Doc:Tea
| Tea Top | Exotic teas | Production/Consumption | Health |
Contents |
About Tea
Tea is made from leaves of Camellia sinensis var.sinensis or var.assamica. The former has small round leaves and the tree height is lower than 4m. It is cold resistant and is cultivated in Japan and China. The assamica has large pointed leaves and its tree height is over 10m. Its leaves contain more tannins and are used for black tea except for Darjeeling, which uses sinensis, in India and Sri Lanka. Both species share the same number of chromosomes and easily crossbreed. Their mix grow in Indochina.
Different tastes and flavors mainly come from manufactural differences. The degree of fermentation is as follows.
Weak (弱い)  Fermentation (醗酵度合)  Strong (強い)
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| White tea 白茶 |
< | Green tea 緑茶 |
< | Oolong tea 烏龍茶 |
< | Black tea 紅茶 |
< | Pu-erh tea 普洱茶 |
Classification of Tea
White Tea
White tea is covered with white hair, because of its special manufacturing process of "no crushing" (minimum treatment). Only 2,000 tons per year is manufactured in Fujian Province, China. The general grade is: Silver Needle > White Peony > Gongmei and Shoumei. Silver Needle with White Hair is made from bulky buds only, White Peony is made from the bud and 1 or 2 leaves. For Silver Needle, young buds are harvested, withered and quickly basket fried (40-50 ℃, 30 min for 250 g) to keep their fermentation minimal. For White Peony, frying temperature is 70-80 ℃ after withering.
Green Tea
It is non-fermented, i.e., produced by frying or steaming (fixation) the fresh leaves to inactivate polyphenol oxidases. Steaming is common in Japan whereas pan-frying is used in China. Assan (assamica) type contains too much tannins and not suitable for green tea. Almost all green tea is consumed in Japan, Vietnam, China, and Indonesia only.
Blue or Oolong Tea
It is produced by partial fermentation before drying. The process is called green leaf shaking (yaoqing), where mildly withered tea leaves are bruised at the edges by hand, and green leaf cooling (liangqing). Good oolong tea leaves have reddish edges with green centers. It is mainly produced in Fujian, Guangdong (both China), and Taiwan. Black oolong tea is usually roasted. Golden-colored oolong tea, produced in Taiwan, is lightly fermented oolong tea (closer to green tea).
Black Tea
Unlike green tea, leaves are withered and rolled to crush leaf cells and release polyphenol oxidases. Black tea in India, Sri Lanka, and Kenya is manufactured by a CTC (crushing, tearing, and curling) machine whereas in China an orthodox rotorvane is used. After rolling, leaves are fermented for 0.5 - 3 hours at 25-35 ℃ with high humidity (>95%). Leaves are fully oxidized and turn golden with floral aroma in this process.
Pu-erh Tea
Raw pu-erh tea is produced by pressing tea leaves and fermenting for years, sometimes for decades. Ripened pu-erh tea, which is more popular, is inoculated with black Aspergillus and fermented under an optimal condition for several months. From Yunnan Pu-erh tea, Aspergillus niger, A. gloucu, and species of Penicillium, Rhizopus, Saccharomyces, and Bacterium are found. A. niger is the most predominant, followed by Saccharomyces spp. [1] Ripened pu-erh tea contains less catechins than raw pu-erh tea, but more gallic acid as the degradation products of catechins (and others). Antioxidant activity is significantly higher for raw pu-erh tea.[2]
- ↑ Jeng KC, Chen CS, Fang YP, Hou RCW, Chen YS (2007) "Effect of microbial fermentation on content of statin, GABA, and polyphenols in pu-erh tea" J. Agric. Food Chem. 55:8787-8792
- ↑ Ku KM, Kim J, Park HJ, Liu KH, Lee CH (2010) "Application of Metabolomics in the Analysis of Manufacturing Type of Pu-erh Tea and Composition Changes with Different Postfermentation Year" J. Agric. Food Chem. 58:345-352
Tea Composition
Catechins
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The major phenolics in green tea include catechins (flavan 3-ols). They are (-)-epigallocatechin-3-gallate (EGCG; 59% of total catechins), (-)-epigallocatechin (EGC; 19%), (-)-epicatechin-3-gallate (ECG; 13.6%), and (-)-epicatechin (EC; 6.4%) [1]. Catechins are converted to theaflavins and thearubigins in black tea [2]. A cup of tea may contain 90 mg of EGCG [3], but in human, EGCG is less bioavailable (i.e. little absorbed) than other green tea catechins. However, the bioavailability is different between species and genotypes [4][5]. |
緑茶中の主なフェノール化合物はカテキン(フラバン3-オール)で、(-)-エピガロカテキン-3-ガレート (EGCG; 全カテキンの59%), (-)-エピガロカテキン (EGC; 19%), (-)-エピカテキン-3-ガレート (ECG; 13.6%)そして(-)-エピカテキン (EC; 6.4%) です。 紅茶ではカテキンはテアフラビンとテアルビジンに変換されます。 コップ１杯のお茶にはおよそ90 mgのEGCGが含まれますがEGCGは他の茶カテキンに比べ、ヒト体内にあまり吸収されません。 生物学的な利用能力は生物種や遺伝型によって変化します。 |
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| Tea type | Green and White Tea | Oolong Tea | Black Tea | ||||||||||||
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| Major Phenolics (フェノール化合物) |
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⇒ oxidation ⇒ intermediate level (中間レベル) |
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After drinking tea, catechins are absorbed in the small intestine, and the plasma level of catechins reach their peaks (between 1-10 µmol/L) in 2 - 4 h [7]. Only less than 2 % of ingested catechins were found in the plasma, and gallated catechins are less bioavailable than non-gallated forms [8]. After 24 h, plasma levels of EGCG and EGC return to baseline, but that of ECG remains elevated in methylated forms[9].
- ↑ McKay DL, Blumberg JB (2002) "The role of tea in human health: An update" J Am Coll Nutr 21:1-13
- ↑ USDA Database for the Flavonoid Contents of Selected Foods, Beltsville 2003
- ↑ Wu CD, Wei GX (2002) "Tea as a functional food for oral health" Nutrition 18(5):443-444
- ↑ Kim S, Lee MJ, Hong J (2000) "Plasma and tissue levels of tea catechins in rats and mice during chronic consumption of green tea polyphenols" Nutr Cancer 37:41-48
- ↑ Loktionov A, Bingham S et al. (1998) "Apolipoprotein E genotype modulates the effect of black tea drinking on blood lipids and blood coagulation factors: A pilot study" Br J Nutr 79:133-139
- ↑ Belitz DH, Grosch W (1997) "Quimica de los Alimentos" Zaragoza Acribia
- ↑ Yang CS, Chen L et al. (1998) "Blood and urine levels of tea catechins after ingestion of different amounts of green tea by human volunteers" Cancer Epidemiol Biomarkers Prev 7:351-354
- ↑ Warden BA, Smith LS, Beecher GR, Balentine DA, Clevidence BA (2001) "Catechins are bioavailable in men and women drinking black tea throughout the day" J Nutr 131:1731-1737
- ↑ Higdon JV, Frei B (2003) "Tea catechins and polyphenols: health effects, metabolism, and antioxidant functions" Crit Rev Food Sci Nutr 43:89-143
Caffeine
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The caffeine content in different types of tea is: black tea > oolong tea > gree tea > fresh tea leaf [1]. More than 200 mg/day caffeine is not advisable and may produce nervousness, sleep disorders, vomits, headaches, epigastric pain, and tachycardia [2]. |
異なる茶に含まれるカフェインの量は 紅茶＞ウーロン茶＞緑茶＞新鮮な茶葉となります。 200 mg/日以上のカフェイン摂取は、イライラ、不眠、吐き気、頭痛、胃痛や頻脈を引き起こすので薦められません。 |
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- ↑ Lin Lin YS, Tsai YJ et al. (2003) "Factors affecting the levels of tea polyphenols and caffeine in te a leaves" J Agric Food Chem 51:1864-1873
- ↑ Varnam AH, Sutherland JP (1994) "Beverages: Technology, Chemistry and Microbiology" Chapman & Hall (London)
- ↑ Cabrera C, Artacho R, Gimenez R (2006) "Beneficial Effects of Green Tea-A Review" J Am Coll Nutr 25(2):79-99
Saponins
| Tea synthesizes different saponins in leaves, seeds, and flower parts. In flower/bud, floratheasaponins are contained 1-2% of its dry weight[1]. Therefore, tea containing flowers bubbles like a soap. |
茶は葉部、種子、花蕾部でそれぞれ特有のサポニンを作ります。特に花にはfloratheasaponinが多く、乾燥重量の1-2%を占め、茶花の入った茶は石鹸のように泡立ちます。 |
| Parts | Major phytochemical contents |
|---|---|
| Leaf | catechins > caffeine >> saponins, flavonoids |
| Flower/bud/pistil | floratheasaponins > flavonols > caffeine >> catechins |
| Seed | theasaponins, assamsaponins >> flavonoids |
- References
- ↑ Yoshikawa M, Morikawa T, Yamamoto K, Kato Y, Nagatomo A, Matsuda H (2005) J Nat Prod 68:1360-1365
