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Green Tea, Health  |  10.19.2019  |  By C. Yu

Health Benefits of Sencha Japanese Green Tea


Sencha or Japanese Green tea has a unique taste and flavor, which some might consider astringent or bitter. Over the years, research has shown the tea contains many nutrients that are believed to have a positive impact on human health.

What is the difference between sencha and other teas? In Japanese Green tea, the heat from steaming stops the action of the oxidative enzymes in the early stages of the manufacturing process, so polymerization of catechins (so-called coalescence) rarely occurs and the number of catechins is not reduced. On the other hand, in Chinese tea (oolong tea) and black tea, the oxidative enzymes change the components in the tea leaves, giving them a unique flavor and aroma. In addition, polymerization of catechins occurs and the number of catechins decreases.

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What are catechins?

Catechins are a type of polyphenol and are the main ingredient in Sencha green tea, which has been called tannin since ancient times. The word “catechin” is derived from the sap of the Acacia catechu, a shrub of the Acaciaceae family from India. The catechins in tea were first identified in 1929 by Dr. Tsujimura and his colleagues at RIKEN. There are four types of catechins with different shapes in tea leaves:

  1. Epicatechin
  2. epigallocatechin
  3. epicatechin gallate
  4. epigallocatechin gallate

In addition, during the process of producing tea beverages, the form of some of the tea beverages is changed by the heat treatment.

  • Epicatechin => Catechin.
  • Epigallocatechin => Gallocatechin
  • Epicatechin gallate => Catechin gallate
  • Epigallocatechin gallate => Gallocatechin gallate

Catechins are very susceptible to oxidation. Sencha green tea is hardly oxidized because the oxidizing enzymes are suppressed during the rough tea production process. However, in oolong tea and black tea, oxidative polymerization products (so-called coalescing catechins, including theaflavins and thearubidins) are made by the oxidizing enzyme. Then the catechins, which are normally colorless, turn from orange to red. This is why oolong tea and black tea have a reddish color.

Studies have shown that catechins increase by about 12-14% in the first steep tea and 14-15% in the second steep of tea. Catechins are also more abundant in the young shoots than in the mature leaves. Tea grown under cover, such as Gyokuro, produces fewer catechins than Sencha (about 10% polyphenols).

In addition, theanine is produced in the roots of the tea plant and is transferred to the leaves. When theanine is exposed to light, it decomposes to make ethylamine, which is converted to catechins. Theanine must be exposed to light to decompose, so when grown under cover, theanine content is high and the production of catechins is reduced. Shade-grown green tea like Matcha and Gyokuro contain a high concentration of theanine, which supports mental function and is often used for anxiety, mental impairment, stress, and other conditions, though there is no scientific evidence to support these uses.

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What is the amino acid, theanine, in tea?

Amino acids contribute to the flavor of tea, and more than half of the amino acids in tea are theanine. Other amino acids in tea leaves include glutamic acid, aspartic acid, arginine, and serine, and it is thought that in addition to these amino acids, organic acids and polyphenols contribute to the overall flavor of the tea.

Theanine is an amino acid unique to tea, found abundantly in the Camellia Sinensis plant. It is more abundant in the early young shoots of the first tea than in the second tea and is greatly reduced in the mature shoots. In addition, when grown covered (not exposed to sunlight) like Matcha and Gyokuro, the formation of amino acids to catechins is suppressed, so the tea leaves remain rich in theanine. For this reason, new tea like Shincha, Matcha, and Gyokuro tea is especially rich in flavor, while a tea-like Bancha has a lighter taste.

The caffeine concentration in tea leachate is about 0.01 to 0.02%, which means that a cup of tea will give you 15 to 30 mg of caffeine. This amount of caffeine should have a fairly strong excitation effect, but it actually stays at a mild effect. This is due to the theanine’s ability to inhibit caffeine excitation, and it is the natural wonder of the tea’s ability to turn a dramatic action into a moderate action.

Cellular experiments have shown that theanine has a protective effect on the nerve cells in the brain. Also, when measuring the brain waves of people who drank theanine, it was found that the alpha wave, which appears more frequently in a relaxed state, increased (according to a survey conducted by the Central Research Institute in Japan. Sencha green tea is thought to be effective in improving athletic performance and endurance, due to caffeine using fat as an energy source). On the other hand, because ammonia is a waste product that increases during exercise, arginine, which promotes ammonia metabolism, and theanine, which has a relaxing effect, are thought to effectively reduce fatigue by combining these ingredients.

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Vitamins and other nutrients in green tea

Vitamins, carbohydrates, fats, proteins, and minerals are called the five macronutrients, and since vitamins are essential nutrients and cannot be made in our bodies, they must be obtained from food and other sources. There are thirteen types of vitamins: water-soluble vitamins and fat-soluble vitamins that are soluble only in oil. Lack of even one of these 13 vitamins can lead directly to skin irritation, numbness in the hands and feet, lethargy, and fatigue. Sencha green tea is known to contain many more vitamins than other foods, and it is also known for its high content. This alone makes tea an excellent beverage. Note that many oolong and black teas do not contain any vitamins, and most of the vitamin C and other vitamins are lost during the manufacturing process.

Vitamin C is necessary for the collagen production process. Therefore, when vitamin C is deficient, the formation of collagen fibers is impaired, blood vessel walls become weak, and scurvy occurs. Vitamin C is also thought to have an important role in preventing lifestyle-related diseases, including cancer, because of its antioxidant properties. Sencha green tea contains the highest amount of vitamin C of all teas, about 1.5 times as much as red peppers, which contain the most vitamin C of all vegetables. Oolong tea, on the other hand, contains only a small amount of vitamin C and black tea does not contain any. Other common vitamins in tea include:

  • Saponin: Saponin is found in all types of teas and is characterized by its frothy nature, as seen in Matcha and other teas. It is contained in about 0.1% of tea leaves and has a strong bitterness and a bitter taste. Saponin is confirmed to have antibacterial and antiviral effects.
  • Fluorine: Fluoride is found in the Camelliaceae family of plants, generally in the mature leaves rather than the young shoots, and most abundantly in Bancha. It forms an acid-resistant coating on the surface of the teeth, making it effective in preventing tooth decay.
  • Minerals (potassium, calcium, phosphorus, manganese, etc.): Minerals have an important role in biological regulation. The tea contains about 5-7% of minerals, mostly potassium (K), calcium (Ca), phosphorus (P), and magnesium (Mg), but also contains small amounts of manganese (Mn), zinc (Zn), and copper (Cu).
  • Chlorophyll (Chlorophyll): Chlorophyll is the green pigment in plants and plays an important role in photosynthesis. Gyokuro and kabushige teas, which are grown under cover, produce large amounts of chlorophyll in order to more effectively absorb low levels of light. As a result, gyokuro and kabushige teas take on a deep, dark green color. Because chlorophyll also has a deodorizing effect, it is used in chewing gum and other products.
  • Fragrance ingredients: There are many types of fragrant substances in tea, from 200 types of sencha green tea to more than 600 types of black tea and oolong tea. However, the amount of aromatic substances, called essential oil, is very small, about 0.005% in green tea and 0.02% in black tea.

Normally, fresh tea leaves have little fragrance, but when the tea leaves are harvested, enzymes work to break down the components of the tea leaves and produce the fragrance. However, in the case of sencha green tea, fermentation is stopped immediately after plucking, so the production of fragrant components is minimal. The fragrance of the tea is enhanced by the heat-roasting process, where the amino acids and sugars react with the heat to produce a fragrant fragrance called hika, which is produced when the tea is heated.

In the case of roasted tea, such as Hojicha, a lot of heated aromatic compounds, which are aromatic, are produced during the roasting process, resulting in a savory flavor. In oolong and black tea, the fragrance components are formed during the fermentation process after the tea is harvested. The fruity aroma of Tieguanyin, the muscat flavor of Darjeeling black tea, and the sweet rose-flower and fruit aroma of fine teas are all formed during the fermentation process. The unique fragrance of these fermented teas is volatile at high temperatures. This is why boiling water is always used when enjoying oolong and black tea.

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