• Clinical Evidence

     

     

    The following journals discuss the effect of Oolong Tea on heart disease, cancer, high blood pressure, cholesterol, inflammation, obesity, and diabetes. The first may be of significance as it was recently added to the United Nations web site; Food & Agriculture of the United Nations. click for full article

     

    Note: Oolong Tea Club neither endorses nor refutes the clinical journals linking Oolong Tea to improved health and well-being. It does, however, endorse the careful scrutiny of contending evidence and encourage further research into the topic. We advise prudence when reviewing such articles, and always to consult your GP if planning to use any substance as a means of altering health.

     

  • Antihyperglycemic Effect of Oolong Tea in Type 2 Diabetes

    Hosoda K, Wang M, Lioa M, Chuang C, Iha M:

    Antihyperglycemic Effect of Oolong Tea in Type 2 Diabetes.

    American Journal of Diabetes. 26:1714 –1718, 2003

  • Oolong tea exhibits antioxidant, anticancer, antiobesity, prevention of atherosclerosis and heart disease, antidiabetes, and antiallergic effects.

    Chen Y, Duen J, Jiang Y, Shi J, Peng L, Xue s, Kakuda Y: Oolong tea exhibits antioxidant, anticancer, antiobesity, prevention of atherosclerosis and heart disease, antidiabetes, and antiallergic effects. Food Reviews International, 27:1–15, 2011

  • Comparison of the antioxidant activity of roasted tea with green, oolong, and black teas

    Satoh H, Tohyama N, Masaksu N; Comparison of the antioxidant activity of roasted tea with green, oolong, and black teas; International Journal of Food Sciences and
    Nutrition 56(8): 551 /559 2005

  • Oolong tea increases energy metabolism in Japanese females

    Komatsu T, Nakamori M,Komatsu K, Hosoda K, Okamura M, Toyama K, Ishikura Y, Sakai T: Oolong tea increases energy metabolism in Japanese females. The Journal of Medical Investigation Vol. 50 2003

  • Anti Obesity Action of Oolong Tea

    Han L, Takaku T, Li J, Kimura Y Okuda H: Anti Obesity Action of Oolong Tea : International Journal of Obesity. 1999; 23: 98-105

  • Heart Disease & Tea

    Khalesi S, Sun J, Buys N, Jamshidi A, •Nikbakht-Nasrabadi E, Khosravi-Boroujeni H; Green tea catechins and blood pressure: a systematic review and meta-analysis of randomised controlled trials: European Journal of Nutrition (2014) 53:1299–1311

     

  • Effects of Green Tea on Wound Healing

     

    Luiza de Almeida Neves A, Komesu M, Angel Sala Di Matteo M. Effects of Green Tea Use on Wound Healing : Internationa Journal of Morphology: 28 (3) :905- 910, 2010.

  • Lowering Blood Glucose

     

    Zhou B, Lovegreen B. Effect of oolong tea on balance performance in naive tea users.

    Journal of Exercise Physiologyonline (JEPonline)

    10 (5) 43-50 2007

  • Tea polyphenols benefit vascular function

    Yung L, Leung F, Wong W, Tian X, Yung W, Chen Z, Yao X, Huang Y; Tea polyphenols benefit vascular function. Inflammopharmacology 16 (2008) 230–234

     

  • Production, Quality, and Biological Effects of Oolong Tea (Camellia sinensis)

    Food Reviews International, 27:1–15, 2011 Copyright © Taylor & Francis Group, LLC ISSN: 8755-9129 print / 1525-6103 online DOI: 10.1080/87559129.2010.518294

    YU LONG CHEN1, JUN DUAN1, YUE MING JIANG 1, JOHN SHI2, LITAO PENG3, SOPHIA XUE2, AND YUKIO KAKUDA 4

    Abstract

     

    Oolong tea is a semi-fermented Chinese traditional tea that dates back centuries and now its unique characteristics are attracting more and more consumers worldwide. The formation of Oolong tea’s special quality is attributed to the proper processing of the fresh tea leaf. The quality of Oolong tea can be evaluated by aroma, flavor, color, and appearance with aroma and flavor being the two most important quality indices. The formation of the distinct aroma of Oolong tea depends largely on the decomposition of lipids and carotenoids. However, other compounds that can be hydrolyzed and/or oxidized also contribute to Oolong tea’s special aroma. During the processing of Oolong tea, some major flavor compounds are formed by the oxidation of catechins, amino acids, and sugars. The flavor of Oolong tea is complex due to the interaction of many different flavor compounds. Oolong tea exhibits antioxidant, anticancer, antiobesity, prevention of atherosclerosis and heart disease, antidiabetes, and antiallergic effects. Management of environmental factors, selection of tea cultivars and improvements in tea production needs to be emphasized to ensure the high quality of Oolong tea. The exact mechanisms responsible for the beneficial health effects of Oolong tea are not known.

     

    Keywords Oolong tea, antioxidant, aroma, flavor, biological activity

     

    Introduction

     

    Oolong tea (Camellia sinensis) is a partially fermented Chinese tea that is oxidized in the range from 10 to 70% during processing. Oolong tea was first produced in the early Song Dynasty (960–1279) but became popular in the Ming Dynasty (1368–1644).(1) The major types of Oolong tea, ‘Wuyi Mountain Rock’, ‘Anxi’, ‘Guangdong Dan Chong/Phoenix Mountain’ and ‘Taiwan’ listed in Table 1 are from four different production regions of China. The production and consumption of Oolong tea worldwide has increased over the past decade and in mainland China, and the production of Oolong tea nearly doubled in the period from 2000 to 2007

    The major distribution of Oolong tea and major cultivars

     

    Regions

    • North Fujian Province South Fujian Province
    • Taiwan
    • Guangdong Province

    Major products

    • Wuyi Rock,
    • Shuixian (Narcissus)
    • Da Hong Pao
    • Rou Gui (Cinnamon)
    • Tieguanyin (Iron Goddess), 
    • Qilan (Orchid) 
    • Shuixian (Narcissus)
    • Wudong 
    • Baozhong
    • Phoenix Dancong
    • Phoenix Narcissus
    • Lingtou Dancong 

    The quality of Oolong tea can be assessed by color, aroma, flavor, and appearance.(2) For example, ‘Wuyi Mountain’ and ‘Phoenix Mountain’ Oolong teas exhibit a dark green or brown color while the color of ‘Tieguanyin’ Oolong is bright to dark green. These color attributes, along with aroma, flavor, and appearance, are used to evaluate the overall quality of Oolong tea. The production of high-quality Oolong tea requires expert knowledge and skill to properly carry out the complex processing procedures that are summarized in Fig. 1.

     

    When the green tea leaves are fermented, the operator must have in-depth knowledge and experience to identify the best time to stop the fermentation. Among the processing procedures, tossing and rolling are the crucial steps in the formation of high-quality Oolong tea.

     

    The Quality of Oolong Tea

     

    The attributes of Oolong tea can be partially correlated with the levels of certain flavor com- pounds. The aromas of Oolong tea are due to linalool, geraniol, 2-phenyl ethanol, benzyl alcohol, methyl salicylate, linalool oxides, (Z)-3-hexanol, and others.(4,5,6,7) The characteristic aromas of Oolong tea are nerolidol, jasmine lactone, methyl jasmonate, and indole.(8) Furthermore, the flavor of Oolong tea infusion is related to a combination of various compounds, such as catechins (bitterness), amino acids (freshness), soluble sugar (sweetness), theaflavins (briskness), and thearubigin (mellowness).(3,9) In addition, the color of Oolong tea infusion can be determined by the major combinations of flavone, catechins, theaflavins, and thearubigins.(10) According to Roberts,(11) the appearance of the leaves in Oolong tea can be related to the proportion of chlorophyll, xanthine, and carotene.

     

    The Aromas of Oolong Tea

     

    Oolong tea has many different kinds of aromas and these different aromas are directly related to the type and extent of processing given to the tea leaves.(8,12) For example, nerolidol, geraniol, jasmine lactone, methyl salicylate, isoeugenol, limonene, and indole are the major volatile compounds in a high-grade Duhngdiing Oolong tea. In a low-grade Oolong tea, Linalool, linalool oxide, benzaldehyde, phenylacetaldehyde, cis-jasmone, hexenyl hexanoate, methyl salicylate, and indole are the major volatile compounds.(13) The formation of these volatile compounds has been investigated extensively, and mainly involves the transformation of higher fatty acids into alcohols and aldehydes, the decomposition of carotenoid into aromatic compounds, and, to a lesser extent, many other hydrolyses and oxidation reactions.(8,14)

     

    Transformation of Higher Fatty Acids into Alcohols and Aldehydes.

     

    The degradation of lipids occurs at the rolling and fermentation stages of Oolong tea processing. More than 60% of all lipid fractions are degraded during tea manufacture.(14) When the leaves are macerated, the lipid-degrading enzymes are released. The tossing and rolling breaks down the lipoprotein membrane structure/storage lipids and releases the fatty acids, which then undergo further degradation.(15) For example, the dehydration of tea leaves increases the activity of the lipoxygenase enzyme, which in turn catalyzes the oxidation of polyunsaturated fatty acids.(16)

     

    Polyunsaturated fatty acids have been identified as precursors of C6 aldehydes and short chain alcohols in tea.(17) Many higher fatty acids, especially the unsaturated higher fatter acids, such as oleic, linoleic, and linolenic acids, are present in the leaves of Oolong tea. Linoleic and linolenic acids, the two dominant free fatty acids in the tea leaves, have been shown to decrease during the processing of Oolong tea.(13) At the same time, the levels of C6 aldehydes, which are considered to be detrimental volatile flavor compounds, are found to increase during the processing of Oolong tea. Accordingly, the presence of C6 aldehydes such as hexanal and hexenal can result in a decline in tea flavor index.(14)

     

    Decomposition of Carotenoids into Aromatic Compounds.

     

    Tea carotenoids are mainly composed of carotenes (α-carotene and β-carotene) and xanthophylls. Much of the α-carotene is hydroxylated to lutein, while some of the β-carotene is converted to corresponding xanthophylls by way of zeaxanthin during the processing of Oolong tea.(18) Many of the aroma compounds formed during tea processing are derived from carotenes,(14) which make them important precursors in the development of Oolong tea aromas.

     

    The decomposition of carotenoids occurs by way of an enzymatic reaction that takes place during withering and fermentation, and also by a pyrolytic reaction during firing.(19) However, the extent of the carotenoid degradation in tea was shown to be much less than in isolated carotenoids, which was believed to be due to the presence of antioxidants such as polyphenols and catechins.(20) The rates of degradation of the various carotenoids can be put into the following order: β-carotene > zeaxanthin > lutein. The β-Ionone is a major degradation product of β-carotene while α-Ionone is the degradation product of 3-hydroxy-5, 6-epoxy ionone. 3, 5-Dihydroxy-4, 5-dihydro-6, 7-dihydro-α-Ionone, Linalool, ketones, and other terpenoid aldehydes are all degradation products present in Oolong tea. The compounds produced from carotenoids contribute some of the major aromas of Oolong tea.(18)

     

    Hydrolysis of Primeverosides and Glucosides and Oxidation of Alcohol, Catechins, and Amino Acids.

     

    In the processing of Oolong tea, a series of enzyme-catalyzed and chemically catalyzed hydrolysis reactions are prevalent. The hydrolysis reactions contribute to the development of the good tea flavor related to the strong ‘roasted aroma’ of Oolong tea. The aroma precursors for the hydrolysis reactions are mainly primeverosidase and glucosides with primeverosides present in greater abundance than glucosides in most tea cultivars.(21) β-D-Glucopyranosides and β-primeverosides

    (6-O-β-D-xylopyranosyl-β-D-glucopyranoside) with aglycons have been identified and quantified in fresh tea leaves.(4 , 5 , 6 , 22 , 23) Meanwhile, 26 synthetic glycosides with the aglycons of the main tea aroma compounds, e.g., (Z)-3-hexanol, benzyl alcohol, 2-phenylethanol, methyl salicylate, geraniol, linalool, and four isomers of linalool oxides, were synthesized in the laboratory. These compounds were used as standards for the direct qualitative and quantitative determination of the glycoside aroma precursors in different tea cultivars.(22) The aroma precursors are found in higher amounts in young tea leaf and decrease in concentration as the tea leaf matures.(21) Glycosidase activity also decreases as tea leaf grows, but remains high in the stems.(21) During the manufacturing process, the primeverosides and glucosides are hydrolyzed by primeverosidase and glycosidase respectively. The hydrolysis products contribute to the alcoholic floral aromas of tea.(7) Hydrolysis of primeverosides and glucosides occurs during the rolling stage.(24)

     

    The oxidization of alcohols, catechins, and amino acids are important reactions in the processing of teas.

     

    During Oolong tea processing, alcohols are oxidized into aldehydes and organic acids, while Geraniol is oxidized into citral and 6-octadecenoic acid and phenylethanol is oxidized into phenylacetaldehyde and phenylacetic acid.(9) The catechins can interact with amino acids through the ‘Strecker reaction’ to release aldehyde or oxidize

    Oolong Tea (Camellia sinensis) 5 into polyphenols. At the rolling and drying stage, some amino acids are easily oxidized into

    ketonic and carboxylic acids, then into aldehydes and alcohols.(9)

     

    Transformation of AminoAcids. 

     

    Theaminoacidcontentshavebeenfoundtofirstdecrease because of the transformation of amino acids, and then to increase because of the degradation of proteins during tea processing.(13) During the processing of Oolong tea, the amino acids can be transformed into aromatic compounds by the Maillard reaction.(9) Meanwhile, leucine could be transformed into α-Ketoisocaproate, then into isoamyl alcohol. Furthermore, some soluble sugars can interact with amino acids and form aromatic compounds such as pyrazines and pyrroles by the Maillard reaction. Significant increases in the amounts of nitrogen-containing compounds, especially pyrazines and pyrroles, occur as the thermal treatment increases.(9) Although the total content of the volatile compounds in Oolong tea increased during the thermal treatments, the content of some floral or woody type volatile compounds such as trans-geraniol, cis-jasmone, Linalool, linalool oxide, and β-ionone decreased after thermal treatments.(25)

     

    The Taste of Oolong Tea

     

    Some of the major flavor compounds formed during the processing of Oolong tea includes mainly oxidative products of catechins, amino acids, and sugars. The flavor of Oolong tea infusions depends largely on the combination of these flavor compounds. Six catechins and catechin gallates, i.e., (+)-catechin (C), (−)-gallocatechin (GC), (−)-epicatechin (EC), (−)-epicatechin gallate (ECG), (−)-epigallocatechin (EGC) and (−)-epigallocatechin gal- late (EGCG) have been identified in Oolong tea.(26) The catechins are associated mainly with bitterness and astringency of Oolong tea infusions. The esters of catechins and their combinations are the dominant components that determine the taste of Oolong tea infusions. Upon heating, the catechins undergo epimerization and cis-trans isomerization (Fig. 2). Some of the isomerization reactions occur at the C-2 position of the flavin-3-ol. For example, EGCG, EGC, ECG, and EC can turn into (−)-gallocatechin gallate (GCG), GC, (−)-catechin gallate (CG), and C, respectively.(27) The esters of catechins can also be hydrolyzed into monomeric catechins and Gallic acid when heated (Fig. 3).(13) In addition, catechins can be oxidized into theaflavins (TF), thearubigin (TR), and theabrowning (TB). TR and TB, are the products of oxidization of TF.(11) Catechins and their oxidation products are mainly responsible for the flavor and astringent character of Oolong tea.(10)

     

    The differentiation of green tea, black tea, Oolong tea, white tea, and Pu-erh tea is based on their contents of free amino acids. The best differentiating amino acids are glutamic acid, asparagine, serine, alanine, leucine, and isoleucine.(28) Theanine is one of the most important amino acids, which can affect the flavor of Oolong tea infusions. Theanine can effectively counteract the bitterness and astringency by increasing the sweetness of the tea infusion. In addition, γ -aminobutyric acid is another important flavor compound in Oolong tea infusion. In the processing of Oolong tea, the content of proteins in the leaf decreases because the proteins are hydrolyzed into amino acids which in turn can be degraded into flavor compounds.(9)

     

    Purine alkaloids are secondary metabolites derived from purine nucleotides(29), such as xanthine, caffeine, theobromine, and theophylline (Fig. 4).(30,31) The purines are important stimulating compounds in tea infusion. The contents of purines differ in tea leaves with different maturities. They are high in young tea leaves and low in old leaves.(9)

    In the tea leaf, the soluble carbohydrates consist of monosaccharides, disaccharides, and oligosaccharides. The polysaccharides are starch, cellulose, hemicellulose, and pectin.

     

    The lignified parts and cellular walls are made up of cellulose, hemicellulose, and lignin, which are high in old tea leaves and insoluble in water. Starch accounts for 0.2–2.0% of the fresh leaf on a weight basis. During the processing of Oolong tea, starch is converted into soluble compounds and volatile flavor compounds, while pectin is changed into pectic acid. All these changes contribute to the final taste of Oolong tea infusion.(9)

     

    Besides the above flavor compounds, there are other bitter compounds such as flavone glycosides and anthocyanidins. Because flavone glycosides can be hydrolyzed to release their aglycone during the processing of Oolong tea, the bitterness intensity of tea infusion can be reduced. As anthocyanidins are present in high concentration in Oolong tea infusions, the tea would taste too bitter, but anthocyanidins can be turned into compounds with no bitterness by hydrolyzing their aglycone.(9)

     

    Health Benefits of Oolong Tea

     

    Tea polyphenols and the catechins and volatile flavor compounds have been shown to reduce the incidence of carcinogenesis, growth of bacteria and the replication of various viruses induce apoptosis, and exhibit anti-allergic effects when an infusion of tea was used.(1)

     

    Antioxidant Activity

     

    Tea polyphenols, including catechins, are effective scavengers of reactive oxygen species in vitro. In the human body, modest transient increases in plasma antioxidant capacity have been demonstrated after the consumption of an infusion of Oolong tea.(32) Studies have also shown that the effects of Oolong tea on reducing oxidative stress problems, especially oxidative DNA damage, are promising.(32) Human studies showed that daily intake of Oolong tea results in significantly lower resting and post-exhaustive exercise levels of plasma malondialdehyde, and significantly lower resting levels of superoxide dismutase activity. These results suggest that the decrease in the lipid peroxidation level was due to the consumption of Oolong tea and its scavenging activity against free radicals.(33)

    Additional in-vitro studies have shown that compounds, such as EC, ECG, EGC, EGCG, TF, TF mono gallate-A, TF mono gallate-B, and TF gallate have very strong antioxidant and lipoxygenase inhibiting activities.(34) In rats, EGC 3-O-gallate can inhibit the progression of renal failure by scavenging free radicals.(35) The 3”-Me-EGCG has a higher inhibitory effect on nitric oxide generation and inducible nitric oxide synthase expression when compared with EGCG, while the 4′′-Me-EGCG and 4′, 4′′-diMe-EGCG are less effective.(36) Besides the tea polyphenols, some of the other volatile com- pounds may have antioxidative activity, such as alkyl compounds with double bonds, 3, 7-dimethyl-1,6-octadien-3-ol, heterocyclic compounds, furfural and benzyl alcohol.(37)

     

    Anticancer Effect

    Studies suggest that Oolong tea extracts have a chemopreventive action against hepatocarcinogenesis and prevent the development of cancer.(38) Oolong tea has a greater antimutagenic effect than green tea and black tea.(39) The anticancer mechanisms of Oolong tea extracts could be based on the inhibition of the invasion and proliferation of cancer cells by polyphenolic compounds and their antimutagenic and anti-inflammatory properties that alter the catalytic activities of P450 enzymes and glucuronosyl transferase.

    Oolong tea extract can result in loss of viability, apoptosis, and cell cycle arrest at the G1 phase in cancer cells, but not in normal cells. At a concentration of 0.04%, Oolong tea extract had a strong inhibitory effect on the invasion and proliferation of hepatoma and murine B16 melanoma cells.(40,41)

     

    The induction of apoptosis and cell cycle arrest are important mechanisms in the inhibition of human stomach cancer cells and these cells can be inhibited with Oolong tea extracts containing polyphenol trimers as the main component.(42) Several catechin compounds are also believed to induce apoptosis in human hystiocytic lymphoma U937 cells. Studies have shown that catechins with a pyrogallol- type structure in the B-ring can induce apoptosis of cancer cells but catechins without a pyrogallol-type structure lack the activity.(43) The trihydroxyl structure of the B ring is essential for EGCG to exert the suppressive effects and the hydroxyl groups on both the 4′-position in the B ring and the 4′′-position in the gallate are crucial for the cell surface binding activity of EGCG.(44)

     

    Oolong tea extract, as an anticancer agent, could act as a nucleophile to scavenge electrophilic mutagens and thereby prevent the appearance of cancer. The compounds EGCG, GC, and caffeine were shown to have antimutagenic activity by the Ames test using the bacterium Salmonella typhimurium.(45) The antimutagenic effects of Oolong tea extracts against mutagens such as N-methyl-N’-nitro-N-nitrosoguanidine, folpet, 2-acetylaminofluorene, benzo[a]pyrene, 9-aminoacridine, aflatoxin B-1, N-nitroso- N-methylurea, and captan were different.(45) Oolong tea extracts inhibited the mutagenicity of 2-amino-3-methylimidazo (4,5-f) quinoline, 3-amino-1, 4-dimethyl-5H-pyridol (4,3b) indole, 2-amino-6-methyldipyrido (1,2-a:3′,2′-d) imidazole, benzo [α] pyrene, and aflatoxin B1, with 90% effectiveness when these five mutagens were present at a dosage level of 1 mg per plate.(38,46) Furthermore, the antigenotoxic effect of Oolong tea extract on 1-nitropyrene (1-NP), 2-nitropyrene (2-NF), 3-nitropyrene (3-NF) and 2,4-Dinitrophenol (DNP) is the strongest among the different teas.(47)

     

    Oolong tea extract exhibits a higher anti-inflammatory activity than green tea or black tea extracts. Tissue inflammation can contribute to cancer development by inducing oxidative damage and promoting cell growth. Inflammation has been shown to play a role in the initiation and/or progression of other cancers, including liver, bladder and gas tric cancers.(48)

     

    The active components with anti-inflammatory activity were found to be catechins, and Oolong tea tannins (the oxidative products of catechins in Oolong tea).(49)

     

    Since P450 enzymes and glucuronosyl transferase are the major agents responsible for the metabolism of many carcinogens, the anticarcinogenesis effects of tea consumption may be due to an alteration in the catalytic activities of the P450 enzymes and glucurono- syl transferase.(50) The effects of genotoxic carcinogens such as heterocyclic amines are reduced by Oolong tea extracts. Oolong tea extracts can inhibit the formation of reac- tive oxygen species and radicals and induce cytochromes P450 1A1, 1A2, and 2B1, and glucuronosyl transferase, which can produce glucuronide. The increased formation of glucuronides represents an important mechanism in detoxification.(50)

     

    Antiobesity Effect

     

    Oolong tea is believed to be beneficial in decreasing human body fat. The fat-decreasing mechanisms are related to the inhibition of pancreatic lipase activity by catechins and the synergistic effects (different entities cooperate advantageously for a final outcome) of thi- amin, arginine, caffeine, and citric acid. 

     

    The catechins from Oolong tea, especially EGCG, appear to have antiobesity properties. The mechanism of their action can be related to certain pathways such as through the modulations of energy balance, endocrine systems, food intake, lipid and carbohydrate metabolism, the redox status, and activities of dif- ferent types of cells (i.e., fat, liver, muscle, and β-pancreatic cells).(51) The inhibition of growth and suppression of lipogenesis may be through the down-regulation of gene expres-sion of fatty acid syntheses in the nucleus and stimulation of cell energy expenditure in the mitochondria.(51) The molecular mechanisms of fatty acid synthase gene suppression by tea polyphenols (EGCG and theaflavins) could result in the down-regulation of the EGFR/P13K/Akt/Sp1 signal transduction pathways.(51)

     

    Theanine-3′-O-gallate in Oolong tea can effectively inhibit pancreatic lipase activity. Meanwhile, homobisflavans A and B, which are typical compounds in Oolong tea leaves, also show stronger inhibitory activities against pancreatic lipase than EGCG. (52) Therefore, the theanine-3′-O-gallate can suppress absorption of meal derived fats. The antiobesity effect of a mixture of thiamin, arginine, caffeine, and citric acid is greater than that of a mixture of arginine and caffeine, and much greater than that of arginine or caffeine alone.(53) It was demonstrated that the antiobesity effects of Oolong tea might be due partially to the effects of caffeine on noradrenaline-induced lipolysis in adipose tissue, and the inhibitory action of some other substance in Oolong tea on pancreatic lipase activity.(54)

     

    Prevention of Atherosclerosis, Heart Disease, and Hypertension

     

    The oxidation of LDL cholesterol, which is a risk factor for atherosclerosis and heart disease, may be inhibited by Oolong tea. One study showed that Oolong tea reduced the formation of 8-hydroxydeoxyguanosine, a marker of oxidative DNA damage.(50) Thus, Oolong tea may have beneficial effects on altering the progression of atherosclerosis in patients with coronary artery disease.(55) Furthermore, another study investigating the possible mechanisms responsible for the reduction of atherosclerosis and heart disease by Oolong tea extracts found that the excretion of lipids into feces was significantly higher in subjects that consumed polyphenol-enriched Oolong tea extract.(56) It appears that Oolong tea extracts could reduce the accumulation of lipids that causes atherosclerosis and heart disease.

     

    It was found that Oolong tea is able to lower the levels of triglyceride better than green tea or black tea, after oral feeding to male Sprague-Dawley rats. Therefore, it has been observed that the relative weight ratios of liver to epididymal adipose tissue are lower in Oolong tea fed groups.(57) Studies have also shown that the partially fermented Oolong tea leaves are more effective in the growth suppression of adipose tissue as compared to the nonfermented green tea leaves.(57)

     

    Energy expenditure is significantly higher after the consumption of Oolong tea than green tea (P < 0.05). In comparison with green tea, Oolong tea contains approximately half the caffeine and EGCG, while polymerized polyphenols of Oolong tea are double of that of green tea. The polymerized polyphenols in Oolong tea can increase energy expenditure.(58) Therefore, more energy expenditure means less accumulation of lipid, which can there- fore lessen the incidence of atherosclerosis and heart disease. Since atherosclerosis can cause hypertension, the prevention of atherosclerosis can also reduce the risk of developing hypertension. Studies have shown that habitual and moderate Oolong tea consumption, 120 ml/d or more for a 1 year period, significantly reduced the risk of developing hypertension in the Chinese population.(59)

     

    Anti diabetes Effect

     

    The polyphenols EC, ECG, and EGCG can inhibit the Na+/glucose cotransporter response, and result in lower glucose concentration.(60) Studies have shown that dietary Oolong tea extract can reduce plasma glucose and have a complicated impact on antioxidant systems in diabetic rats.(61) Several known compounds present in Oolong tea such as EGCG, ECG, tannins, and TF, can enhance the activity of insulin and benefit people with diabetes.(62)

     

    Anti allergic Effect

     

    Oolong tea contains 0.34% (dry weight) EGC-3-O-(3-O-methyl) gallate (EGCG3′′Me) and 0.20% EGC-3-O-(4-O-methyl) gallate (EGCG4′′Me), but neither of the catechin derivatives is produced during the fermentation process.(63) Studies show that EGCG3′′Me and EGCG4′′Me have strong antiallergenic effects. The mechanism of the antiallergic effects of these compounds are based on the strong inhibition of EGCG3′′Me and EGCG4′′Me to mast cell activation through the prevention of tyrosine phosphorylation of cellular pro- tein and histamine/leukotrienes release, and interleukin-2 secretion after Fc epsilon RI cross-linking.(63,64,65) On the other hand, EGCG′′3Me treatment inhibits the Fc epsilon RI cross-linking. The high-affinity IgE receptor, Fc epsilon RI, is found at high levels on basophils and mast cells and plays a key role in a series of acute and chronic human allergic reactions. Studies suggest that EGCG′′3Me could negatively regulate basophil activation through the suppression of Fc epsilon RI expression.(66) Four major tea catechins also show significant inhibitory effects on allergic properties.(67,68)

     

    Antiseptic Effects

     

    The Oolong tea extracts can inhibit a wide range of pathogenic bacteria, including methicillin–resistant Staphylococcus aureus and Yersinia enterocolitica.(69) The Oolong tea extracts show an antibacterial activity against all of the oral streptococci examined, with the highest activity against S. mutans MT8148R. The antibacterial activity of Oolong tea extracts was stronger with the monomeric polyphenol-rich fraction of Oolong tea extract rather than the pure polyphenols. It was shown that some combinations of monomeric polyphenols had higher levels of antibacterial activity, which might be caused by a synergistic effect of the monomeric polyphenols, which can easily bind to the proteins of pathogens to inhibit their activity.(70)

    Glucosyltransferase is an important enzyme involved in dental caries pathogenesis. A dimeric catechin molecule in Oolong tea was identified as dehydrodicatechin A, which markedly inhibits glucosyltransferase from Streptococcus sobrinus 6715. As the degree of polymerization of catechin increases, glucosyltransferase is inhibited more effectively.(71) Studies also showed that the Oolong tea extract could reduce the rate of acid production by mutan streptococci and at the same time reduce their growth rate.(72) As well, Oolong tea products can decrease the cellular surface hydrophobicity of almost all the oral streptococci examined, which will inhibit bacterial adherence to the tooth surfaces.(72)

    Besides the inhibition of oral streptococcus, the Oolong tea extracts can inhibit the activity of Bacillus subtilis, Escherichia coli, Proteus vulgaris, Pseudomonas fluorescens, Salmonella sp. and Staphylococcus aureus.(72) The mechanism of their action are based on the direct inactivation of the bacteria and viruses, by inhibiting their replication enzymes, induction of apoptosis, stimulation of monocytes/macrophages to produce cytokines, and the stimulation of myeloperoxidase dependent iodination of neutrophils.(73)

     

    Conclusions and Future Directions

     

    Oolong tea is a partially fermented tea, major types of which can be found in different areas of China. The quality of Oolong tea is attributed to the aroma, flavor, color, and appearance, in which aroma and flavor are the two most important factors. The formation of aroma in Oolong tea depends largely on their transformation of higher fatty acids, decomposition of carotenoids, hydrolysis of primeverosides and glucosides, oxidation of alcohol, catechins and amino acids, the transformation of amino acids and etc. The flavor of Oolong tea infusions depends largely on the combination of the flavor compounds, which are formed during the processing of Oolong tea, including mainly the oxidative products of catechins, amino acids, and sugars. Oolong tea exhibits antioxidant, anticancer, antiobesity, prevention of atherosclerosis and heart disease, antidiabetes, and antiallergic effects, etc.

     

    The production of Oolong teas has increased greatly in the recent years and is becoming more and more popular around the world. However, the quantity of research on Oolong tea is lacking when compared to that on green and black teas. This is particularly apparent when examining the quality of Oolong tea in relation to environmental factors and manufacturing procedures. The quality of Oolong tea is affected by many factors, including both controllable and non-controllable factors.(74)

     

    Optimization of the controllable factors is one way to increase production of high-quality Oolong tea. The characteristics of cultivars, agronomic practices, and tea processing technologies need to be integrated and studied in more detail to produce higher-quality cultivars to meet the needs of the mar- ket place, to develop new agronomic methods to increase the quality of the fresh Oolong tea leaves, and to improve Oolong tea processing technology. The application of Oolong tea for health purposes is under way, and a number of products have been produced such as tea powders and tea jams. Extraction technologies have advanced with the extraction of polyphones, caffeine, saponin, and polysaccharose from low quality Oolong tea. These activities will bring tea processing and applications into the public eye.(75) In the future, more and more applications for Oolong tea will emerge to satisfy new and different needs around the world.

     

    References

    1. Gong, Z. Chinese Oolong tea (in Chinese); Photography Press of Zhejiang Province: Hangzhou, 2004; 189.

    2. NationalBureauofStatisticsofChina.Chinaruralstatisticalyearbook(2008);Chinastatistical press: Beijing, China, 2008; 419.

    3. Chen,Z.M.ChineseTeaClassic(inChinese);CulturalPressofShanghai:Shanghai,1992;785.

    4. Guo, W.F.; Sakata, K.; Watanabe, N.; Nakajima, R.; Yagi, A.; Ina, K.; Luo, S.J. Geranyl 6-o-β-D-xylopyranosyl-β-D-glucopyranoside isolated as an aroma precursor from tea leaves

      for Oolong tea. Phytochemistry 1993, 33, 1373–1375.

    5. Guo, W.; Hosoi, R.; Sakata, K.; Watanabe, N.; Yagi, A.; Ina, k.; Luo, S. (S) -linalyl,

      2-phenylethyl, and benzyl disaccharide glycosides isolated as aroma precursors from Oolong

      tealeaves. Biosci. Biotechnol. Biochem. 1994, 58, 1532–1534.

    6. Moon, J.H.; Watanabe, N.; Sakata, K.; Yagi, A.; Ina, K.; Luo, S. Trans-and cis-linalool

      3, 6-oxides 6-O-β-D-xylopyranosyl-β-D-glucopyranoside isolated as aroma precursors from

      leaves for Oolong tea. Biosci. Biotechnol. Biochem. 1994, 58, 17422–1744.

    7. Ogawa, K.; Yasuyuki, I.; Guo, W.; Watanabe, N.; Usui, T.; Dong, S.; Tong, Q.; Sakata, K. Purification of a β-primeverosidase concerned with alcoholic aroma formation in tea leaves (cv.Shuixian) to be processed to oolong tea. J. Agr. Food Chem. 1997, 45,

      877–882.

    8. Takeo, T. Production of linalol and geraniol by hydrolytic breakdown of bound forms in disrupted tea shoots. Phytochem. 1981, 20, 2145–2147.

    9. Wang,Z.N.TeaBiochemistry(inChinese);AgriculturePress:Beijing,1982.

    10. Hilton,P.J.;Ellis,R.T.EstimationofmarketvalueofCentralAfricanteabytheaflavinanalysis.

      J. Sci. Food Agr. 1972, 23, 227–232.

    11. Roberts, E.A.H. Economic importance of flavonoid substances: tea fermentation. In The

      Chemistry of Flavonoid Compounds; Geissman, T.A.; Eds.; Pergamon Press: Oxford, 1962;

      468–512.

    12. Chen, L.S.L.; Ou, A.S.M. Comparison of volatile components in Pouchung tea with different

      varieties and extraction methods. J. Chin. Agr. Chem. Soc. 1998, 36, 451–463.

    13. Chen, Y.S.; Tasy, H.R.; Yu, T.H. Studies on the formation of special aroma compounds of Pouchung tea made from different varieties. In Food Flavors: Formation, Analysis, and Packaging Influences (Book Series: Developments in Food Science); Contis, E.T.; Ho, C.T.; Mussinan, C.J.; Parliament, T.H.; Shahidi, F.; Spanier, A.M.; Eds.; Elsevier Science Publ. B V:

      Amsterdam, 1998, 40, 431–442.

    14. Ravichandran, R.; Parthiban, R. Lipid occurrence, distribution and degradation to flavour

      volatiles during tea processing. Food Chem. 2000, 68, 7–13.

    15. Galliard, T. Degradation of plant lipids by hydrolytic and oxidative enzymes. In Recent

      advances in the chemistry and biochemistry of plant lipids; Galliard, T.; Mercer, E.I.; Eds.;

      Academic Press: London, 1975; 398

    16. Takeo, T.; Tsushida, T. Changes in lipoxygenase activity in relation to lipid degradation in

      plucked tea shoots. Phytochem. 1980, 19, 2521–2522.

    17. Sekiya, J.; Numa, S.; Kajiwara, T.; Hatanaka, A. Biosynthesis of leaf alcohol. J. Agric. Biol.

      Chem. 1976, 40, 185–190.

    18. Robinson, J. M.; Owuor, P. O. Tea aroma. In Tea cultivation to consumption; Willson, K.C.;

      Clifford, M.N.; Eds.; Chapman and Hall: London, 1992; 602–647.

    19. Sanderson, G.W.; Graham, H.N. On the formation of black tea aroma. J. Agric. Food Chem.

      1973, 21, 576–585.

    20. Howard,G.E.Thevolatileconstituentsoftea.FoodChem.1978,4,97–106.

    21. Ogawa, K.; Moon, J.H.; Guo, W.F.; Yagi, A.; Watanabe, N.; Sakata, K. A study on tea aroma

      formation mechanism-alcoholic aroma precursor amounts and glycosidase activity in parts of

      the tea plant. Z. Naturforsch., C: Biosci. 1995, 50, 493–498.

    22. Wang,D.M.;Yoshimura,T.;Kubota,K.;Kobayashi,A.Analysisofglycosidicallyboundaroma

      precursors in tea leaves. 1. Qualitative and quantitative analyses of glycosides with aglycons as

      aroma compounds. J. Agric. Food Chem. 2000, 48, 5411–5418.

    23. Moon, J.H.; Watanabe, N.; Ijima, Y.; Yagi, A.; Ina, K.; Sakata, K. Cis- and trans- linalool

      3, 7-oxides and methyl salicylate glycosides and (Z)-3-hexenyl β-D-glucopyranoside as aroma

      precursors from tea leaves for Oolong tea. Biosci. Biotechnol. Biochem. 1996, 60, 1815–1819.

    24. Wang, D.M.; Kurasawa, E.; Yamaguchi, Y.; Kubota, K.; Kobayashi, A. Analysis of glycosidi- cally bound aroma precursors in tea leaves. 2. Changes in glycoside contents and glycosidase activities in tea leaves during the black tea manufacturing process. J. Agr. Food Chem. 2001,

      49, 1900–1903.

    25. Yu,T.H.;Yang,M.S.;Lin,L.Y.;Chang,C.Y.Effectofthermaltreatmentontheflavorformation

      of Oolong tea. Food Sci. Agr. Chem. 1999, 1, 140–147.

    26. Lin, J.K.; Lin, C.L.; Liang, Y.C.; Lin-Shiau, S.Y.; Juan, I.M. Survey of catechins, gallic acid

      and methylxanthines in green, oolong, pu-erh, and black teas. J. Agric. Food Chem. 1998, 46,

      3635–3642.

    27. Seto, R.; Nakamura, H.; Nanjo, F.; Hara, Y. Preparation of epimers of tea catechins by heat

      treatment. Biosci. Biotechnol. Biochem. 1997, 61, 1434–1439.

    28. Alcazar, A.; Ballesteros, O.; Jurado, J.M.; Pablos, F.; Martin, M.J.; Vilches, J.L.; Navalon, A.

      Differentiation of green, white, black, oolong, and Pu-erh teas according to their free amino

      acids content. J. Agric. Food Chem. 2007, 55, 5960–5965.

    29. Zulak, K.G.; Cornish, A.; Daskalchuk, T.E.; Deyholos, M.K.; Goodenowe, D.B.;

    30. Kato,M.;Mizuno,K.;Fujimura,T.;Iwama,M.;Irie,M.;Crozier,A.;Ashihara,H.Purification

      and characterization of caffeine synthase from tea leaves. Plant Phys. 1999, 120, 586–597.

    31. Kato, M.; Mizuno, K.; Crozier, A.; Fujimura, T.; Ashihara, H. A gene encoding caffeine

      synthase from tea leaves. Nature 2000, 406, 956–957.

    32. Higdon, J.V.; Frei, B. Tea catechins and polyphenols: Health effects, metabolism, and antioxi-

      dant functions. Crit. Rev. Food Sci. Nutr. 2003, 43, 89–143.

    33. Tsai, P.H.; Kan, N.B.; Ho, S.C.; Liu, C.C.; Lin, C.C. Effects of Oolong tea supplementation

      on lipid peroxidation of athletes at rest and post-exhaustive exercise. J. Food Sci. 2005, 70,

      S581–S585.

    34. Xie, B.J.; Shi, H.; Chen, Q.Y.; Ho, C.T. Antioxidant properties of fractions and polyphenol

      constituents from green, oolong, and black teas. Proc. Natl. Sci. Counc. Repub. China [B] 1993,

      17, 77–84.

    35. Yokozawa, T.; Dong, E.; Nakagawa, T.; Kashiwagi, H.; Nakagawa, H.; Takeuchi, S.; Chung,

      H.Y. In vitro and in vivo studies on the radical-scavenging activity of tea. J. Agric. Food Chem.

      1998, 46, 2143–2150.

    36. Chiu, F.L; Lin J.K. HPLC analysis of naturally occurring methylated catechins, 3′′- and

      4′′-methyl-epigallocatechin gallate, in various fresh tea leaves and commercial teas and their potent inhibitory effects on inducible nitric oxide synthase in macrophages. J. Agric. Food Chem. 2005, 53, 7035–7042.

    37. Yanagimoto,K.;Ochi,H.;Lee,K.G.;Shibamoto,T.Antioxidativeactivitiesofvolatileextracts from green tea, Oolong tea, and black tea. J. Agric. Food Chem. 2003, 51, 7396–7400.

    38. Matsumoto, N.; Kohri, T.; Okushio, K.; Hara, Y. Inhibitory effects of tea catechins, black tea extract and Oolong tea extract on hepatocarcinogenesis in rat. Jpn. J. Canc. .Res. 1996, 87, 1034–1038.

    39. Yen, G.C.; Chen, H.Y. Comparison of antimutagenic effect of various tea extracts (green, oolong, Pouchong, and black tea). J. Food Prot. 1994, 57 (1), 54–58.

    40. Zhang, G.Y.; Miura, Y.; Yagasaki, K. Effects of green, oolong and black teas and related com- ponents on proliferation and invasion of hepatoma cells. In Animal Cell Technology: Basic & Applied Aspects; Kitagawa, Y.; Matsuda, T.; Iijima, S.; Eds.; Kluwer Academic Publishers: Dordrecht, Netherlands, 1999; 10, 135–139.

    41. Zhang,G.Y.;Miura,Y.;Yagasaki,K.Inductionofapoptosisandcellcyclearrestincancercells by in vivo metabolites of teas. Nutri. Cancer 2000, 38, 265–273.

    42. Hibasami, H.; Jin, Z.X.; Hasegawa, M.; Urakawa, K.; Nakagawa, M.; Ishii, Y.; Yoshioka, K. Oolong tea polyphenol extract induces apoptosis in human stomach cancer cells. Anticancer Res. 2000, 20, 4403–4406.

    43. Saeki, K.; Hayakawa, S.; Isemura, M.; Miyase, T. Importance of a pyrogallol-type structure in catechin compounds for apoptosis-inducing activity. Phytochem. 2000, 53 (3), 391–394.

    44. Yano, Satomi.; Fujimura, Y.; Umeda, D.; Miyase, T.; Yamada, K.; Tachibana, H. Relationship between the biological activities of methylated derivatives of (−)-epigallocatechin-3-O-gallate (EGCG) and their cell surface binding activities. J. Agric. Food Chem. 2007, 55, 7144–7148.

    45. Hour, T.C.; Liang, Y.C.; Chu, I.S.; Lin, J.K. Inhibition of eleven mutagens by various tea extracts, (−)-epigallocatechin-3-gallate, gallic acid and caffeine. Food Chem. Toxicol. 1999, 37, 569–579.

    46. Yen, G.C.; Chen, H.Y. Relationship between antimutagenic activity and major components of various teas. Mutagenesis 1996, 11, 37–41.

    47. Ohe, T.; Marutani, K.; Nakase, S. Catechins are not major components responsible for anti- genotoxic effects of tea extracts against nitroarenes. Mutat. Res. Genet. Toxicol. Environ. Mutagen. 2001, 496, 75–81.

    48. Coussens,L.M.;Werb,Z.Inflammationandcancer.Nature2002,420,860–867.

    49. Nakazato, K.; Takeo, T. Anti-inflammatory effect of Oolong teapolyphenols. Nippon nogeika-

      gaku kaishi 1998, 72, 51–54.

    50. Weisburger, J.H.; Chung, F.L. Mechanisms of chronic disease causation by nutritional factors and tobacco products and their prevention by tea polyphenols. Food Chem. Toxicol. 2002, 40, 1145–1154.

    51. Lin, J.K.; Lin-Shiau, S.Y. Mechanisms of hypolipidemic and anti-obesity effects of tea and tea polyphenols. Mol. Nutr. Food Res. 2006, 50, 211–217.

    52. Nakai, M.; Fukui, Y.; Asami, S.; Toyoda-Ono, Y.; Iwashita, T.; Shibata, H.; Mitsunaga, T.; Hashimoto, F.; Kiso, Y. Inhibitory effects of Oolong tea polyphenols on pancreatic lipase in vitro. J. Agric. Food Chem. 2005, 53, 4593–4598.

    53. Muroyama, K.; Murosaki, S.; Yamamoto, Y.; Odaka, H.; Chung, H. C.; Moon, J. H.; Watanabe, N.; Sakata, K.; Yagi, A.; Ina, K.; Luo, S.J. Studies on the aroma formation mecha- nism of Oolong tea. 3. Trans-linalool and cis-linalool 3, 6-oxide 6-o-β-D-xylopyranosyl-β-D- glucopyranosides isolated as aroma precursors from leaves for Oolong tea. Biosci. Biotechnol. Biochem. 1994, 58, 1742–1744.

    54. Han, L.K.; Takaku, T.; Li, J.; Kimura, Y.; Okuda, H. Anti-obesity action of Oolong tea. Int. J. Obes. 1999, 23, 98–105.

    55. Shimada, K.; Kawarabayashi, T.; Tanaka, A.; Fukuda, D.; Nakamura, Y.; Yoshiyama, M.; Takeuchi, K.; Sawaki, T.; Hosoda, K.; Yoshikawa, J. Oolong tea increases plasma adiponectin levels and low-density lipoprotein particle size in patients with coronary artery disease. Diabetes Res. Clin. Pract. 2004, 65, 227–234.

    56. Hsu,T-F;Kusumoto,A.;Abe,K.;Hosoda,K.;Kiso,Y.;Wang,M.F.;Yamamoto,S.Polyphenol- enriched Oolong tea increases fecal lipid excretion. Eur. J. Clin. Nutr. 2006, 60, 1330–1336.

    57. Kuo,K.L.;Weng,M.S.;Chiang,C.T.;Tsai,Y.J.;Lin-Shiau,S.Y.;Lin,J.K.Comparativestudies on the hypolipidemic and growth suppressive effects of oolong, black, pu-erh, and green tea leaves in rats. J. Agric. Food Chem. 2005, 53, 480–489.

    58. Komatsu, T.; Nakamori, M.; Komatsu, K.; Hosoda, K.; Okamura, M.; Toyama, K.; Ishikura, Y.; Sakai, T.; Kunii, D.; Yamamoto, S. Oolong tea increases energy metabolism in Japanese females. J. Med. Investig. 2003, 50, 170–175.

    59. Yang, Y.C.; Lu, F.H.; Wu, J.S.; Wu, C.H.; Chang, C.J. The protective effect of habitual tea consumption on hypertension. Arch. Int. Med. 2004, 164, 1534–1540.

    60. Hossain, S.J.; Kato, H.; Aoshima, H.; Yokoyama, T.; Yamada, M.; Hara, Y. Polyphenol- induced inhibition of the response of Na+/glucose cotransporter expressed in Xenopus oocytes. J. Agric. Food Chem. 2002, 50, 5215–5219.

    61. Seo,J.S.;Zhejiu,Q.;Jeong,Y.M.EffectofdietaryOolongteaextractsontheconcentrationsof plasma glucose, antioxidant vitamins and minerals in diabetic rats. Faseb J. 2004, 18, 519.

    62. Anderson,R.A.;PolanskyM.M.Teaenhancesinsulinactivity.J.Agric.FoodChem.2002,50,

      7182–7186.

    63. Sano, M.; Suzuki, M.; Miyase, T.; Yoshino, K.; Maeda-Yamamoto, M. Novel antiallergic

      catechin derivatives isolated from Oolong tea. J. Agric. Food Chem. 1999, 47, 1906–1910.

    64. Maeda-Yamamoto, M.; Kawamoto, K.; Matsuda, N.; Sano, M.; Suzuki, N.; Yoshimura, M.; Tachibana, H.; Kawakami, Y.; Kawakami, T.; Hakamata, K. Anti-allergic catechins of tea (Camellia sienesis). In Animal Cell Technology: Basic & Applied Aspects; Shirahata, S.; Teruya, K.; Katakura, Y.; Eds.; Kluwer Academic Publishers: Dordrecht, Netherlands, 2002;

      12, 415–419.

    65. Shiozaki,T.;Sugiyama,K.;Nakazato,K.;Takeo,T.Effectofteaextracts,catechinandcaffeine

      against type-I allergic reaction. Yakugaku Zasshi 1997, 117, 448–454.

    66. Fujimura, Y.; Tachibana, H.; Maeda, Y.M.; Miyase, T.; Sano, M.; Yamada, K. Antiallergic tea catechin, (−)-epigallocatechin-3-O-(3-O-methyl)-gallate, suppresses Fc epsilon RI expression

      in human basophilic KU812 cells. J. Agric. Food Chem. 2002, 50, 5729–5734.

    67. Suzuki, M.; Yoshino, K.; Maeda-Yamamoto, M.; Miyase, T.; Sano, M. Inhibitory effects of tea catechins and O-methylated derivatives of (−)-epigallocatechin-3-O-gallate on mouse type IV

      allergy. J. Agric. Food Chem. 2000, 48, 5649–5653.

    68. Sano, M.; Suzuki, M.; Miyase, T.; Yoshino, K.; Maeda-Yamamoto, M. Novel antiallergic

      catechin derivatives isolated from Oolong tea. J. Agric. Food Chem. 1999, 47, 1906–1910

    69. Yam,T.S.;Shah,S.;HamiltonMiller,J.M.T.Microbiologicalactivityofwholeandfractionated crude extracts of tea (Camellia sinensis), and of tea components. FEMS Microbiol. Lett. 1997, 152, 169–174.

    70. Matsumoto, M.; Tanaka, T.; Maeda, M.; Nakai, M.; Hamada, S.; Ooshima, T. Antibacterial activity of polyphenol components in Oolong teaextract against Streptococcus mutans. Caries Res. 2004, 38, 2–8.

    71. Hamada,S.;Kontani,M.;Hosono,H.;Ono,H.;Tanaka,T.;Ooshima,T.;Mitsunaga,T.;Abe,I. Peroxidase-catalyzed generation of catechin oligomers that inhibit glucosyltransferase from Streptococcus sobrinus. FEMS Microbiol. Lett. 1996, 143, 35–40.

    72. Chou, C.C.; Lin, L.L.; Chung, K.T. Antimicrobial activity of tea as affected by the degree of fermentation and manufacturing season. Int. J. Food Microbiol. 1999, 48, 125–130.

    73. Sakagami, H.; Oi, T.; Satoh, K. Prevention of oral diseases by polyphenols (review). IN VIVO 1999, 13, 155–171.

    74. Odhiambo, H.O.; Owuor, P.O.; Othieno, C.O. Factors affecting tea quality: field variables – a review. Tea 1988, 9, 36–40.

    75. Gong, S.Y. Processing and multiple application of tea in China. In Tea Culture, Tea Food Industry and Tea Tree Breeding in Korea, China and Japan; Park, Y.G.; Shin, D.I.; Eds.; Kyungpook Natl. Univ. Korean Tea Soc: Taegu, South Korea, 2000; 79–95.

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  • Morphology, Manufacturing, Types, Composition and Medicinal Properties of Tea (Camellia sinensis)

    Yumen Hilal*

    Department of Analytical and Food Chemistry, Faculty of Pharmacy, University of Damascus, Syria

    *Corresponding author: Yumen Hilal, Department of Analytical and Food Chemistry, Faculty of Pharmacy, University of Damascus, Syria, Tel: 963-993-296-876; E-mail: yumenhilal@gmail.com.

    Citation: Hilal Y (2017) Morphology, Manufacturing, Types, Composition and Medicinal Properties of Tea (Camellia sinensis). J Bas Appl Pl Sci 1(2): 107.

    Published Date: June 30, 2017.

    Abstract

     

    Fascinating aroma, attractive taste, and many health effects of tea, make it a popular beverage worldwide. All Tea types belong to the same family of the camellias. Applying various manufacturing processes on fresh leaves of Camellia sinensis produces white, green, black, yellow or oolong tea, which their brewers differ in color and taste.

     

    Polyphenols, caffeine and theanine are the main bioactive ingredients in Camellia sinensis. Polyphenols in tea consist mainly of catechins, flavonol-O-glycosides, flavonol-C-glycosides, proanthocyanidins. In addition, black tea contains theaflavins and thearubigins which arising from the catechins during the fermentation.

     

    Many of the health benefits of tea may depend on the biological activities of the considerable concentrations of antioxidants in particular the polyphenols in tea, make its brewer a good candidate to stop the development of some serious diseases such as diabetes, obesity, cavity and cardiovascular diseases. Tea also enhances the immune system and inhibits several kinds of cancers, such as stomach, colon, pancreatic, liver, bladder, lung, and breast cancers. On the other hand, toxic contamination by heavy metals and flavonoids can happen depending on the dose intake of tea.

     

    Keywords: Tea; Types; Production; Polyphenols; Health benefits

     

    Introduction

     

    A Japanese cultural philosopher, Kakuzo Okakura (1862- 1913), styled tea (Camellia sinensis) as a medicine than as a drink. Tea has been considered as a necessary daily element for life and as a ritual element in ancient China and Japan, respectively. The good flavor, attractive aroma and taste, besides its health-promoting effects and being the main caffeine-drink worldwide makes it one of the most common beverages in the world. In ancient China, the effective pharmaceutical activity of tea was known and thus its brewer was used as a medicinal drink.

     

    Historically, tea has important roles not only as ancient health therapy but also as a subject of the visual and literary arts. Tea was painted, drawn and figured on textiles and ceramics. Its shape, color, perfection and social interactions were described in many Odes [1,2].

     

    Tea Plant: Origin, Morphological Characters, Grow and Plucking

     

    Tea, as a plant, belongs to the family of the camellias and it has two main kinds:

    Camellia sinensis belongs to China, Tibet and Japan. It is not a big tree but rather a bush. It is small with 1–2 m tall (Figure 1). It has many stems. Leaves are leathery with matt surfaces. Because leaves are thick and hard, it is difficult to recognize the veins in the lamina. The blade of the leaf is elliptic and it has an obtuse end. The base is straight. The edge has teeth. When the leaves are young, they are smooth with some fine hairs on the bottom, but when they grow older the hairs lessen and even disappear.

     

    The 2 inch leaves are resistant to very cold temperatures and garnet-brown through ox-blood to purple in color [1–4].

     

    Camellia assamica(Masters) or the Assam tea plant belongs to North East India. It is considered small although it is between ten to fifteen meters tall (Figure 2). The trunk of this tree equals the third of its height. It has a strong branch system. Warm weather conditions suit it well. Leaves are dependent, thin, and shiny. They are pointed in shape. We can distinguish marginal veins easily. The leaf blade is usually oval. It is between 8–20 cm long and 3.5–7.5 cm wide. The leaves are either hairless or hairy on the vein below [1–4].

     

    Combining the two species, we have new plants that may be developed to live in different conditions. Like the Camellia assamica sub sp. Lasiocalys (Planch. MS) and the Cambodiensis or southern form of tea which is a small tree that has upright branches and it is between 6–10 m tall (Figure 3).

    This tree needs a great amount of water so the region between the cancer and Capricorn tropics is quite suitable for it. The amount of rain there is between 1000 to 1250 mm a year and the heat is between 10 to 30 degrees which is suitable for this tree. It lives in pieces of land that are 2400 meters high from the sea. Tea bushes must be trimmed every four to five years. This will help them stay healthy and low enough for the people who pick the tea which is known as “Plucking Table ". Any tea bush continues to give good tea for 50 to 70 years, but the amount of tea becomes less after fifty years. Meanwhile, the old bushes are replaced by new trees that are grown on the estate nursery.

     

    Time of picking tea leaves relies on the weather conditions. New leaves can be picked up during spring but seven or twelve days interval should be left between the times of picking. Tea gathering is a hard work. To collect a kilo of unprocessed tea you need two or three thousand tea leaves. People who pick the tea should be skilled and able to choose the right time to gather the new grown leaves. The more tender the leaves the better is the tea. Following picking, the gathered tea is taken to factories where it is processed [1–4].

     

    Classification, Processing, Styles, and Packaging of Tea

     

    Classification of Tea

     

    Tea has always been classified by many ways: by the color of the finished leaves, by the color of the tea liquor, and by the percentage of oxidation during processing. The aim of tea categorization is to gather different sorts of tea with the same qualities. Despite the classification methods used, there is no method could be used to categorize all tea types. However, the similarity in processing method is the easiest way to achieve this.

    Different systems of tea classification are noticed in China and Japan. The six tea Chinese types represent categories that gather tea styles of the same processing methods and finally similar products. Needless to say that Chinese created all the types of tea we drink today. Also, the Chinese are the first people who put the tea classification systems. Most Chinese tea experts recognize these six types of tea: green tea, yellow tea, white tea, oolong tea, black tea, and dark tea. Any of those tea types can be flavored, scented, blended, ground, roasted, aged, or decaffeinated.

    On the other hand Japanese system classifies tea considering the method of processing into three groups: Non-fermented tea, Semi-fermented tea and Fermented tea. The most important aspect in Japanese system is the way of activating of oxidizing enzymes (e.g. polyphenol oxidize of peroxidase) contained in leaves. This fermentation process activates the oxidizing enzymes and thus changes the green tealeaves into brown [3–8].

     

    Other feasible aspect to classify tee types is to use the ratio between total phenolics and sum of the major catechins [9] or to employ the amino acid pattern as a possible criterion [10]. These approaches need standardized extraction procedures and analytical methods to gain an overview on the composition of teas from different origins and it is necessary to ensure the authenticity of the origin [11].

     

     

    Tea Production Process

     

    Different types of tea are produced from fresh tea leaves (Camellia sinensis). The common term for the conversion of tea phenolics is fermentation which is related to the manufacturing of black and Oolong tea. To achieve this conversion, endogenous enzymes are required, especially the polyphenol oxidase. Recently, aeration has been used instead of fermentation because some tea-drinking Muslim countries think that fermentation means that the tea contains ethanol [9].

    Green tea manufacture: Oxidation process is not used when making green tea which helps retain the green color and the delicate flavor. Before rolling green tea, the enzymes are deactivated. Chart in figure 4 explains that there are two different types of processing. In Japanese method the fresh tea leaves are steamed with high temperature (100°C) in order to inactivate the oxidizing enzymes of leaves, rolled and dried to get the ideal Japanese green tea. On the other hand the Chinese method uses panning with higher temperature (300-350°C) instead of steaming to prevent the fermentation. The inactivated enzymes do not decompose chlorophyll so the color stays green.

     

    To make sure that no oxidation happens, the tea leaves are either pan fried (Chinese method) or steamed (Japanese method) which prevents the interaction of the enzymes then it is rolled. Withering process is used for some green tea in China; it is omitted in manufacturing, followed by rolling, drying and sorting processes [2,5,8,12].

     

    Black and Oolong tea manufacture:

     

    Withering black and oolong tea reduces the moisture in the leaves up to 70% (depending on region) and then air is used to remove it in an unvaried way. Twelve to seventeen hours are needed to accomplish this and at the end of this process the leaf is thin and pliable that it can be rolled easily. The rolling process includes putting the tea leaves into a rolling machine which revolves horizontally on the rolling table and gives the tea leaves their stiff looking. After the rolling process starts the oxidation with the leaves breaks open. Oxidation gives the tea its flavor and color. The color of the leaves changes from green, into light brown and then into deep brown. When a rolling process is finished, tea is either put into specific large boxes or displayed on tables so that the enzymes that are inside the tea leaves start to oxidize because they are exposed to the air. To obtain the full fermented Black tea, the tea leaves are treated mechanically in order to enlarge the enzyme conversion of flavanols. Oxidizing process needs between half an hour to 2 hours. To stop the oxidizing process the tea is dried and the total moisture content is down reduced. Otherwise, to get the semi-fermented Oolong tea the oxidation process is stopped early before the fermentation is completed. The leaves are parched, rolled and then dried [2,5,8,12].

     

    White tea manufacture:

     

    This tea is different from other kinds of tea in that it is neither fermented nor the oxidizing enzymes are deactivated. Just the soft white hairy buds with or without the first tea leaves are picked and dried by a very little process and almost stays untouched. Usually, the liquor of white tea is yellow and mild. There is no clear definition for white tea but rather a hint to its geographic origin (found only in Fujian province), the botanical variety (Camellia sinensis var. khenghebaihao and Camellia sinensis var. fudinbaihao), the manufacture (a minimal processing, just drying, no “fermentation”) or the appearance of hairy buds of white tea (figure 5) which differs from green tea buds (Figure 6). Also there is no possibility to differentiate between white and green tea by the ratio between sum of the major catechins and total phenolics [2,5,8,12].

     

    Figure 5: Hairy white tea buds from China.

     

    Yellow and dark Tea manufacture: 

     

    Yellow and dark teas are sort of post-fermented tea which is exposed to the open air for several months and several years, respectively. When these two kinds of tea are exposed to micro flora, humidity and oxygen in the air, they undergo auto-oxidation, fermentation and some reactivated oxidative enzymes in the tea. This kind of fermentation affects the smell and taste of the tea. The taste is no more bitter but mild and gives pleasant mouth feel. This class of tea is known as ‘dark tea’, especially in Chinese culture and the East Asian cultures that are influenced by it, because of the dark brown liquors that this class of tea gives. However, what is called black tea in Western culture is referred to as red tea in East Asian culture. It is necessary to mention that Pu-erh tea is the most famous kind of post-fermented tea. Previous to post-fermentation process the fresh tea leaves should be panned, rolled and dried [2,8,12]. We cannot separate processing and grading since they complete each other, and they are basic for the manufacturing of tea. To be packaged and sold, tea should be first submitted to the skill of blenders [13].

     

    Tea Styles

     

    Every type of tea has certain styles. In order to classify these styles we need to know the processing steps that each one is exposed to, the used plant cultivar, soil, climate, altitude and latitude together with the intention of the tea maker. So many factors give tea its special characteristics like, weather, altitude, moisture and soil. Season and time of picking through the day may have an effect on the characteristics of tea. For a tea style to be considered authentic, it must be made after specific processing steps, a specific cultivar and terroir. Following is the list of the things that make up a tea style in order of importance.

    Variation in Processing: Different ways of processing have an effect on the kind of tea. Among these ways is steaming that is used instead of pan firing which is meant to prevent the enzymes oxidation, percentage of oxidation or different methods of shaping. So the definition of a tea style depends on the differences in the tea processing methods. The shape or colors of the finished leaves, the color or taste of the liquor give teas their names and styles.

     

    Cultivar: Any cultivar of Camellia sinensis may give a tea style or tea type but this outcome may not be authentic. In specific growing regions, cultivars have been bred so that they are processed into a certain style of tea. In such a case there is a mother plant that has been planted especially for commercial production.

    Terroir: A French expression which refers to soil, climate, altitude, and latitude in a particular region. Tea styles can be named either after their grown region, or considered origin if grown in a certain province like white tea, which can only be found in Fujian province in china [1,2,9,12].

     

    Sorting and Packaging

     

    This is the final and the most important stage in the tea process. At this stage the leaves are classified according to their size then according to their type and appearance. Completing sorting, the tea is packed into provided foil paper sacks; so that the tea stays dry. For larger tea leaves, tea boxes are provided to make sure that the tea leaves are not damaged in transit. It is advisable to keep tea in an airtight dark boxes put in a cool and dry place at homes. Retailers usually sell tea in metal tins that are tightly closed. The glass jars that are used for keeping tea should be kept in closed cupboard away from light. We should not store tea in refrigerators as cold increases water condensation which ruins the tea [2,12].

    Ingredients of Tealeaves

     

    The ingredients of the tea leaves are not much different from many other plants. Besides the usual ingredients such as protein, carbohydrate and fat containing tealeaves, some ingredients that give the tea its uniqueness. Key ingredients of the tea leaves and their shares are listed in the dry matter in Table 1 [13].

     

    Vitamins and Minerals in Tea

     

    Tea leaves contain a number of vitamins in very low concentration. The exception is vitamin C (ascorbic acid). In high-quality green teas, the vitamin C content reach up to 0.5% of dry matter. Therefore, one liter of green tea covers more than 50% of the daily requirement of Vitamin C. Due to manufacturing process, the content of all vitamins in black tea is less than in green tea, especially vitamin C [13,14].

    Practically fluoride is the most important Mineral in tea. The content of water-soluble fluorine in tea leaves is highly significant. A cup of tea covers 10–15% of the daily requirement for fluoride to protect against tooth decay [15].

     

    Tea Polyphenols

     

    Phenolic compounds are common ingredients in the plant kingdom. The phenolic compounds are among the phytochemicals, since they are not produced and consumed in the primary metabolism of the plant. Their exact functions in the plant are still unknown, where they are synthesized as repellents against pests and diseases, as growth regulators and as dyes of the plant [16]. They contribute significant character of taste, appearance and shape in many fruit crops for e.g. Fruit juices, wines and teas. They basically determine their color, flavor and stability and thus ultimately their quality [13].

    The scientific community use today polyphenols, or shortly phenols (formerly tannins) for the phenolic compounds of plants. The plant phenolics can be based on their molecular structure into three sub-groups [17]

    • Simple phenols having one aromatic ring and one or more hydroxyl groups, for example, Phenol carboxylic acids.
    • Polyphenols, compounds having at least two aromatic rings, each having at least one aromatic hydroxyl group, for example Flavonoids (Figure 7).
    • Tannin compounds are toxic, high molecular weight compounds consisting of many subunits (12-16 phenolic groups and 5-7 aromatic rings) and mainly found in tree bark and protect the trees against attacks by herbivores.

    Varieties of Phenolic compounds are presented in tea and make up to 30% of the dry weight of the tealeaves. The major tea polyphenols are the catechins, flavonol-O-glycosides, flavonol-C-glycosides, proanthocyanidins and also in black tea theaflavins and thearubigins which arising from the catechins during the fermentation [13,17].

     

     

    Catechins

    In fresh leaves and green tea catechins (Flavanols or Flavan-3-ols) are the most abundant group of phenolic compounds. Most medicinal benefits of the tea can be traced back to these catechins which make up about 70% of the flavonoids fraction.

    The major tea catechins are (-)-epigallocatechin 3-gallate (EGCG), (-)-epigallocatechin (EGC), (-)-epicatechin (EC), (-)-epicatechin 3-gallate (ECG), and (+)-catechin (C) (Figure 8).

     

    The inclusion of catechins in the gut is quite low at 10–30%. The intestinal microflora seems to have an important role in the absorption of the catechins. The bacteria in the intestine can metabolize the catechins so that they are better absorbed. The intestinal mechanisms have to enrich the catechins from oral intake to be absorbed. Among the catechins, EGCG predominates not only in terms of quantity (up to 70% of the total catechin content), it seems the substance which makes up the cancer preventive properties of tea. In the lab, a wide range of effects was detected on the tumor cells [17].

    The catechins have a number of other effects attributed to such as lowering cholesterol levels, lowering blood sugar, anti-bacterial effect, etc [18,19]. Catechins are the main carriers of the health benefits of green tea but they are also toxic in high concentrations (intake of Catechins capsules).

    Proanthocyanidins

    Proanthocyanidins (Figure 9) are Flavanol related compounds which degraded during the fermentation of tea and give bisflavanols [20] (Figure 10). Thus green tea has higher amount of Proanthocyanidins and less bisflavanols, while black tea is relatively rich in bisflavanols. There are at least 16 kinds of Proanthocyanidins presented in tea [21,22].

     

    Theaflavins and Thearubigins

     

    Theaflavins (TFs) (Figure 11) and thearubigins (TRs) (Figure 12) are the two most important groups of oxidation products. In the production of black tea catechins are oxidized, resulting in theaflavins (yellow reddish pigments in tea). Then theaflavins are polymerized to form the typical the black red dyes thearubigins. Where in the majority of the anti-oxidative effect of the flavonoids is lost. Theaflavins and related compounds consist of four major TFs and minor TF and their related compounds [23]. Thearubigins, which is similar to TFs [24], is produced by the enzymatic oxidation of flavanols during the manufacture of black tea. Researchers showed that the chemical structures of TRs are cyclized skeletons, which have linkages between A- and B-rings of catechins [25,26]. However, further studies are now in progress to elucidate all TRs structures.

     

    Flavonols (FOG) and Flavones (FCG)

    The Flavonols (quercetin, kaempferol, and myricetin) are presented in tea in form of their mono- di- and tri-O-glycosides. At least 15 different types of glycosides were isolated from tea [27,28]. Flavonols (Figure13) content is not very much affected by fermentation and the quercetin 3-rhamnoglucoside has the highest concentration among them. Flavonolglycosids. Flavones (Figure13) are presented in tea in form of their C-glycosides in much lower concentrations than FOG. C-glycosides are not hydrolyzed by acids or enzymes [29].

     

    Theanine

    Amino acids comprise another important group of tea components. They make up about 1-4% of the dry weight of tea leaves and have a crucial importance for the fresh and pleasant taste of the tea. The majority of the amino acid portion of the tea leaves (more than 50% for high-quality green teas) is attributable to a particular amino acid, L-Theanine (Figure 14).

     

    Theanine, a derivative of glutamine (N-ethyl-L-glutamine), is contained in tea leaves and other parts of the tea plant (Camellia sinensis) and were first discovered in 1949 in tea leaves. It comes in tea in its L-form in the concentration range of 0.5-2% of the dry weight [32,33]. Theanine is synthesized in the roots of tea plant by means of theanine and glutamic acid synthetase from ethylamine, transported into the leaves, and accumulates there. Together with glutamine and other free amino acids theanine is the non-protein nitrogen pool of the plant [32].

     

    Theanine counteracts the caffeine in the tea. Unlike caffeine theanine (dose-dependent) calms central nervous system [30]. In addition, theanine tastes, along with the other amino acids, sweet and it weakens the bitter taste of catechins. L-theanine is together with, inter alia, aspartic acid, theogallin, gallic acid are responsible of the intensity of the "umami" - taste of green tea [32]. Due to their positive influence on the taste, many efforts are being made to increase the content of amino acids in tea, especially in green tea, from the tea company.

    It was published in many studies that L-theanine shows important effects in different sciences: physiology, biochemistry, pharmacy and medicine, such as neuroprotective, relaxant, anxiolytic and antihypertensive effects. Most professional publications and studies on the pharmacological effect of theanine are based on animal experiments. Theanine may also increase the release of the hormones serotonin and dopamine and thus improve the learning ability [33]. This connection can inhibit the convulsing effect of caffeine in mice, reduce the psychological and physiological stress reactions, and increase mental relaxation and release emotional stress [34].

    However, there are few studies about the effect of the theanine in humans. In a study of 24 healthy volunteers, the effect of L-theanine with and without the co-administration of caffeine has been tested on mental abilities. The administration of theanine alone showed little effects in contrast to the combined administration with caffeine. Thus, theanine does not inhibit, but amplified the stimulating effect of caffeine in humans [35].

    The mood effect of theanine has been examined when combined with caffeine. Theanine alone had few effects on mood. The combination of theanine and caffeine had improved mood effects not seen with either treatment alone [31,36,37]. It even slows the rate of mental responses of the test persons. Theanine decreases blood pressure, which had been previously increased by the administration of caffeine. Hence, theanine may have different central nervous system effects due to different doses [34].

     

    Caffeine

     

    Caffeine (C8H10N4O2, 1,3,7-trimethylxanthine or methyltheobromine) is one of the purines scoring, highly water-soluble plant alkaloid. In addition to tea, it is included also in coffee, cacao and mate. Pure Caffeine was first isolated in 1820 by Friedrich Ferdinand Runge, of coffee beans. The first caffeine-synthesis was carried out in 1895 by Emil Fischer.

    Previously, refers to the caffeine from tea as Teein (also Tein or Theine) to delineate it from the caffeine from the coffee beans. Chemically, caffeine and theine are of course identical (Figure 15). Caffeine is one of the methylxanthines, is willingly soluble in water, colorless and odorless.

     

    The commercial white, green and black tea contains more caffeine (3–5% of the dry weight of tea) than the roasted coffee (1–1.5% of the dry weight of the coffee beans) [35,38]. However, a cup of coffee includes 2 to 3 times more caffeine than a cup of tea because of the difference of preparation. When using 2.5 g of tea infused with 200 ml of water, a cup of tea contains about 60 mg of caffeine [11].

    The caffeine content in tea is influenced by various factors such as: the production area, the height of the region, the weather conditions, and the variety of the tea plant. Also, the caffeine levels in tea vary, because it is a natural product [38].

    The pharmacology of caffeine: Caffeine is the most widely used and consumed psychoactive substance. The effect is based on the excitation of the central nervous system. By blocking adenosine receptors it increases mental activity, it will remove fatigue and strengthened intellectual achievements.

    After oral intake (tea, coffee, cola, energy drinks), caffeine is absorbed rapidly and completely in the gastrointestinal tract. After 15-45 min caffeine reaches its maximum levels in the blood. The half-life in blood is about 5 hours, but is significantly longer in pregnant women and children.

     

    The stimulating effect of caffeine on the central nervous system is the main reason for the consumption of tea and coffee. This effect is mainly due to caffeine interaction with the surface receptors of nerve cells in the cerebrum. In contrast to coffee, the caffeine in tea is presented in bound form; so that it's stimulating effect probably slowly unfolds as the enjoyment of coffee. 100–200 mg of caffeine (2–4 cups of tea) leads to a significant influence of psychological basic functions such as drive and mood. The motor activity is increased (eg. faster typewriting with a lower error rate), the mental tempo faster with less reaction time, lifts the mood, facilitates the learning process. However, the effects are dependent on the habit. They occur in strong tea or coffee drinkers on much weaker than in social drinkers. Another effect of the caffeine, which is also used therapeutically, is pain relief. Caffeine, for example, one of the three drugs in the aspirin Thomapyrin (the other two are aspirin and paracetamol). The conventional wisdom of caffeine as diuretic, urine impulsive action has been refuted. The tea or coffee consumption does not cause more urination than drinking an equal amount of water [11,39].

     

    Health Benefits of Tea

     

    According to researchers, tea has great benefits for human health due to its composition and the very effective ingredients [39,40]. Tea prevents the progression of some diseases that people have. Following are the most important health benefits of tea:

     

    Tea and Cancer

     

    Despite the advanced medical technology for diagnosis and treatment of Cancer, it is still one of the most dangerous diseases that put an end to the life of the person who suffers from it. On the other hand, it is very difficult to kill the tumor cells without harming the normal ones. To target tumor cells biochemical and molecular alternations are applied. Therapies relating to cancer like surgery, chemotherapy, radiation and hormone seem successful but they have their own shortcomings. Almost all cancer drugs have very bad side effects, such as liver damage, oxidative stress and immune suppression because of their concurrent toxic manifestations. Thus, successful cancer chemotherapies should be selective targeting and have low toxicity for normal host tissues [41].

    Natural substances are recently studied to use for prevention of cancer and for reducing the cases of mortality and morbidity related to it. Tea polyphenols is considered one of these natural substances that reduce the risk of cancer because of their proved strong antioxidative properties, which affect the molecular mechanisms involved in angiogenesis, metastasis and regulation of cell death. In addition to antioxidative properties of green tea catechins, studies showed their effects on the molecular mechanisms involved in angiogenesis. Green tea flavonoids and in particular, EGCG which is the major green tea polyphenol possess anti-angiogenic activities that could account for the tumor prevention effects observed with these compounds [2,18,19,42–44].

    Recently epidemiological observations gave some convincing evidence that polyphenolic antioxidants present in the tea and in particular EGCG, EGC and ECG, may decrease the risk of prostate cancer. Some studies on animals and a recent Chinese human study showed that the risk of prostate cancer declined by increasing the consumption of green tea [18,42–44].

    EGCG is expected to have an important role in preventing and treating prostate, colon and also gastric cancer. Because of their biological activity as antioxidant, antiangiogenesis and antiproliferative, green tea catechins may be a good candidate to prevent and treat various kinds of cancer. In Japan, Tea-polyphenols and in particular EGCG are considered a cancer preventive beverage [19,39,41–44].

     

    Most of the relevant mechanisms of cancer prevention by tea polyphenols are not related to their redox properties, but to target molecules, including the inhabitation of selected Protein kinases, matrix metalloproteinases and DNA methyltransferases. Many studies assured that tea and its polyphenols decrease the risk of skin, lung, colon, liver and pancreatic cancer [42–46]. Tea can also benefit white blood cells during chemotherapy treatment [40,43].

     

    Tea and Immune System

     

    Antioxidants stop free radicals and consequently slow degenerative diseases. Free radicals hurt the body cells by causing chain reactions of electron scavenging. The antioxidative activity levels of flavonoids and other polyphenols in tea are very different. The positive immune system effects of tea are due to containing considerable amounts of polyphenols [40,47]. Because of the minimal proceed, green and white teas contain the highest amount of polyphenols [16,48]. Four cups of green tea can give the recommended dietary value of polyphenols (300 to 400 mg).

     

    Tea and cavities

     

    Because tea contains fluoride and other minerals, it fights cavity and maintain hard teeth. The polyphenols exist in tea help fight bacteria in the mouth. In vitro and in vivo experiments clearly show that the group of polyphenols represents a caries-preventive factor of tea. Polyphenols in tea inhibit the degradation of starch in food particles on the teeth by inactivation of amylase. Tannins in black tea have a better activity in the Amylase hemming than catechins in green tea, because of their high molecular weight.

    Tea prevents caries, improves and preserves the tooth substance, reduces cariogenic risk of crackers and cookies as a source of fermentable carbohydrates in the oral cavity [40,49]. This can be regarded as another positive factor of drinking tea.

     

    Tea and Heart Diseases

     

    Worldwide, cardiovascular diseases consider the main cause of morbidity and mortality. Many epidemiological researches refer to the connection between tea consumption and several beneficial cardiovascular effects. These studies indicate that tea flavonoids and catechins inhibit the risk of detrimental cardiovascular diseases, and decrease their mortality rate. Tea catechins decrease oxidative stress, prevent inflammatory events, reduce platelet aggregation and halt the reproduction of vascular smooth muscle cells, so they have the ability to keep from hypertension, atherosclerosis, cardiomyopathy, ischemic heart diseases, cardiac hypertrophy and congestive heart failure.

    The anti-oxidant effect of catechins is accorded by inhibiting pro-oxidant enzymes, scavenging free radicals and stimulating anti-oxidant enzymes. Catechins conflict with vascular growth factors and also reduce the proliferation of vascular smooth muscle cell because of their anti-inflammatory activity. In addition, catechins adjust blood pressure, promote vascular integrity and save vascular endothelial cells [40,41,50–52].

     

    Depending on some animal and human studies, the protect effectivities of cardiovascular diseases of black and green are equal. During the fermentation of black tea, catechins are converted to other compounds (theaflavins and thearubigins), which have in vitro, cardiovascular beneficial effects. Other in vivo studies are required to assure that [52].

     

    Tea and Obesity

     

    Tea as a metabolic stimulant is drunk with each meal for weight loss. Caffeine may increase metabolism of fatty acids for energy and spare glycogen stores. In comparison with other commercial beverages, all kinds of tea offer low calories. Every serving of tea has only four calories and drinking tea without any addition is healthier. Tea-caffeine raises body function so it helps to burn more calories and the tea-polyphenols helps in fat digestion [46,53–55].

     

    Tea and Anti-Diabetic Effects

     

    Diabetes is a disorder of carbohydrate metabolism in which the sugar level increases in the blood beyond the normal level. In diabetic patients, reduced antioxidant defenses are observed and consequently the risk of free radical mediated disease is increased. Some new researches suggest the dietary of flavonoids to lower the risk of diabetes, but the results of a biological effect has yet to be proved directly in humans [56,57]. Chemical analysis has indicated that tea is a source of many flavonoids which are reported to have a glucose-lowering effect in animals [58]. The exact mechanisms of the anti diabetic effects of tea are not clear, although several hypotheses have been proposed. Tea components work like Insulin; they raise the activity of phosphoinositide 3-kinase, tyrosine phosphorylation, mitogen-activated protein kinase of the insulin receptor. Free radical mediated diseases are also known to be reduced by tea components due to their antioxidant properties. Thus tea can be considered as a natural anti-diabetic medicine without any toxicity in animals [58]. Tea is therefore worthy of serious consideration for further investigation in respect of the prevention and treatment of diabetes.

     

    Tea and Skin

     

    The main tea catechins protect the skin from the adverse effects of UV radiation exposer and lower the risk of skin cancers in many animal and in vitro models. Tea catechins may favorably be additive to sun protection cream because of their therapeutic use in several skin diseases such as solar UV radiation-induced inflammation, DNA damage and oxidative stress. Although research on green tea is very promising, future studies that take into consideration dietetic, environmental and life style factors are necessary to understand its contribution to human health [59,60].

     

    Side Effects of Tea

     

    Several good effects of tea on human health are proved for various diseases or issues, but there are some harmful effects too. The flavonoids in tea have the most therapeutic and nutritional benefits. However, they can be toxic, when their consumption exceeds certain limits. They affect human health badly by formation of reactive oxygen species, which harm the lipid membranes and also the DNA [61].

     

    Side effects and toxicity of caffeine are very low. The lethal dose for humans is about 10 grams. Like other ergogenic substances, cause caffeine often abuse effects. For example the athletes drink caffeine as a doping agent to remove fatigue and to strengthen intellectual achievements, but excessive caffeine intake causes headaches. Also consuming larger doses of Caffeine (about 300 mg), lead to symptoms such as Palpitations and hand tremors [62,63].

     

    In addition to several beneficial minerals (magnesium, calcium, potassium, and phosphorus), tea contains also some bad elements (lead and aluminum). Some researchers showed that the brewed teas for three to fifteen minutes contain considerable lead levels (73% to 83%), respectively, and also the aluminum levels were above recommended guidelines. This make tea unsafe beverage for pregnant and lactating women. Tea can have a toxic contamination by heavy metals and that is depending on the dose intake of tea [61,64]. However, the benefits and side effects of tea are still to be studied.

     

    Conclusion

     

    Various types of tea can be obtained from the tea plants Camellia sinensis .L and Camellia assamica by applying different manufacturing processes on the fresh tealeaves. During production processes tea ingredients undergo chemical changes in particularly polyphenols. Thus tea types vary in colour (black, green, white and oolong tea) and taste.

     

    Tea is classified in many ways according to: origin, similarity of final products (green, yellow, white, oolong and black), the grade of fermentation (Non-fermented, Semi-fermented and Fermented), or ratio approach between major tea components.

    Caffeine, theanine and polyphenols are the most effective compounds of tea. Flavonoids have diabetes, cancers and heart diseases prevention effects. Catechins, in particular, (EGCG) inhibit the risk of detrimental cardiovascular diseases and help in inflammation skin therapy caused by solar UV radiation. The ant oxidative activities of Polyphenolsenhance the human immune system and reduce the Obesity. Caffeine helps to burn more calories and digest fat. Tannins hemmed amylase and fight cavity. Although of large positive effects of tea, consuming large amounts of long brewed tea can have a toxic contamination by heavy metals and other ergogenic effects.

     

    More studies and researches are still needed to reveal the benefits and side effects of tea.

     

    Conflict of interest

     

    References

     

    1. Marchand F, Desharnais J. Tea: History, Terroirs, Varieties: Kevin Gascoyne, François Marchand, Jasmin Desharnais, Hugo Americi editors. 2ed edition. Firefly Books; 2014.
    2. Panda H. The Complete Book on Cultivation and Manufacture of Tea. 2nd Revised Edition. Asia Pacific Business Press Inc; 2016.
    3. Tocklai.net. Classification and nomenclature of tea. Tocklai tea research institute. India. 2012. Available from: http://www.tocklai.net/activities/tea-classification/
    4. Hohenegger B. Liquid jade: the story of tea from east to west. 1st ed.  New York: St. Martin's Press; 2006.
    5. Kakuzo O. The Book of Tea. 1st ed. Tokyo: Kodansha International;2005.
    6. Hohenegger B. Steeped in History: The Art of Tea. 1st ed. Los Angeles: Fowler Museum at UCLA;2009.
    7. Gebely T. A New Look at Tea Classification. 2013. Available from: https://worldoftea.org/tea-classification/
    8. Walsh JM. Tea-Blending As a Fine Art. Wentworth Press;1896.
    9. Hilal Y, Engelhardt UH. Characterisation of the white tea-Comparison to green and black tea. J. Verbr. Lebensm. 2007;2(4):414–421. doi:10.1007/s00003-007-0250-3.
    10. Alcazar A, Ballesteros O, Jurado JM, Pablos F, Martin MJ, Vilches JL, et al. Differentiation of green, white, black, Oolong, and Pu-erh teas according to their free amino acids content. J Agric Food Chem. 2007;55:5960–5965. doi: 10.1021/jf070601a.
    11. Engelhardt UH. Authenticity of tea and tea products. In: Ebeler SE, Takeoka GR, Winterhalter P, editors. Authentication of Food and Wine. ACS Symposium series 952: American Chemical Society: Washington DC; 2007. p138–146.
    12. Willson KC, Clifford MN. Tea: Cultivation to consumption. Springer;1992.
    13. Engelhardt UH. Polyphenole in Tee. Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut. 1998.
    14. Deijs WB. Vitamin-C in tea leaf. Recl. Trav. Chim. Pays-Bas. 1940;59(6):567–579.
    15. Lu Y, Guo W, Yang X. Fluoride Content in Tea and Its Relationship with Tea Quality. J. Agric. Food Chem. 2004;52 (14):4472–4476. doi: 10.1021/jf0308354.
    16. Bitsch R. Pflanzliche Phenole und ihre gesundheitliche Wirkung. J Vita Min Spur. 1999;14:16-20.
    17. Clifford M. A nomenclature for phenols with special reference to tea. J Food Sci & Nut. 2001;41:393–397.
    18. Zhao B. The health effects of Tea Polyphenols and their antioxidant mechanism. J Clin Biochem Nutr. 2006;38:59–68.
    19. Gupta J, Siddique YH, Beg T, Ara G, Afzal M. A review on the beneficial effects of tea polyphenols on human health. J International Journal of Pharmacology. 2008;4(5):314–338. doi: 10.3923/ijp.2008.314.338.
    20. Hashimoto F, Nonaka G, Nishioka I. Tannins and Related Compounds. CXIV. Structures of Novel Fermentation Products, Theogallinin, Theaflavonin and DesgalloylTheaflavonin from Black Tea, and Changes of Tea Leaf Polyphenols during Fermentation. J Chem Pharm Bull. 1992;40:1383–1389.
    21. Lakenbrink C. Strukturaufklärung und Bestimmung von Proanthocyanidinen und anderen flavonoiden Inhaltsstoffen des Tees. 2001.
    22. Engelhardt UH, Lakenbrink C, Pokorny O. Proanthocyanidins, Bisflavanols and Hydrolyzable Tannins in Green and Black Teas. In: Shahidi F, Weerasinghe DK, eds. Nutraceutical Beverages. Chemistry, Nutrition, and Health Effects. ACS Symposium Series. 2004;871:254–264. doi: 10.1021/bk-2004-0871.ch019.
    23. Lapczynski S. Untersuchungen über Theaflavine und Flavanole in grünen und schwarzen Tees. 2000. Thesis TU Braunschweig, Germany.
    24. Menet MC, Sang S, Yang CS, Ho CT, Rosen RT. Analysis of theaflavins and thearubigins from black tea extract by MALDI-TOF mass spectrometry. J Agric Food Chem. 200;52(9):2455–61. doi: 10.1021/jf035427e.
    25. Muigai NF,Wanyoko JK,Mahungu SM,ShitandiAA. Catechins depletion patterns in relation to theaflavin and thearubigins formation. Food Chemistry. 2009;115(1):8–14. doi:10.1016/j.foodchem.2008.10.006.
    26. Uchida K, Ogawa K, Yanase E. Structure Determination of Novel Oxidation Products from Epicatechin: Thearubigin-Like Molecules. Molecules. 2016;21(3):273. doi: 10.3390/molecules21030273.
    27. Hilal Y, Engelhardt UH. A new myricetin-rhamnodiglucoside from Camellia sinensis. Nat Prod Res. 2009;23(17):1621–9. doi: 10.1080/14786410902975673.
    28. Scharbert S, Holzmann N, Hofmann T. Identification of the astringent taste compounds in black tea infusions by combining instrumental analysis and human bioresponse. J Agric Food Chem. 2004;52(11):3498–508. doi: 10.1021/jf049802u.
    29. Engelhardt UH, Finger A, Herzig B, Kuhr S. Determination of Flavonol, Glycosides in Black Tea. J. Deutsche Lebensmittel-Rundschau. 1992.88:69–73.
    30. Engelhardt UH. Was man kennt und doch nicht weiß – Theogallin und Theanine, Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut. 2009.
    31. Feldheim W. Theanin – eine Verbindung besonderer Art im Tee. Hamburg: WissenschaftlicherInformationsdienst Tee, Deutsches Tee-Institut. 2001.
    32. Kaneko S, Kumazawa K, Masuda H, Henze A, Hofmann T. Molecular and sensory studies on the umami taste of Japanese green tea. J Agric Food Chem. 2006;54(7):2688–94. doi: 10.1021/jf0525232.
    33. Dimpfel W, Kler A, Kriesl E, Lehnfeld R. Theogallin and L-theanine as active ingredients in decaffeinated green tea extract: II. Characterization in the freely moving rat by means of quantitative field potential analysis. J Pharm Pharmacol. 2007;59(10):1397–403. doi: 10.1211/jpp.59.10.0010.
    34. Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007;74(1):39–45. doi: 10.1016/j.biopsycho.2006.06.006.
    35. Haskell CF, Kennedy DO, Milne AL, Wesnes KA, Scholey AB. The effects of L-theanine, caffeine and their combination on cognition and mood. Biol Psychol. 2008;77(2):113–22. doi: 10.1016/j.biopsycho.2007.09.008.
    36. Nathan PJ, Lu K, Gray M, Oliver C. Neuropharmacology of L-Theanine (N-Ethyl-LGlutamine). J Herb Pharmacother. 2006;6(2):21–30.
    37. Bryan J. Psychological effects of dietary components of tea: caffeine and L-theanine. Nutr Rev. 2008;66(2):82–90. doi: 10.1111/j.1753–4887.2007.00011.x.
    38. Zenger R, Gerhard S. Entkoffeinierung von Tee, Deutscher Teeverband , Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut. 2011.
    39. Renk C. Klinische Studien über Tee (Camellia sinensis), Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut. 2009.
    40. Jain NK, Siddiqi M, Weisburger J. Protective Effects of Tea on Human Health, CAB International. UK: Cromwell Press; 2006.
    41. Scalbert A, Johnson TI, Saltmarsh M. Polyphenols: antioxidants and beyond. Am J Clin Nutr. 2005 Jan;81(1 Suppl):215S–217S.
    42. Ehrnhöfer DE. Inhibitor der amyloiden Proteinaggregation in Grünem Tee: Die Wirkung des Tee-Inhaltsstoffs EGCG gegen Eiweißablagerungen bei Parkinson, Alzheimer und anderen Erkrankungen, Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut. 2010.
    43. Mitscher LA, Dolby V. The Green Tea Book. Garden City Park, NY: Avery Publishing Group;1998.
    44. Jennifer R, Brent A, Vincent A, Paul J, Wilson T. Reading the Tea Leaves: Anticarcinogenic Properties of (-)-Epigallocatechin-3-Gallate. Mayo Clinic Proceedings. 2007;82(6):725–732.
    45. Hajiaghaalipour F, Kanthimathi MS, Sanusi J, Rajarajeswaran J. White tea (Camellia sinensis) inhibits proliferation of the colon cancer cell line, HT-29, activates caspases and protects DNA of normal cells against oxidative damage. J. Food Chemistry. 2014;169:401–410.
    46. Forester SC, Lambert JD. Cancer Preventive Effects of Green Tea Polyphenols, Polyphenols in Human Health and Disease. 2014;2:1309–1322.
    47. Wang W, Yang Y, Zhang W, Wu W. Association of tea consumption and the risk of oral cancer: A meta-analysis, Oral Oncol. 2014;50(4):276–81. doi: 10.1016/j.oraloncology.2013.12.014.
    48. Magrone T, Kumazawa Y, Jirillo E. Polyphenol-Mediated Beneficial Effects in Healthy Status and Disease with Special Reference to Immune-Based Mechanisms. Polyphenols in Human Health and Disease. 2014;1:467–479.
    49. Feldheim W. Die kariespräventive Wirkung von Tee (II): Die Wirkung der Polyphenole, Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut 2000.
    50. Bhardwaj P, Khanna D. Green tea catechins: defensive role in cardiovascular disorders. Chin J Nat Med. 2013;11(4):345–53. doi: 10.1016/S1875-5364(13)60051-5.
    51. Onakpoya I, Spencer E, Heneghan C, Thompson M. The effect of green tea on blood pressure and lipid profile: A systematic review and meta-analysis of randomized clinical trials. Nutr Metab Cardiovasc Dis. 2014;24(8):823–36. doi: 10.1016/j.numecd.2014.01.016.
    52. Lorenz M. The Role of Individual Tea Compounds in Cardiovascular Protective Effects of Green and Black Tea, J. Tea in Health and Disease Prevention. 2013;829–840.
    53. Yajima H. Prevention of Diet-Induced Obesity by Dietary Polyphenols Derived from Nelumbonucifera and Black Tea. J. Polyphenols in Human Health and Disease. 2014;1:135–142.
    54. Uchiyama S, Taniguchi Y, Saka A, Yoshida A, Yajima H. Prevention of diet-induced obesity by dietary black tea polyphenols extract in vitro and in vivo. Nutrition. 2011;27(3):287–92. doi: 10.1016/j.nut.2010.01.019.
    55. Murase T. Anti-Obesity Effect of Tea Catechins in Combination with Exercise, J.Tea in Health and Disease Prevention. 2013;1003–1014.
    56. Park J, Bae J, Im S, Song D. Green tea and type 2 diabetes, J. Integrative Medicine Research. 2014;3(1):4–10.
    57. Banua S, Jabirb NR, ManjunathaNC, Khanc MS, Ashrafb GM, Kamalb MA, et  al. Reduction of post-prandial hyperglycemia by mulberry tea in type-2 diabetes patients. Saudi J Biol Sci. 2015;22(1):32–6. doi: 10.1016/j.sjbs.2014.04.005.
    58. Tang W, Li S, Liu Y, Huang M, Ho C. Anti-diabetic activity of chemically profiled green tea and black teaextracts in a type 2 diabetes mice model via different mechanisms, J Functional Foods. 2013;5(4):1784–1793.
    59. Primavesi L, Piantanida M, Pravettoni V. Studying Tea Polyphenols and Their Protective Effects on Skin, J Polyphenols in Human Health and Disease. 2013;1:849–859.
    60. Heinrich U. Verbesserung der Haut durch Grünen Tee, Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut 2014.
    61. Jain A, Manghani C, Kohli S, Nigam D, Rani V. Tea and human health: The dark shadows, Toxicology Letters. 2013; 220(1):82–87.
    62. Schröder EM. Die Wirkungen von Coffein im Tee. Wissenschaftlicher Informationsdienst Tee. Deutsches Tee-Institut. 1999.
    63. Belitz HD, Grosch W, Schieberle P. Lehrbuch der Lebensmittelchemie. 5th ed. Berlin: Springer-Verlag GmbH; 2001.
    64. Schwalfenberg G, Genuis SJ, Rodushkin I. The Benefits and Risks of Consuming Brewed Tea: Beware of Toxic Element Contamination. J Toxicology. 2013;2013:ID:370460.

     

    Copyright: © 2017 Yumen Hilal. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

    e.

  • Tea masters & the science of making Oolong Tea ..

    Reproduced thanks to the : Journal of food and drug analysis 24 (2016) 500e507

    Oolong tea is Taiwan's world renowned semi-fermented tea (partial oxidation) with an elegant floral aroma and mellow characteristics.

     

    The manufacturing process of this semi- fermented tea includes withering, several rounds of shaking and setting (fermentation or oxidation), firing (fixation), rolling, and drying.

     

    Tea fermentation is the most important stage for quality control. An oxidation reaction occurs in this stage; the catechins in tea leaves are oxidized with time. In this process, catechin monomers are polymerized to form theaflavins, thearubigins, or other oxidation products such as theasinensins or oolongthenin [1,3,4]. These tea chemical components contribute to the color and taste of oolong tea.

     

    Withering

     

    The first step of tea making is withering the fresh tea leaves. As the moisture content of tea flushes decreases, withering reduces the semipermeability of the membranes, thus enabling the catechins stored in the leaf cell vacuoles to flow out of the cytoplasm and come into contact with the oxidase in the cell cytoplasm [5]. From this stage onward, theoxidation of catechins starts and tea fermentation begins.

     

    In the manufacturing of oolong tea, the withering process includes two stages: solar and indoor withering. In solar withering, other than the loss of moisture, the UV radiation of the sunlight also promotes gene expression of intracellular hy- hydrolytic enzymes, b-primeverosidase, and b-glucosidase, and facilitates the hydrolysis of the precursors of volatile organic compounds (VOCs), which are present in the glycosidic form [6,7].

     

    After a short period of solar withering, the tea leaves are moved indoors to continue the withering process. During in- door withering, the tea leaves are shaken three to five times at intervals. Each shaking interval is about 2 hours and is dependent on the temperature, moisture, and the contents of leaves.

     

    The tea master decides when to shake the tea leaves, what the intensity should be, and the duration of the shaking by touching and smelling the leaves. The initial shaking is mild, mainly to redistribute the moisture from the stalk to the leaves, and the stomatal conductance of the tea leaf is decreased after plucking and solar withering [7,8].

     

    After a heavy shaking, the catechins are released from the vacuoles to the cytoplasm [5]. The expression of oxidase is also significantly enhanced, indicating significant oxidation [9]. More- over, the smell of the fermenting tea leaves changes during the entire shaking and setting process. The precursors of the aromatic VOCs undergo oxidation and hydrolysis after the shaking. The hydrolysis of terpene alcohol glycosides

    generates terpene alcohols as the VOCs, while the oxidation of carotenoids and lipids produces lactones, ketones/enols, and other VOCs [10e12]. Thus, the smell of the fresh tea leaves changes in the manufacturing process. Consequently, the resulting VOCs composition contributes to the unique and characteristic aroma of oolong tea.

     

    The tea master monitors the entire process through his/her senses and decides the timing of each step, which is still an art depending on the traditional master apprentice model.

     

    This means that good tea can only be made by hand, not by machinery. If we want to produce tea of high quality, we need more information and parameters about tea fermentation.

     

    To establish a scientific tea manufacturing process, the changes in the chemical contents of tea leaves during the fermentation process should be elucidated. The fermentation duration of oolong tea can be up to 6 - 10 hours. We monitored the changes in the chemical contents of tea leaves during the fermentation stage, before and after each shaking step, to understand the changes in catechin monomers and VOCs in the manufacturing process of the oolong tea.

     

    We can determine the whole picture of the fermentation process through the change of catechins, the raw materials of tea fermentation, and the VOCsdwhat tea masters depend on. According to these data, we provide a theory of tea fermentation for procedures to monitor the manufacturing process.

     

    Reference: Shu-Yen Lin a, Li-Chiao Lo a, Iou-Zen Chen a, Po-An Chen b - Effect of shaking process on correlations between catechins and volatiles in oolong tea - Journal of food and drug analysis 24 (2016)

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