Microbial Fermentation as a Tool to Improve the Antioxidant and Functional Value of Milk Products

Microbial fermentation is attracting attention as a key process in reconstructing the profile of functional components in foods. This review summarizes the main mechanisms by which microbial fermentation generates antioxidants and functional compounds in fermented dairy products. In particular, we focus on (i) the production of bioactive peptides driven by fermentation-induced proteolysis, (ii) modulation of reactive oxygen species (ROS) homeostasis associated with shifts in metabolite composition, and (iii) the remodeling of organic acids, fatty acids, and other low-molecular-weight metabolites. We also discussed an analytical framework for evaluating antioxidant function in various analytical methods such as the 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay, 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, and ferric reducing antioxidant power (FRAP) assay, as well as cell-based measurements of reactive oxygen species (ROS)/nitric oxide (NO) and determining oxidative damage in animal models. Overall, the antioxidant functionality of fermented dairy products should be understood not merely as an increase in radical-scavenging capacity but as the outcome of fermentation-driven molecular remodeling and physiological regulatory effects. This review defines fermented dairy products as functional foods, highlighting the need for an omics-based approach in future fermented food studies.