Assessment of Catechins and other Polyphenols as Parameters of Tea Quality in selected Ecological Zones in Kenya

Abstract

Kenya is the third largest producer of tea in the world after China and India and specializes in the processing and export of black CTC tea. Over 90% of Kenyan teas are sold to the world market through an auction based system that is dependent on the quality of tea on offer. In the tea trade, quality is used to indicate the presence of special desirable attributes in the tea liquor which are detected by visual, smell and taste. The chemical composition of tea is very complex and is currently a subject of broad medicinal and toxicological scientific studies. Previous studies have extensively shown that catechins together with their oxidation products including theaflavins and thearubigins are responsible for the sensory characteristics associated with black tea liquors; astringency or briskness, colour, strength and brightness. This study determined the biochemical profiles of tea grown by small scale farmers in Kisii, Murang’a and Meru ecological zones in Kenya. The levels of catechins were quantified using reversed phase HPLC while total polyphenols content were determined by spectrophotometric analysis. Theaflavins and thearubigin contents were determined by the Flavognost, Roberts and Smith methods respectively. Antioxidant activity of the tea samples was determined using the method of Brand-Williams. This study found that teas grown in the three ecological zones differed significantly in their polyphenols, catechins, theaflavins and thearubigins contents (P < 0.05). Interestingly, tea samples analyzed exhibited high antioxidant activity which differed significantly (p < 0.05) across the zones suggesting potential use of the black teas for medicinal use. Similarities between biochemical profiles and organoleptic evaluation at level P < 0.01 and at p<0.05 depicted positive correlation. This study sets a precedent for the characterization of biochemical profiles of tea from all the tea growingareas in Kenya