ABSTRACT
Tea (Camellia sinensis, Theaceae) is one of the most popular beverages consumed throughout the world. An estimated 2.5 million metric tons of dried tea leaves are manufactured annually.1 The majority of the tea beverages are prepared from the following three types of manufactured teas: green tea, oolong tea, and black tea. Green tea is prepared from fresh leaves and processed rapidly to prevent fermentation. Oolong tea is a partially fermented tea product with a unique avor. Black tea is made by crushing the leaves to cause fermentation prior to the nal drying step. Of all the tea consumed in the world, 78% is black tea, which is usually consumed in the United States, Europe, Africa, and India; 20% is green tea, which is commonly consumed in Asian countries, especially in China and Japan; and 2% is Oolong tea, which is produced in southern China.2,3 Green tea infusions contain approximately 30-40% catechins and other polyphenols and avonols. Black tea infusions contain approximately 3-9% catechins and other polyphenols and avonols.4,5
Green tea has been widely consumed in China and Japan for many centuries, and hence is regarded as safe.6 Presently, 90% of the green tea comes from China and is cultivated on approximately 4 million acres of land.1 The belief in the medicinal powers of tea is so strong in the Orient that the Chinese actually say, “It is better to take green tea than to take medicine.”7 Compared to other processed teas, green tea has more health benets due to minimal processing and a higher content of pharmacologically active components. Tea leaves contain more than 2,000 components, and
13.1 Introduction ................................................................................................. 221 13.2 Effects of Catechins (EGCG, ECG, EGC, and EC) on
Catechol-O-Methyl Transferase .................................................................. 222 13.3 Tea Catechins and the Treatment of Obesity ..............................................228 13.4 Conclusion and Discussion ..........................................................................230 Acknowledgments .................................................................................................. 231 References .............................................................................................................. 231
catechins represent a class of compounds known as tea polyphenols. The major catechins in fresh tea leaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC). The catechin composition depends on the location of cultivation of the tea plant, variety of plant, season of harvest, and process conditions. Catechins are colorless, watersoluble compounds that impart bitterness and astringency to tea infusions. Almost all of the characteristics of tea, such as
taste, color, and aroma, are associated with the catechins. A typical catechin composition would be 10-15% EGCG, 6-10% EGC, 2-3% ECG, and 2% EC.8 The structures of the major catechins are shown in gure 13.1. EGCG is the most abundant catechin and has received by far the most attention in clinical studies. Flavonols such as quercetin and their glycosides are present in lower levels. In addition, caffeine, theobromine, theophylline, and phenolic acids, such as gallic acid, are also present as minor constituents. Caffeine accounts for 3-6% of the dry weight of brewed tea.
