Proximate composition, metal, polyphenol and flavonoid contents of green and black tea in Kampala

Abstract

Uganda is the second leading producer of tea in Africa. However, there are quality and safety concerns of Uganda's tea in the international market. This study determined the proximate composition, the essential and toxic elements, and total polyphenols and flavonoids in green and black tea from selected supermarkets in Kampala. Proximate analysis (moisture, ash content, protein, fat, and carbohydrate) was done as per the procedures of the Association of Official Analytical Chemists (AOAC). Essential elements; sodium (Na), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), manganese (Mn) and iron (Fe), and nonessential elements; mercury (Hg), lead (Pb), cadmium (Cd), arsenic (As), were determined using atomic absorption spectrophotometry (AAS). Total polyphenol and flavonoid contents were determined following the Folin-Ciocalteu method and aluminum chloride using colorimetric assay, respectively. Moisture, fat, protein, ash, crude fiber and carbohydrate levels in the tea ranged from 2.64 to 8.43, 0.87 to 3.74, 12.41 to 29.28, 4.34 to 9.08, 12.12 to 31.46 and 28.65 to 61.13 %, respectively. Lead, As, Cd and Hg were not detected in all samples. Metal concentrations were in the range of 694.95 to 2681.83, 4.53 to 11.77, 17.51 to32.59, 47.60 to 141.17, 39.77 to 280.94, 1.18 to 2.28 and 8.30 to 37.69 mg/kg correspondingly for K, Na, Mg, Mn, Ca, Cu and Fe. The total polyphenol and flavonoid amounts ranged from 82.17 to 159.31 mg GAE/g DW and 122.12 to 183.24 mg RE/g DW, respectively. Moisture and ash contents of the green and black tea were within recommended limits. Tea in Kampala is generally safe for human consumption because of the low levels of toxic elements. The high levels of polyphenols and minerals observed in green tea imply that green tea can be an additional source of these components in the diet. Therefore, drinking green tea may be more beneficial than drinking black tea for consumer.