Isolation and Characterization of Bacillus velezensis SS360-1 from Seed Soy Sauce

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Four bacteria harboring proteinase activity were isolated from seed soy sauce. Thereafter, their proteinase and amylase activities were assayed. Among the four isolated strains, one strain that showed the highest proteinase and amylase activities was selected tentatively as a starter culture for soy sauce and its characteristics for soy sauce starter culture were investigated. The selected strain was identified as Bacillus velezensis based on Gram-staining, spore-staining, and 16S rRNA gene sequences and finally designated as B. velezensis SS360-1. It showed high growth (A600=1.00~4.55) at 0~12% NaCl concentration. The optimum NaCl concentration for its growth was 3% NaCl. B. velezensis SS360-1 also grew well at 0% NaCl condition; however, its growth was dramatically decreased after 12 h incubation at this condition. The off-odor production ability of B. velezensis SS360-1 was investigated using portable odor measurement and GC-MS analysis. B. velezensis SS360-1 showed definitely lower production of off-odor compounds than did B. subtilis KCTC 3014, which was isolated from fermented soybean. Moreover, B. velezensis SS360-1 produced 3-methyl butanal and 2-heptanone, compounds that are considered as pleasant flavored-compounds for soy sauce. These results suggest that B. velezensis SS360-1 can be used as a suitable starter culture for soy sauce.