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The human body is composed of about 7x1027 atoms, of which 4.2x1027 are hydrogen. A hydrogen atom consists of two particles, a proton and an electron. Hydrogen is not found without its electron in ordinary chemistry, as ionized hydrogen is highly chemically reactive. Since the nucleus of an atom is always surrounded by a cloud of electrons in pairs for the atom to be stable, pure hydrogen atom usually exists in pair so that each proton will share a pair of electrons. In the human body, hydrogen is usually combined with oxygen, carbon and nitrogen to form various molecules, including water. In a living cell, energy-producing reactions must take place, involving the transfer of hydrogen atoms or electrons from one molecule to another, known as biological oxidation, in fact initiated by dehydrogenation of the foodstuffs, such as the carbohydrates.
In biological oxidation, the
electrons are brought to the electron transport chain by NADH.
The electron transport chain consists of carriers, including flavoproteins, cytochromes, and ubiquinones. The electrons are passed from one carrier to the next while energy is being produced. The final electron acceptor is irreversibly reduced; it may be oxygen (aerobic oxidation) or another inorganic molecule (anaerobic oxidation). The normal electron transport chain from NADH to oxygen can be illustrated schematically as follows (Midlandtech.Edu.)
During the process of biological oxidation, many atoms will lose an electron temporarily, leaving the atom with an unpaied electron, so that they will take up an electron from an upstream atom, called an electron donor in this normal flow chain of electrons. However, the atom with an unpaired sometimes can rob an electron from a nearby atom which is not in the normal flow chain of electron transportation. Then the molecule containing an atom with an unpaired electron, which is not confined in the normal electron transport chain, is called a “free radical” because it is very reactive and tends to rob another electron from any of its neighboring atoms to make up its electron number in pair. This type of uncontrolled oxidative process (losing an electron) will initiate a free radical chain reaction, which is damaging to the cellular structures, including the DNA in our genes, and is part of the aging process, including cancer formation. Heavy metals, even iron, catalyze the free radical chain reactions several thousands times.
What is 10EGCG® green tea? It is a tea beverage that contains at least 710 mcg/ml (-)epigallocatechin gallate (EGCG). This represents the chemical antioxidant level that the National Cancer Institute (NCI) defines as “typical” green tea used in cancer research and in potential cancer controls. Based on laboratory studies and human data observed in traditional green tea-drinking populations, the NCI calculated the lowest effective anticancer dose in an average adult to be an equivalent of 800 ml per day of this "typical" green tea. Many cancer experts recommend daily consumption of 1.5 times this dose for chemoprevention. Since 1% of dry tea leaves in hot water is customarily used to brew green tea, the typical dry green tea leaves must contain at least 7.1% extractable EGCG in dry weight to meet this NCI standard. [Reference: NCI, DCPC, Chemoprevention Branch and Agent Development Committee, Clinical development plan: tea extracts green tea polyphenols epigallocatechin gallate. J Cell Biochemistry 1996;26S:236-257.]
What is the relationship between EGCG and other chemical names, such as polyphenols, flavonoids (flavanoids), catechins, and antioxidants? EGCG is a specific chemical and can be defined and measured in weight. It is one of the four catechins in green tea, being the most abundant and most active antioxidant of the four. Therefore, it is chosen as the surrogate yardstick to measure the antioxidant level in tea drinks and in tea leaves. EGCG is the most active antioxidant of the tea catechins, which are chemically members of the flavonoid category, which are in turn polyphenols. Not all flavonoids and not all polyphenols have antioxidant properties. After the tea catechins have lost their antioxidant activities, they can still be referred to as flavonoids or polyphenols. Unlike EGCG, the amount of flavonoids or polyphenols in a tea beverage does not reflect its antioxidant strength.
How are green tea leaves graded? Traditionally, green teas are graded by aroma, taste and appearance of the tea leaves. In general, the tips or the young leaves of plants harvested in early spring are the highest grades and have been valued at about two ounces of pure gold per pound for the past 1,000 years in China and Japan. These expensive green teas usually meet the 710EGCG® standard. However, there is no absolute correlation between price and the EGCG level in green teas.
Green tea has four catechin antioxidants (see chemical structures below). The most active antioxidant is (-)-epigallocatechin gallate (EGCG), that has the most phenolic –OH groups, therefore, is used as the surrogate standard for setting its medicinal quality.
The phenolic groups of EGCG serve as electron donors in the sense that they can give up an electron or a hydrogen atom containing an electron without robbing an electron from another atom. These phenolic molecules are capable of making internal adjustment to stabilize their unpaired electron after losing a hydrogen atom. Physiological concentrations of EGCG can prevent free radical-induced chromosomal damage. The two-step hydrogen donation by a phenolic antioxidant is illustrated as follows.
Two-step hydrogen donation by a phelonic antioxidant
ROO. is a lipid free radical with an unpaired electron. After accepting hydrogen atom, it becomes a stable ROOH with a stable electron pair. The phenolic radical (-O.) is relativerly unreactive before forming a quinone.
Oxidation of EGCG can occur in the dry tea leaves and in the tea liquid. The first step of oxidation is degradation of its EGCG while the green tea turns darker in color due to formation of thearubigens shown in the following reaction.
(Formation of Thearubigens)
N-Ethyl-L-glutamine; L-Glutamic acid gamma-(ethylamide)
L-theanine is a special tea amino acid and a biochemical modulator. It has been shown to boost general health.
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