brief information about Tea and its chemistry

1. Tea Chemistry
By- Ram Deshmukh

2. Introduction
Tea refers to:
– the plant Camellia sinensis (Thea sinensis)
– the dried, processed leaf manufactured from it
– extracts derived from the leaf, and
– the beverages prepared from the leaf or extract of the species
Originated in Southeast Asia in an area that includes China and India, and
probably Myanmar, Laos and Vietnam

3. Tea varieties
Two major varieties of Camellia sinensis are
recognized:
→ Chinese variety (sinensis) a smaller-leaved (5-12 cm) plant
→ Assam variety (assamica) a large-leaved (15-20 cm) plant

4. Cont…..
The first harvest is obtained after 4-5 years
The shrub can be used for 60-70 years
Harvesting season depends upon the region and climate and lasts for 8-9
months per year or leaves can be plucked at intervals of 6-9 days all year
round
The younger the plucked leaves, the better the tea quality
The white-haired bud and the two adjacent youngest leaves are plucked
(famous “two-leaves and bud” formula)

5. Types of tea
The enzymatic oxidation of tea
leaves is referred to as fermentation
If the enzymes are allowed to act,
they turn green leaf black (black tea)
If the enzymes are inactivated by
heat, as in blanching, then the leaf
remains green (green tea)
 Black Tea
 Green Tea
 Yellow Tea
 Red Tea
(Oolong)

6. Manufacture of black tea
Withering
• Reduces
moisture from
about 75-80%
to 55-65%
• Moisture
reduction
converts the
turgid leaf to
a flaccid
material that
is easily
Rolling
• It establishes
proper
conditions for
enzymatic
oxidation of
the flavanols
by
atmospheric
oxygen
Fermentatio
• Conversion of
colourless
catechins to a
complex mixture
of yellow-
orange to red-
brown
substances
Firing
Ends
fermentation
process and
reduce moisture
content to 3%

7. Manufacture of green tea
 In contrast to black tea
manufacture, withering and
fermentation stages are omitted in
green tea processing
Picking
Steaming
(95°C)
Rolling
(75ºC)
Drying (90°C)
Grading
Green Tea

8. Composition of Tea (%, dry weight basis)
Constituent Fresh Tea Black Tea
Black Tea
Brew *
Phenolic compounds 30 5 4.5
Oxidized phenolic
compounds
0 25 15
Protein 15 15 Traces
Amino acids 4 4 3.5
Caffeine 4 4 3.2
Crude fiber 26 26 0
Other carbohydrates 7 7 4
Lipids 7 7 Traces
Pigments
(chlorophyll and
caroteniods)
2 2 Traces
Volatile compounds 0.1 0.1 0.1
Minerals 5 5 4.5
* Brewing for 3 minutes

9. Phenolic Compounds
 Phenolic compounds make up 25–35% of the
dry matter content of young, fresh tea leaves.
 Flavanol compounds are 80% of the phenols
 During fermentation the flavanols are oxidized
enzymatically to compounds which are
responsible for the color and flavor of black tea.
 The reddish-yellow color of black tea extract is
largely due to theaflavins and thearubigins

10. Flavonoid
 Flavonoids (or bioflavonoids) - are a class of plant secondary
metabolites.
 They can be classified into:
 flavonoids, derived from 2-phenylchromen-4-one (2-phenyl-1,4-
benzopyrone) structure (examples: quercetin, rutin).
 isoflavonoids, derived from 3-phenylchromen-4-one (3-phenyl-1,4-
benzopyrone) structure
 neoflavonoids, derived from 4-phenylcoumarine (4-phenyl-1,2-
benzopyrone) structure.
 The three flavonoid classes above are all ketone-containing compounds,
and as such, are flavonoids and flavonols. The terms flavonoid
and bioflavonoid have also been more loosely used to describe non-
ketone polyhydroxy polyphenol compounds which are more specifically
termed flavanoids, flavan-3-ols (or catechins).

11. Flavanol
 Flavan-3-ols (flavanols) are a class of flavonoids – term is mainly
used for non-ketone polyhydroxy polyphenols – Flavanoids
 These compounds include the catechins and the catechin gallates.
Chemical structure of Flavan-3-ol
Epigallocatechin (EGC)
Epicatechin (EC)

12. Catechins are the main phenolic compounds present
in fresh tea leaves:
Catechin
Epicatechin
Epicatechin gallate
Epicatechin digallate
Flavanol
 Flavanols (with an "a") are not to be confused
with flavonol (with an "o"), another class
of flavonoids containing a ketone group.
 Gallocatechin
 Epigallocatechin
 Epigallocatechin gallate
 Epigallocatechin digallate

13. Flavonols
 Flavonols (with an "o") are a class of flavonoids that have the 3-
hydroxyflavone backbone
 Their diversity stems from the different positions the phenolic -
OH groups. They are distinct from flavanols (with an "a", like catechin),
another class of flavonoids.
Backbone of a flavanol

14. Flavonols
Flavone backbone
Quercetin Epicatechin

15. GREEN TEA

16. Black Tea
 During fermentation the flavanols are oxidized
enzymatically to compounds which are responsible for the
color and flavor of black tea.
 The reddish-yellow color of black tea extract is largely due
to theaflavins and thearubigins.
 The astringent taste is caused primarily by flavonol-3-
glycosides.
 The catechins are turned from the monomer structure to
become the dimers that are the theaflavins and the
oligomers that are thearubigins

17. Black Tea
Thearubigins are polymeri
c
polyphenols that are
formed during
the enzymatic oxidationTheaflavin
There are chiefly 3 types of theaflavins
in black tea, namely
 Theaflavin (TF-1),
 Theaflavin-3-gallate (TF-2),
 Theaflavin-3,3-digallate (TF-3).
A number of studies have been done
on their possible health effects with
positive results

18. Enzymes
1) Polyphenol oxidases- located within cell of leaf epidermis &
activity rises during withering & rolling
2) Shikimate dehydrogenase- reversibly interconverts
dehydroshikimase & shikimate via phenylalanine pathway
3) Phenylalanine ammonia lyase- catalyse cleavage of
phnylalanine into ammonia & cinnamate
4) Proteinases – cause protein hydrolysis during withering
resulting in rise of peptides & free amino acids
5) Chlorophyllases participate in the degradation of chlorophyll
and transaminases in the production of precursors for aroma
constituents.

19. Amino acids
 Constitute about 1% of dry matter of tea leaves
 Of this 50% is theanine & rest consists of protein forming amino
acids
 Β- alanine is also present
 Green tea contains more theanine than black tea
5-N-ethyl-glutamine

20. Caffeine
 Constitutes 2.5-5.5% of dry matter of tea leaves – importance in the
taste of tea
 Theobromine ( 0.07-0.17%) & theophylline ( 0.002- 0.013%) are
also present
Caffeine

21. Carbohydrates
 Sugars in tea leaves are:
 Glucose (0.72%)
 Fructose (0.4%)
 Sucrose (0.09%)
 Arabinose
 Ribose
 Rhamnose & galactose are bound to glycosides

22. Lipids
 Level is around 7%
 Polar fraction (glycerophospholipids) in young leaves are predominant
 Glycolipid predominate in older leaves

23. Pigments
 Chlorophyll is degraded during tea processing.
 Chlorophyllides and pheophorbides (brownish in
color) are present in fermented leaves, both
being converted to pheophytines (black) during
the firing step.
 Fourteen carotenoids have been identified in tea
leaves. The main carotenoids are xanthophylls,
neoxanthin, violaxanthin and β-carotene
 The content decreases during the processing of
black tea.

24. Minerals
 Contains 5% minerals
 Major element is potassium ( half of mineral content )
 Copper is a constituent of tea catechol oxidase
 Approx 12-18 ppm of copper is necessary to produce enough catechol
oxidase for fermentation

25. Volatile compounds
 Constitute 0.01-0.02% of tea on dry basis
 Black tea contain more volatile compound than green tea

26. Reactions Involved in the Processing of
TeaWithering
 Enzymatic protein hydrolysis yields amino acids of which a part
is transaminated to the corresponding keto acids.
 Both types of acids provide a precursor pool for aroma
substances
 Chlorophyll degradation has significance for the appearance of
the end-product.
 Conversion of chlorophyll into chlorophyllide, a reaction
catalyzed by the enzyme chlorophyllase – more extensive is
undesirable as give rise to pheophorbides (brown) and not the
desired oliveblack pheophytins.
 Increased cell permeability during withering favors the
fermentation procedure. A uniform distribution of
polyphenol oxidases in tea leaves is achieved during the
conditioning step of processing.

27. Reactions Involved in the Processing of
TeaRolling
 Tea leaf is macerated and the substrate and enzymes are
brought together; - The subsequent enzymatic oxidative
reactions are designated as a prerequisite for
fermentation
 In this processing step, the pigments are formed primarily
as a result of phenolic oxidation by the PPO. In addition,
oxidation of amino acids, carotenoids and unsaturated
fatty acids, preferentially by oxidized phenols, is of
importance for the formation of odorants
 The enzymatic oxidation of flavanols via the
corresponding o-quinones gives theaflavins - bright red
color, good solubility
 A second, heterogenous group of compounds, found in
tea after the enzymatic oxidation of flavanols, are the

28. Reactions Involved in the Processing of
TeaRolling
 Aroma development during fermentation is accompanied by an
increase in the volatile compounds typical of black tea.
 They are produced by Strecker degradation reactions of amino acids
with oxidized flavanols.

29. Reactions Involved in the Processing of
Tea
Firing
 During this step there is an initial rise in enzyme
activity (10–15% of the theaflavins are formed
during the first 10 min), then all the enzymes are
inactivated.
 Conversion of chlorophyll into pheophytin is
involved in reactions leading to the black color of
tea.
 A prerequisite for these reactions is high
temperature and an acidic environment. The
undesired brown color is obtained at higher pH’s.
 The astringent character of teas is decreased by

30. Withering

31. Rolling

32. Firing

35. Thank you