Doc:Tea
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Revision as of 16:58, 25 February 2010
Contents |
Classification of Tea (茶の分類)
Green Tea (緑茶)
It is non-fermented, i.e., produced by frying or steaming (fixation) the fresh leaves of Camellia sinensis var.sinensis 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.
Black Tea (紅茶)
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 °C with high humidity (>95%). Leaves are fully oxidized and turn golden with floral aroma in this process.
Oolong Tea (烏龍茶)
It is produced by partial fermentation before drying. The process is called green leaf shaking (yaoqing) and green leaf cooling (liangqing), where mildly withered tea leaves are bruised at the edges by hand. Good oolong tea leaves have reddish edges with green centers. It is mainly produced in Fujian, Guangdong (both China), and Taiwan.
Pu-erh Tea (普洱茶)
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 (茶の組成)
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]. After drinking tea, the plasma level of catechins reach their peaks (between 1-10 µmol/L) in 2 - 4 h [6]. After 24 h, plasma levels of EGCG and EGC return to baseline, but that of ECG remains elevated in methylated forms[7]. |
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%) [1]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[2]。 コップ１杯のお茶にはおよそ90 mgのEGCG [3]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[4][5]。 お茶を飲んだ後、血漿中のカテキン濃度は2-4時間でピーク（1-10 µmol/L)に達します[6]。 24時間後には血漿中のEGCG, EGCは初期値に戻りますが、ECGはメチル化された形で残っています[7]。 |
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The caffeine content in different types of tea is: black tea > oolong tea > gree tea > fresh tea leaf [9]. More than 200 mg/day caffeine is not advisable and may produce nervousness, sleep disorders, vomits, headaches, epigastric pain, and tachycardia [10]. |
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[9]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[10]。 |
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- References
- ↑ 1.0 1.1 McKay DL, Blumberg JB (2002) "The role of tea in human health: An update" J Am Coll Nutr 21:1-13
- ↑ 2.0 2.1 USDA Database for the Flavonoid Contents of Selected Foods, Beltsville 2003
- ↑ 3.0 3.1 Wu CD, Wei GX (2002) "Tea as a functional food for oral health" Nutrition 18(5):443-444
- ↑ 4.0 4.1 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
- ↑ 5.0 5.1 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
- ↑ 6.0 6.1 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
- ↑ 7.0 7.1 Higdon JV, Frei B (2003) "Tea catechins and polyphenols: health effects, metabolism, and antioxidant functions" Crit Rev Food Sci Nutr 43:89-143
- ↑ Belitz DH, Grosch W (1997) "Quimica de los Alimentos" Zaragoza Acribia
- ↑ 9.0 9.1 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
- ↑ 10.0 10.1 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
