Anitoxidant Activities And Structure Of Lactic Acid Bacteria Exopolysaccharides

The exopolysaccharide （EPS） produced by lactic acid bacteria （LAB） not only has goodrheological properties but also is generally recognized as safe. Recently, more and morestudies show that it also possesses good antioxidant activity, which has received muchattention due to its unique advantagement to be natural and safe. In this paper, a highantioxidative EPS produced by the selected LAB strain was extracted and purified. Itsstructure was analyzed, as well as the in vitro antioxidant activity and the protective effects onH₂O₂-induced oxidative damage PC12cells. This will lay a foundation of the application ofEPS in food, medicine and cosmetic field.The crude EPS （CEPS） produced by L. planterum LP6was purified by DEAE-SepharoseFF ion-exchange chromatography and Sepharose CL-6B size exclusion chromatography. Oneof the major fractions EPS-3was accounting for71.3%of the total CEPS content. EPS-3hadnotable antioxidant activities in vitro. Its EC50values of scavenging DPPH·, OH·andO₂^-·radicals were1.38,3.43and0.11mg/mL, respectively. The reducing power A700nmwas0.632at5mg/mL. They were significantly higher than the CEPS and the other two fractions（p<0.05）. Its antioxidant activity could be well preserved and exert in the simulated conditionof human gastrointestinal tract.The UV scanning spectrum showed that EPS-3contained no protein and it was proved tobe homogeneous by the silicon sheet chromatography and high performance gel filtrationchromatography. The average molecular weight was5.73×10⁵Da. Ion chromatographyshowed that EPS-3was a heter-polysaccharide that mainly composed of mannose, glucose,galactose and glucuronic acid in a molar ratio of9:6:3:1. Infrared spectrum suggested that itwas an acidic pyranoid glycan with a little glucuronic acid.EPS-3had obvious protective effect on oxidative damage PC12cells. The cell viabilitywas improved by21.67%when the concentration of EPS-3was200μg/mL. Thetotal-antioxidant capacity, activities of superoxide dismutase and catalase were enhanced by65.81%,41.34%and59.05%, respectively. Meanwhile, the level of malondialdehyde andlactate dehydrogenase were decreased by52.80%and30.24%. Cell morphological studyindicated that EPS-3could maintain cell morphology in good condition and inhibit thedamage of the membrane.In this study, we obtained a high antioxidant activity LAB EPS, confirmed its antioxidantproperties by in vitro and cell experiments. We also analyzed its structural characteristics.This will help to enrich the probiotic theory of LAB and expand the application prospects ofLAB EPS as an antioxidant.