Oxidation of controlled low-temperature vacuum dehydrated and freeze-dried beef and pork

Processes of freeze-drying and controlled low-temperature vacuum dehydration were used for drying beef and pork. The drying-time of controlled low-temperature vacuum dehydration was less than that of freeze-drying. Monolayer moisture contents and surface areas of freeze-dried products were higher than those of products dried by controlled low-temperature vacuum dehydration. The contents of myoglobin decreased and lipid oxidation increased during storage, and more marked effects were seen at higher storage temperatures. Myoglobin degradation in freeze-dried beef and pork was greater than in samples dried by controlled low-temperature vacuum dehydration. (C) 1997 Elsevier Science Ltd. All rights reserved

Density of banana puree as a function of soluble solids concentration and temperature

Density of banana puree was determined in a concentration range from 10 to 80degreesBrix and temperatures between 5 and 80 degreesC. Density values were found to increase with the increase of soluble solids concentration and the decrease of temperature. The results were analyzed to obtain this property as a function of temperature and soluble solids concentration and an equation, statistically significant at a confidence level of 99%, was proposed. For each different concentration. density variation with temperature was found to follow an Arrhenius-type relationship, with activation energy values between 748.36 and 1137.36 J/g-mol and all equations were statistically significant at a confidence level of 99%. A relationship between soluble solids concentration and activation energy was also obtained. (C) 2002 Published by Elsevier Science Ltd

INVESTIGATION OF CONTINUOUS AND INTERMITTENT HEATING ON FAR-INFRARED ASSISTED FREEZE-DRYING

Freeze-drying of sweet potato was studied using continuous and intermittent jar-infrared (FIR) assisted heating in this study. Intermittency levels of alpha = 0, 0.25, 0.5, 0.75, and 1. were applied with a cycle time of 30 min, and it was found that the optimum intermittency level was alpha = 0.5. The continuous (alpha = 1.) and intermittent (alpha = 0.5) FIR-assisted freeze-drying processes were then performed using a three-level, three-factor experimental design and analyzed by response surface methodology (RSM). For both continuous and intermittent freeze-drying, the response variable of drying time was affected by drying temperature (X(1)) and sample thickness (X(3)) at the 5% significance level; total color difference was affected by distance (X(2)) at a 95% confidence level. In addition, rehydration ratio was significantly affected by drying temperature (X(1)) and sample thickness (X(3)) in continuous heating, and by thickness (X(3)) at a 0.1% level of significance. lit both continuous and intermittent FIR-assisted treatments, the coefficients of determination (R(2)) of surface response models of drying time, rehydration ratio, and total color difference were all found to be greater than 0.90. Determination of optimum conditions was based on comparison between the control and FIR-assisted treatments. lit both continuous and intermittent treatments, optimum drying conditions could be established at 20 nun distance front FIR radiator to sample, and controlling the drying temperature in the range of 34 degrees C to 37 degrees C with 6 to 7 min sample thickness. Verification tests indicated that the generated second-order polynomial models were acceptable

Fermentation of banana media by using kappa-carrageenan immobilized Lactobacillus acidophilus

Fermentation media were prepared by using banana as the raw material, and cell immobilization of Lactobacillus acidophilus by K-carrageenan entrapment was applied to enhance the fermentation efficiency. Gel beads of diameters around 3.0 mm were prepared for the immobilized cells, ripe bananas were used for preparation of media, and both free and immobilized cells were employed to carry out the fermentation for 80 h. Cells leaked out from the gel beads and proliferated in the medium solution during the fermentation of immobilized cells. The final viable cell number reached 10(5) CFU/ml in the medium suspension, over 10(8) CFU/(ml gel) in gel beads for the immobilized cell fermentation and around 106 CFU/ml for the free cell fermentation. Immobilized cells withstand the adverse conditions in banana media resulting in better fermentation efficiency compared to free cells. Variation of fructooligosaccharides (FOS) in banana media was not significant in immobilized cell fermentation compared to free cell. Immobilized L. acidophilus fermented banana medium was found to possess symbiotic properties. (C) 2003 Elsevier B.V. All rights reserved

Effects of far-infrared radiation on the freeze-drying of sweet potato

An experimental dryer was developed to determine the drying characteristics of sweet potato during freeze-drying with far-infrared radiation. The experimental drying time of sweet potato cubes dehydrated by three drying methods, i.e., air-drying, freeze-drying, and freeze-drying with far-infrared radiation, were compared, and freeze-drying with far-infrared radiation was found to be able to reduce the drying time of sweet potato. Both constant and falling rate drying periods were observed, and empirical equations were developed to study the behavior of drying rate in falling rate period. On the other hand, four mathematical models were used to describe the drying characteristics of sweet potato during freeze-drying with far-infrared radiation. The coefficients of determination (R-2) in the exponential, Page, and approximate diffusion model were found to be above 0.98, and that of diffusion model was above 0.92. The rank of fitness of those models was Page, approximate diffusion, exponential and diffusion model. The choice of Page model was evident because of the lowest residual as well as RMSE. The Page model described the far-infrared freeze-drying characteristics of sweet potato properly. (C) 2004 Elsevier Ltd. All rights reserved

Chlorophyll stability in spinach dehydrated by freeze-drying and controlled low-temperature vacuum dehydration

Freeze-drying and controlled low-temperature vacuum dehydration were used for the drying of both blanched and unblanched spinach. Monolayer moisture content and solid surface area of dehydrated products were determined by using moisture sorption isotherms and BET equation. Contents of chlorophylls a and b and TEA value were measured, and those variations in dried samples during storage were studied at different storage temperatures of 5, 20, 30, and 45 degreesC. Drying time of controlled low-temperature vacuum dehydration was much less than that of freeze-drying. Solid surface areas of products from freeze-drying were higher than those from controlled low-temperature vacuum dehydration. and blanching also exerted an effect on the increase of solid surface area of dried products. Chlorophyll contents decreased acid TEA value increased with the increase of storage temperature and time. Those phenomena were more significant in the products of freeze-drying than those from controlled low-temperature vacuum dehydration, and more marked in blanched samples compared to unblanched. (C) 2001 Elsevier Science Ltd. All rights reserved