Evaluation of the antioxidant activity of foods in human cells

Antioxidant testing of natural products has attracted increasing interest in recent years, mainly due to the fact that antioxidants can neutralise harmful free radicals in vitro, thus suggesting that an antioxidant-rich diet might provide health benefits. Several methods have been developed to examine the antioxidant potential of foods, including the ferric ion reducing antioxidant power (FRAP), peroxyl radical scavenging capacity (PSC), Trolox equivalent antioxidant capacity (TEAC) and oxygen radical absorbance capacity (ORAC) measurements, among others. However, these chemical assays do not take into consideration key biological parameters that are needed to estimate the potential in vivo effect. In an attempt to better characterize the antioxidant action of natural products, we investigate the effect on intracellular reducing power of aqueous extracts from commercial Camellia sinensis leaves (green, black and white teas), available from an Italian market. The flavonoid contents were determined spectroscopically and the antioxidant activities were assessed using ORAC and PSC assays as well as the cellular antioxidant activity (CAA) method. Our results suggest that although some extracts have a relatively high antioxidant capacity, this rank is dependent on the chemical method used. Moreover, the merely chemical result is sometimes weakly correlated with the cellular defence against oxidative attack. The tested C. sinensis extracts are successfully absorbed at different rates into human cells and among these, green tea had the highest CAA value, followed by white and black teas. Testing the benefits of dietary antioxidants with a cellular model is a great improvement over test tube assays, since it evaluates the antioxidants in a physiological environment and takes into account the complexity of a biological system, thus better reflecting the in vivo situation.