Review
L-theanine—a unique amino acid of green tea and its relaxation effect in humans

https://doi.org/10.1016/S0924-2244(99)00044-8Get rights and content

Abstract

Since ancient times, it has been said that drinking green tea brings relaxation. The substance that is responsible for a sense of relaxation, is theanine. Theanine is a unique amino acid found almost solely in tea plants and the main component responsible for the exotic taste of ‘green’ tea. It was found that L-theanine administered intraperitoneally to rats reached the brain within 30 min without any metabolic change. Theanine also acts as a neurotransmitter in the brain and decreased blood pressure significantly in hypertensive rats. In general, animals always generate very weak electric pulses on the surface of the brain, called brain waves. Brain waves are classified into four types, namely α,β,δ and θ-waves, based on mental conditions. Generation of α-waves is considered to be an index of relaxation. In human volunteers, α-waves were generated on the occipital and parietal regions of the brain surface within 40 min after the oral administration of theanine (50–200 mg), signifying relaxation without causing drowsiness. With the successful industrial production of L-theanine, we are now able to supply Suntheanine™ (trade name of L-theanine) which offers a tremendous opportunity for designing foods and medical foods targeting relaxation and the reduction of stress. Taiyo Kagaku Co., Ltd, Japan won the 1998 ‘Food Ingredient Research Award’ for development of Suntheanine™ at Food Ingredients in Europe (Frankfurt). The judges felt it was a particularly well-documented and fascinating piece of research.

Section snippets

Physiological activity of theanine

Theanine has been known to act antagonistically against paralysis induced by caffeine. It has been revealed that theanine was absorbed quickly in the intestinal tract and showed characteristic physiological activities.

Industrial preparation of theanine

L-theanine is synthesized naturally from glutamic acid and ethylamine in the root and transferred to the young leaves of the tea plant [17]. Many attempts have been made to produce theanine commercially. However, most of them have remained unsuccessful, because of low yields, high cost, or highly complicated processes 18, 19, 20, 21. We have succeeded in developing an enzymatic method to manufacture theanine on an industrial scale.

Application of Suntheanine™

L-theanine can be used for many kinds of food applications, for example, beverages, cookies, candies, ice creams and ice candies.

Conclusion

Since ancient times, it has been said that drinking green tea induces relaxation. We investigated this particular effect. It was confirmed that besides its effect of giving flavor to green tea, Suntheanine™ also had a noticeable relaxation effect.

Most people in modern times who live especially in urban areas are exposed to many kinds of mental pressures.

Suntheanine™ would be an effective way of linking food ingredients to make people feel relaxed.

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