Kefir as a functional probiotic: microbial composition and health effects

Kefir has gained increasing attention as a traditional fermented dairy product with notable probiotic potential. Kefir grains exhibit an irregular, multilobular, and gelatinous structure with a yellowish appearance, consisting of a symbiotic consortium of lactic acid bacteria, acetic acid bacteria, and yeasts. The predominant bacterial genera include Lactobacillus and Lactococcus , while Saccharomyces and Kluyveromyces represent the dominant yeasts. This unique microbial community contributes to the production of diverse bioactive metabolites, including organic acids, peptides, exopolysaccharides, and ethanol, which collectively enhance the functional properties of kefir. Emerging evidence from in vitro , animal, and human studies suggests that kefir exerts multiple health-promoting effects, including gastrointestinal protection, anti-inflammatory, immunomodulatory, antimicrobial, antiallergic, and anti-arthritic activities. These properties highlight its potential as a promising functional food with nutraceutical applications. This review summarizes current knowledge on the microbial composition of kefir grains, fermentation dynamics, and the health benefits of kefir consumption, emphasizing its therapeutic potential in the management of chronic diseases.