Preparation method of instant tea powder by coupling low-temperature vacuum flash extraction and molecular embedding

Abstract

The invention provides a preparation method of low-temperature vacuum flash extraction coupled molecule embedding instant tea powder. The method comprises the following steps: performing low-temperature vacuum and ultrasonic synergistic extraction on a tea leaf raw material, separating to obtain tea soup, and recovering aroma components through an SCC system in the extraction process; concentrating the tea soup into a concentrated solution, and meanwhile, backfilling part of aroma components into the concentrated solution; further adding a composite embedding agent containing endogenous tea protein into the concentrated solution to form an embedding compound, then forming instant tea powder by using a specific drying technology, and meanwhile, backfilling the residual aroma components into the instant tea powder. The instant tea powder prepared by the preparation method realizes dual locking protection of aroma and taste substances, highly restores the flavor of original tea, is instantly dissolved in cold water, is clear and transparent in tea soup, delays oxidation of substances such as tea polyphenol and the like, and improves the storage stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tea processing, and in particular relates to a preparation method of instant tea powder by coupling low-temperature vacuum flash extraction and molecular embedding. BACKGROUND

[0002] Instant tea is a new type of beverage processed from finished tea, semi-finished tea, tea by-products or fresh leaves through extraction, filtration, concentration, drying and other processes, which is easy to dissolve in water and has no tea residue. It has the advantages of convenient brewing and carrying, no pesticide residues, etc. It is divided into pure tea and blended tea. Pure tea includes instant black tea, green tea, oolong tea, pu'er tea, etc. Blended tea includes lemon black tea, milk tea, fruit-flavored instant tea, etc. Its production process includes extraction (using boiling water, ultrasonic extraction, carbon dioxide supercritical extraction, etc. to dissolve the effective components in tea leaves into water), filtration (removing fine particles, suspended impurities or turbid precipitate formed during processing from the extraction liquid), concentration (reducing water content through vacuum concentration, membrane concentration, etc. to improve the efficiency of subsequent drying), and drying (mainly spray drying and freeze drying. Before spray drying, carbon dioxide is introduced into the tea juice to form small bubbles, and after drying, small particles with intermediate space are formed to enhance the instant solubility. Freeze drying is to lower the temperature of tea juice to minus several tens of degrees, then gradually increase the temperature and reduce the pressure to exhaust the sublimated water, so that the instant tea has loose texture and excellent solubility. It can be cold or hot, and can also be used to make cakes, tea-flavored candies, tea-flavored sauces and other foods.

[0003] The traditional production process of instant tea usually involves high-temperature extraction, high-temperature concentration and high-temperature drying, etc. These processes are prone to cause oxidation, volatilization and deterioration of heat-sensitive flavor substances in tea leaves, resulting in weak aroma, bitter taste, dark tea soup, poor cold solubility, and easy caking, which greatly affects the quality and consumer experience of instant tea.

[0004] In order to improve the quality of instant tea, some improvement methods have been proposed in the prior art. For example, low-temperature extraction, vacuum concentration or freeze drying are used to reduce the processing temperature. However, these technologies often have problems such as low efficiency, high cost, high energy consumption or insufficient protection of flavor substances. Especially in terms of aroma retention and fixation, simple physical recovery and addition cannot simulate the flavor hierarchy of the original tea, and the aroma loss is serious and easy to escape again.

[0005] Therefore, it is urgent to develop a preparation method of instant tea powder which can maximize the retention of the color, aroma and taste characteristics of the original tea and has excellent cold solubility. SUMMARY

[0006] The application provides a preparation method of instant tea powder by low-temperature vacuum flash extraction coupled with molecular embedding. Tea leaves are first extracted by low-temperature vacuum extraction combined with ultrasonic wave to obtain tea soup, and aroma components are recovered by an SCC system during the extraction process. Then, the tea soup is concentrated into concentrated liquid, and part of the aroma components is backfilled into the concentrated liquid. The concentrated liquid is further added with a composite embedding agent containing endogenous tea protein to form an embedding complex, and then a specific drying technique is used to form instant tea powder, and the remaining aroma components are backfilled into the instant tea powder. The instant tea powder prepared by the preparation method realizes double locking protection of aroma and taste substances, highly restores the flavor of original tea, and is instantly dissolved in cold water with clear and transparent tea soup, while delaying the oxidation of tea polyphenols and other substances and improving the storage stability.

[0007] The application provides a preparation method of instant tea powder by low-temperature vacuum flash extraction coupled with molecular embedding. Tea leaves are first extracted by low-temperature vacuum extraction combined with ultrasonic wave to obtain tea soup, and aroma components are recovered by an SCC system during the extraction process. Then, the tea soup is concentrated into concentrated liquid, and part of the aroma components is backfilled into the concentrated liquid. The concentrated liquid is further added with a composite embedding agent containing endogenous tea protein to form an embedding complex, and then a specific drying technique is used to form instant tea powder, and the remaining aroma components are backfilled into the instant tea powder. The instant tea powder prepared by the preparation method realizes double locking protection of aroma and taste substances, highly restores the flavor of original tea, and is instantly dissolved in cold water with clear and transparent tea soup, while delaying the oxidation of tea polyphenols and other substances and improving the storage stability.

[0008] The traditional instant tea production process usually involves steps such as high-temperature extraction, high-temperature concentration and high-temperature drying, which can easily cause the oxidation, volatilization and deterioration of heat-sensitive flavor substances in tea leaves, resulting in weak aroma, bitter taste, dark and dull tea soup, poor cold solubility and easy caking of the product. The application solves the problems in the traditional instant tea production process, and uses low-temperature vacuum extraction combined with ultrasonic wave to greatly reduce the damage of heat-sensitive substances. The composite embedding agent added contains endogenous tea protein, which is extracted from by-products such as tea residue, thereby reducing the cost and ensuring the compatibility of the embedding agent and tea components, avoiding the introduction of exogenous substances to affect the flavor, and having specific binding advantages with tea polyphenols.

[0009] In the application, the endogenous tea protein is extracted from by-products such as tea residue, and the corresponding endogenous tea protein is extracted from the corresponding tea residue when preparing instant tea powder of different tea leaves.

[0010] Further, the extraction is carried out under the conditions of a vacuum degree of 0.005-0.01 MPa and a temperature of 40-60°C, and ultrasonic wave is used for auxiliary extraction.

[0011] Low temperature (40-60°C) avoids the oxidation of heat-sensitive flavor substances, and the vacuum environment reduces the volatilization of aroma substances, thereby laying a foundation for the subsequent recovery of aroma by an SCC system.

[0012] Further, the endogenous tea protein is extracted from tea processing by-products; the addition amount of the composite embedding agent is 10%-30% of the mass of the concentrated liquid; and the mass ratio of the endogenous tea protein, cyclodextrin and malt dextrin is 1: (2-4): (1-2).

[0013] The addition amount of the composite embedding agent is too low to fully wrap the active ingredients, and too high to affect the flavor and solubility of the product. The range is the optimal interval selected by experiment. Different tea raw materials have different optimal addition amounts of composite embedding agent during preparation. The addition amount of green tea composite embedding agent is 20%, the addition amount of black tea composite embedding agent is 25%, and the addition amount of oolong tea composite embedding agent is 15%.

[0014] Further, the frequency of the ultrasonic-assisted extraction is 20-40 kHz, the power is 200-500 W, and the extraction time is 5-15 minutes.

[0015] The ultrasonic-assisted extraction improves the extraction rate of tea polyphenols and aroma substances, shortens the extraction time, and improves the production efficiency.

[0016] Further, the cyclodextrin is one or a combination of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and γ-cyclodextrin.

[0017] The three kinds of cyclodextrins all have hydrophobic cavities and can effectively wrap aroma substances, but each adapts to different types of tea. The combination can be adjusted according to demand, improving the flexibility of the scheme.

[0018] In some ways, through screening, β-cyclodextrin is suitable for green tea, hydroxypropyl-β-cyclodextrin is suitable for black tea, and γ-cyclodextrin is suitable for oolong tea.

[0019] Further, the preparation method comprises the following steps: (1) The tea raw material is crushed and extracted to obtain a tea extract, and volatile aroma components are recovered at the same time; (2) The tea extract is separated by solid-liquid separation to obtain tea soup; (3) The tea soup obtained in step (2) is concentrated to obtain a concentrated solution; part of the aroma components recovered in step (1) are backfilled into the concentrated solution; (4) The concentrated solution obtained in step (3) is added with a composite embedding agent to form an embedding complex; (5) The embedding complex obtained in step (4) is dried to form instant tea powder, and the remaining aroma components recovered in step (3) are backfilled into the instant tea powder.

[0020] In step (1), low-temperature quick freezing and ultrafine crushing are used to destroy the cell structure of the tea, and ultrasonic waves are used in combination with a low-temperature vacuum environment to improve the extraction rate of effective components (tea polyphenols and aroma substances) and reduce the oxidation and damage of heat-sensitive substances.

[0021] In step (2), tea residue, macromolecular impurities, and insoluble particles are removed to ensure the clarity of the tea soup and lay a foundation for subsequent concentration and embedding.

[0022] The step (3) concentrates to improve the solid concentration and improve the drying efficiency; meanwhile, the step-by-step aroma backfilling is the key first step of "double flavor locking", and the aroma diffusion is reduced.

[0023] The step (4) wraps the flavor substances and active ingredients through the synergistic effect of the composite embedding agent, prevents oxidation, moisture absorption and caking, and improves the product stability.

[0024] The step (5) forms a multi-dimensional hollow structure through a specific drying technology, improves the cold solubility, realizes double flavor locking through secondary aroma backfilling, and finally restores the original tea flavor of the product.

[0025] Further, the tea raw materials suitable for the instant tea powder preparation method provided by the application include green tea, black tea, oolong tea and dark tea.

[0026] Further, the aroma components in the step (1) are recovered by using a rotating distillation tower SCC system; and the concentration in the step (3) is concentrated to a solid content of 10-30 Brix by using a reverse osmosis membrane or a low-temperature vacuum concentration device.

[0027] The SCC system can efficiently capture volatile aroma substances such as head aroma, and provide high-quality aroma raw materials for subsequent step-by-step backfilling.

[0028] The reverse osmosis membrane and the low-temperature vacuum concentration are both low-temperature processes, which can avoid the deterioration of components caused by high-temperature concentration; and the solid content of 10-30 Brix can ensure the efficiency of the subsequent embedding reaction, and will not cause poor fluidity and uneven mixing due to too high concentration.

[0029] Further, the embedding compound in the step (4) is prepared by reacting at 50-60℃ under high-speed shearing for 30-60 minutes; and the drying in the step (5) is performed by using a freeze-drying or spray-drying technology.

[0030] 50-60℃ can ensure the molecular activity of the composite embedding agent, promote the combination with the components in the tea concentrate, and will not cause oxidation of heat-sensitive substances. The high-speed shearing can fully mix the embedding agent and the concentrate, and avoid insufficient embedding caused by uneven local concentration; and 30-60 minutes is the optimal time for the embedding reaction to reach equilibrium, and too short embedding time will cause incomplete embedding, and too long time will increase energy consumption.

[0031] Further, the recovered aroma components in the steps (3) and (5) are backfilled to the concentrate and the instant tea powder by using an atomization method.

[0032] The atomization can uniformly disperse the aroma components in the form of small droplets, fully contact the concentrate or the dried tea powder, avoid too high local aroma concentration or uneven distribution, and ensure the flavor consistency of the product.

[0033] The atomization mode is matched with step-by-step backfilling, realizes double locking of aroma, and further reduces aroma diffusion.

[0034] Further, the freeze-drying technology includes porous crystallization freeze-drying technology and continuous vacuum freeze-drying technology; the conditions of the freeze-drying technology are pre-freezing temperature-30℃ to-40℃, vacuum degree≤0.001MPa, and analysis stage temperature not more than 60℃; the inlet temperature of the spray drying technology is 160-180℃, and the outlet temperature is 80-90℃.

[0035] Both the porous crystallization freeze-drying technology and the continuous vacuum freeze-drying technology can realize water sublimation at low temperature, avoid component deterioration caused by high-temperature drying, and form a multi-dimensional hollow structure (volume weight 12-18g / 100mL), which significantly improves cold solubility.

[0036] The present application has the following beneficial effects: 1. The low-temperature vacuum flash extraction coupled with ultrasonic extraction technology greatly reduces the damage of heat-sensitive substances, the head aroma is recovered through the SCC system, and the double locking of aroma and flavor substances is realized by combining the molecular embedding and step-by-step backfilling technology, so that the product flavor is highly restored to the original tea; 2. The complex embedding effect of endogenous tea protein, cyclodextrin and maltodextrin effectively prevents component interaction and moisture absorption and blocking, and the multi-dimensional hollow structure is formed by using specific drying technologies such as porous crystallization freeze-drying, which gives the product excellent instant solubility and dispersibility, realizes instant dissolution in cold water, and the tea soup is clear and transparent; 3. The complex embedding agent protects the flavor while delaying the oxidation of tea polyphenols and other substances, and improves the storage stability; 4. The endogenous tea protein is extracted from tea leaf processing by-products, which reduces the cost and has good compatibility with tea ingredients, avoiding the influence of exogenous substances on flavor; 5. The preparation method provided by the present application can be used in many fields such as terminal drinks, solid beverages, food ingredients, health foods, etc. DETAILED DESCRIPTION

[0037] The embodiments of the present application are further described in detail below, and it should be pointed out that the following embodiments are intended to facilitate the understanding of the present application and do not have any limiting effect on the present application, and all the features disclosed in the embodiments of the present application, or all the steps in the disclosed methods or processes, can be combined in any way, except that the features and / or steps are mutually exclusive.

[0038] Example 1, preparation method of low-temperature vacuum flash extraction coupled with molecular embedding instant tea powder 1. Preparation method of low-temperature vacuum flash extraction coupled with molecular embedding instant tea powder A preparation method of instant tea powder coupled with low-temperature vacuum flash extraction and molecular embedding, tea raw materials including green tea, black tea, oolong tea and dark tea, comprising the following specific steps: S1, freeze-drying the tea raw materials at low temperature, crush and place in a closed extraction system, under the conditions of vacuum degree 0.005-0.01 MPa and temperature 40-60℃, use ultrasonic-assisted extraction technology for rapid extraction, obtain tea extract; during the extraction process, use a rotating distillation tower SCC system to recover the volatile aroma components during the extraction process; the frequency of ultrasonic-assisted extraction is 20-40 kHz, the power is 200-500 W, and the extraction time is 5-15 minutes; S2, the tea extract obtained in S1 is first separated by a disc centrifuge, and then refined by an ultrafiltration membrane system to remove macromolecular impurities and insoluble particles, to obtain a clear tea soup; S3, the refined tea soup is concentrated to a solid content of 10-30 Brix by using a reverse osmosis membrane or a low-temperature vacuum concentration device, to obtain a concentrated liquid; at the same time, part of the recovered aroma components in S1 are backfilled into the concentrated liquid in a atomization manner; the reverse osmosis membrane uses a DT disc tube or a ST net tube reverse osmosis membrane; S4, add a composite embedding agent to the concentrated liquid obtained in S3, the total addition amount of the composite embedding agent is 10%-30% of the solid mass of the concentrated liquid; the composite embedding agent is composed of endogenous tea protein, cyclodextrin and malt dextrin in a mass ratio of 1: (2-4): (1-2), and is reacted at 50-60℃ under high-speed shearing for 30-60 minutes to form an embedding composite; the cyclodextrin is one or a combination of β-cyclodextrin, hydroxypropyl-β-cyclodextrin and γ-cyclodextrin; the endogenous tea protein is extracted from tea processing by-products (the endogenous tea protein required for preparing different types of instant tea powder is extracted from the corresponding tea residue), and the specific steps include: a, raw material pretreatment: dry the tea residue in a vacuum drying oven under the conditions of temperature ≤50℃ and vacuum degree ≤10kPa to a moisture content ≤8%, and then use an ultrafine grinder to crush the dried tea residue to a particle size ≤80 mesh, to destroy the cell structure and improve the protein dissolution rate; b, solvent extraction: use water or 0.05 mol / L NaOH, pH 9.0-10.0 dilute alkali solution for extraction at ≤45℃ to dissolve the protein in the tea; c, separation and purification: centrifuge the extraction liquid obtained in step b at 8000-10000 rpm for 15 minutes in a centrifuge to remove insoluble impurities, to obtain a high-purity tea protein solution; d. Concentration and drying: the protein solution is concentrated by nanofiltration (NF) membrane (molecular weight cut-off 200-300 Da) at an operating pressure of 1.5-2.5 MPa and a temperature of ≤40℃, so that the solid content is increased from 2-3% to 15-20%, and then spray-dried at an inlet temperature of 160-180℃, an outlet temperature of 70-80℃, and an atomization pressure of 0.2-0.3 MPa, or the concentrated solution is frozen at -40℃ for 2 hours and then dried at a vacuum degree of <50 Pa and a hot plate temperature of 30-40℃ until the moisture content is ≤5%, to obtain endogenous tea protein powder; S5. The embedding-treated concentrated solution is dried by freeze-drying technology or spray-drying technology; the freeze-drying technology is porous crystallization freeze-drying technology or continuous vacuum freeze-drying technology, and the freeze-drying conditions are: pre-freezing temperature -30℃ to -40℃, vacuum degree ≤0.001 MPa, and analysis stage temperature not exceeding 60℃; the inlet temperature of the spray-drying technology is 160-180℃, and the outlet temperature is 80-90℃; the instant tea powder prepared by the porous crystallization freeze-drying or continuous vacuum freeze-drying has a multi-dimensional hollow structure, and the bulk density is between 12-18 g / 100 mL.

[0039] S6. The remaining aroma components recovered in S1 are backfilled into the dried instant tea powder in an atomized manner, and then vacuum packaged to obtain instant tea powder.

[0040] 2. Preparation method of instant green tea powder by low-temperature vacuum flash extraction coupled with molecular embedding Taking the preparation of instant green tea powder as an example, the specific preparation method is as follows: S1. Take special-grade Longjing green tea as raw material, freeze at -40℃ for 2 hours, then pulverize to 60 mesh by using an ultrafine grinder, and place the pulverized tea powder in a sealed extraction tank, vacuumize to 0.008 MPa, maintain the temperature at 50℃, and start ultrasonic-assisted extraction at a frequency of 28 kHz and a power of 300 W for 10 minutes to obtain green tea extract; during the extraction process, the volatilized aroma components are recovered by an SCC rotary distillation tower system connected to the outlet of the extraction tank and collected in a low-temperature storage tank by condensation; S2. The above extract is first centrifuged at 8000 rpm by a disc centrifuge to remove tea residue, and the obtained supernatant is then refined by using an ultrafiltration membrane system with a molecular weight cut-off of 10 kDa to obtain clear and transparent green tea soup with a green color; S3. The refined green tea soup is concentrated to a solid content of 20 Brix at room temperature by using a DT disc-and-tube reverse osmosis membrane system to obtain green tea concentrate; at the same time, part of the green tea aroma components recovered in S1 are uniformly sprayed into the green tea concentrate by using a precision atomizing nozzle; S4, add a complex embedding agent to the green tea concentrate, the mass ratio of the components of the embedding agent being: endogenous tea protein extracted from green tea dregs: β-cyclodextrin: maltodextrin = 1:3:1.5, the total amount of addition being 20% of the mass of the solids in the concentrate, and the embedding agent and tea concentrate being allowed to react and complex at 55°C for 45 minutes with a high-speed shearing homogenizer at 6000 rpm; S5, inject the embedded concentrate into a freeze-drying chamber, pre-freeze at -35°C for 4 hours, then vacuumize to 0.0008 MPa, perform sublimation drying, and control the temperature of the plate layer at 50°C during the resolution stage, dry to a moisture content of ≤5%, and obtain fluffy and porous green tea powder; S6, uniformly spray the remaining green tea aroma components recovered in S1 onto the dried green tea powder using a precision atomizing nozzle, and then immediately perform vacuum nitrogen filling packaging to obtain the final high-quality cold-soluble instant green tea powder.

[0041] The endogenous tea protein components extracted from green tea in S4 are detected as shown in Table 1.

[0042] Table 1, detection results of endogenous tea protein components extracted from green tea

[0043] The prepared instant green tea powder has a bulk density of 15 g / 100 mL, 0.2 g of the instant green tea powder is poured into 100 mL of pure water at 5°C, shaken gently, and completely dissolved within 10 seconds without any suspended particles or lumps, the tea soup is bright yellow-green, the aroma is fresh and lively, and the taste is mellow and refreshing, being highly similar to the flavor of freshly brewed high-end green tea.

[0044] 3. Preparation method of instant black tea powder by low-temperature vacuum flash extraction coupled with molecular embedding Taking the preparation of instant black tea powder as an example, the specific preparation method is as follows: S1, take Dianhong Gongfu black tea, freeze at -35°C for 1.5 hours, and crush to 80 mesh, then place the black tea powder in an extraction system, vacuumize to 0.006 MPa, maintain the temperature at 55°C, start the ultrasonic wave, the frequency being 35 kHz and the power being 400 W, and extract for 8 minutes to obtain a black tea extract; during the extraction process, the black tea aroma components are recovered by an SCC system and collected in a low-temperature storage tank; S2, after the extract is preliminarily separated by a disc centrifuge, it is refined by an ultrafiltration membrane with a molecular weight cutoff of 15 kDa to obtain a clear black tea soup; S3, the refined tea soup is concentrated by a low-temperature vacuum concentration device at a temperature of 50°C and a vacuum degree of 0.09 MPa to 25 Brix to obtain a black tea concentrate; at the same time, part of the black tea aroma components recovered in S1 are uniformly sprayed onto the green tea concentrate using a precision atomizing nozzle; S4, add a composite embedding agent to the black tea concentrate, the mass ratio of the components being: endogenous tea protein extracted from black tea residue: hydroxypropyl-beta-cyclodextrin: maltodextrin = 1:2.5:2, the total amount of addition being 25% of the mass of the concentrate solids, reaction at 58°C under high shear for 50 minutes; S5, the embodiment uses spray drying, the embedded concentrate is atomized in a centrifugal spray drying tower, the inlet temperature is 170°C and the outlet temperature is 85°C, obtaining fine instant black tea powder; S6, the remaining aroma components recovered in S1 are uniformly sprayed onto the dried instant black tea powder using a precision atomizing nozzle, and finally vacuum packaged.

[0045] The composition of the endogenous tea protein extracted from black tea residue in S4 above is shown in Table 2 below.

[0046] Table 2, composition detection results of endogenous tea protein extracted from black tea residue The instant black tea powder prepared is completely dissolved in 8°C cold water within 12 seconds, the tea soup is bright red, with sweet and mellow honey and potato flavors, and a strong and fresh taste.

[0047] 4. Preparation method of instant oolong tea powder coupled with low-temperature vacuum flash extraction and molecular embedding Taking the preparation of instant oolong tea powder as an example, the specific preparation method is as follows: S1, take Anxi Tieguanyin tea leaves, freeze at -45°C for 3 hours, and crush to 70 mesh, place the oolong tea powder in an extraction system, vacuum to 0.01 MPa, maintain the temperature at 55°C, turn on the ultrasonic wave, the frequency is 25 kHz and the power is 250 W, extract for 15 minutes, obtain oolong tea extract; during the extraction process, the SCC system is used to recover the oolong tea aroma components (unique orchid and milk flavors), which are collected in a low-temperature storage tank after condensation; S2, after preliminary separation by a disc centrifuge, the extract is refined by an ultrafiltration membrane with a molecular weight cut-off of 8 kDa, obtaining a clear oolong tea soup; S3, the refined tea soup is concentrated to 15 Brix by an ST tubular reverse osmosis membrane at a temperature of 50°C and a vacuum degree of 0.09 MPa using a low-temperature vacuum concentration device, obtaining oolong tea concentrate; at the same time, the part of the oolong tea aroma components recovered in S1 are uniformly sprayed onto the oolong tea concentrate using a precision atomizing nozzle; S4, add a composite embedding agent to the black tea concentrate, the mass ratio of the components being: endogenous tea protein extracted from black tea residue: hydroxypropyl-beta-cyclodextrin: maltodextrin = 1:2.5:2, the total amount of addition being 25% of the mass of the concentrate solids, reaction at 58°C under high shear for 50 minutes; S5, the concentrated liquid after embedding is dried by using a continuous vacuum freeze dryer, pre-freezing at-38℃, vacuum degree 0.0005 MPa, and desorption temperature 55℃, to obtain fine instant Oolong tea powder; S6, the remaining aroma components recovered in S1 are uniformly sprayed into the dried instant Oolong tea powder by using a precision atomizing nozzle, and finally vacuum packaged.

[0048] The endogenous tea protein components extracted from the tea residues of Oolong tea in S4 are detected as shown in Table 3.

[0049] Table 3, detection results of endogenous tea protein components extracted from the tea residues of Oolong tea The prepared instant Oolong tea powder has a bulk density of 13 g / 100 mL, excellent cold solubility, golden and clear tea soup after dissolution, long-lasting orchid fragrance, and mellow and sweet taste.

[0050] Example 2, screening of cyclodextrin The compound embedding agent formula added in the preparation of instant tea powder of different tea leaves (green tea, black tea, Oolong tea and black tea) needs to be screened, and the compound embedding agent formula added in the preparation of instant green tea powder in screening example 1 is taken as an example.

[0051] The proportion of endogenous tea protein, cyclodextrin and maltodextrin in the compound embedding agent formula added in the preparation of instant green tea powder in example 1 is fixed as 1:3:1.5, the cyclodextrin is changed to one or a combination of β-cyclodextrin, hydroxypropyl-β-cyclodextrin and γ-cyclodextrin, and other conditions remain unchanged, the cold water dissolution time of the prepared instant green tea powder, the color, aroma and taste of the tea soup after dissolution, and the tea polyphenol retention rate after storage are detected, and the detection results are shown in Table 4.

[0052] Table 4, screening results of cyclodextrin types in the compound embedding agent formula

[0053] According to the results in Table 4, when the type of cyclodextrin is only β-cyclodextrin, the cold water dissolution time of the prepared instant green tea powder is the shortest, the color, aroma and taste of the tea soup after dissolution are the best, and the tea polyphenol retention rate after storage is the highest. Therefore, the cyclodextrin of the compound embedding agent added in the preparation of instant green tea powder is preferably β-cyclodextrin.

[0054] Further, on the basis of the above experiment, the cyclodextrin of the compound embedding agent is fixed as β-cyclodextrin, the proportion of endogenous tea protein, β-cyclodextrin and maltodextrin is changed, and other conditions remain unchanged, the cold water dissolution time of the prepared instant green tea powder, the color, aroma and taste of the tea soup after dissolution, and the tea polyphenol retention rate after storage are detected, and the detection results are shown in Table 5.

[0055] Table 5, screening results of the ratio of the composite embedding agent formulation

[0056] According to the results in Table 5, when the ratio of endogenous tea protein: β-cyclodextrin: maltodextrin is 1:3:1.5, the prepared instant green tea powder has the shortest cold water dissolution time, the best color, aroma and taste effect after dissolution, and the highest tea polyphenol retention rate after storage. Therefore, the ratio of endogenous tea protein: β-cyclodextrin: maltodextrin in the composite embedding agent added during the preparation of instant green tea powder is preferably 1:3:1.5.

[0057] According to the same method as described above, the formulation and ratio of the composite embedding agent added during the preparation of instant black tea and oolong tea powder are screened respectively.

[0058] The cyclodextrin of the composite embedding agent added during the preparation of instant black tea powder is preferably hydroxypropyl-β-cyclodextrin, and the ratio of endogenous tea protein extracted from black tea: hydroxypropyl-β-cyclodextrin: maltodextrin is preferably 1:2.5:2. The instant black tea powder prepared by adding the composite embedding agent of the preferred scheme is dissolved in cold water for 12 seconds; the tea soup is bright red and has honey and potato flavors, and the taste is strong and fresh; the tea polyphenol retention rate after storage reaches 94.1%.

[0059] The cyclodextrin of the composite embedding agent added during the preparation of instant oolong tea powder is preferably γ-cyclodextrin, and the ratio of endogenous tea protein extracted from oolong tea: γ-cyclodextrin: maltodextrin is preferably 1:4:1. The instant oolong tea powder prepared by adding the composite embedding agent of the preferred scheme is dissolved in cold water for 11 seconds; the tea soup is golden and clear, with a long-lasting orchid fragrance, and the taste is mellow and sweet; the tea polyphenol retention rate after storage reaches 93.7%.

[0060] Example 3, comparison of different process methods This example changes the process in Example 1 to compare the differences between the instant tea powders prepared by different processes.

[0061] Process 1: The process provided in Example 1 is used to prepare instant green tea, black tea and oolong tea powders respectively.

[0062] Process 2 (traditional process): The traditional process is used to prepare instant green tea powder: hot water extraction at 90°C for 30 minutes, normal pressure filtration, vacuum concentration to 20 Brix at 85°C, addition of 20% maltodextrin as a carrier, and spray drying at an inlet temperature of 180°C. The obtained instant green tea powder has dark green color, light and slightly burnt aroma.

[0063] Process 3 (non-embedding process): Single low-temperature vacuum flash extraction process for preparing instant green tea powder: low-temperature vacuum flash extraction technology is used to extract active ingredients such as tea polyphenols and amino acids under the conditions of a temperature of 40-50°C, a vacuum degree of -0.08~-0.09MPa, and a time of 15-20 minutes, the molecular embedding step is omitted, and direct spray drying or freeze drying is performed.

[0064] Process 4 (hot extraction process): Instant green tea powder is prepared using boiling water as a solvent: conventional extraction for 30-60 minutes, the extract is centrifuged or filtered by a plate and frame, the composite embedding agent in Example 1 is added, and then spray drying is performed.

[0065] Process 5 (single embedding agent): the same as the preparation of instant green tea powder in Example 1, but the composite embedding agent is changed to a single embedding agent, and the composition of the single embedding agent is a single β-cyclodextrin.

[0066] Process 6 (single embedding agent): the same as the preparation of instant green tea powder in Example 1, but the composite embedding agent is changed to a single embedding agent, and the composition of the single embedding agent is a single maltodextrin.

[0067] Process 7 (no ultrasonic process): the ultrasonic-assisted extraction step in Example 1 is omitted to prepare instant green tea powder, and the remaining steps are the same.

[0068] Process 8 (non-tea embedding agent): the same as the preparation of instant green tea powder in Example 1, but the endogenous tea protein is changed to a non-tea source embedding agent (such as a starch derivative, a synthetic polymer), and the non-tea source embedding agent in this process is taken as a starch derivative.

[0069] The extraction rates of effective substances (including tea polyphenols, caffeine, and aroma substances) of instant tea powder prepared by the above different processes, the dissolution time and the tea soup transmittance, the retention rate of effective substances (including tea polyphenols and L-ascorbic acid) after storage, and the sensory evaluation by experts are detected.

[0070] The tea polyphenol extraction rate detection method: the content of tea polyphenols in tea soup is determined by the pyrogallol method, and the extraction rate is calculated.

[0071] The caffeine extraction rate detection method: the content of caffeine in tea soup is determined by high performance liquid chromatography (HPLC), and the extraction rate is calculated.

[0072] The extraction rate of aroma substances (headspace recovery rate): the content of aroma substances in tea soup is determined by headspace solid phase microextraction-gas chromatography mass spectrometry (HS-SPME-GC-MS), and the extraction rate is calculated.

[0073] The storage condition is: placed in a constant temperature and humidity chamber at 40℃, relative humidity 75% for accelerated storage for 30 days. The tea polyphenol content and L-ascorbic acid content are detected before and after 30 days of storage, the tea polyphenol content is determined by the pyrocatechol method, the L-ascorbic acid content is determined by the 2, 6-dichloroindophenol titration method, and the retention rates of tea polyphenol and L-ascorbic acid are calculated respectively.

[0074] The detection method of the dissolution time is: timing during the process of dissolving the instant tea powder in 5℃ pure water until no visible particles are left.

[0075] The detection method of the tea soup transmittance is: using a spectrophotometer to determine the transmittance of the tea soup at a wavelength of 650nm.

[0076] The method of sensory evaluation is: experts evaluate and score the aroma, taste and color of the tea soup, with a full score of 5.

[0077] The detection results of the instant green tea powder, instant black tea powder and instant oolong tea powder prepared in the above process 1 and the instant green tea powder prepared in process 2 are shown in Table 6; the detection results of the instant green tea powder prepared in the above processes 3-8 are shown in Table 7.

[0078] Table 6, detection results of instant tea powders prepared by process 1 and process 2

[0079] Table 7, detection results of instant green tea powders prepared by processes 3-8

[0080] According to the data in Tables 6-7, the tea polyphenol extraction rate of the instant green tea powder, instant black tea powder and instant oolong tea powder prepared by process 1 (Example 1) is more than 90%, the caffeine extraction rate is more than 80%, and the aroma extraction rate is more than 85%; the cold water dissolution time is within 15 seconds, the tea soup transmittance is more than 95%, the aroma, taste and color scores are more than 4.5; after accelerated storage for 30 days, the tea polyphenol retention rate is more than 90%, the color and aroma change is not obvious, and the L-ascorbic acid retention rate is more than 85%.

[0081] The tea polyphenol extraction rate of the instant tea powder prepared by process 2 (traditional process) is only more than 75%, the caffeine extraction rate is more than 70%, and the aroma extraction rate is more than 65%; the cold water dissolution time is more than 60 seconds and the powder is difficult to dissolve and has clumps, the tea soup transmittance is only more than 80% and is turbid, the aroma, taste and color scores are only more than 3.0; after accelerated storage for 30 days, the tea polyphenol retention rate is more than 85%, the color is obviously brown, the aroma is almost gone, and the L-ascorbic acid retention rate is more than 70%.

[0082] The instant green tea powder prepared by process 3 (non-embedding process) has an aroma substance extraction rate about 20% lower than that of process 1, and a tea polyphenol retention rate about 10% lower than that of process 1 after 30 days of storage, indicating that the molecular embedding technology has a protective effect on heat-sensitive components such as volatile aroma substances and tea polyphenols.

[0083] The instant green tea powder prepared by process 4 (hot extraction process) has a polyphenol oxidation loss rate as high as 20%-25% (process 1 only 8%-10%), and the aroma is single and lacks the fresh feeling of low-temperature extraction, indicating that low-temperature vacuum flash extraction has an advantage in protecting heat-sensitive components.

[0084] The instant green tea powder prepared by processes 5-6 (single embedding agent) has a cold water dissolution time of 20-25 seconds (process 1 only 10-12 seconds), and is prone to precipitation after storage (process 1 has a stability improvement of 15%-20%), indicating that the synergy of the composite embedding agent has a synergistic effect.

[0085] The instant green tea powder prepared by process 7 (non-ultrasonic process) has a tea polyphenol extraction rate 10%-12% lower than that of process 1, and an aroma substance recovery rate 15%-18% lower than that of process 1, indicating that ultrasonic waves have a promoting effect on cell disruption and component release.

[0086] The instant green tea powder prepared by process 8 (non-tea embedding agent) has a bitter taste suppression effect weakened (taste score reduced by 1.0-1.2 points), and a color deterioration speed accelerated by 20%-30% after storage, indicating that endogenous tea proteins have a specific binding effect with tea polyphenols.

[0087] As can be seen, the instant tea powder prepared by process 1 has a significantly higher extraction rate of effective substances (including tea polyphenols, caffeine and aroma substances), tea soup transmittance, and retention rate of effective substances (including tea polyphenols and L-ascorbic acid) after storage, and a significantly shorter dissolution time than the instant tea powders prepared by processes 2-8.

[0088] Although the present application is disclosed as above, the present application is not limited thereto. Any person skilled in the art, without departing from the spirit and scope of the present application, can make various changes and modifications, and therefore the protection scope of the present application should be subject to the scope defined by the claims.

Claims

1. A method for preparing instant tea powder by low-temperature vacuum flash extraction coupled with molecular encapsulation, characterized in that, Tea leaves are extracted at low temperature and vacuum to obtain a concentrated liquid. A composite encapsulation agent is added to the concentrated liquid to form an encapsulation complex. The composite encapsulation agent includes endogenous tea protein, cyclodextrin and maltodextrin.

2. The preparation method according to claim 1, characterized in that, The extraction was performed under vacuum conditions of 0.005-0.01 MPa and temperature of 40-60℃, using ultrasonic-assisted extraction.

3. The preparation method according to claim 1, characterized in that, The endogenous tea protein is extracted from tea processing by-products; the amount of the composite encapsulating agent added is 10%-30% of the mass of the concentrate; the mass ratio of the endogenous tea protein, cyclodextrin and maltodextrin is 1:(2-4):(1-2).

4. The preparation method according to claim 2, characterized in that, The ultrasonic-assisted extraction has a frequency of 20-40kHz, a power of 200-500W, and an extraction time of 5-15 minutes.

5. The preparation method according to claim 3, characterized in that, The cyclodextrin is one of β-cyclodextrin, hydroxypropyl-β-cyclodextrin, and γ-cyclodextrin, or a combination thereof.

6. The preparation method according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Tea raw materials are crushed and extracted to obtain tea extract, while volatile aroma components are recovered; (2) The tea extract is separated into tea liquor by solid-liquid separation; (3) The tea soup obtained in step (2) is concentrated to obtain a concentrate; the aroma components recovered in step (1) are returned to the concentrate; (4) The concentrate obtained in step (3) is added to a composite embedding agent to form an embedding complex; (5) The encapsulated complex obtained in step (4) is dried to form instant tea powder, and the remaining aroma components recovered in step (3) are backfilled into the instant tea powder.

7. The preparation method according to claim 6, characterized in that, The aroma components in step (1) are recovered using a rotary distillation column SCC system; the concentration in step (3) is achieved by using a reverse osmosis membrane or a low-temperature vacuum concentration device to concentrate the tea soup to a solid content of 10-30 Bri.

8. The preparation method according to claim 6, characterized in that, The embedded complex in step (4) is prepared by reacting at 50-60℃ and high-speed shear for 30-60 minutes; the drying in step (5) is carried out by freeze drying or spray drying technology.

9. The preparation method according to claim 6, characterized in that, The aroma components recovered in steps (3) and (5) are atomized and then backfilled into the concentrate and instant tea powder.

10. The preparation method according to claim 8, characterized in that, The freeze-drying technology includes porous crystallization freeze-drying technology and continuous vacuum freeze-drying technology; the conditions of the freeze-drying technology are: pre-freezing temperature -30℃ to -40℃, vacuum degree ≤0.001MPa, and desorption stage temperature not exceeding 60℃; the inlet temperature of the spray drying technology is 160-180℃, and the outlet temperature is 80-90℃.

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