Novel re-fermented tea and preparation method thereof

Abstract

The invention provides novel re-fermented tea and a preparation method thereof. The novel re-fermented tea is prepared through a microwave aroma enhancement technology, an aroma backfilling technology, a compound enzyme stage enzymolysis technology, a microorganism re-fermentation technology and an aroma protection drying technology. The content of amino acid in the tea leaves is increased by treating the tea leaves through the compound enzyme stage enzymolysis technology, and the unique fermentation fragrance of the tea leaves is increased by treating the microorganism re-fermentation technology; the microwave aroma enhancement technology and the aroma backfilling technology increase and retain the original aroma of the tea leaves; and the loss of tea fragrance is further reduced through the fragrance-protecting and drying technical treatment. The re-fermented tea leaves obtained by the preparation method provided by the invention are high in amino acid content and rich in fragrance, meanwhile, fermentation also brings many substances beneficial to human bodies, the selection of the preparation raw materials is not limited, and a new method is provided for preparation of the tea leaves.

Description

Technical Field

[0001] The invention belongs to the technical field of tea preparation, and in particular relates to a novel double-fermented tea and a preparation method thereof. Background Art

[0002] China has a rich variety of tea. According to the processing methods and product characteristics, my country's tea products are divided into green tea, black tea, yellow tea, white tea, oolong tea, dark tea and reprocessed tea. Tea buds and leaves are made into raw tea through withering, rolling, fermentation, drying and other primary processing processes. Then, according to the degree of fermentation, they are made into six types of tea: green tea, black tea, yellow tea, white tea, oolong tea and dark tea.

[0003] As people pay more and more attention to health preservation, the number of tea drinkers is increasing day by day. They not only pursue the taste, but also hope that the aroma is special and has more health-preserving effects. At this stage, reprocessed tea mainly includes scented tea, compressed tea, tea bags, and powdered tea. In addition to its own health-preserving substances, reprocessed tea adds the characteristics of other blended raw materials to give it a special aroma and more health-preserving effects, but does not change the aroma and beneficial substances of the tea itself. Moreover, reprocessed tea is processed again on the basis of finished tea through specific technological means to give it a unique flavor and taste. This process may cause the loss of the original flavor and nutrients of the tea, thereby affecting its taste and health benefits. In addition, during the production process of reprocessed tea, if the process is not appropriate, it may also cause the tea to have odor or other quality problems, further affecting its quality and taste.

[0004] Therefore, it is urgent to explore a tea that can not only improve the taste of tea to meet the current market demand for tea with low bitterness and high freshness, but also develop a reprocessed tea that is rich in new aromas and highly acceptable, improve the quality of reprocessed tea and provide consumers with a tea that has both taste and aroma and contains substances beneficial to the human body. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method of utilizing tea microwave aroma enhancement technology, aroma backfilling technology, compound enzyme stage enzymatic hydrolysis technology, microbial double fermentation technology and aroma protection drying technology, thereby increasing the content of amino acids and EGCG effective substances in the reprocessed tea leaves, increasing the freshness thereof, and providing a special aroma, so as to finally obtain a new type of double fermented tea having a taste that conforms to market trends, contains a special aroma, and contains substances beneficial to the human body.

[0006] On the one hand, the present invention provides a novel method for preparing double-fermented tea, comprising enzymatic hydrolysis treatment in a composite enzyme stage and microbial fermentation treatment.

[0007] At present, most of the processes involving re-fermentation are post-fermentation of dark tea, and the principle is that the finished tea pile changes the fermentation temperature and humidity to affect the sensory evaluation of tea aroma. The new type of re-fermented tea is a re-fermented tea product made by combining the fermentation health concept in other fields with green tea, black tea, oolong tea, white tea, yellow tea, dark tea, and re-processed tea as raw materials through microbial fermentation combined with post-fermentation technology.

[0008] In order to solve the problem of bland aroma and poor taste in tea, there is also a method of preparing a compound enzyme to enzymatically hydrolyze tea. For example, after enzymatically hydrolyzing black tea with a compound enzyme prepared by mixing neutral protease, tannase, neutral cellulase, amylase and koji enzyme, the amino acid content is increased, and the flavor and quality are improved compared with the black tea prepared by the traditional process. However, this process is to mix several enzymes and perform enzymatic hydrolysis at the same time, and the amino acid content of the prepared black tea is mainly increased, while the effect on the content of other substances or the improvement of aroma is limited.

[0009] In view of the defects in the prior art, the present invention proposes the combined use of compound enzyme stage enzymatic hydrolysis treatment and microbial fermentation treatment. On the one hand, according to the characteristics of cellulase, tannase, protease and flavor protease, segmented targeted and sufficient enzymatic hydrolysis is carried out to increase the content of amino acids and EGCG; on the other hand, lactic acid bacteria are added after the compound enzyme stage enzymatic hydrolysis treatment, and the lactic acid bacteria interact with various effective substances and microorganisms in the tea leaves to carry out double fermentation, so that the tea leaves have a unique aroma. At the same time, according to the fermentation characteristics of lactic acid bacteria, organic acids, special enzyme systems, acid bacteria and other substances beneficial to the human body can be produced. The combined use of the two technologies finally obtains a tea with high amino acid content, rich beneficial substances and unique aroma.

[0010] Furthermore, the compound enzyme stage enzymatic hydrolysis treatment includes adding cellulase in the first stage, adding tannase in the second stage, and adding protease and flavor protease in the third stage.

[0011] In order to further increase the amino acid content in the double-fermented tea leaves, the present invention considers using the specificity of enzymes to perform staged enzymolysis, maximizing the conversion of substances such as proteins in tea leaves into metabolites such as amino acids, and screening the optimal composite enzyme for increasing the amino acid content by combination. It was found that the effect of using a single enzyme or a combination of two or three enzymes is not as good as the combination of cellulase, tannase, protease and flavor protease, so the present invention preferably uses a composite enzyme composed of cellulase, tannase, protease and flavor protease.

[0012] In the composite enzyme stage enzymolysis technology provided by the present invention, cellulase is added in the first stage and enzymolysis is carried out under suitable conditions; after the cellulase enzymolysis is completed, tannase is added for further hydrolysis; after the tannase enzymolysis is completed, protease and flavor protease are added, and finally more amino acids are obtained, thereby improving the fresh taste of tea. Different enzymes perform targeted enzymolysis on different substrates in stages, and the substances or effects produced in the previous stage provide a larger scope of action for the enzymes in the next stage, thereby maximizing the content of amino acids in the reprocessed tea.

[0013] Furthermore, the microbial double fermentation treatment is carried out by fermentation with lactic acid bacteria.

[0014] Since the products produced by the prior art that are further fermented with finished tea are concentrated on the post-fermentation of black tea, the principle is that the finished tea pile forms a unique aroma and taste by changing the temperature and humidity, but this technology is still insufficient in meeting the current market requirements for low bitterness and high freshness of tea taste, and the prior art has more or less limitations in exploring the technology of reprocessed tea that is beneficial to the human body. Therefore, the present invention considers one-step treatment of the tea leaves after enzymatic hydrolysis in the composite enzyme stage. In view of the fact that microorganisms produce different aromas during the fermentation process, the present invention further screens the effects of different microbial strains after double fermentation treatment. It was found that the fermentation effect of yeast was not as good as that of lactic acid bacteria. On the one hand, after the fermentation, the tea soup was evaluated, the soup color was dull, produced an unpleasant smell, and the acceptance was low; while when lactic acid bacteria were used as the strain, the tea soup after fermentation was evaluated, the soup color was bright and shiny, the taste was fresh and clean without odor, and the aroma was special and easy to accept. On the other hand, the content of amino acids and aroma substances in tea leaves fermented with 91011 type lactic acid bacteria produced by Danisco is significantly higher than that in tea leaves fermented with yeast. After comparing different types of lactic acid bacteria from different manufacturers, 91011 type lactic acid bacteria produced by Danisco was finally selected. In addition, the pH value of tea leaves gradually decreases during the fermentation process of lactic acid bacteria, which inhibits the growth of harmful bacteria. At the same time, some bacterial flora inside the tea leaves further grow and reproduce and metabolize to generate active substances, which interact with the substances contained in the tea leaves to form unique flavor components.

[0015] In some methods, a small amount of sugar can be added to tea leaves during lactic acid bacteria fermentation, and lactic acid bacteria fermentation can be carried out based on tea leaves to further improve the fermentation effect of tea leaves.

[0016] Furthermore, the method also includes microwave aroma enhancement treatment and aroma backfilling treatment. The microwave aroma enhancement treatment is performed before the enzymatic hydrolysis treatment in the complex enzyme stage to process the tea by microwave heating; the aroma backfilling treatment includes extracting aroma after the microwave aroma enhancement treatment and before the enzymatic hydrolysis treatment in the complex enzyme stage, and imparting aroma after the microbial double fermentation treatment.

[0017] Since the compound enzyme stage enzymatic hydrolysis treatment and the microbial complex fermentation treatment process will cause aroma loss, the present invention first uses microwave aroma enhancement technology to remove the stale taste and rough old smell in the tea leaves before the finished tea leaves are subjected to the compound enzyme stage enzymatic hydrolysis treatment, thereby improving the aroma of the tea leaves; and further uses supercritical carbon dioxide extraction technology to extract and retain the volatile aroma. After the microbial fermentation is completed, the reserved aroma substances are backfilled into the tea leaves, so that the final tea leaves have both the original tea aroma and the unique aroma substances produced by fermentation. The microwave aroma enhancement treatment generates heat through the collision between molecules, thereby making the raw material selection wider. Whether new tea, old tea, famous tea, or bulk tea can be used as raw materials for this technology; and compared with the existing tea processing technology, the aroma backfilling treatment greatly reduces the loss of tea aroma during the processing process and increases the content of volatile aroma substances in the original tea.

[0018] Furthermore, the method also includes a fragrance-protecting drying process, and the fragrance-protecting drying process includes any one or more of a low-temperature drying method and a freeze-drying method.

[0019] In the prior art, most tea preparations are finally dried by high-temperature drying, and the aroma of the tea is seriously lost in a high-temperature environment. The present invention compares the effects of drying, freeze drying and low-temperature drying on tea aroma protection drying after microbial fermentation. The results show that drying will cause the loss of volatile aroma substances in the tea, while freeze drying will cause the tea to be fragile and unformed. The low-temperature drying method uses a temperature condition of 44 to 46°C and a pressure of -0.15 MPa, which not only avoids the loss of aroma caused by high temperature, but also avoids the breakage of leaves caused by freezing, so the low-temperature drying method is preferred.

[0020] Furthermore, the method comprises the following steps:

[0021] (1) treating the finished tea leaves for aroma enhancement by microwave heating to obtain pretreated tea leaves M1;

[0022] (2) extracting volatile aroma substances from the pretreated tea leaves using supercritical carbon dioxide extraction technology, retaining the aroma extract for later use, and obtaining tea leaves M2;

[0023] (3) treating tea leaves M2 by enzymolysis in stages using cellulase, tannase, protease and flavor protease to obtain tea leaves M3;

[0024] (4) tea leaves M3 are fermented by lactic acid bacteria to obtain tea leaves M4;

[0025] (5) backfilling the aroma extract in step (2) into tea leaves M4;

[0026] (6) The tea leaves M4 are subjected to low temperature drying treatment to obtain a new type of double-fermented tea.

[0027] In some embodiments, in step (1), the tea leaves are heated in a microwave at 915 MHz for 5 to 8 seconds to obtain tea leaves M1.

[0028] In some embodiments, the method of the supercritical carbon dioxide extraction technology described in step (2) is specifically as follows: weigh 50g of sample and fill it into a column, set the conditions as an air compressor outlet pressure of 6 to 8Bar, an output valve temperature of 110°C, a circulating water bath temperature of 5°C, fill 50g of pure water into a receiving bottle, turn on the machine, and perform aroma extraction.

[0029] In some embodiments, the enzymatic hydrolysis treatment step of the four enzymes in step (3) is specifically as follows: weigh 0.3% to 0.5% of the weight of the tea leaves M2, dissolve the cellulase in 10% to 15% of the weight of the tea leaves M2 in water, spray the mixture evenly on the tea leaves after fully dissolved, stir evenly, and let stand at 45°C to 50°C for 20 to 30 minutes; after the treatment, weigh 0.2% to 0.4% of the weight of the tea leaves M2, dissolve the mixture in 10% to 15% of the weight of the tea leaves M2 in water, spray the mixture evenly on the tea leaves after fully dissolved, stir evenly, and let stand at 30°C to 35°C for 20 to 30 minutes; after the treatment, weigh 0.4% to 0.7% of the flavor protease and 0.5% to 0.8% of the protease in 10% to 15% of the weight of the tea leaves M2, dissolve the mixture in 10% to 15% of the weight of the tea leaves M2, spray the mixture evenly on the tea leaves after fully dissolved, stir evenly, and let stand at 50°C to 55°C for 3 hours to allow the tea leaves to fully react.

[0030] In some embodiments, the lactic acid bacteria fermentation treatment step in step (4) includes weighing 0.4% to 0.8% of commercially available lactic acid bacteria, 8% to 10% of white sugar, and 45% to 60% of pure water, fully dissolving and evenly spraying them on the surface of the tea leaves M3, and stirring them evenly, placing the tea leaves in a constant temperature box at 37±1°C, covering the surface of the tea leaves with clean gauze, and fermenting them statically for 15 to 18 hours.

[0031] In some embodiments, the aroma backfilling treatment step in step (5) is specifically as follows: the aroma extract obtained in step (2) and tea leaves are placed in a sealed bag, placed in a 50-55°C oven for 25-30 minutes, and the aroma substances are evenly volatilized in the sealed bag by heating, and fully contacted with the tea leaves. Then, the aroma extract is absorbed by the tea leaves, and after the end, the tea leaves are taken out and quickly placed in a -18--10°C freezer for 4-8 hours to lock in the aroma.

[0032] On the other hand, the present invention provides a novel double-fermented tea prepared by the novel double-fermented tea preparation method as described above.

[0033] The double-fermented tea prepared by the method provided by the present invention not only retains the original tea aroma, reduces the loss of aroma, but also increases the aroma of tea fermentation, so that the tea not only has a fermented aroma, but also retains the original aroma. In addition, the amino acid content in the tea is further increased by composite enzymatic hydrolysis and microbial fermentation.

[0034] In another aspect, the present invention provides a use of a composite enzyme for preparing a reagent for increasing the amino acid content of tea leaves, wherein the composite enzyme comprises cellulase, tannase, protease and flavor protease.

[0035] In another aspect, the present invention provides a use of a microorganism for preparing an agent for improving the aroma of tea leaves, wherein the microorganism comprises lactic acid bacteria.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. Using compound enzyme stage enzymatic hydrolysis technology, according to the biological characteristics of different enzymes, enzymatic hydrolysis is carried out at different stages and at different times, which increases the amino acid content in tea and makes the tea have a better fresh taste;

[0038] 2. The compound enzyme stage enzymatic hydrolysis technology is combined with microbial fermentation technology to further increase the content of beneficial substances in tea leaves and give the double-fermented tea a unique fermented tea aroma;

[0039] 3. The use of microwave aroma enhancement and low-temperature drying treatment methods further increases the content of aroma substances in the tea and reduces the loss of tea aroma; the aroma backfilling technology retains the original aroma of the tea and generally improves the aroma substances in the tea. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with the examples. It should be noted that the examples described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on it. The reagents used in this example are all known products and were obtained by purchasing commercially available products.

[0041] Example 1: Preparation of the novel double-fermented tea provided by the present invention

[0042] 1. Take 500g tea leaves as raw material, place them in a microwave oven (Galanz Microwave Appliance Co., Ltd., model WP800SL23-2), microwave condition is 915MHz, microwave for 5s, and obtain tea leaves M1;

[0043] 2. Use a supercritical carbon dioxide extractor (Global Analytical Instrument Co., Ltd., model 7071) with the conditions set as air compressor outlet pressure 6-8 Bar, output valve temperature 110°C, circulating water bath temperature 5°C to extract volatile aroma substances. The extract is retained in a receiving bottle containing 50g of pure water for later use. The extracted tea is M2;

[0044] 3. Weigh 0.3% of the weight of tea leaves M2 cellulase (purchased from Shandong Longkote Enzyme Preparation Co., Ltd.), dissolve it in 10% of the weight of tea leaves M2 water, put it in a spray pot after it is fully dissolved, spray it evenly on the tea leaves, stir it evenly manually, and place it at 45°C for 20 minutes;

[0045] 4. Weigh 0.2% tannase (purchased from Henan Jiapai Biotechnology Co., Ltd.) by weight of tea leaves M2, dissolve it in 10% water by weight of tea leaves M2, spray it evenly on the tea leaves after it is fully dissolved, stir it evenly by hand, and let it stand at 30°C for 20 minutes;

[0046] 5. Weigh 0.4% flavor protease (purchased from Henan Zhongchen Biotechnology Co., Ltd.) and 0.5% protease (purchased from Henan Zhongchen Biotechnology Co., Ltd.) of the weight of tea leaves M2, dissolve them in water that is 10% of the weight of tea leaves M2, spray them evenly on the tea leaves after they are fully dissolved, stir them evenly manually, place them at 50°C for 3 hours, and obtain tea leaves M3 after they are fully enzymolyzed by cellulase, tannase, protease and flavor protease;

[0047] 6. Weigh the weight of tea leaves M2, add 0.4% commercial lactic acid bacteria (purchased from DANISCO, model 91011), 8% white sugar, and 60% pure water, and evenly spray them on tea leaves M3 after fully dissolving. After stirring evenly, place the tea leaves in a 37°C constant temperature box, cover with clean gauze, and ferment for 18 hours to obtain tea leaves M4.

[0048] 7. Place the aroma extract obtained in step (2) and tea leaves M4 in a sealed bag and place them in a 50-55°C oven for 25-30 minutes to allow the aroma substances to evaporate evenly in the sealed bag and fully contact the tea leaves. After the aroma extract is removed, place it in a -18--10°C freezer and freeze it for 4-8 hours.

[0049] 8. Take the tea leaves out of the sealed bag and place them in a low-temperature drying oven. Set the temperature to 45°C ± 1°C and the pressure to -0.15 MPa-(-0.1 MPa). When the moisture content of the tea leaves is ≤5%, the drying is completed to obtain a new type of double-fermented tea leaves.

[0050] Example 2: Verification of the combination of enzymatic hydrolysis and microbial fermentation treatment in the compound enzyme stage

[0051] According to the prior art, different enzymes can increase the amino acid content in tea leaves when used in combination. However, since microorganisms can produce unique fermentation aroma and beneficial metabolites during the fermentation process, this example further explores the effects of combined enzyme hydrolysis and microbial fermentation on the beneficial components and aroma substances in tea leaves, and compares the four treatment methods shown in Table 1. The control is to prepare double-fermented tea without using combined enzyme hydrolysis and microbial fermentation treatment, and the remaining processes and steps are the same as in Example 1. The physical and chemical properties and aroma changes of the prepared double-fermented tea were then analyzed, and the specific detection method is as follows:

[0052] The detection method of amino acids is GB / T 8314-2013 Determination of the total amount of free amino acids in tea; the detection method of tea polyphenols is GB / T 21733 Tea Beverages Appendix A Tea Polyphenols in Tea Beverages Detection Method; the detection method of caffeine is liquid chromatography; the detection method of catechins is liquid chromatography; the detection method of aroma is GC-MS detection method. The test results are shown in Tables 1 and 2, where the changes in catechin content are expressed by its most effective active ingredient, epigallocatechin gallate (EGCG).

[0053] Table 1 Effects of different combined treatments on the physical and chemical indicators of tea

[0054]

[0055] According to the data in Table 1, compared with the control, after the treatment with the composite enzymatic hydrolysis method (combination 1) or the combined treatment with the composite enzymatic hydrolysis and microbial fermentation (combinations 3 and 4), the amino acid and EGCG contents in the tea leaves increased significantly, and the caffeine and tea polyphenol contents in the tea leaves did not change significantly. However, the effect of first microbial fermentation and then composite enzymatic hydrolysis (combination 4) was not as good as the combination of first composite enzymatic hydrolysis and then microbial fermentation (combination 3). Therefore, in order to achieve the purpose of increasing the amino acid content, combination 1 and combination 3 containing the composite enzymatic hydrolysis treatment method are preferred.

[0056] Table 2 Effects of different combined treatments on tea aroma substances

[0057]

[0058]

[0059]

[0060] Note: Peak areas are expressed in scientific notation.

[0061] According to the data in Table 2, it can be seen that tea aroma has a wide variety of substances, including nearly 10 types of substances such as alcohols, aldehydes, acids, esters, and terpenes. Among them, 46 aroma compounds were identified in combination 1, 58 in combination 2, 59 in combination 3 and combination 4, and 40 in the control group, and the aroma composition and content of each combination were significantly different. Compared with the control group, there was no significant difference in the aroma composition and content of combination 1. The aroma composition types and contents of combinations 2, 3, and 4 increased, but the effects of combinations 2 and 4 were not as good as those of combination 3. The content of aroma substances in combination 3 was significantly increased compared with combination 1, such as limonene, 2-butyl-1-octanol, methyl salicylate, myrcene, etc. In summary, the combined treatment method of first using compound enzyme hydrolysis and then microbial fermentation (combination 3) has the best effect in simultaneously increasing the amino acid content and enriching the aroma substances.

[0062] Example 3: Combination screening of complex enzymes

[0063] The amino acids in tea play an important role in human health, including improving immunity, relieving stress, promoting sleep and other multiple functions. However, in the process of processing tea buds into finished tea or reprocessing tea, due to the processing technology, the content of various beneficial substances such as amino acids in tea is low. Therefore, the prior art promotes the conversion of various substances such as protein in tea into beneficial substances such as amino acids by adding a variety of enzymes during the processing process. In order to explore the influence of different types of enzymes on the content of amino acids and other substances in tea when they work in combination, this embodiment provides several different combinations of composite enzymes shown in Table 3 for staged enzymolysis, and the remaining processes and steps are the same as those in Example 1 to prepare the double-fermented tea, wherein the control is that the composite enzyme is not used for enzymolysis. The method for determining the physical and chemical indicators of the prepared double-fermented tea is the same as that in Example 2, and the test results are shown in Table 4.

[0064] Table 3 Different combinations of complex enzymes

[0065]

[0066]

[0067] Table 4 Effects of different complex enzyme combinations on the physical and chemical indicators of tea

[0068]

[0069] According to the results in Table 4, compared with the control group, only tannase (combination 1) was added, and the amino acid and EGCG content in tea increased slightly; adding tannase and protease (combination 2), the amino acid and EGCG content increased, but the increase was not high; adding pectinase and protease (combination 3), the amino acid and EGCG content did not change significantly; adding cellulase and protease (combination 4), the amino acid and EGCG content increased, and the difference in amino acid and EGCG content between combination 2 was not obvious; combining combination 2 and combination 4, adding cellulase, tannase and protease (combination 5), the amino acid and EGCG content increased significantly; adding flavor protease (combination 6) on the basis of combination 5, the amino acid and EGCG content increased significantly. Therefore, the treatment method of adding cellulase, tannase, protease and flavor protease at the same time is preferred.

[0070] Example 4: Comparison of enzymatic hydrolysis sequences of complex enzymes

[0071] In the prior art, multiple enzymes are often compounded before tea fermentation. The present invention innovatively proposes a method of compound enzyme stage enzymolysis, adding different types of enzymes at different stages of fermentation to maximize the promotion of the substances in the tea to generate amino acids and other nutrients. In order to further explore the difference in the effect of enzymolysis of the four enzymes provided by the present invention at different stages, this example performs compound enzyme stage treatment according to the three enzymolysis sequences shown in Table 5, and the remaining processes and steps are the same as those in Example 1 to prepare the double-fermented tea, and then the physical and chemical properties of the double-fermented tea are tested according to the physical and chemical index determination method provided in Example 2, and the results are shown in Table 6.

[0072] Table 5 Order of adding different enzymes

[0073]

[0074]

[0075] Table 6 Effects of different enzymatic hydrolysis sequences on the physical and chemical indicators of tea

[0076]

[0077] As shown in the results of Table 6, the content of nutrients in the double-fermented tea leaves prepared by the enzymatic hydrolysis sequence of combinations 2 and 3 is not as good as that of combination 1, among which the content of amino acids, tea polyphenols and EGCG is significantly reduced. The reason is that cellulase can destroy the cellulose in the cell wall of tea leaves, so adding cellulase in the first stage is conducive to the outflow of substances in the cells; then adding tannin can break the ester bonds in the tea substances to form water-soluble short-chain substances; then adding protease and flavor protease can further hydrolyze the protein peptide bonds of the short-chain substances, and finally obtain more amino acids, thereby improving the fresh taste of tea leaves. If protease is directly added after cellulose enzymatic hydrolysis, some macromolecular substances cannot be effectively utilized and converted into active ingredients. Therefore, only by adding cellulase in the first stage, tannin in the second stage, and protease and flavor protease in the third stage can the content of beneficial substances in tea leaves be effectively increased.

[0078] Example 5: Screening of fermentation microorganisms

[0079] At present, the re-fermentation treatment of finished tea is mostly the post-fermentation treatment of black tea, and its principle is to change the fermentation temperature and humidity to affect the sensory evaluation of tea aroma and other aspects. In combination with the concept of fermentation health in other fields, the concept of microbial re-fermentation is proposed, that is, on the basis of the existing post-fermentation, beneficial microorganisms are added, and the interaction between beneficial bacteria and the effective ingredients and microorganisms in the tea leaves during the microbial fermentation process is used to produce different aromas, and further develop new reprocessed tea leaves with special aromas. In order to explore the palatability of re-fermented tea leaves under different microbial fermentation treatment conditions, this embodiment provides the following different microbial strains for fermentation treatment, and the remaining process steps are the same as in Example 1 for the preparation of re-fermented tea, and the control is no microbial fermentation treatment. Afterwards, the prepared re-fermented tea is subjected to sensory evaluation, and the method is as follows:

[0080] According to the tea sensory evaluation method of GB / T 23776 and combined with personal subjective feelings, the tea soups treated with different microbial fermentation were evaluated. 16 people were invited to participate, including 10 R&D professionals and 6 other non-professionals. The evaluation was conducted through four dimensions: soup color acceptance, aroma acceptance, taste acceptance and overall acceptance. Compared with the control group, those who accepted were marked with "√", those who did not accept were marked with "×", and the number of people who accepted was counted. The survey results are shown in Table 7.

[0081] Table 7 Sensory evaluation of tea after fermentation with different microbial strains

[0082]

[0083] According to the results of Table 7, it can be seen that the tea soup color after adding yeast fermentation has the worst acceptance, and there is deterioration; the overall acceptance of tea after adding lactic acid bacteria fermentation is higher than the acceptance of tea after other microbial fermentation, among which lactic acid bacteria 91011 (danisco) fermented tea has the highest total votes and the highest acceptance. In addition, the physical and chemical indicators and aroma substance analysis results of tea after fermentation treatment with different microbial strains in this embodiment show that the amino acid content in the double fermented tea prepared by fermentation with 5 kinds of lactic acid bacteria (lactic acid bacteria 1, lactic acid bacteria 2, lactic acid bacteria lpc, lactic acid bacteria 092, lactic acid bacteria 91011) is significantly higher than that after yeast fermentation. At the same time, the types of tea aroma substances after 5 kinds of lactic acid bacteria fermentation also increase significantly, but in terms of content, the aroma substance content in the double fermented tea prepared by lactic acid bacteria 91011 fermentation is significantly higher than that of other 4 kinds of lactic acid bacteria. In summary, lactic acid bacteria 91011 is preferably fermented in this embodiment.

[0084] Embodiment 6, the screening of the fragrance protection drying method

[0085] In the last step of the existing tea processing technology, the tea leaves usually need to be dried to facilitate the long-term preservation of tea products. However, the drying method of tea leaves will lead to differences in the quality, taste, aroma and other aspects of the tea leaves due to different processes and conditions. In order to further explore the most suitable drying method for tea leaves, this example compares the effects of three different fragrance-protecting drying methods on the quality of fermented tea leaves. Treatment 1 is freeze-drying, treatment 2 is low-temperature drying, and treatment 3 is traditional drying. The remaining processes and steps are the same as in Example 1 to prepare fermented tea. Afterwards, the aroma of the tea leaves was subjected to a sensory evaluation of the tea soup, using the same evaluation method as in Example 4, and the morphology of the tea leaves was recorded. The results are shown in the table below.

[0086] Table 8 Effects of different drying methods on tea quality

[0087]

[0088] According to the results in Table 8, it can be seen that the tea leaves dried at low temperature and dried at room temperature have no broken appearance, but the aroma of the tea leaves dried at low temperature is more intense and lasting, while the aroma quality of the tea leaves dried at freeze-drying and low temperature is slightly better than that of the dried tea leaves, but the tea leaves after freeze-drying have broken appearance, so the low-temperature drying method for protecting the aroma of the tea leaves is preferred.

[0089] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A novel method for preparing double-fermented tea, characterized in that: It includes enzymatic hydrolysis treatment in the compound enzyme stage and microbial fermentation treatment.

2. The method according to claim 1, characterized in that The compound enzyme stage enzymatic hydrolysis treatment comprises adding cellulase in the first stage, adding tannase in the second stage, and adding protease and flavor protease in the third stage.

3. The method according to claim 1, characterized in that The microbial double fermentation treatment is carried out by fermentation with lactic acid bacteria.

4. The method according to claim 1, characterized in that It also includes microwave aroma enhancement treatment and aroma backfilling treatment. The microwave aroma enhancement treatment is performed before the enzymatic hydrolysis treatment in the complex enzyme stage, and the tea is processed by microwave heating. The aroma backfilling treatment includes extracting aroma after the microwave aroma enhancement treatment and before the enzymatic hydrolysis treatment in the complex enzyme stage, and imparting aroma after the microbial double fermentation treatment.

5. The method according to claim 1, characterized in that It also includes a fragrance-protecting drying process, which includes any one or more of a low-temperature drying method and a freeze-drying method.

6. The method according to claim 5, characterized in that The fragrance protection drying process includes a low-temperature drying method, and the drying temperature is 44-46°C.

7. The method according to claim 6, characterized in that The following steps are involved: (1) treating the finished tea leaves for aroma enhancement by microwave heating to obtain pretreated tea leaves M1; (2) extracting volatile aroma substances from the pretreated tea leaves using supercritical carbon dioxide extraction technology, retaining the aroma extract for later use, and obtaining tea leaves M2; (3) treating tea leaves M2 by enzymolysis in stages using cellulase, tannase, protease and flavor protease to obtain tea leaves M3; (4) tea leaves M3 are fermented by lactic acid bacteria to obtain tea leaves M4; (5) backfilling the aroma extract in step (2) into tea leaves M4; (6) The tea leaves M4 are subjected to low temperature drying treatment to obtain a new type of double-fermented tea.

8. A novel double-fermented tea prepared by the novel double-fermented tea preparation method according to any one of claims 1 to 7.

9. Use of a composite enzyme for preparing a reagent for increasing the amino acid content of tea, characterized in that: The complex enzyme comprises cellulase, tannase, protease and flavor protease.

10. A use of a microorganism for preparing an agent for improving the aroma of tea, characterized in that: The microorganisms include lactic acid bacteria.

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