Black Tea Magic: Overview of Global Research on Human Health and Therapeutic Potentialities  

A.B. Sharangi1 , M.D. Wasim Siddiqui2 , J.E. Davila Avina3
1. Department of Spices and Plantation Crops Faculty of Horticulture, Bidhan Chandra Krishi Viswavidyalaya [Agricultural University], PO: KVV-741252, Mohanpur, Nadia, West Bengal, India
2. Department of Food Science and Technology Bihar Agricultural University, BAC, Sabour, Bhagalpur, Bihar , 813210, India
3. Laboratorio de Bioquímica y Genética de Microorganismos Facultad de Ciencias Biológicas, UANL, Mexico
Author    Correspondence author
Journal of Tea Science Research, 2014, Vol. 4, No. 1   doi: 10.5376/jtsr.2014.04.0001
Received: 19 Nov., 2013    Accepted: 25 Dec., 2013    Published: 02 Jan., 2014
© 2014 BioPublisher Publishing Platform
This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:

Sharangi et al., 2014, Black Tea Magic: Overview of Global Research on Human Health and Therapeutic Potentialities, Journal of Tea Science Research, Vol.4, No. 1 1-16 (doi: 10.5376/jtsr.2014.04.0001)

Abstract

Tea is the second most frequently consumed cheapest non-alcoholic beverage worldwide,   black tea is the most produced type, followed by green and Oolong tea. The venture of this paper is to focus on the latest research efforts regarding the health effects related to consumption of black tea and derive some future research directions towards its therapeutic potentialities. With a view of the above, comprehensive information on the fermentation process, composition, and quality of black tea has been provided. Several major beneficial roles of black tea are antioxidant activity, antiulcer effect, anti-inflammatory effect, antimicrobial properties, anticancer properties, antimutagenic activity along with the attenuating or reducing effects on blood pressure, CHD and cardiovascular disease, atherosclerosis, oxidative damage are important. Moreover, black tea has proven to enhance insulin activity, helps in treating asthma, retard cataract, maintains fluid balance, bone health and dental health, improves mean body mass index and body weight, prevents cellular DNA damage, inhibits HIV, lowers stress hormone levels, etc. The potential effect on human biosynthetic pathways related to oxidative processes as well as that on cognitive performance has also been discussed with citation from various research findings.

Keywords
Camellia sp; Black tea; Polyphenols; Human health; Therapy

Tea stands as the second most consumed non-alcoholic beverage around the world, and it is also the less expensive one (Sharangi, 2009). It is grown mainly in tropical and temperate areas, and made through the harvest of young leaflets (Hampton, 1999). Although the leaves from other plant portions have commercial use, tea basically consists of very few leaves, as many as three, including the terminal young apical buds of the species Camellia assamica, Camelliasinensis. Native from South-East Asia, has been grown since ancient times, Chinese mythology records that tea was discovered by emperor Shen Nung in 2737 BC (Harbowy and Balentine, 1997). The installment of tea as a profitable crop has been proved successful worldwide (Dutta et al., 2010). Tea production has increased considerable in the last years, going from 850 million kg between the years of 2000 and 2003, up to 980 million kg between the years 2004 and 2007. China and India are the main tea producing countries; other countries like Indonesia, Sri Lanka and Kenya contribute to tea production in smaller scale. Currently, it is cultivated in over 30 countries (Eroğlu, 2011).

Tea can be classified into three major forms based on its processing. These forms are black tea, which is fermented or fully aerated, green tea, which is not fermented and, oolong tea, which is partially fermented (Ratnasooriva and Fernando, 2008). The tea consumption globally is divided in black tea, green tea, and Oolong tea, 78%, 20%, and 2% respectively. The majority of black tea is consumed in the western hemisphere, whereas green tea is most common in Asia, in the case of Oolong tea, it is almost restricted to Southern China (Ju et al., 2007; Khan and Mukhtar, 2007). The consumption of tea fits naturally in a healthy life style, which has made tea a popular commodity in the global market.
All the types of tea black, green, and Oolong are made from the leaves of the species Camellia sinensis. The flavor of black tea is usually stronger compared to other less oxidized forms, two varieties account for most of black tea. Orthodox and CTC (Cut– Tear–Curl) operations are performed during production (Hicks, 2009). CTC processed tea posses a strong liquor when brewed, in the other hand , orthodox processed tea delivers a very unique flavor, very appreciated by consumers willing to pay a expensive price.
After black tea is harvest (plucking of tender new leaves), a series of processes take place in order to have the final product, and these include withering, pre-conditioning, CTC, fermentation, and lastly drying (Robertson, 1992). The fermentation process is one of the key components for production of black tea. The fermentation process starts with the cut of green leaves, then they are partially dried, later subject of enzymatic action at high temperatures. The characteristic color we observed in black tea is caused by partial polymerization and oxidation of polyphenols and their esters ( catechins or flavan 3-ol and their gallates) to theaflavin and thearubigin. The known flavor of black tea is most likely due to the release of volatile aromatic aglycones by several glycosidases (Higdon and Frei, 2003; Halder and Bhaduri, 1998). The UK NationalDiet and Nutrition Survey [NDNS] indicated in a study conducted on 7000 adults that people between ages of 50–64 consume more black tea than younger population (ages 19-24) [mean consumption 644 vs 298 ml] Henderson et al (2002).
The paper encompasses various research initiatives related to black tea effects on human health. The main endeavour is to focus on the latest research efforts on some of the important questions regarding the health benefits related to consumption of black tea and derive some future research directions towards its therapeutic potentialities.
2 Black tea fermentation process
Fermentation is basically an oxidation process where the leaves are subject to several treatments which include the removal of moisture by airflow (called withering), pre-conditioning, and CTC which refers to the cutting and maceration of leaves.The fermentation process can be performed in open air conditions, on the floor, or moving conveyor under controlled temperature, humidity, and airflow. Once the intracellular compartments are degraded, the oxidization of polyphenols present in the cell vacuole triggered by enzymes, promotes the formation of theaflavin and thearubigin pigments which characterize black tea, (Robertson, 1992). During this process, the tea leaves gradually change in color going from green to coppery brown, releasing a floral smell. Considering the colour and smell attributes, smell is essential since a strong, unique fragrance emanates from the leaves after optimal fermentation. Monitoring tea aroma during fermentation has been proposed to be achieved through the use of a novel electronic nose-based approach (Bhattacharyya, 2007).
The fermented tea is more beneficial than black tea regarding both, nutrition and therapeutic advantages (Pasha and Reddy, 2005). Teas are available in various fermentation levels from green to black; however, the difference in biochemical composition in relation to fermentation has not been fully investigated. Fermentation of leaves diminishes the antioxidant potential and can result in lowering potential health benefits of flavonoids (Chan et al., 2011).
3 Composition of black tea
Tea is a known rich source of antioxidants compounds, flavonoids, carotenoids, tocopherols, and ascorbic acid, among others (Wu and Wei, 2002). The major phenolic compounds observed to be present in teas include the flavan-3-ols and flavonols. Among the main flavan-3-ols present in green tea are [-]-epicatechin and its gallate derivatives. In contrast, in black tea, these compounds are observed to be present in small amounts which is supposed to be the result of the formation of theaflavins and thearubigins (Finger and Engelhardt, 1991; Balentine et al., 1997). The main flavonols contain lower levels of myricetin and are mainly conjugates of quercetin and kaempferol (Finger et al., 1991; Price et al., 1998; Wang and Sporns, 2000; Finger and Engelhardt, 1991). Other related compounds observed to be present in tea are gallic acid, quinic esters of gallic, coumaric, and caffeic acids, purine alkaloids such as theobromine and caffeine (Keihne and Engelhardt, 1996; Ashihara and Crozier, 1999), proanthocyanidins (Kiehne et al., 1997; Lakenbrink et al., 1999) and traces of flavones (Kiehne and Engelhardt, 1993).
Theaflavins (theaflavin, theaflavin-3-gallate, theaflavin-3′-gallate, and theaflavin-3, 3′-digallate) account for 2~6% of the solids in brewed black tea, these compounds are responsible for the typical color and flavor of black tea. Twenty per cent of the solids present in brewed black tea are polyphenols, thearubigens (characterized by large molecular weights and obscure chemical composition) being the most abundant (Yang and Landau, 2000). Black tea contains low levels of catechins with the highest levels of theaflavins and thearubinins. According to Chan et al (2011) theaflavins and thearubinins have been observed to be as effective as the catechins in the control of cholesterol and prevention of heart diseases and cancer.
The flavonols found in tea have been proved to act as powerful antioxidants and are present in 2~3% of the water-soluble solids from tea leaves. On a dry weight basis, the contents of flavonol such as myricetin, quercetin, and kaempherol in green tea leaves has been observed to range from 0.83-1.59 g/kg, 1.79-4.05 g/kg and 1.56-3.31 g/kg, respectively. In contrast the values in black tea leaves, range from 0.24~0.52 g/kg, 1.04~3.03 g/kg and 1.7~2.31 g/kg, respectively. The particle size of ground leaves has been observed to have a important impact on the concentration of flavonols (Wang and Helliwell, 2001). Tea cream and haze [characterized by lack of clarity] in black tea infusions incremented with the increase of the temperature during the tea extraction process. High-performance liquid chromatography results confirmed that compounds with pyrogallol groups are involved in tea creaming (Liang and Xu, 2002). Taste dilution analyses performed on freshly prepared black tea infusions showed that a series of 14 flavon-3-ol glycosides are the main contributors to the astringent taste perceived when black tea is consumed. Among these glycosides, the apigenin-8-C-[α-L-rhamnopyranosyl-[1→2]-O-β-D-glucopyranoside] was identified for the first time in tea preparations (Scharbert et al., 2004).
During the production of black tea, most catechins are polymerized into more complex molecules called thearubigins. Information about the microbial degradation of these complex polyphenols is minimal; however, hippuric acid has been identified as a major urinary excretion product associated with black tea consumption (Mulder et al., 2005). Quantitative measurements have shown that geraniol along with eight odourants were significantly increased in the infusion as compared to their concentration in the leaves (Schuh and Schieberle, 2006). Only a small quantity was leached into the brew, the majority being retained in the infused leaf/tea residue. Greater carotenoid degradation was observed in the CTC process compared to the orthodox process which is also greater in withered than unwithered, and in the order beta-carotene>zeaxanthin>lutein. Vitamin A value was greater in orthodox tea than CTC tea and varied depending on clones. Carotenoids in tea show a good stability as a result of the presence of antioxidants, such as polyphenols and catechins (Ravichandran, 2002).
4 Quality of black tea
The quality of tea involves parameters such as color, appearance, flavors, and taste. Caffeine is an important factor for quality evaluation (Yao et al., 2006) in the way it indicates briskness and other taste properties (Dev Choudhury et al., 1991). It has been observed the liquor brightness has a negative effect in lower levels of caffeine contents in combination with high levels of epigallo catechin gallate (EGCG) and epicatechin (EC). Higher levels of EGCG and ECG, results in increase caffeine content in green leaf, whereas, the liquor brightness is affected by theaflavins and caffeine contents (Dutta et al., 2011).
Obanda et al. (2001) reported that degradation of individual theaflavins is variable during the fermentation process. Both duration and temperature levels had important effects on decreasing levels of individual theaflavins along with brightness and briskness. ECG and EGCG were found to be the main residual catechins in black tea.
Turkmen et al. (2006) evaluated the effect of water and different organic solvents viz., acetone, N, N-dimethylformamide (DMF), ethanol or methanol at several concentrations on the total polyphenol content and antioxidant activity of black and mate tea. The authors indicated that solvents with different polarity had a significant effect on polyphenol content and antioxidant activity. Polyphenol content was observed to be highly correlated with the antioxidant activity of tea extracts. Enzymatic extraction has been studied to improve the quality of black tea extracts with pretreatment of pectinase and tannase independently, successively and simultaneously. The results observed suggested that the use of a single enzyme, tannase, is preferable for the pre-treatment of black tea (Chandini et al., 2011). Tea tasters have assessed its chemical composition, parameter such as color differences of black tea infusions, and their relationships with sensory quality have been evaluated. Significant correlations between the individual quality attributes had been observed. Among the main factors, content of caffeine, nitrogen, amino acids, polyphenols, gallocatechin (GC), epigallocatechin (EGC), catechin (C), epicatechin (EC), epicatechin gallate (ECG), catechin gallate (CG), total catechins, theaflavin (TF) and theaflavin-30-gallate (TF30G) and infusion colour indicators of ΔL, Δa, Δb and ΔE were observed to be significantly correlated to total quality score (TQS) (Liang et al., 2003).
The metabolic pathways involved in biotransformation of flavonoids present in tea are little known. 1H nuclear magnetic resonance spectroscopy was utilized to obtain nonselective profiles of urine samples collected from three volunteers before and after a single dose of black tea. The major urinary black tea metabolite was confirmed to be Hippuric acid (Daykin et al., 2005). Additional sensory studies affirmed that the flavanol-3-glycosides gives a velvety astringent taste sensation to the oral cavity, contributing as well to the known bitter taste of tea infusions by amplifying the bitterness of caffeine (Scharbert and Hofmann, 2005). Effects of temperature and soaking duration on total phenolic and antioxidant activity of black tea and black and bush tea combined in 50:50 ratio was studied by Shonisani et al. (2011). They recommended brewing tea at 90°C for 3 min for optimum polyphenols and antioxidant activity in the brewed liquor. Normal effects of tea in protecting against cardiovascular disease get blocked by the addition of milk becausecaseinfrom the milk binds to the molecules in the tea that cause the arteries to get relaxed, particularly EGCG (Lorenz et al., 2007). Other studies have found no significant effect of milk on the observed increase in total plasma antioxidant activity (Reddy et al., 2005). Previous studies have observed a beneficial effect of black tea, which was not attributable to the catechin content (Widlansky et al., 2005).
Warden et al (2001) conducted a research to evaluate the bioavailability of catechins from black tea in humans drinking tea throughout the day. Results indicated that approximately 1.68% of ingested catechins were present in the plasma, urine, and feces, and the apparent bioavailability of the gallated catechins was lower than the nongallated forms, confirming thus the bioavalability of catechins.
5 Health Benefits and Therapeutic Potentialities of Black Tea
5.1 Antioxidant activity
Highly reactive free radicals and oxygen species are found in nature from many sources, reactive free radicals oxidize nucleic acids, proteins, lipids, or DNA and can promote and initiate degenerative diseases. Antioxidant compounds like phenolic acids, polyphenols and flavonoids scavengefree radicals including peroxide, hydroperoxide or lipid peroxyl , inhibiting the oxidative mechanisms that could lead to degenerative diseases (Henning et al., 2004). Green and black tea polyphenols have been extensively studied as anti-cancer compounds. In vitro experiments have supported their significant antioxidant activity. The effect of black tea consumption, with and without milk, on the plasma antioxidant activity in humans produces a significant increase in plasma antioxidant activity reaching maximal levels at about 60 min (Henning et al., 2004). Adding milk to black tea did not have a differential effect on the increases in plasma antioxidant activity (Leenen et al., 2000).
Experimental studies have determined that the presence of polyphenols in black tea have a strong antioxidant potential in vitro and in vivo. Ryan and Sutherland (2011) analyzed and compare the total antioxidant capacity (TAC) of five brands of tea, they found that each of the teas was a significant source of antioxidants (7796–10,434 μmol/l FRAP). In this case the addition of milk lowered the TAC of each of the teas. When compared to tea with semi-skimmed bovine milk, each of the five teas presented either significantly higher antioxidant values or no change was observed after the addition of soya milk. The addition of soya milk to black tea may be a useful alternative to semi-skimmed bovine milk if the purpose is to maintain the overall antioxidant potential of the tea.
Luczaj and Skrzydlewska (2004) investigated the effect of black tea on antioxidant effects on the liver, blood serum, and brain of 12-months old rats which were subject to sub-chronical intoxication with ethanol during 28 days. Administration of black tea alone caused an increase in the activity and concentration of antioxidant factors, which was more extensively observed in the liver and serum compared to the brain. Black tea prevented considerably antioxidant parameters against changes caused by ethanol. These results indicate beneficial antioxidant effect of black tea regarding all examined organs, especially the liver.
Antioxidative activities of volatile extracts from six teas (one green tea, one Oolong tea, one roasted green tea, and three black teas) were studied by using an aldehyde/carboxylic acid assay and a conjugated diene assay. All extracts except roasted green tea exhibited dose-dependent inhibitory activity in the aldehyde/carboxylic acid assay (Yanagimoto et al., 2003).
Dietary phenols are antioxidants, and their consumption could be an important factor in the prevention of cardiovascular diseases. Coffee and tea are som
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