Antioxidant Capacities and Total Phenolic Contents of 11 Grape Varieties

Objective:To systematically assess the antioxidant capacities and total phenolic contents of 11 grape varieties. Method:The tested grapes were separated into peels, pulps and seeds, and their fat-soluble, water-soluble and insoluble-bound fractions were extracted. Antioxidant capacities were evaluated using ferric reduce antioxidant power (FRAP) assay and Trolox equivalent antioxidant capacity (TEAC) assay, and total phenolic contents (TPC) were measured by Folin-Ciocalteu method. Besides, correlations between FRAP, TEAC and TPC were analyzed. Results:The FRAP range of grape skin, meat and seeds of different varieties were (112.86±5.98)~(658.93±28.63), (6.89±0.39)~(79.04±3.10), (723.61±29.20)~(1608.34±66.55) μmol Fe (II)/g DW, TEAC range were (37.56±1.17)~(374.52±15.90), (3.02±1.02)~(32.50±1.75), (440.00±19.61)~(887.38±36.18) μmol Trolox/g DW. The range of g DW and TPC were (12.09±0.40)~(73.12±4.28), (1.51±0.13)~(9.37±0.35), (74.01±1.46)~(133.53±1.43) mg GAE/g DW, respectively. In addition, for different soluble fractions, the FRAP, TEAC, and TPC were a fat-soluble portion > a water-soluble portion > a bound portion. FRAP, TEAC and TPC have a good linear correlation (p<0.05). Conclusion:The total phenolic contents and antioxidant activity of different grape varieties, different grape parts and different soluble fractions were quite different. The antioxidant activity of grape skin, meat and seeds was positively correlated with its total phenolic contents, and these phenolic substances were mainly present in fat-soluble and water-soluble extracts, and had the ability to reduce and scavenge free radicals.