Effect of Yeast Fermentation on Volatile Flavor Substances and Nutritional Properties of Rice Bran

To investigate the effect of yeast fermentation on the flavor as well as nutritional properties of rice bran. In this study, volatile flavor substances of rice bran at different fermentation periods (0, 12, 18, 24 and 30 h) were identified by headspace solid-phase microextraction-gas chromatography-mass spectrometry, key volatile substances affecting the flavor of rice bran before and after fermentation were determined by orthogonal partial least squares analysis, and finally a comprehensive sensory evaluation of fermented rice bran was carried out and the changes of its nutritional composition by the optimal time of fermentation were compared. The results showed that the content and types of volatile substances of rice bran changed significantly during the fermentation process, the content of aldehydes in unfermented rice bran accounted for 35.99% and the content of alcohols accounted for 14.21%, and the content of aldehydes decreased to 5.52% and the content of alcohols increased to 60.87% at 30 h of fermentation. Among them, there were 15 key volatile substances. In the sensory evaluation, there was a significant (P<0.05, P<0.01) correlation between key volatile substances and rice bran aroma, and the sensory score of rice bran improved after fermentation, and the best sensory score was obtained for rice bran fermented for 18 h. Nonanal and ethyl nonanoate had the most significant (P<0.01) effects on the overall score of rice bran. In terms of nutritional composition, the protein content of yeast fermented rice bran flour was improved by 38.41% and the fiber content was improved by 18.21%. It indicated that yeast fermentation could not only effectively improve the flavor of rice bran, but also enhance the nutritional properties of rice bran flour as a food ingredient.