L-theanine, also named N-ethyl-glutamine, with CAS number of 3081-61-6 and formula of C7H14N2O3, is a amide compound in white or off-white powder with melting point of 214-215℃, is easily dissolved in water, and has an incense of burned sugar and a taste of monosodium glutamate.

    L-theanine in nature only exists in tea plants accounting of 1%～2% of dry tea in free state, and is the main amino acid in tea accounting of some 50% of free amino acids. L-theanine is essential to human body, which can not synthesize and shall be supplied externally.

    Since ancient time, it has been thought that drinking tea may relax tension of human being, but theanine in tea really plays the role and endows tea with the flavor and outstanding relaxation effect. In modern time, human being endures various spiritual tensions, and tea may enable human being to relax.

    Even if it has been known that L-theanine may inhibit caffeine and improve flavor of tea, more important roles have been found by recent years’ research:

    I. Physiological Action

    Lowering blood pressure: Adjustment of blood pressure mainly relies on catecholamine（CA）and
5-hydroxytryptamine (5-HT), and L-theanine may lower the level of 5-hydroxytryptamine (5-HT). Rat experiments
have demonstrated that L-theanine may obviously lower blood pressure; the higher the dose, more obvious the lowering effect. However, rats with normal blood pressure do not have any lowering effect of blood pressure, which has demonstrated that L-theanine may only have lowering impact of blood pressure on rats with high blood pressure.

    Sedation: It is well known that tea contains caffeine having excitation, but human being during tea drinking feels relaxation, sedation, and at ease. It has been proved that it is due to the action of L-theanine.

    Improvement on Learning Capability: L-theanine has outstanding impact on release or reduction of such neurotransmitters as dopamine and 5-hydroxytryptamine (5-HT), which are closely relevant to memory and learning capability, and it has demonstrated that L-theanine has impact on memory and learning capability. Japanese research has showed that L-theanine feeding to rats is adsorbed by intestinal tract and transferred to liver an brain by blood, and after it enters the brain it increases dopamine, the neurotransmitter in brain mitochondria, which is the precursor of adrenalin and noradrenalin, and plays an important role in exciting neuron in brain. Animal experiments have showed that L-theanine has positive impact on memory and learning capability.

    Relaxation: In general, cerebral cortex of animals and human being may produce weak brain waves, which may classified as α, β, δ, and θ waves in accordance with its frequency, and each wave is connected to a certain spiritual state and α wave is relevant to relaxation. Some experiments have showed that, forty minutes after absorption of L-theanine, α wave has been evidently detected in the brain surface, which shows that L-theanine may accelerate the generation of α wave and induce human being into relaxation.

    II. Application in Food

    L-theanine may be used as food additive and used in such products as beverage, biscuits, candy, ice cream, crystal sugar etc. The reason is as follows:

    L-theanine has an effect to improve food flavor: Cacao drink and ptisan etc have peculiar bitterness or sharp taste, but addition of sweetener has caused an unpalatability. Research has showed that beverage flavor will be greatly improved and flavor improvement will be improved in such other foods as coffee, cocoa, ginseng beverage and beer if 0.01% L-theanine is used as an alternative to sweetener.

    L-theanine has a good stability: If beverage containing L-theanine is heated to 121℃ for up to five minutes, L-theanine in the beverage will not be decomposed. In addition, L-theanine is also stable in a media with PH value of 3.0～6.6. If beverage has been stored for one year at 25℃, L-theanine still shows good stability whether the solution is neutral (PH=6.5) or acidity (PH=3.0).

    L-theanine may accelerate the generation of α wave of brain: α wave may maintain human being at awake, sensitive, and relaxed state of body and spirit. L-theanine will not add any θ wave, so its addition to various foods will not induce any feeling of drowsiness. In accordance with impact of L-theanine on α wave, 50～200 mg L-theanine may have relaxation, and may also have obvious effect on relaxation of being instable emotionally.

    Most of health foods available in the market are disease-preventive or improvement varieties for adults, but it is rare and remarkable that L-theanine does not have hypnosis, but relieve fatigue, lower blood pressure and improve learning capability and memory. Therefore, L-theanine was awarded in International Foods Raw Materials Conference 1998 held in Gemerny. In accordance with survey conducted by authority, L-theanine was the top seller in 2002 among natural anti-cancer or immune enhancement health foods well sold in international pharmaceuticals and health foods.

    III. Medical Application

    Dr. Bukowski and its team from Harvard Medical School recently published a research paper on Proceedings of national Academy of Sciences, which says that L-theanine obtained form such teas as green tea, Wu-lung tea may enhance immune system capability to resist attack from germ, viruses, and epiphyte. The team conducted experiment on volunteers, which has demonstrated that L-theanine may increase human resistance from contagious diseases by five times, and effectively prevent disease-causing microorganism from invasion.

    L-theanine may improve learning capability and memory of brain, have preventive effects against parkinson disease, climacteric syndrome, senile dementia, neuro-malfunction disease, have an effect of cardiac diuretic and hemangiectasis, and is beneficial to prevent hepatic coma, dysmnesia, and hypophrenia.