Identification and control of gas-producing bacteria isolated from the swollen bagged soy sauce

The swelling of soy sauce bags seriously affects product quality and causes food safety problems, which has become an urgent problem to solve in the condiment industry. Here, gas-producing bacteria in the swollen bagged soy sauce were isolated and identified to provide an effective control method for inhibiting their growth and solving the swelling of soy sauce bags. It was found that three gas-producing bacteria isolated from the swollen bagged soy sauce were confirmed as Bacillus amyloliquefaciens (G1), Bacillus sp. (G2) and Bacillus subtilis (P3) using 16S rDNA analysis. The strains' morphologies, growth rates, and physiological and biochemical characteristics were also compared. Further studies yielded the optimal growth time, temperature and pH for the three gas-producing bacteria (B. amyloliquefacien: 24 h, 37 °C, and pH 7; Bacillus sp.: 18 h, 30 °C, and pH 6.5-7.5; B. subtilis: 36 h, 30 °C, and pH 8). Bacillus sp. was more salt tolerant than the other two. Then the antibacterial effect of the combination was tested by the physicochemical index. The results showed that filtering through a 0.22 μm inorganic micro-filtration membrane, sterilizing at 121 °C for 2 min, and adding 1 g/kg potassium sorbate was effective methods to inhibit three gas-producing bacteria and control the swelling of soy sauce.