Physicochemical Properties, Antioxidant Activity and Protective Effect on Oxidative Stress Cells of Vernonia amygdalina Delile Leaf Jiaosu during Fermentation

Vernonia amygdalina Delile leaf was used as raw material to prepare Jiaosu. The change of basic physicochemical indexes were monitored during fermentation, and the antioxidant capacity was determined by the scavenging ability against ABTS⁺ radical and hydroxyl radical, and its protective effect to human normal hepatocytes (WRL-68) on oxidative stress was investigated by cell experiment. Results: Compared with the jiaosu on day 2 and day 55, the pH decreased from 4.24±0.01 to 3.46±0.07, and the content of soluble protein, total sugar, total phenol and total flavonoids decreased from 0.95±0.02, 244.94±4.89, 6.05±0.03, 0.37±0.01 mg/mL to 0.71±0.02, 34.26±0.57, 3.42±0.21 and 0.08±0.01 mg/mL, respectively. The total acid content increased from 0.15±0.01 to 0.95±0.01 mg/mL. The content of ascorbic acid increased from 25.36±0.52 to 28.44±0.01 μg/mL from 2 to 28 days, and then decreased. The ABTS⁺ radical scavenging ability was the strongest on the 18th day 73.72%±0.86%, and the hydroxyl radical scavenging capacity was the highest on the 28th day 54.14%±0.43%. There was a significant positive correlation between ABTS⁺ radical, hydroxyl radical scavenging ability and total acid content (P<0.01). After H₂O₂-injured WRL-68 cell, in cellular ROS significantly decreased, and the activities of antioxidant enzymes SOD, CAT and GSH-Px increased in the Jiaosu treated group. In summary, the Jiaosu of Vernonia amygdalina Delile leaf had strong ability to scavenge free radicals in the middle stage of fermentation, and the ability of WRL-68 cells to resist oxidative stress was improved after pretreatment with it.