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CHAPTER 6

Tea Flavanols AnOverviewIngrid A-L Persson

Department of Medical and Health Sciences Division of Drug ResearchPharmacology

Faculty of Health Sciences Linkoping University Sweden

INTRODUCTION

Flavanols also referred to as catechins are the main secondary metabolites present in the

tea plant Camellia sinensis L (Theaceae) The flavanols belong to the largest group of phenoliccompounds in plants the flavonoids Flavonoids are water-soluble pigments present in the

cytosol andor stored in the vacuole of the plant cell Flavonoids are not essential for the plant

although they take part in their survival eg they serve as communicators between the plant

and the environment

PHOTOSYNTHESIS

It is most likely that the higher vascular plants evolved approximately 400 million years ago via

photosynthesizing bacteria algae mosses and lichen Photosynthesis is the key reaction in theevolution of higher plants eg the tea plant Camellia sinensis L (Theaceae) and plant-derived

substances as tea flavanols Photosynthesis (discovered by Joseph Priestley 1770 and JanIngenhousz 1779) is probably the most important chemical reaction taking place on Earth In

photosynthesis light energy is converted into chemical energy and this is considered to be the

ultimate source of energy sustaining life on Earth The process can be described as two subse-

quent chemical reactions a light-dependent reaction and the Calvin cycle The two are linkedtogether and controlled by enzymes The light-dependent reaction is a photochemical reaction

taking place in the thylakoid membranes of chloroplasts where light energy is transformed into

adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH)

The Calvin cycle (discovered by Melvin Calvin) takes place in the stroma of the chloroplast

and here energy in the form of ATP and NADPH from the light-dependent reaction is used to

convert carbondioxide to carboxyhydrates namely 2 glyceraldehyde-3-phosphate

(Figure 61) in a biochemical reaction In order for the Calvin cycle to continue two-thirds

of the 2 glyceraldehyde-3-phosphate molecule is regenerated so creating one glucose

molecule requires six turns of the Calvin cycle In summary glyceraldehyde-3-phosphate issynthesized by the light-dependent reaction and the Calvin cycle is used to form carbohy-

drate substances eg starch and cellulose which are essential for the plant

BIOSYNTHESIS OF FLAVANOLS

Chemical reactions taking place in organisms are known as metabolism (Greek metabole

change) As mentioned above photosynthesis generates chemical substances named primary

metabolites and these are synthesized in and common to all green plants These primary

Tea in Health and Disease Prevention DOI 101016B978-0-12-384937-300006-9

Copyright 2013 Elsevier Inc All rights reserved

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metabolites are essential for assimilation growth and development and include lipids

proteins amino acids chlorophyll lignin and carbohydrates They are fundamental to

processes such as the formation of energy respiration and transportation of fluid In further synthesis steps often referred to as biosynthesis many plants synthesize a variety of other

organic molecules the so-called secondary metabolites Secondary metabolites are not

essential for life in that they do not take part in the basic processes of the cell However they are

necessary for the survival of the plant eg in defense reproduction or as waste products

Secondary metabolites are produced by the cell and are often stored in the cell vacuole Thereare three main groups of secondary metabolites terpenes (built up from isoprene units C5H8)

alkaloids (alkaline- and nitrogen-containing substances) and phenols (containing a hydroxyl

group bonded to an aromatic hydrocarbon group eg C6H5OH) The flavonoids (Latin flavus yellow) represent the largest group of phenolic compounds in

plants All dietary products originating from plants potentially contain flavonoids over 4000

compounds have been identifiede and the list is still growing (Harborne and Williams 2000)

2 of the carbon-containing substances produced by photosynthesis are converted into flavo-

noids (Harborne and Williams 2000) They are water-soluble pigments present in the cytosol

andor stored in the vacuole of the plant cell The biosynthesis pathway of the flavonoids isprobably the most examined and well known of the secondary metabolites Their biosynthesis

pathway is part of a larger phenylpropanoid pathway producing a range of secondary metab-

olites eg phenolic acids (substances containing a phenolic ring C6H5OH and an organiccarboxylic acid containing at least one carboxyl group -COOH) These phenolic acids are

divided into flavonoids (C6-C3-C6) stilbenes (C6-C2-C6) aurones (heterocyclic molecule) and

apiforols (flavan-4-ol) (Figure 62) Flavonoids are of mixed origin biosynthesized by theshikimic acid pathway and the mevalonic acid pathway (Figure 63)

The basic chemical structure of the flavonoids is based on two six-carbon rings linked by a three-carbon unit (C6-C3-C6) also known as the chalcone structure (Figure 62) which is an

unstable molecule Ring B and the 3-carbon bridge are derived from the shikimic acid pathway

via phenylalanine and p-coumaric acid and the carbons in ring A derive from malonic acid(acetyl-CoA and three malonyl-CoA) The key enzyme in the formation of the chalcone

molecule is chalcone synthase (CHS) The main classesgroups of flavonoids divided

according to differences in the C-ring OH-substituents and double bonds are chalcones

flavanones flavones flavonols isoflavones anthocyanidins and flavanols (Figure 62)

S

Thylakoid membranes

Stroma

NADPH

NADP+

CO2

ATP ADPADP ATP

H2O

O2

FIGURE 61Photosynthesis This overview of photosynthesis shows the

light-dependent reaction taking place in the thylakoid

membranes of the chloroplast and the Calvin cycle taking

place in the stroma of the chloroplast Energy in the form of

ATP (adenosine triphosphate) and NADPH (nicotinamide

adenine dinucleotide phosphate) produced by the light-

dependent reaction are used in the Calvin cycle to convert

hydrogen and carbondioxide to carboxyhydrates 6CO2 thorn

6H2O C6H12O6 thorn 6O2

74

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The flavanols are also referred to as catechins This expression is derived from catechu thename of the extract of Acacia catechu L Fabaceae found in Asia (Kutch district in India) and the

catechins are the main components present in green tea

Each flavonoid group consists of a large number of specific flavonoids which differ in the

number and position of substitution by hydroxylation hydrogenation methylation glyco-

sylation malonylation and sulfation ( Andersen and Markham 2006)

FLAVANOLS

Flavanols may be synthesized via leucoanthocyanidins (flavan-34-diols) by the enzyme

leucoanthocyanidin reductase (LAR) or from anthocyanidins by the enzyme anthocyanidin

reductase (ANR) (Figure 63) LAR removes the 4-hydroxyl from leucoanthocyanidins to formthe 23-trans-flavan-3-ols and ANR converts anthocyanidins forming the 23-cis-flavan-3-ols

LAR and ANR are enzymes belonging to the single-domain-reductaseepimerase

dehydrogenase (RED) protein superfamily ( Andersen and Markham 2006)

Both gallic acid and flavanols are considered as tannins Tannins are larger molecules

consisting of polymerized flavonoids (MacAdam 2009) The most well-known property of

tannins is their ability to bind to protein by their phenolic groups These phenolic groups are

associated with the o-dihydroxy and o-trihydroxy positions in the phenyl ring ( Andersen and

Markham 2006) Two categories of tannins are recognized hydrolysable tannins andcondensed tannins The two types of hydrolysable tannins are gallitannins and ellagitannins

The basic structural unit of hydrolysable tannins is a sugar with its hydroxyl groups esterified to

gallic acid gallo tannins and elligi tannins Condensed tannins are polymers of flavonoid unitslinked together by carbonecarbon bonds These are also called catechin tannins (ie catechin

without gallate) The most common forms of flavonoids found in plants are the glycoside

derivatives except for the flavanols which occur without sugar molecules ie only as aglycones

and this is unique for flavonoids When treated with acids or enzymes condensed tannins are

C A

B

O

O

O

O

O

O

OH

O

O

O+

OH

O

OH

O

O

O

OH

OH OH

OH

Chalcone

FlavoneFlavanone

Isoflavone

FlavonolFlavanol

Anthocyanidin

Stilbene

Aurone

Apiforol

FIGURE 62Chemical Structures of the Main Classes of Flavonoids and Flavonoid-Related Substances

CHAPTER

Tea Flavanols An Overview

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converted to red compounds phlobaphenes also referred to as phlobatannins or catecholtannins (Evans 2009) The condensed tannins are also named procyanidins Procyanidins are

dimers trimers oligomers or polymers of catechins (flavanols) and are common substances

eg in cacao

Catechins ie catechin gallocatechin catechin-3-gallate gallocatechin-3-gallate are intrans configuration (3S) of which (thorn)-catechin is the most common Epicatechins

ie epicatechin epicatechin gallate epigallocatechin and epigallocatechin gallate are in cis

configuration (3R) of which ()-epicatecin is the most common (Figure 64)

()-Epicatechin ()-epicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate (Figure 64) are the four main flavanols in green tea (Persson et al 2006)

Furthermore tea contains gallic acid ()-gallocatechin ()-epicatechin-3-gallate()-catechin-3-gallate ()-gallocatechin-3-gallate and nonproanthocyanins with flavan or

flavan-3-ol constituent units theogallinin theaflavonin desgalloyl theaflavonintheadibenzotropolone A theaflavate A theacitrin A theaflavate B isotheaflavin-3 0-O-gallate

and neotheaflavin-3-O-gallate

TEA

Fresh leaves of Camellia sinensis L (Theaceae) are used to produce white tea the buds and

young leaves are dried in sunlight and lightly oxidized Yellow tea is produced by letting green

Photosynthesis

Monosaccharides

Pyruvic acid

Malonic acid (Malonyl CoA)

Polysaccharides

Acetic acid (Acetyl CoA)

Polyketides

Fats

Fattyacids

Mevalonic acid

Terpenes and Sterols

Shikimic acid

Chorismic acid

Phenylalanine

Cinnamic acid

Coumaric acid

Stilbene

Deoxychalcone

Aurone

Chalcone

Flavanone

Apiforol

Deoxyanthocyanidin

Dihydroflavanol

Leucoanthocyanidin

Dimers Trimers Mixed polymers

Flavanol

Anthocyanidins

Epi-Flavanol

Flavone

Isoflavone

Flavonol

Tetrahydroxyisoflavone

Flavan-34-diol

Deoxyflavonoid

ANR ANS ANS

ANS

FLS

CHS

CHI

F3H

DFR LAR

FNR

2HIS

IFR

FNSI

FNSII

FIGURE 63Overview of the Biosynthesis of Flavonoids Enzymes involved in the biosynthesis of the flavonoids are marked in the figure Anthocyanidin reductase (ANR)

Anthocyanidin synthase (ANS) Chalcone isomerase (CHI) Chalcone synthase (CHS) Dihydroflavonol 4-reductase (DFR) Flavanone 3b-hydroxylase (F3H)

Flavonol synthase (FLS) Flavone synthase I (FNSI) Flavone synthase II (FNSII) Flavanone 4-reductase (FNR) Isoflavone reductase (IFR) Leucoanthocyanidin

reductase (LAR) and 2-Hydroxyisoflavanone synthase (2HIS)

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tea lightly dry before heating Green tea is fresh leaves that have been heated or steamed to

prevent oxidation and black teas are fermented green teas

The flavanols foundin green tea are stableas long as the plantcell is intact In producing blacktea

thegreenleavesof Camelliasinensis arefermentedand thefermentationprocessis known to reduce

the content of tea flavanols (Balentine et al 1997) by action of polyphenol oxidases (PPO)

Compared to green tea the catechin content in black tea is reduced by approximately 85(Balentine et al 1997) and transformed into teaflavin-3-30-digallate and tearubigin (Evans

2009) (Figure 65)

Besides the tea plant catechins are also common in cacao Theobroma cacao L (Malvaceae) wine Vitis vinifera L (Vitaceae) and in many fruits and vegetables

Flavonoids in general serve as communicators between the plant and the environment and

the catechins are no exception Catechin is considered as an allelochemical e ie a substance

that is released by the plant to exclude other species from their close area (thorn)-Catechin acts asan antibiotic and ()-catechin acts as a herbicide (MacAdam 2009)

OOH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

O

OH

OH

OH

O

OH

OH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

OH

O

OH

OH

OH

epicatechin

epicatechin gallate

epigallocatechin

epigallocatechin gallate

FIGURE 64

Chemical Structure of the Four main Flavanols in Tea ( thorn)-catechin ( )-epicatechin ( )-epigallocatechin and ( )-epigallocatechin-3-gallate

Theaflavins

HO

OH

OR

OH

OH

O

OHOR

OH

HO

HO

OH

OR

O

OHOR

OH

HO

COOH

COOH

Thearubigin R = galloyl group

FIGURE 65

Chemical Structure of Tea1047298avins and Tearubigin Present

in Black Tea

CHAPTER

Tea Flavanols An Overview

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WHY ARE THERE FLAVANOLS IN CAMELLIA SINENSIS AND NOTIN ASPALATHUS LINEARIS

Other flavonoids present in Camellia sinensis except catechins are the flavonols quercetin

myricetin and kaempferol These flavonols are also present in Aspalathus linearis Dahlg usedto produce rooibos tea As seen in Figure 63 flavonols are synthesized to form catechins but

this synthesis mechanism is not present in Aspalathus linearis As stated in the Biosynthesissection the reason why some secondary metabolites are formed in some plants but not in

others is not yet known The beneficial properties relating to an intake of green and black teaare related to flavanols and the beneficial properties of rooibos relate to flavonols

SUMMARY POINTS

l Photosynthesis is the most important chemical reaction taking place on Earth converting

light energy into chemical energyl In biosynthesis many plants synthesize a variety of organic molecules the so-called

secondary metabolitesl Flavonoids are of mixed origin biosynthesized by the shikimic acid pathway and the

mevalonic acid pathwayl The main classes of flavonoids are chalcones flavanones flavones flavonols isoflavones

anthocyanidins and flavanolsl ()-epicatechin ()eepicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate are the four main flavanols in green teal Compared to green tea the catechin content in black tea is transformed and reduced by

approximately 85

References

Andersen OM Markham KR 2006 Flavonoids Chemistry Biochemistry and Applications Taylor and Francis

Group Boca Raton FL USA

Balentine DA Wiseman SA Bouwens LCM 1997 The chemistry of tea flavonoids Critical Reviews in Food

Science and Nutrition 37 693e704

Evans WC 2009 Trease and Evans Pharmacognosy 16th international edition SaundersElsevier Ltd Edinburgh

Harborne JB Williams CA 2000 Advances in flavonoid research since 1992 Phytochemistry 55 481e504

MacAdam JW 2009 Structure and Function of Plants Wiley-Blackwell Oxford

Persson IA-l Josefsson H Persson K Andersson RGG 2006 Tea flavanols inhibit angiotensin-converting

enzyme activity and increase nitric oxide production in human endothelial cells Journal of Pharmacy and

Pharmacology 58 1139e1144

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The flavanols are also referred to as catechins This expression is derived from catechu thename of the extract of Acacia catechu L Fabaceae found in Asia (Kutch district in India) and the

catechins are the main components present in green tea

Each flavonoid group consists of a large number of specific flavonoids which differ in the

number and position of substitution by hydroxylation hydrogenation methylation glyco-

sylation malonylation and sulfation ( Andersen and Markham 2006)

FLAVANOLS

Flavanols may be synthesized via leucoanthocyanidins (flavan-34-diols) by the enzyme

leucoanthocyanidin reductase (LAR) or from anthocyanidins by the enzyme anthocyanidin

reductase (ANR) (Figure 63) LAR removes the 4-hydroxyl from leucoanthocyanidins to formthe 23-trans-flavan-3-ols and ANR converts anthocyanidins forming the 23-cis-flavan-3-ols

LAR and ANR are enzymes belonging to the single-domain-reductaseepimerase

dehydrogenase (RED) protein superfamily ( Andersen and Markham 2006)

Both gallic acid and flavanols are considered as tannins Tannins are larger molecules

consisting of polymerized flavonoids (MacAdam 2009) The most well-known property of

tannins is their ability to bind to protein by their phenolic groups These phenolic groups are

associated with the o-dihydroxy and o-trihydroxy positions in the phenyl ring ( Andersen and

Markham 2006) Two categories of tannins are recognized hydrolysable tannins andcondensed tannins The two types of hydrolysable tannins are gallitannins and ellagitannins

The basic structural unit of hydrolysable tannins is a sugar with its hydroxyl groups esterified to

gallic acid gallo tannins and elligi tannins Condensed tannins are polymers of flavonoid unitslinked together by carbonecarbon bonds These are also called catechin tannins (ie catechin

without gallate) The most common forms of flavonoids found in plants are the glycoside

derivatives except for the flavanols which occur without sugar molecules ie only as aglycones

and this is unique for flavonoids When treated with acids or enzymes condensed tannins are

C A

B

O

O

O

O

O

O

OH

O

O

O+

OH

O

OH

O

O

O

OH

OH OH

OH

Chalcone

FlavoneFlavanone

Isoflavone

FlavonolFlavanol

Anthocyanidin

Stilbene

Aurone

Apiforol

FIGURE 62Chemical Structures of the Main Classes of Flavonoids and Flavonoid-Related Substances

CHAPTER

Tea Flavanols An Overview

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converted to red compounds phlobaphenes also referred to as phlobatannins or catecholtannins (Evans 2009) The condensed tannins are also named procyanidins Procyanidins are

dimers trimers oligomers or polymers of catechins (flavanols) and are common substances

eg in cacao

Catechins ie catechin gallocatechin catechin-3-gallate gallocatechin-3-gallate are intrans configuration (3S) of which (thorn)-catechin is the most common Epicatechins

ie epicatechin epicatechin gallate epigallocatechin and epigallocatechin gallate are in cis

configuration (3R) of which ()-epicatecin is the most common (Figure 64)

()-Epicatechin ()-epicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate (Figure 64) are the four main flavanols in green tea (Persson et al 2006)

Furthermore tea contains gallic acid ()-gallocatechin ()-epicatechin-3-gallate()-catechin-3-gallate ()-gallocatechin-3-gallate and nonproanthocyanins with flavan or

flavan-3-ol constituent units theogallinin theaflavonin desgalloyl theaflavonintheadibenzotropolone A theaflavate A theacitrin A theaflavate B isotheaflavin-3 0-O-gallate

and neotheaflavin-3-O-gallate

TEA

Fresh leaves of Camellia sinensis L (Theaceae) are used to produce white tea the buds and

young leaves are dried in sunlight and lightly oxidized Yellow tea is produced by letting green

Photosynthesis

Monosaccharides

Pyruvic acid

Malonic acid (Malonyl CoA)

Polysaccharides

Acetic acid (Acetyl CoA)

Polyketides

Fats

Fattyacids

Mevalonic acid

Terpenes and Sterols

Shikimic acid

Chorismic acid

Phenylalanine

Cinnamic acid

Coumaric acid

Stilbene

Deoxychalcone

Aurone

Chalcone

Flavanone

Apiforol

Deoxyanthocyanidin

Dihydroflavanol

Leucoanthocyanidin

Dimers Trimers Mixed polymers

Flavanol

Anthocyanidins

Epi-Flavanol

Flavone

Isoflavone

Flavonol

Tetrahydroxyisoflavone

Flavan-34-diol

Deoxyflavonoid

ANR ANS ANS

ANS

FLS

CHS

CHI

F3H

DFR LAR

FNR

2HIS

IFR

FNSI

FNSII

FIGURE 63Overview of the Biosynthesis of Flavonoids Enzymes involved in the biosynthesis of the flavonoids are marked in the figure Anthocyanidin reductase (ANR)

Anthocyanidin synthase (ANS) Chalcone isomerase (CHI) Chalcone synthase (CHS) Dihydroflavonol 4-reductase (DFR) Flavanone 3b-hydroxylase (F3H)

Flavonol synthase (FLS) Flavone synthase I (FNSI) Flavone synthase II (FNSII) Flavanone 4-reductase (FNR) Isoflavone reductase (IFR) Leucoanthocyanidin

reductase (LAR) and 2-Hydroxyisoflavanone synthase (2HIS)

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tea lightly dry before heating Green tea is fresh leaves that have been heated or steamed to

prevent oxidation and black teas are fermented green teas

The flavanols foundin green tea are stableas long as the plantcell is intact In producing blacktea

thegreenleavesof Camelliasinensis arefermentedand thefermentationprocessis known to reduce

the content of tea flavanols (Balentine et al 1997) by action of polyphenol oxidases (PPO)

Compared to green tea the catechin content in black tea is reduced by approximately 85(Balentine et al 1997) and transformed into teaflavin-3-30-digallate and tearubigin (Evans

2009) (Figure 65)

Besides the tea plant catechins are also common in cacao Theobroma cacao L (Malvaceae) wine Vitis vinifera L (Vitaceae) and in many fruits and vegetables

Flavonoids in general serve as communicators between the plant and the environment and

the catechins are no exception Catechin is considered as an allelochemical e ie a substance

that is released by the plant to exclude other species from their close area (thorn)-Catechin acts asan antibiotic and ()-catechin acts as a herbicide (MacAdam 2009)

OOH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

O

OH

OH

OH

O

OH

OH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

OH

O

OH

OH

OH

epicatechin

epicatechin gallate

epigallocatechin

epigallocatechin gallate

FIGURE 64

Chemical Structure of the Four main Flavanols in Tea ( thorn)-catechin ( )-epicatechin ( )-epigallocatechin and ( )-epigallocatechin-3-gallate

Theaflavins

HO

OH

OR

OH

OH

O

OHOR

OH

HO

HO

OH

OR

O

OHOR

OH

HO

COOH

COOH

Thearubigin R = galloyl group

FIGURE 65

Chemical Structure of Tea1047298avins and Tearubigin Present

in Black Tea

CHAPTER

Tea Flavanols An Overview

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WHY ARE THERE FLAVANOLS IN CAMELLIA SINENSIS AND NOTIN ASPALATHUS LINEARIS

Other flavonoids present in Camellia sinensis except catechins are the flavonols quercetin

myricetin and kaempferol These flavonols are also present in Aspalathus linearis Dahlg usedto produce rooibos tea As seen in Figure 63 flavonols are synthesized to form catechins but

this synthesis mechanism is not present in Aspalathus linearis As stated in the Biosynthesissection the reason why some secondary metabolites are formed in some plants but not in

others is not yet known The beneficial properties relating to an intake of green and black teaare related to flavanols and the beneficial properties of rooibos relate to flavonols

SUMMARY POINTS

l Photosynthesis is the most important chemical reaction taking place on Earth converting

light energy into chemical energyl In biosynthesis many plants synthesize a variety of organic molecules the so-called

secondary metabolitesl Flavonoids are of mixed origin biosynthesized by the shikimic acid pathway and the

mevalonic acid pathwayl The main classes of flavonoids are chalcones flavanones flavones flavonols isoflavones

anthocyanidins and flavanolsl ()-epicatechin ()eepicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate are the four main flavanols in green teal Compared to green tea the catechin content in black tea is transformed and reduced by

approximately 85

References

Andersen OM Markham KR 2006 Flavonoids Chemistry Biochemistry and Applications Taylor and Francis

Group Boca Raton FL USA

Balentine DA Wiseman SA Bouwens LCM 1997 The chemistry of tea flavonoids Critical Reviews in Food

Science and Nutrition 37 693e704

Evans WC 2009 Trease and Evans Pharmacognosy 16th international edition SaundersElsevier Ltd Edinburgh

Harborne JB Williams CA 2000 Advances in flavonoid research since 1992 Phytochemistry 55 481e504

MacAdam JW 2009 Structure and Function of Plants Wiley-Blackwell Oxford

Persson IA-l Josefsson H Persson K Andersson RGG 2006 Tea flavanols inhibit angiotensin-converting

enzyme activity and increase nitric oxide production in human endothelial cells Journal of Pharmacy and

Pharmacology 58 1139e1144

SECTION 1

Tea Tea Drinking and Varieties

78

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converted to red compounds phlobaphenes also referred to as phlobatannins or catecholtannins (Evans 2009) The condensed tannins are also named procyanidins Procyanidins are

dimers trimers oligomers or polymers of catechins (flavanols) and are common substances

eg in cacao

Catechins ie catechin gallocatechin catechin-3-gallate gallocatechin-3-gallate are intrans configuration (3S) of which (thorn)-catechin is the most common Epicatechins

ie epicatechin epicatechin gallate epigallocatechin and epigallocatechin gallate are in cis

configuration (3R) of which ()-epicatecin is the most common (Figure 64)

()-Epicatechin ()-epicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate (Figure 64) are the four main flavanols in green tea (Persson et al 2006)

Furthermore tea contains gallic acid ()-gallocatechin ()-epicatechin-3-gallate()-catechin-3-gallate ()-gallocatechin-3-gallate and nonproanthocyanins with flavan or

flavan-3-ol constituent units theogallinin theaflavonin desgalloyl theaflavonintheadibenzotropolone A theaflavate A theacitrin A theaflavate B isotheaflavin-3 0-O-gallate

and neotheaflavin-3-O-gallate

TEA

Fresh leaves of Camellia sinensis L (Theaceae) are used to produce white tea the buds and

young leaves are dried in sunlight and lightly oxidized Yellow tea is produced by letting green

Photosynthesis

Monosaccharides

Pyruvic acid

Malonic acid (Malonyl CoA)

Polysaccharides

Acetic acid (Acetyl CoA)

Polyketides

Fats

Fattyacids

Mevalonic acid

Terpenes and Sterols

Shikimic acid

Chorismic acid

Phenylalanine

Cinnamic acid

Coumaric acid

Stilbene

Deoxychalcone

Aurone

Chalcone

Flavanone

Apiforol

Deoxyanthocyanidin

Dihydroflavanol

Leucoanthocyanidin

Dimers Trimers Mixed polymers

Flavanol

Anthocyanidins

Epi-Flavanol

Flavone

Isoflavone

Flavonol

Tetrahydroxyisoflavone

Flavan-34-diol

Deoxyflavonoid

ANR ANS ANS

ANS

FLS

CHS

CHI

F3H

DFR LAR

FNR

2HIS

IFR

FNSI

FNSII

FIGURE 63Overview of the Biosynthesis of Flavonoids Enzymes involved in the biosynthesis of the flavonoids are marked in the figure Anthocyanidin reductase (ANR)

Anthocyanidin synthase (ANS) Chalcone isomerase (CHI) Chalcone synthase (CHS) Dihydroflavonol 4-reductase (DFR) Flavanone 3b-hydroxylase (F3H)

Flavonol synthase (FLS) Flavone synthase I (FNSI) Flavone synthase II (FNSII) Flavanone 4-reductase (FNR) Isoflavone reductase (IFR) Leucoanthocyanidin

reductase (LAR) and 2-Hydroxyisoflavanone synthase (2HIS)

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tea lightly dry before heating Green tea is fresh leaves that have been heated or steamed to

prevent oxidation and black teas are fermented green teas

The flavanols foundin green tea are stableas long as the plantcell is intact In producing blacktea

thegreenleavesof Camelliasinensis arefermentedand thefermentationprocessis known to reduce

the content of tea flavanols (Balentine et al 1997) by action of polyphenol oxidases (PPO)

Compared to green tea the catechin content in black tea is reduced by approximately 85(Balentine et al 1997) and transformed into teaflavin-3-30-digallate and tearubigin (Evans

2009) (Figure 65)

Besides the tea plant catechins are also common in cacao Theobroma cacao L (Malvaceae) wine Vitis vinifera L (Vitaceae) and in many fruits and vegetables

Flavonoids in general serve as communicators between the plant and the environment and

the catechins are no exception Catechin is considered as an allelochemical e ie a substance

that is released by the plant to exclude other species from their close area (thorn)-Catechin acts asan antibiotic and ()-catechin acts as a herbicide (MacAdam 2009)

OOH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

O

OH

OH

OH

O

OH

OH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

OH

O

OH

OH

OH

epicatechin

epicatechin gallate

epigallocatechin

epigallocatechin gallate

FIGURE 64

Chemical Structure of the Four main Flavanols in Tea ( thorn)-catechin ( )-epicatechin ( )-epigallocatechin and ( )-epigallocatechin-3-gallate

Theaflavins

HO

OH

OR

OH

OH

O

OHOR

OH

HO

HO

OH

OR

O

OHOR

OH

HO

COOH

COOH

Thearubigin R = galloyl group

FIGURE 65

Chemical Structure of Tea1047298avins and Tearubigin Present

in Black Tea

CHAPTER

Tea Flavanols An Overview

8162019 3-s20-B9780123849373000069-ch6_flavonepdf

httpslidepdfcomreaderfull3-s20-b9780123849373000069-ch6flavonepdf 66

WHY ARE THERE FLAVANOLS IN CAMELLIA SINENSIS AND NOTIN ASPALATHUS LINEARIS

Other flavonoids present in Camellia sinensis except catechins are the flavonols quercetin

myricetin and kaempferol These flavonols are also present in Aspalathus linearis Dahlg usedto produce rooibos tea As seen in Figure 63 flavonols are synthesized to form catechins but

this synthesis mechanism is not present in Aspalathus linearis As stated in the Biosynthesissection the reason why some secondary metabolites are formed in some plants but not in

others is not yet known The beneficial properties relating to an intake of green and black teaare related to flavanols and the beneficial properties of rooibos relate to flavonols

SUMMARY POINTS

l Photosynthesis is the most important chemical reaction taking place on Earth converting

light energy into chemical energyl In biosynthesis many plants synthesize a variety of organic molecules the so-called

secondary metabolitesl Flavonoids are of mixed origin biosynthesized by the shikimic acid pathway and the

mevalonic acid pathwayl The main classes of flavonoids are chalcones flavanones flavones flavonols isoflavones

anthocyanidins and flavanolsl ()-epicatechin ()eepicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate are the four main flavanols in green teal Compared to green tea the catechin content in black tea is transformed and reduced by

approximately 85

References

Andersen OM Markham KR 2006 Flavonoids Chemistry Biochemistry and Applications Taylor and Francis

Group Boca Raton FL USA

Balentine DA Wiseman SA Bouwens LCM 1997 The chemistry of tea flavonoids Critical Reviews in Food

Science and Nutrition 37 693e704

Evans WC 2009 Trease and Evans Pharmacognosy 16th international edition SaundersElsevier Ltd Edinburgh

Harborne JB Williams CA 2000 Advances in flavonoid research since 1992 Phytochemistry 55 481e504

MacAdam JW 2009 Structure and Function of Plants Wiley-Blackwell Oxford

Persson IA-l Josefsson H Persson K Andersson RGG 2006 Tea flavanols inhibit angiotensin-converting

enzyme activity and increase nitric oxide production in human endothelial cells Journal of Pharmacy and

Pharmacology 58 1139e1144

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Tea Tea Drinking and Varieties

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8162019 3-s20-B9780123849373000069-ch6_flavonepdf

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tea lightly dry before heating Green tea is fresh leaves that have been heated or steamed to

prevent oxidation and black teas are fermented green teas

The flavanols foundin green tea are stableas long as the plantcell is intact In producing blacktea

thegreenleavesof Camelliasinensis arefermentedand thefermentationprocessis known to reduce

the content of tea flavanols (Balentine et al 1997) by action of polyphenol oxidases (PPO)

Compared to green tea the catechin content in black tea is reduced by approximately 85(Balentine et al 1997) and transformed into teaflavin-3-30-digallate and tearubigin (Evans

2009) (Figure 65)

Besides the tea plant catechins are also common in cacao Theobroma cacao L (Malvaceae) wine Vitis vinifera L (Vitaceae) and in many fruits and vegetables

Flavonoids in general serve as communicators between the plant and the environment and

the catechins are no exception Catechin is considered as an allelochemical e ie a substance

that is released by the plant to exclude other species from their close area (thorn)-Catechin acts asan antibiotic and ()-catechin acts as a herbicide (MacAdam 2009)

OOH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

O

OH

OH

OH

O

OH

OH

OH

OH

OH

OH

O

O

OH

OH

OH

OH

OH

O

OH

OH

OH

epicatechin

epicatechin gallate

epigallocatechin

epigallocatechin gallate

FIGURE 64

Chemical Structure of the Four main Flavanols in Tea ( thorn)-catechin ( )-epicatechin ( )-epigallocatechin and ( )-epigallocatechin-3-gallate

Theaflavins

HO

OH

OR

OH

OH

O

OHOR

OH

HO

HO

OH

OR

O

OHOR

OH

HO

COOH

COOH

Thearubigin R = galloyl group

FIGURE 65

Chemical Structure of Tea1047298avins and Tearubigin Present

in Black Tea

CHAPTER

Tea Flavanols An Overview

8162019 3-s20-B9780123849373000069-ch6_flavonepdf

httpslidepdfcomreaderfull3-s20-b9780123849373000069-ch6flavonepdf 66

WHY ARE THERE FLAVANOLS IN CAMELLIA SINENSIS AND NOTIN ASPALATHUS LINEARIS

Other flavonoids present in Camellia sinensis except catechins are the flavonols quercetin

myricetin and kaempferol These flavonols are also present in Aspalathus linearis Dahlg usedto produce rooibos tea As seen in Figure 63 flavonols are synthesized to form catechins but

this synthesis mechanism is not present in Aspalathus linearis As stated in the Biosynthesissection the reason why some secondary metabolites are formed in some plants but not in

others is not yet known The beneficial properties relating to an intake of green and black teaare related to flavanols and the beneficial properties of rooibos relate to flavonols

SUMMARY POINTS

l Photosynthesis is the most important chemical reaction taking place on Earth converting

light energy into chemical energyl In biosynthesis many plants synthesize a variety of organic molecules the so-called

secondary metabolitesl Flavonoids are of mixed origin biosynthesized by the shikimic acid pathway and the

mevalonic acid pathwayl The main classes of flavonoids are chalcones flavanones flavones flavonols isoflavones

anthocyanidins and flavanolsl ()-epicatechin ()eepicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate are the four main flavanols in green teal Compared to green tea the catechin content in black tea is transformed and reduced by

approximately 85

References

Andersen OM Markham KR 2006 Flavonoids Chemistry Biochemistry and Applications Taylor and Francis

Group Boca Raton FL USA

Balentine DA Wiseman SA Bouwens LCM 1997 The chemistry of tea flavonoids Critical Reviews in Food

Science and Nutrition 37 693e704

Evans WC 2009 Trease and Evans Pharmacognosy 16th international edition SaundersElsevier Ltd Edinburgh

Harborne JB Williams CA 2000 Advances in flavonoid research since 1992 Phytochemistry 55 481e504

MacAdam JW 2009 Structure and Function of Plants Wiley-Blackwell Oxford

Persson IA-l Josefsson H Persson K Andersson RGG 2006 Tea flavanols inhibit angiotensin-converting

enzyme activity and increase nitric oxide production in human endothelial cells Journal of Pharmacy and

Pharmacology 58 1139e1144

SECTION 1

Tea Tea Drinking and Varieties

78

8162019 3-s20-B9780123849373000069-ch6_flavonepdf

httpslidepdfcomreaderfull3-s20-b9780123849373000069-ch6flavonepdf 66

WHY ARE THERE FLAVANOLS IN CAMELLIA SINENSIS AND NOTIN ASPALATHUS LINEARIS

Other flavonoids present in Camellia sinensis except catechins are the flavonols quercetin

myricetin and kaempferol These flavonols are also present in Aspalathus linearis Dahlg usedto produce rooibos tea As seen in Figure 63 flavonols are synthesized to form catechins but

this synthesis mechanism is not present in Aspalathus linearis As stated in the Biosynthesissection the reason why some secondary metabolites are formed in some plants but not in

others is not yet known The beneficial properties relating to an intake of green and black teaare related to flavanols and the beneficial properties of rooibos relate to flavonols

SUMMARY POINTS

l Photosynthesis is the most important chemical reaction taking place on Earth converting

light energy into chemical energyl In biosynthesis many plants synthesize a variety of organic molecules the so-called

secondary metabolitesl Flavonoids are of mixed origin biosynthesized by the shikimic acid pathway and the

mevalonic acid pathwayl The main classes of flavonoids are chalcones flavanones flavones flavonols isoflavones

anthocyanidins and flavanolsl ()-epicatechin ()eepicatechin gallate ()-epigallocatechin and ()-epigallocatechin

gallate are the four main flavanols in green teal Compared to green tea the catechin content in black tea is transformed and reduced by

approximately 85

References

Andersen OM Markham KR 2006 Flavonoids Chemistry Biochemistry and Applications Taylor and Francis

Group Boca Raton FL USA

Balentine DA Wiseman SA Bouwens LCM 1997 The chemistry of tea flavonoids Critical Reviews in Food

Science and Nutrition 37 693e704

Evans WC 2009 Trease and Evans Pharmacognosy 16th international edition SaundersElsevier Ltd Edinburgh

Harborne JB Williams CA 2000 Advances in flavonoid research since 1992 Phytochemistry 55 481e504

MacAdam JW 2009 Structure and Function of Plants Wiley-Blackwell Oxford

Persson IA-l Josefsson H Persson K Andersson RGG 2006 Tea flavanols inhibit angiotensin-converting

enzyme activity and increase nitric oxide production in human endothelial cells Journal of Pharmacy and

Pharmacology 58 1139e1144

SECTION 1

Tea Tea Drinking and Varieties

78