This study investigated the antioxidant function of Lactobacillus salivarius M18-6 bacterial suspension, cell-free supernatant and cell contents in vitro, respectively, by testing 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) clearance rate, inhibition of linoleic acid peroxidation rate, hydroxyl radical (·OH) clearance rate, antioxidant related enzyme activity, etc. Furthermore, combined with strain genome information, this study detected the transcription level of 11 genes involved in antioxidant function using real-time fluorescence quantitative PCR. The results showed that activity of scavenging DPPH free radicals and ·OH, and inhibiting linoleic acid peroxidation rate were significantly higher than that of L.rhamnosus GG (P<0.05). Meanwhile, the glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD) activities were also high in the cell-free supernatant of the strain. The results indicated that the cell-free supernatant of L. salivarius M18-6 had strong antioxidant capacity. Under 2.5 mmol/L H2O2 stress, the transcription level of the genes encoding NADH oxidase and superoxide dismutase of the L. salivarius M18-6 were up-regulated by 6.2 and 4.5 times, respectively, and the transcription level of thioredoxin series genes (trxA1, trxA2, trxA3, trx) and catalase(cat) were also up-regulated by more than 2 times. It is speculated that L. salivarius M18-6 might exhibit antioxidant effects by increasing the expression of NADH oxidase and thioredoxin to activate the thioredoxin system, and by up-regulating the expression levels of sod and cat genes to increase the activity of SOD and catalase.
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