Bioactive compounds and antioxidant activity of black and green tea available in Bangladesh

People in Bangladesh are traditionally used to consume mainly black tea. However, some tea manufacturing companies are now producing green tea, though in a small scale. To create new knowledge as well as awareness about the consumption of green tea, the present study was carried out to compare the black and green tea available in Bangladesh based on their bioactive compounds and antioxidant activity. A total of eight brands of black tea and two brands of green tea were bought from the supermarkets. Total phenolics, total tannin, total flavonoids, and caffeine content were measured as bioactive compounds, and antioxidant activity was evaluated by using two different methods such as DPPH (1,1- diphenyl-2-picrylhydrazyl) radical-scavenging activity and ABTS+ radical scavenging activity of methanol extracts of black and green tea. Every bioactive compound in black and green tea was found to be significantly different (P < 0.05). The total phenolic content, on average, was measured at 242.46 mg GAE/g dry extract and 763.41 mg GAE/ g dry extract in black and green tea, respectively. Black tea contained 6.47 mg TAE/g dry extract tannin, whereas green tea had much more tannin content, 14.51 mg TAE/g dry extract, which is more than double in amount. On the other hand, the total flavonoid content was almost double in black tea (61.82 mg QE/g dry extract) compared to green tea (31.85 mg QE/g dry extract). Antioxidant activities were determined at different concentrations of tea samples. At every concentration, green tea presented higher ABTS+ and DPPH radical scavenging activity than black tea. The highest percentage of inhibition was observed at 20 ppm both in black and green tea, finding 98.50 % and 99.07 % inhibition, respectively. Overall, significantly (P < 0.05) higher amount of phenolic compounds as well as antioxidant activity were observed in green tea.