Thesis Abstract

The present study evaluated the phytochemical constituents and in vitro antioxidant potential of different types of tea namely; black tea, un-caffeinated tea, green tea and herbal tea. Radical scavenging capacities of the tea extracts were determined using 2,2-diphenyl-2-picrylhydrazyl (DPPH) assay. Total antioxidant activity was determined using ferric reducing antioxidant power (FRAP) assay. The results showed that the total flavonoid content (TFC) of green tea (215.61±48.83 QE/mg) wassignificantly (p<0.05) higher than that of un-caffeinated tea (184.32±33.62 QE/mg) and herbal tea (167.25±31.25 QE/mg). There was no significant (p > 0.05) difference between the TFC of un-caffeinated and herbal tea samples. However, the TFC of un-caffeinated and herbal tea samples were found to be significantly (p<0.05) higher than that of black tea (142.32±22.73 QE/mg). There was no significant (p > 0.05) difference in the total tannin content (TTC) of un-caffeinated tea (411.55±9.21 GAEmg/ml), green tea (406.83±22.71 GAEmg/ml) and herbal tea (402.74±13.2 GAEmg/ml). However, their TTC were found to be significantly (p < 0.05) higher than that of black tea (325.14±108 GAEmg/ml). The total phenol content (TPC) of green tea (124.81±79.05 GAEmg/ml) was found to be significantly (p < 0.05) higher than that of un-caffeinated tea (63.87±35.76 GAEmg/ml), black tea (51.81±8.90 GAEmg/ml) and herbal tea (15.78±13.02 GAEmg/ml). The antioxidant activity of black tea and herbal tea was found to be significantly (p < 0.05) higher than that of un-caffeinated tea. Green tea showed the least radical scavenging activity. A correlation between the antioxidant capacity and the phytochemical constituent of the teas was observed. A positive correlation (r = 0.060) was observed between the TTC and FRAP of the tea samples, however, a negative correlation (r = -0.137) was observed between the TTC and DPPH radical reducing power of the tea samples. A positive correlation (r = 0.448) was orbserved between the TFC and FRAP as well as between TFC and DPPH (r = 0.347) radical scavenging activities of the tea samples. These findings demonstrated that the green tea, black tea, un-caffeinated tea and herbal tea samples are rich in important phytochemicals such     as flavonoids and tannins), and possess antioxidant potentials. However, the tea types vary in their content of antioxidants and in their antioxidant potential. Based on the FRAP assay, black tea had the highest antioxidant potential while green tea had the least. Conversely, based on the DPPH assay, black tea, un-caffeinated tea and green tea had equal antioxidant potential while herbal tea had the highest antioxidant potential.

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