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.     

果蔬片微波干燥特性及最佳工艺研究

通过对利用微波干燥香蕉片的研究，揭示了微波干燥果蔬片的失水特性。同时，进行四因素三水平的正交实验以及二因素三指标的二次正交回归实验，得出各指标的回归方程，并进行参数优化，从而得到最佳工艺条件：前期发射功率为900W、前期时间2min、后期发射功率397W、后期时间11．3min。     

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.     

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.     

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.     

KINETICS OF OSMOTIC DEHYDRATION OF MANGO

The effects of sucrose syrup concentration (40–70 g/100‐g solution) and temperature (40–90C) on water loss and sucrose uptake by mango mesocarp slices during osmotic dehydration were investigated. The effective diffusivities for mass transfer were determined using the slope method based on the Fickian diffusion model. Water loss and sucrose uptake were proportional to the square root of osmotic contact time, implying that the process is Fickian. The specific mass transfer rate constants and effective diffusivities (D_e), derived from Fick's unsteady‐state diffusion equation, increased with temperature and sucrose syrup concentration. D_e values for water loss and sucrose uptake, which ranged between 2.59 × 10^?6 to 5.12 × 10^?6 m²/h and 1.70 × 10^?6 to 4.14 × 10^?6 m²/h, respectively, were related to absolute temperature using an Arrhenius‐type relationship. The activation energies, which fell in the range previously reported for diffusion‐controlled processes, increased with sucrose syrup concentration and varied from 9.74 to15.16 KJ/mol.     

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 APPLES BY IMMERSION IN CONCENTRATED SUCROSE/MALTODEXTRIN SOLUTIONS

The effect of sucrose:maltodextrin (S:M100) ratios on solids gain (SG) and water loss (WL) was investigated during the osmotic dehydration of apple disks. Concentrated solutions were prepared at 40C with 100:0, 90:10, 70:30, 50:50, 30:70 and 10:90 ratios of (S:M100). The highest score in sensory evaluation was achieved with 90:10 ratio of (S:M100). Three stages of osmotic dehydration can be observed by plotting the shrinkage of apple disks vs the moisture content. The result is that a higher maltodextrin concentration favors volume loss and enhances water loss, increasing the duration of stage 2 osmotic dehydration.     

PILOT PLANT FOR OSMOTIC DEHYDRATION OF FRUITS: DESIGN AND EVALUATION

This work proposes a pilot scale equipment for osmotic dehydration (OD) of apple cubes that consists of a novel agitation‐immersion device, a bag filter and a vacuum evaporator to conduct simultaneously the OD process, filtration and reconcentration of the osmotic solution (OS). The functional method analysis was used to design the pilot plant. Apple cubes (～1 cm³) were dehydrated using a 60 ° Brix sucrose syrup OS at 50C and a syrup/fruit ratio of 5. OD was conducted either with or without reconcentration of the OS. During the OD process particles of fruit were eliminated from the OS by filtration and the OS concentration was kept at 60 ° Brix by reconcentration in the evaporator. A comparison of the dehydration parameters of apple cubes obtained at pilot scale to those obtained at laboratory scale was done to evaluate the performance of the pilot equipment. The results show that the proposed set‐up can be suitable for commercial production of osmodehydrated fruits.