Interactions between Lactococcus ssp. and Brewer’s Yeast Metabolism During the Fermentation and Storage of a Kefir-like Product: Growth Dynamic and Lactose Metabolism

Abstract

Our objective was to study the growth dynamic and the lactose metabolism in a mixed culture, obtained by fermentation of two lactic acid bacteria (Lactococcus lactis, Leuconostoc mesenteroides) and spent brewer’s yeast in order to make use of the bioactive potential of brewer’s yeast in a kefir-type product, free of Lactobacillus ssp. and free of typical kefir yeasts. The fermentation was realized initially in a biofermentor than at larger scale (4l) in an upgraded installation. Lactococcus and Saccharomyces growth was synergistic and dominated the final composition of the product. We noticed a decrease of lactose content in the kefir, more intense than in control. The rate of lactose decrease during storage at low temperatures, was significantly more intense (P<0.05) than in fermentation conditions. We can assume that, the decrease of lactose content during storage was stimulated by the presence of brewer’s yeast in this kefir-like product. The decrease of L(+) lactic acid, especially during storage, was more intense than lactose, due to Saccharomyces metabolism, converting lactic acid to pyruvate, consumed by aerobic respiration and ethanol synthesis. Â