Chemical Components of Tea: The Leaf, Processing, and Health



Author Book Title
 Parliament Ho and Schieberle Caffeinated Beverages
Content Notes Page number
The chemistry of tea ·      Tea leaf contains carbohydrates, proteins, lipids, full complement of genetic material, enzymes, secondary metabolites, high content of methylxanthins and polyphenols, in particular Catechins (flavanols).

·      25% of dry weight is Catechins

·      3.0% flavonols and flavonol glycosides

·      3.0% are caffeine and 0.2% are theobromine

·      “Fermentation” is tea processing simply referring to an enzymatic browning reaction catalyzed by the polyphenol oxidase.

·      The major chemical reaction during tea manufacturing is the oxidative conversion and polymerization of Catechins. The oxidative fermentation of Catechins in tea results in the development of appropriate flavor and color of oolong and black teas.

·      Darkening of the leaf and decrease in astringency.

·      The initial step of fermentation is the oxidation of Catechins to reactive quinones catalyzed by polyphenol oxidase.

·      Polyphenol oxidase can use any of the Catechins as a substrate to form the complex polyphenol constituents found in oolong and black teas.

·      The Major condensation compounds are theaflavins and thearubigins.

·      Other products: theaflagallins, theaflavic acids, theasinensisn, oolongtheanin, theaflavate

·      The oxidation pathways of tea Catechins during the fermentation can be divided into pyrogallocatechol condensation and pyrogallo-pyrogallol condensation.

·      Theaflavins give the characteristic bright orange red color of black yea

·      Account for 1-2% dry weight of the water extractable.

·      Theaflavins consist of

1.     Theaflavin (TF)

2.     Theaflavins-3’-gallate (TF3G)

3.     Theaflavins-3,3’digallate TF3’G)

4.     Theaflavin-3,-3’digallate (TFDG)

v Which are formed by the pair oxidation of Catechins

·      EC+EGC>TF

·      EC+ EGCG>TF3G

·      ECG_EGC>TF3’G


Thearubigens ·      10-20% of dry weight in black tea

·      Major oxidation product of Catechins during fermentation however due to the difficulty encountered in their separation the chemistry is poorly characterized.

Theasinensins and Oolongtheanin formation ·      Theasinensin are compounds formed by the coupling of quinone with catechol or pyrogallol ring of the flavan -3-ol derivatives. Seven theasinensins have been isolated and identified from oolong tea.

·      Oolongtheanin is a second condensation product of catechin. It has a two fused furan ring structure.

Author Book Title
 Zumdahl Chemistry Zumdahl 6th edition


Content Notes Page number
Anti-oxidant ·      Many scientists think oxidation plays a major role in aging.

·      Oxygen molecule and other oxidizing agents in the body apparently can extract single electrons from the large molecules that make up cell membranes, thus making them reactive.

·      The activated molecules can link up changing the properties of the cell membrane. At some point enough of these reactions have occurred that the body’s immune system comes to view the changed cell as an enemy and destroys it.

·      People are affected when the cells are irreplaceable. Nerve cells for example can rarely be regenerated in an adult.

·      Antioxidants benefit the body by neutralizing and removing the free radicals from the blood stream.
Author Book Title
Kevin Gascoyne, Grancois Marchand, JAsmin Desharnais and Humo Americi Tea:History, Terroirs, Varities
In orthodox processing ·      With conventional rolling as much as one quarter of the oxidizable Catechins may remain unchanged, but with more vigorous leaf distortion methods such as Legg-cut, CTC or rotovane, all the oxidizable catechins may be changed.
Tea characters ·      Quality, aroma, flavor, briskness, strength, and color.
Quality ·      Appearance, strength, aroma, quality, character of infused leaf.

·      Trade: quality is used to describe the presence of a special desirable character in the liqueur.

·      Sensation in the mouth or aroma

Aroma ·      Freshly plucked leaf has a spicy acrid smell as of resin, ginger root, or balsam

·      Withered leaf has the smell of apples,

·      Rolling/ pears which fades after which the acrid smell of green leaf returns.

·      Drying leaf takes on a caramel smell or burnt sugar

·      Substances that are the components of the aroma are volatile compounds

Flavor ·      Workers from the Tea Research Institute of Cylon found that among the numerous amino acids in fresh, fermented leaf and dry tea larger quantities of Leucine and isoleucine are produced from proteins by enzymatic action in the leaf grown under warm conditions than in teas drown in cool climates.
In Japan ·      Gas chromatography. The quantity of constitutes which contribute to tea flabor amounts to only 0.017% in black tea.

·      Constituents consist of more than 80 components

·      No less than 135 compounds may be held responsible for quality and flavor.

Caffeine ·      Alkaloidal stimulant increases during stoage of the plucked leaf and during withering. The bitter taste of tea infusion is often thought to be caused by caffeine.

·      Caffeine has only a slight bitter taste, but it gives a drink the refreshing and stimulating character.

Chlorophyll ·      Is transformed during fermentation as is clearly shown by the color change from green to coppery red.

·      Chlorophyll was found to transform into a black compound phaeophytin, which developed after removal of magnesium under the acid conditions of tea processing.

·      Some is changed into chlorophyllide by the enzyme chlorophyllase.

·      Chloropyllide in turn is changed to a brown compound, phaeophorbide, by removal of magnesium.

·      The intensity of black tea is from the amount of chlorophyll in the fresh leaf.

·      By severe leaf distortion processes more chlorophyllase is brought into contact with the substrate resulting in browness of the made tea.

Other constituents ·      Potassium

·      Aluminium and manganese

·      Copper zinc sulpur

·      Pectins

v There is evidence that the resultant pectic acid jelly by forming a coating onto the macerated and fermented leaf, inhibits to some extent the progress of polyphenol ozidation and prevents over fermentation.

v Pectic acid forms a kind of varnish on the outside of the leaf during the early stages of drying.

Enzymes ·      A number of enzymes are operative during tea processing.

·      After the shoots have been detached from the bush the different systems of enzymes start to reach with the corresponding substrate

·      Some of the reactions can only proceed vigorously when an intimate mixture of enzymes and substrates takes place as occurs in the oxidation of the polyphenols after rolling or other forms of leaf distortion.

·      Enzyme activity ceases only when they are denatured by heating

·      Enzyme activity varies with season

·      Oxidase is generally higher in periods of dry weather

·      The breakdown of proteins and pectins already mentioned are also enzymatic transformations

·      Brought on by protease and pectase, respectively

·      Other reactions in which enzymes lay a role are changes in caffeine, amino acids, and phosphates, and development of aroma and breakdown of chlorophyll

Changes During Drying


– Epimerization.

·      Drying reduces moisture content from 60% to 3-4%

·      Almost completely inactivates the polyphenol oxidase

·      Oxidation doesn’t stop immediately once it is in the drying process

·      While temperature rises there is a possibility of an acceleration in oxidation in the initial stages before the enzyme is nearly completely inactivated.

·      The oxidation of the Catechins has practically ceased already although in orthodox manufacture an appreciable proportion remains unoxidized.

·      Sugars are caramelized and that some of the uncahged Catechins in the leaf are altered in structure in a slow process called epimerization.

·      Pectase is assumed that it produces the already mentioned varnish from pectins when the leaf dries.

·      As leaf temperature rises during the drying process the pectase is destroyed.

Ortho-quinones have distinct antiseptic properties and by their action the rolled leaf is largely rendered free from bacteria and fungi. ·      Drying also kills off other organisms which may be collected from stale juice during rolling and processing are destroyed during drying.
Changes after drying ·      Post drying “fermentation”

·      Residual enzymatic activity and improves during the first 2-3 weeks or more

·      Changes in TF’s and TR’s in dried tea were observed.

·      Still unknown how much the enzymatic action and chemical activity are involved in the process of post-fermentation and maturing.

·      Dried tea is a hygroscopic body and readily absorbs moisture from the air, the moisture contents higher than about 6% the tea deteriorates more or less at higher temps.

·      Change is associated with the breakdown of theaflavins and the production of carbon dioxide.

Polyphenol oxidase activity ·      High activity indicates good fermentation while low activity leaf although rich in polyphenols may not produce a satisfactory level of Tf and TR
Plucking ·      7-10 day intervals

·      not too many shoots left from the previous round are plucked in an overgrown stage. Not too few shoots have developed

·      plucking is for high quality tea

·      flush shoots of two leaves and a bud obtained by fine plucking are the best basic material.

·      Pecco (bud) shoots and dormant (banjhi) shoots

Buds and first leaf ·      Richest sources of polyphenols and caffeine, leaves lower down and the stems are proportionally poorer in constituents.

·      The standard of plucking clearly has a great effect on the physical and chemical composition of the leaf and thus on the quality of the made tea.

Coarse plucking vs. fine plucking ·      The amount of tea harvested with course plucking is canceled out by the reduction of quality in the tea.
Damage during and after plucking ·      Workers stuffing the leaves into the basket because they’re being paid by weight

·      A paying system baed on both quatity and quality of the plucked leaf is recommendable

Author Book Title
 Astrid Nehlig Coffee, Tea, Chocolate, and The Brain


Content Notes Page number
Mechanisms of Action of Caffeine on The Nervous System ·      Major pharmacologically active methylxanthine

·      Paraxanthine is a major metabolite of caffeine in humans

·      Theophylline is a minor metabolite

·      Not only caffeine but also the other natural methylxanthines are relevant to effects in humans.

·      In animal models caffeine theophylline and paraxanthine are all behavioral stimulants.

·      Effects of theobromine are weaker

·      Caffeine, theophylline and theobromine have been or are used as adjuncts or agents in medical formulations.

·      They have been used as cardiac stimulants, diuretics, and to treat bronchial asthma.

·      Other therapeutic targets for caffeine include diabetes, parkinsonism, and even cancer

·      Antagonist of andenosine receptors: caffeine, theophylline, and theobromine.


Three major mechanisms must be considered with respect to the actions of caffeine on the peripheral and central nervous system 1.     Blockage of adenosine receptors in particular A1- and A2A-adenosine receptors

2.     Blockade of phosphodiesterases, regulating levels of cyclic nucleotides

3.     Action on ion channels, in particular those regulating intracellular levels of calcium and those regulated by the inhibitory neurotransmitters aminobutyric acid (GABA) and glycine.

·      Caffeine’s effects come in two phases (biphasic)

·      Stimulatory behavioral effects in humans and rodents manifest with plasma levels of 5-20 uM, where as higher doses are depressants

·      The only sites of action where caffeine woul be expected to have a major pharmacological effect at levels of 5-20 uM are the A1 and the A2A adenosine recpetors where caffeine is a competitive antagonist

Andenosine ·
·      The available evidence suggests that most of the effects of caffeine are best explained by blockage of tonic adenosine activation of A1 and A2A receptors.

·      Andenosine A1 receptors are found all over the brain and spinal cord; levels are particularly high in the hippocampus, cortex, and cerebellum

·      A2A receptors have a much more restricted distribution being present in high amounts only in the dopamine-rich regions of the brain, including the nucleus caudatus putamen, nucleaus

The andenosine receptors play two major roles 1.     The activation of potassium channels leading to hyperpolarization and to decreased rates of neuronal firing

2.     Inhibition of calcium channels leading to decrease neurotransmitter release

·      This leads to inhibition of excitatory neurotransmission

·      Andenosine A2A receptors regulate the function of GABAergic neurons of the basal ganglia.

Caffeine metabolites, therophylline and paraxanthine ·      Are even more potent inhibitors of adenosine receptors than the parent compound

·      The weighted sum of all of them must be considered when evaluating the effective concentration of antagonist at the adenosine receptors.

·      Tests done on mice have shown that the stimulating effects of caffeine are due to the blockade of striatal A2A recpetors.

Other effects of caffeine ·      Caffeine elicits the release of epinephrine (adrenaline) 6


Content Notes Page number
Caffeine on Sleep and Wakefulness: An Update ·      Sleep is a part of a 24 hour endogenous arousal cycle with its peak in the afternoon (post lunch dip of arousal, and its decline around 3:00 AM and a low shortly after noon.

·      The behavioral manifestation of the circadian arousal cycle, which has to do with the underlying endogenous variations of adenosine and its metabolites is expressed as sleep and wakefulness.

·      Andenosine can be seen as a sleep-inducing factor, its concentration is higher during wakefulness than during sleep. It accumulates in the brain during prolonged wakefulness and local perfusions as well as systemic administration of adenosine and its agonists induce sleep and decrease wakefulness

·      Adenosine receptor antagonist’s caffeine and theophylline are widely used as stimulants of the central nervous system to induce vigilance and increase time spent awake.

·      Caffeine is an antidote of sleep by its ability to occupy the adenosine receptors in the brain.

Sleep cycle ·      Stages 1 and 2 together form light sleep

·      Stage 2 is the transition from the period of falling asleep to deep sleep

·      Ranging from stage 1-stage 4 to rapid eye movement (REM)

·      Stage three and four represent deep sleep or slow-wave sleep (SWS)

·      When stage 4 is reached there is a quick return to via stages 3,2,1 and to a NREM-sleep

·      REM-sleep shows irregular heart and respiration rate, relaxed muscles, higher threshold to awaken, relatively easy reporting of detailed dreams

·      First half of night NREM-sleep and SWS are found.

·      Second half REM and light sleep are found

·      Period needed to change from NREM to REM is called a sleep cycle

·      Sleep is a biological rhythm largely determined by endogenous physiolocial factors with a free running length of 25 h. There are artificial factors which effect this cycle when people are exposed to demands of the 24-h economy.


Caffeine withdrawal effects ·      Starts on average after 12-24 hours of abstinence and has a peak between 20-48 h

·      Symptoms can include headaches, irritation, lethargy, anxiety, etc.

·      Can start after relatively short-term exposure

·      6-15 doses of 600 mg

Tea may protect from brain areas from stroke/ compared with coffee and stroke ·      Oolong tea is prepared by firing the leaves shortly after rolling to terminate the oxidation and dry the leaves.

·      Green Tea Catechins display pharmacological properties such as anti-carcinogenic activity

Tea and Ischemia ·      Ischemia, the mode of neuronal death is considered to be a continuum between apoptosis and necrosis: ischemic neurons appear cytologically necrotic while exhibiting some biochemical features of apoptosis.

·      Ischemia- induced cell death is active, energy dependent, and the result of a cascade of detrimental events hat include disturbance of calcium homeostasis leading to increased excitotoxiicity, dysfunction of the endoplasmic reticulum and mitochondria, elevation of oxidative stress causing DNA damage, lipid peroxidation, alteration of gene expression, and activation of caspases and endonucleases leading to the final degradation of the genome

Mechanisms of tea-induced protection against ischemia ·      Epidemiological studies suggest that the consumption of tea polyphenols (also called flavonoids) may be associated with reduced risk of coronary heart disease, stroke, and cancer-related deaths.

·      Tea polyphenols are rapidly absorbed into the ciruculation following oral ingestion and are found predominantly after a single administration in the plasma, colon, small intestine, liver, lungs, pancreas, mammary glands, and skin, brain, kidneys, and reproductive organs.

·      Second admin of polyphenol (EGCG) (-)Epigallocatechin-3-gallate

·      Enhances tissue levels in blood, brain, liver, pancreas, bladder, and bones four to six times above those observed after a single administration.

·      This study suggests that daily consumption of tea enables the body to maintain a high organic level of tea polyphenols

·      The antioxidant potential of black tea appears to be negated when consumed with milk

·      Tea polyphenols inhibit the liver enzyme xanthine oxidase which produces reactive oxygen species, and thus act at a early level in the oxidative cascade by inhibiting production rather than only neutralizing already formed reactive oxygen species.

·      Reactive oxygen are largely involved in the pathogenesis of ischemia/reperfusion brain injury.

·      The reactive oxygen species lead to oxidative damage to lipids and DNA. Oxygen radicals, eicosanoids that result from the metabolism of arachidonic acid by lipoxygenase and cyclooxygenase, thromboxane A2, and malondialdehyde are all considered mediators of ischemia/re[erfusion-induced brain injury by altering membrane permeability, inducing brain edema and ultimately leading to neuronal death.

·      Chronic treatment with green tea prior to the ischemic insult or the acute administration of the tea polyphenol EGCG reduces the production of the damaging compounds cited above.

·      The mechanisms underlying these effects are unknown

·      Green tea extracts reduce the activites of the enxymes phospholipase A2 and cyclooxygenase in rat platelets that lead to the enhanced synthesise of eicosanoids.


Astrid, Nehlig. Coffee, Tea, Chocolate, and The Brain. CRC Press, 2004.

Caffinated Beverages, n.d.

Gascoyne, Francois Marchand, Jasmin Desharnais, and Hugo Americi. Tea History Terroirs Varieties. A Firefly Book, 2011.

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