How does the composition of tea change during processing? Why can different fresh leaves make different teas? Today, let's explain how the ingredients in the processing of black tea change and affect the quality.
In fact, it is mainly because of these aspects.
First, the transformation of polyphenols
In the initial production process of black tea, the polyphenols with catechins as the main body are catalyzed by the specific enzyme polyphenol oxidase and peroxidase of polyphenol substances to generate colored oxidation products thearubicins and theaflavins, and partially combine with proteins into insoluble compounds, including
1. Formation of flavin
It is a compound with benzosterone structure formed by oxidative polymerization of pairs of catechins, which is an important component of black tea, plays a decisive role in the color, aroma, taste and quality of black tea, is the main component of black tea soup color "bright", is also an important component of soup flavor strength and freshness, and is also the most important substance that forms the "golden circle" of tea soup; , theaflavins are closely related to the color of black tea soup, the lower its content, the worse the brightness of the soup color, and vice versa, the better, golden yellow. Theaflavins have spicy and strong astringency, which plays an extremely important role in the taste of black tea, affecting the concentration, strength and freshness of black tea soup, especially the strength and freshness;
2. Formation of erythrin
Thearubicin color brown red, is the main component of black tea soup color "red", but also an important substance of soup flavor concentration and strength, but its irritation is not as good as theaflavin, strong astringency, taste sweet alcohol.
3. Formation of fusin;
Is a very complex compound, can be divided into dialysis and non-dialysis two parts, in addition to containing polyphenol oxidation polymerization products, but also contains amino acids, sugars and other conjugates, its color is dark brown, taste bland, slightly sweet, more amount, tea soup taste faint and dark, is the main cause of black tea soup "dark";
4. Conversion of other polyphenols;
In summary, the changes of catechins and other polyphenols in tea are right and wrong in the manufacturing process of black tea; Often active, and intricate;
The polyphenols in tea are the most important substances in the formation of black tea quality, and their content in fresh leaves and changes in quantity and quality during processing are the key to quality formation in black tea manufacturing.
The complex changes of polyphenols in the manufacturing process of black tea (especially the fermentation process) can be roughly divided into the following three parts: (1) unoxidized polyphenols, mainly residual catechins, and mainly ester catechins; (2) water-soluble oxidation products, mainly TF, TR and TB; (3) non-aqueous transformation products.
The relationship between unoxidized polyphenols and the quality of black tea In the fermentation of black tea, a certain number of unoxidized polyphenols are still retained, mainly residual catechins, the main body is ester catechins, these substances are dissolved in water, brewing into the tea soup, is an indispensable part of the concentration and strength of the tea soup, but also the refreshing and irritating ingredients of the tea soup.
Relationship between water-insoluble oxidation products and black tea quality: During the tea fermentation process, some polyphenols and their oxidation products such as o-quinone, TF, TR, TB will bind with proteins to form water-insoluble compounds precipitated on the leaf floor.
The processing includes withering, kneading (cutting), fermentation and drying processes in black tea production. In the enzymatic oxidation of polyphenols, appropriate non-water-soluble red products are necessary to form the color of the base of black tea leaves. Such as TF, TR, the content is low, usually the destruction of chlorophyll is not sufficient, and the appearance of "anthocyanin", is the manifestation of insufficient fermentation, but if the fermentation is excessive, it produces a large number of TB, so that the leaf bottom is red and dark, forming a dark brown leaf bottom color.
Second, the transformation of aromatics
In the manufacture of black tea, the aromatic substances in fresh leaves have undergone extremely profound changes in content and variety. The aroma of black tea is mainly produced in the manufacturing process of black tea, especially the fermentation process, due to the dehydration and respiration of the withering process, the increase of cell permeability, some enzymes begin to be active, so that the binding aroma compounds in the form of glycosides (such as green leaf alcohol, linalool, geraniol, aromatic alcohol, etc.) and its hydrolase β glycosidase contact, aromatic compounds free out. On the other hand, some macromolecular substances such as fats, proteins, polysaccharides, etc. tend to be hydrolyzed, and their hydrolysis products provide a precursor to the formation of the aroma component. In addition, linolenic acid, lipoxygenase, and alcohol dehydrogenase, which are related to the production of alcohols and aldehydes, are also very important for the formation of aroma. Due to withering, the total amount of aroma components can be increased to more than 10 times that of raw fresh leaves, and in a short period of time, it can be increased to the largest cis-3 hexenol, trans-2 hexenol and linalool. During the kneading (cutting) process, the tea tissue and cells are broken, and the chemical components and enzymes in them are fully mixed, and various chemical reactions begin to occur. During fermentation, the formation of aromatic components is caused by oxygen in the air and the reaction between enzymes in the tea leaves and their substrates. The catechins oxidized in fermentation can cause the oxidative degradation of unsaturated fatty acids such as amino acids, carotene, linolenic acid and form volatile compounds, trans-2-hexenal (green leaf aldehyde) is significantly generated, and ionone associations are accompanied by the intense oxidation reaction of fermentation, which is formed by carotene conversion. At this stage, the basic flavor (aroma and taste) characteristic of black tea has been formed. In addition, the hydrolysis reaction of glycosidases of aroma compounds bound to glycoside β s that begin with the withering process is accelerated during the kneading and fermentation phases.
The final stage of the drying process of black tea manufacturing is the process of dehydration and passivation enzymes, the high temperature thermochemical action makes the volatile compounds significantly lost, on the other hand, the aroma compounds generated by heating such as aldehydes, parsley ketonates, lactones and various ionone lines increase, and finally form a very coordinated and complex aroma of black tea.
In short, in the process of black tea manufacturing, the action of enzymes, the coupling oxidation of catechin o-quinones, and conditions such as hydrothermal action and acidity can cause or promote the production of aromatic substances. Common ones are oxidation, reduction, compounding, decomposition, esterification, cyclization, isomerization, deamination and decarboxylation.
Third, carbohydrate conversion
Soluble sugar is not only a taste substance, bringing a sweet and mellow taste to the tea soup, but also in the manufacturing process of black tea, caramelization and carbonine reaction can occur, generating the corresponding aldehydes and pyrroles, pyrazine nitrogen-containing compounds, etc., which play an important role in the formation of the color and aroma of black tea. Such as glucose, fructose, galactose, mannose and sucrose and other mixtures with phenylalanine under heat treatment conditions, can produce rose flower fragrance and straw yellow substances. Excellent black tea often has a fragrance similar to "honey", which is often produced in the "low temperature long baking" when the drying process is full of fire, which is the result of the similar sugar aroma produced by the simple sugar in the tea leaves when baking. However, if you take a sustained high temperature, not only will you consume too many valuable quality ingredients such as amino acids and sugars, but also produce more non-water-soluble melanin and some volatile components, which will make the aroma composition out of balance and damage the quality of tea.
In short, the taste, soup color and aroma of black tea are related to the presence and transformation of soluble sugar, therefore, in the manufacturing process, take appropriate process conditions, so that polysaccharides have more hydrolysis, the content of soluble sugars is improved, and to prevent these soluble sugars from being consumed by excessive breathing, as well as moderate control of carbonine reaction and caramelization, is necessary to improve the quality of black tea in black tea production.
Fourth, the transformation of proteins and amino acids
The amino compounds in tea fresh leaves mainly include proteins and free amino acids. According to the analysis data of Anhui Agricultural College (1962), the protein content of fresh leaves in the manufacturing process of "Qi Hong" is 177%, and the amount of raw tea is reduced to 145% to 175%.
The changes in amino acids in black tea manufacturing are more complicated. In the withering stage of black tea manufacturing, it increased significantly, and the various processes gradually decreased later. In the withering, kneading and fermentation stages of black tea manufacturing, amino acids can be oxidized into alcohol and aldehyde aromas due to the action of enzymes or o-quinones. Amino acids in addition to their own coupling oxidation to form black tea aroma substances alcohol, aldehyde, or the precursor of many aromatic substances in black tea processing, Wickremasinghe (1967) pointed out that the tea aroma with less leucine accumulation during black tea fermentation is better, and observed that labeled leucine formed a labeled mecarboxyproic acid and a small number of volatile substances during fermentation, and proposed the formation of terpene aroma substances with leucine as the precursor and mevalonic acid as the intermediate product:
Leucine→α isohexanate→ isovalecyl CoA→β monoacyl CoA methioneoic acid→ methioneoic acid monoacyl CoA→ mevaleric acid→ carotene→ ionone compounds. Squalene → other terpenes, sterols
In the drying stage of black tea processing, under the action of heat, the change of amino acids is more complicated. Amino acids can be dehydrated directly into pyrazine aromatic components. It can also be dearboxylated at the same time to produce deamination and reduction and other reactions, the formation of phenol, p-methylphenol, indole and other aroma components. In addition, amino acids can also react with carbohydrates (Maillard) and are degraded by Strecker to form aldehydes, pyrazines, pyrrole aromatic substances and melanin.
In addition, amino acids are also involved in the formation of black tea pigments. Vuataz and Braudenberager (1961)
Theamarine (including TF, TB) was isolated from freshly fermented Sri Lankan tea and dried black tea, and through the study of its properties, it was found that there were 05% nitrogen, and after hydrolyzing it, it was found that there were more than a dozen amino acids such as alanine, arginine, glycine, leucine, isoleucine, phenylalanine, lysine, proline, serine, threonine, tyrosine, valine, aspartic acid and glutamic acid. Xiao Weixiang et al. (1992) also extracted purified thearubin (TR) from black tea soup with 0mol/LHCl to hydrolyze on a boiling water bath for 1h, and the hydrolysis product was identified by thin layering of microcrystalline cellulose, confirming the presence of theanine. Hazarika et al. (1984) found in the analysis of theorubin components that amino acids are involved in the composition of TR1, TR2, TR3 and TR4. In the tea soup color reaction, TR1 and TR2 are slightly brown and have a lighter taste, and TR4 is dark brown, which is the component of the darkening of tea soup. TR3 is reddish brown, has a certain degree of convergence, has a certain effect on the alcohol and taste of tea soup, and is most beneficial to the color of tea soup.
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