A low-temperature cold-brewed acid tea passion fruit beverage and a preparation method thereof

Abstract

This invention provides a low-temperature cold-extracted passion fruit tea beverage and its preparation method. The steps are as follows: (1) Preparation of passion fruit juice: After low-temperature pressing, add food-grade hydrogen peroxide aqueous solution, treat with ultraviolet light source, add ascorbic acid to terminate the free radical reaction, and obtain passion fruit juice containing low molecular weight pectin; (2) Preparation of passion fruit tea extract: add passion tea to a mixture of passion fruit juice containing low molecular weight pectin and water, cold extract at low temperature under light-proof conditions, and filter to obtain passion fruit tea extract; (3) Ultrasonic-electric field synergistic treatment: subject the passion fruit tea extract to ultrasonic-electric field synergistic treatment, stir to obtain a nanocomposite system; (4) Blending; (5) Homogenization; (6) Sterilization and filling. This invention uses ultraviolet-free radical synergistic technology to generate hydroxyl radicals to directionally degrade the molecular weight of pectin, and uses its self-assembly characteristics to coat tea polyphenols to form a stable nanocomposite, effectively prolonging the stability period.

Description

Technical Field

[0001] This invention belongs to the field of tea beverage processing technology, specifically relating to a low-temperature cold-extracted acidic tea passion fruit beverage and its preparation method. Background Technology

[0002] Sour tea boasts a unique natural fermentation process—relying on local microbial flora, with a fermentation cycle of 60-90 days. Its polyphenol content is approximately 1.2-1.8 times that of ordinary green tea, with a dry-basis polyphenol content of about 27%. It is also rich in fermentation-derived active substances. Research by Liang Mingzhi et al. has found that sour tea contains 119 volatile components, rich in alcohols, esters, and phenols, giving the product a unique sour aroma and refreshing flavor. However, traditional sour tea has a heavy, slightly bitter flavor, and its consumption is limited to local areas, making it difficult to meet the nationwide market's demand for diverse tastes and portability. Furthermore, its active ingredients are easily lost during processing due to high temperatures and oxidation, hindering the development of this beverage.

[0003] Traditional hot water extraction at high temperatures easily triggers the oxidation and polymerization of tea polyphenols, resulting in a dark brown or yellowish-brown tea liquor that loses its bright transparency, significantly enhances bitterness, and masks the original refreshing taste of sour tea. High-temperature sterilization also destroys heat-sensitive nutrients in tea leaves, such as vitamin C and theanine, leading to a decline in the antioxidant capacity and health benefits of the tea liquor. While it offers advantages such as ease of operation and low cost, it has many disadvantages to product flavor and fails to meet consumer demands. For example, existing technologies using 80℃ hot water extraction of black tea with added chemical stabilizers may result in severe oxidation of tea polyphenols and low vitamin C retention. Currently, novel low-temperature cold extraction technologies, such as ultrasonic-enzyme synergistic extraction, ultrasonic extraction, pulsed electric field extraction, and magnetic induction electric field extraction, can reduce the loss of flavor substances and optimize product taste, which is of great significance for meeting health-conscious consumer demands and promoting the industrialization of ethnic specialty resources.

[0004] Passion fruit is rich in total sugar, crude protein, and minerals such as potassium, calcium, iron, and zinc. It also contains abundant vitamin C and natural organic acids. Its acidic environment can enhance the stability of active ingredients in tea, providing a foundation for natural preservation and synergistic effects. Fan Hongyan et al. have also confirmed that the polyphenolic compounds in passion fruit have strong antioxidant activity, and its polysaccharide components can inhibit the activity of α-amylase and α-glucosidase, helping to control blood sugar. However, for a long time, passion fruit has been mainly used in products such as juice and jam, with limited research on its deep blending with specialty fermented teas.

[0005] However, mixing sour tea and passion fruit juice further lowers the pH, activating endogenous enzymes (polyphenol oxidase PPO, peroxidase POD) and accelerating the oxidative degradation of flavor substances such as tea polyphenols, leading to deterioration in taste and shortened shelf life. Simultaneously, tea polyphenols in the tea infusion form complexes with pectin, proteins, and other macromolecules in the fruit juice through hydrogen bonds and hydrophobic interactions, producing insoluble precipitates that damage the beverage's appearance and commercial value. Traditional methods of adding stabilizers (such as CMC and xanthan gum) not only increase costs but also affect the beverage's taste. Therefore, overcoming these problems and preparing a sour tea passion fruit beverage is the goal of this invention. Summary of the Invention

[0006] Technical problem to be solved: In view of the above problems, the purpose of this invention is to provide a low-temperature cold-extracted passion fruit tea beverage and its preparation method. It adopts ultraviolet-free radical synergistic technology, which generates hydroxyl radicals (·OH) through the synergistic effect of ultraviolet irradiation and trace amounts of hydrogen peroxide. These radicals target and attack the glycosidic bonds of macromolecular pectin in passion fruit juice, accurately degrading the molecular weight of pectin. Then, by utilizing its self-assembly characteristics, it can encapsulate tea polyphenols, which can more effectively form stable nanocomplexes with tea polyphenols and prolong the stability period.

[0007] Technical solution: A method for preparing a low-temperature cold-extracted passion fruit and sour tea beverage, comprising the following steps: (1) Preparation of passion fruit juice: Select fresh passion fruit, take the pulp, press it at low temperature and filter it to obtain crude passion fruit juice; add food-grade hydrogen peroxide solution to the crude passion fruit juice, stir it evenly and let it stand for 1-2 minutes; irradiate it with ultraviolet light source, and immediately add ascorbic acid to terminate the free radical reaction after irradiation; filter it with 100 mesh filter cloth to obtain passion fruit juice containing low molecular weight pectin. (2) Preparation of passion fruit extract from sour tea: Select sour tea, add passion fruit juice containing low molecular weight pectin and water, and extract under light-protected conditions using cold extraction technology at low temperature. After extraction, filter to obtain passion fruit extract from sour tea. (3) The acid tea passion fruit extract was subjected to ultrasonic-electric field synergistic treatment. After the treatment, it was stirred at 45-55 rpm for 4-6 min to obtain the acid tea passion fruit nanocomposite system. (4) Preparation: Add sodium citrate-citric acid buffer to the acid tea passion fruit nanocomposite system to adjust the pH of the system to 3.8-4.2; add sweetener and water, and after fully dissolving, obtain a mixture; (5) Homogenization: Homogenize the prepared beverage; (6) Sterilization: The homogenized beverage is sterilized and bottled to obtain the finished sour tea passion fruit beverage.

[0008] Furthermore, the low-temperature pressing in step (1) includes low-temperature spiral pressing and low-temperature hydraulic pressing, with a pressing temperature of 50-60℃.

[0009] Furthermore, the concentration of the food-grade hydrogen peroxide aqueous solution in step (1) is 30%, and the addition amount is 50-100 μL / kg crude passion fruit juice.

[0010] Furthermore, in step (1), the ultraviolet light source used for irradiation is a flow-through ultraviolet reactor with a wavelength of 280-320nm, a power of 150-200W, an irradiation time of 15-20min, a temperature of 10-15℃ during the treatment process, and a juice flow rate of 0.4-0.6L / min.

[0011] Furthermore, the amount of ascorbic acid added in step (1) is 0.1% of the juice mass.

[0012] Furthermore, the sour tea mentioned in step (2) includes De'ang sour tea, Bulang sour tea and Hani sour tea; the mass-volume ratio of the sour tea, passion fruit juice and water is 1g:(50-60)mL:(50-70)mL; the cold extraction technology includes ultrasonic low-temperature extraction, magnetic induction electric field low-temperature extraction, pulse electric field low-temperature extraction and ultrasonic pulse electric field composite low-temperature extraction; the extraction temperature is 30-40℃ and the extraction time is 15-60min; the filtration method includes filter cloth, centrifugation and vacuum filtration.

[0013] Furthermore, the ultrasonic-electric field synergistic treatment conditions in step (3) are: ultrasonic power 300-600W, frequency 20-40kHz, pulse electric field strength 20-30kV / cm, pulse width 2-8μs, pulse frequency 800-1500Hz, synergistic treatment for 10-20 minutes, and treatment temperature controlled at 10-25℃.

[0014] Furthermore, in step (4), the components by mass are: 100-120 parts of the acid tea passion fruit nanocomposite system, 0.2-0.5 parts of sodium citrate-citric acid buffer, 0.075 parts of sweetener, and 150 parts of water.

[0015] Furthermore, the sweeteners mentioned in step (4) are natural sweeteners (stevioside, erythritol, fructooligosaccharides) and artificial sweeteners (aspartame, acesulfame potassium, sucralose).

[0016] Furthermore, the homogenization process in step (5) is carried out at 15-25 MPa and 20-25 °C, and the homogenization is performed once.

[0017] Furthermore, the sterilization method described in step (6) is one of pasteurization, ultra-high pressure sterilization, electromagnetic wave sterilization, pulse sterilization, and ultrasonic sterilization.

[0018] The present invention also provides a sour tea passion fruit beverage prepared by the above method. Beneficial effects

[0019] 1. This invention first employs UV-radical synergistic technology, generating hydroxyl radicals (·OH) through the synergistic effect of UV irradiation and trace amounts of hydrogen peroxide. These radicals target and attack the glycosidic bonds of macromolecular pectin in passion fruit juice, precisely degrading the pectin molecular weight to 4-10 kDa and controlling the particle size to 40-120 nm. Then, utilizing its self-assembly properties (spontaneous adsorption via hydrogen bonds, ionic bonds, and hydrophobic interactions), it encapsulates tea polyphenols, fundamentally blocking complexation and precipitation, and more effectively forming stable nanocomposites with tea polyphenols. Compared with traditional pectin degradation methods (acid hydrolysis, enzymatic hydrolysis), UV-radical synergistic technology has advantages such as short reaction time, no need for extreme pH conditions, and no chemical residues, maximizing the preservation of pectin's bioactivity and natural structure.

[0020] 2. This invention innovatively utilizes the natural organic acids (pH 2.7-3.5) in passion fruit juice as a cold extraction solvent to achieve an acid-induced enzyme inactivation mechanism. The acidic environment of passion fruit juice significantly shifts the optimal pH range (5.0-7.0) of PPO and POD, causing protonation changes in the three-dimensional structure of the enzymes and disrupting the coordination environment of copper ions at the active center, thereby significantly reducing enzyme activity. Simultaneously, the added ascorbic acid, as a strong reducing agent, can reduce quinones catalyzed by PPO to phenolic substances, blocking the browning chain reaction and further improving the retention rate of tea polyphenols. Compared with traditional water-based cold extraction, passion fruit juice cold extraction can significantly reduce the residual activity of PPO and POD, improve the retention rate of tea polyphenols, and achieve a dual synergistic effect of acid-induced enzyme inactivation and antioxidant activity, effectively solving the flavor degradation problem.

[0021] 3. This invention employs ultrasonic-electric field synergistic treatment on the acidic tea and passion fruit mixture after cold extraction. This directly regulates the particle size and surface charge of complexes such as pectin-tea polyphenols and polysaccharides-tea polyphenols, forming stable nanocomplexes. The ultrasonic cavitation effect generates periodic pressure changes, forming microjets and shear forces, breaking down the aggregates formed during cold extraction into nanoscale particles. The particle size of the complex is controlled within the range of 100-200 nm. The pulsed electric field causes the polar groups (-COOH, -OH) in the complex to oriented, increasing the surface negative charge density and enhancing the electrostatic repulsion between particles. Through the synergistic effect of ultrasonic-electric field, the degree of binding between pectin, polysaccharides, proteins, and tea polyphenols is regulated, forming stable but non-precipitating nanocomplexes, avoiding excessive complexation that leads to the formation of large particles. The nanocomplexes achieve stable dispersion of a high tea polyphenol content system under acidic conditions through multiple mechanisms such as moderate complexation, electrostatic repulsion, and steric hindrance. The product has a precipitation rate of ≤2.3% and an absolute value of zeta potential ≥30 mV within 90 days, effectively solving the problem of appearance deterioration.

[0022] 4. This invention fully utilizes the natural organic acids such as lactic acid and acetic acid produced during the natural fermentation of sour tea as a source, which work synergistically with the natural acidity of passion fruit to form the sweet and sour ratio of the product. It eliminates the need for the addition of exogenous acidulants such as citric acid and malic acid, and can achieve the ideal sweet and sour ratio without adding any exogenous acidulants. At the same time, the acidic environment can inhibit the growth of microorganisms, extend the shelf life of the product, and achieve "natural preservation".

[0023] 5. The product of this invention is rich in tea polyphenols, vitamins and minerals, while enhancing the flavor of sour tea. It can meet consumers' demand for additive-free fruit tea drinks, while bringing high economic and social benefits, contributing to rural revitalization, and has broad prospects. Attached Figure Description

[0024] Figure 1 Sensory evaluation scoring criteria for passion fruit and sour tea beverage; Figure 2 Atomic force microscopy (AFM) images of the acidic tea passion fruit beverages prepared in some of the embodiments and comparative examples; Figure 3 Comparative photographs of the acidic tea passion fruit beverages prepared in some of the embodiments and comparative examples after 90 days of storage; Figure 4 This is a product photo. Detailed Implementation

[0025] This invention proposes a low-temperature cold-extracted passion fruit tea beverage and its preparation method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following will provide a more detailed description of the invention with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0026] The following sour tea is selected from Hani ethnic sour tea fermented using traditional Yunnan techniques (fermentation period ≥ 10 months).

[0027] Example 1 A method for preparing a low-temperature cold-extracted passion fruit acid tea beverage includes the following steps: (1) Preparation of passion fruit juice: Fresh passion fruit was selected, the pulp was taken, and it was pressed at low temperature of 55℃ and 8MPa for 5min. After that, it was filtered through a 120-mesh filter cloth to obtain crude passion fruit juice. 75μL of 30% food-grade hydrogen peroxide aqueous solution was added to 1kg of crude passion fruit juice, stirred evenly and then allowed to stand for 1.5min. It was then irradiated with ultraviolet light source. A flow-through ultraviolet reactor was used. The wavelength of the ultraviolet light source was 300nm and the power was 180W. The irradiation time was 18min. The temperature was maintained at 12℃ during the treatment. The juice flow rate was 0.5L / min. Immediately after the irradiation was completed, 0.1% of ascorbic acid by weight of the juice was added to terminate the free radical reaction. It was then filtered through a 100-mesh filter cloth to obtain passion fruit juice containing low molecular weight pectin. (2) Preparation of passion fruit extract from sour tea: 1g of sour tea was selected, 50mL of passion fruit juice containing low molecular weight pectin and 50mL of water were added, and under the dark conditions, the ultrasonic power and stirring speed were set to 200 W and 180 r / min respectively. The extraction temperature was adjusted to 35℃ and the extraction time was 40min. After the extraction was completed, the mixture was centrifuged at 5000 r / min for 10 min to obtain passion fruit extract from sour tea. (3) The acid tea passion fruit extract was subjected to ultrasonic-electric field synergistic treatment. The ultrasonic power was 400W, the frequency was 30kHz, the pulse electric field strength was 25kV / cm, the pulse width was 5μs, and the pulse frequency was 1000Hz. The synergistic treatment lasted for 15 minutes, and the treatment temperature was controlled at 15℃. After the treatment, the mixture was stirred at 50rpm for 5 minutes to obtain the acid tea passion fruit nanocomposite system. (4) Preparation: Add 0.35g sodium citrate-citric acid buffer (mass ratio 1:2) to the acid tea passion fruit nanocomposite system and adjust the pH of the system to 4.0; add 0.075g oligofructose and 150g water, and after fully dissolving, obtain a mixture; (5) Homogenization: Homogenize the prepared beverage once at 20 MPa and 25 °C; (6) Sterilization: The homogenized beverage is subjected to high pressure instantaneous sterilization (HPP) with the following parameters: low pressure combination 200 MPa / 550 MPa, holding time 12 min, low pressure time ratio 1:2, holding temperature 30℃. After sterilization, the beverage is filled and sealed in a sterile environment (cleanliness level 10,000) using light-blocking and oxygen-blocking PET bottles or aluminum cans to obtain the finished sour tea passion fruit beverage.

[0028] Example 2 The difference between this embodiment and Embodiment 1 is that the amount of hydrogen peroxide added in step (1) is different: In this embodiment, 50 μL of a 30% food-grade hydrogen peroxide aqueous solution was added to 1 kg of crude passion fruit juice, and the remaining steps were the same as in Example 1.

[0029] Example 3 The difference between this embodiment and Embodiment 1 is that the amount of hydrogen peroxide added in step (1) is different: In this embodiment, 100 μL of a 30% food-grade hydrogen peroxide aqueous solution was added to 1 kg of crude passion fruit juice, and the remaining steps were the same as in Example 1.

[0030] Example 4 The difference between this embodiment and Embodiment 1 is that the ultraviolet treatment conditions in step (1) are different: In this embodiment, the wavelength of the ultraviolet light source is 280nm, the power is 150W, the irradiation time is 20min, the temperature is maintained at 10℃ during the treatment process, the juice flow rate is 0.4L / min, and the remaining steps are the same as in Example 1.

[0031] Example 5 The difference between this embodiment and Embodiment 1 is that the ultraviolet treatment conditions in step (1) are different: In this embodiment, the wavelength of the ultraviolet light source is 320nm, the power is 200W, the irradiation time is 15min, the temperature is maintained at 15℃ during the treatment process, the juice flow rate is 0.6L / min, and the remaining steps are the same as in Example 1.

[0032] Example 6 The difference between this embodiment and Embodiment 1 is that the ultrasonic-electric field synergistic processing conditions in step (3) are different: In this embodiment, the ultrasonic power is 500W, the frequency is 35kHz, the pulse electric field strength is 28kV / cm, the pulse width is 6μs, the pulse frequency is 1200Hz, the co-processing time is 12min, the processing temperature is controlled at 18℃, and the remaining steps are the same as in Example 1.

[0033] Example 7 The difference between this embodiment and Embodiment 1 is that the ultrasonic-electric field synergistic processing conditions in step (3) are different: In this embodiment, the ultrasonic power is 300W, the frequency is 25kHz, the pulse electric field strength is 20kV / cm, the pulse width is 2μs, the pulse frequency is 800Hz, the co-processing time is 20min, the processing temperature is controlled at 20℃, and the remaining steps are the same as in Example 1.

[0034] Example 8 The difference between this embodiment and Embodiment 1 is that the ultrasonic-electric field synergistic processing conditions in step (3) are different: In this embodiment, the ultrasonic power is 600W, the frequency is 40kHz, the pulse electric field strength is 30kV / cm, the pulse width is 8μs, the pulse frequency is 1500Hz, the co-processing time is 10min, the processing temperature is controlled at 25℃, and the remaining steps are the same as in Example 1.

[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that hydrogen peroxide is not added in step (1): In this comparative example, 1 kg of crude passion fruit juice was directly subjected to ultraviolet irradiation treatment without the addition of hydrogen peroxide aqueous solution, and the remaining steps were the same as in Example 1.

[0036] Comparative Example 2 The difference between this comparative example and Example 1 is that the amount of hydrogen peroxide added in step (1) is too low: In this comparative example, 25 μL of a 30% food-grade hydrogen peroxide aqueous solution was added to 1 kg of crude passion fruit juice to make the final hydrogen peroxide concentration 0.0125%. The remaining steps were the same as in Example 1.

[0037] Comparative Example 3 The difference between this comparative example and Example 1 is that the amount of hydrogen peroxide added in step (1) is too high: In this comparative example, 150 μL of a 30% food-grade hydrogen peroxide aqueous solution was added to 1 kg of crude passion fruit juice to make the final hydrogen peroxide concentration 0.075%. The remaining steps were the same as in Example 1.

[0038] Comparative Example 4 The difference between this comparative example and Example 1 is that the ultraviolet irradiation time in step (1) is too short: In this comparative example, the wavelength of the ultraviolet light source was 300nm, the power was 180W, the irradiation time was 5min, and the remaining steps were the same as in Example 1.

[0039] Comparative Example 5 The difference between this comparative example and Example 1 is that the ultraviolet irradiation time in step (1) is too long: In this comparative example, the wavelength of the ultraviolet light source was 300nm, the power was 180W, the irradiation time was 30min, and the remaining steps were the same as in Example 1.

[0040] Comparative Example 6 The difference between this comparative example and Example 1 is that, in step (3), ultrasonic treatment is not performed; only electric field treatment is used. In this comparative example, no ultrasonic treatment was performed; only pulsed electric field treatment was used. The pulsed electric field strength was 25 kV / cm, the pulse width was 5 μs, the pulse frequency was 1000 Hz, the treatment time was 15 min, and the treatment temperature was controlled at 15 °C. The remaining steps were the same as in Example 1.

[0041] Comparative Example 7 The difference between this comparative example and Example 1 is that, in step (3), no electric field treatment is performed; only ultrasonic treatment is used. In this comparative example, no electric field treatment was performed; only ultrasonic treatment was used. The ultrasonic power was 400W, the frequency was 30kHz, the treatment time was 15min, and the treatment temperature was controlled at 15℃. The remaining steps were the same as in Example 1.

[0042] Comparative Example 8 The difference between this comparative example and Example 1 is that the intensity of the ultrasonic-electric field synergistic treatment in step (3) is too high: In this comparative example, the ultrasonic power was 800W, the frequency was 50kHz, the pulse electric field strength was 40kV / cm, the pulse width was 10μs, the pulse frequency was 2000Hz, the co-processing time was 30min, the processing temperature was controlled at 30℃, and the remaining steps were the same as in Example 1.

[0043] Comparative Example 9 The difference between this comparative example and Example 1 is that the intensity of the ultrasonic-electric field synergistic treatment in step (3) is too low: In this comparative example, the ultrasonic power was 200W, the frequency was 15kHz, the pulse electric field strength was 15kV / cm, the pulse width was 1μs, the pulse frequency was 500Hz, the co-processing time was 5min, the processing temperature was controlled at 10℃, and the remaining steps were the same as in Example 1.

[0044] Comparative Example 10 The difference between this comparative example and Example 1 is that the ultrasonic-electric field synergistic treatment is not used in step (3).

[0045] Comparative Example 11 The difference between this comparative example and Example 1 is that a high-temperature extraction method is used in step (2): Preparation of passion fruit extract from sour tea: Select 1g of sour tea, add 50mL of passion fruit juice containing low molecular weight pectin and 50mL of water, extract at 90℃ for 15min, and centrifuge at 5000 r / min for 10min to obtain passion fruit extract from sour tea.

[0046] Performance testing: 1. The molecular weight and particle size of low molecular weight pectin in passion fruit juice containing low molecular weight pectin in step (1) were determined using dynamic light scattering (DLS). The results are shown in Table 1 below: Table 1

[0047] As shown in Table 1, by adjusting the amount of hydrogen peroxide added and the UV treatment conditions, low molecular weight pectin with different particle sizes was prepared in Examples 1-5. The low molecular weight pectin prepared in Example 1 had a molecular weight of 5-10 kDa and a particle size of 50-80 nm, which was within the optimal range, providing an ideal basic material for the subsequent formation of stable nanocomposites. In Example 2, the amount of hydrogen peroxide added was slightly low (50 μL), and the insufficient free radical concentration led to incomplete pectin degradation, resulting in a larger molecular weight and particle size (8-12 kDa, 80-120 nm). In Example 3, the amount of hydrogen peroxide added was slightly high (100 μL), and the excessively high free radical concentration led to excessive pectin degradation, resulting in a smaller molecular weight and particle size (4-6 kDa, 40-60 nm). Examples 4 and 5, using different UV wavelengths and power parameters, both yielded relatively ideal low molecular weight pectin. In contrast, Comparative Example 1, lacking a free radical generation mechanism, had limited degradation effect due to UV irradiation alone, with pectin molecular weight still reaching 25-30 kDa and particle size reaching 250-300 nm. Comparative Examples 2 and 3, with their low and high free radical concentrations respectively, resulted in insufficient or excessive pectin degradation. Comparative Examples 4 and 5, with their short or long irradiation times, also had their pectin degradation effects affected.

[0048] 2. The particle size of the pectin-tea polyphenol complex in the passion fruit nanocomposite system in step (3) was determined by dynamic light scattering (DLS). The results are shown in Table 2 below: Table 2

[0049] As shown in Table 2 above, the particle size of the complexes in the examples was controlled by different ultrasonic-electric field synergistic treatment conditions. The pectin-tea polyphenol complex in Example 1 had a particle size of 100-150 nm, which was within the optimal stability range. Examples 6 and 8, due to moderate treatment intensity, had particle sizes of 110-155 nm and 100-145 nm, respectively, showing good treatment effects. However, the particle sizes of the complexes in Comparative Examples 6 and 7 were 220-350 nm and 180-280 nm, respectively, significantly larger than those in Example 1. This indicates that ultrasonic cavitation plays a crucial role in particle size refinement, and electric field polarization plays a key role in charge rearrangement and electrostatic repulsion; both must work synergistically to achieve the best results. Although the particle size of the complex in Comparative Example 8 was small, excessive treatment led to nutrient loss; the particle size of the complex in Comparative Example 9 was too large, resulting in insufficient stability. Comparative Examples 1-5 all had large particle sizes due to poor quality of low-molecular-weight pectin. Comparative Example 10, which did not employ ultrasonic-electric field synergistic treatment, resulted in large-particle complexes formed between tea polyphenols and passion fruit juice macromolecules (pectin, polysaccharides, proteins, etc.) under acidic conditions through hydrogen bonding and hydrophobic interactions. These complexes had particle sizes of 280-420 nm, exhibiting weak electrostatic repulsion, poor stability, and a tendency to precipitate. Comparative Example 11, which used a high-temperature extraction method, accelerated the oxidative polymerization of tea polyphenols. Simultaneously, the high temperature caused denaturation of macromolecules such as pectin and polysaccharides in the passion fruit juice, leading to the formation of even larger-particle complexes with tea polyphenols, with particle sizes of 300-450 nm. This resulted in even worse stability and more severe precipitation.

[0050] 3. The determination of tea polyphenol content in beverages was performed according to GB / T 8313-2018 "Determination of Tea Polyphenols and Catechins in Tea"; the determination of total amino acids was performed according to GB / T 23193-2017 "Determination of Theanine in Tea - High Performance Liquid Chromatography"; the determination of total flavonoids was performed according to SZDB / Z 349-2019 "Determination of Total Flavonoids in Food - Spectrophotometric Method"; the determination of total soluble sugars was performed according to GB 5009.8-2023 "National Food Safety Standard - Determination of Fructose, Glucose, Sucrose, Maltose and Lactose in Food"; and the determination of soluble protein was performed according to GB 5009.5-2025 "National Food Safety Standard - Determination of Protein in Food". The results are shown in Table 3 below. Table 3

[0051] As shown in Table 3, the acidic tea passion fruit beverages prepared in the examples exhibit significant advantages in terms of nutritional content. Example 1 showed a high level of tea polyphenols (125.4 mg / g), total amino acids (34.9 mg / g), total flavonoids (121.9 mg / g), total soluble sugars (135.4 mg / g), and soluble protein (11.0 mg / g) compared to all other examples. This was mainly due to the precise degradation of low-molecular-weight pectin in the passion fruit juice by UV-free radical synergistic technology and its effective encapsulation and protection of tea polyphenols. Examples 6 and 8, with more optimized ultrasonic-electric field synergistic treatment conditions, achieved tea polyphenol contents of 127.9 mg / g and 129.2 mg / g, respectively, the highest among all examples. Flavonoid contents also increased accordingly to 124.3 mg / g and 125.6 mg / g, indicating that moderate synergistic treatment intensity contributes to the dissolution and stabilization of more active ingredients. Comparative Example 1, lacking any UV-free radical treatment mechanism, failed to effectively form low-molecular-weight pectin, resulting in a lack of complexation and stabilization effects on tea polyphenols. Its tea polyphenol content was only 69.4 mg / g, significantly lower than Example 1. Comparative Examples 2-5, due to deviations in hydrogen peroxide addition or UV treatment conditions from the optimal range, had unsatisfactory low-molecular-weight pectin molecular weight or particle size, leading to reduced coating efficiency for tea polyphenols and lower tea polyphenol content than Example 1. Comparative Examples 6 and 7 had tea polyphenol contents of 86.2 mg / g and 77.3 mg / g, respectively, both significantly lower than Example 1's 125.4 mg / g, indicating that the synergistic effect of ultrasonic cavitation and electric field polarization plays a crucial role in the full dissolution and retention of active ingredients. Although Comparative Example 8 achieved a tea polyphenol content of 107.5 mg / g, its total soluble sugar and soluble protein contents were significantly lower than in the examples, suggesting that excessive treatment intensity can lead to the loss of some heat-sensitive nutrients. Comparative Example 9, due to the low intensity of the ultrasonic-electric field synergistic treatment, resulted in poor complex stability, with some tea polyphenols lost due to oxidation or complex precipitation, resulting in a content of only 72.8 mg / g. Comparative Example 10, without ultrasonic-electric field synergistic treatment, saw tea polyphenols form large-particle complexes with undegraded macromolecules (pectin, polysaccharides, proteins, etc.) in passion fruit juice under acidic conditions, leading to poor stability and easy sedimentation; the tea polyphenol content was only 82.9 mg / g. Comparative Example 11, using a high-temperature extraction method (90℃), not only accelerated the oxidative polymerization of tea polyphenols but also destroyed the natural ascorbic acid and organic acid system in passion fruit juice, significantly reducing enzyme inactivation; the tea polyphenol content was only 77.3 mg / g, significantly lower than Example 1, demonstrating the outstanding advantage of the low-temperature cold extraction technology of this invention in preserving active ingredients.

[0052] 4. Sensory evaluation and analysis of the sour tea passion fruit beverage, with scoring criteria as follows: Figure 1As shown in Table 4, the food was evaluated by 10 food professionals based on four dimensions: color (20 points), aroma (20 points), taste (40 points), and texture (20 points), with a maximum score of 100 points. Table 4

[0053] As shown in Table 4, the passion fruit and sour tea beverage prepared in the examples exhibits excellent sensory quality. Example 1 achieved a total sensory evaluation score of 87.6, with scores for color (18.8), aroma (18.9), taste (36.3), and texture (13.6). The overall quality was characterized by a clear, transparent, orange-yellow color; a harmonious and rich aroma of passion fruit and sour tea; a moderately sweet and sour taste with no bitterness; and a uniform and stable texture without sedimentation or layering. Example 6 achieved the highest total sensory evaluation score of 89.2, while Example 8 achieved the same score as Example 1 (87.6). All these results demonstrate that the process parameters of the present invention have a significant effect on improving sensory quality. Comparative Example 1 achieved a total sensory evaluation score of only 66.7, with scores for color (14.5), aroma (14.6), taste (27.6), and texture (10.0). All scores were significantly lower than in Example 1, primarily due to the lack of effective encapsulation of tea polyphenols by low-molecular-weight pectin. Oxidation of tea polyphenols led to browning, and the unstable complex resulted in noticeable precipitation. Comparative Examples 2-5, due to suboptimal low-molecular-weight pectin preparation, exhibited poor complex stability, with sensory scores ranging from 69.2 to 74.3. This was characterized by visible precipitation in the texture and a bland taste due to the loss of active ingredients. Comparative Examples 6 (electric field treatment only) and 7 (ultrasound treatment only) achieved sensory scores of 65.8 and 63.3, respectively, with low scores across all dimensions, particularly in texture (9.8 and 9.4, respectively). This indicates that the synergistic effect of ultrasound-electric field treatment is crucial for forming stable nanocomposites, and that a single treatment method is insufficient to achieve ideal sensory quality. Comparative Example 8 received a sensory score of 71.7. Although its color and texture were acceptable, the high processing intensity led to the loss of some flavor compounds, resulting in a relatively low taste score. Comparative Example 9 received the lowest sensory score of only 61.6. The low processing intensity resulted in extremely poor stability of the complex, a cloudy texture, and significant precipitation, severely impacting the drinking experience. Comparative Example 10 received a sensory score of 63.3. Due to the complete absence of ultrasonic-electric field synergistic treatment, the tea polyphenols in the passion fruit extract formed large-particle complexes with the passion fruit juice molecules, which continued to settle within 90 days, resulting in an extremely poor texture (significant precipitation) and a bland taste (oxidative degradation of tea polyphenols). Comparative Example 11 received a sensory score of 61.6. High-temperature extraction caused severe oxidation and polymerization of tea polyphenols, resulting in a dark brown color and weakened aroma. Simultaneously, the natural ascorbic acid and organic acids in the passion fruit juice were destroyed by the high temperature, and the enzyme inactivation effect was lost, resulting in a distinctly bitter taste. This demonstrates the crucial role of the low-temperature cold extraction process of this invention in maintaining the excellent sensory quality of the product.

[0054] 5. The finished beverage was observed using atomic force microscopy (AFM) (Example 1, Comparative Example 1, and Comparative Example 10 were selected as representative samples), and the results are as follows: Figure 2As shown, within the same scanning range of 2.5μm × 2.5μm, the particle height of Example 1 is approximately 8.22nm, the image is relatively dark, the surface is flat, the roughness is low, the particle size is 100-150nm and the distribution is uniform, with good dispersion; while the particle height of Comparative Example 1 and Comparative Example 10 increases to 29.62nm and 28.63nm respectively, the images become significantly brighter, the particles are irregular, the roughness is high, the particle size reaches 300-450nm and 280-420nm, and severe aggregation or network structure appears. It can be seen that the present invention significantly reduces the height and roughness of the composite by UV-free radical synergistic degradation of pectin and ultrasonic-electric field synergistic treatment, forming a finer, more uniform and stable nanocomposite system.

[0055] 6. Conduct 90-day (4℃ storage) shelf-life tracking tests on finished beverages, including core indicators such as zeta potential (using a zeta potential analyzer), sedimentation rate (calculated by centrifuging and weighing the sediment), tea polyphenol retention rate, color stability, and sensory scores. 90-day sedimentation rate (%) = (90-day centrifuged sediment mass / total sample mass) × 100% Tea polyphenol retention rate (%) = (90-day tea polyphenol content / initial tea polyphenol content) × 100% Color stability (%) = (90-day color score / initial color score) × 100%; the results are shown in Table 5 below: Table 5

[0056] Note: Sensory stability rating criteria: Excellent (sedimentation rate ≤3%, no obvious sedimentation in appearance, uniform taste); Good (3% < sedimentation rate ≤5%, slight sedimentation but does not affect drinking); Average (5% < sedimentation rate ≤8%, obvious sedimentation but acceptable); Poor (sedimentation rate >8%, obvious sedimentation, seriously affecting the drinking experience).

[0057] From Table 5 and Figure 3As can be seen, the examples exhibited excellent stability during the 90-day shelf life (stored at 4°C), all achieving an "excellent" sensory stability rating. Example 1 had an initial zeta potential of 38.0 mV, which remained at 36.1 mV after 90 days. The precipitation rate after 90 days was only 1.8%, the tea polyphenol retention rate was as high as 91.2%, and the color stability reached 98.4%. This fully demonstrates that the nanocomposite achieves stable dispersion of the acidic system with high tea polyphenol content through multiple stabilization mechanisms such as appropriate complexation, electrostatic repulsion, and steric hindrance, effectively avoiding browning and precipitation caused by the oxidative degradation of tea polyphenols. Examples 6 and 8, due to their optimized ultrasonic-electric field synergistic treatment intensity, exhibited higher zeta potentials, maintaining high levels of 37.5 mV and 37.9 mV respectively after 90 days. They also showed lower precipitation rates, high tea polyphenol retention rates of 92.0% and 92.5% respectively, and excellent color stability of 98.4%, demonstrating the best shelf-life stability. Although their complex particle size was not the smallest, their higher zeta potential, more uniform charge distribution, and stronger electrostatic repulsion resulted in the best overall stability. In contrast, Comparative Example 1 had an initial zeta potential of only 18.7 mV, which dropped significantly to 15.6 mV after 90 days. Its precipitation rate was as high as 10.2%, tea polyphenol retention rate was only 65.1%, and color stability was only 91.0%. Lacking the stabilizing effect of low-molecular-weight pectin, the tea polyphenols rapidly oxidized and degraded in the acidic environment, leading to a continuous decrease in zeta potential and subsequent aggregation and sedimentation of the complex. Comparative Examples 2-5, due to the low molecular weight or particle size of the pectin deviating from the optimal range, had insufficient coating efficiency for tea polyphenols, resulting in poor complex stability and low zeta potential. After 90 days, the precipitation rate was as high as 7.1%-10.5%, and the tea polyphenol retention rate was only 63.0%-74.0%. Comparative Examples 6 and 7, using only a single treatment method, had zeta potentials of only 17.2 mV and 19.0 mV, respectively, which further decreased to 14.5 mV and 15.9 mV after 90 days, with precipitation rates as high as 11.0% and 10.5%, respectively. This indicates that the ultrasonic cavitation effect refines the particle size of the complex, and the electric field polarization effect increases the surface charge density; both synergistically, the best stabilization effect is achieved. Although Comparative Example 8 had a high zeta potential, the excessive treatment intensity led to the over-degradation of some low molecular weight pectin, reducing its coating capacity. After 90 days, the precipitation rate was 5.2%, and the sensory stability was only "medium." Comparative Example 9, due to its excessively low ultrasonic-electric field synergistic treatment intensity, exhibited the lowest zeta potential, which plummeted to 13.0 mV after 90 days. The precipitation rate was as high as 12.1%, the tea polyphenol retention rate was only 63.0%, and the sensory stability was the worst. Comparative Example 10, which did not employ ultrasonic-electric field synergistic treatment at all, resulted in the formation of large-particle complexes with passion fruit juice macromolecules, with a particle size of 280-420 nm. The zeta potential was only 14.8 mV, and the electrostatic repulsion was extremely weak. After 90 days, the precipitation rate reached as high as 12.5%, the tea polyphenol retention rate was only 62.2%, and the color stability was only 86.6%, severely impacting the beverage's appearance and commercial value.Comparative Example 11 uses a high-temperature extraction method, which causes the pectin, polysaccharides and other macromolecules in passion fruit juice to denature due to the high temperature, forming larger complexes with tea polyphenols. These complexes have the lowest zeta potential and the worst stability. This demonstrates the core technological advantage of the present invention, which combines low-temperature cold extraction with ultrasonic-electric field synergistic treatment to achieve excellent shelf-life stability of the product.

[0058] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a low-temperature cold-extracted passion fruit sour tea beverage, characterized in that, Includes the following steps: (1) Preparation of passion fruit juice: Select fresh passion fruit, take the pulp, press it at low temperature and filter it to obtain crude passion fruit juice; add food-grade hydrogen peroxide aqueous solution to the crude passion fruit juice, stir it evenly and let it stand; use ultraviolet light source for irradiation treatment, and immediately add ascorbic acid to terminate the free radical reaction after irradiation; filter it with filter cloth to obtain passion fruit juice containing low molecular weight pectin. (2) Preparation of passion fruit extract from sour tea: Select sour tea, add passion fruit juice containing low molecular weight pectin and water, and extract under light-protected conditions using cold extraction technology at low temperature. After extraction, filter to obtain passion fruit extract from sour tea. (3) The acid tea passion fruit extract was subjected to ultrasonic-electric field synergistic treatment. After the treatment, it was stirred at 45-55 rpm for 4-6 min to obtain the acid tea passion fruit nanocomposite system. (4) Preparation: Add sodium citrate-citric acid buffer to the acid tea passion fruit nanocomposite system to adjust the pH of the system to 3.8-4.2; add sweetener and water, and after fully dissolving, obtain a mixture; (5) Homogenization: Homogenize the prepared beverage; (6) Sterilization: The homogenized beverage is sterilized and bottled to obtain the finished sour tea passion fruit beverage.

2. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, The low-temperature pressing mentioned in step (1) includes low-temperature screw pressing and low-temperature hydraulic pressing, with a pressing temperature of 50-60℃.

3. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, The concentration of the food-grade hydrogen peroxide aqueous solution in step (1) is 30%, and the addition amount is 50-100 μL / kg crude passion fruit juice.

4. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, The ultraviolet light source used for irradiation in step (1) is a flow-through ultraviolet reactor with a wavelength of 280-320nm, a power of 150-200W, an irradiation time of 15-20min, a temperature of 10-15℃ during the treatment, and a juice flow rate of 0.4-0.6L / min.

5. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, The amount of ascorbic acid added in step (1) is 0.1% of the juice mass.

6. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, The sour tea mentioned in step (2) includes De'ang sour tea, Bulang sour tea and Hani sour tea; the mass-volume ratio of the sour tea, passion fruit juice and water is 1g:(50-60)mL:(50-70)mL; the cold extraction technology includes ultrasonic low-temperature extraction, magnetic induction electric field low-temperature extraction, pulse electric field low-temperature extraction and ultrasonic pulse electric field composite low-temperature extraction; the extraction temperature is 30-40℃ and the extraction time is 15-60min; the filtration method includes filter cloth, centrifugation and vacuum filtration.

7. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, The ultrasonic-electric field synergistic treatment conditions described in step (3) are: ultrasonic power 300-600W, frequency 20-40kHz, pulse electric field strength 20-30kV / cm, pulse width 2-8μs, pulse frequency 800-1500Hz, synergistic treatment for 10-20 minutes, and treatment temperature controlled at 10-25℃.

8. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, In step (4), the components by mass are: 100-120 parts of the acid tea passion fruit nanocomposite system, 0.2-0.5 parts of sodium citrate-citric acid buffer, 0.075 parts of sweetener, and 150 parts of water.

9. The method for preparing a low-temperature cold-extracted passion fruit acid tea beverage according to claim 1, characterized in that, The homogenization process in step (5) is carried out at 15-25 MPa and 20-25 °C, and the homogenization is performed once.

10. A sour tea passion fruit beverage prepared by the method according to any one of claims 1-9.

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