Protective effects of bioactive phenolics from jujube (Ziziphus jujuba) seeds against H₂O₂–induced oxidative stress in neuronal PC-12 cells

Ziziphus jujuba (jujube) seeds were extracted with 60% (v/v) aqueous ethanol assisted by homogenization and sonication followed by fractionation into n-hexane, chloroform, ethyl acetate, n-butanol, and water. The ethyl acetate fraction exhibited the highest levels of total phenolics (102.05 mg gallic acid equivalents/g fraction), total flavonoids (35.43 mg catechin equivalents/g fraction), and antioxidant capacity (271.67 and 66.02 mg vitamin C equivalents/g fraction in respective ABTS and DPPH assays) among the fractions tested. Ultra-high-performance liquid chromatography-electrospray ionization-tandem mass spectrometry analysis of the ethyl acetate fraction revealed 12 phenolic compounds: 3,4-dihydroxybenzoic acid, methyldopa, p-coumaric acid, dihydro-p-coumaric acid, rutin, isoquercetin, kaempferol 3-O-rutinoside, 3-O-cis-p-coumaroylalphitolic acid, 2-O-cis-p-coumaroylalphitolic acid, 3-O-trans-p-coumaroylalphitolic acid, 3-O-cis-p-coumaroylmaslinic acid, and 3-O-trans-p-coumaroylmaslinic acid. Phenolic compounds generally increased viability, reduced lactate dehydrogenase release, and attenuated intracellular oxidative stress in PC-12 cells. The results of this study suggest that Z. jujuba seeds may serve as an effective source of antioxidative agents to reduce oxidative stress and enhance neuronal cell viability.