Functional Characterization of Postbiotics and Paraprobiotics Derived from Selected Kluyveromyces lactis Strains

This study characterized postbiotic and paraprobiotic preparations originating from Kluyveromyces lactis strains to assess their biochemical composition and functional potential. Fourteen strains were screened for in vitro probiotic characteristics, with five superior strains selected for further postbiotic and paraprobiotic production, mainly due to exhibiting high viability index in synthetic gastrointestinal conditions (viability index > 70%), moderate to high binding capacity in terms of hydrophobicity and autoaggregation, and elevated DPPH radical scavenging activity (> 30%). The resulting preparations displayed distinct bioactive profiles. Postbiotics exhibited significantly higher phenolic content and antioxidant capacity than paraprobiotics and were characterized by a phenolic-rich composition, dominated by quercetin, gallic acid, and 3-hydroxybenzoic acid. The postbiotics were further assessed for their biofilm-inhibition activity against several food-borne biofilm-forming pathogens. Among them, postbiotics from ANO7 showed the strongest inhibition, a maximum biofilm reduction of 97.10 ± 1.54% against Staphylococcus aureus ATCC 25,923. The free amino acid profile of ANO7 postbiotic comprised 39 amino acids, with leucine (3088.95 mg/L) predominant, an essential amino acid index of 88.1%, and detectable γ-aminobutyric acid (GABA). The findings highlight the technological and functional relevance of K. lactis ANO7-derived postbiotics as non-viable bioactive ingredients with potential applications in functional foods, natural antimicrobial strategies, and nutritional enhancement.