KINETICS of OSMOTIC DEHYDRATION of COCONUT

Osmotic dehydration rates were determined for coconut over a range of osmotic solution concentration (40–70°B) and temperature (25–45C). A semi-empirical relation for kinetics of osmotic dehydration has been proposed, which indicates the moisture diffusion as a function of concentration of osmotic solution and its temperature. Good agreement was observed between the observed and predicted values (correlation coefficient 0.90). the effective diffusion coefficients of water in coconut during osmotic dehydration were estimated and also the activation energy of the osmotic dehydration process of coconut was found as 1.75 × 10⁴ J/kg-mole.     

KINETICS OF OSMOTIC DEHYDRATION IN ORANGE AND MANDARIN PEELS

The nutritional and health properties of some citrus peel components such as pectin, flavonoids, carotenoids or limonene make interesting developing processing methods to obtain peel stable products, maintaining its quality attributes, increasing its sweetness and improving its sensory acceptability. In this sense, osmotic dehydration represents a useful alternative by using sugar solutions at mild temperature. Kinetics of osmotic treatments of orange and mandarin peels carried out at atmospheric pressure and by applying a vacuum pulse at the beginning of the process were analysed at 30, 40 and 50C, in 65 °Brix sucrose, 55 °Brix glucose and 60 °Brix rectified grape must. Vacuum pulse greatly affected mass transfer behavior of peels due to the greatly porous structure of albedo. So, PVOD treatments greatly accelerate the changes in the product composition in line with an increase in the peel sample thickness. In osmotic processes at atmospheric pressure, sample impregnation occurs coupled with osmotic process, but much longer treatments are required to achieve a reasonable concentration degree which assures sample stability. Low viscosity osmotic solutions seems recommendable in order to promote both diffusional and hydrodynamic transport, in vacuum pulsed pretreatments at mild temperatures.     

OSMOTIC DEHYDRATION OF FRUIT

Influence of the osmosis time on the stability of processed cherries ("Vittoria", "Durone Nero I" and "Starking" cultivars) was studied.
The cherries were osmo-dehydrated for two, four, six hours, vacuum packed, pasteurized and then analyzed for ascorbic acid, glucose, fructose and maltose content by HPLC, for pH, total titrimetric acidity, dry matter, color and for organoleptic characteristics, during the process and up to six months of storage.
The dehydration of the fruit and the exchange with the osmotic syrup took place chiefly during the first two hours of the process. No substantial differences were noted though, in the cherries, processed at different time, both for chemical and organoleptic characteristics. Color data showed the importance of the variety in order to obtain good products. Thus it was concluded that a two hours'osmodehydration process is suitable to achieve very acceptable products.     

OSMOTIC DEHYDRATION OF KIWIFRUIT (ACTINIDIA CHINENSIS): FLUXES AND MASS TRANSFER KINETICS

Pulsed‐Vacuum‐Osmotic‐Dehydration of kiwifruit (Actinidia chinensis) was studied using two kinds of osmotic solution: sucrose (65 Brix) and concentrated grape juice (63 Brix), three temperatures (25, 35 and 45C) and four vacuum pulse times (0, 5, 10 and 15 min). Experimental results enabled the mass transfer kinetics for water and solutes to be studied (compositional changes of the liquid fraction and changes in the liquid fraction/solid matrix ratio). The impregnation of samples, because of the vacuum pulse, was higher when concentrated grape juice was used as the osmotic solution, probably due to its lower viscosity. The effective diffusivity (D_e) was obtained for each experimental condition and the results show higher diffusivities for vacuum‐pulsed treatments, although differences between treatments with different vacuum‐pulse time could not be observed. D_e values were slightly greater for treatments with concentrated grape juice. The activation energies (E_o) were obtained by fitting the data to the Arrhenius equation.     

OSMOTIC DEHYDRATION OF STRAWBERRIES IN A BATCH RECIRCULATION SYSTEM

Physical and chemical characteristics of two cultivars of strawberries during osmotic dehydration in sucrose and glucose solutions were investigated. Temperature was found to have a significant effect on the water and sugars (glucose, fructose and sucrose) exchange between strawberry and the osmotic solution. Mass transfer was found not to be significantly different between cultivars. Glucose gain was found to be higher than sucrose for the strawberries osmotically dehydrated in glucose and sucrose solutions at the same mole fraction, respectively. Sugars other than the osmotic sugar were found to decrease in concentration during the osmotic process. The combination of 63% sucrose solution with 25C process temperature for 2 h was able to remove more than 40% of moisture and load less than 0.1% of sucrose in the strawberries.     

FORMULATION OF BEVERAGES CONTAINING BYPRODUCTS OF OSMOTIC DEHYDRATION OF LOWBUSH BLUEBERRIES

The manufacture of osmotically dehydrated lowbush blueberries, Vaccinium angustifolium, produces a liquid byproduct, blueberry extract (BE), containing sugar and blueberry juice. The unique blueberry color and flavor in BE were utilized in a simple beverage containing spring water, 30% or 50% BE (w/v), and 0.1% or 0.2% citric acid. The beverages with 50% BE had significantly higher (p ≤ 0.001) brix and were significantly (p ≤ 0.001) darker, less red, and more blue. Fifty consumers rated the beverages containing 50% BE as significantly more acceptable in color (p ≤ 0.001) and fruit flavor (p ≤ 0.05), but least acceptable (p ≤ 0.001) for sweetness. Samples with 0.2% citric acid were significantly higher (p ≤ 0.001) in overall acceptability. BE can be used to provide flavor and color in fruit beverages while reducing a waste disposal problem for blueberry processors.     

OPTIMIZATION OF OSMOTIC DEHYDRATION PROCESS OF CARROT CUBES IN SUCROSE SOLUTION

ABSTRACT

For optimization of the osmotic dehydration process of carrot cubes in sucrose solution by response surface methodology (RSM), the experiments were conducted according to face‐centered central composite design. The independent process variables for the osmotic dehydration process were osmotic solution concentrations (45–55°Brix), temperature (35–55C) and process durations (120–240 min). Statistical analysis of results showed that all the process variables had a significant effect on all the responses at 5% level of significance (P < 0.05). The osmotic dehydration process was optimized by RSM for maximum water loss, rehydration ratio, retention of color, sensory score and minimum solute gain. The optimum process conditions were 52.5°Brix sucrose syrup concentration, 49C osmotic solution temperature and 150‐min process duration.

PRACTICAL APPLICATIONS

The process of osmotic dehydration can be used for the preparation of shelf‐stable products for the purpose of use during off‐season. The quality of preosmosed carrots is much superior to the product dehydrated with the convectional method of convective dehydration. The osmotically dehydrated carrots can be used for cooking as vegetables after rehydration or can be added directly into soups, stews or casseroles before cooking. If the product is blanched before osmotic dehydration, the process can be used successfully for the preparation of carrot candy.     

REUSE OF SUCROSE SYRUP IN PILOT-SCALE OSMOTIC DEHYDRATION OF APPLE CUBES

Osmotic dehydration (OD) treatments of apple cubes were carried out in a pilot plant, which consisted of an OD vessel, a filter, a vacuum evaporator, and recirculating pumps. The osmotic solution (OS) was maintained at 59.5 ± 1.5 °Brix and 50C by reconcentration in the evaporator, and suspended particles were eliminated by filtration. OS was reused to process 20 batches of apple cubes, maintaining a constant OS/fruit ratio of 5/1 (w/w) by addition of new OS. Evolution of pH, titratable acidity, soluble solids, water activity, color, reducing sugars, and microbial load in the OS was evaluated along the OD process. The OD parameters and the apple color were determined. Values of the physicochemical properties of the OS stabilized after 10 treated batches. A microbial load of 2590 ± 330 CFU/mL was observed in the OS at the end of 20 OD treatments. Water loss, solids gain and color of dehydrated apple cubesobtained in OD process with reuse of the OS were similar to those found in an OD process carried out with a nonrewed OS.     

海鳗盐渍过程中的渗透脱水规律研究

研究了海鳗在盐渍过程中的渗透脱水规律。海鳗经盐渍发生了物理、化学和组织的变化。温度对鱼体盐渍的重量变化影响不是决定性的，食盐浓度是影响鱼体重量变化的关键因素；温度和浓度对于食盐渗透速度的影响是显著的，并且为正相关。电镜显示经过盐渍后的肌肉组织结构变硬和嚼密。在盐卤中氨基酸随着盐渍温度的提高溶出的数量增加。随着盐渍浓度的提高，盐卤中的氨基酸溶出的数量减少。而鱼体肌肉蛋白质的分解，盐渍浓度对其有较大影响。这些研究对于海鳗的腌制生产具有实际指导意义。     

OPTIMIZATION of OSMOTIC DEHYDRATION of CAULIFLOWER

Osmotic dehydration of cauliflower as influenced by temperature (40-90 C), salt concentration (5-25%), ratio of brine to material (2-4, w/w) and time (5-180 min), was studied through central composite rotatable design (CCRD) under response surface methodology. Responses of weight loss (%) and salt pickup (%) were fitted to polynomials of second degree requiring 6 and 7 terms, respectively, with multiple correlation coefficients of 0.97 and 0.98. the fitted functions were optimized for maximum weight loss and with 4% salt pickup using a flexible polyhedron search method. Out of four such optimum sets one was selected based on the actual weight losses in the verification experiments with larger batch sizes, color and appearance, texture and rehydration properties of the dried materials. the optimum conditions required the material to be processed at 80C for 5 min in 2 times (w/w) of 12% brine. the selected optimum as well as two other optimum sets also inactivated polyphenol oxidase which causes enzymatic browning.     

INFLUENCE OF OSMOTIC DEHYDRATION ON THE VOLATILE PROFILE OF GUAVA FRUITS

ABSTRACT

The effect of osmotic dehydration (OD) on the volatile compounds of guava fruits was studied. Osmotic treatments were carried out at atmospheric pressure, at continuous vacuum and by applying a vacuum pulse (5 min under vacuum and the remaining time at atmospheric pressure) at different temperatures (30, 40 and 50C) and times (1, 2 and 3 h). The volatile compounds of fresh and dehydrated samples were obtained by simultaneous distillation–extraction, and were analyzed by gas chromatography/mass spectrometry. In general, OD caused changes in the concentration of volatiles, depending on the process conditions. The use of lower temperatures and shorter treatment times can diminish the loss of volatiles with respect to the fresh samples. The greatest damage to volatiles loss is produced at 50C for up to 2 h under both pulsed and continuous vacuum. The lowest total volatiles loss occurred at 30 and 40C for up to 3 h under pulsed vacuum or atmospheric pressure.

PRACTICAL APPLICATIONS

Consumer demand for high‐quality products with freshlike characteristics has promoted the development of a new category, minimally processed fruits and vegetables. Although these products present, as distinguishing features, simplicity in use and convenience, they generally perish more quickly than the original raw material because of tissue damage caused by mechanical operations. The use of osmotic dehydration process has been presented as a tool for the development of minimally processed fruits. The slight water activity reduction promoted by the process may provide stable products with good nutritional and sensorial quality and with characteristics similar to those of the fresh products. The application of minimal processing to tropical fruits can represent an interesting world market. Fruit flavor is an important quality factor that influences consumer acceptability, and for this reason, its study is relevant in the minimally processed food product.

     

APPLICATION OF RESPONSE SURFACE METHODOLOGY FOR THE OSMOTIC DEHYDRATION OF CARROTS

Osmotic dehydrations of carrot cubes in sodium chloride salt solutions at different solution concentrations, temperatures and process durations were analyzed for water loss and solute gain. The osmotically pretreated carrot cubes were further dehydrated in a cabinet dryer at 65C and were then rehydrated in water at ambient temperature for 8–10 h and analyzed for rehydration ratio, color and overall acceptability of the rehydrated product. The process was optimized for maximum water loss, rehydration ratio and overall acceptability of rehydrated product, and for minimum solute gain and shrinkage of rehydrated product by response surface methodology. The optimum conditions of various process parameters were 11% salt concentration, 30C osmotic solution temperature and process duration of 120 min.     

MODELING AND OPTIMIZATION OF OSMOTIC DEHYDRATION OF BANANA FOLLOWED BY AIR DRYING

The process of osmotic dehydration followed by air drying was studied, modeled and optimized for the dehydration of bananas, which are an extremely perishable fruit unable to withstand freezing and, as such, need to be dried in order to preserve the fruit for later use. The mathematical model was validated with experimental data and the simulations show how the operating conditions affect the process. Process optimization was performed to obtain the best operating conditions that would reduce the total processing time. The results show the advantage of using moderate to high sucrose concentrations (55–65°Brix) for the osmotic solution, reduced pressure and the use of the osmotic treatment to reduce the total processing time of fruit drying.     

OPTIMIZATION OF VACUUM PULSE OSMOTIC DEHYDRATION OF CANTALOUPE USING RESPONSE SURFACE METHODOLOGY

The optimum levels of vacuum pressure, concentration of osmotic solution and dehydration time for vacuum pulse osmotic dehydration of cantaloupe were determined by response surface methodology (RSM). The response surface equations ( P < 0.05 and lack of fit > 0.1) explain the 97.6, 88.0 and 97.1% of the variability in weight loss, water loss and °Brix increase, respectively, at 95% confidence level. The canonical analysis for each response indicated that the stationary point is a saddle point for weight loss and °Brix increase, and a point of maximum response for water loss. The region that best satisfied all the constraints (low values in weight loss and °Brix increase, and high value in water loss) is located within the intervals from 49.5 °Brix to 52.5 °Brix for concentration and from 75 min to 84 min for dehydration time at a vacuum pulse of 740 mbar.