The effect of temperature and time in a fluidized bed dryer, the concentration of biopolymcr treatment and blanching time on quality attributes of dehydrated carrots was evaluated by response surface methodology. Optimization maximized rehydration ratio and minimized bulk density and carotene loss. Based on surface responses and contour plots, optimum conditions were: drying temperature of lSo"C, exposure time of 12.5 minutes, biopolymer concentration of 1.40%, and blanching time of 12 minutes. Expcrimcntally determined values for rehydration ratio, bulk density, and carotene loss in product processed under the optimum conditions were very close to the predicted values of 9.5, 0.05, and 15.7%, respectively.

Analyses showed raw jicama had a texture profile between white potato and Chinese water chestnut. Histological examination showed Chinese water chestnut had uniform cell sizes and intercellular spaces with relatively thick cell walls. Jicama had varied cell sizes, irregular intercellular spaces and thin cell walls. Canning reduced crispness of jicama by 65% and that of water chestnut by 20% of that of raw produce. Jicama had endogenous pectin methyl esterase activity.

A process for the production of high quality dehydrated potato cubes by high temperature fluidized bed (HTFB) initial drying followed by tunnel drying was optimized by response surface methodology. Drying temperature (T), exposure time in HTFB drier (t) and concentration of biopolymers (C) as pretreatment were determined as the most important factors affecting rehydration ratio, puffing, nonenzymatic browning and water holding capacity in the finished product. Optimum conditions for 0.95 cm potato cubes were: T = 145°C; t = 10 min; C = 1.2% and blanching time (b) = 4.5 min. Values predicted by the surface response model for rehydration ratio, bulk density, nonenzymatic browning and expressible fluid at the optimum were 5.75, 0.156, 0.20 and 4.8%, respectively. These values were experimentally varified and very close agreement between experimental and predicted values were obtained.

The penetration pattern of biopolymers in plant tissue during processing was studied. Carrot dices were infused with dye-dextran standards of different molecular weights (TlO, T40, T70 and T500). Polymers of smaller size were found within the intercellular spaces and the cell walls. Larger polymers were found only in broken cells near the surface of the tissue. Biopolymers of small size were theorized to provide strength to the cell wall of plant tissue and assist in maintaining cellular integrity during dehydration. This was further verified in that the dextrans of molecular weight of 10,000 produced best quality dehydrated carrots with high rehydration ratio, more retention of carotenoids and high water-holding capacity.

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