Screening And Characterization Of Lactic Acid Bacteria With Antioxidant Activity In Fermented Vegetables

Oxidative stress is an imbalance of the oxidation-antioxidation system in the body’s environment When the amount of free radicals produced by the body is greater than its own scavenging ability.A lot of related results have proved that oxidative stress could cause various diseases such as asthma,allergies,diabetes and so on.It is necessary to increase the body’s antioxidant defense ability to improve human health.Lactic acid bacteria（LAB）are safe,stable and non-toxic.Lactic acid bacteria strains are used to eliminate excess free radicals,inhibit oxidative damage,and treat related diseases are a viable potentiallyoption.In this study,LAB strains were mainly isolated from Chinese traditional fermented vegetables.The target strain was screened by a series of antioxidant indexes and probiotic indexes in vitro.We established the D-galactose-induced oxidative stress model to explore its antioxidative properties in vivo.The purpose is to lay a theoretical foundation for the development of antioxidant products.The main results are as follows:（1）481 lactic acid bacteria strains were isolated from 13 different Chinese traditional fermented vegetable samples collected from 41 different areas of China.481 strains’antioxidant capacity were measured by DPPH·free radical scavenging ability,OH·free radical scavenging ability,reducing ability,and Fe²⁺chelating ability and lipid peroxidation inhibition rate.Eight lactic acid bacteria strains with stronger antioxidant capacity were screened,which were named by SC12,SC34,GX235,YN295,JX306,GX328,GZ394,GZ430.Among them,LAB strain JX306 showed stronger anti-oxidation ability in vitro,the strongest scavenging ability against DPPH·was 37.29%,the highest reducing ability was 83.95%,the strongest lipid peroxidation inhibitory activity was 28.14%and stronger Fe²⁺chelating ability was54.38%,stronger hydroxyl radical scavenging ability was 37.90%.（2）The probiotic characteristics indicators of simulated bile tolerance,simulated gastrointestinal fluid tolerance,cell hydrophobicity,and self-agglutination capacity were measured,the strain JX306 showed the highest survival rate in bile salt,gastric and intestinal solutions.The survival rates were 78.28%for simulated bile,53.05%for simulated gastric fluid,42.07%for simulated intestinal fluid,86.82%for cell hydrophobicity and 45.52%for self-agglutination capacity.Therefore,JX306 was selected as the target strain for further experiments.After morphological,physiological,biochemical and genetic identification,the strain JX306 was identified as Lactobacillus fermentum.（3）L.fermentum JX306 was examined for its antioxidant capacities in D-galactose-induced oxidative stress model.These results explained that L.fermentum JX306 could decrease significantly malondialdehyde（MDA）levels and improve the activity of glutathione peroxidase（GSH-Px）and total antioxigenic capacity（T-AOC）in serum,kidney and liver.Meanwhile,L.fermentum JX306 could upregulate remarkably the transcriptional level of antioxidant-related enzyme genes such as peroxiredoxin1（Prdx1）,glutathione reductase（Gsr）,glutathione peroxidase（Gpx1）and thioredoxin reductase（TR3）in the liver.In addition,histopathological observations showed that L.fermentum JX306 can inhibit effectively the oxidative damage of kidney and liver in D-galactose-induced oxidative stress model.（4）16S rDNA analysis of intestinal microbial composition showed that L.fermentum JX306 could increase Firmicutes/Bacteroidetes ratio,increase the abundance of beneficial bacteria such as Lactobacillus,uni.Lachnospiraceae,Ruminococcaceae,Roseburia,Butyricicoccus,and Blautia.It is benefical to improve intestinal microbial composition.