Abstract: The aim of this research was to explore the effects of different soaking methods namely, hot water soaking, and soaking in water at ambient temperature after ultrasonic and microwave pretreatments, and chemical and enzymatic pretreatments on the water adsorption percentage and volume expansion percentage of mung bean. At the same time, the internal microstructure of mung bean was observed by microstructure electron microscope and kinetic studies on the water absorption were carried out. The results showed that the water absorption percentage of mung bean increased reaching saturation as immersion time and temperature increased, but the saturated water absorption percentage was significantly reduced with increasing immersion time. The saturated water absorption percentages and expansion percentages with different soaking treatments were different. The water absorption kinetic equations for four soaking treatments were as follows: 1) hot water soaking at different temperatures: y20 = 0.056x + 0.002 (R2 = 0.945, 20 ℃), y40 = 0.235x + 0.085 (R2 = 0.978, 40 ℃), and y60 = 1.057x + 0.332 (R2 = 0.983, 60 ℃); 2) ultrasonic and microwave treatment: yu = 0.182x + 0.001 (R2 = 0.988, ultrasonic treatment), and ym = 0.116x + 0.081 (R2 = 0.982, microwave); 3) chemical treatment: ya = 0.029x + 0.051 (R2 = 0.963, acetic acid), ysb = 0.036x + 0.027 (R2 = 0.838, sodium bicarbonate), ysc = 0.057x + 0.054 (R2 = 0.957, sodium carbonate); 4) enzymatic treatment: yc = 0.122x + 0.051 (R2 = 0.999, cellulase), yh = 0.101x + 0.103 (R2 = 0.854, hemicellulase), and yp = 0.098x + 0.002 (R2 = 0.990, pectase). The results of kinetic studies showed that both physical and chemical treatments could increase the water absorption percentage of mung bean, and ultrasonic and enzymatic treatments could significantly shorten the soaking time.

Key words: mung bean, soaking treatment, water absorption percentage, water absorption kinetics