Effect of wheat bran steam explosion pretreatment on flavors of nonenzymatic browning products

Wheat bran, which contains a large amount of cellulose, is used as a raw material to produce soy sauce, but it is hard to degrade during fermentation. Steam explosion (SE) is efficient in hydrolyzing the cellulose for enhancing enzymatic digestion and solvent accessibility. In this study, we applied a SE at a sufficiently high pressure to damage the integrity of the wheat bran structure and modify it to assume a layered form. We found that cellulose, hemicellulose, and lignin structures were collapsed by SE pretreatment, which was indicated by their changes in Fourier transform infrared spectroscopy (FTIR). The amounts of cellulose, hemicellulose, and lignin decreased by 5.8%, 21.4%, and 43.4%, respectively, under 1.5 MPa, resulting in the significant reduction of sugar and amino acid nitrogen. The co-reaction of nonenzymatic browning after SE pretreatment resulted in an intense increase in flavor (overall feeling), as determined by electronic nose analysis and sensory evaluation. In conclusion, SE pretreatment under 1.0 MPa was proven to be the most optimal state for the production of aroma compounds (volatile compounds), which are essential for soy sauce production.