Tannins in tea

Tea is known to have benefits such as anti-antioxidants and artificial coloring. It may because tea leaves contain active chemicals such as tannins. As a natural part of every tea plant, tannins contribute to the growth process and health benefits of all teas, as well as the color and flavor.

Tannins (commonly referred to as tannic acid) are water-soluble polyphenols, molecular weight between 500 and 3 000, which, in addition to displaying the classic reactions of phenols, can precipitate alkaloids, gelatine, and other proteins.” Tannins are a diverse class of compounds and have various effects on health.

They are also used as antiseptics and astringents. Antioxidant activities confer upon the anti-carcinogenic and anti-mutagenic properties of tannins. Antimicrobial properties of tannins are shown against diverse group of bacteria, fungi and viruses.

Tannin with chemical formula C76H52O46 is a polyphenol compound that is colorless to yellowish, which can affect the tea itself taste, color and aroma. Tannins give tea astringency, color, and flavor. Tannins also cause darker colors in tea, which can be perceived as a sign of flavor strength. In fact, the development of tannins is unrelated to that of the aromatic compounds that create variety in tea flavor.

Tannins are mainly found in the cell vacuoles or in the cuticle (here cells don’t interfere with plant processes: only after death and cell breakdown do they become active in metabolic processes)
Tannins in tea

Bioactive compounds in tea

Tea contains various bioactive components, such as polyphenolic compounds (catechins and epicatechins), theaflavins, flavonol glycosides, L-theanine, caffeine, theobromine, and volatile organic substances.

Many studies have indicated that tea and its bioactive components possess multiple health functions, including antioxidation, anti-inflammation, immuno-regulation, anticancer, cardiovascular-protection, anti-diabetes, anti-obesity, and hepato-protection.

These bioactive components are responsible for the astringency, flavor, aroma, and taste of the tea as well as its health beneficial effects.

The phytochemical components are involved in the prevention and cure of many illnesses like cardiovascular diseases, malignancy, digestive dysfunction, and metabolic disorders like obesity, diabetes.

Catechins are a type of polyphenol and are the main astringency component in green tea, long known as tannins. There are four main types of catechins found in tea leaves.
*Epicatechin
*Epigallocatechin
*Epicatechin gallate
*Epigallocatechin gallate

Catechins in tea are not only essential in plant physiology but also tremendously beneficial to human health, acting as antioxidants, as well as anti-inflammatory, anti-allergic, antihypertensive, anticancer, and antimicrobial agents

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 addition, other polyphenols like gallic acid, chlorogenic acid, ellagic acid, galloylquinic acid, kaempferol-3-O-glucoside (kaempferol-3-G) and various flavonoids are also found in tea.

Tea flavonoids show strong antioxidant properties. Epigallocatechin gallate (EGCG) is thought to reduce inflammation, aid weight loss, and help prevent heart and brain disease. Numerous health benefits associated with drinking green tea are typically credited to its EGCG content

As an antioxidant, EGCG protects body cells from damage associated with oxidative stress and suppresses the activity of pro-inflammatory chemicals produced in your body, such as tumor necrosis factor-alpha.

Caffeine and other methylxanthine regulate the intracellular second messenger levels. 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.
Bioactive compounds in tea

Polyphenols of catechins

Catechins (flavan-3-ols) belong to the group of polyphenols. Catechins can be harvested from a variety of sources including many herbs, fruits, vegetables, beverages, algae, and confectionary items. But their contents and types vary considerably among various sources.

Catechins are flavonoid derivatives that play a major role in determining the taste of the tea (bitter, astringent, and slight sweet tastes) as well as possessing health benefits in disease prevention.

The four main catechins that occur in green tea are (-)-epicatechin (EC), (-) epicatechin-3-gallate (ECG), (-)-epigallocatechin (EGC), and (-)-epigallocatechin-3-gallate (EGCG). Of these catechins, EGCG and EGC are found in the highest amounts in green tea and have been the subject of most of the studies.

A positive correlation between green tea consumption and cardiovascular health due to several actions such as antioxidative, antihypertensive, anti-inflammatory, antiproliferative, antithrombogenic, and anti-hyperlipidemic etc., is well established based upon epidemiological and experimental studies.

Catechins have been reported to be useful in combating aging and age related disorders like cancer, cardiovascular disorders and neurodegenerative diseases.
Polyphenols of catechins

Antioxidants in tea: Activity and health benefits

Tea is rich in polyphenolic compounds with antioxidant properties, mainly quercetin and catechin, and these compounds may inhibit oxidative damage to DNA, lipid, carbohydrate and protein.

Tea is widely considered as a health-promoting beverage, and the beneficial effects generally associated with green tea have been attributed to its polyphenol content, particularly to catechins and their antioxidant activity.

Flavonoids exhibit anti-inflammatory properties; it was confirmed that they can also reduce blood pressure, strengthen the cell walls of blood vessels, and improve the immune system.

Its polyphenolic compounds appear to lower cholesterol levels, improve cardiovascular health and help guard against some cancers. In some studies, tea has been associated with antiallergic action and antimicrobial properties.

Moreover some epidemiological studies have associated consumption of tea with a lower risk of several types of cancer including those of the stomach, oral cavity, oesophagus and lungs.

Antioxidants are important in living organisms as well as in food because they may delay or stop formation of free radical by giving hydrogen atoms or scavenging them.

The ability to scavenge for free radicals by tea polyphenols due to possession of a phenolic hydroxyl group attached to the flavan-3-ol structure has been associated with teas’ therapeutic action against free radical mediated diseases. The mechanism of oxidation reactions is strictly dependent on the chemical structure of the compound.

Free radicals are known to contribute to numerous disorders in humans including cancer, artheroscerolosis, arthritis, ischemia, Central Nervous System (CNS) injury, gastritis, dementia, renal disorders and Acquired Immune Deficiency Syndrome (AIDS)

Antioxidants in tea:  Activity and health benefits  

Drinking tea can reduce high blood pressure

A study (published Archives of Internal Medicine 2012) of 95 patients from Western Australia suggested that drinking three cups a day of black tea can reduce blood pressure by 2-3 mmHg in both systolic and diastolic blood pressure.

Black tea is a good source of flavonoids. Flavonoids protect LDL cholesterol from oxidation, and this can reduce the risk of atherosclerosis, stroke, hypertension and heart attack.

Oral administration of tea polyphenols also yielded a decrease of blood pressure in patients. The reported active substances include tea extracts, polyphenols and tea tannin. Tea tannins (2 to 4 mg orally) could reduce the systolic blood pressure in rats. Investigation proved that tea components, especially TFDG and EGCG showed beneficial effect.

In addition, theanine, an amino acid found in tea produces a calming effect on the brain. It induces a feeling of relaxation and was found to be effective lowers the blood pressure of spontaneous hypertensive rates.

Tea polyphenols and caffeine may also ameliorate the development of hypertension by improving the renal circulatory state as a result of its direct action on the kidney, including the activation of the kinin-kallikrein-prostaglandin system in the kidney.
Drinking tea can reduce high blood pressure

Epicatechins compound in tea

Green tea is another excellent dietary source of polyphenols. The most abundant the polyphenolic compound in green tea is epigallocatechin gallate (EGCG); other catechins such as epicatechin (EC), epigallocatechin (EGC) and epicatechin gallate (ECG) are also present.

The active constituents responsible for photoprotective efficacy in green tea are called epicatechins or epicatechin derivatives. These epicatechins are also commonly called as ‘polyphenols’ and are easily soluble in water and organic solvents like acetone, ethanol, etc.

During processing of tea, these epicatechins get polymerized and from more complex polymerized molecules called theaflavins and thearubigins. A typical black tea contains 3-10% epicatechins, 3-6% theaflavins, 12-18% thearubigins and other components.

Studies have shown that polyphenol provide antioxidants and anti-inflammatory activities in nature and have been shown to possess anti-carcinogenicity activity.
Epicatechins compound in tea

What are tannins?

Tea is a popular beverage throughout the world. It is pleasant and mildly stimulating. Tannins are a family of astringent compounds called polyphenols.

Polyphenols constitute over 48.5% of the total solids in a cup of tea. They’re found in several kinds of plants, including dark sorghum, some apples and yerba mate, a popular South American drink made from the leaves and branches of an evergreen tree.

Tea is often included in the list of tannins-containing foods.   The tea leaves contain varying amounts of tannins: Green teas, which have unfermented leaves, contain the most tannins; black teas including pekoe, which are fermented, contain the fewest.

By definition, tannins are biologically active, that is tannins bond protein, a process that is pH dependent. Most of the phenolic groups in tannins are free. Tannins have a molecular weight between 500 and 3000, and generally are soluble in water.

Tannins are usually divided into two classes: those can be hydrolyzed (react with water) and those that cannot.  The nonhydrolysable tannins found in tea are condensation polymers of catechin.

The occurrence of tannins is reported in unripe fruits such as mango, dates and persimmons. The tannins diminish in amounts as the fruits ripen.

Other food sources of tannins are grapes (condensed tannins, on average 5000 mg/kg of grapes). Grape juice, wines (red wine: 1.2 – 4l4 g/L of wine) and some sorghum grain varieties.
What are tannins? 

Theabrownin in tea

Tea pigments have several components: theaflavins, thearubigins and theabrownin.

Theabrownin is the main bioactive component derived from the process of fermentation of black pu-erh tea.

It was formed during oxidation of polyphenols of tea leaves. It was reported that the cellulases and pectinases produced by microorganisms, together with polyphenol oxidase, play an important role in theabrownin formation.

The tea pigment theabrownin gives pu-erh its characteristics brown color and plays an important role in the sensory properties of the final product but its pharmaceutical-like properties are not well understood.

Theabrownin are characterized by high molecular weight and complex structure. They dissolve easily b water and not in organic solvents like ethyl acetate.

Animal studies showed that theabrownin has a significant blood lipid-lowering in hyperlipidemic rats. It was hypothesized that TB would regulate the activity of key enzymes involved in lipid metabolism and accelerate the catabolism of exogenous cholesterol.
Theabrownin in tea

Polyphenols in tea

Tea is the most widely consumed beverage in the world after water. The daily consumption is around 3 billion cups per day.

Regular intake of tea is associated with improved antioxidant status in vivo, which may contribute to lowering the risk of coronary heart disease, stroke, and certain type of cancers.

The polyphenols in tea mainly include the following six groups of compounds: flavonols, hydroxy-4-flavonols, anthocyanins, flavones, flavonols, and phenolic acids.

Among these, the flavonols mainly catechins are most important and occupy 60-80% of the total amount of polyphenols in tea.

The tea plant is known to contain seven kinds of major catechins and traces of various other catechin derivatives.

These catechins are present in all part of the tea plant; 15-30% are present in the tea shoots, and there is also a high content in the second and third leaves.

About 90-95% of the flavonols undergo enzymatic oxidation to products which are closely responsible for the characteristics color of tea infusion and its taste.

During the manufacturing of tea, the content of polyphenols increases slightly at the beginning of withering but decreases right after.

Although the trend for the changes of polyphenols appears similar in different varieties the absolute content of polyphenols are different among them.
Polyphenols in tea

Effect of Green Tea Bioactive Compounds on Bone Health

Epidemiologic evidence showed an association between green tea consumption and the prevention of age-related bone loss in elderly women and men. Green tea support healthy bones and teeth both by protecting osteoblast from destruction by free radicals. Green tea also found to inhibiting the formation of osteoclasts.

The green tea protects bone health by proposed mechanisms:
*Green tea and its bioactive components increased osteoclastic apoptosis through a caspase-3 activation mechanism.

*Bioactive ingredients in green tea enhance bone formation, by enhancing osteoblastogenesis and suppress bone resorption in various bone loss models.

Green tea polyphenols increase serum osteocalcin, bone mineral density (BMD), trabecular volume, strength of femur, trabecular thickness and bone formation.

*Green tea and its active components are proven to mitigate the deterioration of bone microstructure as well as the loss of bone mass and strength due to aging, aging plus sex hormones deficiency or chronic inflammation.

*Mitigating bone loss through antioxidative reaction.

*Mitigating bone loss through anti-inflammatory action. Green tea and theaflavin enriched tea plant extract reduces expression of inflammatory mediators and cytokines in animal models.

*Through its high content of fluoride and vitamin K1.
Effect of Green Tea Bioactive Compounds on Bone Health

Active antioxidants in tea

Antioxidants are compounds that help the body to fight harmful free radicals. They accomplish this by circulating throughout the system and neutralizing unpaired electrons, rendering them inactive.

The free radicals occur naturally in the body but excess amount increases the risk of coronary attacks and cancer.

Tea is rich in polyphenolic compounds with antioxidant properties, mainly quercetin and catechin, and these compounds may inhibit oxidative damage to DNA, lipid, carbohydrate and protein.

Oxidative damage is associated with various chronic diseases, including cancer, coronary heart disease, cataract and dementia, and it has been suggested that consumption of tea may lower the risk of chronic disease by improving oxidative/antioxidant balance.

Black tea contains a significant amount of theaflavin compounds that make an important contribution to antioxidant activity, but their effectiveness varies with the individual theaflavin.

The domination of theaflavins are simple theaflavin, theaflavin-3-gallate, theaflavin-3’-gallate, theaflavin-3,3’-gallate which comprises 0.3% - 2% of the dry matter of black tea.

Green tea polyphenols are composed of numerous teas of catechin. Studies show that habitual green tea consumption causes in increase in plasma antioxidant status and a quantitative reduction of free radical-induced markers of lipid peroxidation.
Active antioxidants in tea