Tea, the most widely consumed plant-based beverage in the world [1] , is processed from young and tender shoots of the tea plant (Camellia sinensis, family Theaceae) and historians have linked its consumption to almost 5000 years back [2] . Tea can be broadly classified according to the processing methods as; un-aerated tea (green tea), semi-aerated tea (Oolong tea), fully aerated tea (black tea) or post-aerated tea (pu-erh tea) [3] . The beverage has over time gained popularity as a “health drink” due to the numerous beneficial medicinal properties that have been attributed to its polyphenolic content as evidenced by in vitro and animal studies [4] -[6] . Indeed, a growing body of research describing many putative benefits of regular tea consumption such as antibacterial [7] , antimicrobial [8] [9] , anti-diabetic [10] , antioxidant [11] -[14] , anti-viral effects [15] -[17] among others have been reported. Based on how the young tender shoots of the tea plant (raw material for tea manufacture) are handled during the manufacture process, different types of tea products with different biochemical profiles can be obtained [18] . This is because the nature and quality of a given tea product is mainly dependent on the chemical composition of the young tea shoots and the reactions they undergo during the manufacture process [19] . Further, several research findings have shown that tea contains a myriad of compounds, a portion of which end up in the tea liquor during the tea brewing process. Such compounds include; flavonoids, proteins, amino acids, enzymes, vitamins and a number of trace elements such as iron, zinc, copper and fluoride [20] - [27] .

Theanine (γ-glutamylethylamide), a non-protein amino acid, is a glutamic acid analog commonly identified in tea. It constitutes between 1% and 2% of the dry weight of the tea leaves and about 50% of total free amino acids [28] . It is the major “umami” (good taste) component of tea [29] and its favorable physiological effects on mammals have been reported; influence on the functionality of the brain [30] , mitigation of mental and physical stress due to its ability to cross the blood-brain barrier [31] - [33] and boosting of immunity against infection by enhancing the disease-fighting ability of gamma delta T cells [34] . Besides being a major tea producer of tea globally, data on the L-theanine of Kenyan tea as well as that from other countries commercially available locally is scarce. Thus, the objective of this study was to establish the L-theanine contents of different types of tea commercially available in the Kenyan market. Data obtained could be an important source of information with regard to quality, standards and nutrition.

L-theanine was eluted at the 6^th minute and a sample of chromatogram obtained is as shown in Figure 1.

The mean L-theanine content in the test tea samples ranged from below the Limit of Detection (LOD) of the method employed, 0.01% to 1.60% on a dry weight (d.w.) basis as shown in Figure 2. Generally, green teas were shown to contain the highest L-theanine contents followed closely by black teas. The mean L-theanine content in Kenyan black tea was 1.02% d.w. and was not significantly different (p > 0.05) from the Rwandan (BT1 = 0.98% d.w.; BT2 = 1.19% d.w.) and Ugandan (BT2 = 0.90% d.w.) black teas. However, one of the Ugandan tea samples had L-theanine content lower than the quantitation limit of the current method (<0.01%

d.w.). On the other hand, black teas from Cameroon and Sri Lanka had L-theanine contents of 0.48% and 0.52% d.w. respectively. These were significantly (p < 0.05) lower than those of Kenyan and Ugandan black tea. Rwandan green teas, GT1 (1.60% d.w.) and GT2 (1.16% d.w.) contained the highest L-theanine contents. These mean L-theanine contents were significantly (p < 0.05) different and higher than that of Kenyan and Sri-Lankan green teas which contained 0.12% and 0.14% d.w. of L-theanine. Six of the seven flavoured teas analysed had L-theanine contents that could not be quantified using the current method (<0.01%). This possibly implies that these teas majorly contained the flavours and less of tea.

Many studies have reported the L-theanine content in different teas [36] - [38] . In the current study, Kenyan green tea commercially available in the market (GTF) had an L-theanine content of 1.2 mg/g (0.12% d.w.). These levels are in agreement with those reported by [39] . However, as seen in the current studies data, a number of factors may influence the L-theanine content in tea. These include the type of tea, in the current case green or black tea, where green teas have been shown to have higher levels of L-theanine. Indeed, a number of researchers have reported some of the other factors that influence the L-theanine content in tea including; effects of origin, cultivar variety, leaf age, growing area, horticultural practices and plucking season, and the microorganism used for fermentation on metabolites of green tea products [35] [40] - [43] .

The L-theanine of black tea in the current study was 10.2 mg/g in this study and was in agreement with those reported by [41] who report a mean L-theanine content of 9.1 mg/g. Thus, with 50 to 200 mg of L-theanine being reported to reduce blood pressure in animal models [44] and comparing to the L-theanine content of Kenyan green tea it means one should take more than 20 cups of tea in a day. This is not practical but with the Rwandan green tea (1.60% d.w.) it means one should take 2 cups of tea to achieve the health benefits of L-theanine. However, a disturbing revelation of the current study’s findings is the very low L-theanine content of flavoured teas. With L-theanine being solely found in tea (Camellia sinensis), it should be safe to assume that any tea product should contain it. Thus, the current findings possibly imply that these teas majorly contained the flavours and consumption of these teas will be of little or no health benefit.

The levels of L-theanine varied with the type and origin of the tea product studied. Green teas generally contained high levels of L-theanine with flavored teas containing little or no (<0.01%) L-theanine. These data should therefore be used as a basis of setting regulations for the ratios of tea to flavours of “flavoured teas” to ensure that such teas actually contain tea in them. Indeed, this will go a long way in increasing the volumes of tea sold and subsequently consumed.

The authors acknowledge the Tea Research Institute Director for funding and granting us permission to publish this work.

The authors declare none.

JanetToo,JohnWanyoko,ThomasKinyanjui,KelvinMoseti,FrancisWachira, (2016) Quantitative Estimation of γ-Glutamylethylamide in Commercially Available Made Teas [Camellia sinensis (L.) O. Kuntze, Theaceae] in Kenya. American Journal of Plant Sciences,07,55-62. doi: 10.4236/ajps.2016.71006