PREVENTIVE
MEDICINE
21, 334-350
(1992)
Green Tea Composition, Consumption, Polyphenol Chemistry’ HAROLD 256 Broad
PH.D.’
N. GRAHAM,
Avenue,
Englewood,
and
New
Jersey
07631
Tea is grown in about 30 countries but is consumed worldwide, although at greatly varying levels. It is the most widely consumed beverage aside from water with a per capita worldwide consumption of approximately 0.12 liter per year. Tea is manufactured in three basic forms. Green tea is prepared in such a way as to preclude the oxidation of green leaf polyphenols. During black tea production oxidation is promoted so that most of these substances are oxidized. Oolong tea is a partially oxidized product. Of the approximately 2.5 million metric tons of dried tea manufactured, only 20% is green tea and less than 2% is oolong tea. Green tea is consumed primarily in China, Japan, and a few countries in North Africa and the Middle East. Fresh tea leaf is unusually rich in the flavanol group of polyphenols known as catechins which may constitute up to 30% of the dry leaf weight. Other polyphenols include flavonols and their glycosides, and depsides such as chlorogenic acid, coumarylquinic acid, and one unique to tea, theogallin (3-galloylquinic acid). Caffeine is present at an average level of 3% along with very small amounts of the other common methylxanthines, theobromine and theophylline. The amino acid theanine (5-Nethylglutamine) is also unique to tea. Tea accumulates aluminum and manganese. In addition to the normal complement of plant cell enzymes, tea leaf contains an active polyphenol oxidase which catalyzes the aerobic oxidation of the catechins when the leaf cell structure is disrupted during black tea manufacture. The various quinones produced by the enzymatic oxidations undergo condensation reactions which result in a series of compounds, including bisflavanols, theaflavins, epitheaflavic acids, and thearubigens, which impart the characteristic taste and color properties of black tea. Most of these compounds readily form complexes with caffeine. There is no tannic acid in tea. Thearubigens constitute the largest mass of the extractable matter in black tea but their composition is not well known. Proanthocyanidins make up part of the complex. Tea peroxidase may be involved in their generation. The catechin quinones also initiate the formation of many of the hundreds of volatile compounds found in the black tea aroma fraction. Green tea composition is very similar to that of the fresh leaf except for a few enzymatically catalyzed changes which occur extremely rapidly following plucking. New volatile substances are produced during the drying stage. Oolong tea is intermediate in composition between green and black teas. 0 1992 Academic
Press. Inc.
INTRODUCTION
Useful consideration of the physiological and pharmacological effects of tea requires background information concerning production, leaf composition, availability of the various types of tea, and, most importantly, the chemical changes that take place during the manufacture of the various commercial products. Consumption patterns of the different types of tea beverages should also be noted, As i Presented at the First International Symposium on the Physiological and Pharmacological Effects of Camellia sinensis (Tea), March 4-6, 1991, American Health Foundation, New York City. Jointly sponsored by The Tea Council and the National Tea Association. ’ Formerly of the Thomas J. Lipton Co. 334 0091-7435192
$5.00
Copyright 0 1992 by Academic Press, Inc. All tights of reproduction in any form reserved.
PROCEEDINGS:
PHYSIOLOGICAL
AND PHARMACOLOGICAL
EFFECTS
OF TEA
335
polyphenols are the most significant group of tea components, their complex chemistry should be understood in some detail. This article is intended to provide such information. TEA PRODUCTION
Tea is the plant, leaf, or beverage originating from what is now considered a single species--Camellia sinensis (L.) 0. Kuntze. Two major varieties are recognized-sinensis and assamica. In the field the obvious difference observed between the major varieties is leaf size. Var. sinensis is small-leaved (5-12 cm). Var. assamica may have leaves up to 20 cm in length. Much hybridization has occurred. Breeding, vegetative propagation, and selection have resulted in the emergence of thousands of lines with varying properties, including compositional differences. In general, the China teas (var. sinensis) are more cold resistant and therefore suited for cultivation in the more temperate climates. The tea plant originated in Southeast Asia and is presently cultivated in over 30 countries. The principal tea producing countries of the world are listed in Table 1 (1). The term green tea refers to the product manufactured from fresh leaf while preventing oxidation of the polyphenolic components. These are the substances of the greatest importance to this symposium. Black tea manufacture is carried out so as to ensure a high degree of enzymatically catalyzed aerobic oxidation of the leaf polyphenols followed by a series of chemical condensations. Oolong tea is partially oxidized. World production of tea has increased steadily with only a few minor reversals. Increased production is largely due to improved yields obtained by the implementation of modern horticultural practices and by replacement of older plants with recently developed high yielding varieties. The establishment of these new clones by careful plant selection or even by tissue culture also allows for the incorporation of other desirable properties that could result in modified compositions designed to meet pharmacological as well as conventional crop needs. Production of tea by major types is shown in Table 2 (1). Green tea production is carried out in relatively few countries as shown in Table 3 (1). Oolong tea production is confined to China (approx. 50,000 tons) and Taiwan (approx. 10,000 tons).
PRINCIPAL
India China Sri Lanka Kenya Indonesia Turkey Note.
TABLE 1 TEA PRODUCING COUNTRIES (1990) 715 540 230 200 150 130
USSR Japan Iran Bangladesh Malawi Vietnam Argentina
Total dry wt of ten measured in thousands of tons.
110 90 55 45 40 40 35
336
HAROLD
N. GRAHAM
TABLE WORLD
2
TEA PRODUCTION
BY TYPE (1990)
Black Green Oolong
1940 515 60
Total
251s
Note. Total dry wt of tea measured in thousands of tons.
Aside from water, tea is the most consumed beverage in the world. Assuming a 100: 1 ratio of water to tea for beverage preparation, world tea consumption must be about 0.12 liter per day per capita. Consumption is far from uniform. Large segments of the world’s population drink virtually no tea. Representative data showing the disparate consumption patterns are shown in Table 4 (1). Green tea is consumed primarily in Japan, China, and some parts of the Middle East and North Africa. As is well known, not only does tea consumption vary from country to country, but also there is enormous variation in any given population. This ranges from no tea at all to as many as 20 or more cups per day. This high level of consumption is tolerable physiologically since the total caffeine content of 20 cups is less than 1 g. TEA COMPOSITION Tea composition varies with climate, season, horticultural practices, variety, and the age of the leaf, i.e., the position of the leaf on the harvested shoot. Data shown in Table 5 reflect a representative tea but variations may be considerable (2).
The polyphenols constitute the most interesting group of tea leaf components, especially the catechin group of the flavanols. Six of these occur in considerable quantities in fresh leaf. Simple catechin structures are shown in Fig. 1. Two configurations are possible but most of the catechin mass is in the so-called “epi-” form. When three hydroxy groups are present on the “B” ring the substances are known as gallocatechins as shown in Fig. 2. Another variation results from the esterification of the OH group on the pyran ring with gallic acid. The catechin gallates are illustrated in Fig. 3. The principal catechins are present at high concentrations in young tea leaf as shown in Table 6 (2). Catechin concentration is highly dependent on leaf age. The leaf bud and the TABLE GREEN
China Japan Indonesia Vietnam USSR
3
TEA PRODUCTION
310 90 40 30 20
Note. Total dry wt of tea measured in thousands of tons.
(1990)
Taiwan India Sri Lanka Bangledesh
8 8 1 1
PROCEEDINGS:
PHYSIOLOGICAL
AND PHARMACOLOGICAL TABLE
TEA CONSUMPTION
Ireland United Kingdom USSR Germany France Italy Turkey Japan Pakistan India China Thailand
337
4
IN SELECTED
3.04 2.81 0.87 0.18 0.18 0.06 2.19 0.96 0.93 0.58 0.30 0.01
Note. Consumption
EFFECTS OF TEA
COUNTRIES
Chile Canada United States Mexico New Zealand Australia Tunisia Egypt Morocco South Africa Nigeria
0.86 0.55 0.34 ‘co.01 1.59 1.12 1.43 1.33 1.11 0.56 0.02
of tea measured in kilograms per capita (average for years 1987-1989).
first leaf are richest in epigallocatechin gallate (3). Catechin levels also vary greatly with varietal differences. Green tea is often manufactured from tea leaf with somewhat lower catechin levels than leaf used for black tea manufacture. Catechins are the predominant group of substances in green tea and they are the most significant of all tea components. As will be shown, they play the most important role in the series of oxidations and condensations which occur during the production of black tea. The catechins are colorless, astringent, water soluble compounds. They are readily oxidizable, although their oxidation potentials vary. This property has been exploited through their use as food antioxidants. They retard rancidity in fats and oils by quenching free radical peroxide activity brought about by aerobic oxidation. Based on the concentrations required for 50% inhibition of oxidation, the inhibitory effect of some tea leaf catechins on the aerobic oxidation of linoleic acid is similar to that of BHA (4). In biological systems oxygen is an important acceptor of electrons, leading to the formation of active oxygen and hydroxyl free radicals. Scavenging effects of green tea extracts and green tea polyphenol fractions are superior to those of ascorbic acid (vitamin C) and tocopherol (vitamin E) with respect to some active oxygen radicals but are less pronounced with hydroxyl free radicals (5). Effects depend on the particular free radical system under investigation. The gallocateTABLE COMPOSITION
Polyphenols Methyl xanthines Amino acids Organic acids Carotenoids Volatiles Note. Composition
5
OF FRESH GREEN
36 3.5 4 1.5 co. 1 ‘co. 1
measured in % dry wt.
TEA LEAF
Carbohydrates Protein Lignin Lipids Chlorophyll, etc. Ash
25 15 6.5 2 0.5 5
338
HAROLD
N.
GRAHAM
OH
OH OH
HO
HO
(+) Catechin
(-) Epicatechin
FIGURE 1
chins and the catechin gallates exhibit the strongest radical quenching properties (6).
In recent years, with the development of more sophisticated separation and identification techniques, other catechins and related products have been identified in fresh tea leaf but little quantitative data have been reported (7). These include a catechin digallate and some methylated catechins. A novel group of compounds called chalcan-flavans has also been identified. These are bimolecular combinations of a catechin attached to a chalcone derivative. Bisflavanols (also known as theasinensins) occur in green leaf (7). These are dimeric gallocatechins linked by C-C bonds at the “B” rings as indicated in Fig. 4. They will be discussed further under black tea because of their additional formation during its production. Dimeric proanthocyanidins are also present in fresh tea leaf (7). These may also be considered condensation products of the catechins but linked by C-C bonds between an “A” ring and a pyran ring. They will be discussed further under black tea. The monomeric anthocyanidins, cyanidin and delphinidin, are the flavone equivalents of epicatechin and epigallocatechin, respectively (Fig. 5). Flavonols occur both in the free state and as glycosides of glucose, rhamnose, and possibly other sugars (8). Their structures are analagous to those of the flavanols but represent a different state of oxidation. The flavonols also play a part in the reactions which occur during black tea manufacture. The depsides of tea are condensation products of two different hydroxy acids (9). Examples are chlorogenic and p-coumarylquinic acids. Theogallin is derived from gallic and quinic acids (Fig. 6). It may be unique to tea (9). Free gallic acid is present in tea leaf and enters into interesting oxidation reactions during the manufacture of black tea. Quinic acid, as would be expected from OH
OH OH
HO
HO
(+) Gallocatechin
OH
(-) Epigallocatechin
FIGURE 2
PROCEEDINGS:
PHYSIOLOGICAL
AND
PHARMACOLOGICAL
EFFECTS
OF TEA
339
H”qg$$ OH H”q$$$o 0 (-) Epicatechin
0
OH gallate
(-) Epigallocatechin
OH gallate
FIGURE 3
its inclusion in tea depsides, is also found in fresh leaf, although it was not recognized until quite recently (10). In addition to the normal complement of amino acids in tea leaf, there is also present an unusual amino acid known as theanine. It is an N-methylated derivative of glutamine (11). It constitutes about one half of the total amino acid content. Its presence in green tea is said to correlate with beverage quality. The popularity of tea is partly due to the presence of moderate amounts of caffeine (254.5%). Other methyl xanthines, theobromine and theophylline, are also present but in very small quantities, 0.1 and 0.02%, respectively (12). Trigalloylglucose has been identified as a component of green leaf (7). While its structure is reminiscent of tannic acid, the latter contains five galloyl groups bonded to the glucose molecule with four or tive additional galloyl groups attached with depside linkages. Trigalloylglucose has not been observed in manufactured green or black tea, perhaps because of hydrolysis to the free acid and glucose. The protein fraction includes the enzymes normally associated with plant cell metabolism. The enzymes responsible for catechin synthesis have been identified. Of greatest interest is tea polyphenol oxidase which catalyzes the aerobic oxidation of the catechins. In the growing plant the enzyme is physically separated from the polyphenol substrates contained in the leaf cell vacuoles. The molecular weight is approximately 140,000. Copper is a required cofactor (13). Polyphenol oxidase activity is greatest in the youngest leaf. High levels are important for successful black tea production. Tea peroxidase has also been reported to enter into the pathway of polyphenol oxidation during tea processing (14). Other enzymes of interest in tea are glucosidases which catalyze the hydrolysis of several aroma precursors (15), lipoxidases which are responsible for the generation of volatile aldehydes (16), and the enzymes responsible for methyl xanTABLE
6
PRINCIPAL FRESH LEAF CATECHINS (+)-Catechin (-)-Epicatechin (- )-Epicatechin
gallate
l-2 1-3 3-6
Note. Catechins measured in % dry wt.
( + )-Gallocatechin ( -)-Epigallocatechin (- )-Epigallocatechin Total 16-30
gallate
1-3 3-6 7-13
340
HAROLD
N.
GRAHAM
HO
OH
Bisflavanols R.H or Galloyl
FIGURE
4
thine synthesis. There is nothing exceptional about the carbohydrate, lipid, or lignin fractions. Carotenoids are present at low levels but they are important precursors of tea aroma. Violaxanthine, p-carotene, neoxanthin, and lutein are among those identified (17). The volatile fraction of fresh green tea is extremely small but important in determining the acceptance of the tea beverage. More than 60 volatile components have been identified in fresh tea leaf. They include alcohols, carbonyls, esters, acids, and cyclic compounds (18). This fraction is greatly augmented in variety and quantity during tea manufacture. Volatiles in fresh leaf have not been studied as thoroughly as those in green and black teas. It is difficult to determine which substances are actually present in the freshly plucked leaf and which are artifacts of handling. The mineral content of tea is roughly similar to that of most plants. Tea tends to accumulate aluminum and manganese, depending on soil conditions. Copper is essential for polyphenol oxidase activity as will be discussed. Tea is relatively rich in potassium, calcium, magnesium, and fluoride (19). MANUFACTURE The primary goal in the manufacture catechins. The steps include plucking,
OF GREEN TEA of green tea is the preservation of the leaf rapid enzyme inactivation by steaming or OH OH
HO
dH Cyanldin
R-H R=OH
Delphinidin
FIGURE
5
PROCEEDINGS:
PHYSIOLOGICAL
AND
PHARMACOLOGICAL
EFFECTS
OF
TEA
341
HO Thwgallin
FIGURE 6
pan firing, rolling, and high temperature air drying. Glycosides of aromatic and terpene alcohols found in the growing leafare rapidly hydrolyzed after plucking to form the free volatile alcohols. In Japan enzyme inactivation is generally carried out by steaming in large rotating cylinders for 2&50 set followed by a series of twisting and drying steps designed to produce a desirable appearance and reduce moisture gradually to about 3%. Tea so produced is called sencha and is graded into several quality categories (20). Most Chinese green tea is produced by rapid pan tiring or roasting followed by twisting and drying. In India a China-style green tea is manufactured by using long, rotating heated cylinders for the inactivation step. Dwell time may be 7-10 min (21). The several styles of green tea manufacture must result in compositional differences. It would be highly desirable for all reports of feeding studies or in vitro experimentation to specify clearly the tea processing techniques which were utilized. The rolling process imparts a twist which improves appearance. During the final drying step many new aromatic compounds are formed which impart important characteristics of green tea flavor. Green tea composition is similar to that of the fresh leaf with regard to the major components. GREEN TEA BEVERAGE COMPOSITION
Green tea beverage composition varies with the origin of the leaf and with manufacturing conditions. Careful manufacture results in a light yellow-green infusion exhibiting virtually no catechin oxidation. Many of the investigations of dried green tea composition have been carried out by utilizing exhaustive extraction techniques with organic solvents. Little is known about the ability of a normal hot aqueous infusion to extract some of the compounds recently reported in dried green tea leaf. Green tea beverage composition is shown in Table 7 (22). The tiring step at the end of manufacture generates hundreds of volatile compounds. Components reported to be significant in the aroma of high quality green tea beverage are shown in Table 8 (23).
342
HAROLD
N. GRAHAM
TABLE I COMPONENTS OF GREEN TEA BEVERAGE Catechins Flavonols Other flavanoids Theogallin Other depsides Ascorbic acid Gallic acid Quinic acid
3042 5-10 2-4 2-3 1 l-2 0.5 2
Other organic acids Theanine Other amino acids Methylxanthines Carbohydrates Minerals Volatiles
4-5 4-6 4-6 7-9 lo-l.5 6-8 0.02
Nore. Components measured in wt % of extract solids.
MANUFACTURE
OF BLACK TEA
Most of the world’s tea is consumed as black tea beverage. Basic steps in black tea production are plucking, withering, maceration (rolling), and drying. Plucking is predominantly a hand operation but is being supplanted in some areas with mechanical harvesters, usually with the inclusion of more coarse leaf, resulting in decreased catechin levels. Withering lowers the moisture level and renders the leaf more workable in preparation for the maceration step. It is that latter step which disrupts cell structure and initiates oxidation. The processing equipment is designed to ensure intimate contact among the polyphenol oxidase, the polyphenols, and the atmospheric oxygen. Oxidation is allowed to proceed for 45-90 min, depending on ambient temperature, the nature of the leaf, and the style of tea being produced. Temperatures between 20 and 30°C with high humidity and ample exposure of the macerated leaf to air represent desirable oxidation conditions. During this period leaf color and aroma change markedly (24). The enzymatic oxidation step results in the formation of quinones and is the key reaction that initiates all of the subsequent changes which occur (16). Until the early part of the century the process was believed to be a microbial fermentation. The first step in the oxidation of the catechins is illustrated in Fig. 7. The oxidation of the gallocatechins is illustrated in Fig. 8. The catechin quinones react in several complex manners. The quinone derived from a simple catechin or its gallate may react with a quinone derived from a gallocatechin or its gallate to form seven-membered ring compounds known as theaflavins. These contain the benztropolone group. The formation of theaflavin TABLE
8
SIGNIFICANT GREEN TEA AROMA COMPONENTS Benzaldehyde Benzyl alcohol Cyclohexanones Dihydroactinodiolide Geraniol cis-Hexene-3-01 Hexenyl hexanoate
Ionones cis-Jasmone Linalool Linalool oxides Nerolidol Phenylethanol Theaspirone
PROCEEDINGS:
PHYSIOLOGICAL
AND
PHARMACOLOGICAL
HO
EFFECTS
OF
TEA
343
HO FIGURE
7
itself is shown in Fig. 9. The formation of the several possible theaflavin gallates is illustrated in Fig. 10. Each of these has been identified in black tea (12). Theaflavins are orange-red astringent compounds which contribute importantly to black tea beverage color and taste, although they are present only at levels of 1.S2.5% in the dry leaf. They diminish in quantity if the fermentation period is extended. Theaflavin levels are positively correlated with black tea quality (25). There is some evidence concerning the antioxidative properties of theaflavin. Most individual black tea fractions have not yet been investigated with regard to that property. Gallocatechin quinones, both in the free or gallated forms, may couple to form a series of bisflavanols (26). As mentioned earlier these compounds have also been found in fresh green leaf but they are synthesized additionally during the manufacturing process as illustrated in Fig. 11. The bisflavanols (theasinensins) are colorless compounds that are present only in very small quantities in black tea and are assumed to undergo further changes as fermentation proceeds. Their impact on black tea properties is probably minimal. All of the predictable bisflavanols have been identified in black tea. Gallic acid is not a substrate for tea polyphenol oxidase but its quinone can be generated by reaction with the quinones derived from some of the catechins. Reaction between gallic acid quinone and catechin quinones leads to the formation of other benztropolone molecules known as theaflavic acids (27) (Fig. 12). They are analagous in structure to the theaflavins. Epitheaflavic acids are deep red in color. All of the predicted forms are found in black tea but in very small quantities. They are also assumed to take part in further reactions. Compounds known as theaflagallins have also been isolated from black tea. They contain the benztropolone structure and have been synthesized from gallocatechins and gallic acid under mild oxidizing conditions (28). The mechanism for the formation of the theaflagallins is not known but they may be formed by the condensation of two quinones both originating from trihydroxy molecules in contrast to the requirements for the formation of the theaflavins and the epitheaflavic acids.
HO
ti0 FIGURE
8
344
HAROLD
N. GRAHAM
Ycyyc”
+
HO catechin quinone
mqyg:
HO gallocatechin
+
quinone
OH OH
OH
HO
+
co2
OH Theaflavin FIGURE
9
All of the well-characterized products of catechin together with the residual unoxidized catechins of black amount), account for less than 20% of the fresh leaf black tea manufacture most of the catechin mass is
HO
oxidation just discussed, tea (5-10% of the original catechin content. During converted to a less well-
HO + HO catechin
HO gallocatechin
quinone
quinone
OH
OH OH
HO
dH Theaflavin gallates R=H or GaNoyl FIGURE
10
+
co2
PROCEEDINGS:
PHYSIOLOGICAL
AND
PHARMACOLOGICAL
EFFECTS
OF
TEA
345
0 HO
+
HO
Ii0
gallocatechin quinone
gallocatechin quinone HO
OH
Eisflavanols R=H or Galloyl
FIGURE
11
defined group of compounds known as thearubigens. The thearubigen fraction is a mixture of substances, red-brown in color, with a molecular weight distribution of 1000-40,000 (22). The wide range reported may partly be the result of rapid molecular condensation during holding in aqueous solution. Thearubigens readily
HO HOOC -
+ OH
HO
epicatechin quinone
gallic acid quinone t OH
HO OH
bH
Epitheaflavic Acid R=H or Galloyl
FIGURE
12
+
co2
346
HAROLD
N.
GRAHAM
form insoluble complexes with caffeine and are primarily responsible for the phenomenon of “creaming” when hot black tea infusions are cooled. The thearubigens are separated from other tea components and partially resolved by solvent extraction and chromatographic techniques. The structures of the thearubigen components and the mechanism of their formation are incompletely known. The high oxidation potentials of some of the catechin quinones formed in the first steps of fermentation may be responsible for the oxidation of theaflavins, bisflavanols, and epitheaflavic acids and the subsequent incorporation of their oxidation products into the thearubigen complex. Flavonols and depsides may also be involved. Their diminuition during prolonged fermentation supports this hypothesis (29). Small amounts of hydrogen peroxide formed during fermentation may be activated by the tea peroxidase system to produce an additional oxidizing system that could attack the flavanoid pyran ring and form proanthocyanidin condensation polymers (Fig. 13). These compounds are also believed to be part of the thearubigen fraction as its acid hydrolysis leads to the formation of the monomers, cyanidin and delphinidin (30). Only a small proportion of thearubigen appears to be so constituted. It is obvious that a large proportion of black tea components originating from the catechins is not yet well characterized. Enzymic activity is terminated by use of a hot air dryer in which moisture is reduced to about 3%. Further darkening of the leaf occurs as chlorophyll is converted to pheophytins and pheophorbide. Other organochemical processes occur and many additional aromatic compounds are formed. The polyphenol oxidation
HO
Proanthocyanidin i&H
FIGURE
or OH
13
PROCEEDINGS:
PHYSIOLOGICAL
AND
PHARMACOLOGICAL
and condensation products and the volatile nants of black tea taste.
EFFECTS
OF
substances are the primary
BLACK TEA BEVERAGE
TEA
347
determi-
COMPOSITION
It is difficult to state a definitive composition for black tea beverage as tea varieties and style of manufacture differ markedly even within a single growing area. Methods of beverage preparation also vary greatly. A beverage might be prepared by extracting one part of tea with 100 parts of boiling water for about 3 min. An extract concentration of 0.30-0.35% is normally obtained. Such a beverage will exhibit cloudiness and precipitation on standing. The precipitate, known as cream, is generally correlated with good quality. It is composed of thearubigens, thaflavins, caffeine, some occluded protein, and other large molecules. An approximate composition of the whole beverage is shown in Table 9 (3 1). As indicated, unoxidized catechins are found in black tea beverage at as high a level as 10% of the extract solids. Black tea aroma is extremely complex and within the very small mass of volatile compounds over 600 substances have been identified. Most of these are formed from lipids, amino acids, carotenoids, and glucosides during the fermentation and tiring steps (32). Some of the most significant components are shown in Table 10. There is no tannic acid (pentadigalloylglucose) in tea leaf or beverage. Confusion often arises from the use of the term “tannins” in referring to the catechins and to black tea catechin oxidation products. Since these substances do not have the properties of the common tanning agents used to manufacture leather, it is not a useful term to apply to tea components and its use should be discontinued. OOLONG
TEA MANUFACTURE
The manufacture of oolong teas allows for a short period of oxidation. The process is carried out in several different ways and products vary with respect to the degree of catechin oxidation which is effected. Pouchong tea is considered to be about fi fermented compared with black tea; normal oolong tea is considered to be about ‘/t fermented (33). Oolong tea extracts contain catechins at a level of 8-20% of the total dry matter. Oolong tea composition would be expected to be intermediate between green and black teas. During the last 3 years, however, a large number of new flavanoids have been isolated from oolong tea and identified. These include: TABLE PRINCIPAL
Catechins Theaflavins Thearubigens Flavonols Phenolic acids and depsides Amino acids
COMPONENTS
9
OF BLACK
3-10 34 12-18 6-8 lo-12 13-15
Note. Components measured in wt % of extract solids.
TEA
BEVERAGE
Methylxanthines Carbohydrates Protein Mineral matter Volatiles
8-11 15 1 10 co. 1
348
HAROLD
N. TABLE
GRAHAM 10
SIGNIFICANTBLACKTEAAROMACOMPONENTS Benzyl alcohol Dihydroactinidiolide Geraniol Hexenyl hexanoate @Ionone cis-Jasmone Linalool
Linalool oxides Methyl salicylate Nerolidol Phenylacetaldehyde Phenylethanol Terpineol Theaspirone
(a) new epigallocatechin esters (p-hydroxybenzoyl and cinnamyl) (34); (b) new theasinensins (bisflavanols) and a new structural type called oolong theanin, probably formed by oxidation of one of the B rings of a theasinensin (35); (c) dimeric catechins having methylene bridges between the two pyran rings, designated oolonghomobisflavins (36); (d) epigallocatechin gallate esterified on the pyran ring with ascorbic acid (36); and (e) a series of eight dimeric proanthocyanidins composed of the common catechins (36). These compounds have not been found in the other two main tea types; not all known black and green tea components have been found in oolong tea. It is probable, however, that oolong tea contains most of the components of both black and green tea although in significantly different proportions. It would be expected that some of the more transitory products of catechin oxidation might be found only in trace amounts in black tea. This is apparently the case for the bisflavanols (theasinensins). It may also be more difficult to detect small amounts of some substances in black tea than in oolong tea because of the masking effect of the large, intractable thearubigen mass. When the most sophisticated chromatographic and analytical tools are brought to bear on any particular tea, as has been recently the case for the oolongs, it is easy to see why new compounds are detected and identified. This does not preclude their presence in teas previously examined with cruder procedures. The techniques practiced in oolong tea production, i.e., controlled partial oxidation, should allow for the production of teas with preferred compositions for organoleptic or pharmaceutical purposes. CONCLUSION
It is obvious that as much as tea has been researched, its composition is still not adequately known. In view of its interesting pharmacological properties it would be desirable for a program of analytical investigation to be carried out on welldefined teas in a quantitative manner. Teas used in pharmacological studies should be characterized with respect to type, source, and method of manufacture. It would be desirable to specify analytical data such as caffeine and catechin contents. When extracts or fractions of tea are used, methods of preparation should also be specified. The ideal situation would entail the production and proper storage of large
PROCEEDINGS:
PHYSIOLOGICAL
AND
PHARMACOLOGICAL
EFFECTS
OF
TEA
349
quantities of “standard” black, green, and oolong teas of several appropriate types. The teas, along with their analytical data, should be made available to investigators concerned with their pharmacological and biochemical properties. A further refinement would be the preparation of standard dried aqueous extracts of these teas, obviating variations in sample preparation for in viva and in vitro experimentation. REFERENCES 1. Annual Bulletin of Tea Statistics. London: International Tea Committee, 1990. 2. Lunder T. Tannings of green and black tea: Nutritional value, physiological properties and determination. Farm Tijdschr Belg 1989; 66:3ti2. 3. Bhatia I, Ullah M. Qualitative and quantitative study of the polyphenols of different organs and some cultivated varieties of tea plant. J Sci Food Agric 1968; 19:535. 4. Tanizawa H, Toda S, Sazuka Y, Taniyama T, Hayashi T, Arichi S, Takino Y. Natural antioxidants. I. Antioxidative components of tea leaf (Thea. sinensis). Chem Pharm Bull 1984; 32:201 l-2014. 5. Zhao B, Li X, He R, Cheng S, Wenjuan X. Scavenging effect of extracts of green tea and natural antioxidants on active oxygen radicals. Cell Biophys 1989; 14:175-185. 6. Uchida S, Edamatsu R, Hiramatsu M, Mori A, Nonaka G, Nishioka I, Niwa M, Ozaki M. Condensed tannins scavenge oxygen free radicals. Med Sci Res 1987; 15:831-832. 7. Hashimoto F, Nonaka GI. Tannins and related compounds. LXXVII. Chem Pharm Bull 1989; 37:77-85. 8. Wickremasinghe R. In: Chichester C, Mrack E, Stewart G, Eds. Advances in Food Research. New York: Academic Press, 1978:229. 9. Stagg G, Swaine D. The identification of theogallin as 3-galloylquinic acid. Phytochemistry 1971; 10:1671-1673. 10. Sakata K, Sakuraba S, Yagi A, Ina K, Hara T, Takeo T. Isolation and identification of (-)quinic acid as an unidentified major tea component. Agric Biol Chem 1985; S&1919-1921. 11. Cartwright R, Roberts E, Wood D. Theanine, an amino acid N-ethylamide, present in tea. J Sci Food Agric 1954; 5:597-599. 12. Graham H. Tea: The plant and its manufacture; chemistry and consumption of the beverage. In: Spiller G, Ed. The Methyl Xanthine Beverages and Foods: Chemistry, Consumption, and Health Effects. New York: Alan R. Liss, 1984:29-74. 13. Gregory R, Bendall D. The purification and some properties of polyphenol oxidase from tea. Biochem J 1966; 101:56%581. 14. Dix M, Fairley C, Millin D, Swaine D. Fermentation of tea in aqueous suspension: Influence of tea peroxidase. J Sci Food Agric 1981; 32:920. 15. Yano M, Okada K, Kubota K, Kobayashi A. Studies on the precursors of monoterpene alcohols in tea leaves. Agric Bull Chem 1990; 54:1023-1028. 16. Owuor P. Flavour of black tea-A review. Tea 1986; 7:29-42. 17. Venkatakrishna S, Pemechandra B, Cama H. Comparative study of the effects of processing on the carotenoid composition of Chinese and Assamese tea. Agric Biol Chem 1976; 40:2367-2371. 18. Yinfang H, er al. Study on the chemical constituents of the volatile oils from the fresh leaves of Camellia sinensis. Acta Bot Sin 1982; 24:440-450. 19. Natesan S, Ranganathan V. Content of various elements in different parts of the tea plant of black tea from southern India. .I Sci Food Agric 1990; 51:125. 20. Joy T. Green tea manufacture: Japanese style. Tea Coffee Trade J 1986; 158:22-23. 21. Forster K. Tea types and their processing in China. Tea Coffee Trade J 1990; 162:26-32. 22. Millin D, Rustidge D. Tea manufacture. Proc Biochem 1967; 2:9. 23. Kosuge M, Aisaka H, Yamanishi T. Flavor constituents of Japanese pan-fired green teas. Eiyo to Shokuryo 1981; 34:545-549. 24. Reeves S, Owuor P, Othieno C. Biochemistry of black tea manufacture in Kenya. Trop Science 1987; 27~21-23.
350
HAROLD
N. GRAHAM
25. Ullah M, Gogoi N, Barruah D. The effect of withering on fermentation of tea leaf and development of liquor characters of black teas. J Sci Food Agric 1984; 35:1142-l 147. 26. Vuataz L, Brandenberger H. Plant phenols. III. Separation of fermented and black tea polyphenols by cellulose column chromatography. J Chromatogr 1961; 5: 17-3 1. 27. Berkowitz J, Coggon P, Sanderson G. Formation of epitheaflavic acid and its transformation to thearubigens during tea fermentation. Phytochemistry 1971; l&2271-2278. 28. Nonaka G, Hashimoto F, Nishioka I. Tannins and related compounds. XXXVI. Isolation and structures of theatlagallins, new red pigments from black tea. Chem Pharm BuU 1986; 34~6145. 29. Millin D. Factors affecting the quality of tea. In: Quality Control in the Food Industry, 2nd ed., Vol. 4. New York: Academic Press, 1987: 127-160. 30. Cattell D, Nursten H. Phyfochemistry 1976; l&1%7-1970. 31. Sanderson G, Ranadive A, Eisenberg L, Farrel F, Simons R, Manley C, Coggon P. Contribution of polyphenolic compounds to the taste of tea. In: Charalambous G, Katz I, Eds. Phenolic, Sulfur, and Nitrogen Compounds in Food Flavors. ACS Symposium Series. No. 26. Washington, DC: American Chemical Society, 1976. 32. Takeo T, Manhanta P. Why CTC is less fragrant. Two and a Bud 1983; 30~76-77. 33. Yamanishi T. Tea, coffee, cocoa, and other beverages. In: Teranishi R. Ed. Recent Advances in Flavor Research. New York: Dekker, 1981:231. 34. Hashimoto F, Nonaka G, Nishioka I. Tannins and related compounds. LVI. Isolation of four new acylated flavan-3-01s from oolong tea. Chem Pharm Bull 1987; 35:611-616. 35. Hashimoto F, Nonaka G, Nishioka I. Tannins and related compounds. LXIX. Isolation and structure elucidation of B,B-linked bisflavanoids, theasinensins D-G and oolongtheanin from oolong tea. Chem Pharm Bull 1988; 36:167f&1684. 36. Hashimoto F, Nonaka G, Nishioka I. Tannins and related compounds. XC. Ascorbyl(- )epigallocatechin-3-0-gallate and novel dimeric flavan-3-01s: Oolonghomobisflavans A and B, from oolong tea. Chem Pharm Bull 1989; 37:3255-3263. Received August 21, 1991 Revised February 27, 1992 Accepted February 27, 1992
