Analysis of theanine, glutamic acid, aspartic acid and arginine in tea
Tea contains about 1% to 4% of amino acids, the main amino acids are theanine, glutamic acid, aspartic acid and arginine. Theanine, in particular, is almost unique to tea, accounting for 1% to 2% of the dry matter of tea and about 50% of all amino acids. Therefore, when discussing the amino acids of tea, the main research is on theanine.
Theanine (L-theanine) is primarily found in the leaves of Camellia sinensis and has been widely studied for its unique bioactive properties contributing to both tea quality and health benefits (Vuong et al., 2011).
Amino acid is a very important metabolite of the nitrogen cycle. Nitrogen nutrients are absorbed by the roots, and then transported to the buds and leaves and other parts of the tea tree, and the tea tree grows taller. Meanwhile, more and more natural amino acids will be accumulated, which are discovered and used by people. Amino acids in tea not only reflect the supply and transformation of tea tree nutrition, but also have a direct and important impact with the quality of tea. It is almost indispensable.
Higher free amino acid content, especially theanine, is associated with premium tea quality and is often used as a marker in tea grading (Chen et al., 2020).
Most amino acids in tea are fresh, refreshing and sweet, and some are slightly sour. If the content of amino acids in the tea is high, the taste will be fresh, refreshing and sweet. If the content of tea polyphenols with pungent taste is also appropriate, then the taste will be mellow.
The balance between free amino acids and polyphenols determines the umami and bitterness profile of tea infusions (Narukawa et al., 2010).
Detection of the content of the free amino acids in tea, mainly focus on theanine, which is used to measure the quality of tea.
Quantitative analysis of theanine and other amino acids is typically carried out by HPLC with pre-column derivatization using reagents such as o-phthalaldehyde (OPA) (Zhu et al., 2016).
The main effects of theanine:
Depression treatment
At present, theanine has been used to treat depression, which is the most common psychosis in the world. It is estimated that more than 100 million people in the world suffer from different degrees of depression, and the incidence of depression is as high as 1.5%. At present, western antidepressants, such as sertraline and paroxetine, are mainly used to treat depression. Although these drugs can effectively control the symptoms of depression, the side effects such as drowsiness, blurred vision, and high blood pressure are very obvious. If used for a long time, especially in large doses, it will cause great harm to patients. Drugs made with theanine can avoid these side effects. Health products manufacturers in the United States, Japan and other countries have developed and marketed a number of pure natural antidepressant capsules, whose major constituent is theanine and helper constituents are natural sedatives such as pineapple root extracts and hypericin. These capsules have a remarkable curative effect and have no side effects after long-term use.
Clinical studies have shown that L-theanine supplementation may reduce symptoms of anxiety and depression, likely due to its effects on neurotransmitter modulation (Hidese et al., 2019). At this point it is important to accentuate that L-Theanine should not be seen as an appropriate drug for the treatment of depression. For health and medical issues it is highly recommended to consult a proper doctor or psychiatrist.
Protecting nerve cells
Theanine can inhibit the death of nerve cells caused by transient cerebral ischemia and has a protective effect on nerve cells. The death of nerve cells is closely related to glutamate, an excitatory neurotransmitter. The excess of glutamate will lead to the death of nerve cells, which is usually the cause of diseases such as Alzheimer’s. Theanine and glutamic acid are similar in structure and will compete for binding sites, thereby inhibiting the death of nerve cells. Theanine may be used for the treatment and prevention of brain disorders such as strokes like cerebral embolism and cerebral hemorrhage, blood deficiency during brain surgery or brain injury and senile dementia.
Experimental models suggest that theanine provides neuroprotective effects by antagonizing glutamate receptors and reducing oxidative stress (Kakuda, 2011).
Enhancing the efficacy of anti-cancer drugs
The incidence and mortality of cancer remain high, and drugs developed for the treatment of cancer often have strong side effects. Therefore, in cancer treatment, a variety of drugs that inhibit the side effects of anti-cancer drugs should also be used. Theanine itself has no antineoplasmic activity, but it can improve the activity of many antitumor drugs. When used in combination with antitumor drugs, theanine can prevent antitumor drugs from flowing out of tumor cells and therefore enhance the anti-cancer effect. Theanine can also reduce the side effects of antitumor drugs, such as regulating the lipid peroxidation level and relieving the reduction of white blood cells and bone marrow cells. Theanine also has the effect of inhibiting the infiltration of cancer cells, and infiltration is a necessary way for cancer cells to spread, therefore theanine can inhibit the spread of cancer.
Preclinical studies suggest that theanine enhances the cytotoxicity of chemotherapeutic agents like doxorubicin while reducing damage to healthy tissues (Tsuneki et al., 2004).
Sedation
Caffeine is a well-known stimulant, but people feel relaxed, calm and happy when drinking tea. It has been confirmed that this is mainly the effect of theanine.
L-theanine has been shown to modulate alpha brain waves, promoting a relaxed but alert mental state when combined with caffeine (Gomez-Ramirez et al., 2007).
Regulating neurotransmitters in the brain
Theanine affects the metabolism and release of neurotransmitters such as dopamine in the brain, and brain diseases caused by these neurotransmitters may also be regulated or prevented.
L-theanine modulates dopaminergic and serotonergic signaling pathways, contributing to its mood-enhancing and anxiolytic properties (Nathan et al., 2006).
References:
- Vuong QV, Bowyer MC, Roach PD. “L-Theanine: properties, synthesis and isolation from tea.” J Sci Food Agric. 2011;91(11):1931-1939.
- Chen Q, et al. “Amino acids in tea leaves as quality indicators.” Food Chem. 2020;334:127539.
- Narukawa M, et al. “Taste characteristics of (L)-theanine and its synergistic effect with other Umami substances.” Chem Senses. 2010;35(8):693-700.
- Zhu Y, et al. “Simultaneous determination of theanine and free amino acids in tea by HPLC.” Food Anal Methods. 2016;9:2493-2501.
- Hidese S, et al. “Effects of L-theanine on stress-related symptoms and cognitive functions in healthy adults: a randomized controlled trial.” Nutrients. 2019;11(10):2362.
- Kakuda T. “Neuroprotective effects of theanine and its preventive effects on cognitive dysfunction.” Pharmacol Res. 2011;64(2):162-168.
- Tsuneki H, et al. “Enhancing effect of theanine on antitumor activity of doxorubicin.” Biol Pharm Bull. 2004;27(5):773-775.
- Gomez-Ramirez M, et al. “The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness.” Nutr Neurosci. 2007;10(4-5):191-198.
- Nathan PJ, et al. “The neuropharmacology of L-theanine (N-ethyl-L-glutamine): a possible neuroprotective and cognitive enhancing agent.” J Herb Pharmacother. 2006;6(2):21-30.