Microbial Exopolysaccharides, Redox Modulation, and Antioxidant Activity in Fermented Foods.

Oxidative stress, caused by the excessive production of reactive oxygen and nitrogen species, contributes to cellular damage and chronic diseases. Fermented foods are increasingly recognized for their antioxidant properties, which are strongly influenced by microbial metabolism during fermentation. This review examines three major microbial mechanisms involved in antioxidant enhancement in fermented foods: exopolysaccharide (EPS) production, release of matrix-bound bioactive compounds, and microbial modulation of redox conditions. Microbial EPS contribute through radical scavenging and metal chelation, while microbial enzymes increase the bioavailability of phenolic compounds, peptides, and other antioxidant molecules. In addition, microbial metabolic activity influences the redox environment of fermented systems through electron-transfer processes and reducing metabolites. By integrating these complementary mechanisms, this review provides a comprehensive framework linking microbial biotransformation and redox modulation to the antioxidant properties of fermented foods, and highlights their potential for the development of functional fermented products.