Impact of steam explosion pretreatment of defatted soybean meal on the flavor of soy sauce

Abstract

Steam explosion (SE) can improve the degradation efficiency of macromolecules such as defatted soybean meal (DSM). In this study, the physicochemical properties and the fermentation characteristics of SE-pretreated DSM were investigated. As shown by scanning electron microscopy (SEM), the dense structure of DSM was clearly cracked with larger voids. Under the pressure of 1.5 MPa, cellulose and hemicellulose were degraded by 50.7% and 71.1% respectively. When DSM treated with different SE pressure was applied to the soy sauce fermentation process, the content of amino acid nitrogen was increased 2-folds higher compared to the control, and the fermentation time has been greatly reduced. Simultaneously, the alcohols content of SS-1.5 sample was more than three times that of the control, particularly in the production of higher alcohols such as 2-methyl-1-butanol. The aldehydes, which contribute to the fruity and smoky-like aroma of soy sauce, increased significantly in both content and types (e.g., decanal, isobutyraldehyde, and 2-methylbutyraldehyde). The typical umami flavor and sauce-like aroma of soy sauce were considerably improved after SE-pretreated DSM. Taken together, SE pretreatment improved the utilization rate of raw materials and the quality of soy sauce flavor.