Kefir yeasts enhance probiotic potentials of Lactobacillus paracasei H9: The positive effects of coaggregation between the two strains

This study investigated pure Lactobacillus paracasei H9 tolerance to simulated gastrointestinal juices and adhesion to intestinal mucosa cells without yeasts, with viable yeasts (VY) and with different pretreated yeasts. Three models including gastric secretion tolerance (GST), intestinal juice tolerance (IJT) and sequential gastrointestinal tolerance (SGT) were respectively employed to assay the tolerance of L. paracasei H9, whilst Caco-2 cell line was used to investigate the bacterial adhesion. Particularly, the co-aggregation ability of the two strains at pH values of 2.0, 8.0 and 7.2 was originally carried out to study relations to the bacterial probiotic potentials. Results showed that yeast counts in the range from 3.0 to 5.0 log CFU mL− 1 could gradually increase the viability of L. paracasei H9 in SGT. The bacterial viability in the three tolerance models and the adherent number to Caco-2 cells were significantly improved with addition of VY (P < 0.05). The L. paracasei H9 with VY in gastric juice at pH 2.0 and intestinal juice at pH 8.0, respectively, exhibited higher aggregation percentage compared with that of single L. paracasei H9 at 37 °C (P < 0.05). The aggregation ability of L. paracasei H9 with VY at pH 7.2, which might contribute to increase the adhesion of the bacteria, also excelled that of L. paracasei H9 (P < 0.05). It is deduced that proteins of the bacterial cell surface and polysaccharides in yeast cell walls play important roles in co-aggregation of the two strains and the microbial adhesion specificity to Caco-2 cells. The co-aggregation of the two strains also contributes to enhancing probiotic potentials of L. paracasei H9.

► The kefir strain of Lactobacillus paracasei H9 exhibits probiotic potentials. ► Kefir yeasts can enhance the bacterial probiotic potentials. ► Coaggregation of the two strains contributes to increasing the potentials.