Postbiotics—defined as non-viable microbial cells together with their wide repertoire of polymers, peptides, nucleotides, and metabolites—have emerged as promising bioactive agents with antimicrobial, antioxidant, and immunomodulatory functions. Compared to probiotics, postbiotics provide enhanced safety, extended shelf-life, and improved compatibility with food matrices. Despite their potential, yeast-based postbiotics remain underexplored, as most current studies focus on lactic acid bacteria.

In this context, Kluyveromyces marxianus and Kluyveromyces lactis stand out as non-conventional yeasts with desirable traits. Both exhibit rapid growth, thermotolerance, and versatile metabolic capabilities and are increasingly regarded as probiotic candidates due to their tolerance to gastrointestinal stresses. Their cell wall components further support postbiotic relevance: K. marxianus produces branched α-mannans and nucleotide-rich lysates upon autolysis, whereas K. lactis generates β-glucans even under stress. These features highlight their dual role as emerging probiotics and valuable sources of postbiotic bioactives.

This study compares the postbiotic potential of S. boulardii YUS5—a clinically established probiotic yeast—with K. lactis ATCC8585 and K. marxianus BSK105, using both whole-cell lysates and cell-free supernatants, as well as co-culturing strategies. By linking probiotic candidacy to postbiotic functionality, this work introduces yeast-only systems as innovative platforms for food and health biotechnology.