The shrinkage in dehydration of root vegetables such as carrots, potatoes, sweet potatoes and radishes was investigated. The samples were dried in flowing hot air. The surface areas were measured by photographing the samples. Three drying models were postulated for the formulation of the relation between the changes of the surface area and the moisture contents. The uniform drying model, which in the case of drying is that the shrinkage in volume equals the volume of water lost by the evaporation, agreed with the measured values during the early stages of the drying. The core drying model by assuming the formation of the dried layer at outer side of material was better in agreement with the experimental results. The semicore drying model, which is the intermediate model between the uniform and the core drying model, and the empirical equations of the shrinkage were also considered.

The mechanism of cooking rice was investigated in this study. The rheological method using the parallel plate plastometer was adopted for measurement of the degree of cooking. The range of temperatures measured ran from 75-150°C. Experimental results showed that cooking rate followed the equation of a first order chemical reaction. We designated the proportional constant as the cooking rate constant, but the slope of Arrhenius plots of the cooking rate constants changed around 110°C. The activation energy of cooking at temperatures below 110°C and above 110°C was about 19,000 and 8,800 cal/mol respectively. The influences of water soaking time before cooking were also studied. We concluded that the cooking process comprises two mechanisms; at temperatures below 1 10°C the cooking rate is limited by the reaction rate of rice components with water; and at temperatures above 110°C it is limited by the rate of diffusion of water through the cooked layer toward the interface of uncooked core where the reaction occurs. The reaction rate constant and the diffusion coefficient of water were calculated by assuming the core model or shell-type model.

The gelatinization rate of rice and potato starches were investigated. The rheological method, using a capillary tube viscometer, was applied for the measurement of the gelatinization degree. The gelatinization rates were measured for the rice and potato starches at temperature ranges of 70-85 and 60~63°C respectively. The rate parameter in the rate equation was given as the Arrhenius equation. The equivalent values of the activation energy for the rice and potato starches were about 14 and 230 k&/g-mol respectively. We concluded that the gelatinization rate of starches is limited by the chemical reaction rate and/or the physical transforming rate of starch components wi-ih water.