However, every living organism has antioxidant mechanisms to counteract oxidative stress (1). Apart from the endogenous antioxidant mechanisms, the supplementation of antioxidants through diet may be used to reduce the detrimental effects of oxidative stress on human health as suggested by our previous studies (12,13). Some of the most well known food sources of antioxidants are grapes and wine (14). Our research group has conducted several studies on the antioxidant properties of grapes which are attributed mainly to their polyphenolic content (15–21). We have also conducted a series of studies on the antioxidant activity of extracts from grape stems, a by-product of the winemaking process which has been little investigated (15,22–25). For example, in one of our previous studies, we demonstrated that grape stem extracts are rich in bioactive polyphenols (e.g., flavonoids, stilbenes and phenolic acids) (22) and exhibit strong free radical scavenging activity in vitro (15).