The aim of the present work was to quantify caffeine and total phenolic content and to evaluate the antioxidant activity in commercially available black tea, green tea, Turkish coffee and traditional Omani qahwa. Aqueous extracts of tea and coffee samples prepared by decoction were subjected to the phytochemical screening test for phenols and caffeine. Caffeine in the samples was quantified with the help of a linear regression equation obtained from the standard plot. Total phenolic and flavonoid contents in the tea and coffee were estimated colorimetrically. Antioxidant activity of the samples was investigated by DPPH (1, 1 diphenyl picrylhydrazyl) free radical assay and phosphomolybdenum methods. All the test extracts showed the presence of phenolic compounds and caffeine. The results indicated a variation in caffeine content, phenolic content, flavonoid content and antioxidant activity between the two extracts and among same extracts with different brand names. In general, Mumtaz black tea was found to contain the highest caffeine (24.44 mg/g) and phenolic content (8.27 mg/g of GAE). It also showed the highest total antioxidant activity (10.46 mg/g of ascorbic acid equivalent) but surprisingly its flavonoid content and antioxidant activity by DPPH method was lower than other samples. Tea was found to be richer in phenols and caffeine but Omani qahwa showed better antioxidant activity. It can be concluded that phenolic content and the antioxidant activities depend on the origin, brands and additives of these beverages that may lead to variation in the content and bioactivity.
Maryam F Hasan, Wed S Aldaraji, Dhanalakshmi UM, Shah A Khan and M Ali.