Structural identification and antioxidant potency evaluation of pomelo vinegar polyphenols

Polyphenols are the main antioxidant ingredient of honey pomelo vinegar. However, the antioxidant contributions of various individual phenolics to total polyphenols and antioxidant mechanism are unclear. In this study, phenolic compounds were identified, and the antioxidant potency and antioxidant contribution of individual phenolics were analyzed. The antioxidant mechanism was also studied in HepG2 cells. A total of seven phenolics were identified, including naringin, narirutin, rhoifolin, vanillic acid, methyl hesperidin, vicenin-2, and ferulic acid; among which, ferulic acid had the highest extracellular antioxidant potency, while methyl hesperidin had the lowest. Without considering the synergistic effect of the phenolics, naringin, ferulic acid, and vicenin-2 were major contributors to the antioxidant potency of pomelo vinegar polyphenols (PVP) using four antioxidant assays. PVP at the concentrations of 20 μg/mL and 100 μg/mL had a protective effect against H2O2-induced oxidative damage to HepG2 cells. PVP also reduced lactic dehydrogenase (LDH) release and reactive oxygen species (ROS) accumulation in cells. The western blotting results revealed that PVP promoted translocation of NFE2-related factor 2 (Nrf2) from the cytoplasm to the nucleus and up-regulated the expression of its governed antioxidant enzymes such as NAD(P)H: quinone oxidoreductase 1 (NQO1), heme oxygenase-1 (HO-1), glutathione S-transferase A2 (GSTA2), and glutamate-cysteine ligase catalytic subunit (GCLC). In summary, PVP could serve as a potential therapeutic agent for oxidative stress-related disorders.