Green tea (Protocatechuic acid) dược liệu kháng HL60
The appearance of green tea in three different stages: (from left to right) the infused leaves, the dry leaves, and the liquid. (Notice that the infused leaves look greener than the dry leaves.)
| |
| Type | Tea |
|---|---|
| Country of origin | China |
| Region of origin | East Asia |
| Ingredients | Tea leaves |
Green tea is a type of tea that is made from Camellia sinensis leaves that have not undergone the same withering and oxidation process used to make oolong and black tea.[1] Green tea originated in China, but its production has spread to many countries in Asia.
Several varieties of green tea exist, which differ substantially because of the variety of C. sinensis used, growing conditions, horticultural methods, production processing, and time of harvest.
Contents
[hide]History[edit]
A book written by Lu Yu in 600-900 AD (Tang Dynasty), "Tea Classic" (simplified Chinese: 茶经; traditional Chinese: 茶經; pinyin: chájīng), is considered important in green tea history. The Kissa Yojoki (喫茶養生記 Book of Tea), written by Zen priest Eisai in 1191, describes how drinking green tea may affect five vital organs, the shapes of tea plants, flowers and leaves, and how to grow and process tea leaves.
Brewing and serving[edit]
Steeping, or brewing, is the process of making tea, generally using two grams of tea per 100 ml of water or about 1 teaspoon of green tea per 150 ml cup. Higher-quality teas, like gyokuro, use more tea leaves and are steeped multiple times for short durations.
Steeping temperatures range from 61°C (142°F) to 87°C (189°F) and times from 30 seconds to three minutes.
Generally, lower-quality green teas are steeped hotter and longer while higher-quality teas are steeped cooler and shorter, but usually for multiple times (2-3 typically). Steeping too hot or for too long results in the release of excessive amounts of tannins, leading to a bitter, astringent brew, regardless of initial quality. The brew’s taste is also affected by the steeping technique. Two important techniques are to warm the steeping container beforehand to prevent the tea from immediately cooling down and to leave the tea leaf in the pot and gradually add more hot water as you drink the tea.
Extracts[edit]
Green tea extracts have been used in traditional Chinese and Indian medicine for a variety of uses.[3]
Green tea leaves are initially processed by soaking in an alcohol solution, which may be further concentrated to various levels; byproducts of the process are also packaged and used. Extracts may be sold in liquid, powder, capsule, or tablet form.[4] Decaffeinated versions are also available.[5]
Green tea extract supplements are accessible over the counter in various forms. Standardized green tea extract is 90 percent total polyphenols, and 1 capsule equals 5 cups of tea.[6][7]
Health effects[edit]
| Nutritional value per 100 g (3.5 oz) | |
|---|---|
| Energy | 4 kJ (0.96 kcal) |
0 g
| |
0 g
| |
0.2 g
| |
| Vitamins | |
| Thiamine (B1) |
(1%)
0.007 mg |
| Riboflavin (B2) |
(5%)
0.06 mg |
| Niacin (B3) |
(0%)
0.03 mg |
| Vitamin B6 |
(0%)
0.005 mg |
| Vitamin C |
(0%)
0.3 mg |
| Minerals | |
| Calcium |
(0%)
0 mg |
| Iron |
(0%)
0.02 mg |
| Magnesium |
(0%)
1 mg |
| Manganese |
(9%)
0.18 mg |
| Potassium |
(0%)
8 mg |
| Sodium |
(0%)
1 mg |
| Other constituents | |
| Water | 99.9 g |
| Caffeine | 12 mg |
| |
| Percentages are roughly approximated using US recommendations for adults. | |
Regular green tea is 99.9% water, provides 1 Calorie per 100 mL serving, is devoid of significant nutrient content (table) and contains phytochemicals, such as polyphenols and caffeine. Polyphenols found in green tea include epigallocatechin gallate (EGCG), epicatechin gallate, epicatechins and flavanols,[1] which have antioxidant, anticarcinogen, anti-inflammatory, and anti-radiation biochemical effects in vitro.[4] Other components include three kinds of flavonoids, known as kaempferol, quercetin, and myricetin.[8] A remarkably higher content of myricetin is detected in tea and its extracts than in many other plants, and this high concentration of myricetin may have some implications for the experimentally-observed bioactivity of tea and its extracts in vitro.[4]
Although numerous claims have been made for the health benefits of green tea, human clinical research has not provided conclusive evidence of any effects.[1][9][10] In 2011, a panel of scientists published a report on the claims for health effects at the request of the European Commission: in general they found that the claims made for green tea were not supported by sufficient scientific evidence.[9] Although the mean content of flavonoids and catechins in a cup of green tea is higher than that in the same volume of other food and drink items that are traditionally considered to promote health,[11]flavonoids and catechins have no proven biological effect in humans.[9][12]
Cancer[edit]
There is no conclusive evidence that green tea helps to prevent or treat cancer in people.[10][13] A review of existing studies concluded that while suggestive evidence existed, it did not amount to a clear indication of benefit.[13]
Daily consumption of black tea (but not green tea) has been associated with a significant reduction in death from all cancers.[14] There is limited evidence to suggest that green tea consumption may be associated with a slightly lower risk of esophageal cancer in the Chinese population, a lower risk of lung cancer in women, and a lower risk of oral cancer in Asian people.[15][16][17] A 2015 meta-analysis of nine prospective cohort studies concluded that a high amount of green tea consumption may be associated with a lower risk of liver cancer in Asian women.[18] This association was not seen in Asian men or when one cup of green tea was consumed daily.[18] Similarly, another analysis of observational data conducted in 2012 suggested that green tea consumption may have a favorable effect on lung cancer risk. The observed effect was strongest in those who consumed more than seven cups of green tea daily.[19] A 2011 meta-analysis of epidemiological studies found limited evidence that green tea consumption may be associated with a moderately reduced risk of liver cancer in Chinese and Japanese people.[20] Limited evidence suggests that green tea consumption is not associated with the risk of developing pancreatic cancer or prostate cancer.[21][22] The link between green tea consumption and stomach cancer risk is unclear due to inconsistent evidence.[23]
Green tea interferes with the chemotherapy drug bortezomib (Velcade) and other boronic acid-based proteasome inhibitors, and should be avoided by people taking these medications.[24]
Cardiovascular disease[edit]
Observational studies have shown a correlation between daily consumption of green tea and a lower risk of death from cardiovascular disease. In a 2015 meta-analysis of such observational studies, an increase in one cup of green tea per day was correlated with a 5% lower risk of death from cardiovascular causes.[14] Green tea consumption may be correlated with a reduced risk of stroke.[25][26][27] Meta-analyses of randomized controlled trials have found that green tea consumption for 3–6 months appears to lower systolic and diastolic blood pressures a small amount (about 3 mm Hg each).[27][28][29][30][31]
Glycemic control[edit]
Green tea consumption lowers fasting blood sugar but in clinical studies the beverage's effect on hemoglobin A1c and fasting insulin levels was inconsistent.[27][32][33]
Hyperlipidemia[edit]
Drinking green tea or taking green tea supplements decreases the blood concentration of total cholesterol (about 7 mg/dL), LDL cholesterol (about 2 mg/dL), and does not affect the concentration of HDL cholesterol.[27][34] A 2013 Cochrane review performed a meta-analysis of longer-term randomized controlled trials (>3 months duration) and concluded that green tea consumption lowers total and LDL cholesterol concentrations in the blood.[27][28]
Inflammation[edit]
A 2015 systematic review and meta-analysis of 11 randomized controlled trials found that green tea consumption was not significantly associated with lower plasma levels of C-reactive protein levels (a marker of inflammation).[35]
Mortality risk[edit]
Daily consumption of green tea is significantly correlated with a lower risk of death from any cause; an increase of one cup of green tea per day is linked with a 4% lower risk of death from any cause.[14] A separate analysis found that an increase of three cups of tea or green tea per day was associated with a lower risk of total mortality in Asians and women.[25]
Weight loss[edit]
There is no conclusive evidence that green tea aids in weight loss.[36]
Toxicity[edit]
Moderate, regular, and habitual consumption of green tea is safe;[10] however, there are reports of liver toxicity in humans after consuming high doses (10–29 mg/kg/day) of green tea extract dietary supplements,[37] and high doses may act as a pro-oxidant to damage DNA.[4]
Production[edit]
Growing, harvesting and processing[edit]
Green tea is processed and grown in a variety of ways, depending on the type of green tea desired. As a result of these methods, maximum amounts of polyphenols and volatile organic compounds are retained, affecting aroma and taste. The growing conditions can be broken down into two basic types − those grown in the sun and those grown under the shade. The green tea plants are grown in rows that are pruned to produce shoots in a regular manner, and in general are harvested three times per year. The first flush takes place in late April to early May. The second harvest usually takes place from June through July, and the third picking takes place in late July to early August. Sometimes, there will also be the fourth harvest. It is the first flush in the spring that brings the best-quality leaves, with higher prices to match.
Green tea is processed using either artisanal or modern methods. Sun-drying, basket or charcoal firing, or pan-firing are common artisanal methods. Oven-drying, tumbling, or steaming are common modern methods.[38] Processed green teas, known as aracha are stored under low humidity refrigeration in 30- or 60-kg paper bags at 0–5 °C (32–41 °F). This aracha has yet to be refined at this stage, with a final firing taking place before blending, selection and packaging take place. The leaves in this state will be re-fired throughout the year as they are needed, giving the green teas a longer shelf-life and better flavor. The first flush tea of May will readily store in this fashion until the next year's harvest. After this re-drying process, each crude tea will be sifted and graded according to size. Finally, each lot will be blended according to the blending order by the tasters and packed for sale.[39]
Production by country[edit]
 | This section needs to be updated. (May 2017) |
2006 Green tea production and export (in thousands of metric tons)[40]
|
Import of Japanese tea[edit]
| This section needs to be updated. (October 2016) |
On 17 June 2011, radioactive cesium of 1,038 becquerels per kilogram was detected at Charles de Gaulle airport in France in tea leaves imported from Shizuoka Prefecture, Japan as a result of the Fukushima Daiichi nuclear disaster, which was more than twice as much as the restricted amount of 500 becquerels per kilogram designated by the European Union. The government of France announced that they rejected the tea leaves, which amounted to 162 kilograms (357 lb).[41] The governor of Shizuoka Prefecture Heita Kawakatsu stated that "there is absolutely no problem when they [people] drink them because it will be diluted to about ten becquerels per kilogram when they steep them even if the leaves have 1,000 becquerels per kilogram," which was a consequence of own examinations of the prefecture.[42] Minister for Consumer Affairs and Food Safety Renhō stated on 3 June 2011, that "there are cases in which aracha are sold as furikake [condiments sprinkled on rice] and so on and they are eaten as they are, therefore we think that it is important to inspect tea leaves including aracha from the viewpoint of consumers' safety."[43]
Green tea by country[edit]
China[edit]
| Chinese name | |||
| |||
| Traditional Chinese | 綠茶 | ||
|---|---|---|---|
| Simplified Chinese | 绿茶 | ||
| Hanyu Pinyin | lǜchá | ||
| |||
Loose leaf green tea has been the most popular form of tea in China since the Southern Song dynasty.[44][45] While Chinese green tea was originally steamed, as it still is in Japan, after the early Ming dynasty it has typically been processed by being pan-fired in a dry wok.[46] Other processes employed in China today include oven-firing, basket-firing, tumble-drying and sun-drying.[47] Green tea is the most widely produced form of tea in China, with 1.42 million tons grown in 2014.[48]
Popular green teas produced in China today include:
- Biluochun
Produced in Jiangsu, this tea is named after the shape of the leaves, which are curled like snails.[49] - Chun Mee
Known in English by its Cantonese name, and popular outside China. It has a plum-like flavor.[50] - Gunpowder tea
A tea which is tumble-dried so that each leaf is rolled into a small pellet that resembles gunpowder.[51] - Huangshan Maofeng
A type of maofeng tea grown in the microclimate of the Huangshan mountain range in Anhui province. Maofeng teas are harvested by plucking intact two equal-sized leaves and a bud together.[52] - Longjing
Also known as "Dragon Well" tea, the English translation of its name. Grown near Hangzhou in Zhejiang province, Longjing is the most well-known pan-fired Chinese green tea. Its flavor derives partly from the terroir of the region in which it is produced.[49] - Lu'an Melon Seed
Grown in Anhui province. Unlike typical Chinese teas, two leaves are plucked separately from each branch, with no bud and no stems. Harvested later in the season, it has a grassier flavor than typical Chinese green teas.[53] - Taiping Houkui
Grown in Anhui province. Uses a cultivar with an unusually large leaf. The production process flattens the tea leaves, creating the so-called "two knives and a pole" shape from the leaves and stem.[54] - Xinyang Maojian
A type of maojian tea grown in Xinyang, Henan province.[55] Maojian teas are harvested by plucking a bud and one leaf together.[52]
Japan[edit]
Tea seeds were first brought to Japan in the early 9th century by the Buddhist monks Saicho and Kukai. During the Heian period (794–1185), Emperor Saga introduced the practice of drinking tea to the imperial family. The Zen Buddhist priest Eisai (1141–1215), founder of the Rinzai school of Buddhism, brought tea seeds from China to plant in various places in Japan. Eisai advocated that all people, not just Buddhist monks and the elite, drink tea for its health benefits.[56]
The oldest tea producing region in Japan is Uji, located near the former capital of Kyoto.[56] It is thought that seeds sent by Eisai were planted in Uji, becoming the basis of the tea industry there.[57] Today, Japan's most expensive premium teas are still grown in Uji.[58] The largest tea producing area today is Shizuoka Prefecture, which accounts for 40% of total Japanese sencha production.[59][58] Other major tea producing regions include the island of Kyushu and the prefectures of Shiga, Gifu, and Saitama in central Honshu.[58]
All commercial tea produced in Japan today is green tea,[60] though for a brief period black tea was also produced in the late 19th and early 20th centuries. Japanese tea production is heavily mechanized, and is characterized by the use of modern technology and processes to improve yields and reduce labor. Because of the high cost of labor in Japan, only the highest quality teas are plucked and processed by hand in the traditional fashion.[61]
Japanese green teas have a thin, needle-like shape and a rich, dark green color. Unlike Chinese teas, most Japanese teas are produced by steaming rather than pan firing. This produces their characteristic color, and creates a sweeter, more grassy flavor. A mechanical rolling/drying process then dries the tea leaves into their final shape.[60] The liquor of steamed Japanese tea tends to be cloudy due to the higher quantity of dissolved solids.[62]
Most Japanese teas are blended from leaves grown in different regions, with less emphasis on terroir than in the Chinese market. Because of the limited quantity of tea that can be produced in Japan, the majority of production is dedicated to the premium tea market. Bottled tea and tea-flavored food products usually use lower-grade Japanese-style tea produced in China.[63]
Although a variety of commercial tea cultivars exist in Japan, the vast majority of Japanese tea is produced using the Yabukita cultivar developed in the 1950s.[64]
Popular Japanese green teas include:
- Bancha
A lower-grade tea plucked from the same bushes used to produce sencha. It has a somewhat bolder flavor, and is plucked each season after sencha production is finished.[65] - Genmaicha
Made by combining sencha tea leaves with toasted puffs of rice. - Gyokuro
Grown under shade for three weeks prior to plucking, gyokuro is one of the most exclusive varieties of tea produced in Japan.[66] The shading technique imparts a sweeter flavor, and produces a particularly rich color thanks to the higher amounts of chlorophyll in the shaded leaf. Gyokuro tea is associated with the Uji region, the first tea-growing region in Japan. It is often made using smaller-leaf cultivars of the tea plant.[67] - Hojicha
This type of tea is made by roasting sencha or bancha leaves with kukicha twigs.[68] - Kabusecha
Similar to gyokuro, kabusecha is shaded for only a week prior to plucking. Its flavor is somewhat between that of gyokuro and normal sencha.[66][67] - Kukicha
A blended tea made of sencha leaves and stems.[69] - Matcha
Like gyokuro, matcha is shaded before plucking. The plucked and processed leaf is called tencha. This product is then ground into a fine powder, which is matcha. Because the tea powder is very perishable, matcha is usually sold in small quantities. It is typically rather expensive.[68] Matcha is the type of tea used in the Japanese tea ceremony. It is prepared by whisking the tea with hot water in a bowl, until the surface is frothy. If the water is too hot, the tea may become overly bitter.[70] - Sencha
This type of tea is produced throughout the tea season, and is the standard style today, representing 80% of all tea produced in Japan.[71] 90% of sencha is grown from the Yabukita cultivar.[64] - Shincha
The first early harvest of tea, plucked before the first flush, is called shincha. Shincha is made from the youngest new growth leaves, and is plucked from early April to early May. Shincha typically refers to the early harvest of sencha, but can refer to any type of tea plucked early in the season, before the main harvest. Because of the limited quantities in which it is produced, shincha is highly prized and expensive to obtain.[72]
Korea[edit]
| Korean name | |
| |
| Hangul | 녹차 |
|---|---|
| Hanja | 綠茶 |
| Revised Romanization | nokcha |
| McCune–Reischauer | nokch'a |
| IPA | [nok̚.tɕʰa] |
According to Record of Gaya cited in Memorabilia of the Three Kingdoms, the legendary queen Heo Hwang-ok, a princess of the Ayodhya married to King Suro of Gaya, brought the tea plant from India and planted it in Baegwolsan, a mountain in current Changwon.[73]:3 However, it is a widely held view that systematic planting of tea bushes began with the introduction of Chinese tea culture by the Buddhist monks around the 4th century.[74] Amongst some of the earliest Buddhist temples in Korea, Bulgapsa (founded in 384, in Yeonggwang), Bulhoesa (founded in 384, in Naju) and Hwaeomsa (founded in Gurye, in 544) claim to be the birthplace of Korean tea culture.[74] Green tea was commonly offered to Buddha, as well as to the spirits of deceased ancestors.[74] Tea culture continued to prosper during the Goryeo Dynasty, with the tea offering being a part of the biggest national ceremonies and tea towns were formed around temples.[75] Seon-Buddhist manners of ceremony prevailed.[75] During the Joseon Dynasty, however, Korean tea culture underwent secularization, along with the Korean culture itself.[75] Korean ancestral rite jesa, also referred to as charye (차례; 茶禮, "tea rite"), has its origin in darye (다례; 茶禮, "tea rite"), the practice of offering tea as simple ancestral rites by the royal family and the aristocracy in Joseon.[75]
Tea culture of Korea was actively suppressed by the Japanese during the Japanese forced occupation period (1910‒1945), and the subsequent Korean War (1950‒1953) made Korean tea tradition even harder to survive.[76] The restoration of the Korean way of tea began in the 1970s, around Dasolsa.[76] Commercial production of green tea in South Korea also began only in the 1970s,[77] and was still 20% of Taiwan and 3.5% of Japan in 2012.[78][79] Green tea is not as popular as coffee or other types of Korean teas in modern South Korea. The annual consumption per capita of green tea in South Korea in 2016 was 0.16 kg (0.35 lb), compared to 3.9 kg (8.6 lb) coffee.[80] Recently however, as the coffee market reached a saturation point, South Korean tea production doubled during 2010‒2014,[81] as did tea imports during 2009-2015,[82] despite very high tariff rate (513.6% for green tea, compared to 40% for black tea, 8% for processed/roasted coffee, and 2% for raw coffee beans).
Korean green tea can be classified into various types based on several different factors. The most common is the flush, or the time of the year when the leaves are plucked (and thus also by leaf size).
- Ujeon
Ujeon (우전; 雨前; lit. "pre-rain"), or cheonmul-cha (첫물차; lit. "first flush tea"), is made of hand-picked leaves plucked before gogu (20–21 April).[83][84][85] The ideal steeping temperature for ujeon tea is 50 °C (122 °F).[86] - Sejak
Sejak (세작; 細雀; lit. "thin sparrow"), or dumul-cha (두물차; lit. "second flush tea"), is made of hand-picked leaves plucked after gogu (20–21 April) but before ipha (5–6 May).[83][84][85] The tea is also called jakseol (작설; 雀舌; lit. "sparrow tongue") as the tea leaves are plucked when they are about the size of a sparrow's tongue.[84] The ideal steeping temperature for sejak tea is 60–70 °C (140–158 °F).[86] - Jungjak
Jungjak (중작; 中雀; lit. "medium sparrow"), or semul-cha (세물차; lit. "third flush tea"), is made of leaves plucked after ipha (5–6 May) until the mid May.[83][84] The ideal steeping temperature for jungjak tea is 70–80 °C (158–176 °F).[86] - Daejak
Daejak (대작; 大雀; lit. "big sparrow"), or kkeunmul-cha (끝물차; lit. "final flush tea"), is made of tea leaves plucked in late May and after.[84] It is usually made into tea bags or used in cooking.[84] The ideal steeping temperature for daejak tea is 80–90 °C (176–194 °F).[86]
The mode of preparation also differs:
- Ipcha (yeopcha)
The synonyms ipcha (잎차; lit. "leaf tea") and yeopcha (엽차; 葉茶; lit. "leaf tea") refer to loose leaf tea, often in contrast to tea in tea bags. As the words mean "leaf tea", they can also be used in contrast to powdered tea.[87] - Garucha (malcha)
The synonyms garucha (가루차; lit. "powder tea") and malcha (말차; 末茶; lit. "powder tea") refer to powdered tea.[88][89]
Leaf teas are processed either by roasting or steaming.
- Deokkeum-cha (bucho-cha)
Roasting is the most common and traditional way of tea processing in Korea. Also translated into "pan-fried tea", the deokkeum-cha (덖음차; lit. "roasted tea") or bucho-cha (부초차; 麩炒茶; lit. "roasted tea") varieties are richer in flavour.[90][91][92] - Jeungje-cha
Steaming is less popular in Korean green tea processing, but the method is still used in temple cuisine. Tea prepared with steamed tea leaves, called jeungje-cha (증제차; 蒸製茶; lit. "steamed tea"), are more vivid in colour.[93]
Southern, warmer regions such as Boseong in South Jeolla Province, Hadong in South Gyeongsang Province, and Jeju Island are famous for producing high quality tea leaves.[94]
- Banya-cha
Banya-cha (반야차; 般若茶; lit. "prajñā tea") is one of the most renowned Korean green tea.[95] The steamed tea is developed by Buddhist monks in Boseong.[citation needed] The tea is grown on sandy loam near mountains and sea.[citation needed] The word banya is a Korean transliteration of the Buddhist concept prajñā. - Jungno-cha
Jungno-cha (죽로차; 竹露茶; lit. "bamboo dew tea") is one of the most renowned Korean green tea.[96] The roasted variety of tea is made of tea leaves grown among the bamboo in Gimhae, Hadong, and Jinju in South Gyeongsang Province.[97]
Green tea can be blended with other ingredients.
- Hyeonmi-nokcha
Nokcha (green tea) blended with hyeonmi-cha (brown rice tea) is called hyeonmi-nokcha (현미녹차; 玄米綠茶; lit. "brown rice green tea"). - Remon-nokcha
Nokcha (green tea) blended with lemon is called remon-nokcha (레몬 녹차; lit. "lemon green tea").
Other countries[edit]
![[icon]](https://en.wikipedia.org/wiki/File:Wiki_letter_w_cropped.svg){kind=small}
In Canada, green tea is defined as a dry-based mixture and the sale of it is regulated by the Canadian Food Inspection Agency (CFIA). It is one of the foods for which a standard of identity is specified according to the Food and Drug Regulations. It should contain not less than 33% water-soluble extractive (determined by official method FO-37 which is the determination of water-soluble extractive in tea) and the total ash should between 4% to 7%.[98]
