Sustainable Utilization of Dairy Byproducts for Cultivating Lactic Acid Bacteria and Producing Bioactive Exopolysaccharides with Antioxidant and Antibacterial Properties

Microorganisms produce extracellular exopolysaccharides (EPS), either tightly bound or loosely attached to their surfaces. This study investigated lactic acid bacteria (LAB) for producing bioactive EPS using low-cost dairy by-products. Six LAB strains, identified as Lactobacillus and Lactococcus species from cheese, produced EPS yields of 3.0–26.5 g/L and viscosities of 20–44 cp, surpassing synthetic media. EPS from isolate CH3 exhibited strong antibacterial activity against foodborne pathogens, including Salmonella Typhimurium, Escherichia coli O157:H7, Shigella sonnei, Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus, and Bacillus subtilis, with inhibition zones up to 36.6 mm, exceeding kanamycin. Antioxidant activity ranged from 32.64% to 79.6%, confirming its bioactive potential. Structural analysis by ¹H NMR revealed both linear and cyclic polysaccharides. Combining LAB strains did not enhance EPS yield or bioactivity, highlighting CH3 as the most promising strain. It also displayed probiotic traits, including tolerance to bile salts, acidic pH, and high NaCl, plus resistance to antibiotics (streptomycin, nalidixic acid, ciprofloxacin). Its strong antibacterial effect against B. subtilis, E. coli, and S. Typhimurium further supports its application. These findings emphasize dairy by-products as sustainable substrates for functional EPS and probiotics, with isolate CH3 showing great potential in food safety, health, and biotechnology.