Profiling for antihypertensive amino acid (theanine) in selected Kenyan tea clones

Abstract

Tea is a beverage and also a stimulant that is consumed by many people all over the world. It contains various bioactive compounds like alkaloids, polyphenols, and amino acids among others. Amino acids play the role of moderating taste of the tea infusion. Theanine is a unique amino acid found in the Camellia sinensis species and has been reported to reduce high blood pressure, improve learning and concentration and reduce premenstrual symptoms. This study was conducted to determine the content of theanine in different partitions of the tea shoot (four leaves and a bud), green and black tea processed from different selected Kenyan tea clones including one purple coloured tea clone and made tea commercially available in the Kenyan market. High performance liquid chromatography (HPLC) was used to quantify the levels of theanine. The results were analyzed statistically by carrying out ANOVA and Least Significant Difference test using MSTAT statistical package to determine if the levels of theanine were significantly different based on the different clones that were analyzed. The theanine content in the different partitions of the tea shoot varied, with the internodes having the highest amounts in the two clones that were analyzed (3.26 % dw) and the first leaf contained the lowest amounts (0.22 % dw). Among the leaves and the buds, theanine was more concentrated in the younger tissues. Theanine levels in the black and green tea processed from the selected tea clones varied with clones, seasons and also processing with green tea having higher levels than black tea in most clones. Green tea on average contained 0.80 % dw of theanine with TRFK 31/8 having the highest (1.20 % dw) and TRFK 303/216 having the lowest (0.50 % dw) theanine content. Black tea on average contained 0.69 % dw theanine with TRFK 56/89 having the highest (0.97 % dw) and TRFK 7/14 having the lowest (0.43 % dw) theanine content. Based on the current findings, theanine can be considered a tea marker since all the tea clones analyzed in this study contained some amount of theanine. Further, significant differences in the theanine content in the clones and during the three seasons considered (July- September, October - December and January - March) were observed. Theanine levels in the made tea in the Kenyan market were significantly different from each other and some teas did not contain theanine and these were majorly the flavoured teas. Kenyan black tea contained 1.02 % dw of theanine and this was comparable to teas from Rwanda, Tanzania and Uganda thus adding value to the Kenyan tea that can be marketed as a health drink. Theanine is a tea marker since all the test clones in the study contained it and would recommend people with hypertension to drink tea.