Antioxidant capacities and total polyphenol content of nine commercially available tea juices measured by an in vitro digestion model

The total antioxidant capacity and total polyphenol content of 9 tea juices were examined following in vitro digestion model. Results show that there was a significant variation in total antioxidant capacity [16,392.30 ± 111.64–22,340.23 ± 46.73 μmol VC/L (DPPH), 3,194.24 ± 14.76–13,795.07 ± 37.46 μmol Trolox/L (ABTS), 2,540.61 ± 59.79–7,951.57 ± 31.91 μmol Trolox/L ferric reducing antioxidant power (FRAP)] and total polyphenol content (265.84 ± 9.52–876.62 ± 6.59 μg GAE/mL). Following the in vitro digestion, most of the juices of antioxidant capacities and 7 juices of the total polyphenol content were decreased. Before the in vitro digestion, a highly positive correlation was found between the total polyphenol content and FRAP value. After the gastric phase of digestion, there was a very strong positive linear correlation between the total polyphenol content and total antioxidant capacity. After the duodenal phase of digestion, the correlation between the total polyphenol content and total antioxidant capacity was very weak, and also, a very weak linear correlation was found between the antioxidant assays.