Study On Drying Process Of Edamame By Hot-air And Vacuum Microwave Combination

The combined application of various drying methods is one of the trends in modern drying technology, which uses the advantages of different drying methods suitable for different phases of a drying process in order to improve power efficiency of the drying equipment. This study compared various drying operations for edamames in terms of drying efficiency and product quality, designed a combination drying process using hot-air in the initial phase and vacuum microwave in the final phase, experimentally optimized and mathematically modelled the whole process, and established the mass transfer model thereof. The optimum drying process thus established provided satisfactory product quality, lower power consumption, and improvements in equipment productivity.The drying effects of vacuum microwave, hot-air, vacuum freezing, and combination hot-air & vacuum microwave drying was evaluated on thin layer with hot-air drying and drying were investigated on edamames in terms of vitamin C and chlorophyll retention, product shrinkage and rehydration properties, color, textural characteristics, and microstructure. Combination hot-air & vacuum microwave drying greatly lessened drying time as compared with hot-air and vacuum freeze drying; and provided similar product quality as compared with freeze and vacuum microwave drying. Combination hot-air & vacuum microwave drying demonstrated significant superiority over hot-air drying to guarantee good product quality. Hence, combination hot-air & vacuum microwave drying deserves promoted application both for economical and product quality considerations.Hot-air drying has advantages of rapid removal the surface water of materials without causing damages to product quality during the initial drying phase, yet disadvantages of extremely low drying rate in the final stage; and vacuum microwave drying has advantages of higher drying rate for removal of residual water in the materials with least damages to products, yet disadvantages of difficulty in oven chamber moisture release in the initial stage, which will increase oven loads. However, combination drying consisted of hot-air drying followed by vacuum microwave drying will fundamentally solve these problems. The drying process parameters were optimized and obtained.The changes in moisture content, drying rate and surface temperature of edamames were examined during hot-air drying and vacuum microwave drying, respectively. Nonlinear regression and multiple linear regression procedures were used to estimate the parameters associated with the drying models, from which a semi-empirical mathematical model was developed for predicting the thin layer drying kinetics of edamames during combination hot-air drying and vacuum microwave drying. This model was proved to be in good agreement with the experimental results under all drying conditions. The moisture diffusivity...