Green Tea

Health Benefits and Applications

Yukihiko Hara

• Publisher: CRC Press
• Year: 2001
• eBook ISBN: 9781135566876
• Topic: Médecine
• Subtopic: Sciences de l'alimentation

A comprehensive overview of the inherent properties, chemical and biochemical functions, actions for lowering the risks of cardiovascular and infectious diseases and cancers, and underlying mechanisms of tea polyphenols. It reveals the bioantimutagenic potency of epigallocatechin gallate (EGCg) found in green tea.

1
Introduction to the History of Tea

I. ORIGINS AND BEGINNINGS

Today the tea bush is known as Camellia sinensis (L.) O. Kuntze of which there are two varieties: var. sinensis and var. assamica. In 1690, E. Kaempfer, a German medical doctor cum botanist who came to Japan from Holland and observed the habit of tea drinking among the people, named the bush ‘‘thea.’’ In 1753, the famed botanist C. Linne´ gave to it the name of Camellia sinensis changing his original naming of Thea sinensis. Since then the nomenclature of the tea bush has been confused between these two names. In 1958, a British botanist J. R. Sealy classified all plants in the genus Camellia and tea was given the name it has today (1).

Tracing the origin of the tea bush is laborious work, since it spans countless numbers of geological years from the Tertiary period on and covers vast mountainous areas in south-eastern Asia. General consensus attributes the birth of the tea bush to the area we now call Southwestern China. Tea is cultivated successfully in many different countries of the world and consumed in almost every part of the world, but for most people the association of tea with China remains strong. The discovery of a tea bush deep in Assam, India, with leaves much larger than the Chinese one, stirred up controversy over the original birthplace of C. sinensis. This discovery was made in 1823 by R. Bruce, and the bush in Assam was in later years classified as C. sinensis var. assamica. Despite wide morphological differences between the varieties sinensis and assamica and their hybrids, genetic differences between these varieties are negligible. Today the birthplace of the tea bush is assumed to be the Southwestern China, centered in the Yunnan district (2).

The history of tea drinking is another matter of controversy. Tea leaves have probably been utilized, drunk, eaten, pickled, etc., by mountain tribes since time immemorial. The custom’s spread and acceptance among Chinese culture and its documentation within Chinese writings are two different matters. In other words, we have two possible approaches in tracing the history of tea usage: anthropological or archival. Chinese legend claims that tea consumption goes back as far as 2737 B.C. Around that time, Sheng Nung, a legendary Emperor known as the Divine Healer, discovered the healing power in tea leaves and taught people ways in which tea could be consumed. The first credible documentary reference on tea was made in 59 B.C. in a servant’s contract, which stated that his duties included the making of tea and going to the city to buy it. Although it seems to be impossible to exactly pinpoint the advent of tea drinking, the most reliable overall book on tea was published in A.D. 780. Written by Lu Yu, who described the botany, cultivation, and processing of tea, as well as the utensils and proper way of drinking tea, etc., in detail, Tea Classics or Tea Sutra and has been the Bible for people involved with tea ever since. The only contemporary counterpart with such an encyclopedic description was published in 1935, All About Tea, by W. Ukers (3).

The history of tea drinking is another matter of controversy. Tea leaves have probably been utilized, drunk, eaten, pickled, etc., by mountain tribes since time immemorial. The custom’s spread and acceptance among Chinese culture and its documentation within Chinese writings are two different matters. In other words, we have two possible approaches in tracing the history of tea usage: anthropological or archival. Chinese legend claims that tea consumption goes back as far as 2737 B.C. Around that time, Sheng Nung, a legendary Emperor known as the Divine Healer, discovered the healing power in tea leaves and taught people ways in which tea could be consumed. The first credible documentary reference on tea was made in 59 B.C. in a servant’s contract, which stated that his duties included the making of tea and going to the city to buy it. Although it seems to be impossible to exactly pinpoint the advent of tea drinking, the most reliable overall book on tea was published in A.D. 780. Written by Lu Yu, who described the botany, cultivation, and processing of tea, as well as the utensils and proper way of drinking tea, etc., in detail, Tea Classics or Tea Sutra and has been the Bible for people involved with tea ever since. The only contemporary counterpart with such an encyclopedic description was published in 1935, All About Tea, by W. Ukers (3).

II. TEA AS A PANACEA

The tea that today is commonly consumed in countries all over the world was once revered for its curative powers. Some of the earliest mentions of tea in Chinese literature refer to it as a remedy for a diverse range of complaints (4). Gradually though, tea became more and more commonly consumed and its role in society started to shift from that of a highly esteemed panacea to one of being simply a refreshing and habitual beverage.

The importance of tea for Tibetans or for nomadic people in peripheral China is something special even today. These people seem to consume much of their vital elements from tea as well as from the milk of their herd. The habit of tea drinking is so deeply ingrained in their daily life that tea has become something beyond just a beverage; they seem to have an element of addiction to tea, which is an integral part of their lives. The beneficial influence of tea on health has been felt by people since those beginning days in tea’s history when it was regarded as being a cure for almost everything. Some of those claims to tea’s efficacy still sound rather exaggerated, but others are, in fact, proving to have some scientific basis.

Debate on its blessings and evils has accompanied tea from the very beginning and throughout its establishment in various countries; still today there remains some controversy due to the presence of caffeine in this widely consumed beverage. China’s reverence of tea was adopted by some in the Western world, but met with skepticism and outright opposition by others. The controversy was already raging in Europe in the years when tea was introduced. For as many who praised tea for its desirable effects on the body, there appeared to be as many who denounced it as being positively harmful or, at least, inconsequential.

In England during the seventeenth century, tea became famous through its introduction in the coffee shops where it was positively portrayed as a drink for good health. Advertisements in these establishments proclaimed tea’s benefits to their customers. The first of these papers appeared in a coffee house (named ‘‘Garraways’’) run by Thomas Garway, who pioneered the sale of prepared tea in England. Among other things, it was claimed that tea was good for curing headaches, colds, fevers, and stomach problems, as well as preventing sleepiness and stimulating the appetite and digestion (3). With this persuasive advertising it is no wonder that drinking tea became such a popular pastime.

III. TEA AS A TAXABLE PRODUCT

It is fitting that China, the country where tea was first popularized, introduced the first tea tax. This was in the eighth century under the Tang dynasty. In those years of the Tang dynasty, silk produced in China was bartered for horses bred by western nomadic tribes (5). In the following Sung dynasty, tea replaced silk, and the tea–horse barter system was established. In the Ming dynasty, this practice became so popular that in 1398 it was reported that 250 tons of tea were bartered for 13,584 horses. This shows that the production of tea was widespread in China during this time and that tea constituted a considerable revenue for the government.

In England, too, where there is no production of tea, it was the widespread use of tea that prompted the government to impose a tax. The proprietors of coffee houses were required to obtain a license and pay a duty every month. In spite of the tax, tea prospered and in time outstripped both coffee and cocoa in popularity. This seems to have been due to a number of factors, one of which was the Queen of England’s partiality to tea. Catherine of Braganza, a Portuguese princess who married Charles II in 1662, brought to the English court her love of tea. Ladies of the upper class began to follow this tea-drinking fancy, which eventually spread to include members of all classes and both sexes. Another reason for tea’s success could have been that the production of coffee was dominated by the Dutch, thus making it difficult for England to procure sufficient amounts. Instead, she turned her attention to establishing strong trading links in tea with Asia—and so England became a country where tea drinking was prevalent.

The United States, too, could have been a nation of tea drinkers. It started out along that track, but events of history took over to determine the destiny of tea in America. Introduced to the colonies around the middle of the seventeenth century, most probably by Dutch immigrants, tea soon produced its own fashionable culture. Tea gardens, where entertainment was provided from morning to night, came into being. All this enthusiasm was squashed, however, with the imposition of a tea tax. While it was not a large amount, rather than pay the duty, the colonists smuggled in tea from Holland. But loathe to miss out on the market in America, England put into action a more ominous plan, which allowed the British East India Company a monopoly to export tea directly from China, cutting out the middlemen. England’s twofold policy of imposing a tax on one hand and monopolizing the market with cheaper teas on the other, kindled the protests of colonists, particularly those who earned their living by smuggling. For the early Americans, the prevailing opinion was that to yield to England’s manipulation was to sacrifice independence.

In spite of this mood of opposition, England stubbornly refused to bend and the tea was shipped. The climax of this volatile situation in 1773 was what is now known in history as the Boston Tea Party. While the ships lay stranded in Boston harbor, forbidden to unload their cargo of tea and refused custom’s clearance to sail back home, the citizens of Boston took matters into their own hands. A group of men disguised as Mohawk Indians rushed onto the ships, seized the tea chests, then proceeded to ax open each one and empty them into the sea. So it was that amenial tax marked the beginning of America’s struggle for independence and was responsible for the demise of tea in America. Even today, we regard the United States as a nation of coffee drinkers, although tea has started to make a comeback with its growing reputation as a beverage conducive to promoting good health.

Another historically revolutionary incident in which tea played a role was the opium war. In the late eighteenth century, imports of tea from China to England were steadily increasing. The British government taxed it heavily in an attempt to finance expenditures for the war in America. To curtail smuggling that arose because of the heavy tax, the tax was reduced, which in turn increased consumption. Eventually the East India Company had no silver to pay for the tea. With no better option available, they allowed opium to be cultivated in India and, in effect, bartered it for tea. This malpractice continued into the nineteenth century, and trade was expanded even more at the sacrifice of the many Chinese addicted to opium. After many vain appeals and controls attempting to ban this trade, the Ching dynasty finally arrested the addicts and confiscated the opium. The British government’s retaliation for these actions by the Chinese was the opium war, which ended with the Nanching Treaty in 1842. Heavy compensation and the opening of five free ports as well as the cession of Hong Kong was the price paid by the subdued Ching dynasty. Greed for tea sacrificed many people and kept Hong Kong under foreign sovereignty for more than 100 years.

IV. DEVELOPMENT OF TEA CULTURE IN JAPAN

Tea drinking, which may have started as the preparation of a beverage from the raw leaves of wild tea trees in boiling water by mountain tribes in southern China, developed into a social rite of exquisite refinement in many parts of the world and reached its ultimate form in Japan. Early visitors from Europe in the sixteenth century found tea in China to be a popular medicinal drink, whereas in Japan they found that tea held a completely different status. They were impressed by the way people drank tea in a certain aesthetic–religious ritual. From early Japanese history, Japan has been heavily influenced by Chinese culture. Tea was introduced, along with Buddhism, from China in the eighth century or earlier. Tea growing and the habit of drinking tea then lapsed for another 400 years. A resurgence occurred, however, in the twelfth to thirteenth centuries when Buddhist priests who had studied in China brought back tea seeds and planted them in many parts of the country. Yeisai, the founder of the Rinzai sect of Zen Buddhism in Japan, wrote the first book on tea, Tea and Health Promotion, in 1214, in which he emphasized the virtue of tea drinking based on the experience and the beliefs he had learned in China. The Buddhist priests not only found the beverage useful for keeping them awake during their meditation, but also found that it relieved them of their physical fatigue. Tea drinking gradually spread from being popular not only among the priests and religious orders but also among the common people.

In the fifteenth to sixteenth centuries, with the advent of noted tea masters with Zen-sect Buddhist backgrounds, tea was elevated to a religion of aestheticism, teaism. Teaism is a cult founded on the worship of the beautiful, the love of nature through simplicity of materials. It is performed as ‘‘Cha-noyu’’ or the tea ceremony. Tea masters such as Sen-no Rikyu in the sixteenth century, along with his predecessors and successors, perfected the art of the tea ceremony under the patronage of the then reigning lord of warring Japan. The followers of Sen-no Rikyu and other tea masters established separate schools of teaism that, even until the present day, abide by a certain decorum in the serving and appreciation of tea. Tea ceremony used to be the art of men, but today many people, particularly young women about to enter into marriage, take tea ceremony lessons and learn how to appreciate and behave in their daily life through serving tea. In the formal tea ceremony, the guests are ushered into a small and seemingly humble cottage designed to accommodate no more than five persons. A host, the tea master, who is considered to be a master of artistic life, makes and serves tea to the guests, who should appreciate the whole setting: the garden, the path, the tea house itself, the hanging scroll, the arranged flowers, the sweet cakes served, etc., as well as the tea utensils used. The tea served in the tea ceremony is called matcha (pronounced ‘‘mahcha’’) and is powdered tea of the highest quality. Matcha is beaten with lukewarm water with a whisk in a small porcelain bowl and served. It is said that teaism representsmuch of the art and spiritual background of Japanese life.

V. THE CHEMICAL HISTORY OF TEA

While the history of tea drinking is ancient, investigation into the chemical components of tea is in comparison quite recent. Tea is composed of unique constituents among other plants. Caffeine is found only in a few other plants other than tea. Theanine, which is unique to tea, is a kind of amino acid constituting more than half the total amount of amino acids in tea. Major catechins in tea are also unique to tea. Vitamin C was found to be contained in tea after it was discovered in lemons. Tea aroma is an area that attracted the interest of scientists who had been seeking one single compound that represents tea, a search which has yet been in vain. In 1827 caffeine was discovered in tea. At that time it was given the name theine, but when it was proven that the structure and properties of this substance were exactly the same as caffeine that was identified in coffee in 1820, the name theine was dropped. In 1924, vitamin C was discovered in green tea by two Japanese scientists, M. Miura and M. Tsujimura, under Professor U. Suzuki.

The astringency of tea, too, was investigated extensively by Tsujimura. In the years 1927 to 1935, Tsujimura isolated epicatechin, epicatechin gallate, and epigallocatechin. With great effort, she purified them and determined their structural formulas. In 1950, with the new technique of column chromatography, the British scientist A. B. Bradfield succeeded in isolating epigallocatechin gallate and determined its structure by x-ray diffraction method. Tsujimura later identified her compound as being the same. Thus, the main four catechins in tea, which make up the major group of compounds in the soluble solids of tea, were identified in the early 1950s and Tsujimura, along with Bradfield, gained worldwide renown for their pioneering work. Later in the 1950s, E. A. H. Roberts clarified the steric complications of individual catechins in Britain, using the technique of two-dimensional paper chromatography. He is also known for his research on polyphenolic compounds, theaflavins, and thearubigins in black tea. Later, around 1963–1965, Y. Takino et al. confirmed the benzotropolone structure of theaflavins. The chemistry of tea polyphenols in that of broader plant polyphenols was well reviewed by E. Haslam (6).

Aroma components in tea were first researched more than 150 years ago by Mulder, who discovered essential oil in fresh tea leaves. In the 1930s, S. Takei and R. Yamamoto et al. were among the earliest scientists to contribute to our knowledge of tea aroma. Methods at that time were rather crude and tons of tea, not to mention time and patience, were necessary to isolate sufficient material for separation and identification of individual components. The work of these professors (Takei, who focused mainly on green tea, and Yamamoto, who focused on Taiwan black tea) became a vital basis for future research in the field. They identified more than 30 compounds from green and black teas. Following in their steps, T. Yamanishi, successor of Professor Tsujimura, also became renowned worldwide for her work, which involved isolating aroma components by gas chromatography (5). Today more than 600 aroma compounds have been identified.

Theanine, γ-ethylamide of glutamic acid, was discovered in 1950 by Y. Sakato. Theanine constitutes the ‘‘umami’’ or sweet taste in tea, particularly that of Gyokuro (the best quality green tea in Japan, see Chapter 20), and constitutes 2% of tea. The antagonistic action of theanine against the stimulating action of caffeine in the nervous system and its vitalizing action on brain neurons are areas of interest that could be studied...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Foreword
• Preface
• Acknowledgments
• 1 Introduction to the History of Tea
• 2 Biosynthesis of Tea Catechins
• 3 Fermentation of Tea
• 4 Methods of Extracting Polyphenolic Constituents of Tea Leaves
• 5 Antioxidative Action of Tea Polyphenols
• 6 Radical Scavenging Action
• 7 Antibacterial Action
• 8 Methicillin-Resistant Staphylococcus Aureus
• 9 Anticariogenic Action
• 10 Antiviral Action of Tea Polyphenols
• 11 Prevention of Cancer by Tea Polyphenols
• 12 Lipid Lowering Effects
• 13 Hypoglycemic Action of Tea Polyphenols
• 14 Hypotensive Action of Tea Polyphenols
• 15 Effects on Intestinal Flora
• 16 The Fate of Tea Catechins After Oral Intake
• 17 Efficacy of the Health Benefits of Black Tea or Black Tea Polyphenols
• 18 Toxicology
• 19 Practical and Industrial Applications
• 20 Tea in Japan