Screening Of Antioxidative Lactobacillus And Studying On The Antioxidant Activity

Oxidation is essential for living organisms'life activities, but oxidative stress often occurred with abnormally high levels of reactive oxygen species (ROS), which can damage biological molecules and plays a significant pathological role in human disease. The native antioxidative systems in organisms are not enough to prevent them from the oxidative damage. The addition of antioxidant may be a suitable choice to help reduction of oxidative damage. But the chemical syntheses of antioxidants have security problems, so the natural products are valued. Lactic acid bacteria (LAB) are food grade bacteria with a generally regarded as safe status, which are widely used in food fermentation. In the study, we selected two antioxidant Lactobacillus form 25 Lactobacillus: Lactobacillus Helveticus LLB and Lactobacillus pentosus Lp-B. On this basis, we studied on biological characteristics and the gastrointestinal tolerance. We also determined the cell-free extract antioxidant activity with change of culture conditions. The antioxidant fermented milk and antioxidant mechanism were studied in further study.In the present study, the LAB strain LLB and Lp-B were screened from 25 isolates of LAB according to the in vitro resistance to hydrogen peroxide, theα-diphenyl-β-picrylhydrazyl (DPPH) free radical-scavenging ratio. The results showed that, the two strains had the resistance to hydrogen peroxide, the DPPH free radical-scavenging ratio by cell-free extracts of LLB and Lp-B 109 cfu/mL LAB were 24% and 22%. Studying on the growth characteristics and the gastrointestinal tolerance showed that the two strains can grow in 18% of the concentration of sodium chloride and pH 2.5. At the same time, the strains were resistant to bile salt and trypsin and pepsin.According to the traditional morphological characters, physiological and biochemical properties, as well as chemical characteristics, LLB belonged to Lactobacillus helveticus, LLB belonged to Lactobacillus helveticus.In different culture time, different temperature, different pH and different cell concentration, we determined the change of antioxidant activity. The result showed that the optimal growth temperature, culture time and pH were 37℃. In 18h, the in vitro resistance to hydrogen peroxide, the DPPH free radical-scavenging ratio and reducing activity of LLB were 45%, 32% and 95μmol/mL; Lp-B were 32%, 23% and 82μmol/mL. At 37℃, the in vitro resistance to hydrogen peroxide, the DPPH free radical-scavenging ratio and reducing activity of LLB were 44%, 30% and 98μmol/mL; Lp-B were 38%, 23% and 85μmol/mL. When the pH was 8, the in vitro resistance to hydrogen peroxide, the DPPH free radical-scavenging ratio and reducing activity of LLB were 45%, 33% and 99μmol/mL; Lp-B were 36%, 25% and 89μmol/mL. The antioxidant activity of strains increased with the increase of cell concentration.The study found that the antioxidant activity of fermented milk concerned with the degree of hydrolysis, they are affected by fermentation time, fermentation temperature and solids content. The result showed that the antioxidant activity and the DH increased with the extended fermentation time and the solids content. At 37℃, the in vitro resistance to hydrogen peroxide, the DPPH free radical-scavenging ratio, reducing activity and DH of LLB were 32%, 52%, 65μmol/mL and 6.6%; Lp-B were 26%, 45%, 51μmol/mL and 5.6%.Moreover, the content of free amino acids is analyzed. Hydrophobic amino acids and aromatic amino acids in milk fermentation are 46.7% and 35%, which are better than unfermented milk. So hydrophobic amino acids and aromatic amino acids could improve the antioxidant properties of fermented milk.