Antioxidant activity and the tocopherol and phenol contents of grape residues

The antioxidant activity and the tocopherol and polyphenol contents of organic grapevines residue were analyzed after Soxhlet extraction of grape seeds and skin with ethanol and petroleum ether. The highest antioxidant activity was determined for the ethanol extract of the seeds and was 58.65 μM Trolox/mg, which was four times higher than for the ethanol extract of the skin at 14.24 μM Trolox/mg. It was comparable to that of the alpha-tocopherol (62.28 μM Trolox/mg) and butylated hydroxyanizol (69.55 μM Trolox/mg). A concentration of 29.5 μg/mL ethanol seed extract was needed to decrease the initial DPPH radical concentration by 50%. The high antioxidant activity was because of the high tocopherol (402.28 mg/kg) and total phenols contents (113.7 gallic acid equivalent (g/kg)) in the seeds. The dominant polyphenol in the ethanol seed extract was coumaric acid (10.97 g/kg). The dominant polyphenols in the ethanol skin extracts were rutin (6.79 g/kg), quercetin (3.75 g/kg), and catechin (3.99 g/kg), which can be used in functional foods to reduce risk factors for several human diseases.