Enhancing laccase-induced soybean protein isolates gel properties by microwave pretreatment

Soybean protein isolate (SPI) is an important food ingredient used to prepare for soy products. However, protein gel formed from individual SPI exhibits poor gelation properties. In this study, effects of microwave pretreatment at various power (0-600 W) on gel properties of laccase-induced gel were investigated. After microwave pretreating, gel strength of treated samples was over 2.2 times that of untreated. Microwave heating dramatically promoted water-holding capacity and storage modulus of laccase-induced SPI gel. Marked reducing happened in free SH group, since laccase catalyzed cross-linking between phenols and its derivatives, which facilitated the connection of disulfide bonds. In addition, microwave pretreatment changed the secondary structure of the gel samples as determined by Fourier transform infrared spectroscopic analysis. Intuitively, a more compact structure was observed by SEM. Hence, microwave pretreatment is effective in improving the gelation properties of laccase-induced SPI gel and may be used as an effective method in food industry. Practical applications As an indispensable ingredient, Soybean protein isolate (SPI) was wildly used in food industry to produce kinds of soy products. However, its poor gel properties impeded a further application of this low-cost ingredient. In this study, SPI was pretreated by microwave which destroyed its compact structure and exposed the reactive sites of enzyme. Then, microwave pretreatment SPI was induced by laccase to catalyze cross-linking between phenols and its derivatives since the groups were common exist in SPI. The laccase-induced SPI gel couple with microwave pretreatment possessed a more excellent gel property, which can be potentially used to produce high-quality soy products in food industry.