In vitro and in vivo antioxidant activity of musts and skin extracts from off-vine dried Vitis vinifera cv. “Tempranillo” grapes

The phenolic composition and antioxidant activity of musts and skin extracts from Tempranillo grapes dried for variable lengths of times were examined here. Both were found to increase in the grape must with increasing drying time, but the opposite trend was observed in the skin extracts. The antioxidant activity of the must and skin was largely due to anthocyanins. Also, the anthocyanins fraction exhibited the highest antioxidant activity per gram of phenolic compound in the musts and skin extracts at the end of the drying process, polymeric pigments and high-molecular-weight procyanidins were also prominent in this respect. In vivo antioxidant activity in terms of protein oxidation and survival of Saccharomyces cerevisiae cells previously incubated with 10 μg/mL of polyphenols from the musts and skins and exposed to hydrogen peroxide was also measured. Both extracts exerted a protective effect against oxidative stress, the effect increasing with increasing dehydration time and being somewhat higher for skin than for must. Thus, must and skin from dehydrated grapes possess antioxidant properties, which allow the latter, a by-product of sweet wine, to be used as a natural source of antioxidants.