Suggested mechanism for the effect of sweeteners on radical scavenging activity of phenolic compounds in black and green tea

The present work aims to evaluate the relation between the antioxidant activities and phenolic compound contents of two tea samples (green and black) mixed with or without sweeteners (sucrose or aspartame). The aqueous extracts were screened for total polyphenol and flavonoids contents. Antioxidant activities of extracts were tested using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical method and 2, 2-azino-bis [ethylbenzthiazoline-6-sulfonic acid] (ABTS) methods using butylated hydroxyl anisole as standard compound. In addition, we identified polyphenols compounds using high performance liquid chromatography (HPLC). The results indicated that the antioxidant activity was higher against ABTS radical more than DPPH radical. Also, there is positive correlation between the antioxidant activity and phenolic compounds content presented in water extracts of tea samples. The results also indicated that addition of table sugar to green tea significantly decreased the antioxidant activity (from 95.8% to 90.6% with 4.0% sucrose). However, the same table sugar in black tea increased the antioxidant activity (from 87.0% to 91.9% with 4.0% sucrose). The analysis using HPLC showed that caffeine was the most predominant individual compounds in green and black tea without and with 1.0% sucrose (6081.8, 8772.1, 6474 and 3755 mu g/100g, respectively). However, cinnamic acid showed the lowest content in the same tea samples (0.21, 0.25, 0.19 and 0.18 mu g/100g respectively). Pyrogallol, catechol, epicatechin, ellagic, protocatchuic were significantly higher in green tea than in black tea.