1 Introduction

Tea (Camellia sinensis L.), a cultivated evergreen plant, is native to China, later spread to India, Japan, Europe, Russia and ultimately to the New World in late 17th century. It is now being regarded as the most promising item in the global trade (Table1). Chinese emperor King Shen Nong (ca. 2700 BC) consumed the world’s first cup of tea when the leaves of the Camellia sinensis plant floated accidentally into his pot of boiling water, (Segal 1996). Archeological evidence confirmed that tea has been consumed by humans for over 500,000 years (Jelinek, cited in McKenna et al., 2000). Cultivated tea has its origins in India, China, Burma and Thailand (McKenna et al., 2000). Dutch merchants, followed by the British were the first to begin carrying tea back to Europe for commercial trade with tea’s place in European culture firmly established by the mid-17th century (McKenna et al., 2000). 

Tea is found in many different types. However, the most commonly consumed are black, green and oolong tea. From the same plant species, C. sinensis L., green, oolong and black tea are made which are differing in their appearance, organoleptic taste, chemical content and flavour due to varied degrees of fermentation. Green tea is unfermented, with the leaves being heated or steamed soon after being picked to prevent the fermentation that takes place with black tea (Segal, 1996). Black tea is fully fermented green tea which is prepared through a method of rolling with the release of juices and enzymes from the leaves initiating the fermentation process.

Oolong tea is partially fermented green tea, providing a mid-point between green and black tea (Segal, 1996).In Indian traditional medicine, green tea is said to act as a mild excitant, stimulant, diuretic and astringent as well as a remedy for fungal infections caused by insects (Nadkarni, cited in McKenna et al. 2000). Chinese traditional medicine uses green tea for the treatment of flatulence, regulation of body temperature, promotion of digestion and the improving of mental processes, with its actions stated as being astringent, a cardio tonic, a central nervous system stimulant, and a diuretic (Snow, cited in McKenna et al., 2000). In Western medicine and more recently as shown in animal, human and in vitro studies, much attention has been focused on the antioxidant activity of tea, most particularly of green tea and its effect on the prevention of cancer, heart disease and arthritis, reducing the damaging effects of stress, and in aiding weight loss (Cooper et al., 2005).

2 Tea, the chemical constituents and activities of polyphenols 

The chemical components of tea leaves include polyphenols (catechins and flavonoides), alkaloids (caffeine, theobromine, theophylline, etc.), volatile oils, polysaccharides, amino acids, lipids, vitamins (e.g., vitamin C), inorganic elements aluminum, fluorine and manganese), etc. However, the polyphenols are primarily responsible for the beneficial healthful properties of tea. The flavonoides have antioxidant, anti-inflammatory, anti allergic and anti microbial effects. Green tea contains six primary catechin compounds namely catechin, gallocatechin, epicatechin, epigallocatechin, epicatechin gallate and epigallocatechin gallate (EGCG), the later being the most active component. The polyphenols content of green tea and black tea varies from 30% to 40% and 3% to 10%, respectively. There are active hydroxyl hydrogen’s in the molecular structure of green tea polyphenols that can end the chain reaction of excessive free radicals that (otherwise) result in pathological changes in the human body. Tea polyphenols can increase the activity of glutathione peroxidase and superoxide dismutase and the scavenging rate is much stronger than vitamins C and E. The anti-carcinogenic mechanism includes both cellular immune function and the inhibition of tumor growth. Much of the attributed therapeutic benefits of green tea are due to the presence of four major catechins - epicatechin (EC), epigallocatechin (ECG), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG) (Table 2 and Figure 1 & 2). 

3 Types of Tea and Processing

Once the tea leaf is plucked, it is processed in the factory to bring out the flavors in it. There are essentially two types of teas: Orthodox, and CTC. The Orthodox tea is the whole leaf tea that is generally popular in the west, but in India, CTC tea is wildly popular for the type of tea they make there, called Chai, involving boiling the tea over and over to extract the most out of it.

White tea

Recently popular, white tea is produced when two leaves and a bud are picked just before sunrise to preserve the moisture in the leaf. This tea is characterized by a delicate flavor with very little color, however it is highly priced because a day’s picking produces only about 1-2 kgs. Although it is called white tea, the tea does have some light green color characteristic of the newest buds originating on the bush. The buds are steamed to destroy the enzymes that would otherwise destroy the tea and dried either in the dryer or in the sun.

Green tea

Green tea is produced by steaming the leaves to destroy the enzymes that might otherwise ferment the leaves. The leaves are then rolled either by hand or by mechanical rollers, to bring out the juices in the leaves that are responsible for its flavor. The rolled leaves are then fired to dry them. The entire process of rolling and firing is repeated several times until the leaves are completely dry. The process of producing green tea is very exacting because variation in the drying time can result in fermentation of the leaves which spoils its flavor.

Black Tea

The most widely consumed beverage, black tea is a close cousin to the Oolong in that if the tea is fermented long enough, the leaves turn black, and hence the term black tea. The exact time of rolling is determined by the size of the leaf, with smaller leaf being rolled for shorter period than larger leaf. Rolling induces fermentation of the leaf, and when the leaf is judged to be appropriately fermented, the process is slowed by allowing the leaves to cool off on ventilated trays for 3 to 4 hours. Finally, the fermentation process is stopped by drying the teas under hot blowers, at which point the tea leaves turn from reddish hue to black. The teas are then passed through various sieves to grade them.

Oolong Tea

Oolong teas are semi fermented teas that are partially fermented before drying to preserve the natural flavors. The process of producing Oolongs begins with picking of the two leaves and a bud, generally early in the morning. The leaves are then partially dried indoors to promote fermentation. When the leaves start turning red - at a stage, when 30% of the leaves are red, and the rest 70% are green, the leaves are rubbed repeatedly by hand or mechanically to generate flavor and aroma, and finally dried over charcoal. The final stage in production of Oolong teas is blending the teas to produce the characteristic flavor of the garden or the brand.

The γ-amino butyric acid (GABA) tea is popular by consumers in Taiwan in recent years. The GABA tea, also called Gaborone tea, is the special tea enriched with GABA by anaerobic conditions of fresh tea leaves. The GABA is a non-protein aqueous amino acid and is one of the major inhibitory neurotransmitters in the central nervous system. The main difference between GABA and green tea is the contents of GABA, glutamic acid, alanine, aspartic acid, total catechins, epigallocatechin gallate (EGCG) and epicatechin (EC), especially the first two components (Wang, Tsai, Lin, & Ou, 2006).

The traditional method of making or brewing a cup of tea is to place loose tea leaves, either directly or in a tea infuser, into a tea pot or tea cup and pour freshly boiled water over the leaves. 

After a few minutes, the leaves are usually removed, either by removing the infuser or by straining the tea while serving. Most green teas should be allowed to steep for about two or three minutes, although some types of tea require as much as ten minutes, and others as little as 30 seconds. The strength of the tea should be varied by changing the amount of tea leaves used, not by changing the steeping time. The amount of tea to be used per amount of water differs from tea to tea, but one basic recipe may be one slightly heaped teaspoon of tea (about 5 ml) for each teacup of water (200–240 ml) prepared as above. Stronger teas, such as Assam, to be drunk with milk, are often prepared with more leaves, and more delicate high-grown teas such as a Darjeeling are prepared with somewhat fewer (as the stronger mid-flavours can overwhelm the champagne notes). The best temperature for brewing tea depends on its type. Teas that have little or no oxidation period, such as a green or white tea, are best brewed at lower temperatures, between 65 and 85 °C, while teas with longer oxidation periods should be brewed at higher temperatures around 100 °C (Table 3). The higher temperatures are required to extract the large, complex, flavourful phenolic molecules found in fermented tea. In addition, boiling reduces the dissolved oxygen content of water. Dissolved oxygen would otherwise react with phenolic molecules to turn them brown and reduce their potency as antioxidants. To preserve the antioxidant potency, especially for green and white teas brewed at a lower temperature, water should be boiled vigorously to boil off any dissolved oxygen and then allowed to cool to the appropriate temperature before adding to the tea. An additional health benefit of boiling water before brewing tea is the sterilization of the water and reduction of any dissolved VOCs, chemicals which are often harmful.

Some tea sorts are often brewed several times using the same leaves. Historically in China, tea is divided into a number of infusions. The first infusion is immediately poured out to wash the tea, and then the second and further infusions are drunk. The third through fifth are nearly always considered the best infusions of tea, although different teas open up differently and may require more infusions of hot water to produce the best flavour.  

One way to taste a tea, throughout its entire process, is to add hot water to a cup containing the leaves and after about 30 seconds to taste it. As the tea leaves unfold (known as The Agony of the Leaves), they expose various parts of themselves to the water and thus the taste evolves. Continuing this from the very first flavours to the time beyond which the tea is quite stewed will allow an appreciation of the tea throughout its entire length. 

Antioxidant content, measured by the lag time for oxidation of cholesterol, is improved by the cold-water steeping of varieties of tea.

4 Tea manufacturing 

Black tea 

In the West, water for black tea is usually added near the boiling point of water, at around 99 °C. Many of the active substances in black tea do not develop at temperatures lower than 90 °C. Lower temperatures are used for some more delicate teas. The temperature will have as large an effect on the final flavour as the type of tea used. The most common fault when making black tea is to use water at too low a temperature. Since boiling point drops with increasing altitude, it is difficult to brew black tea properly in mountainous areas. It is also recommended by the British that the teapot be warmed before preparing tea, easily done by adding a small amount of boiling water to the pot, swirling briefly, and then discarding it. 

Western black teas are usually brewed for about four minutes and are usually not allowed to steep for less than 30 seconds or more than about five minutes (a process known as brewing or mashing in Britain). In many regions of the world, however, boiling water is used and the tea is often stewed. For example in India, black tea is often boiled for fifteen minutes or longer as a strong brew is preferred for making Masala chai. When the tea has brewed long enough to suit the tastes of the drinker, it should be strained while serving. Popular varieties of black tea include Assam, Nepal, Darjeeling, Nilgiri, Turkish and Ceylon teas. Sharangi et al (2014) focused on the latest research efforts regarding the health effects related to consumption of black tea and derived some future research directions towards its therapeutic potentialities.

Green tea

Water for green tea, according to regions of the world that prefer mild tea, should be around 80 to 85 °C (176 to 185 °F); the higher the quality of the leaves, the lower the temperature. Hotter water will produce a bitter taste. However, this is the method used in many regions of the world, such as North Africa or Central Asia, where bitter tea is appreciated. For example, in Morocco, green tea is steeped in boiling water for 15 minutes. In the West and Far East, a milder tea is appreciated. The container in which the tea is steeped, the mug or teapot, is often warmed beforehand so the tea does not immediately cool down. High-quality green and white teas can have new water added as many as five or more times, depending on variety, at increasingly higher temperatures. 

Oolong tea 

Oolong teas should be brewed around 80 to 100 °C (176 to 212 F), and the brewing vessel should be warmed before pouring in the water. Yixing purple clay teapots are the traditional brewing-vessel for oolong tea (Delete this sentence). For best results, spring water should be used, as the minerals in spring water tend to bring out more flavour in the tea. High quality oolong can be brewed multiple times from the same leaves, and unlike green tea, it improves with reuse. It is common to brew the same leaves three to five times, the third steeping usually considered the best. In the Chinese and Taiwanese Gongfu tea ceremony, the first brew is not drunk at all but disposed of as it is considered a wash of the leaves rather than a proper brew(Figure 4). 

5 Global Research on tea antioxidant and bioactive compounds: Status and potentialities

An antioxidant is a molecule that inhibits the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When the chain reaction occurs in a cell, it can cause damage or death to the cell. Antioxidants terminate these chain reactions by removing free radical intermediates, and inhibit other oxidation reactions. They do this by being oxidized themselves, so antioxidants are often reducing agents such as thiols, ascorbic acid, or polyphenols. 

Bioactive substance or a compound has a biological activity if it has direct effects on a living organism. These effects can both be adverse or beneficial depending on the substance, the dose or the bioavailability. Or a type of chemical found in small amounts in plants and certain foods (such as fruits, vegetables, nuts, oils, and whole grains)( Delete this sentence). Bioactive compounds have actions in the body that may promote good health. They are being studied in the prevention of cancer, heart disease, and other diseases. Examples of bioactive compounds include lycopene, resveratrol, lignan, tannins, and indoles. Ramalho et al (2013) determined total phenolic compounds in several types of black tea either in granule or bag form and verified the effect of infusion time on the availability of these compounds. Eight different brands of tea were analyzed, the total phenolic content was determined, identification and quantified. Higher concentrations of propyl gallate (43 mg.g−1), caffeine (67 mg.g−1), gallic acid (0.9 mg.g−1), catechin (48 mg.g−1) and rutin (12 mg.g−1) were found in Brazilian samples while chlorogenic acid (4 mg.g−1) and p-coumaric acid (7 mg.g−1) were found in Indian teas. It was concluded that these teas are good sources of dietary phenolic compounds and the content of these compounds in the beverage is higher with the longer infusion time. Costa et al., (2012) analyzed total phenolics, total flavonoids and ascorbic acid contents, as well as DPPH scavenging activity of several commercial samples, namely green tea and other herbal infusions, dietary supplements, and fruit juices, available in the Portuguese market. Deete et al (2012) studied for antioxidants and anti-glycation properties of tea in correlation with their total phenolics, flavonoids, and non-flavonoids contents of Thai herbal teas in comparison with conventional teas. Significant differences were observed among the tea infusions. Only Stevie and sap pan herbal teas had primary antioxidants and anti-glycation capacities comparable to C. sinensis. However, purple velvet, mulberry and false mallow herbal teas were exceptionally stronger in metal chelating capacity than the C. sinensis teas. Thai herbal teas could be choices of interest for healthy beverages and could be new dietary sources for bioactive compounds. Antioxidant properties (AOP) of thirteen tropical and five temperate herbal teas were screened byChan et al (2010). Comparisons were made with green, oolong and black teas of Camellia sinensis. The AOP studied were total phenolic content, radical-scavenging activity, ferric-reducing power and ferrous ion-chelating ability. Tropical herbal teas were more diverse in types and more variable in AOP values than temperate herbal teas. Herbal teas generally had lower antioxidant values than teas of C. sinensis. Exceptions were lemon myrtle, guava and oregano teas with AOP comparable to black teas. 

The effect of different extraction conditions and storage time of prepared infusions on the content of bioactive compounds of green teas and their antioxidant capacity were investigated by Komes et al (2010). Among the tested green teas Twinings of London was recognized as the richest source of phenolic compounds (3585 mg/L GAE of total phenols). The most abundant phenolic constituents of green tea were flavan-3-ols, of which EGCG was prevailing in all teas (94.54–357.07 mg/L). The highest content of caffeine, as the most abundant methylxanthine, was determined in powdered green tea. Regardless of the extraction conditions all green teas exhibited significant antioxidant capacity in vitro, which was in correlation with their phenolic content, confirming that green tea is one of the best dietary sources of antioxidants The antioxidant activities of green tea were investigated by Jun et al (2011). The results showed that the phenolic contents and the antioxidant activities were greatly influenced by high pressure. 

Teas are important sources of bioactive compounds that can play a role in preventing human diseases.Loranty et al., (2010) identified and quantified carotenoids and chlorophylls in commercial dry herbal and fruit teas and determined their availability in infusions made from these teas. Teas derived from roots or seeds contained negligible quantities of pigments. Wang et al, (2006) investigated the bioactive components of GABA (c-aminobutyric acid) tea as compared with green tea produced in Taiwan. The results showed that moisture, total free amino acids, crude fat, Hunter L value, total nitrogen, free fatty acids and reducing sugar did not differ significantly between GABA tea and green tea. However, GABA tea had higher Hunter a and b values, while green tea had higher total catechin and ascorbic acid contents (p < 0.05). Of major catechins, epicatechin and epigallocatechin gallate were found to be lower in GABA tea than in green tea. For free amino acids, GABA, alanine, ammonia, lysine, leucine and isoleucine were found to be significantly higher in GABA tea, while the glutamic acid, aspartic acid, and phenylalanine were higher in green tea (p < 0.05). Theanine, tryptophan, valine, threonine and methionine were not found to be different between the two kinds of tea(Table 4).

Lin et al (2012) reported that the bioactive components and antioxidant properties of extracts were affected by the ethanolic concentrations and temperatures. Among catechins, epigallocatechin gallate was the main catechin in all extracts, followed by epigallocatechin, epicatechin, epicatechin gallate, gallocatechin and gallocatechin gallate. The polyphenolic bioactive composition and the antioxidant properties of Mauritian commercial black and fresh tea leaves were evaluated by Ramma et al (2005). Hot water infusates contained high levels of total phenols, total proanthocyanidins and total flavonoids. The ferric reducing antioxidant power (FRAP) and Trolox equivalent antioxidant capacity (TEAC) assays were used to assess the antioxidant potential of tea infusates with the following order of potency: Ouvagalia tea > Buccaneer’s choice > Black Label > Red Label > Extra > Corson > Chartreuse > La Flora > 3-Pavillons. In general, the fresh tea leaves had high levels of total phenols, total flavonoids, total proanthocyanidin and exhibited greater antioxidant potentials when compared with black teas. Thus Mauritian black teas and fresh tea leaves can be rich sources of polyphenolic compounds and antioxidants, which may be highly relevant to the maintenance of normal health and disease management, an observation that has led to the commencement of a clinical trial study to assess cardiovascular health in Mauritius. Atoui et al., (2005) evaluated the antioxidant activity of tea. About 60 different flavonoids, phenolic acids and their derivatives have been identified. An et al (2004) studied the polyphenols of green tea leaf and investigated the effect of irradiation on changes of biological and anti-microbial activities. The anti-microbial activities against Staphylococcus aureus and Streptococcus mutans were higher in the irradiated sample, which showed inhibition of microorganisms tested at a lower concentration than those of the non-irradiated sample. Results indicated that irradiation of polyphenols, the major bioactive compounds in green tea, may maintain the biological activities and even increase the anti-microbial activity. The results also demonstrated that irradiation of green tea polyphenols, for removal of dark colour, may be applicable in the food or cosmetic industries. Yang and Liu (2013) highlighted the major bioactive compounds responsible for the health benefits of tea. Seven types of tea were extracted using boiling water. To more fully characterise the antioxidant profiles and possible associated health benefits of these tea types, the total water-soluble solid content, phenolics, flavonoids, and antioxidant and ant proliferative activities were quantified. Green tea leaves (GTL) were found to have the highest phenolic content (128.7 ± 1.7 mg g _1, P < 0.05), followed by teas of decaffeinated green tea bag (DGTB), green tea bag(GTB), black tea bag (BTB), decaffeinated BTB, black tea leaves and oolong tea leaves (OTL). The results displayed that phenolic/flavonoid content was well correlated with antioxidant activity. 

Vinson et al (1998) determined that phenols contain in tea are responsible for its antioxidant activity. The pure catechins and phenolic acids found in tea are more powerful than the antioxidant vitamins C, E and S-carotene in an in vitro lipoprotein oxidation model. Comparison of the tea fractions indicated that both catechins and theaflavins contribute to the teas' antioxidant characteristics. Black and green teas were not significantly different in phenol content, in antioxidant strength as measured by IC50, or in antioxidant potential as measured by the phenol antioxidant index (PAOXI). The PAOXI of teas was significantly higher than grape juices and wines. Tea catechins and both green and black tea exhibited potent lipoprotein bound antioxidant activity. Phenol antioxidants from tea were calculated to be a large source of antioxidants in the U.S. 

The antioxidant activity and the total phenolics content of various tea extracts (Table 5) were analyzed byLiebert et al (1999). For measuring the antioxidant activity, the Trolox equivalent antioxidant capacity (TEAC) test and the low density lipoprotein (LDL) oxidation test were used. In all cases the antioxidant activity as well as the content of the phenolics increased with the brewing time. Antioxidant activity was well correlated with the corresponding total phenolics content. The results of the LDL oxidation test varied more than those of the TEAC test.  

Karakaya and Nehir (2006) found increased activities of phenolic compounds and antioxidant due to the inverse relationship between degenerative diseases and consumption of polyphenol rich foods (Table 6). Both black tea infusion and black tea dialysate inhibited ABTS radical cation oxidation by 99.43% and 42% respectively. Infusions of sage, linden flower, fresh nettle, dried nettle leaves inhibited ABTS radical  

Values are expressed as mean± standard deviation cation oxidation by 39.61%, 96.70%, 70.80% and 95.50% respectively. Although total phenols of black tea dialysate decreased by 96.48%, total antioxidant activity decreased by 57.76%. Ten µM catechin and 10µM quercetin showed 100% inhibition on ABTS radical cation oxidation. However, Trolox and ferulic acid showed 100% inhibition at 20 µM concentrations. Total antioxidant activity of a cup of black tea was found to be equal to 10 μM of quercetin, 10 μM of catechin, 20 μM of Trolox and 20 μM of ferulic acid. Total antioxidant activity of black tea dialysate was slightly higher than both 5 µM of Trolox and 5 µM of ferulic acid. Genovese et al (2010) reported that the potential health benefits attributed to green tea and its catechins such as antioxidant effects, cancer chemoprevention, and weight loss have led to a huge increase of green tea products in the food market. The objectives of this work were to analyze and compare these products in terms of phenolic contents and in vitro antioxidant capacity including tea bags, dehydrated leaves, and ready-to-drink preparations after standardization of the infusion preparation procedure.  

Hajimahmoodi et al (2008) reported that green tea which is important sources of bioactive compounds have been used in folk medicine for many centuries. Antioxidant activity of methanolic (50%) extracts of five green tea samples was investigated according to Ferric reducing ability power method. Total antioxidant activity varied from 0.554±0.042 in Avicen green tea sample to 3.082±0.150 mmoL FeII/g in Chinas green tea and total phenolic content ranged from the 0.030±0.001 in Avicen green tea sample to 0.196±0.012 g gallic acid per gram dry weight in Ahmad green tea. Green tea samples possess relatively high antioxidant activity due to contribution of phenolic compounds. The study showed that green tea samples which are more frequently consumed in Iran are strong radical scavengers and can be considered as good sources of natural antioxidants for medicinal and commercial uses. Hossain et al (2009) found antioxidant activities, ranging from 62.82% to 89.04%, and variations in total phenolics, ranging from 7.14 to 9.71 mg caffeic acid/g dry weight of the methanol extracts. Anti-oxidative potency of the methanol extracts was comparable to that of pure quercetin and the synthetic antioxidant butylated hydroxylanisole (BHA). A rapid GC method was developed for the separation and determination three flavonoids; desmodol (DES), triangularin (TRI) and 2′,4′-dihydroxychalcone (DIHY) in tea samples (Table 7 and Fig 5).

6 Protective role of bioactive and antioxidant properties of different teas

 GREEN TEA

 Catechin

• Inhibition of hypertension, anti-tumorigensis, antioxidant effect, strengthening of capillaries
• Anti hypercholestolemia, maintaining elasticity of the skin, antimicrobial activity

Caffeine

Promotion of wakefulness, ease in fatigue and sleeplessness, diuretic effect. 

Theanine

Antagonistic effect against convulsive action of caffeine (no jittery side effects), inhibition of hypertension, improvement of brain function. 

Flavonoids 

Promotion of a physical sensation of relaxation,strengthening of blood vessels, prevention of halitosis 

Vitamin C

• Antioxidant effect, Prevention of flu, Health maintenance of skin and mucous membranes
• Radical scavenging effect
• Hypoglycemic effect

Vitamin E

• Radical scavenging effect, antioxidant effect, health maintenance of cells. 

Zinc

• Maintains taste, vision and smell; supports immune system, fights colds and influenza.  

Saponins

• Anti-fungal activity, anti-inflammation, anti -allergenic activity, anti-obesity.

White tea

White tea can help to prevent heart disease, cancers and stroke, as well as helping to treat diabetes. High levels of calcium and fluoride help maintain healthy teeth, gums and bones. White tea is an excellent addition to your daily routine. 

Oolong tea 

Oolong Teas are unique because they span an oxidation range of 20-80%, where some are closer to green teas, and others are more similar to black teas. However, although catechins decrease with oxidation, theaflavin and thearubigin levels increase. These polyphenols help in defending the body against stroke, dementia, heart disease and cancer. In addition to this, oolong teas have long been believed to aid in digestion. (Part of this sentence has been deleted)

Black Tea

Black tea prevents heart disease, stroke and cancer, and lowers cholesterol.
 

7 Therapeutic potentialities of tea (Camellia sinensis L.)

Acts as antioxidant
Fights against variable forms of cancer
Reduces risk of cardiovascular diseases
Treats respiratory diseases and corrects skin disorder
Aids in indigestion and prevents diabetes
Improves oral health, Keeps away from liver disease
Gives a boost to immunity and burns fat 

8 Future strategies with special reference to the developing countries

In order to materialize the full potential of photochemical/functional foods, a holistic, concerted, multidisciplinary approach is imperative,  involving workers in diverse fields such as nutrition, medical sciences, epidemiology, statistics, immunology, analytical and organic chemistry, biology, biochemistry, agriculture, food science, food technology and engineering. The future of functional foods like tea Black teas preventing heart disease, stroke and cancer, agriculture, food science, food technology and depends on the unequivocal demonstration of their efficacy in promoting health. A practical approach for developing countries would be to keep abreast of advances in human health research in developed countries and concentrate efforts on the identification of local sources of photochemical for which the scientific evidence is strong. Accurate quantification of the photochemical, including monitoring and enhancing of their levels throughout the food chain, and product development for the domestic and international markets could then be accomplished. The importance of databases on antioxidants and bioactive compounds cannot be overemphasized. In fact, reliable data on food composition is a prerequisite to a successful epidemiological study. Agronomic and post-harvest handling and processing measures can be taken to insure high levels of these compounds in the diet. The possibility that manipulation of phytochemical metabolism by expensive molecular techniques may not substantially improve phytochemical contents beyond what can be achieved by traditional means should also be taken into account.  

Identifying bioactive compounds in tea and establishing their health effects are active areas of scientific inquiry. There are exciting prospects that select bioactive compounds will reduce the risk of many diseases, including chronic diseases such as cardiovascular disease. Because of the number of bioactive compounds and the diversity of likely biological effects, numerous and diverse experimental approaches must be taken to increase our understanding of the biology of bioactive compounds. Recognizing the complexity of this biology, sophisticated experimental designs and analytical methodologies must be employed to advance the field. The discovery of novel health effects of bioactive compounds will provide the scientific basis for future efforts to use biotechnology to modify/fortify foods and food components as a means to improve public health. 

9 Conclusion  

Tea is a pleasant, popular, user-friendly, cheaper and safe drink that is undoubtedly more a medicine than a beverage with high potential in contributing future therapeutics towards human well being. The bioactive compounds present in tea namely polyphenols (catechins and flavonoides), alkaloids (caffeine, theobromine, theophylline, etc.), volatile oils, polysaccharides, amino acids, lipids, vitamins (e.g., vitamin C), inorganic elements (e.g., aluminum, fluorine and manganese), etc having plethora of wonders and magic are now of increasing interest for the scientists and researchers working globally in this direction. An organised and integrated effort is necessary to harness all the potentials of tea and to explore the hidden ones in the days to come. 

References

An B.J., Kwak J.H., Son J.H., Park J.M., Lee J.Y., Jo C. and Byun M. W., 2004,   Biological and anti-microbial activity of irradiated green tea polyphenols, Food Chemistry, 88: 549–555
http://dx.doi.org/10.1016/j.foodchem.2004.01.070

Atoui A. K M., Ansouri A., Boskou G. and Kefalas P., 2005, Tea and herbal infusions: Their antioxidant activity and phenolic profile, Food Chemistry, 89: 27–36
http://dx.doi.org/10.1016/j.foodchem.2004.01.075

Chan E. W. C., Lim Y.Y., Chong K.L., Tan J. B. L. and Wong S.K., 2010, Antioxidant properties of tropical and temperate herbal tea, Journal of Food Composition and Analysis, 23: 185–189
http://dx.doi.org/10.1016/j.jfca.2009.10.002

Cooper R., Morré D.J. and Morré D.M., 2005, Medicinal Benefits of Green Tea:  Part I. Review of Noncancer Health Benefits. The Journal of Alternative and Complementary Medicine, 3:521-528
http://dx.doi.org/10.1089/acm.2005.11.521

Cooper R., Morré D. J and Morré D. M., 2005, Medicinal Benefits of Green Tea:  Part II. Review of Anticancer Properties. The Journal of Alternative and Complementary Medicine, 11: 639-652
http://dx.doi.org/10.1089/acm.2005.11.639

Costa A. S. G., Nunes M. A., Almeida I. M. C., Carvalho M.R., Barroso M. F., Alves R. C. and Oliveira M. B. P. P., 2012, Teas dietary supplements and fruit juices: A comparative study regarding antioxidant activity and bioactive compounds. Journal of Food Science and Technology, 49: 324-328
http://dx.doi.org/10.1016/j.lwt.2012.02.030

Deetae P., Parichanon P., Trakunleewatthana P., Chanseetis C. and Lertsiri S., 2012, Antioxidant and anti-glycation properties of Thai herbal teas in comparison with conventional teas, Food Chemistry, 133: 953–959
http://dx.doi.org/10.1016/j.foodchem.2012.02.012

Hajimahmoodi M., Hanifeh M., Oveisi M. R., Sadeghi N. and Jannat B., 2008, Determination Of Total Antioxidant Capacity Of Green Teas, Iran. J. Environ. Health. Sci. Eng, 5:167-172

Hossain M. A., Salehuddin S. M., and Rahman A. 2009, Flavonoid contents and ant oxidative effect of tea samples, Asian Journal of Food and Agro-Industry, 2:421-432
 

Maps of World.2014, http://www.mapsofworld.com/world-top-ten/tea-ex porting-countries.html accessed on 12 Jan 2014
 

Joe A., Vinson Ph.D., Yousef A. and Dabbagh M.A., 1998, Tea Phenols: Antioxidant Effectiveness of teas tea component tea fraction and their binding with Lipoproteins, Nutrition Research, 18:1067-1075
http://dx.doi.org/10.1016/S0271-5317(98)00089-X
 

Jun X., Deji S., Ye L. and Rui Z., 2011, Micro mechanism of ultrahigh pressure extraction of active ingredients from green tea leaves. Food Control, 22: 1473-1476
http://dx.doi.org/10.1016/j.foodcont.2011.03.008
 

Karakaya S. and Nehir S. 2006, Total Phenols and Antioxidant Activities of Some Herbal Teas and In Vitro Bioavailability of Black Tea Polyphenol, GOÜ. Ziraat Fakültesi Dergisi, 23:1-8
 

Kodama D. H., Lajolo F. M. and Genovese M. I., 2010, Flavonoids total phenolics and antioxidant capacity: comparison between commercial green tea preparations, Ciênc. Tecnol, Aliment Campinas, 30:1077-1082
http://dx.doi.org/10.1590/S0101-20612010000400037
 

Komes D., Horzic D., AK A. B. and Vulic I., 2010, Green tea preparation and its influence on the content of bioactive compounds, Food Research International, 43:167–176
http://dx.doi.org/10.1016/j.foodres.2009.09.022
 

Liebert M., licht U., Bohm V. and Bitsch R., 1999, Antioxidant properties and total phenolics content of green and black tea under different brewing conditions, Zeitschrift fur lebensmittelubter suchung und-Forchung A, 208:217-220
 

Lin S.D., Mau J.L. and Hsu C.A. 2012, Bioactive components and antioxidant properties of g-amino butyric acid GABA tea leaves. Food Science and Technology, 46: 64-70
 

Loranty A. and Rembiałkowska E., 2010, Identification quantification and availability of carotenoids and chlorophylls in fruit herb and medicinal teas. Journal of Food Composition and Analysis, 23: 432–441
http://dx.doi.org/10.1016/j.jfca.2010.01.007
 

McKenna D.J., Hughes K. and Jones K. 2000, Green Tea Monograph. Alternative Therapies in Health and Medicine, 6: 61-84
 

Ramalho. S. A., Nigam. N., Oliveira G. B., de Oliveira P.A., Oliveira T., Silva M. and Narain N. 2013, Effect of infusion time on phenolic compounds and caffeine content in black tea, Food Research International, 51: 155–161
http://dx.doi.org/10.1016/j.foodres.2012.11.031
 

Ramma A. L.,  BahorunT., Crozie R. A.,  Zbarsky V. D.,  Dexter D.T. and Aruoma O. I. 2005, Characterization of the antioxidant functions of flavonoids andproanthocyanidins in Mauritian black teas. Food Research International, 38:357–367
http://dx.doi.org/10.1016/j.foodres.2004.10.005
 

Sharangi A.B., 2009, Medicinal and therapeutic potentialities of tea Camellia sinensis L. Food Research International,42: 529–535
http://dx.doi.org/10.1016/j.foodres.2009.01.007
 

Sharangi A.B., Siddiqui M.W. and Dávila Aviña, J.E., 2014, Black Tea Magic: Overview of Global Research on Human Health and Therapeutic Potentialities, Journal of Tea Science Research,4: 1-16
 

Segal M.,1996, Tea: A Story of Serendipity. Retrieved September 27 2005 from http://www.fda.gov/fdac/features/296_tea.html.
 

Stewart A.J. Mullen W. and Crozier A. ,2005, On-line high-performance liquid chromatography analysis of the antioxidant activity of phenolic compounds in green and black tea. Molecular Nutrition and Food Research, 49: 52-60
http://dx.doi.org/10.1002/mnfr.200400064
 

Wang H. F., Tsai Y. S., Lin M. L., and Ou A. S. M., 2006, Comparison of bioactive components in GABA tea and green tea produced in Taiwan, Food Chemistry, 96: 648–653
http://dx.doi.org/10.1016/j.foodchem.2005.02.046
 

Yang J. and Liu R. H., 2013, The phenolic profiles and antioxidant activity in different types of tea, International Journal of Food Science and Technology, 48: 163–171
http://dx.doi.org/10.1111/j.1365-2621.2012.03173.x