Isolation and identification of psychrotrophic lactic acid bacteria in godo, the traditional fermented soy food in Japan

Abstract

Godo is a traditional fermented soy food made in Aomori prefecture, Japan. It is mainly made of soybeans, rice koji, and salt. Since godo ripens during the long and severe winter in northeast Japan, it is assumed that lactic acid bacteria inhabiting godo have cold tolerance. We aimed to investigate the presence or absence of psychrotrophic lactic acid bacteria in godo. The viable counts of estimated lactic acid bacteria ranged from 10⁶ to 10⁸ cfu/g. In addition, aerobic and anaerobic microorganisms were detected in four godo products though the microbial population differed from sample to sample. Twenty-two bacterial strains were able to be isolated from godo, and all of the isolated strains were Gram-positive and catalase-negative. Some of the isolates grew well at 10°C. The carbohydrate fermentation profile of the selected three strains was determined by API50 CHL analysis. These strains were identified as Leuconostoc mesenteroides, and Latilactobacillus sakei by 16S rRNA gene sequence analysis. Leuconostoc mesenteroides strains HIT231 and HIT252, and Latilactobacillus sakei strain HIT273 could grow at 5°C in MRS broth, but their optimum growth temperature was 20°C-30°C. These results suggest that psychrotrophic lactic acid bacteria presumed to be derived from rice koji are present in godo, which is one of the factors in the low temperature ripening of godo in winter.