Effect of Lactobacillus plantarum or Enterococcus faecalis as co-inoculants with Aspergillus oryzae in koji making on the physicochemical properties of soy sauce

Soy sauce fermentation is largely mediated by bacteria, including several non-salt-tolerant bacterial species. The present study aimed to compare the use of Aspergillus oryzae alone or in co-inoculation with Lactobacillus plantarum or Enterococcus faecalis on the resulting enzymatic activity, content of phenolic compounds, free amino acids, organic acids, and antioxidant capacity of soy sauce. Co-inoculation significantly increased acid protease, beta-glucosidase, and pectinase activities during koji making. Additionally, the contents of total phenols, total flavonoids, organic acids, amino acids, isoflavones, as well as the antioxidant capacity were higher during moromi fermentation using co-inoculants compared to those obtained when A. oryzae was used as single inoculant. Overall, co-inoculation of A. oryzae with L. plantarum or E. faecalis during koji making was shown to effectively promote the production of active substances in soy sauce. Practical Application In this study, Aspergillus oryzae in mixed inoculation with Lactobacillus plantarum or Enterococcus faecalis could be effectively used in koji making for soy sauce. The use of co-inoculants in koji making effectively promoted the production of active substances in soy sauce, hence it is improving health benefits, whilst diversifying the use of raw materials and the application value of soybean meal.