Antioxidant and 'natural protective' properties of kiwifruit

Kiwifruit are nutrient-dense fruit with a reputation for promoting good health. Although this could be attributed to the high vitamin C content of kiwifruit, other phytochemicals could also provide health benefits. Kiwifruit are commonly reported to be a good source of vitamin E and in addition contain phenolics and carotenoids. The antioxidant properties of kiwifruit have received attention as possible mechanisms for their health-promoting effects. In this review, the antioxidant capacity of kiwifruit is discussed in the context of biologically relevant in vitro assays for predicting antioxidant activity in a biological setting compared with chemical antioxidant assays, and the ability of kiwifruit to protect cells from dying after exposure to an oxidative insult by hydrogen peroxide (cytoprotection). Some recent data are included, where extracts from twenty kiwifruit genotypes, derived from germplasm held at The New Zealand Institute for Plant & Food Research Ltd, were compared for their cellular antioxidant activity and cytoprotection, using human gut-derived epithelial cell lines. Our knowledge of how this type of result is currently reflected in vivo is summarised, together with the 'naturally protective' properties of kiwifruit that involve modulating immune responses in a positive way. Finally, the ways in which these antioxidant and natural protective properties of kiwifruit may influence human health and wellness are discussed.