Abstract: Based on the composition of odor and taste substances and amino acids, this study evaluated the elimination efficiency of the yeasty flavor from yeast extract by fermentation with single and mixed cultures of Lactococcus lactis, Streptococcus lactis and Lactobacillus plantarum. The results showed that lactic acid bacterial fermentation reduced the yeasty odor (propionic acid and isovaleric acid) from yeast extract, but the overall flavor profiles of yeast extracts fermented with different cultures were significantly different. The effect of mixed culture fermentation was more pronounced than that of single culture fermentation, and the effect of the mixed culture of L. lactis and S. lactis was the best. After fermentation by the mixed culture of L. lactis and S. lactis, the level of the yeasty odorant isovaleric acid in yeast extract was decreased by 86.73%, the concentration of alcohols with fruity and flowery aroma was increased from 0.77 to 10.73 ng/mL, the lactic acid concentration was 10.60 g/L, the concentration of the flavor precursor amino acid phenylalanine was increased by 112.91 mg/L, and the concentration of umami taste substances (inosinate and guanylate) was increased by 0.02 g/L. The fermented sample had a well-balanced flavor and taste.

Key words: lactic acid bacterial; yeast extract; yeasty flavor; amino acids; odorous substances