Probiotic potential and phytase-producing capacity of yeast isolated from Thai traditional fermentation starter...

Phytate is an anti-nutrient factor that chelates micronutrients, thereby reducing their bioavailability and impairing nutrient absorption in humans and animals. This study aimed to isolate and assess potential probiotic yeast strains with phytase capability from Thai traditional fermentation starters. Three yeast isolates revealed antagonistic activity against pathogenic bacteria in preliminary probiotic screening and demonstrated phytate-degrading capabilities through phytase activity. Among the selected yeast strains, isolate NS104-STR showed the highest extracellular phytase activities (0.142 ± 0.001 U/mL and 0.126 ± 0.001 U/mg protein). Phylogenetic analysis based on 18 s rDNA and/or TSI gene regions identified this strain as closely related to Pichia kudriavzevii. Pichia kudriavzevii NS104-STR displayed several desirable probiotic attributes. This strain exhibited broad-spectrum bacteriostatic activity and tolerance to acidic conditions (≥ 10⁶ CFU/mL at pH 2.0 and ≥ 10⁸ CFU/mL at pH 3.0 for 3 h of exposure) as well as survival in 0.3-0.6% bile salts after 24 h of exposure (> 100% survival rate) (p ≤ 0.05). Furthermore, it also displayed high cell surface hydrophobicity (65.65 ± 0.35%), auto-aggregation capacity (61.08 ± 0.25%), and strong adhesion to Caco-2 epithelial cells (66.39 ± 0.69%). Pichia kudriavzevii NS104-STR was capable of co-aggregating with pathogens and significantly inhibited their adhesion to Caco-2 cells in competition exclusion assays (> 50% of inhibition rate), especially E. coli ATCC 25922 (67.68 ± 0.18% of inhibition rate) (p ≤ 0.05). Importantly, P. kudriavzevii NS104-STR was non-hemolytic and susceptible to various antibiotics and antimycotics. These results suggest that Pichia kudriavzevii NS104-STR may serve as a promising potential phytase-producing probiotic yeast, with valuable applications in enhancing the nutritional quality of food and feed products.