Preparation method of quinoa-fruit compound beverage

Abstract

The application discloses a kind of preparation methods of quinoa-fruit composite beverage, belong to the technical field of beverage processing. Including S1 raw material pretreatment (quinoa pretreatment is through acid protease and natural kiwi fruit protease double-enzyme synergistic hydrolysis in kiwi juice, combined with gradient temperature and grinding, to prepare high-viscosity enzymatic modification quinoa pulp;Raspberry pretreatment is prepared by freeze-drying, ultrafine grinding and enzymatic modification quinoa pulp wrapping suspended raspberry seed pulp, while adding tea polyphenol, glycerol and composite buffer to prepare color protection and crosslinking resistant raspberry juice), S2 deployment and homogenization, S3 sterilization and filling. The application solves the problems of quinoa protein acid denaturation aggregation, quinoa PPO-mediated raspberry anthocyanin oxidation browning and raspberry seed retention and suspension stability, taste adaptation and nutritional conflict mentioned in the background art through the three stages of "raw material pretreatment, deployment and homogenization, sterilization and filling".

Description

Technical Field

[0001] This invention belongs to the field of beverage processing technology, specifically a method for preparing a quinoa-fruit compound beverage. Background Technology

[0002] Quinoa is rich in protein, dietary fiber, and various minerals, providing the body with essential nutrients for sustained energy and basic physiological functions, giving it a natural advantage in the health beverage industry. Fruits are important sources of natural flavor and active ingredients, precisely compensating for quinoa's shortcomings in specific nutrients and flavors. For example, raspberries have a natural berry flavor that neutralizes the mild grain taste of quinoa, and they also contain high concentrations of anthocyanins, vitamin C, and unique active substances, forming a complementary system with quinoa's protein and dietary fiber, effectively enhancing the nutritional diversity of the complex.

[0003] However, the following technical problems need to be solved in the process of combining quinoa and raspberries:

[0004] Firstly, raspberry seeds are rich in unsaturated fatty acids and vitamin E. Removing the seeds to improve the taste would directly lead to the loss of these nutrients. However, when the seeds are retained, their density is much higher than that of quinoa colloid. Even after being ultra-finely ground, they will still settle quickly after being stored at room temperature, forming a noticeable sediment layer. Furthermore, the hard seeds can cause a gritty feeling in the mouth, ruining the delicate taste of the beverage. Conventional homogenization methods can only delay this in the short term and cannot solve the long-term suspension problem.

[0005] Secondly, the water-soluble proteins in quinoa are prone to denaturation and aggregation in the acidic environment of raspberry juice, forming visible flocculent precipitates in a short period of time, affecting the uniformity of the beverage's appearance.

[0006] Thirdly, the PPO (polyphenol oxidase) naturally present in quinoa is activated when mixed with raspberries. This activates both the oxidative browning of quinoa's own polyphenols and accelerates the degradation of raspberry anthocyanins, causing the beverage's color to change from a bright red to a dark brownish-red in a short period. Conventional color-protecting agents can only slightly delay oxidation and cannot fundamentally inhibit the catalytic effect of PPO.

[0007] Therefore, it is extremely important to provide a method for preparing a quinoa-raspberry complex beverage that inhibits acidic denaturation and aggregation of quinoa protein, blocks PPO-mediated anthocyanin oxidative browning, and preserves nutrients. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a quinoa-fruit complex beverage, in order to solve the problems of acid denaturation and aggregation of quinoa protein, oxidative browning of raspberry anthocyanins mediated by quinoa PPO, and nutritional conflicts between raspberry seed retention and suspension stability, and taste compatibility in the prior art.

[0009] The objective of this invention is achieved through the following technical solution:

[0010] A method for preparing a quinoa-fruit complex beverage includes the following steps:

[0011] S1. Raw material pretreatment:

[0012] S11. Quinoa Pretreatment: Select plump quinoa grains, add 5-7 times its weight of purified water, 0.10%-0.15% acidic protease, and 8%-12% kiwi juice (utilizing the natural kiwi protease in kiwi juice to form a dual-enzyme synergistic system with acidic protease, improving the protein hydrolysis rate, and supplementing natural mucopolysaccharides to lay the foundation for subsequent suspension), and soak at 40-45℃ for 4-6 hours; then raise the temperature of the soaking solution to 58-62℃ and keep it at that temperature for 8-12 minutes, and then raise it to 82-86℃ (temperatures below 82℃ cannot effectively remove the bitter saponins in quinoa, and temperatures above 86℃ will destroy the mucopolysaccharides and vitamins in kiwi juice) and keep it at that temperature for 10-15 minutes; then add 2.0-3.0 times its weight of purified water, grind to a particle size of 120-140 mesh, and obtain enzymatically modified quinoa slurry;

[0013] S12. Raspberry pretreatment: Juice the raspberries to obtain raspberry seeds and raspberry juice;

[0014] Raspberry seeds are freeze-dried and ultra-finely pulverized to 150-200 mesh. Then, 5-7 times the weight of the raspberry seeds are added to the enzymatically modified quinoa pulp (if it is less than 5 times, the raspberry seeds cannot be fully coated and will easily settle). After stirring thoroughly at 50-55℃, a suspended raspberry seed pulp is obtained.

[0015] Add tea polyphenols, kiwi juice, and food-grade glycerin to raspberry juice, stir thoroughly at 33-37℃, then add sodium citrate-dipotassium hydrogen phosphate composite buffer to adjust the pH to 3.8-4.2 to obtain color-protecting and anti-crosslinking raspberry juice.

[0016] S2. Preparation and Homogenization: First, add the enzymatically modified quinoa pulp and the compound stabilizer to the preparation tank and stir thoroughly at 30-35℃. Then, add the color-protecting and anti-crosslinking raspberry juice, suspended raspberry seed pulp, and ultrafine kiwi seed powder in sequence, stirring thoroughly. Finally, add white sugar, potassium sorbate, and pectin lyase, stirring thoroughly before performing gradient homogenization. The compound stabilizer includes low-methoxyl pectin and gum arabic (this order of addition is extremely important; the enzymatically modified quinoa pulp and the compound stabilizer are added first because the high viscosity of the quinoa pulp supports the dissolution and dispersion of the stabilizer. If the low-viscosity components are added first, the stabilizer is prone to agglomeration. The color-protecting and anti-crosslinking raspberry juice is then added to ensure uniform dispersion of tea polyphenols to inhibit PPO). To enhance activity, glycerol is pre-binded to the mucopolysaccharide to prevent high-temperature turbidity. Kiwi seed powder is then added to prevent premature adsorption of raspberry seeds, thus ensuring suspension and antioxidant effects. Finally, pectin lyase is added to degrade the kiwi mucopolysaccharide, avoiding high-temperature turbidity and preventing premature addition that could disrupt the underlying colloidal network.

[0017] S3: Sterilization and filling: Ultra-high temperature instantaneous sterilization is adopted, and after cooling, the product is filled in a nitrogen environment to obtain the finished product.

[0018] As one possible implementation method of this application, when heating from 58-62℃ to 82-86℃, the temperature is increased in a gradient of 2-3℃ / min. Too rapid a heating rate results in a large temperature difference between the inside and outside of the quinoa grains, making it difficult for the inner saponins to fully dissolve, and residual saponins give the beverage a bitter taste. Too low a heating rate results in excessively long heating times, causing the activity of the two enzymes to decrease slowly below 82℃, reducing the protein hydrolysis rate, and making it easier for unhydrolyzed large protein molecules to aggregate and precipitate in an acidic environment.

[0019] As some possible implementations of this application, in step S12, the added tea polyphenols, kiwi juice, and food-grade glycerin are 0.03%-0.05%, 0.02%-0.04%, and 0.04%-0.06% of the raspberry juice mass, respectively.

[0020] As some possible implementations of this application, in step S2, the gradient homogenization method is as follows: the mixture is fed into a high-pressure homogenizer, and homogenized for the first time at a pressure of 23-27 MPa, and then homogenized for the second time at a pressure of 26-30 MPa, controlling the particle size to 2-4 μm.

[0021] As one of the possible implementation methods of this application, the specific steps of step S3 are as follows:

[0022] S31: Employs dual-stage ultra-high temperature instantaneous sterilization: first heat to 98-102℃ and hold for 0.8-1.2 seconds, then raise the temperature to 135-140℃ and hold for 2.0-3.0 seconds;

[0023] S32: Cool to 25-30℃, use food-grade nitrogen with a purity ≥99.9% and a pressure of 0.10-0.15MPa for back pressure filling, control the oxygen content in the container to ≤1%, and seal to obtain the finished product.

[0024] As one possible implementation of this application, in step S12, the raspberry pretreatment stage, 0.06%-0.10% by weight of kiwifruit seed shell polyphenol-β-cyclodextrin inclusion complex is also added.

[0025] As one possible implementation of this application, the compound stabilizer further includes konjac glucomannan, and the mass ratio of low methoxyl pectin, gum arabic, and konjac glucomannan is 1:(1.8-2.2):(0.2-0.4).

[0026] As one possible implementation method of this application, after freeze-drying the raspberry seeds in step S12 and before ultrafine grinding, the raspberry seeds are treated with low-temperature plasma in an argon atmosphere. The treatment power is 180-220W and the treatment time is 5-8 minutes, which can effectively etch the surface wax and introduce hydroxyl and carboxyl active groups. If the raspberry seeds are ultrafine ground and then treated with plasma, the specific surface area of ​​the powder increases significantly, the van der Waals forces between particles are enhanced, and agglomeration is likely to occur. During subsequent plasma treatment, only the outer layer of the agglomerated particles can be etched, while the inner wax layer remains, which makes it impossible to solve the problem of wax-induced crystallization of konjac glucomannan.

[0027] As one possible implementation method of this application, the preparation method of the compound stabilizer after adding konjac glucomannan is as follows: first, the konjac glucomannan is enzymatically hydrolyzed by pectin methyl esterase; then, the hydrolyzed konjac glucomannan is mixed with low-methoxyl pectin and gum arabic to form a compound stabilizer.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This invention effectively solves the problems mentioned in the background art, such as acidic denaturation and aggregation of quinoa protein, quinoa PPO-mediated oxidative browning of raspberry anthocyanins, and the nutritional conflicts between raspberry seed retention and suspension stability, and taste compatibility, through three stages: "raw material pretreatment, blending and homogenization, sterilization and filling". Specifically, the invention addresses these issues through three stages: raw material pretreatment, blending and homogenization, and sterilization and filling.

[0030] ① Addressing the issues of "nutrient retention and suspension stability of raspberry seeds": By freeze-drying and ultra-fine grinding raspberry seeds at low temperatures, heat loss of nutrients such as unsaturated fatty acids and vitamin E is avoided, while eliminating the mouth-grinding sensation caused by the seeds. Then, high-viscosity enzymatically modified quinoa slurry (containing natural mucopolysaccharides from kiwifruit) obtained from quinoa pretreatment is used to encapsulate the raspberry seed powder. The colloidal network of the quinoa slurry fixes the raspberry seed powder to improve the sedimentation problem caused by density differences. Finally, gradient pressure homogenization further improves suspension stability, ultimately achieving the goal of no significant sedimentation during long-term storage, effectively preserving the nutrients in raspberry seeds, and effectively solving the long-term suspension problem and the rough taste problem.

[0031] ② Regarding the issue of "acidic denaturation and aggregation of quinoa protein": By simultaneously adding acidic protease and kiwi juice (containing natural kiwi protease) during the quinoa pretreatment stage, the two enzymes work together to hydrolyze the large protein molecules into small peptide molecules, effectively preventing denaturation and aggregation. At the same time, a compound buffer is used to stabilize the pH of the system within a suitable range, preventing pH fluctuations from exacerbating protein aggregation. The compound stabilizer in the compounding stage can further inhibit aggregation, ultimately achieving long-term free flocculent sedimentation in the beverage and improving the uniformity of appearance.

[0032] ③ Regarding the issue of "quinoa PPO-mediated anthocyanin oxidative browning": By adding tea polyphenols to raspberry juice, the activity of quinoa PPO is directly inhibited, reducing its catalytic oxidation of polyphenols and anthocyanins. At the same time, kiwi juice is added to supplement the ascorbic acid-glutathione complex. This complex has stronger antioxidant stability than regular vitamin C and can preferentially bind to free radicals to protect anthocyanins from oxidation. This results in a high anthocyanin retention rate during long-term storage of the beverage, preventing the color from turning from bright red to brownish-red, and maintaining the color and functional value of the beverage.

[0033] In summary, the quinoa-fruit complex beverage prepared using the method of this invention achieves significant quality improvement: sedimentation rate ≤0.8% after 30 days of storage at room temperature; stratification rate ≤5.0% after 24 hours at pH 3.6, exhibiting excellent appearance uniformity; turbidity ≤95 NTU after high-temperature sterilization; anthocyanin retention rate ≥88% after 10 days of storage at room temperature; browning degree ΔE ≤5.7 after 30 days of refrigeration at 0-4℃, maintaining a bright red color for a long time; hexanal content ≤0.6 mg / kg after 7 days of refrigeration at 0-4℃, with no rancid odor; saponin content ≤0.06 g / kg, with no bitter taste. The final product is a complex beverage with stable suspension, bright color, pure flavor, and complete nutrient retention, fully meeting the quality requirements for industrial production and long-term storage.

[0034] 2. During high-temperature sterilization, kiwifruit mucopolysaccharides and raspberry organic acids easily cross-link to form aggregates, leading to increased turbidity. By adding food-grade glycerol to the raspberry juice and stirring at a constant temperature, the hydroxyl groups of glycerol preferentially undergo pre-esterification with the carboxyl groups of raspberry organic acids, occupying the active sites of the carboxyl groups to reduce the chance of cross-linking with kiwifruit mucopolysaccharides during subsequent high-temperature sterilization, thus reducing turbidity after high-temperature sterilization. At the same time, pectin lyase is added. Pectin lyase cleaves the glycosidic bonds of pectin substances in raspberry juice, reducing the pectin content in the system and reducing its chance of cross-linking with kiwifruit mucopolysaccharides, thus avoiding the formation of large aggregates. Ultimately, the turbidity of the beverage after high-temperature sterilization meets the requirements, solving the turbidity problem.

[0035] 3. Although this invention improves the stability of quinoa protein in acidic environments through dual-enzyme hydrolysis and addresses oxidation issues using methods such as tea polyphenols and nitrogen filling, certain risks still exist in long-term low-temperature refrigeration (0-4℃): the small-molecule peptides produced by quinoa hydrolysis can react with unreacted organic acids in raspberry juice at low temperatures to form brown peptide-organic acid condensates, causing the beverage color to change from light red to dark brown and producing fine precipitates. Conventional color-protecting agents can only address oxidative browning and are ineffective against this type of condensation reaction, failing to guarantee the quality during long-term low-temperature storage. This invention addresses this by adding a kiwifruit seed shell polyphenol-β-cyclodextrin inclusion complex. The kiwifruit seed shell polyphenols preferentially bind to quinoa small-molecule peptides through hydrogen bonding and other interactions, forming a stable complex that blocks the contact between the peptides and the organic acids in the raspberries. Simultaneously, the β-cyclodextrin-encapsulated polyphenols are slowly released, continuously clearing protons generated by the ionization of organic acids in the system and inhibiting the formation of peptide-organic acid condensates at low temperatures.

[0036] 4. When the compound stabilizer only includes low-methoxyl pectin and gum arabic, it is difficult to cope with extreme pH fluctuations (such as pH fluctuations of ±0.4 caused by sudden temperature changes during transportation). For example, when the pH drops to 3.6, the gel structure of low-methoxyl pectin will shrink rapidly due to protonation, failing to fix raspberry seeds and quinoa particles; when the pH rises to 4.4, gum arabic will adsorb with quinoa protein, forming flocculent precipitates. This invention adds konjac glucomannan, which has stronger pH tolerance, to the compound stabilizer. It can form an interpenetrating network gel structure with kiwi polysaccharide, significantly reducing the shrinkage rate of the colloidal network, while increasing the viscosity of the beverage system to a suitable range, improving tolerance to pH fluctuations, and effectively solving the stability problem under extreme conditions.

[0037] 5. While adding konjac glucomannan to the compound stabilizer solves the pH fluctuation stratification problem, in cold chain transportation scenarios involving repeated freeze-thaw cycles (-2~0℃), the residual wax on the surface of raspberry seeds causes konjac glucomannan to transform from a uniformly dispersed colloidal state into a dense solid substance with regularly arranged molecular chains. Simultaneously, the 2-4μm particles formed by gradient homogenization adsorb surrounding konjac glucomannan molecules, accelerating the aggregation and growth of these solid substances, ultimately leading to the problem of bottom sedimentation and upper clear liquid separation in the beverage. This invention treats raspberry seeds with low-temperature plasma in an argon atmosphere. On the one hand, this etches and removes the surface wax, preventing the wax from inducing the formation of dense solid substances by konjac glucomannan. On the other hand, it introduces hydrophilic groups such as hydroxyl and carboxyl groups onto the surface of the raspberry seeds, making it easier for the raspberry seeds and konjac glucomannan to fuse, avoiding separation due to interfacial repulsion. This prevents the 2-4μm particles from adsorbing konjac glucomannan and forming large aggregates, ultimately effectively solving the problem of bottom sedimentation and upper clear liquid separation.

[0038] 6. Even after removing the wax coating from raspberry seeds, konjac glucomannan still faces the risk of crystallization at low temperatures. Its molecular chains have high regularity, and even without wax induction, some molecules may slowly form tiny crystals at cold chain temperatures of -2 to 0°C, affecting stability over long-term storage. This invention utilizes pectin methyl esterase to enzymatically hydrolyze konjac glucomannan, cleaving the methyl ester groups and breaking the regularity of the molecular chains. The treated compound stabilizer is less prone to crystallization at low temperatures, solving the crystallization and stratification problem in cold chain freeze-thaw scenarios. Detailed Implementation

[0039] Example 1

[0040] S1. Raw material pretreatment:

[0041] S11. Quinoa pretreatment: Select 100g of plump quinoa grains, add 600g of purified water, 0.12g of Aspergillus niger-derived acidic protease (enzyme activity 80,000 U / g), and 10g of kiwi juice, and soak at 42℃ for 5 h; raise the temperature of the soaking solution to 60℃ and keep it at 10 min, then raise the temperature to 84℃ at a gradient rate of 2.5℃ / min and keep it at 12 min (stirring rate 180r / min during the heating process); then add 250g of purified water and grind it to a particle size of 130 mesh using a colloid mill to obtain enzymatically modified quinoa slurry.

[0042] The preparation method of kiwifruit juice is as follows: Select 1000g of fresh kiwifruit with a ripeness of 80%-85%, wash and remove the stems, cut into small cubes of 1-2cm, add 200g of purified water, and crush for 5 minutes using a high-speed tissue homogenizer (10000r / min). Remove the pulp by passing through a 100-mesh nylon sieve to obtain the original kiwifruit juice. Centrifuge the original kiwifruit juice at 4℃ and 3000r / min for 15 minutes, and take the supernatant as the finished kiwifruit juice. Testing showed that the kiwifruit juice contained 55-60U / mL of kiwifruit protease, which can form a dual-enzyme synergistic system with the acidic protease in S11. Simultaneously, the concentration of kiwifruit mucopolysaccharide in the juice was 1.2-1.5g / L, which can provide colloidal support for subsequent raspberry seed suspension and system stability.

[0043] S12. Raspberry pretreatment: Select 500g of raspberries that are 75% ripe, juice them using a twin-screw juicer, and separate the raspberry seeds and raspberry juice.

[0044] Raspberry seeds were freeze-dried at a vacuum of 15 Pa and -38°C for 9 h, and then ultra-finely pulverized to 180 mesh under nitrogen. 20 g of raspberry seed powder was taken and 120 g of enzymatically modified quinoa slurry was added. The mixture was stirred at 52°C and 200 r / min for 35 min to obtain a suspended raspberry seed slurry.

[0045] Add 0.12g of tea polyphenols, 0.09g of kiwi juice (same as step S11), and 0.15g of food-grade glycerin to 300g of raspberry juice. Stir at 35℃ and 200r / min for 35min. Then add 0.3g of sodium citrate-dipotassium hydrogen phosphate composite buffer (mass ratio 2:1) to adjust the pH to 4.0 to obtain color-protecting and anti-crosslinking raspberry juice. This color-protecting and anti-crosslinking raspberry juice is the core acidic component of the beverage, and the final beverage pH is roughly consistent with the pH of 4.0 adjusted in this step.

[0046] S2. Mixing and homogenization:

[0047] S21. Weigh the raw materials according to the following mass ratio: 40g of enzymatically modified quinoa pulp, 30g of color-protecting and anti-crosslinking raspberry juice, 12g of suspended raspberry seed pulp, 6g of white sugar, 1g of ultrafine kiwi seed powder (particle size 5-10μm), 0.05g of potassium sorbate, 0.02g of pectin lyase (enzyme activity 5000U / g), and 0.15g of compound stabilizer [0.05g of low methoxyl pectin (methoxyl content ≤7%, degree of esterification 30-40%), 0.1g of gum arabic (viscosity 300-500mPa・s at 25℃, 10% aqueous solution)].

[0048] S22. First, add the enzymatically modified quinoa pulp and the compound stabilizer to the mixing tank, and stir for 16 min at 32℃ and 230 r / min. Then, add the color-protecting and anti-crosslinking raspberry juice, suspended raspberry seed pulp, and ultrafine kiwi seed powder in sequence, and stir for 10 min. Finally, add white sugar, potassium sorbate, and pectin lyase, and stir until dissolved. [If the pH of the system deviates from 4.0 (fluctuation exceeds ±0.2) at this time, a small amount of sodium citrate-dipotassium hydrogen phosphate composite buffer can be added to adjust it to 4.0]; send the mixture to a high-pressure homogenizer, and homogenize it for the first time at 25 MPa pressure and the second time at 28 MPa pressure at 43℃, controlling the particle size to 2-4 μm.

[0049] S3. Sterilization and filling:

[0050] S31. A two-stage ultra-high temperature instantaneous sterilization method is adopted. First, the homogenized mixture is heated to 100°C and held for 1 second, then heated to 138°C and held for 2.5 seconds. This two-stage ultra-high temperature instantaneous sterilization method can inactivate acidic protease and kiwifruit protease.

[0051] S32. Cool the sterilized mixture to 28°C, and use food-grade nitrogen with a purity of 99.9% and a pressure of 0.12MPa for back pressure filling (nitrogen flow rate of 8L / min, filling speed of 120mL / s), control the oxygen content in the container to ≤1%, and seal to obtain the finished beverage.

[0052] Example 2

[0053] Compared to Example 1, the raspberry juice processing step in step S12 has been adjusted, and the adjusted step is as follows:

[0054] Add 0.12g of tea polyphenols, 0.09g of kiwi juice, 0.15g of food-grade glycerol, and 0.24g of kiwi seed shell polyphenol-β-cyclodextrin inclusion complex (0.08% of raspberry juice by weight) to 300g of raspberry juice. Stir at 35℃ and 200r / min for 40 min, then add 0.3g of sodium citrate-dipotassium hydrogen phosphate composite buffer and adjust the pH to 4.0 to obtain color-protecting and anti-crosslinking raspberry juice.

[0055] The preparation method of kiwifruit seed shell polyphenol-β-cyclodextrin inclusion complex is as follows: Take 50g of kiwifruit seed shells, extract with 70% ethanol at a solid-liquid ratio of 1:10 under reflux at 60℃ for 2.5h, concentrate the extract to 1 / 5 of the original volume using a rotary evaporator at 60℃ and a vacuum degree of 0.08MPa, freeze-dry to obtain powdered polyphenol extract, mix the extract with β-cyclodextrin at a mass ratio of 1:5, stir at 50℃ for 3h to form kiwifruit seed shell polyphenol-β-cyclodextrin inclusion complex.

[0056] The remaining steps and parameters are the same as in Example 1.

[0057] Example 3

[0058] Compared to Example 2, the compound stabilizer in step S21 is replaced with 0.045g of low methoxyl pectin, 0.09g of gum arabic, and 0.015g of konjac glucomannan (viscosity of 2000-3000mPa・s at 25℃, 1% aqueous solution).

[0059] The remaining steps and parameters are the same as in Example 2.

[0060] Example 4

[0061] Compared to Example 3, the raspberry seed treatment step in step S12 and the preparation method of the compound stabilizer in step S2 have been adjusted. The adjusted steps are as follows:

[0062] Raspberry processing in S12: Raspberry seeds were freeze-dried at a vacuum of 15 Pa and -38°C for 9 hours, and then treated with low-temperature plasma in an argon atmosphere (processing power 200 W, processing time 6 min). Immediately after treatment, the seeds were ultra-finely pulverized to 200 mesh under a nitrogen protective atmosphere. 20 g of the treated raspberry seed powder was taken and 120 g of enzymatically modified quinoa slurry was added. The mixture was stirred at 52°C and 200 r / min for 35 min to obtain a suspended raspberry seed slurry.

[0063] The preparation method of the compound stabilizer in S2 is as follows: Take 0.015g of konjac glucomannan and add 0.5g of purified water to prepare an aqueous solution; add 0.0003g of pectin methyl esterase (enzyme activity 2000U / g) to the aqueous solution, and enzymatically hydrolyze for 15min at 40℃ and 300r / min. Then add 0.045g of low-methoxyl pectin and 0.09g of gum arabic, and mix thoroughly to obtain the compound stabilizer. The remaining steps and parameters are the same as in Example 3.

[0064] Comparative Example 1

[0065] Compared to Example 1, the pH of the color-protecting and anti-crosslinking raspberry juice was adjusted to 3, while the remaining steps and parameters were the same as in Example 1.

[0066] Comparative Example 2

[0067] Compared to Example 1, the pectin lyase was removed, while the remaining steps and parameters were the same as in Example 1.

[0068] Comparative Example 3

[0069] Compared to Example 1, the ultrafine kiwi seed powder was removed, while the remaining steps and parameters were the same as in Example 1.

[0070] Comparative Example 4

[0071] Compared to Example 1, the 120g of enzymatically modified quinoa pulp in step S12 was replaced with 120g of purified water, while the remaining steps and parameters were the same as in Example 1.

[0072] Experimental Example

[0073] Quinoa-fruit complex beverages prepared in Examples 1-4 and Comparative Examples 1-4 were tested for the following indicators, and the test results are shown in Table 1-2.

[0074] 1. Stability-related index testing.

[0075] (1) Sedimentation rate determination: Take 50 mL of each experimental group of beverage and place it in a 25℃ room temperature environment for 30 days without shaking. After 30 days, centrifuge at 3000 r / min for 15 min, collect the bottom sediment and dry it to constant weight, calculate the sedimentation rate, sedimentation rate = (dry weight of sediment / total mass of beverage) × 100%.

[0076] (2) Determination of stratification rate: Take 50 mL of beverage from each experimental group, adjust the pH to 3.6 with 0.1 mol / L citric acid solution, and then adjust the pH to 4.4 with 0.1 mol / L sodium hydroxide solution (to simulate pH fluctuation during transportation), and let it stand at room temperature for 24 h; observe the volume of the supernatant, calculate the stratification rate, stratification rate = (volume of supernatant / total volume of beverage) × 100%.

[0077] (3) Low-temperature freeze-thaw crystallization rate determination (for groups containing konjac glucomannan): Take 50 mL of beverage from each experimental group, freeze at -2℃ for 12 h, thaw at 25℃ for 12 h, and repeat the freeze-thaw cycle 3 times; after freeze-thaw, centrifuge at 3000 r / min for 15 min, collect the bottom crystals and dry them to constant weight, calculate the crystallization rate, crystallization rate = (dry weight of crystals / total mass of beverage) × 100%.

[0078] (4) Turbidity determination after high-temperature sterilization: After the beverages in each experimental group were sterilized by two-stage ultra-high temperature instantaneous sterilization (100℃ / 1s→138℃ / 2.5s), they were cooled to 25℃ and the turbidity was measured by a turbidity meter (unit: NTU).

[0079] Table 1:

[0080]

[0081] As can be seen from Table 1:

[0082] Examples 1-2 utilize a dual-enzyme synergistic hydrolysis and viscous carrier encapsulation to form a basic stable system, effectively solving the core problems of the background technology. During quinoa pretreatment, acidic protease and natural kiwi protease in kiwi juice work together to hydrolyze large quinoa proteins into small peptides, adapting to the acidic environment of raspberry juice. After ultrafine grinding of raspberry seeds, they are encapsulated in enzymatically modified quinoa pulp containing kiwi mucopolysaccharides, and sedimentation is counteracted by a colloidal network, resolving the contradiction of "raspberry seeds easily sinking when left in, and losing nutrients when removed from seeds". During formulation, pectin lyase degrades kiwi mucopolysaccharides, avoiding high-temperature cross-linking and turbidity. Low-methoxyl pectin and gum arabic synergistically inhibit protein aggregation, ensuring uniform appearance.

[0083] Example 3, based on Example 2, adds konjac glucomannan to improve pH fluctuation tolerance and freeze-thaw crystallization resistance. Konjac glucomannan has a stable structure within a pH range of 3.6-4.4 and forms an interpenetrating network with kiwifruit mucopolysaccharide, reducing colloidal shrinkage and solving the problem of easy stratification under extreme pH fluctuations in Examples 1-2.

[0084] Example 4, based on Example 3, uses low-temperature plasma to treat raspberry seeds and pectin methyl esterase to hydrolyze konjac glucomannan, thus solving the problems of freeze-thaw crystallization and layering during cold chain processing.

[0085] Comparative Example 1: The pH of the raspberry juice was adjusted to 3.0. The strong acidity caused the quinoa protein peptides to aggregate and the low-methoxyl pectin to shrink, making it impossible to fix the particles and resulting in severe precipitation and stratification. At high temperatures, the acidity accelerated the hydrolysis of mucopolysaccharides, exacerbating the turbidity.

[0086] In Comparative Example 2, the pectin lyase was removed, and the macromolecular kiwifruit mucopolysaccharide cross-linked with organic acids to form aggregates at high temperatures, resulting in a sharp increase in turbidity.

[0087] In Comparative Example 4, pure water was used instead of enzymatically hydrolyzed modified quinoa pulp. Without the viscous carrier, the raspberry seeds settled rapidly due to the lack of colloidal network fixation. When the pH fluctuated, the system lacked the support of polysaccharides and was prone to stratification. During freeze-thaw cycles, there was no quinoa pulp to provide synergistic protection, and the wax on the surface of the raspberry seeds induced the formation of a large number of crystals.

[0088] 2. Detection of color, nutrient retention and flavor indicators.

[0089] (1) Anthocyanin retention rate determination: High performance liquid chromatography was used to detect the anthocyanin content (calculated as cyanidin-3-glucoside) of each experimental group of beverages immediately after preparation and after 10 days of storage at room temperature, and the retention rate was calculated as follows: retention rate = (content after 10 days of storage / initial content) × 100%.

[0090] (2) Determination of browning degree at low temperature: Take 50 mL of each experimental group of beverage and refrigerate at 0-4℃ for 30 days. Use a colorimeter to detect the browning degree ΔE before and after refrigeration (the larger the ΔE value, the more severe the browning). The browning degree ΔE is calculated using the CIE LAB color difference system (ΔE=√[(ΔL*)²+(Δa*)²+(Δb*)²], where L is lightness, a is red-greenness, and b* is yellow-blueness); sensory judgment criteria: when ΔE≤6, the color of the beverage does not change significantly (it is still bright red), and when ΔE>6, obvious browning can be observed with the naked eye.

[0091] (3) Low-temperature oxidation off-odor related indicators (hexanal content): Take 50 mL of each experimental group of beverages, refrigerate at 0-4℃ for 7 days, and use headspace gas chromatography to detect hexanal content (there is no obvious rancid smell when the hexanal content in the beverage is ≤0.6mg / kg, and consumers will perceive off-odor when it exceeds 1.0mg / kg).

[0092] (4) Saponin content determination: The saponin content in the beverages of each experimental group was tested (the saponin content in quinoa beverages was ≤0.06g / kg and had no obvious bitter taste, while it exceeded 0.1g / kg and affected the taste).

[0093] Table 2:

[0094]

[0095] Note: “—” in Tables 1 and 2 indicates that the indicator was not detected.

[0096] Table 2 shows that:

[0097] In Example 1: The tea polyphenols added during the pretreatment of raspberry juice can inhibit the PPO activity in quinoa, reducing its catalytic oxidation of raspberry anthocyanins and its own polyphenols; the small molecule peptides produced by the double enzyme hydrolysis of quinoa are not easy to aggregate under a limited pH environment, avoiding degradation caused by the adsorption of anthocyanins by protein aggregates; the colloidal network of the enzymatically modified quinoa pulp can also encapsulate the unsaturated fatty acids of raspberry seeds, reducing contact with oxygen and delaying the generation of oxidative off-flavors.

[0098] Examples 2-4 introduce kiwifruit seed shell polyphenol-β-cyclodextrin inclusion complexes based on Example 1. The kiwifruit seed shell polyphenols in the inclusion complex can bind to quinoa small molecule peptides, blocking the low-temperature condensation reaction of peptides with raspberry organic acids, avoiding the formation of brown peptide-organic acid condensates, and reducing the degree of low-temperature browning.

[0099] In Comparative Example 1, the pH of raspberry juice was adjusted to 3.0. Under this acidic condition, the optimal activity of quinoa PPO was activated, which greatly increased the rate of anthocyanin degradation. At the same time, it accelerated the condensation reaction between quinoa small molecule peptides and raspberry organic acids, generating a large amount of brown substances, which caused the browning degree to soar. Excessive acidity also destroyed the stability of unsaturated fatty acids in raspberry seeds, accelerated oxidation to produce hexanal, and produced a distinct rancid taste.

[0100] Comparative Example 3, due to the removal of ultrafine kiwifruit seed powder, lost the natural antioxidant barrier of tocopherols and phytosterols contained in it, causing the unsaturated fatty acids of raspberry seeds to be directly exposed to oxygen and kiwifruit protease environment. The rate of fatty acid oxidation catalyzed by protease increased significantly, resulting in flavor deterioration.

[0101] In Comparative Example 4, pure water could not encapsulate the unsaturated fatty acids and anthocyanins in raspberry seeds. The former oxidized rapidly to produce a large amount of hexanal, while the latter was easily degraded by contact with oxygen and PPO due to the lack of colloidal protection. At the same time, without the constraint of a colloidal network, quinoa small molecule peptides and organic acids reacted freely to generate more brown condensates, increasing the degree of browning.

Claims

1. A method for preparing a quinoa-fruit complex beverage, characterized in that, Includes the following steps: S1. Raw material pretreatment: S11. Quinoa pretreatment: Select plump quinoa grains, add 5-7 times its weight of purified water, 0.10%-0.15% acidic protease, and 8%-12% kiwi juice, and soak at 40-45℃ for 4-6 hours; then heat the soaking solution to 58-62℃ and keep it at that temperature for 8-12 minutes, and then heat it to 82-86℃ and keep it at that temperature for 10-15 minutes; then add 2.0-3.0 times its weight of purified water, grind it to a particle size of 120-140 mesh, and obtain enzymatically modified quinoa slurry; S12. Raspberry pretreatment: Juice the raspberries to obtain raspberry seeds and raspberry juice; Raspberry seeds were freeze-dried and ultra-finely pulverized, and then 5-7 times the weight of the raspberry seeds were added to enzymatically modified quinoa pulp. After stirring thoroughly at 50-55℃, a suspended raspberry seed pulp was obtained. Add tea polyphenols, kiwi juice, and food-grade glycerin to raspberry juice, stir thoroughly at 33-37℃, then add sodium citrate-dipotassium hydrogen phosphate composite buffer to adjust the pH to 3.8-4.2 to obtain color-protecting and anti-crosslinking raspberry juice. S2. Preparation and Homogenization: First, add the enzymatically modified quinoa pulp and the compound stabilizer to the preparation tank and stir thoroughly at 30-35℃. Then, add the color-protecting and anti-crosslinking raspberry juice, suspended raspberry seed pulp, and ultrafine kiwi seed powder in sequence and stir thoroughly. Finally, add white sugar, potassium sorbate, and pectin lyase and stir thoroughly. Then, perform gradient homogenization. The compound stabilizer includes low-methoxyl pectin and gum arabic. S3: Sterilization and filling: Ultra-high temperature instantaneous sterilization is adopted, and after cooling, the product is filled in a nitrogen environment to obtain the finished product.

2. The method for preparing a quinoa-fruit compound beverage according to claim 1, characterized in that, In step S11, when the temperature is increased from 58-62℃ to 82-86℃, the temperature is increased at a gradient rate of 2-3℃ / min.

3. The method for preparing a quinoa-fruit compound beverage according to claim 1, characterized in that, In step S12, the added tea polyphenols, kiwi juice, and food-grade glycerin are 0.03%-0.05%, 0.02%-0.04%, and 0.04%-0.06% of the raspberry juice mass, respectively.

4. The method for preparing a quinoa-fruit compound beverage according to claim 1, characterized in that, In step S2, the gradient homogenization method is as follows: the mixture is fed into a high-pressure homogenizer, and homogenized for the first time at a pressure of 23-27 MPa, and then homogenized for the second time at a pressure of 26-30 MPa.

5. The method for preparing a quinoa-fruit compound beverage according to claim 1, characterized in that, The specific steps of step S3 are as follows: S31: Employs dual-stage ultra-high temperature instantaneous sterilization: first heat to 98-102℃ and hold for 0.8-1.2 seconds, then raise the temperature to 135-140℃ and hold for 2.0-3.0 seconds; S32: Cool to 25-30℃, use food-grade nitrogen with a purity ≥99.9% and a pressure of 0.10-0.15MPa for back pressure filling, control the oxygen content in the container to ≤1%, and seal to obtain the finished product.

6. The method for preparing a quinoa-fruit compound beverage according to claim 1, characterized in that, In step S12, the raspberry pretreatment stage, 0.06%-0.10% of kiwifruit seed shell polyphenol-β-cyclodextrin inclusion complex by weight of raspberry juice is also added.

7. The method for preparing a quinoa-fruit compound beverage according to claim 6, characterized in that, The compound stabilizer also includes konjac glucomannan, and the mass ratio of low methoxyl pectin, gum arabic, and konjac glucomannan is 1:(1.8-2.2):(0.2-0.4).

8. The method for preparing a quinoa-fruit compound beverage according to claim 7, characterized in that, After freeze-drying the raspberry seeds in step S12 and before ultrafine grinding, the raspberry seeds are treated with low-temperature plasma in an argon atmosphere, with a treatment power of 180-220W and a treatment time of 5-8 minutes.

9. The method for preparing a quinoa-fruit compound beverage according to claim 8, characterized in that, The preparation method of the compound stabilizer after adding konjac glucomannan is as follows: first, konjac glucomannan is enzymatically hydrolyzed by pectin methyl esterase; then, the hydrolyzed konjac glucomannan is mixed with low-methoxyl pectin and gum arabic to form a compound stabilizer.

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