Separation, Identification, and Characterization of Food Spoilage Bacteria in Soy Sauce
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Abstract:
Lactic acid bacteria (LAB) and Enterobacter species commonly cause spoilage in traditional fermented foods. In this study, three bacterial strains suspected to cause food spoilage were isolated from traditional Chinese grain soy sauce and swollen canned soy sauce. The morphological and physiochemical characteristics and 16S rRNA sequences of the strains were studied. Using PCR-restriction fragment length polymorphism (PCR-RFLP), enterobacterial intergenic consensus–PCR (ERIC-PCR), and species-specific PCR, these strains were identified as Enterobacter aerogenes, Enterococcus faecium (isolated from grain soy sauce), and Lactobacillus acidipiscis (isolated from swollen canned soy sauce). The results showed that E. aerogenes possessed very strong gas-producing abilities, and L. acidipiscis was also a weak gas-producer. When the three bacterial strains were inoculated into soy sauce products, slight changes in the pH values of products were observed. In addition, all of the isolates were temperature-, pH-, and salinity tolerant. Both E. aerogenes and E. faecium are opportunistic pathogens and are potentially harmful to consumers. Furthermore, the presence of L acidipiscis in soy sauce could cause gas production and a reduction in pH, thus resulting in spoilage. The separation and identification of three bacterial strains were important to ensure adequate quality and food safety of soy sauce.
