Amylase, protease, and lipase-producing microbes of local origin as potential starter cultures for low-salt moromi fermentation

Abstract

High salt concentration (18%-22% NaCl) is essential for halophilic microbes to grow and develop aroma during soy sauce fermentation. Due to health concerns, recent efforts have focused on reducing salt during fermentation by introducing novel yeast species. However, the natural fermentation of soy sauce involves a more complex microbial community essential for achieving optimal sensory qualities. This study aimed to select potential bacterial and fungal species from traditional soy sauce factories in Indonesia for use in low-salt fermentation. Isolates that showed positive enzymatic activities at 20%, as well as 5% NaCl, were subjected to growth profile characterisation in tryptic soy broth (TSB) with different salt concentrations (0%, 5%, and 20%) and pH (4.0, 5.0, and 6.0). A total of 47 bacterial and 39 fungal isolates were obtained. Fourteen bacterial and 12 fungal isolates demonstrated positive enzymatic activities at 20% and 5% NaCl. The majority of bacterial strains were identified as Bacillus subtilis, while most of the fungal isolates belonged to the Aspergillus genus (Aspergillus oryzae and Aspergillus tamarii). The majority of Bacillus isolates performed rapid growth in 5% NaCl and relatively low pH (5.0), indicating their potential application in low-salt soy sauce production.