Isolation, characterization, and biotechnological application of novel glutaminase-producing Bacillus strain for quality enhancement in soy sauce

Glutaminase plays a crucial role in nitrogen metabolism and is of vital significance for soy sauce production. In this study, the high glutaminase-producing strains, Bacillus pumilus -T1-11 and Bacillus safensis -T3-20, were isolated from fermented moromi through a two-step screening process. T1-11 displayed intracellular glutaminase activity of 146.39 ± 8.14 U/g, while T3-20 presented 139.26 ± 15.62 U/g, and both strains maintaining activity in Secondary Screening medium(SRM). Culture conditions were optimized by adjusting nitrogen/carbon sources, glutamine, NaCl, and pH. T1-11 achieved the maximum activity of 5716.95 ± 168.18 U/g in optimized medium and T3-20 reached peak activity of 4927.72 ± 62.79 U/g. The application of T1-11 and its enzyme extracts in soy sauce fermentation was evaluated. The moromi fermented with 7.0 log CFU/mL inoculum for 2 d showed the peak glutaminase activity (98.99 ± 15.13 U/g), significantly enhancing umami flavor, as confirmed by sensory and biochemical analyses. In extracted soy sauce, a 6.0 log CFU/mL inoculum cultured for 14 d total glutamic acid content to 82.78 ± 0.53 mmol/L. These modifications significantly enhanced the umami characteristics of soy sauce, demonstrating the potential application of this strain in improving the quality of traditional fermented food .