Biological activities, biosynthetic capacity and metabolic interactions of lactic acid bacteria and yeast strains from traditional home-made kefir

Given the widespread industrial and domestic use of probiotic blends based on combinations of lactic acid bacteria (LAB) and yeasts to produce fermented foods or beverages that are supposed to provide health benefits, this study aimed to generate knowledge and concepts on biologically relevant activities, metabolism and metabolic interactions in yeast/LAB communities. For this, the postbiotic capabilities of three probiotic candidates, including two lactic acid bacteria (i.e., Lactococcus lactis subsp. hordniae and Lactococcus lactis subsp. lactis) and the yeast Pichia kudriavzevii, isolated from a traditional home-made kefir, were explored combining an assortment of bioassays with a GC-MS footprint metabolomic strategy. Cell-free supernatants from cultures showed antimicrobial/antioxidant activity and inhibited biofilm formation by Salmonella sp. Several bioactive secondary metabolites (including tyrosol, phenylethyl alcohol, 2,3-butanediol, erythritol, tryptophol, putrescine, cadaverine, 3-phenyllactate, 2-hydroxyisocaproate) were detected which may contribute to the odor and flavour of the fermented products and their effects on human body.