Effect of Microwave Pretreatment on Water Absorption Characteristics, Appearance and Starch Properties of Adzuki Bean

This study aimed to improve the water absorption rate of adzuki bean at room temperature by producing cracks in adzuki bean epidermis via microwave pretreatment. Adzuki bean was pretreated by microwave at 80~800 W for 10~50 s, and then the changes in its appearance, starch properties and water absorption characteristics in water and pectinase solution were monitored. When the microwave power and treatment time increased, some cracks appeared on the epidermis, the volume increased, the starch was partially gelatinized, and thus the water absorption rate of adzuki bean in both water and 0.20 mg/mL pectinase solution at 25 ℃ was significantly increased. After microwave pretreatment at 800 W for 30 s, some cracks appeared on the surface, the bean remained as compact particles, and the volume was slightly increased; partial starch granules were destroyed and gelatinized, accompanying by the vanish of polarized cross; the rate of water absorption (6 h) increased by 28.78% and 30.89% in water and pectinase solution, while the saturated water absorption in water decreased by 10.64%, and showed no significant decrease in pectinase solution. Overall, microwave pretreatment could improve the water absorption rate of adzuki bean and the improvement was related to the formation of cracks on epidermis and the partial gelatinization of starch. The results could provide a theoretical guide for the applications of microwave in coarse grain processing.