Catechins: definition, structure, green tea, black tea, cocoa

CONTENTS

What are catechins?

Catechins or flavanols, with flavonols such as quercetin, and flavones such as luteolin, are a subgroup of flavonoids among the most widespread in nature.
Flavanols and proanthocyanidins, together with anthocyanins and their oxidation products, are the most abundant flavonoids in human diet.

Chemical structure of catechins

Chemically they differ from many other flavonoids as:

  • they lack the double bond between positions 2 and 3 of the C ring;
  • they not have a keto group at position 4;
  • they have a hydroxyl group in position 3, and for this reason they are also called flavan-3-ols.
Catechins
Fig. 1 – Basic Flavanol Skeleton

Another distinctive feature of flavan-3-ols is their ability to form oligomers (two to ten units) or polymers (eleven or more units, up to 60 units) called proanthocyanidins or condensed tannins.

Catechins in foods

Flavanols commonly found in plant-derived food products are catechin, epicatechin, gallocatechin, epigallocatechin, and their gallic acid ester derivatives: catechin gallate, gallocatechin gallate, epicatechin gallate, and epigallocatechin gallate or EGCG.

Catechins
Fig. 2 – Flavanols

Flavanols present with higher frequency are catechin and epicatechin, which are also among the most common known flavonoids, and almost as popular as the related flavonol quercetin.
Cocoa and green tea are by far the richest sources in flavanols. In these foods the main flavonoids are catechin and epicatechin (cocoa is also a good source of epigallocatechin), but also their gallic acid ester derivatives, the gallocatechins.
However, they are also present in many fruits, especially in the skins of apples, blueberries (Vaccinium myrtillus) and grapes, in vegetables, red wine and beer, and peanuts.
As in many cases flavanols are present in the seeds or peels of fruits and vegetables, their intake may be limited by the fact that these parts are discarded during processing or while eaten.
Furthermore, in contrast to other flavonoids, catechins are not glycosylated in foods.
Proanthocyanidins, that is polymeric flavan-3-ols, are also commonly found in plant-derived food products. Their presence has been reported in the skin of peanuts and almonds, as in the berries.

Catechins in green and black tea

Green tea is an excellent source of flavonoids. The main flavonoids present in the leaves of the tea (as in cocoa beans) are catechin and epicatechin, monomeric flavanols, together with their gallate derivatives such as EGCG.
Epigallocatechin gallate is the most abundant catechin in green tea and it seems to have an important role in determining green tea benefits, as the reduction of:

  • vascular inflammation;
  • blood pressure;
  • concentration of oxidized LDL.

Black tea (fermented tea) contains fewer monomeric flavanols, as they are oxidized during fermentation of the leaves to more complex polyphenols such as theaflavins (theaflavin digallate, theaflavin-3-gallate, and theaflavin-3′-gallate, all dimers) and thearubigins (polymers).
Theaflavins and thearubigins are present only in the tea; their concentrations in brewed tea are between 50- and 100-folds lesser than in tea leaves.

It should be noted that tea epicatechins are remarkably stable to heat in acidic environment: at pH 5, only about 15% is degraded after seven hours in boiling water (therefore, adding lemon juice to brewed tea does not cause any reduction in their content).

Catechins in cocoa and cocoa products

Cocoa has the highest content of polyphenols and flavanols per serving, a concentration greater than those found in green tea and red wine. Most of the flavonoids present in cocoa beans and derived products, such as black chocolate, are catechin and epicatechin, monomeric flavanols, but also epigallocatechin, and their derivatives such as the gallocatechins; among polymers, proanthocyanidins are also important.

Catechins in fruits, vegetables, and legumes

Catechin and epicatechin are the main flavanols in fruits. They are found in many fruits in different concentrations, respectively, between 5-3 and 0.5-6 mg/100 g fresh weight.
On the contrary, gallocatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate are present in various fruits such as red grapes, berries, apples, peaches and plums, but in very low concentrations, less than 1mg/100 g fresh weight.
Except for lentils and broad beans, few legumes and vegetables contain catechins, and in very low concentrations, less than 1.5 mg/100 g fresh weight.

References

de la Rosa L.A., Alvarez-Parrilla E., Gonzàlez-Aguilar G.A. Fruit and vegetable phytochemicals: chemistry, nutritional value, and stability. 1th Edition. Wiley J. & Sons, Inc., Publication, 2010

de Pascual-Teresa S., Moreno D.A. and García-Viguera C. Flavanols and anthocyanins in cardiovascular health: a review of current evidence. Int J Mol Sci 2010;11:1679-1703. doi:10.3390/ijms11041679

Han X., Shen T. and Lou H. Dietary polyphenols and their biological significance. Int J Mol Sci 2007;9:950-988. doi:10.3390/i8090950

Manach C., Scalbert A., Morand C., Rémésy C., and Jime´nez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr 2004;79(5):727-47 doi:10.1093/ajcn/79.5.727

Tsao R. Chemistry and biochemistry of dietary polyphenols. Nutrients 2010;2:1231-1246. doi:10.3390/nu2121231

Published by Dr. Nicola Tazzini

Nicola Tazzini, MS in Biology Sciences Doctor Tazzini graduated "Summa cum Laude" at the University of Pisa on Nov. 11th, 1996 after 1½ year, carried out in the laboratory of Biochemistry of the Department of Biochemistry and Physiology of the Faculty of Natural, Physical and Mathematical Sciences. The subject of his thesis was "Studies about the mechanism of cytotoxicity of the combination of deoxyadenosine and deoxycoformicine on a cell line derived from a human colon carcinoma" (see References). He registered as a Biologist at the University of Pisa on May 10th, 1998. He specialized "Summa cum Laude" in "Biochemistry and Clinical Chemistry" in Oct. 30th, 2001 at the Department of Biological Chemistry of the Faculty of Medicine and Surgery of the University of Parma. The subject of his thesis was: "Analyses of ematochemical, enzymatic and non-enzymatic parameters with antioxidant activity in young professional athletes". He has started his activity of Nutritionist on Feb. 02nd, 2002. He attended the following courses related to the activity of Nutritionist. 2000 1. Pasta in human nutrition. Associazione Biologi Nutrizionisti Italiani. 2. Course of forming and updating in nutrition and health: roll of Biologist. Associazione Scientifica Biologi Pisa. 2001 1. Elements of nutrition. Associazione Scientifica Biologi Pisa. 2002 1. Nutrition as healthy factors, professional update. Associazione Biologi Nutrizionisti Italiani. 2003 1. Nutrition as healthy factors- first part. Associazione Biologi Nutrizionisti Italiani. 2004 1. Nutrition as healthy factors- second part. Associazione Biologi Nutrizionisti Italiani. 2. Nutrition in childhood. Associazione Biologi Nutrizionisti Italiani. 3. Sport activity, growth and correct nutrition. Associazione Biologi Nutrizionisti Italiani. 4. Nutrition and tumor. PLANNING congressi Srl. 2005 1. Doping: guidelines and diagnostic assessments: legal, biochemical, medical and toxicological aspects. Restless Architech of Human Possibilities S.a.s. 2. Nutrition in the third age: nutritional issues and proper nutritional habits. Associazione Biologi Nutrizionisti Italiani. 3. Technical legislation evolution and ethics in development of the profession. Ordine Nazionale dei Biologi. 2006 1. Sport and nutrition. Syntonie S.r.l. 2. Nutrition and prevention: choose to stay healthy. Ordine Nazionale dei Biologi. 3. Pathology nutrition and legislation aspects. Syntonie S.r.l. 4. Nutrition: guidelines. Ordine Nazionale dei Biologi. 2007 1. Nutrition topics: food as welfare tool: physiological and pathological balance factors. Ordine Nazionale dei Biologi. 2008 1. Outdoor and indoor environment. Resources and balances. Ordine Nazionale dei Biologi. 2. Biologist ’profession in the current technical legislation evolution. Ordine Nazionale dei Biologi. 3. Prevention of childhood obesity: nutritional strategies from pregnancy to school age. Ordine Nazionale dei Biologi. 2009 1. Nutrition, the cornerstone. Nutritional and health needs in the era of the genome. S.I.N.U. 2010 1. The evolution of food safety. Ordine Nazionale dei Biologi. 2. Food safety and correct nutrition. Associazione Scientifica Biologi Pisa and Ordine Nazionale dei Biologi. 2011 1. Role of coffee in physiological and pathological states. CMGRP Italia S.p.A. Reference 1. Bemi V., Tazzini N., Banditelli S., Giorgelli F., Pesi R., Turchi G., Mattana A., Sgarrella F., Tozzi M.G., Camici M. Deoxyadenosine metabolism in a human colon-carcinoma cell line (LoVo) in relation to its cytotoxic effect in combination with deoxycoformycin. Int J Cancer 1998;75(5):713-20. doi:https://doi.org/10.1002/(SICI)1097-0215(19980302)75:53.0.CO;2-1 2. Cassandra Studio . Nutraceuti e cibi funzionali. Youcanprint, 2015 3. Singh A.N., Baruah M.M. & Sharma N. Structure based docking studies towards exploring potential anti-androgen activity of selected phytochemicals against prostate cancer. Sci Rep 2017;7(1):1955. doi:10.1038/s41598-017-02023-5 4. Wee T.T., Lun K.R. Teaching science in culturally relevant ways: ideas from Singapore teachers. World Scientific, 2014

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