Kefir as a source of postbiotics: Functional compounds, health benefits, and applications

Abstract

Kefir-derived postbiotics, including non-viable microbial cells, bioactive metabolites, extracellular vesicles, exopolysaccharides such as kefiran, organic acids, peptides, and protein hydrolysates, have emerged as promising functional biomolecules with significant biotechnological potential. Produced by the complex microbial consortia of kefir grains—comprising lactic acid bacteria, yeasts, and acetic acid bacteria—these compounds exhibit a broad range of health-promoting properties, including antimicrobial, antioxidant, immunomodulatory, anti-obesity, anticancer, antiallergic, and bone-protective activities. Growing evidence supports their safety and efficacy, particularly when generated under standardized and controlled fermentation conditions, highlighting their potential applications in functional foods, nutraceuticals, animal nutrition, metabolic therapies, and cosmeceutical formulations. However, traditional or non-standardized kefir fermentations may present compositional variability and safety concerns, such as biogenic amine formation. Additional challenges include limited clinical validation, inconsistencies in regulatory frameworks, and difficulties in process standardization. Future advances in precision fermentation, omics-based characterization, personalized nutrition approaches, and well-designed clinical trials are expected to address these limitations and facilitate the rational development and industrial application of kefir-derived postbiotics as versatile bioactive ingredients.