DETECTION AND ENUMERATION OF LACTIC ACID BACTERIA, ACETIC ACID BACTERIA AND YEAST IN KEFIR GRAIN AND MILK USING QUANTITATIVE REAL-TIME PCR

Kefir is a unique fermented dairy product that is produced by a mixture of lactic acid bacteria, acetic acid bacteria and yeast. In this study, a culture-independent quantitative real-time polymerase chain reaction (PCR) technique was used to enumerate lactic acid bacteria, acetic acid bacteria and yeast in kefir grain and kefir milk using group-specific primers. The most abundant microbial groups were lactic acid bacteria and acetic acid bacteria, followed by yeast (P<0.05) in both kefir grain and kefir milk. The most leading genera of lactic acid bacteria and yeast were Lactobacillus/Lactococcus (P<0.05) and Candida, respectively. All microbial groups were present in lower numbers in kefir milk than in kefir grain (P<0.05), except for Enterococcus and Saccharomyces groups. This is the first report to characterize the number of specific microbial populations in kefir grain and kefir milk using quantitative real-time PCR. In conclusion, we successfully established the methods for the quantification of microorganisms in kefir grain and kefir milk using group-specific quantitative real-time PCR and provided quantitative microbiological information for quality control of kefir. Practical ApplicationsThis report describes the enumerative methods of microorganisms in the kefir grain and kefir milk using group-specific quantitative real-time PCR assay. It could facilitate the microbiological quality control of kefir-fermented milk and grain and can be used in further studies to understand the fermentation process of kefir milk. In addition, the results provide basic information on the number of lactic acid bacteria, acetic acid bacteria and yeast in kefir grain and kefir milk.