Green tea leaves have many beneficial health activities including anti-inflammatory, anti-carcinogenic, anti-mutagenic, antioxidative and antimicrobial and hypolipidemic effects[38, 39]. Those beneficial effects are largely originated from the biological effects from L-Theanine as below:
Ingestion of theanine has been reported to facilitate the generation of alpha brain waves, which are associated with a relaxed but alert mental state. In addition, theanine is reported to promote the release of the inhibitory neurotransmitterγ-aminobutyric acid [GABA], which in turn regulates dopamine and serotonin levels in the brain. Thus, theanine consumption has been closely associated with relaxation and improved learning ability.
A recent study found that ingestion of 50 mg of L-theanine dissolved in 100 mL of water could elicit a significant effect on the general state of mental alertness or arousal in subjects by increasing alpha-wave brain activity. Another study also found a link between theanine consumption [200 mg]and the reduction of anxiety. Other studies have shown that consumption of theanine in combination with caffeine could further improve concentration and learning ability. For example, the intake of a combination of 250 mg L-theanine and 150 mg caffeine was found to enhance rapid simple reaction time, fast numeric working memory reaction time and improve verification accuracy during reading tasks. A separate study found that consuming a combination of 100 mg L-theanine and 50 mg caffeine improved both speed and accuracy performance during attention-switching tasks performed 60 min after ingestion and reduced susceptibility to distracting information in memory tasks at 60 and 90 min following ingestion.
Moreover, it is thought that theanine may provide effective prophylaxis and treatment for Alzheimer’s disease as it has been reported to exert neuro-protective effects through inhibition of the N-methyl-D-aspartate [NMDA]subtype of glutamate receptors and its related pathways in a transgenic neuronal cell model.
Theanine has also recently been linked to cancer prevention. Liu et al found that theanine was linked to the inhibition of the in vivo and ex vivo growth of human non-small cell lung cancer and leukaemia cell lines. In another study, Friedman et alfound that theanine intake was associated with the induction of apoptosis in four cancer cell lines of breast, colon, hepatoma and prostate origin.
In addition to enhanced antitumour activity, theanine can reduce the adverse effects of the cancer treatment drug, doxorubicin by providing protection against damage caused by doxorubicin to normal tissue. It also acts as a biochemical modulator to improve the therapeutic efficacy of doxorubicin by suppressing the efflux of the drug from cancer cells, thereby increasing the effective doxorubicin concentration in the tumour.
Recent studies have also found that theanine was linked with regulation of blood pressure, promotion of weight loss and improvement of the immune system[51,53]. Injection of L-theanine at a dose rate of 2 g kg−1 was found to significantly reduce blood pressure in spontaneously hypertensive rats. In humans, consumption of a single dose of 200 mg of theanine was also found to reduce blood pressure and, more importantly, theanine was found to antagonise the negative effect of caffeine increasing blood pressure, when the latter was consumed as a single 250 mg dose.
In addition, co-administration of L-theanine and L-cystine was reported to enhance antigen-specific immunoglobulin G [IgG]production, partly through augmentation of glutathione [GSH]levels and T-helper cell [Th2]-mediated responses. Similarly, co-treatment of L-theanine with L-cystine was found to improve the immune response via an increase in GSH production, which significantly prevented weight loss associated with infection in aged mice.
Sources and synthesis
The tropical and temperate regions of Asian, African, South American countries are considered the main origin of tea plant [C. sinensis or Thea sinensis]. It is a member of Theaceae family. The majority members of Theaceae family are obtained from India, Sri Lanka, China, and Japan. The physiological properties and colour e.g. black, white, green, yellow or oolong tea strongly depends upon the degree of fermentation and processing conditions. L-theanine is mainly derived from a non-edible mushroom of Xerocomus badius, and C. sinensis. It is an amino acid which accumulates in the leaves of tea like C. sasanqua and C. japonica. In tea, L-theanine is responsible for a strong smell [aroma]in general and in particular it is linked with tea umami taste. From the compositional viewpoint, L-theanine comprises approximately 50% of the tea contents. Whereas, the dry tea contains 1–3% of L-theanine only, this higher or lower ratio of L-theanine can vary depending on several factors i.e. cultivation zone, production season, processing techniques, class of tea, time and type of harvest, etc. Additionally, the harvested tea at the beginning of summer is reported to have more theanine compared with tea harvested in late summer. Moreover, L-theanine concentration also depends on the type/class of tea. According to one study, a specific type of C. sinensis var. Sinensis has more L-theanine contents as compared to the C. sinensis var. Assamica. Besides natural L-theanine, the synthetic L-theanine [SuntheanineTM]is also available as a racemic mixture of D- and L-forms of ethylamine and L-glutamine. It is typically obtained from ethylamine and L-glutamine with the use of glutaminase enzyme. Evidently, literature evidences that L-theanine is stable in acidic conditions[25, 26].
Theanine was first chemically synthesised in 1942 by Lichtensteinwith a yield of 90 g kg−1 by treating pyrrolidone-5-carboxylic acid with aqueous ethylamine for 20 days at 37 ?C. A number of other synthetic approaches have since been developed including a large-scale production method involving the reaction of γ -benzyl glutamate in the presence of trityl chloride and ethylamine [339 g kg−1]and a two-step approach involving initial dehydration of L-glutamic acid to L-pyrrolidone carboxylic acid followed by ring opening in the presence of ethylamine to yield theanine [374 g kg−1]. More recently, theanine was produced in four steps starting from commercially available N-phthaloyl-L-glutamic acid, which was dehydrated to the corresponding cyclic anhydride by reaction with acetic anhydride and then the ring was opened by reaction with ethylamine. Subsequent de-protection of the amine unit with hydrazine hydrate gave theanine with a 700 g kg−1 overall yield.
In the tea plant, theanine is bio-synthesised from glutamic acid and ethylamine by the enzyme theanine synthetase. However, the enzyme is very labile and cannot be used to produce the amino acid in commercial quantities. Therefore, other methods for the enzymatic synthesis of theanine have been developed using bacterial enzymes such as glutaminase, glutamine synthetase and γ-glutamyl-transpeptidase.
The enzyme glutamine synthetase and related enzymes, originating from Escherichia coli, Pseudomonas taetrolens.Methylovorus mays , and Bacillus subtilis, have been utilized for the synthesis of theanine from glutamic acid and ethylamine. Unlike the glutaminase biosynthetic pathway discussed previously, this glutamic acid transformation, while using a cheaper and more stable starting material, requires a continuous supply of ATP to drive the reaction. Another non-ATP-dependent biosynthetic pathway, involving γ -glutamyltranspeptidase from E. coli and glutamine as the starting substrate, has also been successfully developed but the reaction requires a high concentration of ethylamine to drive the conversion of glutamine to theanine[31, 36, 37].
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Amino acid analog of glutamine and component of green tea. Shown to bind to AMPA, Kainate, NMDA and group I mGlu receptors. Displays neuroprotective effects in vivo . Promotes self-renewal of human embryonic stem cells (hESC).
White Crystalline Solid
ChEBI: A N5-alkylglutamine where the alkyl group is ethyl. It has been isolated from green tea.
Theanine is an abundant non-protein derived amino acid that was first isolated from green tea leaves in the late 1940s by Sakato
. Theanine has been named as 2-amino-4-[ethylcarbamoyl]butyric acid by the International Union of Pure and Applied Chemistry [IUPAC]. However, it has also been referred to as γ -glutamylethylamide, 5-N-ethylglutamine, γ -glutamyl-L-ethylamide, γ -ethylamino-L-glutamic acid and γ -L-glu-ethylamide.2–5 Similar to other amino acids in nature, theanine is a chiral species and occurs in nature predominantly as the L-[S]enantiomer [Fig. 1], while synthetic theanine is normally prepared as a racemic mixture of L- and D-forms
Theanine is responsible for a unique taste constituent of the tea, producing a caramel flavor and an attractive aroma and that helps to alleviate tea polyphenols astringency and caffeine bitterness
. Technical, safety and toxicological evaluation suggested that theanine is a safe and non-toxic photogenic food supplement. L-theanine was synthesized chemically for the first time from aqueous ethylamine and pyrrolidone carboxylic acid
. L-theanine has been studied as a food additive and functional food in relation to human nutrition. It has noticeable bioactivities including anti-cerebral ischemia-reperfusion injury, stress-reducing, antitumor, anti-aging, and anti-anxiety activities[5, 6]
stated that dietary supplementation of L-theanine is a feasible way to mitigate reactive oxygen species [ROS]-induced damage.
Theanine is considered to be a unique amino acid in nature because, with the exception of being found in the basidiomycete mushroom Xerocomus badius, its occurrence appears to be limited to the Camellia genus, mostly the tea-producing plants C. sinensis var. sinensis and C. sinensis var. assamica and some closely related species such as C. japonica and C. sasanqua
In the leaves of the tea plant species, theanine accounts for about 500 g kg−1 of the free amino acids. Many of these amino acids are involved in producing the distinctive aroma and taste of tea and theanine has been linked with giving tea its distinctive umami taste
Because of its contribution to taste, the theanine content in tea leaves correlates highly with tea quality and price; the teas with a high content of theanine are normally evaluated as having a higher quality and thus command a higher price
. Theanine occurs in the cotyledons, shoots and roots of the tea plant seedling and it is biosynthesized from glutamic acid and ethylamine via the enzyme theanine synthetase
Figure 1 The chemical structure of L-Theanine
A non-protein amino acid mainly found naturally in the green tea plant. It may have activity in modulating the metabolism of cancer chemotherapeutics agents
Theanine, like the protein-based amino acids, exists as a zwitterionic species and is a colorless crystalline solid [needles, melting point 214–216 ?C]. Studies on the buffering capacity of green tea extracts suggest the pKa of the theanine amino group to be[10, 12]. The pKa of the carboxyl unit was not formally quantified due to interference from other acidic species. However, comparisons with close structural analogues such as glutamine suggest the value lies in the range 2.1–2.5 Theanine is stable under acidic conditions but undergoes base hydrolysis to yield glutamic acid and ethylamine[2, 14]. During infusion, theanine does not react chemically with any of the other tea components. This is in contrast to catechins, which can precipitate from solution as a result of π stacking interactions with caffeine[15, 16]or can react with proteins and enzymes such as lipoxygenase, α-amylase, pepsin, trypsin and lipase.
Of the tea components, theanine exhibits a higher water solubility [385 g L−1 at 0 ?C, 556 g L−1 at 100 ?C]than caffeine [21.7 g L−1]and the catechins [e.g. epigallocatechin gallate, 5 g L−1]; this permits a very effective diffusion of theanine from tea during hot-water infusions [2, 17]. The relative insolubility of theanine in organic solvents such as methanol and chloroform allows for its easy separation from caffeine and the catechins, which possess a molecular rather than a zwitterionic structure.
Theanine has a complex umami taste[18-20].It also exhibits a synergism with the common umami flavouring agents monosodium glutamate and the purine nucleoside inosine 5’-monophosphate, which leads to an enhancement of the umami taste experience.The term umami is a Japanese-derived expression and it is classified as the fifth taste after sweet, salt, bitter and sour[19, 20]. Most of the typical umami substances are divided into two groups: L-α-amino acids, usually represented by monosodium glutamate and 5’-ribonucleotides and their derivatives, usually represented by inosine 5’-monophosphate or disodium 5’-guanylate[19, 20].