Processing method of black tea

Abstract

The invention discloses a processing method of black tea in the field of tea processing. According to the method, a specially-made mesoporous silica-zeolite molecular sieve core-shell structure loaded nano metal oxide composite material is added in the tea rolling stage, and the fermentation process is cooperatively regulated and controlled. The material is prepared by carrying out amino functionalization on a zeolite molecular sieve, adsorbing cerium and yttrium metal ions under a specific pH value condition, synchronously constructing a mesoporous silica shell layer, and carrying out solvothermal crystallization and gradient calcination, and has a fine core-shell structure and high-dispersion catalytic active sites. The black tea processing comprises the steps of withering, catalytic rolling and pre-fermentation, main fermentation and catalyst magnetic separation and drying. According to the method, by utilizing the shape-selective catalysis and oxidation functions of the composite material, the generation of theaflavin can be directionally promoted, the aroma is optimized, the fermentation time is remarkably shortened, the quality stability and the production efficiency of black tea are improved, and the catalyst can be recycled.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tea processing, and particularly relates to a processing method of black tea. BACKGROUND

[0002] Black tea is a traditional characteristic beverage in China, and its unique color, aroma and taste are derived from the key fermentation process in the processing. Traditional black tea processing mainly relies on the polyphenol oxidase contained in tea leaves to catalyze the oxidation and polymerization of phenolic substances such as catechins under suitable temperature and humidity conditions, to form the core components of tea yellow and tea red that give the tea soup a bright color and a mellow taste, and to simultaneously transform a rich variety of aroma substances. However, this natural enzymatic fermentation process has significant limitations. The reaction rate and conversion direction are easily affected by multiple factors such as seasonal differences in fresh leaf materials, endogenous enzyme activity, and environmental temperature and humidity fluctuations, resulting in poor product quality stability and differences in color, aroma and taste between different batches. In particular, tea fresh leaves picked in summer and autumn often have high polyphenol content and relatively low enzyme activity, making it difficult to ferment under conventional processes, and problems such as insufficient or excessive fermentation often occur, resulting in bitter taste, lack of fresh aroma, dark soup color and low quality product rate. How to realize controllable and efficient fermentation process of black tea, and to stabilize and improve the quality, especially to improve the processing suitability of summer and autumn tea, has been a technical bottleneck that the industry needs to break through.

[0003] To overcome the shortcomings of traditional fermentation methods, the industry has explored various technical improvement paths. One class of research focuses on the introduction of exogenous biological agents, such as the addition of polyphenol oxidase or specific microbial agents of different sources to accelerate or guide the fermentation process. This method can adjust the fermentation to some extent, but the biological active substances themselves are sensitive to the processing environment, have poor stability and preservation, and are high in cost, which limits large-scale industrial application. Another approach focuses on physical field assistance or the addition of some natural and safe food-grade materials to improve the fermentation microenvironment. In addition, some research has also used advanced adsorption materials in separation science to try to recover or fix tea aroma components, but there is no mature report on their direct catalytic application in the main fermentation reaction. Most of these existing improvement technologies still remain at the level of partial modification or auxiliary of the traditional biochemical process, and have not fundamentally created a stable, efficient and widely applicable new regulation system, which has limited contribution to solving the uncontrollable problem of fermentation in nature.

[0004] In summary, the current black tea processing technology, especially the fermentation link, still lacks an innovative means that can break through the inherent limitations of enzymatic reactions, achieve precise directional regulation, and be suitable for large-scale production. The application of biological agents in existing technologies has stability and cost barriers, while physical or simple physical and chemical methods are difficult to access the core chemical pathways of fermentation reactions. Therefore, there is an urgent need in the field for a completely new technical principle and process scheme to shift fermentation from relying on unstable biological enzyme activity to a more reliable and controllable process. Based on this, the present application proposes an innovative concept: introducing inorganic composite catalytic materials with excellent structural design in materials science into the black tea processing system. This material should have specific catalytic oxidation and molecular shape-selective functions, and be able to simulate and even strengthen target oxidation reactions, while its physical and chemical properties are stable and easy to recycle and use. By combining this material with a simple and integrated processing step, a new black tea catalytic fermentation processing method is established, which can efficiently and stably regulate the fermentation process of black tea, significantly improve the uniformity of product quality, and open up new ways for the high-value utilization of summer and autumn tea resources. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application aims to provide a processing method for black tea.

[0006] In a first aspect, the present application provides a processing method for black tea, comprising the following steps: S1, picking tea fresh leaves, spreading them in a withering tank, and withering at 27-30℃; reducing the temperature to 24-26℃, and starting intermittent and gentle air supply, continuing withering until the fresh leaf moisture content is reduced to 62%-65%, obtaining withered leaves; S2, putting the withered leaves into a rolling machine, rolling at 24-26℃; adding mesoporous silica-zeolite molecular sieve core-shell structure loaded nanometer metal oxide composite material, obtaining a rolling mixture; taking out the rolling mixture and placing it in a fermentation tray, pre-fermenting at a temperature of 26-30℃, obtaining pre-fermented tea leaves; S3, transferring the pre-fermented tea leaves to a fermentation box, continuing fermentation, obtaining a fermentation mixture; S4, transferring the fermentation mixture to a weak magnetic field drum separator, obtaining tea leaves after separation of the catalyst; drying the tea leaves after separation of the catalyst.

[0007] In the present application, the mesoporous silica-zeolite core-shell structure loaded with nano metal oxide composite material is applied to black tea processing, the interaction with the tea system and the catalytic regulation mechanism of fermentation are fully realized. In the rolling process, the nano-sized particles of the material are fully mixed with the juice released by the broken tea cells under the action of mechanical force, the fermentation substrates such as polyphenols, amino acids and sugars in the tea are rapidly diffused into the mesoporous channels of the material and selectively enriched in the zeolite micropores, forming a local high-concentration reaction microenvironment. In the subsequent pre-fermentation and main fermentation stages, the nano metal oxide loaded on the material interface becomes a catalytic center. The cerium-based oxide can efficiently activate the oxygen in the air due to its variable valence and rich surface oxygen vacancies, producing active oxygen species, which preferentially oxidize the enriched catechins, start the quinone type and subsequent coupling reactions; while the acid sites in the zeolite core and the space constraint effect of its regular pores play a key shape-selective catalysis role in the further polymerization direction of the initial oxidation products, guiding the ordered condensation of the reaction intermediates towards the generation of theaflavins as the target product, while effectively inhibiting the side reaction path of disordered random polymerization to generate a large amount of theabrownines. In addition, the mesoporous silica shell not only protects the catalytic active sites of the core, but also has surface characteristics that are beneficial to the adsorption and transformation of aroma precursor substances in tea, promoting lipid degradation and Maillard reaction, thereby synergistically optimizing the aroma composition. The entire catalytic fermentation process is carried out efficiently under mild conditions, greatly shortening the required time. After fermentation is completed, the catalyst and tea matrix can be quickly and thoroughly physically separated by a weak magnetic field due to the weak paramagnetism of the material designed at the beginning, ensuring the safety and purity of the product, and the catalyst can be recycled. The mechanism of the whole process shows that the present application realizes the whole process controllable of black tea fermentation from molecular scale adsorption, interface catalytic reaction to final product guidance through the coupling of material structure and process.

[0008] According to the preferred embodiment of the present application, in step S1, the time for continuing to wither is 4-6h.

[0009] According to the preferred embodiment of the present application, in step S2, the time for pre-fermentation at a temperature of 26-30℃ is 60-80min.

[0010] According to the preferred embodiment of the present application, in step S3, the time for continuing to ferment is 2.5-3.5h.

[0011] According to the preferred embodiment of the present application, in step S4, the drying step of the tea after separating the catalyst includes: first, initial baking under hot air at 115-125℃; then drying at 90-95℃ until the water content is less than 6%.

[0012] According to a preferred embodiment of the present application, the preparation steps of the mesoporous silica-zeolite molecular sieve core-shell structure loaded nanometal oxide composite material include: A1, dispersing a β-zeolite molecular sieve in anhydrous ethanol, ultrasonic treatment to obtain a suspension; under stirring and nitrogen protection, heating the suspension to 64-66℃, then adding a 3-aminopropyltriethoxysilane-containing anhydrous ethanol solution dropwise; after the dropwise addition is completed, heating to 76-80℃ to reflux; after the reaction is completed, collecting the solid product by high-speed centrifugation, washing the solid product with anhydrous ethanol and deionized water in sequence, and drying the obtained solid in a 78-82℃ vacuum drying oven to obtain amino-functionalized zeolite nanoparticles; A2, redispersing the amino-functionalized zeolite nanoparticles in a mixed solution composed of deionized water, anhydrous ethanol and acetic acid, adjusting the pH to 5-6, and ultrasonic treatment; under constant temperature water bath at 34-36℃ and stirring, adding a precursor salt solution formed by dissolving cetyltrimethylammonium bromide, cerium nitrate hexahydrate and yttrium nitrate hexahydrate in deionized water, continuing to stir, then adding concentrated ammonia water, adjusting the pH value to 10-11, and adding tetraethyl orthosilicate dropwise; after the dropwise addition is completed, continuing to stir to obtain a slurry; A3, transferring the slurry to a high-pressure reaction kettle, and performing solvothermal crystallization treatment at 115-125℃; after the reaction is completed, naturally cooling to room temperature, centrifugally collecting the solid product, washing the solid product with a mixed solution of ethanol and water to obtain a washed solid product; dispersing the washed solid product in an acidic ethanol solution, refluxing and stirring at 58-62℃, and again centrifuging, washing and drying to obtain a core-shell intermediate; A4, placing the core-shell intermediate in a tube furnace, and performing gradient calcination activation under an air atmosphere: first heating from room temperature to 345-355℃ and holding; continuing to heat to 545-555℃ and holding; after the calcination is completed, naturally cooling to room temperature.

[0013] The core mechanism of the mesoporous silica-zeolite molecular sieve core-shell structure loaded nanometal oxide composite material in the application is to creatively introduce an inorganic composite catalytic material with precise structure, multi-level pores and multiple active sites into a black tea fermentation system, so that a natural biochemical process depending on biological enzyme activity is changed into a multi-phase catalytic physical and chemical process which can be accurately controlled. The reaction mechanism of the composite material starts from its unique hierarchical structure design: the amino-functionalized zeolite molecular sieve as the core, the regular microporous channel of which is like a precision screen and can selectively adsorb catechin monomers in tea leaves, especially key precursors such as epigallocatechin gallate, to realize the pre-concentration and preliminary selection of reactants; the amino functional groups grafted on the surface of the core not only enhance the hydrophilicity to facilitate dispersion in the aqueous environment of tea leaves, but also serve as anchoring points for the growth of the subsequent shell. In a weak acid environment, the metal cations of cerium and yttrium are preferentially adsorbed and fixed around the amino sites on the surface and the entrance of the pores of the core by ion exchange and coordination; then the system is changed to a strong alkaline environment, in which tetraethyl orthosilicate rapidly hydrolyzes and condenses, and under the guidance of a surfactant template, a silica shell with ordered mesoporous structure is self-assembled outside the zeolite core. This shell limits the adsorbed metal ions to the core-shell interface, and in the subsequent solvothermal and gradient calcination processes, these metal ions are converted into yttrium and cerium composite nanometal oxide clusters rich in oxygen vacancies. The finally formed core-shell composite material has the zeolite core with shape-selective adsorption and acidic sites, the mesoporous shell with nanoreaction space and diffusion regulation function, and the highly active nanometal oxide at the interface with oxidation-reduction catalytic ability, which constitute a synergistic and continuous catalytic sequence that can simulate and optimize the key path of polyphenol oxidation.

[0014] According to the preferred embodiment of the application, in step A1, the time for refluxing at 76-80 DEG C is 12-14h.

[0015] According to the preferred embodiment of the application, in step A2, the time for continuing stirring is 24-30h.

[0016] According to the preferred embodiment of the application, in step A3, the time for refluxing and stirring at 58-62 DEG C is 24-30h.

[0017] According to the preferred embodiment of the application, in step A4, the time for continuing heating to 545-555 DEG C is 5-10h.

[0018] Compared with the prior art, the application has the following beneficial effects: The black tea processing method and the special composite catalytic material thereof provided by the present application introduce a new artificial regulation mechanism in the core fermentation link of black tea production through interdisciplinary technology integration, thereby bringing a series of comprehensive technical effects which are significantly superior to traditional processes, and realizing multi-dimensional improvement of black tea quality, production efficiency and resource utilization.

[0019] Firstly, in terms of core product quality indicators, the present application realizes precise directional regulation and overall optimization of the color, taste and aroma composition of black tea. The multiphase catalytic system constructed by the special composite catalytic material can efficiently and stably promote the key conversion of catechin to theaflavins. This process not only significantly increases the total amount of theaflavins ultimately generated, but also, through the shape-selective catalytic properties of the material itself, guides the reaction towards the generation of specific conformational theaflavins, thereby making the finished black tea soup color present more bright red and excellent characteristics, and forming a clear "gold ring" at the edge of the tea cup. At the same time, the catalytic process effectively inhibits the disordered excessive conversion of polyphenols to theabrownins, ensuring that the tea soup is bright red and not dark, and the taste is mellow and not astringent. In terms of aroma, the regulation of the composite material to the fermentation micro-reaction environment promotes the conversion of lipid degradation products and glycoside aroma precursor substances to more sweet floral, fruity volatile components, such as increasing the proportion of beneficial components such as ionone and jasmonate, significantly reducing the grassy smell easily produced in traditional processes, and ultimately forming a sensory quality with high and sharp aroma, harmonious and persistent fruit aroma. This controllable intervention in the formation path of color, aroma and taste completely changes the quality fluctuations caused by relying on natural enzyme activity in the past, and makes the product quality, especially the processing quality of coarse and old raw materials such as summer and autumn tea, achieve unprecedented stability and outstanding improvement.

[0020] Secondly, in terms of production process and efficiency, the present application brings revolutionary progress and realizes the goals of efficient, stable and energy-saving industrial production. The traditional natural fermentation process relying on biological enzymes is time-consuming and sensitive to temperature and humidity, while the inorganic catalytic material introduced in the present method has stable and high-activity catalytic sites, which can significantly shorten the core fermentation time under mild conditions, greatly improving the production efficiency and equipment turnover rate. More importantly, the present method changes the fermentation from an uncontrollable biological process to a controllable physical and chemical process, and the influence of environmental parameter fluctuations on product quality is minimized, ensuring the uniformity of different batches of products. The method has wide adaptability to raw materials, especially it can effectively solve the "fermentation difficulty" problem of summer and autumn tea caused by the imbalance of the proportion of its internal components. By adding a strong catalytic oxidation ability, it makes up for the deficiency of its endogenous enzyme activity, thereby converting the seasonal raw materials that were previously difficult to make high-quality black tea into high-quality products, significantly expanding the raw material sources and time window of high-quality black tea production, and improving the overall utilization value of tea resources.

[0021] Finally, the "catalysis-separation" integrated process designed by the present application embodies high environmental friendliness and economic sustainability. The special composite material is carefully designed to have weak paramagnetism by introducing specific metal elements in the synthesis stage, so that after the completion of the fermentation task, it can realize efficient and clean separation and recovery of the catalyst particles and the tea matrix by means of a simple weak magnetic field separation device. This design not only avoids the residue and pollution of foreign additives to the final tea product, ensuring the absolute safety of food, but also enables the high-value catalytic material to be recycled for multiple uses, effectively reducing the cost of each use, and removing the economic barriers to the industrial application of this high-tech. In summary, the present application not only provides a production method of high-quality black tea, but also builds an innovative technology platform integrating efficient catalysis, quality control, resource adaptation and circular economy, which has a profound promoting effect on the transformation and upgrading of black tea and even the entire tea processing industry. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of the present application, the present application lists the following examples. Those skilled in the art should understand that the examples are only to help understand the present application, and should not be regarded as a specific limitation on the present application.

[0023] Example 1

[0024] The present example provides a processing method of black tea, comprising the following steps: The preparation steps of the mesoporous silica-zeolite core-shell structure loaded with nano metal oxide composite material are as follows. First, 10.0 g of β zeolite molecular sieve is weighed and placed in a 500 mL beaker, and 200 mL of anhydrous ethanol is added. The beaker is placed in an ultrasonic cleaner and ultrasonically treated at a frequency of 40 kHz for 30 min to obtain a uniform suspension. The suspension is transferred to a 500 mL three-necked round-bottom flask equipped with a mechanical stirrer, reflux condenser, constant-pressure dropping funnel, and nitrogen inlet tube. The mechanical stirring is started at a speed of 300 rpm, and dry nitrogen is continuously introduced into the system at a flow rate of 50 mL / min. An oil bath is used to heat the suspension to 65°C and maintain the temperature. Then, an ethanol solution of 3-aminopropyltriethoxysilane is slowly added through the constant-pressure dropping funnel, and the solution is prepared by mixing 3.0 mL of 3-aminopropyltriethoxysilane with 100 mL of anhydrous ethanol, and the dropping rate is 2 mL / min. After the addition is completed, the oil bath temperature is increased, and the reaction mixture is heated to 78°C, and the reaction is refluxed and condensed for 13 h. After the reaction is completed, the mixture is transferred to a centrifuge tube and centrifuged at 10,000 rpm for 10 min to collect the solid product. The supernatant is poured off, and 100 mL of anhydrous ethanol is added to the solid, which is vortexed and then centrifuged. This washing step is repeated three times. Then, 100 mL of deionized water is used for washing three times. The washed solid is placed in a vacuum drying oven at 80°C and dried at -0.1 MPa for 12 h to obtain amino-functionalized zeolite nanoparticles. Next, 5.0 g of amino-functionalized zeolite nanoparticles is weighed and re-dispersed in a mixed solution consisting of 200 mL of deionized water, 80 mL of anhydrous ethanol, and 2.0 mL of glacial acetic acid. The pH is adjusted to 5.5 by adding a dilute acetic acid solution while monitoring with a pH meter. The mixture is ultrasonically treated for 60 min to obtain a dispersion. The dispersion is transferred to another 500 mL three-necked flask and placed in a constant-temperature water bath at 35°C with mechanical stirring at 300 rpm. 0.60 g of cetyltrimethylammonium bromide, 0.72 g of cerium nitrate hexahydrate, and 0.38 g of yttrium nitrate hexahydrate are weighed and dissolved in 10 mL of deionized water to obtain a precursor salt solution. The solution is added to the three-necked flask at one time, and the stirring is maintained at 35°C and 300 rpm for 2 h. Then, 2.0 mL of concentrated ammonia is slowly added to the reaction system to adjust the pH to 10.5. Subsequently, 2.0 mL of tetraethyl orthosilicate is slowly added at a rate of 1 mL / h using a syringe pump. After the addition is completed, the stirring is continued at 35°C and 300 rpm for 28 h to obtain a slurry. The slurry is transferred to a 500 mL polytetrafluoroethylene-lined high-pressure reaction kettle, which is sealed and placed in a forced air drying oven for solvothermal crystallization treatment at 120°C for 36 h. After the treatment is completed, the contents are cooled to 25°C naturally. The contents are centrifuged at 10,000 rpm for 10 min to collect the solid.The supernatant was discarded, 50 mL of a mixture of dehydrated ethanol and deionized water at a volume ratio of 1:1 was added to the solid, which was vortexed and then centrifuged, and this washing process was repeated three times. The solid was transferred to a round-bottom flask, and 200 mL of an acidic ethanol solution prepared from dehydrated ethanol and concentrated hydrochloric acid at a volume ratio of 95:5 was added. A reflux device was connected, and the mixture was stirred under reflux in an oil bath at 60°C for 28 h. The solid was again centrifuged and washed with the ethanol-water mixture three times, and finally dried in a vacuum drying oven at 80°C for 12 h to obtain the core-shell intermediate. Finally, the core-shell intermediate was placed in a tube furnace, and air was passed at a flow rate of 200 mL / min, first heated from 25°C to 350°C at a rate of 2°C / min, and then held at 350°C for 3 h; then heated from 350°C to 550°C at a rate of 5°C / min, and then held at 550°C for 8 h. After the calcination was completed, the temperature was allowed to cool to room temperature naturally, and the final composite material was obtained.

[0025] The steps for processing black tea using the above composite material are as follows. 1000 g of fresh tea leaves were picked and evenly spread in a withering trough, with a leaf thickness of about 3 cm. The withering was carried out at 28°C and a relative humidity of 70% for 2 h. Then, the temperature was lowered to 25°C, the relative humidity was increased to 80%, and the intermittent gentle air supply system was started, with 10 min of air supply followed by 20 min of stop, and the cycle was repeated, and the withering was continued for 5 h. After withering, the moisture content of the fresh leaves was reduced to 64%, and withered leaves were obtained. All the withered leaves were put into a rolling machine, and the temperature was set to 25°C, and rolling was carried out for 70 min. After 5 min of rolling, 8.0 g of the above composite material was evenly added. After rolling, a rolling mixture was obtained. The mixture was taken out and loosely piled in a fermentation tray, with a leaf thickness of about 15 cm. The fermentation tray was placed in a fermentation room, and the pre-fermentation was carried out at 28°C and a relative humidity of 90% for 70 min, and pre-fermented tea leaves were obtained. Then, the tea leaves were transferred to a fermentation box, and the main fermentation was carried out at 28°C and a relative humidity of 85%, with the introduction of oxygen-enriched air with an oxygen concentration of about 35% into the box, for 3 h, and a fermentation mixture was obtained. After fermentation, the mixture was introduced into a weak magnetic field drum separator to separate and recover the catalyst powder, and tea leaves were obtained. The tea leaves were immediately sent to a drying machine, and initial drying was carried out at 120°C for 15 min, and then the temperature was adjusted to 93°C, and drying was continued until the moisture content of the tea leaves was 5.5%, and the finished black tea was obtained.

[0026] Example 2

[0027] The difference between this example and Example 1 is that the preparation steps of the mesoporous silica-zeolite core-shell structure loaded nanometal oxide composite material are as follows. 8.0 g of β zeolite is weighed, added to 160 mL of anhydrous ethanol, and ultrasonically treated for 30 min to obtain a suspension. The suspension is heated to 65°C under stirring and nitrogen protection, and then 2.4 mL of 3-aminopropyltriethoxysilane is added dropwise in 80 mL of anhydrous ethanol at a drop rate of 2 mL / min. After the drop, the temperature is raised to 78°C for reflux reaction for 12 h. After the reaction, centrifugation is performed, and the solid is washed with 80 mL of anhydrous ethanol and 80 mL of deionized water for three times, respectively, and dried at 80°C under vacuum for 12 h to obtain the amino-functionalized zeolite particles. 4.0 g of the particles is dispersed in a mixture of 160 mL of deionized water, 64 mL of anhydrous ethanol, and 1.6 mL of glacial acetic acid, and the pH is adjusted to 5.5 with acetic acid, and ultrasonic treatment is performed for 60 min. Under stirring and 35°C water bath, a precursor salt solution formed by dissolving 0.48 g of cetyltrimethylammonium bromide, 0.58 g of cerium nitrate hexahydrate, and 0.30 g of yttrium nitrate hexahydrate in 8 mL of deionized water is added, and stirring is performed for 2 h. The pH is adjusted to 10.5 by adding 1.6 mL of concentrated ammonia water, and then 1.6 mL of tetraethyl orthosilicate is added dropwise, and after the drop, stirring is continued at 35°C for 24 h to obtain a slurry. The slurry is transferred to a high-pressure reaction kettle, and crystallization treatment is performed at 120°C for 24 h. After cooling, centrifugation is performed, and the solid is washed with an ethanol-water mixture for three times. The intermediate is dispersed in 160 mL of an acidic ethanol solution, and stirring is performed under reflux at 60°C for 24 h. Centrifugation and washing are performed again and drying is performed. Finally, the dried product is calcined in an air atmosphere: increased to 350°C at a rate of 2°C / min, maintained for 3 h, and then increased to 550°C at a rate of 5°C / min, maintained for 5 h, and cooled to obtain the final composite material.

[0028] In the processing of black tea, 1000 g of fresh leaves is picked, wilted at 30°C for 1.5 h, adjusted to 26°C and intermittently blown to continue wilting for 4 h, until the water content is 62%. Rolled at 26°C for 60 min, during which 6.0 g of the above composite material is added. After taking out, pre-fermentation is performed at 30°C for 60 min, and then main fermentation is performed at 30°C under the condition of oxygen-rich air for 2.5 h. After fermentation, the catalyst is recovered by a weak magnetic field separator, and the tea leaves are first dried at 125°C for 12 min, and then dried at 95°C until the water content is 5.0%.

[0029] Example 3

[0030] The difference between this example and Example 1 is that the preparation steps of the mesoporous silica-zeolite core-shell structure loaded nanometal oxide composite material are as follows. 12.0 g of β zeolite is weighed, added to 240 mL of anhydrous ethanol, and ultrasonically treated for 30 min to obtain a suspension. The suspension is heated to 65°C under stirring and nitrogen protection, and then 120 mL of a solution containing 3.6 mL of 3-aminopropyltriethoxysilane in anhydrous ethanol is added dropwise at a rate of 2 mL / min. After the dropwise addition, the temperature is raised to 78°C and refluxed for 14 h. After the reaction, centrifugation is performed, and the solid is washed with 120 mL of anhydrous ethanol and 120 mL of deionized water for three times each, and dried at 80°C under vacuum for 12 h to obtain the amino-functionalized zeolite particles. 6.0 g of the particles is dispersed in a mixture of 240 mL of deionized water, 96 mL of anhydrous ethanol, and 2.4 mL of glacial acetic acid, and the pH is adjusted to 5.5 with acetic acid, and ultrasonically treated for 60 min. Under stirring and a 35°C water bath, a precursor salt solution formed by dissolving 0.72 g of cetyltrimethylammonium bromide, 0.86 g of cerium nitrate hexahydrate, and 0.46 g of yttrium nitrate hexahydrate in 12 mL of deionized water is added, and stirred for 2 h. The pH is adjusted to 10.5 by adding 2.4 mL of concentrated ammonia water, and then 2.4 mL of tetraethyl orthosilicate is added dropwise, and after the dropwise addition, the stirring is continued at 35°C for 30 h to obtain a slurry. The slurry is transferred to a high-pressure reaction kettle, and crystallized at 120°C for 48 h. After cooling, centrifugation is performed, and the solid is washed with an ethanol-water mixture for three times to obtain an intermediate. The intermediate is dispersed in 240 mL of an acidic ethanol solution, and stirred at 60°C under reflux for 30 h, and then centrifuged, washed, and dried again. Finally, the dried product is calcined in an air atmosphere: raised to 350°C at a rate of 2°C / min, maintained for 3 h, then raised to 550°C at a rate of 5°C / min, and maintained for 10 h, and after cooling, the final composite material is obtained.

[0031] In the processing of black tea, 1000 g of fresh leaves is picked, wilted at 27°C for 2.5 h, adjusted to 24°C and intermittently blown to continue wilting for 6 h, to a water content of 65%. Rolled at 24°C for 80 min, during which 10.0 g of the above composite material is added. After removal, pre-fermented at 26°C for 80 min, and main-fermented at 26°C under oxygen-rich air conditions for 3.5 h. After fermentation, the catalyst is recovered by a weak magnetic field separator, and the tea is initially dried at 115°C for 18 min, and then dried at 90°C to a water content of 6.0%.

[0032] Comparative Example 1

[0033] The difference between the present comparative example and Example 1 is that the mesoporous silica-zeolite core-shell structure loaded nanometal oxide composite material is not added in the present comparative example. During the processing of black tea, 1000 g of tea fresh leaves are picked, and the withering and rolling processes are the same as those in Example 1. The tea leaves obtained after rolling are not subjected to pre-fermentation, but are directly placed in a fermentation room at 28°C and a relative humidity of 90% for traditional natural fermentation, with a total time of 6 h. After the fermentation is completed, the tea leaves are not subjected to magnetic separation, but are directly subjected to the same drying procedure as in Example 1, i.e., initial drying at 120°C for 15 min, and then drying at 93°C until the water content is 5.5%.

[0034] Comparative Example 2

[0035] The difference between the present comparative example and Example 1 is that the mesoporous silica-zeolite core-shell structure loaded nanometal oxide composite material is not added in the present comparative example. During the processing of black tea, 1000 g of tea fresh leaves are picked, and the withering and rolling processes are the same as those in Example 1. The tea leaves obtained after rolling are not subjected to pre-fermentation, but are directly placed in a fermentation room at 28°C and a relative humidity of 90% for traditional natural fermentation, with a total time of 6 h. After the fermentation is completed, the tea leaves are not subjected to magnetic separation, but are directly subjected to the same drying procedure as in Example 1, i.e., initial drying at 120°C for 15 min, and then drying at 93°C until the water content is 5.5%.

[0036] Comparative Example 3

[0037] The difference between the present comparative example and Example 1 is that the mesoporous silica-zeolite core-shell structure loaded nanometal oxide composite material is not added in the present comparative example. During the processing of black tea, 1000 g of tea fresh leaves are picked, and the withering and rolling processes are the same as those in Example 1. The tea leaves obtained after rolling are not subjected to pre-fermentation, but are directly placed in a fermentation room at 28°C and a relative humidity of 90% for traditional natural fermentation, with a total time of 6 h. After the fermentation is completed, the tea leaves are not subjected to magnetic separation, but are directly subjected to the same drying procedure as in Example 1, i.e., initial drying at 120°C for 15 min, and then drying at 93°C until the water content is 5.5%.

[0038] According to the test specifications of national and industry standards, the performance tests of the present application are carried out on the finished black tea products prepared in Examples 1-3 and Comparative Examples 1-3, and the test methods cover physicochemical component analysis, aroma substance identification, sensory quality evaluation, and catalyst recovery rate evaluation.

[0039] The contents of theaflavins, thearubigins, and theabrownins were determined by high performance liquid chromatography (HPLC): 1.000 g of pulverized tea sample was accurately weighed, and 50 mL of 70% methanol aqueous solution was added for extraction in a 70℃ water bath for 30 min. After cooling, the sample was diluted to volume and filtered. The filtrate was filtered through a 0.45 μm filter membrane before injection. The chromatographic column was a C18 column, the column temperature was 30℃, the mobile phase was 2% acetic acid aqueous solution and acetonitrile, gradient elution was used, the flow rate was 1.0 mL / min, and the detection wavelength was 280 nm. Quantitative calculation was performed using theaflavins as a reference by external standard method; and the ratio of thearubigins to theabrownins was calculated.

[0040] Aroma component analysis employed headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (GC-MS): 2.000 g of tea sample was weighed and placed in a 20 mL headspace vial. After equilibration at 60 °C for 10 min, a 50 / 30 μm DVB / CAR / PDMS extraction head was used for headspace adsorption at 60 °C for 40 min. Subsequently, the sample was desorbed at 250 °C for 5 min at the GC-MS inlet for detection. The chromatographic column was an HP-5MS capillary column, with a programmed temperature increase from 40 °C for 3 min, followed by a rise at 5 °C / min to 250 °C and a hold for 5 min. The mass spectrometry interface temperature was 280 °C, the ionization mode was EI, and the scan range was m / z 35-450. The relative percentage content of each aroma component was determined by comparison with the NIST standard spectral library and area normalization.

[0041] The sensory evaluation is conducted according to national standard methods. A group of five professionally trained tea tasters independently score each coded tea sample in a standard evaluation room, evaluating five factors: appearance, liquor color, aroma, taste, and infused leaf appearance. The weights of each factor are 25%, 10%, 25%, 30%, and 10%, respectively. The arithmetic mean score is then used as the final sensory score.

[0042] Catalyst recovery rate was determined by gravimetric method: the mass of catalyst powder collected by a weak magnetic field drum separator after fermentation was recorded and compared with the mass of catalyst added before processing. The calculation formula is: recovery rate = (mass of recovered catalyst / mass of added catalyst) × 100%.

[0043] The performance test data above are shown in Table 1.

[0044] Table 1 Performance Test Results Test item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Theaflavin content (%) 1.28 1.05 1.18 0.52 0.61 0.75 Thearubigin / theabrownin ratio 3.9 3.4 3.6 2.1 2.4 2.8 Total amount of characteristic aroma (relative %) 68.5 65.2 66.8 45.3 48.7 58.1 Total score of sensory evaluation (percentage) 92.5 90.0 91.0 86.5 87.0 88.5 Catalyst recovery rate (%) 95 93 94 Not applicable Not applicable 92

[0045] As can be seen from the above, Examples 1-3 systematically solve the three core problems in existing black tea processing technology compared to Comparative Examples 1-3.

[0046] First, compared to traditional processes that rely entirely on endogenous enzymes in tea leaves, this embodiment introduces a specially formulated composite material to transform the uncontrollable natural enzymatic fermentation into a highly efficient and stable multiphase catalytic process. This directly solves the technical bottlenecks of traditional processes, such as long fermentation times, low efficiency, and significant susceptibility to raw materials and environmental influences in terms of quality. This embodiment requires only 2.5-3.5 hours of primary fermentation, achieving a theaflavins content of 1.05-1.28% and a sensory score above 90 points; while Comparative Example 1, using a traditional fermentation process lasting up to 6 hours, only achieved a theaflavins content of 0.52% and a sensory score of 86.5 points. This demonstrates that the present invention significantly improves fermentation efficiency and quality stability, making it particularly suitable for summer and autumn tea raw materials with insufficient endogenous enzyme activity.

[0047] Secondly, compared to using only physical adsorption materials, the composite material in this example achieves active and precise catalysis of the fermentation reaction through precise chemical design and functionalization modification. Comparative Example 2, using only unmodified raw zeolite, showed slightly better performance in various indicators than the traditional process, but the improvement was limited, indicating that simple physical adsorption is insufficient for regulating complex oxidative polymerization reactions. In contrast, this example constructs anchoring sites through amino functionalization and forms a core-shell structure with shape-selective catalytic capabilities, creating an optimized microenvironment for the reaction and thus achieving directional guidance of the theaflavins production pathway. Finally, the nano-metal oxides supported in this example are key to its highly efficient catalytic activity.

[0048] Comparative Example 3 used a core-shell material free of yttrium and cerium oxides, with a theaflavin content of 0.75%, which, although higher than Comparative Examples 1 and 2, was still significantly lower than all other examples. This confirms the indispensable role of nano-yttrium oxide-cerium oxide as the catalytic active center in activating oxygen and initiating and accelerating the catechin oxidation reaction. Furthermore, the catalyst in these examples achieved a high magnetic separation recovery rate of 93-95%, successfully solving the industrialization challenges of difficult separation, potential residues, and high costs associated with exogenous additives.

[0049] In summary, the embodiments of the present invention, through the synergistic effect of multiple components and multiple structures of composite materials, organically combine the shape-selective adsorption of zeolite, the reactor function of mesoporous shells, and the oxidation catalytic ability of nano-metal oxides to form a complete catalytic system, thereby simultaneously overcoming multiple technical problems in traditional black tea processing, such as low efficiency, unstable quality, extensive control, and difficulty in catalyst recovery.

Claims

1. A method for processing black tea, characterized in that, Includes the following steps: S1. Pick fresh tea leaves and spread them thinly in a withering trough. Wither at 27-30℃. Lower the temperature to 24-26℃ and turn on intermittent gentle airflow to continue withering until the moisture content of the fresh leaves drops to 62%-65%, thus obtaining withered leaves. S2. Put the withered leaves into a rolling machine and roll them at 24-26℃; add mesoporous silica-zeolite molecular sieve core-shell structure supported nano metal oxide composite material to obtain a rolling mixture; take out the rolling mixture, place it in a fermentation pan, and pre-ferment at 26-30℃ to obtain pre-fermented tea. S3. Transfer the pre-fermented tea leaves to a fermentation box and continue fermentation to obtain a fermented mixture; S4. Transfer the fermentation mixture to a weak magnetic field drum separator to obtain tea leaves after catalyst separation; dry the tea leaves after catalyst separation.

2. The processing method for black tea according to claim 1, characterized in that, In step S1, the withering time continues for 4-6 hours.

3. The processing method for black tea according to claim 1, characterized in that, In step S2, the pre-fermentation time at a temperature of 26-30℃ is 60-80 minutes.

4. The processing method for black tea according to claim 1, characterized in that, In step S3, the fermentation time continues for 2.5-3.5 hours.

5. The processing method for black tea according to claim 1, characterized in that, In step S4, the drying process of the tea leaves after catalyst separation includes: firstly, initial drying under hot air at 115-125℃; then drying at 90-95℃ until the moisture content is below 6%.

6. The method for processing black tea according to any one of claims 1-5, characterized in that, The preparation steps of the mesoporous silica-zeolite molecular sieve core-shell structure supported nano-metal oxide composite material include: A1. β-zeolite molecular sieves were dispersed in anhydrous ethanol and sonicated to obtain a suspension. Under stirring and nitrogen protection, the suspension was heated to 64-66℃, and then anhydrous ethanol solution containing 3-aminopropyltriethoxysilane was added dropwise. After the addition was complete, the temperature was raised to 76-80℃ and refluxed. After the reaction was completed, the solid product was collected by high-speed centrifugation. The solid product was washed with anhydrous ethanol and deionized water in sequence, and the obtained solid was dried in a vacuum drying oven at 78-82℃ to obtain amino-functionalized zeolite nanoparticles. A2. The amino-functionalized zeolite nanoparticles were redispersed in a mixed solution of deionized water, anhydrous ethanol, and acetic acid, and the pH was adjusted to 5-6. The mixture was then sonicated. Under constant temperature water bath of 34-36℃ and stirring, a precursor salt solution formed by dissolving hexadecyltrimethylammonium bromide, cerium nitrate hexahydrate, and yttrium nitrate hexahydrate in deionized water was added. The mixture was stirred continuously, and then concentrated ammonia was added to adjust the pH to 10-11. Tetraethyl orthosilicate was added dropwise. After the addition was completed, the reaction was stirred to obtain a slurry. A3. Transfer the slurry to a high-pressure reactor and perform solvothermal crystallization treatment at 115-125℃. After the reaction is completed, allow it to cool naturally to room temperature, collect the solid product by centrifugation, wash the solid product with a mixture of ethanol and water to obtain the washed solid product. Disperse the washed solid product in an acidic ethanol solution, reflux and stir at 58-62℃, centrifuge again, wash, and dry to obtain the core-shell intermediate. A4. Place the core-shell intermediate in a tube furnace and perform gradient calcination activation in an air atmosphere: first, raise the temperature from room temperature to 345-355℃ and hold; then raise the temperature to 545-555℃ and hold; after calcination, allow it to cool naturally to room temperature.

7. The method for processing black tea according to claim 6, characterized in that, In step A1, the reflux reaction time at 76-80℃ is 12-14 hours.

8. The method for processing black tea according to claim 6, characterized in that, In step A2, the stirring reaction continues for 24-30 hours.

9. The method for processing black tea according to claim 6, characterized in that, In step A3, the reflux stirring time at 58-62℃ is 24-30h.

10. The method for processing black tea according to claim 6, characterized in that, In step A4, the temperature is further increased to 545-555℃ and held for 5-10 hours.