Exopolysaccharide (EPS)-Producing Streptococcus thermophilus: Functional and Probiotic Potential

This study presents a characterization of exopolysaccharide (EPS)-producing Streptococcus thermophilus strains isolated from goat milk, including information about structural and functional characteristics of EPS. The isolates exhibited efficient lactose fermentation, broad carbohydrate utilization, and desirable enzymatic activities for technological applications, particularly aminopeptidases and acid phosphatase, while lacking harmful enzymes and virulence traits. Among the four strains studied, GM4 emerged as a particularly promising probiotic due to its sensitivity to all tested antibiotics, high β-galactosidase activity (56.2 × 10³ Miller units), moderate antioxidant capacity (scavenging 22.7% of DPPH and 5.7% hydroxyl radicals), cholesterol-lowering ability (26.9%), high auto-aggregation capacity (46.8%), and co-aggregation (>30%) with key foodborne pathogens including Escherichia coli, Listeria monocytogenes, and Staphylococcus aureus. GM4 produced an EPS with high dextranase resistance, and its production was enhanced in lactose-enriched media (yield = 2.58 g/L). The purified EPS consisted of two heteropolysaccharides (12.0 kDa and 112 kDa), primarily composed of glucose (Glc, 53%) and mannose (Man, 29%), with minor contributions from uronic acids (8%), ribose (6%), arabinose (2%), and galactose (2%). Key glycosidic linkages included (1→4)-Glc, (1→2,6)-Man, (1→2)-Man, and (1→4,6)-Glc. Functional assays demonstrated notable antioxidant activity, with 52.5% DPPH and 12.9% hydroxyl radical scavenging at 3 mg/mL EPS. These findings highlight S. thermophilus GM4 as a safe, technological, and functional candidate for dairy and probiotic applications, with its EPS exhibiting properties suitable for functional food incorporation.