Populations and potential association of Saccharomyces cerevisiae with lactic acid bacteria in naturally fermented Korean rice wine

Abstract

The microbial populations focused on predominant yeast species and lactic acid bacteria (LAB) in 15 commercial makgeolli brands, where a fungal starter nuruk was used were examined. Viable yeast counts were obtained on yeast potato dextrose (YPD) and MRS agar containing sodium azide. MRS-C (0.1% cycloheximide supplemented) was used for selective counts of LAB. Saccharomyces cerevisiae was found to be predominant in the 15 samples tested, with an average count of 4.6×107 CFU/mL. Contrary to the earlier studies, Lactobacillus plantarum and Weissella cibaria were shown as predominant LAB species with an average count of 1.7×107 CFU/mL. Surprisingly, as many as 7 log viable cells/mL were present at the ethyl alcohol concentration of 6–7%. The data from real-time PCR also indicated that the yeast populations remains almost constant during the refrigerated storage of 12 days, while that of LAB decrease slightly first 9 days and increase after then, despite the overall increase in acidity. Data from the differential microbial counts suggest that yeast S. cerevisiae might be associated with 2 LAB species, L. plantarum and W. cibaria, under ethyl alcohol stress during the turbid rice wine fermentation.