Koumiss (Fermented Mare's Milk) as a Functional Food: Bioactive Proteins, Peptides, and Future Perspectives

Fermented mare's milk, or koumiss, has been consumed for centuries across Central Asia for its nutritional and therapeutic value. Mare's milk differs from bovine milk by its near 1:1 casein-to-whey ratio, high lysozyme and lactoferrin, abundant immunoglobulins, and low β-lactoglobulin, which enhance digestibility, reduce allergenicity, and increase antimicrobial activity. During fermentation, lactic acid bacteria and yeasts transform this substrate into a reservoir of bioactive proteins, peptides, and metabolites. Multi-omics profiling has identified more than 2300 peptides and over 350 metabolites, including sequences with angiotensin-converting enzyme (ACE)-inhibitory, antioxidant, antimicrobial, and immunomodulatory activities. Preclinical and limited clinical data indicate potential benefits for lipid metabolism, cardiovascular function, and gut health. Mechanistically, these effects appear to arise from synergistic actions of native proteins, fermentation-derived peptides, and probiotic consortia. Technological advances such as rational starter culture design, controlled proteolysis, and microencapsulation offer strategies to enhance bioactive yield and stability. However, standardized fermentation protocols and clinical validation remain necessary to position koumiss as a scientifically supported functional food.