the bacterial spores in 215 a food are damaged sub-lethally by heat, the vegetative cells derived from such spores will lack vitality 216 and therefore, they will be inhibited by fewer or lower hurdles. In some foods, stability is achieved 217 during processing by a sequence of hurdles, which are important in different stages of a fermentation 218 leading to a stable final product. 219 Example 7. A sequence of hurdles operates in fermented sausages and probably in ripened cheeses or 220 fermented vegetables. 221 Example 8. Finally, example 8 illustrates the possible synergistic effect of hurdles, which likely relates to a 222 multitarget disturbance of the homeostasis of micro-organisms in foods. 223 224 Conclusions 225 Microbial safety, sensoric and nutritional quality of most foods, is based on a combination of 226 several preservative methods (i.e., heating, chilling, drying, salting, curing, acidification, oxygen removal, 227 and fermentation). For centuries, combined methods were applied empirically in food preservation. The 228 preservative factors were called hurdles and their interactions the hurdle effect. The logical next step 229 was to modify and optimize the hurdles in foods. This approach was called intelligent hurdle technology. 230 Moreover, physiological aspects of micro-organisms (homeostasis, metabolic exhaustion, and stress 231 reactions) were taken into consideration in order to improve the stability and safety of hurdle-technology 232 foods. The ambitious goal for a gentle but more effective preservation of foods is now multitarget 233 preservation (i.e., hitting simultaneously several essential targets within the microbial cells by 234 hurdles taken from different target classes). This would lead to a synergistic effect of hurdles and 235 could advance food preservation far beyond the state-of-the-art known today. More than 60 potential 236 hurdles for the preservation of foods have been described and the number of useful hurdles is by no 237 means complete. Even the most advanced food preservation methods (e.g., pulsed technologies) are 6 238 more effective if applied in combination with traditional hurdles. Therefore, hurdle technology in the 239 future will probably remain the cornerstone of food preservation. It is gratifying to learn that intelligent 240 hurdle technology is equally applicable in industrialized and developing countries for the preservation of 241 foods 242 243 REFERENCES 244 • 245 intermediate moisture foods and combined methods technology. Food Research International, 25, 159- 246 65. Aguilera, J.M. & Parada Arias, E. (1992). CYTED-D AHI: an Ibero American project on 247 • 248 Alimentos de Humedad Intermedia Tradionales de lberoameri­ ca.Instituto Politecnico Nacional, Mexico, 249 557 pp. Aguilera, J.M., Chirife, J., Tapia, M.S., Welti, J. & Parada Arias, E. (1990). lnventario de 250 • 251 old example of tissue preservation by hurdle technology. Lebensm.­Wiss. u.­Technol., 24,9-11. Chirife, J., Favetto, G., Ballesteros, S. & Kitic, D. ( 1991). Mummification in ancient Egypt: an 252 • 253 Pastirrna. Fleischwirtschaft, 67, 101-5. El-Khateib, T., Schmidt, U. & Leistner, L. (1987}. Mikrobiologische Stabilitat von tiirkischer 254 • 255 Micro­organisms, eds R. Whittenbury, G.W. Gould, J.G. Banks & R.G. Board. FEM Symposium, 44, 256 220-8. Gould, G.W. ( 1988). Interference with homeostasis - food. In Homeostatic Mechanisms in 257 • 258 Mitteilungsblatt Bundesanstalt Fleischforschung Kulmbach, 84, 5890-3. 259 • 260 233-6. Hammer, G.F. & Wirth, F. ( 1984). Wasseraktivitats-( aw­)Verrninderung bei Leberwurst. Leistner L. (1992b). Linkage of hurdle technology with HACCP. Meat Focus International, 1, 261 • 262 Downey), 553-557. London: Applied Science Publishers Ltd. [This is the first introduction of the hurdle 263 effect, which is fundamental for food preservation by combined methods]. Leistner L. (1978). Hurdle effect and energy saving. Food Quality and Nutrition, (ed. W.K. 264 • 265 Downey. Applied Science Publishers, London, pp. 553-7. Leistner, L. ( 1978). Hurdle effect and energy saving. In Food Quality and Nutrition, ed. W.K. 266 • 267 and intermediate moisture food types. In Properties of Water in Foods in Relation to Quality and 268 Stability, eds D. Simatos & J.L. Multon. Martinus NijhoffPublishers, Dordrecht, pp. 309-29. Leistner, L. (1985). Hurdle technology applied to meat products of the shelf stable product 269 • 270 Fleischerzeugnissen, ed. L. Leistner. Bundesanstalt fiir Fleischforschung, Kulmbacher Reihe Band 10, pp. 271 1-21. 272 • 273 151-8. Leistner, L. (1990). Was sind sichere Produkte? In Sichere Produkte bei Fleisch und Leistner, L. (1992a). Food preservation by combined methods. Food Research International, 25, 274 • 275 von Rohwurst. Fleischwirtscha.ft, 72,432-8. Stiebing, A. & Rodel, W. (1992). Kontinuierliches Messen der Oberfliichen- Wasseraktivitat 276 7 277 278 279 Figure 1. Eight examples of the hurdle effect that facilitate understanding of the application of 280 hurdle technology in food preservation. See text for details. Symbols have the following meaning: F, 281 heating; t, chilling; aw, water activity; pH, acidification; Eh, redox potential; pres., preservatives; K-F, 282 competitive flora; V, vitamins; N, nutrients. Leistner L. (1992a,b). 8