Investigation of the microbial changes during koji‐making process of Douchi by culture‐dependent techniques and PCR‐DGGE

Abstract

Summary Douchi as a traditional fermentation soyfood with an acquired taste had been appreciated by consumers for thousands of years in China and few Asian countries. Unfortunately, few studies had been conducted on the changes of microbial community during the koji‐making process, and whether the pathogenic microorganisms involving the fermentation process is still unclear. Therefore, the PCR‐denaturing gradient gel electrophoresis (DGGE) targeting the 16S and 18S rRNA genes was applied to characterise the dynamic changes of Bacteria , Bacilli and Fungi during koji‐making process. The results of DGGE showed that eleven species of bacteria, nine species of bacilli and seven species of Fungi had been detected during the koji‐making progress, of which the Bacillus subtilis and Aspergillus oryzae belonged to the dominant microorganisms. Also, eleven strains were isolated from Koji‐making samples and were identified as B. subtilis , Bacillus amyloliquefaciens , A. oryzae , Brachybacterium sp., Aspergillus niger , Staphylococcus saprophyticus , Micrococcus sp., Staphylococcus gallinarum , Absidia corymbifera , Saccharomyces cerevisiae , Malassezia sp.; Our results revealed that pathogenic microorganisms were involved in the koji‐making process, but the probiotic microorganisms occupied the dominant position of community in the koji‐making process.