Anticandidal activity of Lactobacillus spp. in the presence of galactosyl polyols

Yeasts have a substantial impact on the contamination and loss of food. In this study, we applied bacteria of the genus Lactobacillus as natural biopreservatives. Anticandidal strains of bacteria were selected from among 60 strains of bacteria grown which were each with nine polyols or galactosyl polyols. Polyols and galactosyl polyols can act as prebiotics for lactic acid bacteria and can enhance the antifungal properties of bacteria by affecting their metabolism. The galactosyl polyols significantly improved the anticandidal activity of most of the bacteria we tested. Based on the screening, the most promising strains of bacteria were selected, and their metabolites (both primary and secondary) and enzymatic activity were characterized in the presence of polyols and galactosyl polyols. The qualitative and quantitative content of bacterial metabolites depended both on the bacterial strain and the type of culture medium. A wide variety of antifungals produced by bacteria, such as fatty acids, hydroxy fatty acids, and other acidic products with potential antagonistic activity (phenyllactic acid or hydroxyphenyllactic acid) were detected. The bacteria produced a high concentration of phenyllactic acid in the presence of galactosyl polyols (up to 84.3 mg/L). This finding could suggest that this metabolite may have a significant impact on the antifungal properties of lactobacilli against yeast. Galactosyl polyols influenced the enzymes involved in the synthesis of fatty acids and hydroxylated fatty acids (esterase lipase, acid phosphatase, and α-glucosidase). The mechanism of the antifungal effect of lactobacilli may be based on the synergistic effect of their primary and secondary metabolites, in particular phenyllactic acid.