Green tea offers an array of unique taste sensations, including astringency, bitterness and full-bodied flavor. Green tea also comprises a large number of components that are said to be beneficial to human health. These components have a diverse range of effects.
Catechins are a type of polyphenol and are the main astringency component in green tea, long known as tannins. Catechin was first isolated from the Indian plant extract catechu (from the plant acacia catechu, a tree of the fabaceae family, acacia genus), from which it derives its name. Tea catechin was first isolated by Dr. Michiyo Tsujimura in 1929 at RIKEN (The Institute of Physical and Chemical Research) in Japan. There are four main types of catechins found in tea leaves.
Catechins oxidize extremely easily. In green tea, since the process for making crude tea involves halting the action of oxidizing enzymes, most of the catechins remain unoxidized. In oolong and black teas, the action of oxidizing enzymes produces oxidized polymers (complex catechins, such as theaflavins and thearubigins).Unlike catechins, which are colorless in aqueous solution, these oxidized catechins become orange or red. This is what gives oolong and black teas their distinctive reddish color. Ichibancha has a catechin content of approximately 12-14%, while Nibancha has a catechin content of approximately 14-15%. The catechin content of young shoots (first or second leaf) is higher than mature leaves (third or fourth leaf). In teas that have been grown using cover culture to block out most light, such as Gyokuro, the generation of catechins is suppressed, giving such teas a lower catechin content than Sencha (approximately 10% as polyphenols). Theanine is produced in the roots of the tea bushes, and migrates to the leaves. Theanine is broken down when exposed to light, producing ethylamino, which in turn changes into catechin. Since theanine does not break down if it is not exposed to light, teas high in theanine and low in catechin may be produced by using covered culture.
Drinking tea when tired from work or study can make a person feel refreshed. This is an effect of caffeine, which is present in tea. Although there is not a great difference in caffeine content depending on the period in which the tea is picked, such as between Ichibancha and Nibancha, similar to catechin and amino acid (theanine), there is a higher caffeine content in young shoots and mature leaves tend to contain less. Among teas that have been roasted at high temperature, such as Hojicha, the caffeine is sublimated (changed directly from a solid to a gaseous state) and is said to decrease. The main effects of caffeine include increased alertness and a mild diuretic effect. Since caffeine has a stimulant effect on the central nervous system (CNS), it can ward off drowsiness and increase the capacity for mental or physical labor. If one consumes caffeine and then does a moderate amount of physical exercise, before the muscles’ internal energy source (glucose or glycogen) is used, there is a phenomenon whereby fat is used as an energy source, thereby helping enhance stamina. Furthermore, tea is said to be effective for preventing hangovers. This is also an effect of caffeine, whereby alcohol is metabolized more rapidly. Historically, it is thought that tea has was adopted as a preferred drink by humans owing to the refreshing effects from caffeine.
Amino Acid (Theanine)
Tea has unique characteristics of full-bodied, rich flavor (Umami) and sweetness. Simultaneously, it also has a relaxing effect. A type of amino acid called theanine are largely responsible for these characteristics. Amino acids are the component in tea that contributes full-bodied flavor and sweetness. Of these amino acids, more than 60% are theanine, which is unique to tea. Theanine has a structure similar to that of glutamine, with its particular trait being a refined, rich flavor and sweetness. Amino acids other than theanine present in tea leaves include glutamine, asparagine, arginine and serine. Theanine is present in the tea plant (Camellia sinensis), other camellia and sasanqua but does not occur in any other plants. The theanine content of Ichibancha is higher than Nibancha, and even within Ichibancha, the theanine content of younger shoots is higher. In mature leaves, the theanine level drops away dramatically. If tea is grown using cover culture (shaded from sunlight), as is the case with Gyokuro, the generation of catechins from amino acids is suppressed, resulting in a high theanine content in the tea leaves. Consequently, Shincha and Gyokuro have a rich, full-bodied flavor (Umami), whereas Bancha has a much lighter flavor. The caffeine content of infused tea beverage is approximately 0.01-0.02%. This translates to approximately 15-30mg of caffeine per cup of tea consumed. Although this amount of caffeine should result in a very strong stimulant effect, in fact, the stimulant effect is quite gentle. The reason for this is that theanine acts to limit the stimulant effect of caffeine. Thanks to this property, a potentially dramatic stimulant effect is instead transformed into a moderate effect. This may be regarded as one of the excellent natural attributes of tea. In experiments on animals, theanine has shown properties for suppressing high blood pressure and protecting central nervous system cells. Measurements of the brain waves of people who have consumed theanine reveal that there is an increase in α-waves (according to research by the ITO EN Central Research Institute), which are produced particularly when a person is in a relaxed state.
Vitamins have various effects on the human body. Although vitamins are essential nutrients, they cannot be produced within the body. Regularly drinking green tea, which is full of vitamins, is good for your health. Vitamins, along with saccharides, lipids, proteins and minerals, are one of the five primary nutrients used by the body. Although vitamins are essential nutrients, they cannot be produced within the human body, and must be acquired through food. There are 13 types of vitamins, which are classified into water-soluble vitamins, which dissolve in water, and fat-soluble vitamins, which only dissolve in fat. A deficiency in even one of these 13 vitamins can result in skin disorders, numbness in the hands and feet, sluggishness and fatigue. Green tea is known for having more vitamins in higher concentrations than other foods, and this fact alone makes tea a superior beverage. Many types of oolong and black tea contain few vitamins, with Vitamin C and other vitamins mostly lost during the production process.
Vitamin B2 is essential for regular development. A deficiency in Vitamin B2 can result in cracked and red lips and inflammation of the mouth and tongue. One hundred grams of Sencha includes around 1.4mg of Vitamin B2, more than 4 times that of parsley, spinach and Jew’s marrow, which have some of the highest concentrations among foods.
Vitamin C is a necessary nutrient in the production of collagen. Vitamin C deficiency results in lost formation of collagen fibers, weakening vascular walls and causing scurvy. Vitamin C also acts as an antioxidant and is believed to play an important role in the prevention of lifestyle-related diseases such as cancer. Sencha contains the most Vitamin C of any tea, around 1.5 times that of red peppers, which have one of the highest concentrations among vegetables. In contrast, oolong tea contains very little Vitamin C and black tea contains none at all.
The nutrient folic acid assists in the formation of red blood cells, and pregnant mothers are recommended to take it as it acts to prevent the onset of fetal neural tube defects (NTD). Its relationship to the prevention of arterial sclerosis, colon cancer, dementia and Alzheimer’s Disease is also becoming clear, making it the most studied vitamin in recent years. Green tea (Matcha and Sencha) contains more than five times the folic acid of spinach or parsley, and around the same amount as dried seaweed, which has one of the highest concentrations of any food. Black tea contains only a small amount of folic acid.
β-carotene is absorbed through the intestinal walls and is then converted mainly by the liver to Vitamin A as necessary, in effect acting as the precursor of Vitamin A (pro-Vitamin A). Vitamin A aids in the maintenance of night vision, and among teas β-carotene is found in particularly high quantities in Matcha, which contains five times the β-carotene of carrots.
Vitamin E has been shown to act as an antioxidant that works to protect lipids within the body from oxidizing. Cells are made up of fat-soluble and water-soluble parts, and Vitamin E works in the fat-soluble part of the cell. Sencha contains around 32 times the Vitamin E found in spinach and around two times that found in chili peppers, and hardly any foods have it in higher concentration. However, as Vitamin E does not dissolve in water, it is best taken through powdered green tea or Matcha.
Saponins and Other Components
Tea is effective in preventing tooth decay and high blood pressure, as well as bad breath and other health problems. This is due to the different components found in tea.
Saponins are found in all teas, and result in the frothing seen in teas like Matcha. Tea leaves contain around 0.1% saponins, which give it its strong bitterness and astringency.
Saponins have anti-fungal, anti-inflammatory, and anti-allergy properties and have been shown to lower blood pressure and prevent obesity and influenza (according to studies by the ITO EN Central Research Center).
Fluorine is found in large quantities in the plant Camellia japonica, and in general mature leaves contain more fluorine than younger leaves, with Bancha containing the most fluorine among teas. It forms the acid-resistant outer layer on the teeth’s surface and is effective in preventing cavities.
γ-aminobutyric acid （GABA）
GABA is formed when raw leaves are left without oxygen. These are processed into dry tea leaves to make Gabalong tea. GABA contains elements that have been reported in animal testing of Gabalong tea to reduce blood pressure.
Minerals play an important role as bodily regulators. Tea contains around 5-7% minerals, mainly potassium (K), calcium (Ca), phosphorus (P), and magnesium (Mg), as well as small quantities of manganese (Mn), zinc (Zn) and copper (Cu).
Chlorophyll is the component that gives plants their green color and plays an important role in photosynthesis. In teas that have been grown using cover culture to block out most light, such as Gyokuro and Kabusecha, the tea tries to make the most of the limited light available, resulting in higher levels of chlorophyll. This results in the deep green color of Gyokuro and Kabusecha. The deodorizing effect of chlorophyll has led it to be used in chewing gum.
Tea contains an immense number of fragrance components, with around 200 in green tea and more than 300 in black tea. However, the essence, or “Seiyu” that makes up the tea’s fragrance occurs in very small quantities, only around 0.005% in green tea and 0.02% in black tea. Raw tea leaves contain very little fragrance, but when harvested, enzymes work to disperse the individual tea leaf components and release their fragrance. However with green tea, as the fermentation process is halted soon after harvest, the fragrance has little time to develop, and as much of the fragrance is released during the tea leaf production process, the tea is left with a very delicate fragrance. The fragrance of teas is developed through the heating process, where the amino acids and saccharides react to the heat to form the tea’s wonderful fragrance. Vitamin U is also created during the heating process of Gyokuro, Tencha and high-grade Sencha. Vitamin U is a key ingredient in gastrointestinal drugs and is an effective against gastric ulcers. The distinctive “green laver aroma” of high-grade teas is created with the release of Vitamin U. With Hojicha, many fragrance components are released during the roasting process, resulting in an aromatic taste. The fragrance components of oolong tea and black tea are created during the fermentation process following harvest. The fruity aroma of the tekkannon variety of oolong tea and the muscat aroma of darjeeling black tea, as well as the sweet rosy or fruity aroma of high-grade black teas, are all created in the fermentation process. The unique fragrance of fermented teas such as these is realized through high temperatures. This is why oolong tea and black tea are most delicious when enjoyed hot. The fragrance of tea helps people to relax and relieve stress, making tea desirable as a sort of aroma therapy.