Since cranberry skin is thick and has low porosity, skin pretreatments were considered before drying in order to facilitate water diffusion. Mechanical and chemical pretreatments were considered, by cutting the fruits in half, by making pin holes in each cranberry, and by dipping the fruits in an alkaline solution. / A second pretreatment seemed necessary when drying cranberries in order to reduce their tartness. Cranberries were osmotically dehydrated, by immersing them in osmotic solutions of sucrose or high fructose corn syrup. / Once the pretreatment conditions were selected, four drying methods were tested on the pretreated cranberries. These methods included hot air drying, freeze-drying, vacuum drying and a combination of hot air and microwaves. A quality evaluation of the dried samples was also performed, including evaluation of overall appearance, taste, color, water activity, rehydration capacity and texture. (Abstract shortened by UMI.)

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The current study was conducted for evaluating the effects of two different strategies viz., phase control and cycle control, on the microwave/air drying process. A phase-controlled electrical power regulator was developed and connected in series with the original cycle-controlled power regulator of an existing domestic microwave oven. The microwave oven was further modified such that combined microwave and convectional drying can be accommodated. / The system performance was evaluated. It was observed that phase-controlled power regulator could be successfully used for quasi-continuous (fast-switching) power regulation with the maximization of power efficiency. The degradation of output microwave power was recorded and the nonuniform distribution of microwave field in the cavity was also verified. / The effects of phase control and cycle control were evaluated through combined microwave and convective drying of potato samples. Results showed that different power control methods had different impacts on drying kinetics and product quality. In both drying modes, the drying time increased with the decrease of microwave power density and the increase of air velocity. The drying rates of cycle-controlled drying are significantly higher than those of phase-controlled drying. In terms of rehydration capacity the phase-controlled drying mode produced better results. The product colour and sensory attributes were independent of the power control methods.

Graduation date: 1954

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No description available.

No description available.

No description available.

No description available.