Tea leaves

The leaves of Camellia sinensis are similar to most plants in general morphology and contain all the standard enzymes and stmctures associated with plant cell growth and photosynthesis (10—12). Unique to tea plants are large quantities of flavonoids and methylxanthines, compounds which impart the unique flavor and functional properties of tea. The general composition of fresh tea leaves is presented ia Table 1. 

Minerals and Ash. The water-soluble extract solids which iafuse from tea leaves contain 10—15% ash. The tea plant has been found to be rich in potassium (24) and contains significant quantities of calcium, magnesium (25), and aluminum (26). Tea beverages are also a significant source of fluoride (27), owing in part to the uptake of aluminum fluoride from soils (28,29). 

Volatiles or Aroma. The essential oil, or aroma, of tea provides much of the pleasing flavor and scent of green and black tea beverages. Despite this, volatile components comprise only - 1% of the total mass of the tea leaves and tea infusions. Black tea aroma contains over 300 characterizing compounds, the most important of which are terpenes, terpene alcohols, lactones, ketones, esters, and spiro compounds (30). The mechanisms for the formation of these important tea compounds are not fully understood. The respective chemistries of the aroma constituents of tea have been reviewed... 

There are four main theaflavins common to black teas, and a second group of minor theaflavins, including the isotheaflavins (55) and neotheaflavins (57) (Table 5). The total theaflavin concentration in black tea leaves does not usually exceed 2% and can be as low as 0.3%. At most, only 10% of the catechins in tea flush can be accounted for as theaflavins in black tea and the fate of the remaining catechins is less clear. Theaflavins can be readily determined by direct hplc analysis of tea beverages (48,58,59). 

Firing. A hot-air oven having forced circulation in a countercurrent mode is used to dry the fermented tea leaves and inactivates the key enzymes required for fermentation. The firing process generally occurs over an 18—20-min period, which is optimum for normal process efficiencies. 

The two isomeric butanals, n- and isobutyraldehyde, C HgO, are produced commercially abnost exclusively by the Oxo Reaction of propylene. They also occur naturally ia trace amounts ia tea leaves, certain oils, coffee aroma, and tobacco smoke. 

Caffeine occurs in tea leaves, coffee beans, and cola nuts. Morphine is obtained from unripe opium poppy seed pods. Coniine, extracted from hemlock, is the alkaloid that killed Socrates. Fie was sentenced to death because of unconventional teaching methods teacher evaluations had teeth in them in ancient Greece. 

Aoki, S. (1986). Interaction of light and low temperature in depression of photosynthesis in tea leaves. Japanese Journal of Crop Science, 55, 496-503. 

The differences in types of tea are due not to the variety of the tea, but rather to the tea processing. The same basic tea leaves can produce green, black or oolong teas, although some varieties of tea leaves are more suited to certain types of tea. So-called herbal teas are produced from mixtures of flowers, berries, peels, seeds, leaves and roots from many different plants. They are quite different from tea. However, combinations of these herbal materials and tea leaves are also present in the market. 

Proanthocyanidins are an important group of di- to oligomeric flavonoids in plants. Four proanthocyanidins (procyanidin B3, prodelphinidin B4, ECG-(4 8)-ECG and GC-(4 8)-EGCG) were determined quantitatively in tea. The amounts in fresh tea leaves were between 1 and 2 g/kg per compound (Nakabayashi, 1991). The occurrence of proanthocyanidins may serve as a criterion for the differentiation between fermented and non-fermented teas (Kiehne et al, 1997). 

Commercial green tea leaves contain ascorbic acid (vitamin C) about 280 mg per 100 g dried leaves. Vitamin E in tea leaves is around 24-80 mg/lOOg dry weight but, because of its lipophilicity, solubility is low in tea infusions. The content of B vitamins in tea is around 8-15 mg/lOOg (Cheng and Chen 1994). 

Strong infusions are made by soaking tea leaves in alcohol/water mixtures (the catechin content is about 2% w/v). 

It is necessary to offer consumers a consistent level of quality in their products. To achieve this, tea leaves, their extracts and the consumer products themselves need to be standardised and monitored throughout their shelf life. Furthermore,... 

DU Q z, LI M J, CHENG Q K, CHENG Q and LU c Y (1997) The study on separation catechins from tea leaves and transforming gallate-catechins into nongallate-catechins . Res Develop Basic Agric and High Technol, 1, 40-47. 

WANG H and HELLIWELL K (2001) Determination of flavonols in green and black tea leaves and green tea infusions by high-performance liquid chromatography , Foot/Res Intern, 34, 223-7. 

Fujimori, N., Suzuki, T., and Ashihara, H., Seasonal variations in biosynthetic capacity for the synthesis of caffeine in tea leave, Phytochemistry, 30,2245,1991... 

Note Formula for cups per day (kg/year x 1000)/352 = grams per day/2.27 = cups per day. 2.27 is the assumption of tea leaves used per cup. Kilograms per population is the average consumption per head of total population. All data is based on imported and (where applicable) locally produced tea. 

In addition to all of the expected enzyme systems present in leaf tissue, fresh tea leaves contain a high level of polyphenol oxidase that catalyzes the oxidation of the catechins by atmospheric oxygen. Tea polyphenol oxidase exists as series of copper-containing (0.32%) isoenzymes. The major component has a molecular weight of about 144,000.54 The enzyme is concentrated in the leaf epidermis.55 Soil copper deficiency is sometimes responsible for inadequate oxidation during processing.56... 

Often the leaves of C. sinensis are prepared in a very unique manner, such as in Tibet, where, for example, tea leaves are boiled overnight on an open fire, with a pinch of alkaline soda added. After the tea is strained, yak butter and salt are added and the concoction is vigorously pumped in a churn to a frothy brew. The tea is then poured back into the pot, reheated and served. 

Caffeine consumption is primarily due to coffee, tea and soft drinks. In the U.S., it is estimated that coffee contributes to 75% of the total caffeine intake, tea is 15%, and soda with caffeine accounts for 10% 5 chocolate and other caffeine-containing foods and medications contribute relatively little to overall caffeine exposure. Caffeine also varies by sources tea leaves contain 1.5 to 3.5% caffeine kola nuts contain 2% caffeine and roasted coffee beans contain 0.75 to 1.5% caffeine.6 Coffee varies in caffeine content some analyses have estimated that caffeine may range from 0.8 to 1.8%, depending on the type of coffee.7 Crops of coffee, tea, and cocoa are very similar in their production periods and their useful life in production. Typically coffee, tea, and cocoa trees can be productive with crops every 5 years for a total period of 40 years,8 or an estimated 8 yields per tree. 

By weight, tea leaves have double the caffeine as coffee beans 25 however, the caffeine content is greatly diluted during preparation. Caffeine in tea has been reported to range from 2.7 to 4.1% in selected varieties of tea,7 comparable with an estimate of 4% caffeine content in tea.26 While tea is the most commonly consumed caffeinated beverage, the caffeine content is only one third to one half that of coffee, contributing less to overall caffeine exposure than coffee. 

As shown in Table 7, tea produced in Asia contributed to over 80% of the worldwide crop in 1994.16 China and India are the primary growers of tea leaves and they not only export but retain much of the tea for domestic consumption. African production is only 13% of the worldwide production and South American production was 72,000 metric tons in 1994. 

Plots of boiling points, hunts for data, corrections, slide rules, log paper, eraser dirt, pencil shavings, and all the rest of the paraphernalia that takes the place of tea leaves and crystal spheres in the life of the scientific clairvoyant, were brought into play, he joked. 

Polyphenoloxidase (PPO, EC 1.14.18.1) is one of the most studied oxidative enzymes because it is involved in the biosynthesis of melanins in animals and in the browning of plants. The enzyme seems to be almost universally distributed in animals, plants, fungi, and bacteria (Sanchez-Ferrer and others 1995) and catalyzes two different reactions in which molecular oxygen is involved the o-hydroxylation of monophenols to o-diphenols (monophenolase activity) and the subsequent oxidation of 0-diphenols to o-quinones (diphenolase activity). Several studies have reported that this enzyme is involved in the degradation of natural phenols with complex structures, such as anthocyanins in strawberries and flavanols present in tea leaves. Several polyphenols... 

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