Characteristics of the soy sauce taste and koji enzyme profiles as affected by soybean traits

Soybean is the main raw material for soy sauce fermentation and has a significant impact on the quality of soy sauce. Understanding the impact of soybean traits on the soy sauce quality is important for the development of the industry. The present study compared the traits of 12 soybeans and the quality of their fermented kojis and soy sauces, revealing the differences in total sugar and protein content may be the key factors responsible for differences in soy sauce characteristics. On this basis, 6 representative soybeans including 3 high protein and low total sugar content soybeans (HPLS) and 3 low protein and high total sugar content soybeans (LPHS) were selected for further study. Results of the changes in enzyme activities during koji-making fermentation showed that neutral protease and beta-glucosidase activities were higher in HPLS kojis, while acid protease and xylanase activities were higher in LPHS kojis after 24 h of fermentation. Differences in enzyme activity further caused variations in the soy sauce quality and formed some correlations with soy sauce tastes, such as xylanase and umami (r = 0.885), kokumi (r = 0.916). The intensities of umami and kokumi were higher in LPHS soy sauces, which had a higher dipeptides content of X-Glu, X-Thr, X-Ser and Gly-X.