Microbial mechanisms, biochemical pathways, and health implications of lactic acid Fermentation in milk: A comprehensive review with special Reference to water buffalo (Bubalus bubalis) milk and curd

Milk is a biologically complex secretion evolved to provide optimal nutrition, immune protection, and physiological support for mammalian offspring. Its composition varies across species, stages of lactation, and environmental conditions, influencing its functional, nutritional, and technological properties. Fermentation by lactic acid bacteria (LAB) represents one of the earliest and most important biotransformations of milk, enhancing shelf life, digestibility, sensory attributes, and potential health benefits. LAB drives milk fermentation by converting lactose into lactic acid and, through proteolysis, citrate metabolism, and exopolysaccharide production, collectively shaping the texture, flavour, and microstructure of fermented dairy products such as curd, yoghurt, and cheese. Water buffalo (Bubalus bubalis) milk, widely used in South and Southeast Asia, is distinguished by its high fat, casein, mineral, and vitamin content, making it particularly suitable for curd production. Compared with cow milk, buffalo milk forms a firmer, more elastic curd with higher yield and lower syneresis due to its greater casein content, larger casein micelles, and higher colloidal calcium phosphate. These compositional characteristics influence coagulation behaviour, curd firmness, and overall processing performance during dairy fermentation. Organic acids generated during fermentation selectively inhibit spoilage microorganisms by disrupting their proton motive force, while allowing LAB to persist, thereby extending product shelf life. Regular consumption of fermented dairy products containing live LAB supports gut microbial balance, enhances immune function, and may provide metabolic, cardiovascular, and neurocognitive benefits. In addition, the reduced lactose content and increased lactic acid concentration in fermented milk may benefit individuals with lactose intolerance and type 2 diabetes by lowering glycaemic impact and potentially contributing to improved metabolic regulation. This review synthesizes contemporary evidence on the biochemistry, microbiology, nutritional attributes, curd-formation properties, and health implications of lactic acid fermentation, with special emphasis on water buffalo (Bubalus bubalis) milk and curd.