Determination of low molecular weight polyphenolic constituents in grape (Vitis vinifera sp.) seed extracts: Correlation with antiradical activity

Ethyl acetate extracts of seeds originating from nine Hellenic native and international Vitis vinifera varieties cultivated in Greece were screened for their contents of characteristic polyphenols. The compounds determined were principal constituents of low molecular weight, including gallic acid (GA), catechin (CT), epicatechin (ECT), epigallocatechin (EGC), epicatechin gallate (ECG), epigallocatechin gallate (EGCG), and the procyanidins B1 and B2 (dimers). Total content varied from 55.1 to 964 mg per 100 g of seeds, the average being 380 mg per 100 g. The most abundant polyphenol was CT, accounting for 49.8% of the total content, followed by ECT (26.0%), ECG (9.3%), procyanidin B1 (5.8%), and procyanidin B2 (5.1%), whereas EGC and GA were minor constituents. The assessment of the in vitro antiradical activity (AAR), employing the stable radical DPPH, showed that there is a significant correlation with total polyphenol content (r2=0.6499, P<0.01). The correlations with the individual compounds, however, revealed that procyanidin B1 may be one of the most important radical scavengers in grape seed extracts (r2=0.7934, P<0.002), despite its low contribution to the overall polyphenol content.