From Yeast Probiotics to Postbiotics: A Continuum Model and Yeast-Specific Functional Perspective.

Growing interest in probiotics and postbiotics has expanded research beyond living microorganisms and highlighted the functional importance of microbial cells, metabolites, and structural components. However, current conceptual frameworks still primarily focus on bacteria, while yeasts, despite their industrial, nutritional, and clinical importance, remain underrepresented. Owing to their eukaryotic organization, complex cell wall architecture, specialized secretory pathways, and ability to produce diverse bioactive molecules, yeasts exhibit functional properties that are distinct from those described for bacterial probiotics and postbiotics. In this review, we examine the relationship between yeast probiotics and yeast-derived postbiotics and propose the concept of a yeast-biotic continuum, which describes biological functionality as a dynamic progression from living cells, through active metabolism and released bioactive factors, to inactivated cells and postbiotic preparations. In this approach, postbiotics are viewed not as static end products but as steps in a continuous biological process influenced by cell viability, environmental conditions, and interactions with the surrounding microbiota. We discuss major yeast-derived bioactive components, including β-glucans, mannoproteins, metabolites, peptides, and extracellular vesicles, together with their roles in immune modulation, epithelial barrier support, pathogen interference, and fungi-bacteria-host interactions. Finally, we highlight current challenges, emerging technologies, and future opportunities for yeast-derived biotics.