Isolation, Identification of Leuconostoc mesenteroides HDE1 and Anti-oxidation and Milk Coagulability of Its Extracellular Polysaccharide

In order to expand the source of exopolysaccharides (EPS) from lactic acid bacteria, obtain EPS from lactic acid bacteria with clear source, stable yield and excellent biological characteristics. In this study, a strain of lactic acid bacteria with high EPS production was isolated and screened from self-made orange fermentation liquid by slime producing colony method. Morphological observation, 16S rDNA sequence analysis results and API 50 CHL test were combined to identify the strain. Antioxidant and milk coagulation characteristics of the lactic acid bacteria EPS were studied by antioxidant and milk coagulation test. Results showed that: A 16S rDNA fragment of Leuconostoc mesenteroides with 1444 bp was obtained, and its GenBank number was OM302141. The contents of total sugar, protein and uronic acid in strain HDE1 EPS were 41.73%±1.74%, 0.29%±0.03% and 7.69%±0.42%, respectively. The EPS showed good antioxidant activity when the concentration was 3 mg/mL. When the concentration of EPS was 5 mg/mL, the scavenging ability of DPPH, ABTS⁺ and H₂O₂^- free radical reached 50.00%±0.05%, 40.00%±0.02% and more than 50%. The hydroxyl scavenging ability was 49.96%±0.03%, and the total reducing power of EPS was 38.82%±0.09%. Milk curdling results showed that HDE1 could make skim milk with 3% (w/v) sucrose coagulate completely at 36 h. These results indicated that strain HDE1 EPS had good antioxidant and milk condensation properties, showing good application potential in food, medicine and probiotics.