Tea flavor quality improving method based on microbial solid state fermentation

Abstract

The invention discloses a tea flavor quality improving method based on microbial solid state fermentation, which comprises the following steps: step 1, raw material treatment: performing fixation, rolling and drying treatment on tea leaves to obtain pretreated tea leaves; step 2, treatment of strains for fermentation, inoculation and culture of aspergillus oryzae, saccharomycetes and lactic acid bacteria, extraction and preparation of a strain mixed solution; step 3, inoculated fermentation: performing inoculated mixing on the strain mixed solution obtained in the step 2 and the pretreated tea leaves obtained in the step 1, and then putting the tea leaves inoculated with strains into a fermentation tank for fermentation treatment to obtain fermented tea leaves; and step 4, performing post-treatment on the tea leaves: performing drying treatment on the fermented tea leaves obtained in the step 3, and performing screening treatment to obtain the drinkable fermented tea leaves. According to the technical scheme, the content of tea polyphenols in the obtained tea leaves is 12.3%, the total amount of amino acids is 3.8%, the content of the tea polyphenols is reduced, the bitter taste of tea water is effectively reduced, and the fragrance of the tea water is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tea processing, in particular to a tea flavor quality improvement method based on microbial solid-state fermentation. BACKGROUND

[0002] As a traditional economic crop and beverage in China, the flavor quality of tea directly determines the commodity value of tea. The flavor quality of tea is mainly determined by active ingredients such as tea polyphenols, amino acids, caffeine, and aroma substances, and the fermentation process is a key link for regulating the transformation of these active ingredients and forming a unique flavor.

[0003] Traditional tea fermentation relies on natural fermentation by microorganisms carried by tea leaves. This method has the following disadvantages: first, the microbial community structure is unstable during fermentation, and the dominant bacteria are not clear, resulting in large differences in tea flavor quality between batches; second, the fermentation period is long, usually several days to several tens of days, and the production efficiency is low; third, the natural fermentation process is easily contaminated by foreign bacteria, which may produce odor substances and affect the quality of tea; fourth, the conversion efficiency of bitter and astringent substances (such as tea polyphenols) in tea is low, and the finished tea is prone to have heavy bitterness and single aroma.

[0004] Therefore, we propose a tea flavor quality improvement method based on microbial solid-state fermentation to solve the above problems. SUMMARY

[0005] The present application aims to provide a tea flavor quality improvement method based on microbial solid-state fermentation to solve the problems raised in the background.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0007] A tea flavor quality improvement method based on microbial solid-state fermentation, comprising the following steps:

[0008] Step 1, raw material processing, mainly including fixation, rolling and drying treatment of tea leaves, then obtaining pretreated tea leaves, selecting fresh black tea as raw material, using steam fixation method for fixation, then placing in a rolling machine, then placing the rolled tea in an oven, drying at 65℃ to a moisture content of 35%, obtaining pretreated tea leaves.

[0009] Step 2, fermentation strain treatment, mainly including inoculation, culture and extraction and preparation of Aspergillus oryzae, yeast and lactic acid bacteria to prepare a mixed bacterial suspension, after culture, centrifugal collection of bacterial cells, washing 3 times with sterile physiological saline, preparing Aspergillus oryzae suspension, yeast suspension and lactic acid bacteria suspension with a concentration of 5x10 CFU / mL, obtaining a complex bacterial suspension.

[0010] Step three, inoculation and fermentation, the mixed bacteria solution obtained in step two is inoculated with the pretreated tea leaves obtained in step one, and then the inoculated tea leaves are placed in a fermentation tank for fermentation treatment to obtain fermented tea leaves; the mixed bacteria solution and the pretreated tea leaves are inoculated, fully stirred and uniformly mixed, and then placed in a solid-state fermentation tank with a temperature and humidity control system for fermentation for 5 days to obtain fermented tea leaves.

[0011] Step four, tea leaf post-treatment, the fermented tea leaves obtained in step three are dried, and after screening treatment, drinkable fermented tea leaves are obtained; the fermented tea leaves are placed in a vacuum drying box, and then screened with a screen, and dust and impurities are removed by electrostatic impurity removal to obtain finished tea leaves with improved flavor quality.

[0012] Preferably, the fresh tea leaf fixation in step one is controlled at 100-120 DEG C, the fixation time is 3-5 min, the rolling speed of the rolling machine is 35-40 r / min, and the rolling time is 20-30 min.

[0013] Preferably, the aspergillus oryzae in step two is first inoculated in a potato glucose culture medium, the yeast is inoculated in a wort culture medium, and the lactic acid bacteria is inoculated in an MRS culture medium.

[0014] Preferably, the aspergillus oryzae and the yeast in step two are cultured under normal temperature conditions, the yeast in step two is cultured under normal temperature anaerobic conditions, and the culture time of the three is 40-48 hours, 30-36 hours and 40-48 hours, respectively.

[0015] Preferably, the three bacteria in step two are obtained by centrifugal treatment, and are washed in physiological saline, and then are mixed in a ratio of 2:1:1 to obtain a bacteria suspension.

[0016] Preferably, the mixed bacteria in step three is 6%-10% of the weight of the tea leaves, the fermentation tank is a solid-state fermentation tank with a temperature and humidity control system, the stirring is sterile mechanical stirring, the stirring time is 5-10 min each time, and the oxygen content in the tank during the stirring process is controlled to be 5-10%.

[0017] Preferably, the drying environment in step four is controlled at 50-60 DEG C, and the screening structure of the screening equipment used in step four is a 30-mesh screen.

[0018] Compared with the prior art, the beneficial effects of the present application are:

[0019] The tea flavor quality improving method based on microbial solid fermentation adopts the complex strain composed of aspergillus oryzae, yeast and lactic acid bacteria for solid fermentation, the three kinds of strains have synergistic effect, aspergillus oryzae can produce rich protease and cellulase, promote the hydrolysis of protein in tea to amino acid, the degradation of cellulose to soluble sugar, reduce the crude fiber content of tea, yeast can convert soluble sugar into ethanol, ester and other aroma substances, improve the fruity and floral levels of tea, lactic acid bacteria can produce lactic acid and other organic acids, react with alkaloids in tea, reduce the bitterness, and at the same time improve the mellow taste of tea, through the synergistic metabolism of complex strains, the directional conversion of active ingredients in tea is realized, and the flavor quality of finished tea is significantly improved. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] The present application provides a tea flavor quality improving method based on microbial solid fermentation technical solution:

[0022] Embodiment:

[0023] A tea flavor quality improving method based on microbial solid fermentation, comprising the following steps:

[0024] Step one, raw material treatment, mainly including the fixation, rolling and drying treatment of tea leaves, and then obtaining pretreated tea leaves.

[0025] Step two, fermentation strain treatment, mainly including inoculation, culture, extraction and preparation of aspergillus oryzae, yeast and lactic acid bacteria to obtain a mixed strain solution.

[0026] Step three, inoculation and fermentation, inoculating and mixing the mixed strain solution obtained in step two with the pretreated tea leaves obtained in step one, then placing the tea leaves inoculated with the strain into a fermentation tank for fermentation treatment to obtain fermented tea leaves.

[0027] Step four, tea post-treatment, drying the fermented tea leaves obtained in step three, and then screening to obtain drinkable fermented tea leaves.

[0028] In step one, the fixation of fresh tea leaves is controlled at 100℃-120℃ for 3-5 minutes. The rolling speed of the rolling machine is 35-40 r / min for 20-30 minutes. Specifically, fresh black tea leaves are selected as raw materials and fixed with steam at 110℃ for 4 minutes. Then, the leaves are placed in a rolling machine and rolled at 35 r / min for 25 minutes. The rolled tea leaves are then placed in an oven and dried at 65℃ until the moisture content is 35%, thus obtaining pre-treated tea leaves.

[0029] In step two, *Aspergillus oryzae* is first inoculated into potato dextrose medium, yeast into malt extract medium, and lactic acid bacteria into MRS medium. The *Aspergillus oryzae* and yeast in step two are cultured with shaking at room temperature, while the yeast in step two is cultured under anaerobic conditions at room temperature. The culture times for the three are 40-48 hours, 30-36 hours, and 40-48 hours respectively. All three bacterial strains in step two are obtained by centrifugation and washed with physiological saline. Then, the three are mixed in a 2:1:1 ratio to obtain the desired bacterial strain. The specific procedure for preparing the suspensions is as follows: Aspergillus oryzae is inoculated into potato dextrose medium and cultured with shaking at 30℃ and 180 rpm for 48 h; yeast is inoculated into malt extract medium and cultured with shaking at 28℃ and 180 rpm for 36 h; and lactic acid bacteria are inoculated into MRS medium and cultured anaerobically at 37℃ for 48 h. After the culture is completed, the bacterial cells are collected by centrifugation and washed three times with sterile physiological saline to prepare Aspergillus oryzae suspension, yeast suspension, and lactic acid bacteria suspension with a concentration of 5×10 CFU / mL. Then, the three bacterial suspensions are mixed at a mass ratio of 2:1:1 to obtain a compound bacterial suspension.

[0030] In step three, the mixed microbial strains account for 6%-10% of the tea weight. The fermentation tank is a solid-state fermentation tank with a temperature and humidity control system. The material is turned using a sterile mechanical turning method, with each turning taking 5-10 minutes. During the turning process, the oxygen content inside the tank is controlled at 5-10%. In step four, the drying environment is controlled at 50℃-60℃. The sieving equipment used in step four has a 30-mesh screen. The specific operation involves placing the fermented tea leaves in a vacuum drying oven and drying them at 55℃ and a vacuum degree of 0.085MPa until the moisture content is 7%. Then, the leaves are sieved using a 30-mesh screen, and dust and impurities are removed using an electrostatic purification method to obtain a finished tea product with improved flavor and quality.

[0031] After fermentation, experiments showed that the tea contained 12.3% tea polyphenols and 3.8% total amino acids. Compared with tea produced by traditional fermentation methods, the tea polyphenol content was reduced, which effectively reduced the bitterness of the tea and improved its aroma.

[0032] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving the flavor quality of tea based on microbial solid-state fermentation, characterized by, It comprises the following steps: Step one, raw material processing, mainly including the fixation of tea, rolling and drying treatment, and then get the pretreated tea; Step two, fermentation of strain treatment, mainly including the inoculation, culture and extraction and preparation of Aspergillus oryzae, yeast and lactic acid bacteria mixed liquid; Step three, inoculation and fermentation, the mixed liquid of the strain obtained in step two and the pretreated tea obtained in step one are inoculated and mixed, and then the tea inoculated with the strain is placed in the fermentation tank for fermentation treatment, and the fermented tea is obtained; Step four, tea post-processing, the fermented tea obtained in step three is dried, and after screening treatment, the drinkable fermented tea is obtained.

2. The method for improving the flavor quality of tea based on microbial solid-state fermentation according to claim 1, characterized in that: The fixation of fresh tea in step one is controlled at 100-120℃, the fixation time is 3-5min, the rolling speed of the rolling machine is 35-40r / min, and the rolling time is 20-30min.

3. The method for improving the flavor quality of tea based on microbial solid-state fermentation according to claim 1, characterized in that: The Aspergillus oryzae in step two is first inoculated in the potato glucose culture medium, the yeast is inoculated in the malt juice culture medium, and the lactic acid bacteria is inoculated in the MRS culture medium.

4. The method for improving the flavor quality of tea based on microbial solid-state fermentation according to claim 1, characterized in that: The Aspergillus oryzae and yeast in step two are cultured under normal temperature condition, the yeast in step two is cultured under normal temperature anaerobic condition, and the culture time of the three is 40-48h, 30-36h and 40-48h respectively.

5. The method for improving the flavor quality of tea based on microbial solid-state fermentation according to claim 1, characterized in that: The three kinds of bacteria in step two are obtained by centrifugal treatment, and need to be washed in physiological saline, and then mixed in the ratio of 2:1:1, and the obtained is the bacterial suspension.

6. The method for improving the flavor quality of tea based on microbial solid-state fermentation according to claim 1, characterized in that: The mixed strain in step three is 6%-10% of the weight of tea, the fermentation tank is a solid state fermentation tank with temperature and humidity control system, the stirring is sterile mechanical stirring, the stirring time is 5-10min each time, and the oxygen content in the tank is controlled at 5-10% during stirring.

7. The method for improving the flavor quality of tea based on microbial solid-state fermentation according to claim 1, characterized in that: The drying environment in step four is controlled at 50-60℃, and the screening structure of the screening equipment used in step four is 30 mesh screen.