Biochemistry Of A Tea Leaf by AN SHIM TEA


Tea (Camellia Sinensis) is the most complex and diverse plant speaking about its chemical composition. The total number of compounds included in its composition is about 300. Some of them have not yet been identified, and the biochemical role of some of them is defined only in general terms. By the way, the chemical composition of freshly picked green tea leaf and dry tea obtained from this leaf is not the same. Dry tea has a more complex chemical composition, which is formed during its processing.

In the tea leaf, there are three main groups of phytochemicals: alkaloids, flavonoids, and tannins.

are nitrogen-containing heterocyclic compounds with high functional activity, which include three main compounds: caffeine, theobromine, and theophylline. There is more caffeine in tea than coffee, but its effect is softer. This is because caffeine in tea is associated with tannin and forms theine. Theine gives bitterness to tea and has a tonic effect on the body, improves mental performance, increases activity, and stimulates the cardiovascular and central nervous systems. Different teas contain a different percentage of caffeine from 1 to 5%. Being associated with tannin, caffeine is eliminated faster from the body than a pure alkaloid, which eliminates the danger of caffeine poisoning with frequent use of tea. There is evidence that theine, which forms in tea leaves during the growth of plants, is contained in large quantities in high-quality varieties of green tea from the first(spring) harvest. In addition to theine, tea contains minor amounts, about 0.5% (by weight) of dry tea leaves, other alkaloids: theobromine and theophylline, which have a vasodilator and diuretic effect.

Along with the beneficial alkaloids, tea contains guanine, which upon prolonged heating or prolonged standing of brewed tea can turn into guanidine, which has a toxic influence.

are represented in tea mainly by catechins, which determine the quality and beneficial properties of a tea drink, especially green tea. The more polyphenols in dry tea, the higher the quality of the infusion: and the better the color, astringency, and aroma of the drink. Tea leaf’s catechins reduce the fragility and permeability of capillaries, normalize human tissue respiration, prevent the development of atherosclerosis, take an active part in the metabolism of complex proteins, affect the activity of enzymes, especially the enzyme telomerase, which regulates cell division processes. Green tea epigallocatechin gallate increases the activity of the main enzymes of osteogenesis, increases bone mineralization, and blocks the activity of osteoclasts. It is effective in sepsis and rheumatoid arthritis. In addition, tea catechins are powerful antioxidants that neutralize the action of free radicals. They contribute to the binding of various toxic substances and their removal from the body. Have astringent and bacteriostatic effects. Catechins inhibit the development of diseases such as Alzheimer's and Parkinson's. Currently, tea bioflavonoids have a wide range of pharmacological properties, such as immunostimulating, cardio, radio, hepatic, neuroprotective, antithrombotic, antiallergic, antitumor, and antiviral.

Tea is one of the richest sources of antioxidants. In green tea, catechins make the main contribution to antioxidant activity, and in black tea, theaflavins and thearubigins. Due to antioxidant properties, black and green teas effectively inhibit the development of atherosclerosis.

are a mixture of polyphenolic compounds and their derivatives. They prevent the development of oncological processes, lower blood pressure, and have antimicrobial, disinfecting, and antioxidant effects. White and green teas are the richest in tannins. One of the representatives of tannins is tannin or teotannin. Its content in green tea is two times more than in black. The oxidation products of tannins - quinones, formed during the processing of tea, oxidize other substances of the tea leaf and form aromatic products involved in the creation of tea aroma.
Tea saponins, called tea saponins, have antioxidant and antimicrobial effects. Recently it has been established that this group of phytochemicals of tea has antiallergic, hypotensive, anti-inflammatory, lipid-lowering, and anti-carcinogenic effects. The research suggests new aspects of the use of tea in the prevention of several pathological processes.
An important amino acid of tea is theanine, which provides the taste of green tea: sweetish and savory. In tea, there are almost all the most important vitamins. In particular, it contains provitamin A-carotene, which provides the functional state of the mucous membranes of the eye, nose, pharynx, larynx, and respiratory tract; B vitamins, contributing to the normal functioning of the endocrine glands, nervous system, as well as improving the condition of skin and hair. Ascorbic acid, which has an antimicrobial anti-inflammatory effect, stimulates the immune system, and the body's defenses, and affects the synthesis of proteins in the connective tissue and blood formation. Green tea contains 2-3 times more vitamin C than lemons and oranges. Fat-soluble vitamins A, K, D, and E are found in the tea leaf extraction oil. Essential oils are also found in tea. Despite their extremely small amount, they are the reason for a unique tea aroma. Tea contains various macro and microelements. These are iron, manganese, magnesium, sodium, silicon, calcium, potassium, phosphorus, and also microelements such as iodine, fluorine, copper, gold, and some others. All of them, being in the form of a colloid, dissolve in water and enter the tea infusion.

The taste of tea consists of sweet, sour, bitter, umami, and astringent. Poly-amino acids are the main component of umami taste. Phenols and especially catechins are a source of astringency. Soluble carbohydrates and some amino acids contribute to sweetness. The bitter substances are mostly purine bases, especially caffeine and anthocyanins. Sourness is given by organic acids. The quantity and proportions of these components determine the taste of tea infusion.