Alcohol-brewing properties of acid- and bile-tolerant yeasts co-cultured with lactic acid bacteria isolated from traditional handmade domestic dairy products from Inner Mongolia

•6 acid and bile tolerant yeast and LAB were isolated from Inner Mongolian dairy foods.•Saccharomyces cerevisiae SY1 strain from khȍrȍnggȍ produced ethanol in sake brewing model.•Lactobacillus plantarum strains ZL1 and KL1 were isolated as weak and strong milk fermenter, respectiely.•S. cerevisiae SY1 produced high level of ethanol in a co-culture with L. plantarum ZL1.•However, S. cerevisiae SY1 could not produce high level of ethanol with L. plantarum KL1.

In this study, acid- and bile-tolerant yeast and lactic acid bacteria (LAB) were isolated from Inner Mongolian cheeses (khuruud, zȍȍkhii, tsur) and an alcoholic drink (saaliin arhi) and its starter (khȍrȍnggȍ), and the alcohol-brewing capacities of the isolates were tested. Among 69 yeast and 89 LAB isolates, 6 typical yeast (5 Saccharomyces cerevisiae and 1 Naumovozyma castellii) and 6 LAB (Lactobacillus plantarum) strains were selected on the basis of acid tolerance (pH 3.5), bile tolerance, and/or lactose fermentation properties. The selected yeasts, particularly the S. cerevisiae SY1 strain isolated from khȍrȍnggȍ, produced high levels of ethanol in both a small Japanese sake brewing model and in grape juice fermentation. Among the selected L. plantarum strains, ZL1 and KL1, isolated from zȍȍkhii and Saaliin arhi, respectively, showed weak and strong lactose fermentation in milk. Although a monoculture of S. cerevisiae SY1 could not produce ethanol during milk fermentation, it produced high levels of ethanol in a co-culture with L. plantarum strain ZL1. In contrast, in co-culture with a more vigorous lactose fermenter, strain KL1, S. cerevisiae SY1 was not able to produce a comparable level of ethanol. These results demonstrate co-fermentation roles for yeast and LAB in traditional fermented dairy foods.