Abstract: Electron spin resonance (ESR) spectroscopy was used to investigate the antioxidant activity of four proanthocyanidin extracts from wine grape seeds (designated as GSP0, GSP1, GSP2 and GSP3, respectively) and compared with spectrophotometry as a control. GSP3 had the strongest DPPH radical scavenging activity as determined by both methods. After 30 min of reaction at concentrations below 40 mg/L, a positive correlation between scavenging rate and GSP3 concentration was observed. At concentrations above 40 mg/L, the DPPH radical scavenging activity of GSP3 tended to be stable. Higher scavenging rates were obtained for all four proanthocyanidin extracts using ESR than spectrophotometry. After 30 min of reaction, the DPPH radical scavenging rates of GSP0 and GSP3 at various concentrations were determined using ESR to be in the range of 35.99%—99% and 52.45%—99%, respectively, whereas those obtained using spectrophotometry were in the range of 7.06%—78% and 29%—95%, respectively.

Key words: ESR, spectrophotometry, proanthocyanidin, DPPH