Tea

What’s in your Tea

There are nine main chemical components of tea as a fresh leaf. They are polyphenols (sometimes called tannins), alkaloids, protids, organic acids, glucids, lipids, cholorphylls, mineral salts, and volatile substances. Each of these can be further divided into subcategories. Percentages and exact chemical makeup will vary according to many factors, including plant varietal, soil and weather conditions, and leaf age. Processing of the tea leaves causes chemical reactions to occur further changing the chemical makeup.

Polyphenols are a group of chemicals (catechins) that generally have antioxidant properties, and contribute color to many plants. The polyphenols present in tea–which account for roughly a third of a leaf’s dry matter–include flavonols, anthocyanins (pigments), and phenolic acids (which can contribute to astringency and bitterness). Catechin and epicatechin are epimers, with (-)-epicatechin and (+)-catechin being the most common optical isomers found in nature. Catechin was first isolated from the plant extract catechu, avove, from which it derives its name. Catechins constitute about 25% of the dry weight of fresh tea leaf, although total catechin content varies widely depending on clonal variation, growing location, seasonal/ light variation, and altitude. They are present in nearly all teas made from Camellia sinensis, including white tea, green tea, black tea and Oolong tea. Epigallocatechin gallate is the most abundant catechin in tea.

The health benefits of catechins have been studied extensively in humans and in animal models. Reduction in atherosclerotic plaques was seen in animal models. Reduction in carcinogenesis was seen in vitro.

Many studies on health benefits have been linked to the catechin content. According to Norman Hollenberg, professor of medicine at Harvard Medical School, epicatechin can reduce the risk of four of the major health problems: stroke, heart failure, cancer and diabetes. He studied the Kuna people in Panama, who drink up to 40 cups of cocoa a week, and found that the prevalence of the “big four” is less than 10%. He believes that epicatechin should be considered essential to the diet and thus classed as a vitamin. Science Daily March 12, 2007

According to one research, epigallocatechin-3-gallate is an antioxidant that helps protect the skin from UV radiation-induced damage and tumor formation.

Green tea catechins have also been shown to possess antibiotic properties due to their role in disrupting a specific stage of the bacterial DNA replication process.

Catechins, when combined with habitual exercise, have been shown to delay some forms of aging. Mice fed catechins showed decreased levels of aging. Oxidative stress was lowered in cell mitochondria, as well as increase in mRNA transcription of mitochondria related proteins.

Common tea flavonols include quercetin, campherol, and myrecetin. Quercetin is a powerful antioxidant, and all three are anti-inflammatories. During the oxidizing processes of tea leaves, some flavanols such as EGCG combine to form larger molecules of thearubigins and theaflavins, which are also powerful antioxidants. They also give highly oxidized tea its coppery or reddish color when infused.

Three main alkaloids are found in the fresh tea leaf: Caffeine (also known as theine when produced by the tea plant), theobromine, and theophylline. Caffeine is a stimulant that can contributes to bitterness. Theobromine is a diuretic, and theophylline is a respiratory stimulant sometimes used in asthma medication. However, although caffeine can make up as much as 4% of dry leaf matter, the other two alkaloids make up half a percent or less.

Protids are a category of proteins and amino acids contributing less than a quarter of dry matter in a fresh leaf. One of the most interesting of the amino acids is theanine, which has relaxing properties when ingested. Some of the scent of tea is caused by the breakdown of certain proteins.

Glucids are a host of substances that provide the majority of the leaf structure–cellulose, pectins, and lignins. However, other glucids, such as monosaccharides and polysaccharides, can give a slight sweetness to the tea.
Common mineral salts in the tea leaf include flourine, potassium, calcium, and magnesium. The leaf does not contain sodium, however.

Although making up a tiny percentage of the leaf mass, volatile substances form part of the aroma of tea. Over 300 different substances have been identified–some claim over 600. Some of the compounds which give tea some of its floral aroma include geraniol and nerolidol (both of which give a rose scent), lanalool (something akin to lily-of-the-valley), terpineol (lilac), phenylethanol (a generally light floral fragrance), methoxybenzaldehyde (vanilla), both Z-jasmone and jasmine lactone (a jasmine-like scent), B-ionone (violets), and hexanoics (varying from geranium or generally flowery to fruit).[1] Nutty flavors in tea can be divided into two groups. The first are those with an almond-like flavor and include 2-acetylthiazole, furfaral, and 5-methyl-furfaral. The other group produces a more hazelnut-like flavor: 2-acetylthiazole, 4-methylthiazole, and trimethylpyrazine. Together (with a few that are not found in tea), these six substances are the same ones that produce almond and hazelnut flavors in wine as well. Other substances may give tea a nutty flavor but not be present in wine.

Black teas tend to have a broader spectrum of aroma compounds, but oolongs have higher concentrations of a few, giving the impression that oolongs are more floral in aroma.

The remaining compounds are either present in very small amounts, or tend not to transfer into water during tea brewing. For example, even though lipids, or fatty acids, are present in the tea leaf, they are fat-soluble (not water-soluble), and only a negligible amount make it into brewed tea. Organic acids such as vitamin C are present in fresh leaf, but tea processing destroys it. Chlorophylls make up a very small percentage of total leaf mass, and contribute to the color of the leaf.