A freeze-dried roxburgh pear red tea, a preparation method thereof and an application thereof

Abstract

The application discloses a freeze-dried roselle black tea and a preparation method and application thereof, and belongs to the technical field of food processing. The application provides a preparation method of the freeze-dried roselle black tea, which comprises the following steps: taking out the core of roselle to obtain roselle husks, filling the roselle husks with fermented black tea, carrying out low-temperature color protection treatment after low-temperature standing, then carrying out low-temperature pre-freezing, vacuum freeze-drying, and low-temperature vacuum aroma extraction, so as to obtain the freeze-dried roselle black tea. The application solves two technical difficulties of pre-freezing parameter selection and low-temperature vacuum aroma extraction, avoids the problem of nutrient decomposition caused by high temperature, and simultaneously optimizes the product flavor, appearance, brewing performance and long-term storage stability on the basis of maximizing the retention of active nutrients of roselle. The freeze-dried roselle black tea prepared by the application also has strong antioxidant effect, can help to improve appetite, and has good palatability, so that the freeze-dried roselle black tea is suitable for long-term continuous drinking.

Description

Technical Field

[0001] This invention belongs to the field of food technology, and in particular relates to a freeze-dried prickly pear black tea, its preparation method, and its application. Background Technology

[0002] Prickly pear is rich in heat-sensitive active nutrients such as vitamin C, SOD, and flavonoids. When combined with black tea, it can blend fruit aroma and tea flavor. The existing compound prickly pear black tea on the market all use traditional hot air high-temperature drying process. The standard process is: removing the core and filling the fresh fruit, long-term hot air drying at 60-80℃, and high-temperature baking to enhance the aroma. The existing methods for preparing prickly pear black tea have the following technical defects: (i) High temperature destroys active nutrients: The drying and baking temperature is higher than 60℃ for a long time, and vitamin C, SOD and flavonoids are easily oxidized and decomposed, with less than 40% of active substances remaining, resulting in a significant decrease in the nutritional value of the product; (ii) Prominent flavor defects: High temperature baking produces a burnt and bitter taste, which masks the natural fresh aroma of prickly pear; (iii) Poor brewing experience: High temperature drying causes the pulp to shrink and become dense, and the pores to close, resulting in a slow extraction of nutrients and flavors during brewing; (iv) Poor storage stability: The moisture content of the dried product is too high, and there is no low temperature color protection process. It is easy to oxidize, turn black and moldy after being stored for several months; (v) Defects in raw material processing: Most processes do not completely remove the prickly pear seeds, and the bitter substances in the seeds are incorporated into the tea soup, affecting the drinking taste. Summary of the Invention

[0003] In view of this, the purpose of this invention is to provide freeze-dried prickly pear black tea, its preparation method and application. By setting specific pre-freezing and low-temperature aroma enhancement parameters, the problem of nutrient decomposition caused by high temperature is avoided. On the basis of maximizing the preservation of the active nutrients of prickly pear, a product with good flavor, appearance, brewing performance and long-term storage stability is obtained. It also has a strong antioxidant effect, helps to improve appetite, and is palatable for long-term continuous consumption.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing freeze-dried prickly pear black tea, comprising the following steps: removing the core of the prickly pear to obtain the prickly pear shell, filling the prickly pear shell with fermented black tea, allowing it to stand at low temperature, then performing a low temperature color protection treatment, followed by low temperature pre-freezing, vacuum freeze-drying, and low temperature vacuum aroma enhancement to obtain freeze-dried prickly pear black tea.

[0005] Preferably, the fresh leaves are withered, rolled, fermented at 25-29℃ and 85-95% humidity for 1-5 hours, and then dried to obtain fermented black tea.

[0006] Preferably, the withering time is 9-13 hours, the kneading time is 80-100 minutes, and the drying temperature is 60-65°C for 20-30 minutes.

[0007] Preferably, the temperature for the low-temperature settling is 3-5°C and the time is 20-40 minutes.

[0008] Preferably, the low-temperature color protection temperature is 2-6℃ and the time is 15-20h; the low-temperature color protection uses a citric acid aqueous solution with a mass percentage of 0.08-0.13% as the impregnation solution.

[0009] Preferably, the low-temperature pre-freezing step includes: pre-freezing at -35~-45℃ for 5-9 hours.

[0010] Preferably, the vacuum freeze-drying step includes: setting a vacuum degree of 9-19 Pa, raising the temperature to -5~-15℃ at 0.3-0.7℃ / min for 12-16 hours, and then maintaining the vacuum environment and raising the temperature to 18-22℃ at 0.8-1.2℃ / min for 3-7 hours.

[0011] Preferably, the low-temperature vacuum aroma extraction temperature is 30-40℃, the time is 15-21 min, and the vacuum degree is 10-18 Pa.

[0012] This invention provides freeze-dried prickly pear black tea obtained by the preparation method described above.

[0013] This invention provides freeze-dried prickly pear black tea obtained by the preparation method, or the application of the freeze-dried prickly pear black tea in the preparation of antioxidant products.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention involves filling fermented prickly pear shells into black tea, followed by low-temperature static treatment for color preservation, low-temperature pre-freezing, vacuum freeze-drying, and low-temperature vacuum aroma enhancement. This approach overcomes two major technical challenges: selecting appropriate low-temperature pre-freezing parameters and low-temperature vacuum aroma enhancement. It avoids problems such as oxidation of heat-sensitive components, aroma volatilization, and difficulty in removing bound water, maximizing the retention rate of vitamin C, flavonoids, SOD, and tea polyphenols in the product while preserving the original aroma. Compared to the existing traditional hot-air drying process for prickly pear black tea, which suffers from high-temperature nutrient loss, poor flavor, short storage period, and low brewing efficiency, this invention develops a complete low-temperature vacuum freeze-drying process. This produces a product with high active ingredients, excellent flavor, appearance, brewing performance, and stability. It also has strong antioxidant properties, helps improve appetite, and is palatable for long-term continuous consumption. Attached Figure Description

[0015] Figure 1 The rolling process for preparing black tea.

[0016] Figure 2 The fermentation process for preparing black tea.

[0017] Figure 3 The process of filling and compounding freeze-dried prickly pear black tea.

[0018] Figure 4 The process of screening freeze-dried prickly pear.

[0019] Figure 5 The images show a comparison between the products prepared in Example 3 and Comparative Example 1. The top image shows the freeze-dried prickly pear black tea prepared in Example 3, and the bottom image shows the prickly pear black tea prepared in Comparative Example 1.

[0020] Figure 6 The images show a comparison of the brewing processes of the products prepared in Example 3 and Comparative Example 1. The left side shows the freeze-dried prickly pear black tea prepared in Example 3, and the right side shows the prickly pear black tea prepared in Comparative Example 1.

[0021] Figure 7 The images show a comparison of the brewing processes of the products prepared in Example 3 and Comparative Example 1. The left side shows the freeze-dried prickly pear black tea prepared in Example 3, and the right side shows the prickly pear black tea prepared in Comparative Example 1. Detailed Implementation

[0022] This invention provides a method for preparing freeze-dried prickly pear black tea, comprising the following steps: removing the core of the prickly pear to obtain the prickly pear shell; filling the prickly pear shell with fermented black tea; subjecting the tea to low-temperature settling followed by low-temperature color protection treatment; then pre-freezing at low temperature; vacuum freeze-drying; and low-temperature vacuum aroma enhancement to obtain freeze-dried prickly pear black tea. This method, through the coordinated regulation of multiple steps including low-temperature settling, low-temperature color protection, low-temperature pre-freezing, vacuum freeze-drying, and low-temperature vacuum aroma enhancement, produces a product that maximizes the retention of active ingredients in the freeze-dried prickly pear black tea and exhibits good appearance, brewing properties, and stability. Antioxidant experiments and statistical analysis of volunteer tea-drinking experiences show that the freeze-dried prickly pear black tea prepared by this invention also has significant antioxidant effects. Volunteers who consumed it experienced improved appetite, and its palatability is suitable for long-term continuous consumption. This invention preferably uses the Guinong No. 5 prickly pear planted in Gujiao Town, Longli County, Guizhou Province.

[0023] In this invention, fresh leaves are withered, rolled, fermented at 25-29℃ and 85-95% humidity for 1-5 hours, and then dried to obtain fermented black tea. This invention preferably uses fresh leaves of the Bird King variety grown in high-altitude communities in Yunwu Town, Guiding County. The withering time is 9-13 hours, preferably 10-12 hours, and more preferably 11 hours; the rolling time is 80-100 minutes, preferably 85-95 minutes, and more preferably 90 minutes; the drying temperature is 60-65℃ and the time is 20-30 minutes, preferably 61-64℃ and the time is 22-28 minutes, and more preferably 62-63℃ and the time is 24-26 minutes. This invention's withering process removes excess moisture from the fresh leaves, reduces leaf brittleness, increases the toughness of the tea cell walls, making them less prone to breakage during subsequent rolling, and avoids excessive water loss. It maximizes the retention of vitamins, flavonoids, and aroma precursors in the tea leaves, and reduces the premature volatilization and degradation of heat-sensitive active ingredients. This invention utilizes a kneading process that tears the tea leaf's outer skin and cell structure, allowing the tea's internal substances (tea polyphenols, amino acids, tea polysaccharides, and aromatic compounds) to spill onto the leaf surface. This increases the contact area for subsequent fermentation, making it easier for the tea's effective components to dissolve and combine with the active components of the prickly pear during subsequent freeze-drying. The fermentation process after kneading transforms a large number of aroma precursors into characteristic aromas of black tea, desensitizes some strongly astringent substances, and reduces the astringency of the tea liquor. Furthermore, the drying process after fermentation significantly reduces the total amount of water that needs to be removed through sublimation during subsequent freeze-drying. Short-term heating inactivates polyphenol oxidase, locking in the current level of oxidation and flavor compounds, preventing further oxidation and deterioration in subsequent processes.

[0024] In this invention, the low-temperature settling temperature is 3-5℃ and the time is 20-40 minutes, preferably 3.5-4.5℃ and 25-35 minutes, and more preferably 4℃ and 30 minutes. This invention involves filling the prickly pear with fermented black tea and then setting it at a low temperature to allow the tea aroma and prickly pear fruit aroma to initially infuse and blend, inhibiting excessive polyphenol oxidase reaction and preventing oxidation and deterioration of the black tea flavor and active ingredients. This invention uses a fixed tea-to-prickly pear shell ratio of 0.8-1.2g black tea per single prickly pear shell. Fermented black tea is manually or automatically filled into the hollow prickly pear shell, ensuring a full filling without overflow, and the black tea is completely enveloped by the fruit pulp.

[0025] In this invention, the low-temperature color protection temperature is 2-6℃ and the time is 15-20 hours, preferably 3-5℃ and 16-19 hours, and more preferably 4℃ and 18 hours. The low-temperature color protection uses a 0.08-0.13% (by mass) citric acid aqueous solution as the impregnation liquid, preferably 0.09-0.12%, and more preferably 0.1%. This invention's low-temperature color protection treatment of prickly pear black tea after low-temperature settling can inhibit the oxidative browning of vitamin C, polyphenols in prickly pear, and theaflavins in black tea, locking in the original color of the raw materials, preventing the finished product from turning black and dull, achieving color protection and appearance preservation. It can also slow down the degradation of active ingredients, stabilize the antioxidant substances in prickly pear and black tea, and prevent material deterioration, improving the quality of raw materials before freeze-drying and the storage stability of the finished product. After the low-temperature color-protected prickly pear black tea is impregnated, it is cooled by cold air to thoroughly remove surface free moisture and prevent freezing and clumping during the freeze-drying stage.

[0026] In this invention, the low-temperature pre-freezing step includes: pre-freezing at -35~-45℃ for 5-9 hours, preferably at -38~-43℃ for 6-8 hours, and more preferably at -40℃ for 7 hours. This invention arranges the filled tea fruits in a single layer on a tray. Low-temperature pre-freezing freezes all the moisture inside the fruit pulp and tea leaves into solid ice crystals. During pre-freezing, the freeze dryer's cold trap is simultaneously lowered to -50℃ to prepare for vacuum sublimation. This invention allows the internal moisture of the material to completely condense into solid ice crystals, preventing the material from melting and splashing, and causing structural collapse during freeze-drying and vacuuming, thus ensuring the final appearance. Low-temperature freezing also significantly reduces the oxidation and decomposition of vitamin C, polyphenols, and flavor substances in prickly pear and black tea, maximizing the preservation of active ingredients and original color.

[0027] In this invention, the vacuum freeze-drying step includes: setting a vacuum degree of 9-19 Pa, raising the temperature to -5 to -15°C at a rate of 0.3-0.7°C / min for 12-16 hours, then maintaining the vacuum environment and raising the temperature to 18-22°C at a rate of 0.8-1.2°C / min for 3-7 hours; preferably, setting a vacuum degree of 10-18 Pa, raising the temperature to -8 to -13°C at a rate of 0.4-0.6°C / min for 13-15 hours, then maintaining the vacuum environment and raising the temperature to 19-21°C at a rate of 0.9-1.1°C / min for 4-6 hours; more preferably, setting a vacuum degree of 19 Pa, raising the temperature to -10°C at a rate of 0.5°C / min for 14 hours, then maintaining the vacuum environment and raising the temperature to 20°C at a rate of 1.0°C / min for 5 hours. This invention involves first sublimating and drying prickly pear black tea after low-temperature pre-freezing, causing the internal ice crystals to directly sublimate into water vapor which is then captured by a cold trap, removing 85% of the free water. Then, a second desorption drying process is performed under vacuum to remove bound water, reducing the moisture content of the finished product to ≤6%. This invention combines pre-freezing with vacuum freeze-drying, allowing water to sublimate directly under vacuum without passing through a liquid state. The entire process is kept below 40°C, ensuring minimal loss of heat-sensitive nutrients.

[0028] In this invention, fresh prickly pear fruit is rich in ascorbic acid. Improper temperature control during the freeze-drying and desorption drying stage leads to the decomposition of vitamin C. At the same time, the volatility of organic acids is unbalanced, resulting in an overly sour or bland finished product. This invention adopts a segmented temperature-controlled sublimation process. After pre-freezing, a sublimation heating process is carried out at an extremely slow rate, which allows the ice crystals to sublimate slowly while reducing the decomposition of heat-sensitive substances. The heating rate in the secondary desorption stage balances the volatility of organic acids and preserves the activity of vitamin C.

[0029] In this invention, the co-freeze-drying of black tea leaves and prickly pear can easily lead to uneven drying. Black tea has a dense structure, while prickly pear has large pores. When the two are freeze-dried together, the ice crystal formation rate is inconsistent, resulting in incomplete drying in some areas. Long-term storage can easily lead to moisture absorption and softening, posing a risk of mold growth. This invention adds a low-temperature rehydration process to the tea leaves before pre-freezing. The prickly pear black tea leaves with filling are placed in a 4°C environment for rehydration, controlling the difference in moisture content between the tea leaves and the prickly pear to within 5%. This is combined with a slow-rate sublimation process during vacuum freeze-drying, synchronizing the ice crystal formation and sublimation rates of the two materials and avoiding incomplete drying in some areas.

[0030] In this invention, excessively rapid sublimation drying can cause the fruit pulp to collapse and aromatic substances to escape; excessively slow sublimation rates lengthen the production cycle and increase production costs. By fixing the rate combination of "one sublimation and two desorptions," the collapse of the prickly pear fruit shell and the escape of aromatic substances are avoided through slow sublimation, while the reasonable acceleration of the second desorption shortens the production cycle, thus controlling production costs while ensuring product quality.

[0031] In this invention, the low-temperature vacuum aroma extraction temperature is 30-40℃, the time is 15-21 min, and the vacuum degree is 10-18 Pa. Preferably, the temperature is 33-38℃, the time is 16-20 min, and the vacuum degree is 12-16 Pa. More preferably, the temperature is 35℃, the time is 18 min, and the vacuum degree is 14 Pa. This invention sets specific temperatures and times in the aroma extraction step to release the honey aroma of black tea and the sweet fruity aroma of prickly pear, without destroying Vitamin C and eliminating the burnt smell produced by high-temperature baking. The specific temperature does not destroy the heat-sensitive active substances such as Vitamin C, SOD, and polyphenols in prickly pear and black tea, but only gently volatilizes off-flavors and enriches the natural aroma of black tea and prickly pear. Compared with traditional high-temperature aroma extraction, the retention rate of active ingredients is higher. Precise temperature and time control within a specific short period can fully highlight the complex fruit and tea aromas while preventing browning and burnt flavor caused by prolonged heating. Compared with conventional aroma extraction processes, the finished product has superior aroma purity and appearance stability.

[0032] In this invention, vacuum freeze-drying typically preserves the freshness of tea, but some prominent floral and fruity aromas are weaker than those from low-temperature hot air drying, and the aroma profile is easily altered. Furthermore, some volatile substances condense in the condenser under vacuum conditions, making them difficult to recover. However, the low-temperature vacuum drying and low-temperature vacuum aroma enhancement methods employed in this invention can significantly prevent the volatilization of low-boiling-point aromatic substances or the condensation of volatile substances in the condenser. This results in freeze-dried prickly pear black tea that, after brewing, possesses a prominent and clear wild prickly pear aroma, a harmonious and full-bodied fruit acidity, a sweet and refreshing tea soup, a gentle bitterness, and an aroma that combines the original floral and fruity notes with the sweetness of black tea, significantly enhancing the flavor profile.

[0033] The present invention also provides freeze-dried prickly pear black tea obtained by the preparation method described above.

[0034] The present invention also provides freeze-dried prickly pear black tea obtained by the preparation method or the application of the freeze-dried prickly pear black tea in the preparation of antioxidant products.

[0035] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Unless otherwise specified, the following embodiments are all conventional methods.

[0037] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0038] Example 1 1. Raw material screening and pretreatment (1) Select fresh prickly pears of the year harvested in Gujiao Town, Longli County, Guizhou Province, with a single fruit diameter of 4.2cm, nine-tenths ripe and free from rot and insect holes. Remove damaged fruits manually, hollow out the core longitudinally, and keep the whole hollow fruit shell. Rinse twice with running water, and air dry the surface of the fruit peel with cold air at an ambient temperature of 4℃ to prevent the prickly pear polyphenols from oxidizing and turning black.

[0039] (2) Black Tea Preparation: Fresh leaves of Bird King variety tea planted in the high-altitude group in Yunwu Town, Guiding County, were selected. The leaves were withered for 9 hours, rolled for 80 minutes, and fermented at 25℃ and 85% humidity for 1 hour. Suitable temperature and humidity promoted the conversion of tea polyphenols, generating the characteristic aroma of black tea. Afterwards, the leaves were initially dried at 60℃ for 20 minutes to stabilize the moisture content of the dry tea at 12%. The tea was then sieved through a 20-mesh screen to remove broken leaves for later use. The rolling process is as follows: Figure 1 As shown, the fermentation process is as follows: Figure 2 As shown.

[0040] 2. Core-filling composite (tea and fruit fusion) A fixed ratio of 1g fermented black tea to a single hollow prickly pear shell is used. The fermented black tea is manually and quantitatively filled into the hollow prickly pear shell, ensuring a full filling without overflow. After filling, the shell is placed in a constant temperature environment of 3℃ for 20 minutes. Under this low-temperature environment, the honey aroma of the black tea and the fruit aroma of the prickly pear slowly infuse and blend, preventing premature aroma evaporation caused by high temperatures. The filling process is as follows: Figure 3 As shown.

[0041] 3. Low-temperature color protection pretreatment Prepare a 0.08% food-grade citric acid aqueous solution as a color-protecting impregnation solution. Impregnate at 3℃ for 15 hours. The low temperature system inhibits the oxidative browning of tannins and polyphenols in prickly pear. After impregnation, drain with cold air at 3℃ to completely remove free surface moisture and prevent ice and clumps from forming on the fruit surface during the subsequent pre-freezing stage.

[0042] 4. Low-temperature pre-freezing (a key step before freeze-drying) After filling, the tea fruits are laid out in a single layer on a stainless steel freeze-drying tray, without stacking. The freeze dryer is pre-frozen at -35℃ for 5 hours to completely solidify the free and bound water inside the fruit pulp and tea leaves into solid ice crystals. Simultaneously, the freeze dryer's cold trap is lowered to -35℃ to prepare for vacuum sublimation drying. This process is completed using a domestically common LGJ-100 vacuum freeze dryer.

[0043] 5. Vacuum freeze drying: The core process, with the material temperature below 40℃ throughout the process, avoiding heat-sensitive nutrient loss.

[0044] (1) One-time sublimation drying: vacuum degree 9Pa, freeze dryer plate temperature is increased to -5℃ at 0.7℃ / min, and kept warm for 12h. The ice crystals inside the fruit directly sublimate into water vapor and are captured by the cold trap, removing 85% of the free water. (2) Secondary analysis and drying: Maintain a vacuum sealed environment, raise the plate temperature to 18℃ at 1.2℃ / min, and keep it at the temperature for 3 hours to remove the bound water inside the material. The overall moisture content of the final product is controlled to be ≤6%.

[0045] 6. Unloading, Warming, and Sorting: After freeze-drying, the vacuum chamber is slowly ventilated for warming. The porous and loose prickly pear black tea fruits are gently removed. Broken fruits and underfilled defective products are manually sorted, with only intact samples retained for the next process. The freeze-dried prickly pear black tea screening process is as follows: Figure 4 As shown.

[0046] 7. Low-temperature vacuum aroma enhancement (special flavor optimization process): The aroma is enhanced for 15 minutes in a low-temperature vacuum environment at 30℃ and 10Pa, releasing the honey aroma of black tea and the sweet fruit aroma of prickly pear. The low-temperature conditions throughout the process do not destroy heat-sensitive active substances such as vitamin C and SOD, and eliminate the burnt taste produced by high-temperature baking.

[0047] 8. Aseptic sealing packaging and storage: The entire process is carried out in a Class 10,000 clean food workshop, using food-grade aluminum foil composite bags. After replacing the air with nitrogen, the packaging is individually heat-sealed to isolate oxygen and moisture. The finished product is stored in a cool, dry place at room temperature, with a shelf life of 18 months.

[0048] Example 2 1. Raw material screening and pretreatment (1) Select fresh prickly pears of the year harvested in Gujiao Town, Longli County, Guizhou Province, with a single fruit diameter of 4.0cm, nine-tenths ripe and free from rot and insect holes. Remove damaged fruits manually, hollow out the core longitudinally, and keep the whole hollow fruit shell. Rinse twice with running water, and air dry the surface of the fruit peel with cold air at an ambient temperature of 4℃ to prevent the prickly pear polyphenols from oxidizing and turning black.

[0049] (2) Preparation of black tea: Fresh leaves of Bird King variety planted in the high mountains of Yunwu Town, Guiding County are selected. They are withered for 13 hours, rolled for 100 minutes, fermented at 29℃ and 95% humidity for 4 hours. The appropriate temperature and humidity promote the conversion of tea polyphenols and generate the characteristic aroma of black tea. Then, they are initially dried at 65℃ for 30 minutes to control the moisture content of the dry tea to stabilize at 12%. The broken pieces are removed by 20-mesh sieve and set aside.

[0050] 2. Filling and compounding: With a fixed tea-fruit ratio of 0.9g fermented black tea / single hollow prickly pear shell, fermented black tea is manually and quantitatively filled into the hollow prickly pear shell, filling it fully without overflowing; after filling, it is placed in a constant temperature environment of 5℃ for 40 minutes. Under the low temperature environment, the honey aroma of black tea and the aroma of prickly pear fruit slowly infiltrate and blend, avoiding the premature volatilization of aroma caused by high temperature.

[0051] 3. Low-temperature color protection pretreatment: Prepare a 0.13% food-grade citric acid aqueous solution as the color protection soaking solution, and soak at 5℃ for 20 hours. The low-temperature system inhibits the oxidation and browning of tannins and polyphenols in prickly pear. After soaking, air dry at 5℃ to completely remove free surface moisture and prevent the fruit surface from freezing and clumping during the subsequent pre-freezing stage.

[0052] 4. Low-temperature pre-freezing: The filled tea fruits are laid flat in a single layer on a special stainless steel tray for freeze-drying, without stacking. The freeze dryer is pre-frozen at -45℃ for 9 hours to completely solidify the free and bound water inside the fruit pulp and tea leaves into solid ice crystals. Simultaneously, the freeze dryer's cold trap is lowered to -45℃ to prepare for vacuum sublimation. This process is completed using a domestically common LGJ-100 vacuum freeze dryer.

[0053] 5. Vacuum freeze drying (1) Sublimation drying: vacuum degree 19Pa, freeze dryer plate temperature is increased to -15℃ at 0.3℃ / min, and kept warm for 16h. The ice crystals inside the fruit directly sublimate into water vapor and are captured by the cold trap, removing 85% of the free water. (2) Secondary analysis and drying: Maintain a vacuum sealed environment, raise the plate temperature to 22°C at 0.8°C / min, and keep it at the temperature for 7 hours to remove the bound water inside the material. The overall moisture content of the final product is controlled to be ≤6%.

[0054] 6. Discharge, reheating and sorting: The steps are the same as in Example 1.

[0055] 7. Low-temperature vacuum aroma enhancement: The aroma is enhanced for 15 minutes in a low-temperature vacuum environment at 40℃ and 18Pa, releasing the honey aroma of black tea and the sweet fruity aroma of prickly pear. The low-temperature conditions throughout the process do not destroy heat-sensitive active substances such as vitamin C and SOD, and eliminate the burnt smell produced by high-temperature baking.

[0056] 8. Aseptic sealing and storage: The steps are the same as in implementation 1.

[0057] Example 3 1. Raw material screening and pretreatment (1) Processing of fresh prickly pear: Select fresh prickly pears of the same year harvested in Gujiao Town, Longli County, Guizhou Province, with a single fruit diameter of 4.5cm, nine-tenths ripe and free from rot and insect holes. Remove damaged fruits manually, hollow out the core longitudinally, and keep the whole hollow fruit shell. Rinse twice with running water, and air dry the surface of the fruit peel with cold air at an ambient temperature of 4℃ to prevent the prickly pear polyphenols from oxidizing and turning black.

[0058] (2) Preparation of black tea: Fresh leaves of Bird King variety planted in the high mountains of Yunwu Town, Guiding County are selected. They are withered for 12 hours, rolled for 90 minutes, fermented at 28℃ and 90% humidity for 3 hours. The appropriate temperature and humidity promote the conversion of tea polyphenols and generate the characteristic aroma of black tea. Then, they are initially dried at 63℃ for 25 minutes to control the moisture content of the dry tea to stabilize at 12%. The broken pieces are removed by 20-mesh sieve and set aside.

[0059] 2. Filling and compounding: With a fixed tea-fruit ratio of 1g fermented black tea / single hollow prickly pear shell, fermented black tea is manually and quantitatively filled into the hollow prickly pear shell, filling it fully without overflowing; after filling, it is placed in a constant temperature environment of 4℃ for 30 minutes. Under the low temperature environment, the honey aroma of black tea and the aroma of prickly pear fruit slowly infiltrate and blend, avoiding the premature volatilization of aroma caused by high temperature.

[0060] 3. Low-temperature color protection pretreatment: Prepare a 0.1% food-grade citric acid aqueous solution as the color protection soaking solution, and soak at 4℃ for 18 hours. The low-temperature system inhibits the oxidation and browning of tannins and polyphenols in prickly pear. After soaking, air dry at 4℃ to completely remove free surface moisture and prevent ice and lumps from forming on the surface of the fruit during the subsequent pre-freezing stage.

[0061] 4. Low-temperature pre-freezing: The filled tea fruits are laid flat in a single layer on a special stainless steel tray for freeze-drying, without stacking. The freeze dryer is pre-frozen at -40℃ for 8 hours to completely freeze the free and bound water inside the fruit pulp and tea leaves into solid ice crystals. Simultaneously, the freeze dryer's cold trap is lowered to -50℃ to prepare for vacuum sublimation drying. This process is completed using a domestically common LGJ-100 vacuum freeze dryer.

[0062] 5. Vacuum freeze drying (core process, no high temperature throughout) (1) One-time sublimation drying: vacuum degree 10Pa, freeze dryer plate temperature is increased to -10℃ at 0.5℃ / min, and kept warm for 16h. The ice crystals inside the fruit directly sublimate into water vapor and are captured by the cold trap, removing 85% of the free water. (2) Secondary analysis and drying: Maintain a vacuum sealed environment, raise the plate temperature to 20°C at 1°C / min, and keep it at the temperature for 6 hours to remove the bound water inside the material. The overall moisture content of the final product is controlled to be ≤6%.

[0063] 6. Discharge, reheating and sorting: The steps are the same as in Example 1.

[0064] 7. Low-temperature vacuum aroma enhancement: The aroma is enhanced for 20 minutes in a low-temperature vacuum environment at 35℃ and 14Pa, releasing the honey aroma of black tea and the sweet fruity aroma of prickly pear. The low-temperature conditions throughout the process do not destroy heat-sensitive active substances such as vitamin C and SOD, and eliminate the burnt smell produced by high-temperature baking.

[0065] 8. Aseptic sealing and storage: The steps are the same as in Example 1.

[0066] Comparative Example 1: Existing Traditional Hot Air Drying Process The difference from Example 3 is that after removing the core and filling the core, the product is dried with hot air at 70°C for 24 hours, followed by high-temperature baking at 110°C for 120 minutes to enhance the aroma. There is no low-temperature pre-freezing or vacuum freeze-drying process. The remaining steps are the same as in Example 3.

[0067] Comparative Example 2: Changes in Low Temperature Parameters The difference from Example 3 is that the sample pre-freezing temperature is adjusted to -20℃, while the rest of the procedures are the same as in Example 3.

[0068] Comparative Example 3 omits the low-temperature vacuum aroma extraction process. The difference from Example 3 is that the 35°C vacuum aroma extraction step is not performed; the remaining steps are the same as in Example 3.

[0069] Experimental Example 1 The appearance, various indicators, and stability of the prickly pear black tea prepared in Examples 1-3 and Comparative Examples 1-3 were investigated. The appearance of the products from Example 3 and Comparative Example 1 is as follows: Figure 5 As shown in the image and the appearance of the tea soup. Figure 6 As shown.

[0070] The vitamin C content of prickly pear black tea was determined according to GB 5009.86-2016; SOD enzyme activity was determined according to the pyrogallol auto-oxidation spectrophotometric method; total flavonoids were determined according to the sodium nitrite-aluminum nitrate spectrophotometric method; moisture content of prickly pear black tea was determined according to GB 5009.3-2016; and tea polyphenols were determined according to the Folin-Ciocalteu spectrophotometric method in GB / T 8313-2018. Each group of samples was tested in triplicate, and the average value was taken.

[0071] Sensory evaluation was conducted under standardized brewing conditions: tea-to-water ratio 1g:50ml, water temperature 90℃, and steeping time 3 minutes. The brewing state and the extraction of substances were observed. Ten certified tea tasters with more than five years of experience were invited to taste the tea brewed for 3 minutes and conduct blind tasting and scoring. The final score for each sample was the average of the scores given by the ten tasters.

[0072] Table 1. Results of moisture content, composition, and scoring for each group of products.

[0073] Table 2 Results of product performance and stability assessment for each group

[0074] As shown in Tables 1 and 2, the comparison of Examples 1-3 indicates that extending the vacuum aroma extraction time in a suitable temperature environment results in better integration of the prickly pear fruit aroma and the black tea aroma, higher retention of internal substances, and stronger storage stability. Example 3 is the optimal freeze-drying solution.

[0075] Compared with the vacuum freeze-dried samples of Examples 1-3, the product of conventional high-temperature drying in Comparative Example 1 has a distinct burnt and bitter taste, firm pulp, and dark brown discoloration, resulting in significant loss of active nutrients, slow brewing speed, poor flavor, and short storage period; combined with Figure 6 As can be seen from the brewed tea, the tea soup of the hot-dried sample is dark in color, while the tea soup of the freeze-dried prickly pear black tea is clear and golden, fully demonstrating the advantages of the freeze-drying process of this invention.

[0076] Compared with the vacuum freeze-dried samples of Examples 1-3, Comparative Example 2 was not fully frozen, and local clumps formed after freeze-drying. The finished product had a slight burnt smell and a shriveled and clumped appearance. This proves that the parameter range of pre-freezing combined with low-temperature freeze-drying in this invention is an essential condition for achieving high content of active substances. Products outside this range show a significant decline in quality.

[0077] Comparing the samples of Comparative Example 3 and Example 3, the product prepared in Example 3 has a rich and harmonious aroma, thus proving that the low-temperature vacuum aroma extraction method set in this invention is a key process for improving the flavor of the product.

[0078] Experiment Example 2 Physicochemical indicators were tested on the freeze-dried prickly pear black tea prepared in Example 3 and the prickly pear black tea prepared in Comparative Example 1. Sensory brewing tests were also conducted according to tea evaluation standards. Brewing conditions: tea-to-water ratio 1g:50ml, water temperature 90℃, steeping time 3min. The tea infusion after steeping was as follows: Figure 7 As shown in the table. The indicators of the tea infusions after steeping were tested in both groups. The methods for testing each indicator are as follows: Vitamin C was determined by high performance liquid chromatography (HPLC) according to GB 5009.86-2016; tea polyphenols were determined by the Folin-Ciocalteu spectrophotometric method according to GB / T 8313-2018; theaflavins were determined by HPLC according to GB / T 30483-2013; titratable total acid was determined by acid-base titration according to GB 12456-2021; water extract was determined by gravimetric method according to GB / T 8305-2018; total flavonoids were determined by sodium nitrite-aluminum nitrate spectrophotometric method; and SOD enzyme activity was determined by pyrogallol autoxidation spectrophotometric method. Two small fruits, two medium fruits, and one large fruit from each group were tested for the above indicators. The lowest and highest values ​​of the five samples were taken as the range values ​​for statistical analysis. The test results are shown in Table 3.

[0079] Table 3 Results of the two sets of detection indicators

[0080] Hot-air dried prickly pear black tea and freeze-dried prickly pear black tea at -40℃ undergo significant changes in their internal components due to the difference in drying temperature, resulting in differences in flavor and taste. Differences in tea polyphenol content: Continuous high temperature from hot air drying promotes the continuous oxidation and polymerization of tea polyphenols, resulting in a large accumulation of bitter and astringent substances; low temperature during freeze drying inhibits excessive oxidation of tea polyphenols, resulting in less bitter and astringent substances. Taste profile: Hot-air dried tea has a prominent bitter and astringent taste; freeze-dried tea has a milder bitter and astringent taste.

[0081] Titrizable total acidity (organic acids) difference: High temperature environment causes a large amount of organic acids such as citric acid and malic acid in prickly pear to decompose and be lost. Taste performance: Hot air drying results in a weak fruit acidity and a thin sweet and sour flavor; freeze-dried tea soup has a harmonious and full fruit acidity, with a rich mountain sweet and sour flavor.

[0082] Differences in theaflavin content: High temperatures easily cause the oxidation and loss of theaflavins produced during the fermentation of black tea. Theaflavins are the core substances responsible for the sweet and mellow taste of tea. Taste profile: Hot-air dried tea has a weaker sweet and mellow taste; freeze-dried tea has a more pronounced sweet and mellow aftertaste.

[0083] Differences in Vitamin C, Total Flavonoids, and SOD Enzyme Activity: Hot air drying significantly reduced the activities of Vitamin C, total flavonoids, and SOD enzyme; freeze-drying at -40℃ preserved the original active substances of prickly pear to the maximum extent. The endogenous floral and fruity aroma substances of prickly pear were retained simultaneously with the heat-sensitive substances. Aroma and Flavor Characteristics: Long-term baking with hot air produced a roasted aroma, while the original wild fruit aroma of prickly pear was weak; the freeze-dried sample showed a high-pitched floral and fruity aroma of wild prickly pear, with a harmonious blend of tea and prickly pear aromas, without a heavy roasted note.

[0084] Differences in water extracts: Freeze-dried prickly pear black tea has intact pores, making it easier to extract water-soluble flavor substances. Taste profile: Freeze-dried tea liquor contains sufficient flavor substances, resulting in a full-bodied and complex flavor; hot-air dried tea liquor has insufficient flavor substance extraction and a thin flavor.

[0085] Based on the above test data Figure 7 It is known that existing traditional prickly pear black tea generally uses hot air drying for dehydration, keeping the material in a medium-high temperature environment of 40-65℃ for extended periods. This sustained high temperature causes the continuous oxidation and polymerization of tea polyphenols in the prickly pear and tea leaves, resulting in a large accumulation of bitter and astringent substances. Simultaneously, a significant amount of endogenous organic acids and low-boiling-point volatile aromatic substances from flowers and fruits in the prickly pear are degraded and lost. The high temperature also induces the Maillard reaction, forming a roasted aroma. When brewed, prickly pear black tea produced through hot air drying exhibits a weak original fruity aroma, a light fruity acidity, a pronounced roasted flavor in the tea soup, a prominent bitterness and a lack of freshness, and a single flavor profile. The tea soup is a dark orange-yellow, and the tea leaves are a dark brown.

[0086] This invention employs a -40℃ low-temperature vacuum freeze-drying process to dehydrate raw materials. The materials are pre-frozen at -40℃, and drying is achieved through ice crystal sublimation in a low-temperature vacuum environment, avoiding prolonged high-temperature heating throughout the process. The ultra-low temperature significantly inhibits excessive oxidation of tea polyphenols, reducing the formation of large amounts of bitter substances. Organic acids such as citric acid and malic acid, as well as various volatile floral and fruity aroma components in the prickly pear are largely preserved. Flavor compounds such as theaflavins and thearubigins formed during black tea fermentation remain stable and do not undergo excessive oxidation. Compared to hot-air dried prickly pear black tea, the freeze-dried prickly pear black tea of ​​this invention, after brewing, exhibits a high and clear aroma of wild prickly pear, a harmonious and full-bodied fruit acidity, a sweet and refreshing tea soup, and a gentle bitterness. The aroma combines the original floral and fruity notes with the sweetness of black tea, without a heavy roasted flavor, significantly enhancing the flavor profile. The tea soup is bright golden yellow, and the infused leaves are a vibrant yellow-green.

[0087] Experimental Example 3 1. Experimental Objective: To explore the active substances and antioxidant potential of freeze-dried prickly pear black tea and the drinking experience of different groups of people through instrumental detection of active ingredients, in vitro antioxidant test, and observation experiment of volunteers of different ages, and to analyze the nutritional value characteristics of daily brewing and drinking.

[0088] 2. Experimental Samples: Experimental group (freeze-dried prickly pear black tea prepared in Example 3), control group 1 (ordinary black tea), and control group 2 (freeze-dried prickly pear fruit). The ordinary black tea and freeze-dried prickly pear fruit were from Guizhou Yanggenghong Tea Industry Co., Ltd.

[0089] 3. Experimental Design The in vitro free radical scavenging capacity was determined using the DPPH assay.

[0090] Age-Segmented Volunteer Drinking Observational Experiment: Volunteers were divided into three groups: youth (18-30 years old), middle-aged (31-50 years old), and middle-aged and elderly (51-65 years old), with 5 healthy volunteers in each group. All participants had no tea allergies or serious underlying gastrointestinal diseases. A blinded trial was conducted, with uniform brewing water temperature, tea quantity, and brewing time, and participants drank the tea at the same location for 14 consecutive days. Volunteers filled out daily record sheets, noting the taste of the tea and their subjective feelings after drinking it.

[0091] 4. Experimental Results The results of component analysis showed that freeze-dried prickly pear black tea contained vitamin C, SOD, total flavonoids, and tea polyphenols; ordinary black tea contained almost no vitamin C or SOD, and pure freeze-dried prickly pear fruit contained no tea polyphenols. The compound product had a richer variety of active ingredients.

[0092] In vitro antioxidant assays showed that the freeze-dried prickly pear black tea prepared in Example 3 had a significantly better antioxidant effect than control groups 1 and 2. The freeze-dried prickly pear black tea prepared in this invention exhibits a synergistic effect of multiple active substances, possesses higher free radical scavenging capacity, and demonstrates strong antioxidant potential. Volunteer observations revealed that participants in the youth, middle-aged, and elderly groups generally reported that pure prickly pear was intensely sour and astringent, making it difficult to drink long-term; the freeze-dried prickly pear black tea balanced the prickly pear's sourness with a milder, less irritating flavor. Participants also reported that moderate consumption of the tea's natural organic acids helped improve appetite, making it palatable for long-term, continuous consumption.

[0093] 5. Experimental Conclusions Based on comprehensive component analysis, in vitro antioxidant experiments, and observations of age-group volunteers, the freeze-dried prickly pear black tea, under normal brewing conditions, allows for the intake of various natural active substances and provides multiple dietary benefits. Among these, SOD, vitamin C, flavonoids, and tea polyphenols work synergistically to help scavenge free radicals, reduce oxidative stress, and exhibit strong antioxidant effects. It also provides a sustainable source of natural vitamins and polyphenols, enriching daily beverage nutrition and supplementing dietary intake. The freeze-dried prickly pear black tea prepared in this invention combines natural organic acids from prickly pear with black tea, resulting in a mellow flavor. Moderate consumption can help stimulate appetite. This invention's technical solution improves upon the astringency of pure prickly pear, making the taste more palatable and suitable for long-term daily consumption, ensuring a continuous intake of active nutrients.

[0094] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing freeze-dried prickly pear black tea, characterized in that, The process includes the following steps: removing the core of the prickly pear to obtain the prickly pear shell, filling the prickly pear shell with fermented black tea, letting it stand at low temperature, then performing a low temperature color protection treatment, followed by low temperature pre-freezing, vacuum freeze drying, and low temperature vacuum aroma enhancement to obtain freeze-dried prickly pear black tea.

2. The preparation method according to claim 1, characterized in that, Fresh leaves are withered and rolled in sequence, fermented at a temperature of 25-29℃ and a humidity of 85-95% for 1-5 hours, and then dried to obtain fermented black tea.

3. The preparation method according to claim 2, characterized in that, The withering time is 9-13 hours, the kneading time is 80-100 minutes, and the drying temperature is 60-65℃ for 20-30 minutes.

4. The preparation method according to claim 1, characterized in that, The temperature for the low-temperature settling is 3-5℃ and the time is 20-40 minutes.

5. The preparation method according to claim 1, characterized in that, The low-temperature color protection temperature is 3-5℃ and the time is 15-20h; the low-temperature color protection uses a citric acid aqueous solution with a mass percentage of 0.08-0.13% as the impregnation solution.

6. The preparation method according to claim 1, characterized in that, The low-temperature pre-freezing step includes: pre-freezing at -35~-45℃ for 5-9 hours.

7. The preparation method according to claim 1, characterized in that, The vacuum freeze-drying steps include: setting a vacuum of 9-19 Pa, raising the temperature to -5 to -15°C at a rate of 0.3-0.7°C / min for 12-16 hours, then maintaining the vacuum environment and raising the temperature to 18-22°C at a rate of 0.8-1.2°C / min for 3-7 hours.

8. The preparation method according to claim 1, characterized in that, The low-temperature vacuum aroma extraction process involves a temperature of 30-40℃, a time of 15-21 minutes, and a vacuum degree of 10-18 Pa.

9. Freeze-dried prickly pear black tea obtained by the preparation method according to any one of claims 1-8.

10. The use of freeze-dried prickly pear black tea obtained by any one of claims 1-8 or the freeze-dried prickly pear black tea of ​​claim 9 in the preparation of antioxidant products.

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