Structural characteristics and antioxidant properties of exopolysaccharides isolated from soybean protein gel induced by lactic acid bacteria

This is the first report on the structure and antioxidant property of exopolysaccharide (EPS), which was extracted from soybean protein isolate gels induced by lactic acid bacteria (LAB). EPSs were named AEPS (L. acidophilus), CEPS (L. casei), MEPS (L. mesenteroides) and LEPS (L. lactis). EPS was primarily composed of glucose, galactose and glucuronic acid, existed as random coils, and appeared as round lumps and chains. NMR showed that EPS was composed of α-glycosidic bond (δ5.0–6.0 ppm) and β-glycosidic bonds (δ4.5–5.0 ppm). The peaks near at 1644 cm−1 and 590 cm−1 correspond to uronic acid and sulphate groups, respectively. CEPS had the highest ability to scavenge DPPH (58.98 ± 1.54%), hydroxyl (64.89 ± 1.46%) and ABTS (64.89 ± 1.46%) free radicals. The monosaccharide composition-antioxidant activity relationships were identified using multiple linear regression analysis. This study could help promote the application of both EPS and LAB in functional soybean products.