Isolation, NMR Characterization, and Comparative In Vitro Antioxidant Evaluation of Resveratrol from Grape Seeds (Vitis vinifera L.)

Objective: The present study aimed to isolate, characterize, and evaluate the in vitro antioxidant potential of resveratrol from grape seeds (Vitis vinifera L.) obtained from local markets in Erzincan, Türkiye. It is hypothesized that the unique microclimate of that region enhances the bioactive profile of local grape varieties, making them a significant source of natural antioxidants.Methods: Grape seeds (500 g) were extracted using 100% methanol via reflux for 4 hours (three replicates). The crude extract (30 g) underwent liquid-liquid extraction with ethyl acetate to yield a concentrated phenolic fraction (2 g). For isolation, Sephadex LH-20 adsorbent was used as the stationary phase and eluted with methanol. Structural characterization was conducted using 1H and 13C NMR spectroscopy. The antioxidant capacity of the isolated resveratrol was determined through DPPH and ABTS radical scavenging assays, comparing results with standard antioxidants (Trolox, BHA, BHT, and Ascorbic acid).Results: Chromatographic purification yielded 10 mg of pure trans-resveratrol. The structure was firmly verified by NMR spectroscopy, with the high olefinic coupling constant (J = 16.3 Hz) suggesting the trans structure. In antioxidant experiments, Trans-resveratrol demonstrated notable DPPH radical scavenging action (IC₅₀ = 17.33 ± 1.22 µg/mL). Trans-resveratrol outperformed Trolox (7.22 ± 0.24 µg/mL) and ascorbic acid (8.22 ± 0.37 µg/mL) in the ABTS test, with an IC₅₀ of 6.84 ± 0.47 µg/mL.Conclusion: The findings demonstrate that grape seeds from Erzincan markets are an excellent source of highly bioactive trans-resveratrol. The isolated compound exhibited exceptional antioxidant efficiency, particularly in the ABTS assay where it surpassed several commercial standards. These results suggest that local grape varieties possess significant potential as natural sources for high-purity bioactive agents in the nutraceutical and pharmaceutical sectors.