Screening of antioxidative properties and total phenolic compounds of various extracts of three different seed of grape varieties (Vitis vinifera L.) from Turkish flora.

This study was designed to examine the in vitro antioxidant activities and total phenolic contents of various extracts prepared by using solvents of varying polarity from three different seed of grape varieties (Vitis vinifera L.) of which local names are Siyah gemre, Adana Karasi and Tilki kuyrugu in Turkish folk medicine, respectively. The extracts were screened for their possible antioxidant activity by two complementary test systems namely DPPH free radical scavenging and beta-carotene/linoleic acid. In the first case, polar fractions of the methanol extracts of grape seeds exerted excellent activity patterns than those of non-polar fractions, while hexane and dichloromethane extracts did not exhibited activity. Among the polar ones, the most active extract was Adana karasi (5.90 +/- 0.20 microg mL(-1), followed by Tilki kuyrugu and Siyah gemre (6.40 +/- 0.50 microg mL(-1) and 6.90 +/- 0.40 microg mL(-1), respectively). In DPPH system, grape seeds exerted two-fold greater antioxidant activity than that of synthetic antioxidant BHT. In beta-carotene/linoleic acid test system, inhibition of linoleic acid oxidation was effectively achieved by polar and non-polar extracts of Siyah gemre. In this system, polar extracts exhibited greater antioxidant activity than those of non-polar ones, whereas hexane and dichloromethane extracts had no activity. The amount of total phenolics was highest in polar and non-polar extracts of grape seeds. Especially, a positive correlation was observed between total phenolic content and antioxidant activity of polar extracts. As estimated from the results given above, amount of phenolic compounds were less in hexane and dichloromethane extracts than the others. In conclusion, antioxidant potentials of polar and nonpolar methanol extracts could be attributed to their high phenolic content.