Vacuum Drying Characteristics and New Prediction Model for Changes in Moisture Content of Adzuki Beans

Abstract

　The vacuum drying method was applied to the drying of adzuki beans in this study. The effects of vacuum level and temperature on the drying rate and sample quality (intact bean kernel and hull) of adzuki beans were examined at various temperatures (20～70℃) and vacuum pressure levels (0.07～0.10 MPa). Broken and cracking sample beans were not observed under any measurement conditions. The drying rate of the sample was faster with vacuum drying than with hot air drying. The vacuum drying method was found to be applicable to adzuki beans with a moisture content of 25% on a dry basis or less at temperatures of 20～70℃. A new drying model related to temperature and vacuum level was developed to estimate changes in the moisture content of adzuki beans during vacuum drying with sufficient accuracy for practical use. The effective diffusion coefficients of the sample were estimated using Fick's second diffusion model, and they were shown to be a function of temperature and vacuum level.