Structural characterization, antioxidant activities and physicochemical properties analysis of a galactose-rich exopolysaccharide produced by Limosilactobacillus fermentum YL-11

Lactobacilli-derived exopolysaccharides (EPSs) are widely regarded as safe and have been employed as potential natural, non-toxic additives and functional agents in food industry. The structural properties of a galactose-rich exopolysaccharide produced by Limosilactobacillus fermentum YL-11 (YL-11 EPS) were investigated with chemical and instrumental analysis. The YL-11 EPS was determined to have a molecular weight (Mw) of 13.2 kDa. Nine different types of glycosidic bonds were identified in YL-11 EPS. The inferred structure of the YL-11 EPS contained the backbone of-*2)-(3-D-Galp-(1-*[3)-(3-D-Galp-(1]4-* 3)-(3-D-Galp-(1-* 3)-(3-D-Galp-(1-*, with two side chains, (3-D-Galp-(1-* 6)-alpha-D-Manp-(1-* 6)-[alpha-D-Glcp-1-*2]-alpha-D-Manp-(1-* 3)-[alpha-D-Glcp-1-*6]-alpha-D-Glcp-(1-* 3)-[alpha-D-Glcp-1-*6]-alpha-D-Glcp-(1-* with an acetyl group at the O-3 position of-*2,6-alpha-D-Manp-1-* and alpha-L-Araf(1-*, which were present at the C6 location of the 1,3-(3-D-Galp. The YL-11 EPS showed concentration-dependent antioxidant activities and the DPPH, ABTS, hydroxyl groups and superoxide radicals scavenging rates of 10 mg/ mL YL-11 EPS reached 61%, 74%, 35.4% and 40%, respectively. The YL-11 EPS also has a beneficial protective impact on H2O2-injured cells, which pretreatment with YL-11 EPS can substantially decrease ROS levels and enhance SOD enzyme activity. Additionally, the YL-11 EPS exhibited good thickening properties and thermal stability. The EPS's structural information and physicochemical properties provide a basis for studying their structure-function relationships.