Osmotic Dehydration

The effect of different pre-treatments (i.e. osmotic dehydration in 10, 15 and 20°Brix NaCl solution and drying air temperature of 50, 60 and 70°C) on drying behaviour of onion slices were investigated. The onion slices were dried in a laboratory model tray dryer. Drying of onion slices occurred in falling rate period. Five thin-layer drying models (Exponential, Page, Henderson and Pabis, Logarithmic and Power law) were fitted to the moisture ratio data. Among the drying models investigated, the Page model satisfactorily described the drying behaviour of onion slices. The effective moisture diffusivity of pre-treated samples was higher than that of non-treated samples

The effect of osmotic dehydration on the volatile fraction of kiwi fruit was studied, as well as the effect of freezing and frozen storage. Osmotic treatments were carried out in sucrose solutions until the kiwi fruit reached 30°Brix, at atmospheric pressure (OD) and by applying a vacuum pulse (PVOD), by using 45 and 65°Brix sucrose. Volatile compounds of fresh, dehydrated

Water and sucrose transfer were quantitatively investigated during osmotic dehydration of carrot slices using response surface methodology with the sucrose concentration (40–60%, w/w), temperature of sucrose solution (40–60 °C) and immersion time (0.5–6.0 h) being the independent process variables. Quadratic regression equations describing the effects of independent process variables on the water loss (WL) and sucrose gain (SG) were developed. It was found that immersion time and concentration of sucrose solution were the most significant factors affecting the WL during osmotic dehydration of carrots followed by temperature. Effect of temperature and time were more pronounced for SG than the concentration of sucrose solution. It is suggested that the regression equations obtained in this study can be used to find optimum conditions for the desired sensory and physical properties of sweet carrot products such as preserves.

Fulfilling the food demand of a growing population is the biggest challenge as lot of food globally got wasted due to improper storage and processing. Osmotic dehydration offers high-quality preservation and maintenance of the integrity of fruits & vegetables. Response surface methodology was performed to estimate the main effect of osmotic dehydration process on quality attributes of carrot and beetroot cubes. Higher values of the osmotic solution of salt and sucrose at sample to solution ratio of 1:5 had provoked higher flows of water and solutes through the carrot and beetroot cubes. The range of NaCl concentration varies from 4-12 % w/v in carrot and 12-16 % w/v in beetroot for 2, 4 and 6 hour. However, sucrose concentration varies from 40-60o Brix in both carrot and beetroot. Quality attribute of carrot and beetroot including ascorbic acid, carotenoid, total phenol etc. didn’t changed on recommended process variables 50o Brix of sucrose + 8 % w/v sodium chloride for carrot and ...

This study was conducted to investigate effects of varying levels of pretreatments (blanching temperature and osmotic concentration) on rehydration characteristics, nutrient retention and sensory acceptance of solar-dried carrot slices. Blanching is used to combat the problems of discoloration by enzymes. Osmotic pretreatment enhances drying rate, reduces nutrient degradation during drying and storage and results in good quality dehydrated carrot. The carrot samples were blanched at 55, 65 and 75°C for 45 minutes, soaked in 5%, 10% and 15% salt solutions for 5 hours and dried using an indirectly heated passive type solar dryer. Rehydration capacity of the dried carrots was determined by soaking 20 g sample in hot water at 95°C for 10 minutes and rehydration kinetics was carried out by soaking 5 g samples at 75, 85 and 95°C. Blanching temperature, osmotic concentration, and their interaction significantly affected the physicochemical properties of the carrot slices. High values of rehydration capacity (157.19) and low lixiviated soluble solids (5.47°B) were determined for samples treated at blanching temperature of 55°C. Similarly the smallest salt concentration (5%) resulted in the highest value (188.65) of rehydration capacity and lowest value (4.25°B) of lixiviated soluble solids. The interaction of 65°C blanching temperature with 5% osmotic concentration produced the highest  rehydration capacity (214.65) and that of 55°C with 5% gave the lowest (4.20°B) soluble solid loss. The highest soluble solid loss corresponded to samples treated with 15% salt solution combined with all levels of blanching temperature. Best nutrient retentions (5.25% protein db, 2.49% fat db, 2.17% fiber db and 71.94 ppm β-carotene) were recorded for samples treated at 55°C whereas the 5% salt solution resulted in 2.88% fat, 2.46% fiber and 73.89 ppm β-carotene. The highest crude protein (5.68% db) and crude fiber (2.99% db) were recorded for the combination of 55°C with 15%, and the highest crude fat (3.20% db) and β-carotene (74.97 ppm) were obtained from the samples subjected to 55°C and 5%. High total ash contents were associated to high levels of osmotic concentrations irrespective of the blanching temperatures. Concerning the sensory acceptance, color, flavor, taste, texture and overall acceptance of samples blanched at 55°C and soaked in 10% solution were most liked. A first-order kinetic model was used to describe the rehydration kinetics in terms of rehydration rate constant (k) and equilibrium moisture content (Me). A better rehydration performance was observed corresponding to the samples treated at 55°C blanching temperature and soaked in 5% salt solution. In most cases, the physicochemical, nutritional and sensory acceptance of the samples treated with 55°C blanching temperature and 5% salt concentration and combination of the two was observed to be superior to other treatment levels.

The osmotic processes induce not only water and solute fluxes in the tissue but also changes in cellular structure, depending on the ratio in which different transport mechanisms act in the system: osmo-diffusional transport of water and solutes and hydrodynamic gains of external solution. The latter is more important in porous tissues, especially when submitted to vacuum impregnation process. In

Consumers increasingly demand convenience foods of the highest quality in terms of natural flavor and taste, and which are free from additives and preservatives. This demand has triggered the need for the development of a number of nonthermal approaches to food processing, of which high-pressure technology has proven to be very valuable. A number of recent publications have demonstrated novel and diverse uses of this technology. Its novel features, which include destruction of microorganisms at room temperature or lower, have made the technology commercially attractive. Enzymes and even spore forming bacteria can be inactivated by the application of pressure-thermal combinations, This review aims to identify the opportunities and challenges associated with this technology. In addition to discussing the effects of high pressure on food components, this review covers the combined effects of high pressure processing with: gamma irradiation, alternating current, ultrasound, and carbon dioxide or anti-microbial treatment. Further, the applications of this technology in various sectors—fruits and vegetables, dairy, and meat processing—have been dealt with extensively. The integration of high-pressure with other matured processing operations such as blanching, dehydration, osmotic dehydration, rehydration, frying, freezing / thawing and solid-liquid extraction has been shown to open up new processing options. The key challenges identified include: heat transfer problems and resulting non-uniformity in processing, obtaining reliable and reproducible data for process validation, lack of detailed knowledge about the interaction between high pressure, and a number of food constituents, packaging and statutory issues.

The effect of drying method on bulk density, substance density, porosity, and shrinkage of quinces at various moisture contents was investigated. Samples were dehydrated with four different drying methods: conventional drying in fluid bed and tray driers, infrared assisted air drying, osmotic dehydration combined with conventional air drying and freeze drying. All the properties except substance density were affected by drying method. Bulk density of freeze dried materials decreased with decreasing moisture content while for all other dehydration processes, bulk density and porosity increased with decreasing moisture content. Freeze dried materials developed the highest porosity whereas the lowest was obtained using osmotic dehydration. Freeze dried samples had limited shrinkage. Simple mathematical models were used to correlate the above properties with the material moisture content. For the substance density, a single non-linear equation gave accurate predictions irrespective of drying methods. Although differences in shrinkage with the drying method were detected, the same model as a function of moisture content could be used for all drying methods but with different coefficients.

Response surface methodology was used to determine the optimum processing conditions that yield maximum water loss and weight reduction and minimum solid gain and water activity during osmotic dehydration of potatoes. Temperature (20–60 °C), processing time (0.5–8 h), sucrose (40–60% w/w) and salt (0–15% w/w) concentrations were the factors investigated with respect to water loss (WL), solid gain (SG), weight reduction (WR) and water activity (aw). Experiments were designed according to Central Composite Rotatable Design with these four factors each at five different levels, including central and axial points. Experiments were conducted in a shaker (Thermoshake-Gerthardt) with constant agitation of 200 rpm and solution to sample ratio of 5/1 (w/w). With respect to water loss, solid gain, weight reduction and water activity, both linear and quadratic effects of four variables were found to be significant. For each response, second order polynomial models were developed using multiple linear regression analysis. Analysis of variance (ANOVA) was performed to check the adequacy and accuracy of the fitted models. The response surfaces and contour maps showing the interaction of process variables were constructed. Applying desirability function method, optimum operating conditions were found to be temperature of 22 °C, sucrose concentration of 54.5%, salt concentration of 14% and treatment time of 329 min. At this optimum point, water loss, solid gain, weight reduction and water activity were found to be 59.1 (g/100 g initial sample), 6.0 (g/100 g initial sample), 52.9 (g/100 g initial sample) and 0.785, respectively.

The effects of NaCl and osmotic dehydration on the linear viscoelastic behavior of duck egg yolk were evaluated. An increase in NaCl concentrations from 0% to 3.0% (w/w) resulted in a remarkable change in the linear viscoelastic behavior by inducing a sol–gel transition, specifically. The transition was more pronounced when 1.5% (w/w) NaCl was incorporated. The effect of dehydration on aggregation and network formation was predominant than that of the NaCl addition. Nevertheless, at a lower degree of dehydration, the addition of NaCl could modulate the viscoelastic behavior of duck egg yolk, resulting in a well-developed gel network. Addition of NaCl into duck egg yolk could stabilize the protein molecules as evidenced by an increase in denaturation temperature as well as a delay in gel network formation. As visualized by a scanning electron microscope, the denser network with smaller voids was observed in duck egg yolk gel with increasing NaCl concentration and degree of dehydration.

Micro- and macrostructural changes in apple slices during osmotic dehydration were studied. Samples were immersed into 25.0% (w/w) glucose or 34.6% (w/w) sucrose aqueous solutions at 30 °C until water and solid contents were almost constant (≅350 min). They were removed after selected times, and examined for thickness, volume, bulk and solid–liquid densities, porosity, water activity, water loss, solids gain and microscopic aspects. At relatively short times, significant weight and volume losses were observed for both treatments arising from the fast water loss. The solid–liquid density of glucose or sucrose treated samples increased slowly along the process. However, the bulk density increased up to a certain value and then fluctuated with increasing time, showing in some cases another pronounced increase for long times of treatment. Fruit porosity values decreased in line with the increase in bulk density values. At the end of the osmotic treatments in glucose or sucrose solutions, there was a recovery in porosity, although the values were lower than for fresh fruit. The changes in bulk density, porosity and volume of apple tissue along osmotic process were closely supported by microstructural and structural observations (using light microscopy and environmental electron scanning microscopy) and explained by considering osmosis as a multicomponent diffusion process through porous media and due to the relaxation of the viscoelastic shrunken cell walls.

The objective of this study was to develop calcium enriched osmo-dehydrated apple slices by impregnation at atmospheric pressure. Osmotic dehydration (OD) was carried out using 50°Bx sucrose solutions with 4% and 8% calcium lactate (CL) at atmospheric pressure for 16 hours followed by dehydration. It was found that, the calcium incorporated in 50 gm of osmo-dehydrated apple slices meets up to 27% of the, Recommended Dietary Allowance (RDA) of calcium for adults in India. Moisture content of all the samples were much below the maximum limit of moisture content (20% m/m). Non-enzymatic browning was significantly (p<0.05) lower in slices which were treated with calcium. Microbiological quality was better in sample treated with 8% calcium lactate. The sensory panel did not observe any signicant differences in appearance, flavor, sweetness, texture and overall acceptability in any of the sample. Thus, it can be concluded that a healthy and nutritious ready to eat calcium enriched apple slices were developed by applying simple and inexpensive atmospheric impregnation method without affecting sensory characteristics.

Jams are made from fruit and sugar mixed in proportions so that the final product contains a minimum fruit content of 30% and 45°Brix minimum. Traditional manufacturing methods require concentration by heat treatments, which promotes quality changes that affect sensory and nutritional properties, the latter related mainly to ascorbic acid losses. An alternative to concentration is to incorporate previously dehydrated fruit, avoiding thermal treatment. Osmotic dehydration with sugar solutions has been described as a suitable method for preserving fruit quality to a great extent. On the other hand, osmotic solution becomes enriched with water-soluble fruit components after osmotic treatment. In this work, the production of kiwi and orange jam by using osmotically dehydrated fruits mixed with osmotic solution, without thermal treatment, has been studied. Physical (colour and mechanical properties) and physico-chemical properties (aw, °Brix, moisture content, pH, acidity) of obtained products have been analysed and compared with those determined for commercial available products.