Separation, Identification, And Characterization Of Contaminant Microorganism In Swollen Canned Soy Sauces

Soy sauce(Jiang you) have been consumed for centuries as acondiment in China. Nowadays, soy sauces are the subject of worldwide interest. Soy sauce contains antihypertensive and anticarcinogenic components and possesses antimicrobial and antiplatelet activities. However, the swollen canned soy sauce sharply tampered with the quality offinal products. Until now, the reason of swollen canned soy sauce is still limited. In this study, the discrepancies of physiochemical and microbial contaminants in the normal and swollen canned soy sauces, which collected from three different regions(southern, northern and central regions) in China, were investigated.⑴ The physiochemical characteristics innormal and swollen canned soy sauces, including p H, total acidity, salinity, deoxidize sugar, lactic acid and acetic acid, were analyzed using basic chemical tests and HPLC. No obviously difference of acetic acid content and the salinity(usually in 16%~18%)were obtained in normal and swollen canned soy sauces. However, the lactic acid concentrations of the swollen canned samples were significantly higher than those in the normal samples, and the reducing sugar concentrations of the swollen canned samples were significantly lower than those in the normal samples. These results indicated that the physiochemical characteristics were changed in the swollen canned soy sauces.⑵ Comparison of microbial contaminants between normal and swollen canned soy sauces were performed using plate techniques and nested PCR-denaturing gradient gel electrophoresis(DGGE). Plate technique showed that four diverse species of Bacillus(B. subtilis, B. oleronius and B. flexus) were present in the swollen canned samples. The PCR-DGGE profiles showed that four lactic acid bacteria(LAB), including Lactobacillus acidipiscis, L. pobuzihii, L. piscium and another Lactobacillus sp., were involved in the swollen canned samples. The dominant contaminated bacteria in normal soy sauce are B.subtilis, B. oleronius, L. piscium, L. pobuzihii, while B. subtilis, B. oleronius, B. flexus, L. piscium, L. pobuzihii, L. acidipiscis, Lactobacillus sp. are the dominant contaminated bacteria inspoilage samples. However, much less bacterial contaminants were detected in the normal samples. These results confirmed the existence of Bacillussp. and LAB in the packaged soy sauce products, and suggested that these contaminants might play a role in the swollen canned soy sauces.⑶L. acidipiscis isolated from soy sauces in this study produced little gas. To further monitor the gas-producing strains, another two gas-producing bacteria(Enterobacteraerogenes, Enterococcus faecium) were isolated from koji samples. Our results showed that E.aerogenes possessed strong gas-producing abilities. Slight changes in the p H were observed after the three bacterial strains were inoculated into soy sauce products. In addition, all of the isolates were temperature-, p H-, and salinity tolerant. The separation and identification of three bacterial strains were important to ensure adequate quality and food safety of soy sauce.In this study, we analyzed the microbial contaminants involved in the swollen canned soy sauce and provided experimental basis and technical information to support the up gradation of quality control during soy sauce fermentation.