From Probiotic Screening to Postbiotic Potential: An Integrated In Vitro Assessment of Endogenous Non-Saccharomyces Yeast Isolates

Yeasts isolated from fermented foods have attracted increasing attention for their probiotic potential; however, studies on yeast-derived postbiotics remain limited. In this study, endogenous yeast strains belonging to Kluyveromyces marxianus (n = 3), Yarrowia lipolytica (n = 3), Pichia fermentans (n = 3), and Debaryomyces hansenii (n = 3) were evaluated for their in vitro probiotic properties. A multi-criteria decision-making analysis using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) identified K. marxianus ETP12, P. fermentans SJ2023, and Y. lipolytica ARTP9.2 as the most promising strains for postbiotic production. Among them, K. marxianus ETP12 exhibited the highest functional potential and was subjected to comprehensive postbiotic characterization. The postbiotic of K. marxianus ETP12 was further characterized for total phenolic content, antioxidant capacity (DPPH and ABTS scavenging activities), phenolic compound profile, biofilm inhibition capacity, free amino acid composition, and fatty acid profile. The results revealed a diverse phenolic composition, primarily consisting of fumaric acid, quercetin, gallic acid, and quinic acid. A total of 29 essential, non-essential, and bioactive amino acids were identified, with lysine, leucine, and glycine as the predominant components. Fatty acid profiling indicated the predominance of palmitic and stearic acids, accompanied by medium-chain fatty acids. Notably, it exhibited strong biofilm-inhibition activity against S. aureus ATCC 25923 and C. sakazakii ATCC 29544. Overall, these findings demonstrate that K. marxianus ETP12 represents a valuable source of multifunctional postbiotics with potential applications in the development of functional foods and nutraceuticals.