Determination of tannin content, phenolic content and antioxidant activity of rooibos tea, green tea and black tea from commercial tea bag / Azza Faiza Mohammad Taib … [et al.].

Various teas like Rooibos, black, and green tea offer unique benefits through antioxidants that protect cells from free radicals. Tannin, an antioxidant in tea, has health advantages but may hinder iron absorption, reducing the nutritional value of tea. Thus, this study aims to determine the total tannin content (TTC), total phenolic content (TPC), and antioxidant activity of Rooibos tea, green tea, and black tea. This study also aims to determine the correlation between TPC and TTC with antioxidant activity. The total tannin content and total phenolic content were measured using the Folin-Ciocalteu method. The antioxidant activity was evaluated using the DPPH radical scavenging assay. Green tea exhibited the strongest antioxidant activity with an IC50 value of 15.01 μg/mL and possesses high phenolic content (56.57 mg GAE/g), and high tannin content (101.75 mg TAE/g). Black tea also showed strong antioxidant activity with an IC50 value of 18.93 μg/mL with a total phenolic content of 46.18 mg GAE/g and a total tannin content of 41.37 mg TAE/g. Similarly, Rooibos tea also showed strong antioxidant activity with an IC50 value of 25.11 μg/mL but Rooibos tea had a lower tannin content (38.75 mg TAE/g), and lower phenolic content (36.95 mg GAE/g) compared to green tea and black tea. Hence, the teas ranked by antioxidant strength are Rooibos < black < green tea. By using Pearson’s correlation coefficient, total phenolic content was found closely associated with antioxidant activity with r = 0.984. Total tannin content, on the other hand, was weakly associated with antioxidant activity with r = 0.178. Consequently, the study's findings suggest that a higher total phenolic content corresponds to stronger antioxidant activity, whereas elevated total tannin content does not necessarily indicate higher antioxidant activity. Therefore, according to all values, Rooibos tea is a better option than green and black tea.