Bio-chemical Index of Tea Color

Shade of colour in made tea and brightness in the infusion are two important attributes besides aroma and taste. Colour, the attractiveness of made tea, always influences consumers in deciding the product to be purchased. Unexpected colour may possibly be a sign of poor quality tea. Colour and appearance are the consequent of clonal characteristics resulting from the technical manipulation during the manufacture of tea. Appearance is also a contributing factor in assessing the quality of tea. It was also indicated that there was a distinct relationship between the amount of theaflavins and thearubigins contents and mouth feel of liquor. Theaflavins and thearubigins appeared to be the key factors of golden yellow and brownness of the liquor respectively, while pheophytin and pheophorbide derived from chlorophylls contributed towards the blackish brown appearance of black teas.




Theaflavins, (TF) the golden yellow pigment, constitute around 0.5%- 2% of dry wt., depending on the type of manufacture of black tea. The attractive colour of the tea infusion is due to theaflavins and it emerges as an important quality index of black tea. TF are responsible for the development of the bright colour and brisk taste of the liquor. These compounds are mostly formed during the maceration stages in black tea manufacture. These groups of compounds contribute about 30% of the total colour and are the result of rolling and fermentation. Theaflavins are unique having a seven-member benzotropolone ring. Theaflavins also provides briskness, freshness and aliveness to the infusion, which is highly valued in taster’s parlance. The different types of Theaflavins are Theaflavin, Isotheaflavin, Neotheaflavin, Theaflavin-3-gallate, Theaflavin-3′-gallate, Theaflavin-3,3′-digallate, Epitheaflavic acid, Epitheaflavic acid-3-gallate, theaflavic acid, Epitheaflavic acid-3′-gallate. Recently, some new theaflavins has been isolated namely, neotheaflavin-3-monogallate, isotheaflavin-3′-monogallate and theacitrin A.


Thearubigins (TR), the orange-brown compounds constituting about 6 to 18% of dry weight are another important group of pigments formed during the processing of black tea. They are heterogeneous complexes and are responsible for taste, total colour and body of the liquor. They contribute around 35% of the total colour and also plays a significant role in brown appearance of made tea. Thearubigins are difficult to separate from the other tea components. Roberts (1962) defined thearubigins as acidic, brown phenolic pigments. Later, evidence from chemical degradation led to the conclusion that thearubigins are polymeric proanthocyanidins. The thearubigin anions are more deeply coloured than the undissociate form and the colour due to thearubigin is determined by the relative proportion of anions and undissociate forms. Colour of thearubigins is therefore dependent on pH of water and acidic pH reduces the intensity of colour. Tea brewed in hard water is darker in colour. Thearubigins are separated as coloured complexes. Five coloured complexes have been separated in Sri Lanka in 1967 of which the two deeply coloured fractions were found to contain corilagin, theanine and protein. Three of the less coloured complexes also contain corilagin, theanine, theogallin, chlorogenic acid etc. Three thearubigin fractions have been separated at Tocklai (Hazarika, 1984) of which the low molecular weight fraction is reddish brown in colour and is astringent. It consists of amino acids, caffeine, fatty acids, theogallin and traces of chlorogenic acid and chlorophyll. This fraction has important contribution to quality. The other two fractions were light brown and ashy coloured and were complexes of amino acids, chlorogenic acids, p-coumarylquinic acids. Biogenetic pathways to thearubigins cannot be established till the structures have been fully elucidated, but it has been demonstrated that thearubigins form directly from catechin as well as by oxidative degradation of theaflavins.

Flavour compounds of black tea

Flavour of tea can be divided into two components. One is an inherent flavour due to the presence of some compounds in the leaves which do not undergo changes and the other is acquired flavour due to the transformation of different compounds during processing. More than 700 compounds have been identified so far, as contributing to flavour either positively or negatively. The main sources of these compounds are carotenoids/terpenoids, lipids and amino acids. The C6 aldehydes and C6 alcohols namely, cis-3-hexenal, trans-2-hexenal, cis-3-hexenol, trans-2-hexenol etc., are derived from lipids/fatty acids. This group compounds impart undesirable grassy odour. Carotenoids/terpenoids are the main sources of floral flavour of black tea which are geraniol, linalool and its oxides, -ionone, ß-ionone, nerollidol, etc. Phenylacetaldehyde, 2-methyl butanal are derived from amino acid phenylalanine and leucine respectively during processing of black tea. During the drying stage of black tea manufacture around 50% of the volatile aroma constituents is lost. Further loss occurs during storage of the products.

Enzymes associated with colour and flavour development

The important enzymes associated with the production of colour, appearance and flavour aere polyphenol-oxidase (PPO), peroxidase (PO), chlorophyllase, ß-glucosidase, lipase and lipoxygenase. The colour formation in tea was observed to be dependent primarily on the levels of PPO and PO enzymes. The PPO activity of tea shoots was resolved into isozymes 1 and 2. The activity of isozyme 2 was found to be low in the first and second flushes and high in rain and autumn flushes. Isozyme 1 was predominant in leaf tissues. Isozyme variations were also observed between the leaf and the stem. Highest activity of both PPO and PO were observed on rolling, decrease of the former and increase of the latter were the result of mechanical injury, leading to the oxidative polymerization (enzymic browning) of fermented black tea. The PPO, PO and catechin contents found to be highest in good TV-clones and in young shoots which decreased with maturity. During withering and rolling there was initial increase in PPO and PO enzyme activities, followed by decrease. Thus during withering and early part of fermentation both PPO and PO- mediated oxidation lead to the production of golden yellow coloured theaflavins, while PO-mediated reactions were found to produce predominantly thearubigins in over-fermented leaves. In the leaf tissues enzyme induced oxidative breakdown of unsaturated fatty acids and carotenoids occurred extensively which produced characteristic aroma associated with flavour. The activity of the enzyme chlorophyllase increased during withering. This enzyme could also withstand heat treatment during drying. The lipoxygenase activity enhanced during withering. Among the fatty acids, the maximum degradative changes occurred in linolenic acid during processing. Off flavour developed during prolonged storage of tea was found to be associated with lipoxygenase activity. Fatty acid composition in relation to lipolytic and lipoxygenase activities in tea leaf shoots, from different stages of tea processing was investigated in a series of black tea manufacturing experiments. More degradation of fatty acids and higher lipoxygenase activity were characteristics of over-withered tea leaves. The oxidative breakdown of fatty acids was higher in the later part of the rolling process, while lipolytic activity was more prominent in the withering process as well as the earlier stage of rolling. A gradual decline of lipoxygenase activity as well as fatty acid contents were recorded during the fermentation and drying processes. Lipoxygenase activity was highest in the third leaf followed by second leaf, first leaf, stem and the bud. Lipoxygenase exhibited highest activities during rainy seasons, while ß-glucosidase enzyme activity was highest during first and second flushes. On the other-hand, ß-glucosidase activities were higher in younger leaves, which decreased as the leaf ages and were exceptionally high in stem. ß-glucosidase enzymic hydrolysis produced terpenes, aliphatic and aromatic alcohols during processing with characteristic flavour and aroma.



Contents of some important & characteristic volatile flavour compounds (VFC) in orthodox and CTC black tea (Assam jat)

Orthodox tea
CTC tea
E-2-hexenyl formate
Linalool oxide (furanoid-Z)
Linalool oxide (furanoid-E)
Phenyl acetaldehyde
Z-3-Hexenyl caprorate
Methyl salicylate
Benzyl alcohol
2- Phenyl ethanol
Z-Jasmone +ß-Ionone
Total b

aRatio of the area of each compound to the area of internal standard on the chromatogram.
bsum of each ratio


Flavour volatiles in different flushes

China clone (TV17) contained higher contents of linalools and their oxides than in Assam clone (TV12). The second flush teas of both clones contained higher terpene contents than those of the corresponding rains flush tea. By and large, orthodox teas contained flavoury attributes like higher levels of terpenes e.g. linalools and their oxides, whereas CTC teas showed higher levels of non-terpenes e.g. hexanal and phenylacetaldehyde.

Plucking and leaf quality

Two and a bud shoot contained higher polyphenols, water soluble solid and caffeine contents than in coarsely plucked shoot and therefore quality was better in the former. Morning plucked shoots contained higher polyphenols than those of the afternoon plucked shoots. A considerable impact on quality of leaf after harvest during transportation to the factory was reported due to rise in temperature. This rise in temperature, which was recorded to be as high as 50°C depended on the packing density of leaf and the time required for transportation. Quality of leaf can be retained to a large extent if the rise in temperature can be restricted to 40°C with transportation time of 45 minutes. Increase in damaged leaf due to transportation and packing density resulted loss of catechins which ultimately resulted in loss of TF and TR with considerable impact on quality.

Variation of amino acids, sugars and chlorophylls in different cultivars, seasons and stages of manufacture

Amino acid levels were low in clone TV1 and high in TV 15 and TV18, chlorophyll contents were higher in Cambod clones. During withering the levels of sugars decreased, amino acids increased except theanine which was found to decrease during processing. Chlorophylls were degraded to pheophorbides and pheophytins during fermentation and drying, while sugar increased due to breakdown of polysaccharides. Chlorophylls and their degradation products contributed towards appearance. Amino acids and chlorogenic acids were higher in stem than in leaf. Phenyl alanine is converted to phenyl acetaldehyde, a flavour compound of black tea during fermentation.

Difference in major chemical composition in Assam and Darjeeling teas

The total polyphenol contents of Darjeeling teas were somewhat lower than those of the corresponding teas of the N.E. Indian plains. Caffeine and amino acid contents of teas were similar, whereas the TF and TR contents were found comparable with those of some orthodox plains teas giving light liquor.

Volatile components of Assam and Darjeeling teas in relation to agro practices

Volatile flavour compounds of Assam and Darjeeling teas were investigated. Grassy flavour was attributed to aldehydes such as hexenal and hexanal derived from degradation of fatty acids. These aldehydes were predominant in CTC teas. Alcohols such as hexenols, linalool and its oxides having fruity aroma were predominant flavour components of orthodox teas. The difference in flavour components was observed in the tea cultivars, fineness of plucking and method of processing. Fine plucking produced higher linalools, linalool oxides, geraniol and methyl salicylate but coarse plucking produced more hexanal. Linalools and their oxides were higher in tea shoots plucked in seven days interval as compared to those in shoots of nine and eleven days plucking rounds. Tea shoots withered to 60% produce more linalool and methyl salicylate, while leaf withered to 75% contain more hexenal and hexanal. Darjeeling teas contained high linalool, linalool oxides, geraniol, nerolidol and methylsalicylate, but teas contained more phenylacetaldehyde and hexenal. An aroma index based on terpenoid to non-terpenoid ratio and its relationship with fineness of plucking was indicated. The major flavour volatiles were primarily developed during withering and rolling of tea shoots.

Biochemical Changes During Tea Processing

Withering: Loss of moisture, increase in cell membrane permeability, initiation of polyphenol oxidase/ peroxidase activity, breakdown of chlorophylls, breakdown of proteins releasing amino acids, degradation of carbohydrates, increase in caffeine and inorganic phosphate contents and the development of flavour volatiles.

Rolling: Enhanced levels of polyphenols oxidase/Peroxidase activity, production of flavour compounds and degradation of chlorophylls.

Fermentation: Polyphenols are oxidized and then condensed to form theaflavins, thearubigins etc.; chlorophylls are degraded and some of flavour components are produced from lipids, amino acids, carotenoids and terpenoids.

Drying: Loss of moisture, inactivation of enzymes, loss of soluble solids, development/loss of some flavour components and phaeophytin produced from chlorophylls.