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

People worldwide consume a variety of teas, including Rooibos tea (red Rooibos tea), black tea, and green tea. Various teas 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 nutritional value from food. Thus, the objective of this study is to determine the tannin content, phenolic content, and antioxidant activity of different tea types (Rooibos tea, green tea, and black tea). This study also aims to determine the correlation between TPC and TTC with antioxidant activity by DPPH. The total tannin content and total phenolic content were measured using Folin-Ciocalteu method. Additionally, the antioxidant activity of the teas was evaluated using DPPH radical scavenging assay. Green tea exhibited a low IC50 value for DPPH (15.01 μg/mL), high phenolic content (56.57 mg GAE/g), and high tannin content (101.75 mg TAE/g). Rooibos tea had the lowest tannin content (38.75 mg TAE/g), and low phenolic content (36.95 mg GAE/g) but exhibit a higher IC50 value for DPPH (25.11 μg/mL). Black tea exhibited moderate amount of phenolic content (46.18 mg GAE/g), tannin content (41.37 mg TAE/g), and IC50 value for DPPH (18.93 μg/mL). Hence, the antioxidant activities of the teas ranked as follows: Rooibos tea < black tea < green tea. By using Pearson’s correlation coefficient, total phenolic content was found closely associated with antioxidant activity with r = 0.984 while total tannin content 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 tannin content, phenolic content and antioxidant activity value, Rooibos tea is considered the best compared to green tea and black tea.