THE CHARACTER OF TEA
The Chinese character for tea is comprised of three parts: the upper part symbolizes “plant” or “grass”; the middle section refers to “man,” especially man’s locale on earth; the bottom portion represents “tree” or “being rooted.” The sum of this character’s elements creates the Chinese pictorial for tea as, “The revered plant that sustains man in his situation on earth.”
Tea buds and leaves have a complex chemical structure and contain all of the carbohydrates, proteins, lipids, enzymes, and genetic material pertaining to leaf growth and photosynthesis. The tea beverage is an expression of methylxanthine alkaloids (caffeine, which gives tea its bitter taste; theobromine; and theophylline); polyphenols, the catchin and catchin-derived antioxidants; and theanine, an amino acid that is believed to act as the neurotransmitter responsible for tea’s ability to induce relaxation despite the caffeine present. In Japan gyokuro tea is made from leaf that is plucked from shaded tea bushes. Shading interrupts the normal leaf activity and stimulates an abundance of theanine production; the Japanese believe that shaded teas contain the highest amount of theanine possible. In addition, tea contains proteins, polysaccharides; minerals; vitamins B1, B2, and C; and fluoride. It is often erroneously stated that tea contains tannic acid—this is not true. Tea does contain tannins, however; these are complex members of the flavonoid group that give tea its characteristic astringency.
Although fresh tea buds and leaves are comprised of 75 to 80 percent water, the polyphenol components of tea reside in the remaining 20 to 25 percent of solid matter, and the percent will differ between classes of tea. Polyphenols are antioxidants, a broad class of phytochemical compounds found in most plant matter, vegetables, and fruits, as well as in such beverages as beer, coffee, cocoa, wine, and tea. Food chemists have counted more than eight thousand known polyphenols in the plant world (more than 50 percent of these are flavonoids). Researchers are putting these naturally occurring compounds under the microscope to study the potential role they play in boosting our immune systems, maintaining healthy bacteria in the gastrointestinal tract, and preventing or delaying the onset of disease.
Tea polyphenols are important because they halt the damaging effects of oxidation, a process of molecular DNA damage that occurs when the formation of unstable toxic molecules known as free radicals develop within the human body. If left unchecked, deficiencies in our antioxidant quotient will allow these rogue molecules to change the ability of our normal, healthy cells to function properly, a process known as oxidative damage. Free radicals scavenge healthy cells and rob them of their vital cell material, creating a chain reaction of cellular damage that can lead to immune system malfunctions, chronic illness, premature physical deterioration, and organ disease. Oxidation deficiencies can also occur within the human body as a result of repeated exposure to unhealthful conditions that we encounter every day. Some of these risks are eating processed foods that lack vitamins and minerals and that contain an abundance of fats and sugars, secondhand cigarette smoke, exposure to cleaning solvents and chemicals, and of course cigarette smoking, and drug and alcohol abuse.
Tea’s Beneficial Antioxidants
Our bodies respond to the negative effects of free radicals by utilizing defensive antioxidant molecules present in our systems to detoxify or counter-attack these harmful effects. Scientists and nutritionists encourage us to make deposits into the bank account of good health and long life by increasing the level of antioxidants in our bodies. This is easily and sensibly achieved by adding to our diets delicious foods that are rich in naturally occurring antioxidants, such as fruits and vegetables. Another way is by following the Asian lead of drinking several cups of tea each day.
Tea buds and leaves plucked from Camellia sinensis (not “tisanes” or “herbal” infusions made from herbs, twigs, or flowers or fruit infusions made from citrus, berries, and spices) contain a specific group of antioxidant compounds known as flavonoids. The flavonoids in tea are composed of two groups of substances—flavonols and flavanols. Tea is richest in flavanols, and tea researchers are zeroing in on this group. The tea flavanol group contains substances known as catechins—tea’s most important antioxidant arsenal of defense against free radicals.
The fact that green tea undergoes less internal change from fresh leaf means that it contains the largest quantity of intact catechins. Green tea catechins consist of four antioxidant compounds—EC (epicatechin), ECG (epicatechin gallate), EGC (epigallocatechin), and EGCG (epigallocatechin gallate). This last compound is the most abundant catechin in green tea and the most bioactive of the group. These compounds also contribute the light-yellow to golden-green color of brewed green tea and the fresh, clean, vegetal “green jade” flavors that connoisseurs seek in early spring-plucked green tea.
Despite the recent attention paid to the healthful nature of green and white tea, all classes of tea contain polyphenols. The differing methods of leaf manufacture for black, green, oolong, scented, and white teas (see chapter 3) also results in the formation of different polyphenols within the leaves in each class of tea. For black tea, after leaf withering and during the leaf-rolling stages of manufacture, polyphenol oxidaze enzymes that are present in the fresh leaf interact to cause the catechins to oxidize. These oxidized catechins link together to form derived tannins known as theaflavins (catechin dimers), antioxidant substances that contribute to the characteristic orange/red color, brightness, briskness, and flavor of black tea. These substances combine with caffeine to influence astringency.
Theaflavins consist of several fractions—theaflavin, theaflavin 3-gallate, and theaflavin 3,3’-digallate. During this process other catechin compounds oxidize into thearubigins, additional derived tannins formed in tea during oxidation. The method and conditions of oxidized tea manufacture affects the proportions of antioxidant theaflavins to thearubigins present in the tea and thus the corresponding flavor, character, and astringency found in the cup. The longer tea is oxidized and the darker in color it is, the more thearubigins it contains. Both theaflavins and thearubigins contribute the orange-red and red-brown color spectrum that defines the appearance of oxidized tea.
White tea is more aligned with green tea (although some leaf styles of white tea undergo a slight withering) and pu-erh tea more closely follows suit with black tea. Oolong tea, a semioxidized tea, contains the reverse antioxidant proportions of black tea; it has a higher concentration of theaflavins and a lower concentration of thearubigins. But, in fact, some researchers believe that the activation of tea enzymes during the manufacture of black tea may result in the formation of antioxidant compounds that are more powerful in preventing some disease than those contained in green tea.
Research on Tea
Much tea research is ongoing in private laboratories and university research centers across the United States, including the Beltsville Human Nutrition Research Center, the University of Kansas at Lawrence, the National Cancer Institute, the USDA Human Nutrition Research Center on Aging at Tufts University, and the Linus Pauling Institute at Oregon State University. Many questions remain unanswered about the potential that tea has for fighting and preventing disease.
Although it is too soon to know tea’s role in disease prevention and cure, tea drinking does provide many healthful benefits. Tea contains no additives or artificial sweeteners, and when consumed without the addition of sugar or dairy, it contains no calories. Tea drinking increases daily fluid intake, helps to maintain a healthy, active metabolism and circulatory system, acts as an antiviral, contributes to oral health by inhibiting bacterial plaque, acts as an anti-inflammatory, and is a rich source of vitamins. The antioxidant levels in green tea have been reported to be a hundred times more effective than vitamin C and twenty-five times better than vitamin E in protecting our immune systems.
The list of medical conditions and diseases that researchers hope to find tea useful for combating or forestalling focuses on certain cancers, heart disease, diabetes, stroke, th
e onset of Alzheimer’s, and liver diseases. To date, clinical studies regarding tea consumption and health remain inconclusive when it comes to understanding just how far tea can go to prevent or delay the onset of disease. Early reporting about the potential healthful benefits of tea took great liberties assigning tea with much hoped for but unproven disease prevention and fighting abilities. Although much tea research and hundreds of clinical trials are actively being conducted in the areas of health and disease, it is vital, however, for consumers to be able to discern between fact and overstatement. A study published by the U.S. Department of Agriculture has reported that “the number of well-designed, carefully controlled dietary intervention studies, which show cause and effect, is limited, and this represents a critical gap in our understanding of these compounds as they relate to health promotion and disease prevention.” Until concrete facts have been proven, the buzzwords surrounding tea as a potential disease fighter should be discussed as just that. We would be wise to use such qualifiers for tea as “it has the potential to” or “is thought to aid in” or “may assist with.”
Laboratory testing is sometimes at odds in determining the actual measurable antioxidant content of tea within each class. In fact, a study conducted by the UCLA Center for Human Nutrition tested more than eight national brands of green and black tea and came up with staggeringly different antioxidant levels, not only for each class of tea but for each tea tested within its own class. This is disheartening for those looking for pat answers but should come as no surprise. Many variables pertaining to tea and the production of tea arise that make standardization difficult to control and predict. Once one adds any number of variables particular to human biology and disease into the picture, many additional conditions occur to further cloud the results.
Consider the following reports on antioxidant content. In the September 2001 issue of the Journal of Nutrition, a research study by Lai Kwok Leung and others addressed the question of the antioxidant content in black and green teas. To quote their findings: “All data presented here suggest that drinking black tea has benefits equal to those of drinking green tea in terms of the antioxidant capacity.”
But in a separate study reported in a letter to the editor of the Journal of Nutrition in 2002 by Ki Won Lee and others, these researchers reached a different conclusion. This group reported in their findings “the antioxidant capacity per serving of green tea (463 milligrams) was much higher than that of black tea (239 milligrams).” And another report conducted by the Antioxidants Research Laboratory within the Human Nutrition Research Center on Aging concluded findings of 235 milligrams of antioxidants in one six-ounce cup of green tea. The UCLA Center for Nutrition Study found the antioxidant content of several brands of green tea to range from 217 to 53 milligrams and from 164 to 38 milligrams in black tea in a three-minute infusion of each type of tea. Research conducted by Jeffrey Blumberg, associate director of the Jean Mayer USDA Human Nurtrition Research Center on Aging at Tufts University, concludes that the same percentage of flavonoids is present in a brewed cup of green (16 percent) or black (15.6 percent) tea.
Conflicting conclusions underscore the fact that different batches of green tea will contain unequal quantities of catechin, just as the theaflavin/thearubigin content of black tea will also vary. This is to be expected. The polyphenol content of fresh tea leaf varies from country of origin and from region to region within each country (because of the clonal varieties of tea bushes in question). There are also variances based on the time of the season that the leaf was plucked and the position of the leaf on the bush (the younger the leaf, the more antioxidants it contains). Fresh leaf that has been subjected to the least amount of oxidation during manufacture (green tea incurs no oxidation, and budset white tea incurs little oxidation) contains the most catechins. In the case of black and oolong teas the oxidation levels reached when producing these teas vary by percentage-point differences (15 to 80 percent oxidation) that make it impossible to measure percentages of theaflavin/theagrubigin content with any consistency.
Even when comparing green teas to other green teas, or black teas to other black teas, these geographic and seasonal differences present different circumstances that yield differing amounts of polyphenols. Tea researchers at the Sichuan Agricultural University in Ya’an explained to us that they believe that the optimum polyphenol content in green tea is realized in tea that is made using one leaf and a bud. But the argument can also be made that the polyphenol content of budset green or budset white tea is even higher. Whole-leaf tea will no doubt yield different results than tea found in a teabag, and each will differ when tea is consumed hot or with ice, or with milk or sugar. One must also take into account the size of the measure of tea used, the length of time that the tea steeps, and the temperature of the water.
Many studies have also shown positive indicators for tea polyphenols when performed in tests in vitro, but the same tests often fail to confirm results or do not show consistent results when conducted in clinical trials on human study participants. Individual variations in the ability of people or groups of people with different ethnicities to absorb the available bionutrients in tea and to metabolize them efficiently yield differing results. Body type, age, gender, diet, and nutritional habits add further to the variables.
In June 2005 the Food and Drug Administration (FDA) addressed green tea’s role as a cancer preventive or cancer fighter. Their ruling declared that there was “no credible evidence” that green tea cuts breast cancer or prostate cancer risk, or is a fighter of other cancers, including lung, gastric, colon, rectal, pancreatic, esophageal, skin, ovarian, or liver cancers. And again in 2006 the FDA denied a Japanese tea company use of the advertising claims that green tea may reduce the risk of cardiovascular disease by stating that there was “no credible evidence” to support this claim.
Despite this broad-based rejection, tea may yet prove itself as a chemo-preventive mechanism that can fight disease and maintain wellness in certain situations. From all of these questions one thing is clear, however: research and human clinical studies must continue. The reasons to drink tea are the same now as they have been for centuries: Tea is a pleasure beverage with a sensory appeal and an enormous feel-good attitude that delivers great, satisfying flavor. Tea has virtually no negative side effects, and helps students and workers maintain alertness and mental clarity.
Surely there are many possible benefits from drinking tea that have not yet been discovered. For instance, at Pace University in New York City, Milton Schiffenbauer, PhD, professor of microbiology, has conducted research that concludes that white tea is more effective than green tea as an antiviral and antibacterial when added to toothpaste or used as an oral agent.
So, when it comes to tea, think tonic not curative, healthful collaborator not redeemer. Mix it up and drink tea from all of the fascinating classes of tea. Drink tea to relax and connect with the spiritual nature of life’s simple pleasures. Enjoy the flavors and the subtle and not so subtle differences waiting to be discovered in the world of tea offerings, and should the rich doses of flavanoids in each cup of tea be determined to cure what ails you, you will be ahead of the curve.
Caffeine in Tea
Reminiscent of the legends regarding early coffee consumption, the record of humankind’s use of the tea plant suggests that if it did not contain caffeine, the beverage that we know today would not have evolved. Were it not for caffeine, the people of mainland Southeast Asia might not have tolerated the bitter, nasty taste of early tea preparations long enough to allow it to evolve into the pleasure beverage that we know today. Throughout tea’s journey from fresh leaves chewed for their mild stimulation, then to their use as a component of primitive concoctions of fresh or dried leaf combined with other edibles (trail mix of a sort), to a boiled tincture central to Eastern medicine, caffeine was the constant that inspired experimentation.
In its native wild state Camellia sinensis is a rugged plant indeed, both in habit and in taste. As with most i
ndigenous medicinals, the passage of time and changes in use have led to the extraction of caffeine in a pure, more refined form. Botanical improvements and experimentation with brewing techniques persuaded the world to embrace an incredibly pleasant beverage that hid for centuries beneath the veil of folk medicine. The quixotic narratives of the “origin” of both coffee and tea, while romantic and lovely, overlook the practical and valuable roles that these two plants have played in the evolution of stimulants and thirst-quenching beverages. The 1820s were quite an invigorating decade for stimulants: caffeine was first discovered in coffee in 1820, and the stimulant theine was discovered in tea in 1827. Theine was later identified as the primary stimulant in several other ingestible plants, most notably maté, the South American shrub or tree. It didn’t take long for chemists to recognize that caffeine and theine were one and the same, so the term theine is rarely used today.
Drinking tea bespeaks a quest that
one offers to his friends for the
and of the heart.
—SOGAKU OF THE HAYAMI SCHOOL
Caffeine is a bitter alkaloid, the methylxanthine known as 1,3,7-trimethylxanthine, and is found naturally in at least sixty-three types of plants, most notably coffee, tea, and cacao. It acts as a stimulant to the central nervous system. It is extremely close in chemical structure to theobromine, the main alkaloid in cacao. Caffeine is considered to be safe for most people when consumed at a dose of 0.3 grams or less per day. This equates to approximately five cups of tea, each brewed full-strength. Having followed many of the studies on caffeine as well as volumes of speculative writing about the caffeine content of tea, we can say only this truth with certainty: there is caffeine in tea.
The Story of Tea Page 42
