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.
In addition, during the manufacturing process for tea beverages, owing to heat processing, some catechins change form.
Epicatechin → Catechin
Epigallocatechin → Gallocatechin
Epicatechin gallate → Catechin gallate
Epigallocatechin gallate → Gallocatechin gallate
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 proper