SUMMARY
Introduction: Grapevine is a valuable source of active health-promoting substances, in particular polyphenols, i.e., flavonoids and phenolic acids, with antioxidant, anti-inflammatory, antibacterial, antiviral and anticancer properties. Grape seeds, peels and leaves also provide a rich source of antioxidants.The aim of the study was to evaluate the antioxidant activity of aqueous and alcoholic extracts of various parts of the Vitis vinifera.Materials and methods: Fresh and frozen grapevine fruits and leaves of a red variety, cultivated by the authors, were evaluated for antioxidant potential. Extracts were prepared with an ultrasound-assisted extraction at 40 kHz for 15, 30 or 60 min. Methanol, ethanol and isopropanol aqueous solutions, as well as water, were used as extractants. Antioxidant activity was determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azinobis(ethylbenzothiazoline-6 sulphonic acid) (ABTS) methods.Results: The antioxidant potential of extracts prepared from both fresh and frozen plant material was observed. The highest activity, evaluated with the DPPH method, was found in methanolic extracts of fresh leaves, obtained after a 60 min extraction. Similarly, a high activity was observed for frozen grapevine leaf extracts. The highest antioxidant capacity, evaluated by the ABTS method, was found in frozen leaves extracted with isopropanol for 60 min. Freezing and thawing markedly increased the antioxidant properties of the extracts.Conclusions: Extracts from both fresh and frozen parts of the Vitis vinifera showed antioxidant activity, and leaf extracts seemed to be particularly valuable. The freezing-thawing process had a beneficial effect on antioxidant potential and should be considered a useful method to increase extraction efficiency of antioxidants to be used to obtain valuable cosmetic, pharmaceutical or food products.