RU2426441C2 - Method for production of tea products enriched with theaflavins - Google Patents

Abstract

FIELD: food industry.

SUBSTANCE: one provides for a method for production of a tea product enriched with theaflavins; the method involves a stage of tea raw material enzymic fermentation in the presence of added exogenic epicatechin.

EFFECT: development of an effective method for production of a tea product enriched with theaflavins.

15 cl, 5 tbl, 15 ex

Description

FIELD OF THE INVENTION

The invention relates to the field of tea processing. In particular, it relates to a method for producing a tea product enriched in theaflavins.

State of the art

Any discussion of the prior art in the text of the description should in no way be construed as an admission that this prior art is widely known or forms part of the general knowledge in the art.

Theaflavins are compounds that are characterized by the presence of a benzotropolone ring in them and which are formed during the oxidative fermentation of tea leaves or during fermentation in the production of black tea. Theaflavins are unique compounds of black tea and oolong tea (red tea), in which there are four main types of theaflavins - theaflavin (TF1), theaflavin-3-monogallate (TF2), theaflavin-3'-monogallate (TF3) and theaflavin -3-3'-digallate (TF4). In tea leaves, epicatechin (EC) and epicatechin gallate (ECG) are simple catechins, while epigallocatechin (EGC) and epigallocatechin gallate (EGCG) are gallocatechins, which are involved in the formation of four types of theaflavins. Oxidative biotransformation of catechins, like other biotransformation processes, is a complex process involving many reactions that result in theaflavins dimers and high molecular weight compounds known as thearubigins.

Theaflavins are known to have antioxidant, antimicrobial, and anti-inflammatory properties. Theaflavins have been reported to be quite effective against various diseases, including cancer, cardiovascular diseases and cerebrovascular diseases, diabetes and hypercholesterolemia. However, the usual level of theaflavins in tea is 1-2% in terms of dry weight, depending on factors such as geographical origin and type of tea. Therefore, the production of tea products with elevated levels of theaflavins is highly desirable. In the past, researchers have attempted to enrich tea products with theaflavins based on different approaches.

Cloughley & Ellis (J. Sci. Food Agric. 31 (1980) 924-934) describes a method for enriching tea with theaflavins by performing a low pH fermentation step. However, tea obtained by this method may contain residual acidity, which can cause coagulation of milk when it is added during the preparation of a tea drink with milk.

US 6113965 (2000, Lipton) discloses a method for producing theaflavin by separating it from a suspension, which is the product of oxidative fermentation of green leaf tea pre-treated with tannase before oxidative fermentation. This document also discloses methods for preparing theaflavin-enriched extracts and provides tea soluble tea powders and products.

However, enrichment with theaflavin obtained by the aforementioned method is rather limited, and therefore there is still a need for tea products with elevated levels of theaflavin.

In addition to this, prior art methods are found to be expensive, and therefore there is a need to develop a cost-effective method for producing theaflavin-enriched tea products.

An object of the present invention is to eliminate or correct at least one of the drawbacks of the prior art or provide a useful alternative.

One of the objectives of the present invention is the provision of a method of manufacturing enriched with theaflavins tea product containing elevated levels of theaflavins in comparison with the methods of the prior art.

Another objective of the present invention is to provide a method for the production of theaflavins-enriched tea product in a cost-effective manner.

The authors of the present invention quite unexpectedly found that the presence of exogenous epicatechin in the enzymatic fermentation of tea raw materials leads to theaflavins enriched tea product.

Disclosure of invention

According to the present invention, there is provided a method of manufacturing a theaflavin-enriched tea product, comprising the step of subjecting the tea raw materials to enzymatic fermentation in the presence of added exogenous epicatechin.

Preferably, the enzymatic fermentation according to the present invention is carried out with the participation of endogenous enzymes of tea raw materials.

According to one preferred aspect of the invention, the amount of said epicatechin is from 35 to 750, more preferably from 75 to 520, most preferably from 120 to 260 mg / g dry weight of soluble solids in said tea raw material. According to a preferred aspect, epicatechin is added to the tea raw materials before fermentation.

The tea raw materials are preferably treated with tannase before or during the fermentation process.

According to a preferred aspect, the fermentation is carried out in the presence of added water. The amount of added water is preferably from 0.1 to 500 g / g soluble solids in tea raw materials.

Terminology

The term “tea raw materials” as used herein refers to any material obtained from a plant of Camellia sinensis or Camellia assamica, or to any material obtained by processing said plant material.

The term "tea product" in the context of the description refers to any product obtained from tea raw materials. It includes (but the entire list is not limited to those mentioned here) black tea, oolong tea (Oolong tea, semi-fermented, red tea), instant tea and green tea. It also includes a suspension containing a mixture of the tea product with water.

The term “theaflavins enriched,” as used herein, refers to a tea product with a higher level of theaflavins, including TF1, TF2, TF3, and TF4, as compared to the raw tea stock. In particular, the tea product typically contains a higher amount of theaflavins / gram dry weight of soluble solids of the tea product compared to the number of theaflavins / gram dry weight of soluble solids in the tea raw materials.

The term "tea leaves" as used herein includes leaves, buds, and other parts of the plant Camellia sinensis or Camellia assamica.

The term dhool ("dhool") as used herein refers to macerated tea leaves. Maceration of tea leaves can be carried out by traditionally used methods, such as twisting, chopping twisted tea leaves (CTC), blending using a kitchen mixer, etc.

The term “enzymatic fermentation” as used herein refers to oxidative biotransformation involving enzymes. Fermentation can be carried out with the participation of endogenous enzymes of tea raw materials capable of enzymatic fermentation. Non-limiting examples of such tea raw materials include tea leaves and dhul ("dhool"). Fermentation can also be carried out using an exogenous enzyme and the corresponding cosubstrate.

The term "mainly inactivated endogenous enzymes" refers to tea raw materials subjected to the stage of inactivation of enzymes endogenously present in tea raw materials. In typical cases, inactivation is achieved by heating, i.e. exposing the exposure step to temperatures above 100 ° C, also known as fire drying. Examples of tea raw materials with inactivated mainly endogenous enzymes include instant tea and green tea.

The term "soluble solids of tea raw materials" in the context of the description means the amount of solids provided by (a) contacting the tea raw materials with water at 90 ° C for 1 hour, (b) separation of the liquid phase from insoluble solids by centrifugation / filtration (filter from Whatman paper 541) and (c) evaporating water from the liquid phase to obtain soluble solids.

The term "in terms of dry weight" in the context of the description refers to the composition, expressed as a ratio or wt.% In terms of dry matter, i.e. excluding moisture. The term "in terms of fresh weight" in the context of the description refers to the composition, expressed as wt.% Material, including moisture. In typical cases, tea leaves contain about 70% moisture and about 30% solids. In the total solids content, soluble solids typically comprise about 40 wt.% (In terms of dry weight). Thus, ~ 12% of soluble solids in terms of fresh weight is equivalent to ~ 40% of soluble solids in terms of dry weight. It should be noted that the above typical numbers are representative, and the actual numbers may vary to some extent depending on geographical origin, varieties of tea and humidity.

The term "suspension fermentation" in the context of the description refers to the fermentation of tea raw materials, in which the ratio of added water to tea raw materials is more than 2: 1 in terms of fresh weight or 6.7: 1 in terms of dry weight, and 17: 1 in terms of soluble solids.

The term "solid state fermentation" as used herein refers to enzymatic fermentation of tea raw materials in which the ratio of added water to tea raw materials is less than 2: 1 in terms of fresh weight or 6.7: 1 in terms of dry weight and 17: 1 in in terms of soluble solids. In typical cases, the ratio of added water to tea raw materials is less than 2: 1 in terms of soluble solids.

The term "exogenous epicatechin" as used herein refers to epicatechin, which is externally added to tea raw materials, and does not include epicatechin, which may be present in tea raw materials.

Enzymatic activity is expressed in units of activity or simply in units. Tannase activity units are taken from the supplier data. The activity of exogenous enzymes such as polyphenol oxidase (PPO) and peroxidase (POD) can be determined as follows.

Polyphenol Oxidase Test (PPO)

PPO is determined spectrophotometrically using (+) - catechin as a substrate. The sample is carried out in a 3 ml reaction mixture containing 3 mM catechin in 0.1 M phosphate-citrate buffer with a pH of 5.5. An aliquot of 150 μl of a freshly prepared 60 mM catechin stock solution in a mixture of water (70% v / v) with ethanol (30% v / v) is used to provide a catechin concentration of about 3 mM in the reaction mixture. An enzyme solution in the appropriate dilution is added to initiate the reaction, and the mixture is incubated at 40 ° C for 10 to 20 minutes. The reaction is stopped by adding 200 μl of a solution containing acetonitrile (60% vol./about.), Acetic acid (10% vol./about.) And water (30% vol./about.). Then the spectral absorption capacity (SPS) is determined at 400 nm, and the activity is calculated taking into account the existing dependence: 1 unit activity = an increase in SPS by 0.001.

Peroxidase Assay (POD)

The POD assay is identical to the PPO assay, except that the reaction mixture contains another 7.3 mM hydrogen peroxide. The required amount of hydrogen peroxide is provided by 1.5% (w / v) stock solution. The reaction mixture is incubated for 10 to 20 minutes at 30 ° C. Then the reaction is stopped, as described above, and the spectral absorbance (SPS) at 400 nm is determined. Activity is also calculated taking into account the dependence: activity of 1 unit = increase in ATP by 0.001.

The implementation of the invention

According to the present invention, there is provided a method of manufacturing a theaflavin-enriched tea product, comprising the step of subjecting the tea raw materials to enzymatic fermentation in the presence of added exogenous epicatechin.

Preferably, the enzymatic fermentation according to the present invention is carried out using endogenous tea raw material enzymes capable of such fermentation.

Exogenous epicatechin sold on the market can also be used (for example, from Sigma, Herbs-Tech, etc.). Other sources of exogenous epicatechin that can be added according to the present invention include epicatechin-rich extracts of other plant materials, such as cocoa, grape juice, etc.

The method according to the present invention can be carried out in the presence of other exogenous catechins (including epicatechin gallate, epigallactocatechin and epigallactocatechin gallate) added together with exogenous epicatechin. Preferably, the ratio of exogenous epicatechin to total exogenous catechins exceeds the ratio of endogenous epicatechin to total endogenous catechins in tea raw materials.

The preferred amount of added exogenous epicatechin is selected so that the molar ratio of the total amount of epigallocatechin to the total amount of epicatechin is from 1: 1 to 1:16, preferably from 1: 1.5 to 1:10, more preferably from 1: 2 to 1: 9.

According to one preferred aspect of the invention, the amount of epicatechin added is from 35 to 750, preferably from 75 to 520, more preferably from 120 to 260 mg / g dry weight of soluble solids in tea raw materials.

According to a preferred aspect, if tea leaves are used as tea raw materials, epicatechin is added to the tea leaves immediately after collection. According to an alternative preferred aspect, epicatechin is added to the tea leaves before harvesting.

Preferably, the tea raw materials are substantially unfermented, i.e. not previously subjected to enzymatic fermentation. In particular, it is preferable that the mass ratio of the total amount of catechins to theaflavins in said tea raw materials is more than 10, preferably more than 20, more preferably 50 to 10,000. Alternatively or additionally, the tea raw materials preferably contain no more than 10 mg, more preferably 5 mg, most preferably 2 mg of theaflavin / g dry weight of soluble solids. It is particularly preferred that the tea raw materials do not contain mainly theaflavins.

The method according to the present invention preferably includes the step of treating the tea raw materials with tannase before or during the above fermentation.

According to a preferred aspect, the step of treating tea raw materials with tannase is carried out before fermentation. The tannase treatment is preferably carried out in a nitrogen atmosphere (to prevent fermentation) at an appropriate temperature and for an appropriate period of time. Suitable modes can be determined experimentally. According to an alternative preferred aspect, the step of treating the tea raw materials with tannase is carried out in a fermentation process. Preferably, the amount of tannase is from 0.08 to 8, more preferably from 0.2 to 4, most preferably from 0.4 to 2 mg / gram dry weight of soluble solids in tea raw materials.

According to a preferred aspect, the fermentation is carried out in the presence of added water. The amount of water added is preferably from 0.1 to 500 g / g dry weight of soluble solids of tea raw materials. In one preferred aspect, the amount of added water is from 0.1 to 17, more preferably from 0.1 to 10, most preferably from 0.1 to 2 g / g of soluble solids of tea raw materials, which leads to fermentation in solid condition. According to an alternative preferred aspect, the amount of added water is from 17 to 500, more preferably from 20 to 400, most preferably from 25 to 200 g / g of soluble solids of tea raw materials, which leads to fermentation in suspension.

According to a preferred aspect, the tea raw material is tea leaves containing endogenous enzymes capable of enzymatic fermentation, and the method comprises the steps of:

(a) withering tea leaves;

(b) maceration of withered leaves;

(c) subjecting the macerated tea leaves to enzymatic fermentation in the presence of added exogenous epicatechin and

(g) fire-drying, preferably to a temperature of about 120 ° C., to obtain theaflavin-enriched black tea.

The method described above preferably includes a step of treating the tea raw material with tannase before or in the process of step (c), i.e. enzymatic fermentation.

According to another preferred aspect, the tea raw material is tea leaves containing endogenous enzymes capable of enzymatic fermentation, and said method comprises the steps of:

(a) withering of said tea leaves;

(b) maceration of the dried leaves and adding to the macerated tea leaves from 17 to 500 g of water / g of soluble solids to obtain a suspension;

(c) exposing the suspension to enzymatic fermentation in the presence of added exogenous epicatechin to obtain a theaflavin-enriched suspension.

The method described above preferably includes a step of treating the tea raw material with tannase before or in the process of step (c), i.e. enzymatic fermentation.

Theaflavin-enriched suspension may preferably be dried to reduce its moisture content to <5% to produce theaflavin-rich black tea. In another preferred aspect, insoluble solids are separated from theaflavins-enriched suspension to form a theaflavins-rich solution. Theaflavin-rich solution may preferably be dried to produce a theaflavin-rich tea product, which may, for example, be added to black tea, green tea, oolong tea, or instant tea. According to an alternative preferred aspect, theaflavin-rich solution can be coated onto black tea, green tea or oolong tea, followed by drying to produce theaflavin-enriched tea.

According to another preferred aspect, enzymatic fermentation is carried out using an exogenous enzyme and cosubstrate. Fermentation using an exogenous enzyme and cosubstrate is preferred if the tea stock contains inactivated, mainly endogenous enzymes. Examples of tea raw materials with inactivated, mainly endogenous enzymes are green tea or instant green tea. Fermentation of the suspension is preferable if the tea raw material contains inactivated, mainly endogenous enzymes.

The desired combination of the exogenous enzyme and the corresponding cosubstrate is selected so that such a combination is capable of fermenting tea raw materials.

According to a preferred aspect, the exogenous enzyme is polyphenol oxidase and the corresponding cosubstrate is oxygen. According to another preferred aspect, the amount of said polyphenol oxidase is from 1.5 × 10 ⁴ to 1.5 × 10 ⁷ , more preferably from 3.5 × 10 ⁴ to 1.5 × 10 ⁶ , most preferably from 7.5 × 10 ⁴ to 7.5 × 10 ⁵ units / g dry weight of soluble solids in the specified tea raw materials. Polyphenol oxidase can be purchased on the market, for example, from Worthington, or can be extracted and purified from a suitable plant material.

According to another preferred aspect, the exogenous enzyme is peroxidase and the cosubstrate is hydrogen peroxide. Peroxidase can be purchased on the market, for example, from Sigma, or can be extracted and purified from a suitable plant material. According to a further preferred aspect, the amount of said peroxidase is from 1.5 × 10 ⁴ to 1.5 × 10 ⁷ , more preferably from 3.5 × 10 ⁴ to 1.5 × 10 ⁶ , most preferably from 7.5 × 10 ⁴ to 7.5 × 10 ⁵ units / g dry weight of soluble solids in the specified tea raw materials.

Preferably, the amount of said hydrogen peroxide is from 7 to 700 mg, more preferably from 15 to 300 mg, most preferably from 35 to 100 mg / g dry weight of soluble solids in said tea raw materials.

According to a preferred aspect, the tea raw material is green tea or instant green tea, and the method comprises the steps of:

(a) adding to tea raw materials from 17 to 500 g of water / g of soluble solids to obtain a suspension;

(b) exposing the suspension to enzymatic fermentation by adding an exogenous enzyme and cosubstrate in the presence of added exogenous epicatechin to obtain a theaflavin-enriched suspension.

The method described above preferably includes a step of treating the tea raw materials with tannase before or in the process of step (b), i.e. enzymatic fermentation.

Theaflavin-enriched slurry may preferably be dried to reduce its moisture content to <5 wt.% To produce theaflavin-rich black tea. In another preferred aspect, insoluble solids are separated from theaflavins-enriched suspension to form a theaflavins-rich solution. Theaflavin-rich solution may preferably be dried to produce a theaflavin-rich tea product, which may, for example, be added to black tea, green tea, oolong tea, or instant tea. According to an alternative preferred aspect, theaflavin-rich solution can be coated onto black tea, followed by drying to yield theaflavin-rich black tea.

According to another preferred aspect, theaflavin-enriched suspension obtained by the above method is applied as a coating to black tea to obtain theaflavin-enriched black tea.

According to another preferred aspect, theaflavin-enriched suspension is coated as a coating on instant tea to produce theaflavin-enriched instant tea.

Examples

The invention is described below with reference to specific examples, which are given solely for the purpose of illustrating the invention and in no way limit the scope of the invention.

Materials and methods

Table 1 lists the materials used in the examples.

Table 1 Materials used Ingredient Ingredient form Source and geographical origin of the ingredient Tea leaves Frozen (stored at -80 ° C) Tea Plantations South India Dhool A mass made from tea leaves frozen by immersion in liquid nitrogen, followed by mixing in a kitchen blender Epicatechin Sigma aldrich Tannase CT-50 Stock solution 1 g / l Kikkoman, Japan

Theaflavin analysis method

Theaflavin Extraction

The total level of theaflavins was determined in an aqueous methanol extract.

Samples from solid state fermentation were subjected to extraction with 70% methanol at ~ 80 ° C for 10 min at a ratio of high-water methanol solution to dhool equal to 16.7: 1 in terms of fresh weight. A sample of the extract was diluted in a 1: 1 ratio with a solution containing 90% v / v. water, 10% v / v acetonitrile, 0.5 g / l ascorbic acid and 0.5 g / l ethylenediaminetetraacetic acid (EDTA), to prevent oxidation of theaflavins and catechins.

In the case of a suspension fermentation system, said extract was prepared by adding the required amount of 100% methanol to the aqueous suspension to obtain a composition of 70% methanol and 30% water. The amount of methanol added was 2.33 times the amount of water present, so extraction was carried out at a ratio of aqueous methanol solution to dhool equal to 16.7: 1 in terms of fresh weight or ~ 55.7: 1 in terms of dry weight. With such a high ratio of 70% methanol to dhul, quantitative extraction of theaflavin was achieved at ~ 80 ° C and an extraction time of 10 min.

Theaflavin Analysis

Samples were stored at ~ 80 ° C; theaflavins were analyzed by high performance liquid chromatography (HPLC) with diode array detection.

To analyze theaflavins, the Shimadzu HPLC system was used with a column filled with octadecyl silica (C18) (Nova-pak from Waters) with an internal diameter of 3.9 mm and a length of 150 mm; detection was carried out at 380 nm; the column temperature was 40 ° C, the injection volume was 20 μl and the flow rate was 1 ml / min. The mobile phases for theaflavin analysis were a 2% (v / v) solution of acetic acid in water (mobile phase A) and acetonitrile (mobile phase B). To separate theaflavins after equilibrating the column with 8% buffer A for 5 minutes, a gradient of 8% B to 69% B was used for 50 minutes. High-purity theaflavins sold on the market served as standards for quantification.

Solid fermentation

Solid fermentation was carried out at room temperature (~ 25 ° C) by distributing 5 g of dhul on a flat surface under ambient conditions. The fermentation time was 90-120 minutes. When performing solid state fermentation with the participation of tannase, the dose of the latter was 1.67 mg / g of soluble solids in tea raw materials. Water containing the required amount of epicatechin or epicatechin and tannase was added to dhul at a ratio of 1.7: 1 (in terms of soluble solids).

The amounts of epicatechin and tannase added during solid state fermentation in various examples are shown in Table. 2.

table 2 Solid State Fermentation Examples Example Epicatechin (mg / g soluble solids in dhul) Tannase (mg / g soluble solids in dhul) Comparative Example A 0 0 one 35 0 2 118 0 3 258 0 Comparative Example B1 0 0 Benchmark B2 0 1,67 four 35 1,67 5 118 1,67 6 258 1,67 7 518 1,67

Examples 1-7 are examples of the methods of the present invention, while comparative examples A, B1 and B2 are beyond the scope of the invention.

Suspended Fermentation

Fermentation in suspension was carried out in shaken flasks at 30 ° C using an orbital shaker operating at 190-200 rpm. In a fermentation experiment, 5 g (in terms of fresh weight) of dhul were used with a ratio of water to soluble solids of 41.7: 1 (or 5: 1 in terms of fresh weight). The required amount of epicatechin was added to the resulting suspension before fermentation. The fermentation time was 90 minutes. When conducting fermentation in a suspension state with the addition of tannase (whose activity was 50,000 units of tannase activity / g, from Kikkoman), the dose of the latter was 0.83 mg / g of soluble solids using a mother solution of 1 g / l.

The amounts of epicatechin and tannase added during suspension fermentation in various examples are shown in Table 3.

Table 3 Suspension Fermentation Examples Example Epicatechin (mg / gram soluble solids in dhul) Tannase (mg / gram soluble solids in dhul) Comparative Example C 0 0 8 35 0 9 118 0 10 258 0 eleven 518 0 Comparative Example D1 0 0 Comparative Example D2 0 0.83 12 35 0.83 13 118 0.83 fourteen 258 0.83 fifteen 518 0.83

Examples 8-15 are examples of the methods of the present invention, while comparative examples C, D1 and D2 are beyond the scope of the invention.

results

In all examples, the total content of theaflavins in tea products was determined; the results obtained are summarized in table 4 (solid state fermentation) and table 5 (suspension fermentation).

Table 4 The total content of theaflavins in solid state fermentation Example The total content of theaflavins in the tea product (wt.% In terms of dry weight) Comparative Example A 1.3 one 1.8 2 2,4 3 1.9 Comparative Example B1 1.9 Benchmark B2 3,1 four 4.3 5 4.0 6 4.9 7 5.2

From the above, it is obvious that the tea products of examples 1-4, prepared by a method comprising the enzymatic fermentation step in the presence of exogenous epicatechin, contained elevated levels of theaflavins compared to the tea product of comparative example A.

Likewise, the tea products of examples 5-8, prepared by a method comprising the enzymatic fermentation step in the presence of exogenous epicatechin and tannase, contained elevated levels of theaflavins compared to the tea products of comparative examples B1 and B2.

Table 5 The total content of theaflavins in suspension fermentation Example The total content of theaflavins in the tea product (wt.% In terms of dry weight) Comparative Example C 1.9 8 2.0 9 2.6 10 3,1 eleven 2.9 Comparative Example D1 1.9 Comparative Example D2 3,7 12 5.1 13 6.4 fourteen 6.0 fifteen 6.4

From the above it is obvious that the tea products of examples 8-11, prepared by a method comprising the enzymatic fermentation step in the presence of exogenous epicatechin and externally added water, contained elevated levels of theaflavins compared to the tea product of comparative example C.

Likewise, the tea products of Examples 12-15, prepared by a method including the enzymatic fermentation step in the presence of exogenous epicatechin, tannase and externally added water, contained elevated levels of theaflavins compared to the tea products of Comparative Examples D1 and D2.

Of all the examples described above, it is also clear that theaflavins increased as the level of epicatechin increased to about 300 mg / g dhul dry weight. With a further increase in the level of epicatechin to approximately 500 mg / g dry weight of dhul, either leveling or a decrease in the level of theaflavins was noted.

Based on this, it can be argued that the introduction of epicatechin at a level exceeding 750 mg / g of dry weight of dhul is unlikely to lead to a further increase in theaflavin content or is economically viable.

Thus, according to the present invention, it has become possible to produce tea products enriched with theaflavins by performing solid state enzymatic fermentation as well as suspension enzymatic fermentation in the presence of exogenous epicatechin and in the presence or absence of tannase.

Claims (15)

1. A method of manufacturing a tea product enriched with theaflavins, comprising the step of subjecting the tea raw materials to enzymatic fermentation in the presence of added exogenous epicatechin. 2. The method according to claim 1, in which the amount of said epicatechin is from 35 to 750 mg / g dry weight of soluble solids in said tea raw material. 3. The method according to claim 1, comprising the step of treating the tea raw materials with tannase before or during said fermentation. 4. The method according to claim 3, in which the amount of said tannase is from 0.08 to 8 mg / g dry weight of said soluble solids. 5. The method according to claim 1, wherein said fermentation is carried out in the presence of added water. 6. The method according to claim 5, in which the amount of said water is from 0.1 to 500 g / g dry weight of soluble solids in said tea raw material. 7. The method according to any one of the preceding paragraphs, wherein said tea raw material is tea leaves containing endogenous enzymes capable of said enzymatic fermentation, and said method comprises the steps of:
(a) withering of said tea leaves;
(b) maceration of withered leaves;
(c) subjecting the macerated tea leaves to enzymatic fermentation in the presence of added exogenous epicatechin and
(g) fire drying to obtain theaflavins-enriched black tea. 8. The method according to any one of claims 1 to 6, wherein said tea raw material is tea leaves containing endogenous enzymes capable of enzymatic fermentation, and said method comprises the steps of:
(a) withering of said tea leaves;
(b) maceration of the dried leaves and adding to the macerated tea leaves from 17 to 500 g of water / g of soluble solids to obtain a suspension;
(c) exposing the suspension to enzymatic fermentation in the presence of added exogenous epicatechin to obtain a theaflavin-enriched suspension. 9. The method according to claim 1, wherein said fermentation is carried out by adding an exogenous enzyme and cosubstrate. 10. The method according to claim 9, in which the specified tea raw material contains inactivated, mainly endogenous enzymes. 11. The method according to claim 9, wherein said exogenous enzyme is polyphenol oxidase and said cosubstrate is oxygen. 12. The method according to claim 9, in which said exogenous enzyme is peroxidase, and said cosubstrate is hydrogen peroxide. 13. The method according to any one of claims 9-12, wherein said tea raw material is green tea or instant tea, and said method comprises the steps of:
(a) adding to tea raw materials from 17 to 500 g of water / g of soluble solids to obtain a suspension;
(b) subjecting the suspension to enzymatic fermentation by adding exogenous epicatechin and cosubstrate in the presence of added exogenous epicatechin to obtain a theaflavin-enriched suspension. 14. The method according to any one of claims 1 to 6 or 9-12, in which the mass ratio of the total number of catechins to theaflavins in said tea raw material is more than 10. 15. The method according to any one of claims 1 to 6 or 9-12, wherein said tea raw material contains not more than 10 mg of theaflavins / g dry weight of soluble solids.