Effect of salt concentration on Chinese soy sauce fermentation and characteristics

The effect of salt concentration on soy sauce fermentation was studied. Four groups of soy sauce samples with 8%, 12%, 16%, and 20% salt concentrations were prepared and their physicochemical parameters, non-volatile metabolites (organic acids, free amino acids, and biogenic amines), volatile metabolites, and microbial abundance were analyzed during the whole fermentation. The sensory characteristics of the final products were also assessed. Salt concentration significantly affected the microbial abundance and metabolite profiles during soy sauce fermentation, resulting in different characteristics among samples. The RT-qPCR analysis showed that the microbial abundance in lower salted soy sauce was higher. Correspondingly, the accumulation of total acid and the decrease of reducing sugar were observed in lower salted soy sauce, aggravating the sourness of soy sauce. The levels of free amino acids and biogenic amines (detected by HPLC) in lower salted soy sauce were higher, resulting in a taste of umami but making unsafe soy sauce. Additionally, HS-SPME/GC-MS analysis showed that several distinctive volatile compounds were absent in lower salted soy sauce. Sensory evaluation revealed that the highest total score for the quality of soy sauce was obtained through fermentation under 16% salt concentration. This study helped deepen our understanding of the effect of salt on soy sauce fermentation and provide a theoretical data reference for low salt soy sauce development.