Tea chemistry

1. Tea Chemistry 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

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) 20-07-2012 Manoj Solanki

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) 20-07-2012 Manoj Solanki

6. Manufacture of black tea 20-07-2012 Manoj Solanki

7. Manufacture of green tea In contrast to black tea manufacture, withering and fermentation stages are omitted in green tea processing 20-07-2012 Manoj Solanki

8. Composition of Tea (%, dry weight basis) Constituent Fresh Tea Black Tea Black Tea Brew * Phenolic compounds 30 5 4.5 Oxidized phenolic compounds 25 15 Protein 15 15 Traces Amino acids 4 4 3.5 Caffeine 4 4 3.2 Crude fiber 26 26 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 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

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 flav a noids , flavan-3-ols (or catechins ). 20-07-2012 Manoj Solanki

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) 20-07-2012 Manoj Solanki

12. Catechins are the main phenolic compounds present in fresh tea leaves: Catechin Epicatechin Epicatechin gallate Epicatechin digallate Flavanol Flav a nols (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 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

14. Flavonols Flavone  backbone  Quercetin Epicatechin 20-07-2012 Manoj Solanki

15. GREEN TEA 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

17. Black Tea Thearubigins  are polymeric  polyphenols  that are formed during the enzymatic oxidation Theaflavin 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 20-07-2012 Manoj Solanki

18. Enzymes Polyphenol oxidases - located within cell of leaf epidermis & activity rises during withering & rolling Shikimate dehydrogenase - reversibly interconverts dehydroshikimase & shikimate via phenylalanine pathway Phenylalanine ammonia lyase - catalyse cleavage of phnylalanine into ammonia & cinnamate Proteinases – cause protein hydrolysis during withering resulting in rise of peptides & free amino acids Chlorophyllases participate in the degradation of chlorophyll and transaminases in the production of precursors for aroma constituents. 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

21. Carbohydrates Sugars in tea leaves are: Glucose (0.72%) Fructose (0.4%) Sucrose (0.09%) Arabinose Ribose R hamnose & galactose are bound to glycosides 20-07-2012 Manoj Solanki

22. Lipids Level is around 7% Polar fraction ( glycerophospholipids ) in young leaves are predominant Glycolipid predominate in older leaves 20-07-2012 Manoj Solanki

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. 20-07-2012 Manoj Solanki

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 20-07-2012 Manoj Solanki

25. Volatile compounds Constitute 0.01-0.02% of tea on dry basis Black tea contain more volatile compound than green tea 20-07-2012 Manoj Solanki

26. Reactions Involved in the Processing of Tea Withering 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. 20-07-2012 Manoj Solanki

27. Reactions Involved in the Processing of Tea Rolling 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 thearubigins - a group of compounds responsible for the characteristic reddish-yellow color of black tea extracts 20-07-2012 Manoj Solanki

28. Reactions Involved in the Processing of Tea Rolling 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. 20-07-2012 Manoj Solanki

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 the formation of complexes between phenolic compounds and proteins 20-07-2012 Manoj Solanki

30. Withering 20-07-2012 Manoj Solanki

31. Rolling 20-07-2012 Manoj Solanki

32. Firing 20-07-2012 Manoj Solanki