Preparation technology of concentrated clear asparagus juice

Abstract

The invention belongs to the technical field of fruit and vegetable juice processing, and provides a preparation technology of concentrated clear asparagus juice. According to the process, high retention rate and efficient clarification of functional components of asparagus are realized through the steps of gradient heat treatment, composite enzymolysis, two-stage centrifugal separation, enzyme deactivation-ultrafiltration coupling, low-temperature concentration and the like. Particularly, a complex enzyme preparation in a specific ratio is combined with a 50kDa ultrafiltration membrane, so that the membrane pollution index is reduced by 60% while the clarification effect is ensured. The rutin retention rate of the concentrated clear asparagus juice produced by the process reaches 82.7%, and the turbidity is 1t; the method has remarkable technical advantages and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of fruit and vegetable juice processing technology, and specifically relates to a preparation process for concentrated asparagus juice. Background Technology

[0002] With the popularization of health-conscious consumption, asparagus, rich in heat-sensitive functional components such as rutin and asparagine, as well as dietary fiber, is experiencing continuous growth in demand in the functional food and beverage sector. However, traditional asparagus juice processing technology faces significant technical bottlenecks, severely restricting product quality and production efficiency, specifically manifested in the following ways: Low enzymatic hydrolysis efficiency and incomplete degradation: Existing processes mostly use a single enzymatic hydrolysis system, which has limited ability to degrade pectin and cellulose, resulting in pectin residue rate >15% and cellulose residue rate >15%. This not only affects the juice yield but also increases the subsequent filtration load and causes the product turbidity to exceed the standard.

[0003] Severe loss of heat-sensitive ingredients: Traditional processes rely on high-temperature treatment (>100℃) to inactivate enzymes and sterilize, resulting in a loss rate of more than 40% of heat-sensitive functional ingredients such as rutin and asparagine, which greatly reduces the nutritional value and functional attributes of the product and makes it difficult to meet consumers' demand for highly active ingredients.

[0004] Poor centrifugal separation effect and severe membrane fouling: After conventional centrifugation, the turbidity is still >50 NTU, requiring multi-stage filtration to meet the standard, which prolongs the production cycle; at the same time, the flux decay rate of ultrafiltration membrane is as high as 30% / batch, and the membrane fouling is severe. Frequent cleaning or replacement of membrane modules leads to a surge in production costs, becoming a major obstacle to large-scale production.

[0005] The aforementioned technical deficiencies have created a chain of bottlenecks in the entire "enzymatic hydrolysis-separation-membrane treatment" process: incomplete enzymatic hydrolysis increases the difficulty of subsequent separation, high-temperature treatment exacerbates the loss of functional components, and membrane fouling further limits the optimization potential of the enzymatic hydrolysis and separation processes. The industry urgently needs an integrated, low-energy-consumption, and high-retention asparagus juice processing technology that can improve enzymatic hydrolysis efficiency, reduce heat-sensitive losses, and minimize membrane fouling, while achieving controllable turbidity and stable flux. This would overcome the limitations of traditional processes and promote the high-quality, high-efficiency production of asparagus functional beverages. Summary of the Invention

[0006] To address the above-mentioned technical problems, this invention proposes a process for preparing concentrated asparagus juice. This process provides an asparagus juice production method that maximizes the retention of functional components, improves clarification efficiency, and reduces membrane fouling.

[0007] This invention provides a process for preparing concentrated asparagus juice, comprising the following steps: (1) Heat treatment: Take the asparagus juice and use gradient heat treatment. The specific process is to heat it in a tube at 90-95℃ and keep it at that temperature for 15 minutes, and then cool it down to 55℃ at a rate of 15-25℃ / min. (2) Enzymatic hydrolysis: Add compound enzyme preparation, mix evenly, and enzymatically hydrolyze at 30-60℃ for 1.5-2.5h; The compound enzyme preparation is made by mixing at least two of pectinase, amylase, cellulase, hemicellulase and protease, wherein the amount of any one of the pectinase, amylase, cellulase, hemicellulase and protease is 0.1‰-0.4‰ of the volume fraction of asparagus turbid juice. (3) Sterilization, enzyme inactivation, and ultrafiltration: Inactivate enzymes at 70-100℃ for 10-20s, filter with a 50kDa ultrafiltration membrane to obtain filtrate; (4) Centrifugation: Centrifuge the filtrate horizontally at 8000 rpm, then centrifuge it on a disc at 12000 rpm and collect the supernatant. (5) Concentration: The supernatant is concentrated at low temperature to obtain concentrated asparagus juice, which has a soluble solids content of 18-65°Brix. The temperature gradient of the low temperature triple-effect concentration is 65-75℃→55-65℃→45-55℃. (6) Degassing, sterilization and bottling: The concentrated asparagus juice is degassed, then sterilized by UHT ultra-high temperature instantaneous sterilization and bottling to obtain the product asparagus juice.

[0008] Preferably, in (1), the soluble solids content of the asparagus turbid juice is 9°Brix, and the cooling rate of the gradient heat treatment is 20°C / min.

[0009] Preferably, in (2), the cellulase is a C1+Cx complex; the pectinase activity is ≥30000U / g; the amylase is a 50℃ resistant type; the cellulase is a C1+Cx complex; the hemicellulase is dominated by xylanase; and the protease is a neutral protease.

[0010] Preferably, in (3), the transmembrane pressure of the ultrafiltration membrane is 0.4-0.6 MPa.

[0011] The present invention has the following advantages and effects compared with the prior art: (1) The process of gradient heat treatment at 90-95℃ + rapid cooling (15-25℃ / min) effectively avoids the degradation of heat-sensitive functional components caused by traditional high temperature (>100℃); the low temperature triple-effect concentration system controls the temperature gradient from 65-75℃ to 55-65℃ to 45-55℃, and with precise control of vacuum degree -0.086 / -0.09MPa, while ensuring the soluble solids content of 18-65°Brix, further reduces the loss of heat-sensitive components; (2) The compound enzyme preparation is made by mixing equal amounts of pectinase (activity ≥30000U / g), 50℃ resistant amylase, C1+Cx compound cellulase, xylan-dominant hemicellulase and neutral protease, and is combined with a 50kDa ultrafiltration membrane (transmembrane pressure 0.4-0.6MPa) and enzyme inactivation-ultrafiltration coupling equipment; the two-stage centrifuge unit (8000rpm horizontal centrifugation + 12000rpm disc centrifugation) makes the final turbidity <2NTU, which is far superior to the turbidity of more than 50NTU in the traditional process, reducing the number of subsequent filtration steps; (3) The PLC precise control of the automated system devices (tubular heating-heat preservation integrated equipment, five-element enzyme automatic addition device, enzyme inactivation-ultrafiltration coupling equipment, two-stage centrifuge unit, low temperature triple-effect concentration system) ensures accurate matching of parameters of each unit, reduces human operation error, realizes continuous production, improves process stability and product consistency, provides key technical support for high-quality and large-scale production of asparagus functional beverages, and has significant technological advancement and economic value. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of the present invention; Figure 2 Block diagram of a graded UHT sterilization control system; Figure 3 This is a process flow diagram for a triple-effect falling film evaporator. Detailed Implementation

[0013] To enable those skilled in the art to better understand the present invention, the present invention will now be further described in conjunction with specific embodiments.

[0014] Example 1: like Figure 1 As shown, the process flow of this invention is as follows: concentrated asparagus juice → heat treatment → enzymatic hydrolysis → pasteurization → centrifugation → concentration → degassing → sterilization → filling. The specific preparation process steps are as follows: (1) Heat treatment: Take 9°Brix asparagus turbid juice and use gradient heat treatment. The specific process is to use a tubular heating-heating integrated equipment, heat at 95°C in a tubular manner and then heat for 15 minutes, and then rapidly cool down to 55°C at a rate of 20°C / min. (2) Enzymatic hydrolysis: The compound enzyme preparation was added using a five-element enzyme automatic addition device and enzymatically hydrolyzed at 50°C for 2 hours; The preparation process of the compound enzyme preparation is as follows: take pectinase, amylase, C1+Cx compound cellulase, hemicellulase and protease and dissolve them in asparagus turbid juice, and take 0.4‰ of the volume of the asparagus turbid juice to be enzymatically hydrolyzed and mix them evenly. (3) Pasteurization, enzyme inactivation and ultrafiltration: The liquid after enzymatic hydrolysis needs to be pasteurized at 75°C for 15 seconds. The purpose is to kill most of the enzymes and pathogenic microorganisms such as yeast, and to preserve the original flavor and nutritional value of the food to the greatest extent. Then, the solution was filtered using a 50 kDa ultrafiltration membrane with a transmembrane pressure of 0.5 MPa to obtain the filtrate. (4) Centrifugation: The filtrate is then centrifuged. When the centrifuge is working, the drum and the screw will rotate at high speed in the same direction with a certain differential speed. After the material enters the inner cylinder of the conveying screw from the feed pipe, it is accelerated into the drum. Under the action of centrifugal force, the heavier solid phase is deposited on the drum wall to form a sludge layer, while the lighter liquid phase gathers towards the center of the drum to form a clear liquid. The screw conveyor rotates in the same direction as the drum but with a differential speed, which will continuously push the deposited solid phase to the cone end of the drum and discharge it through the sludge discharge port. The liquid phase overflows through the overflow hole at the large end of the drum, thus realizing continuous solid-liquid separation.

[0015] First, large particles are separated by horizontal centrifugation at 8000 rpm (which can continuously separate 3.3 tons per hour). Then, the supernatant is obtained by disc centrifugation at 12000 rpm (which can continuously separate 5 tons per hour). The combination of the two-stage centrifuge units can improve separation efficiency, reduce intermediate steps, reduce energy consumption, and improve production continuity.

[0016] (5) Concentration: The supernatant is concentrated using a low-temperature triple-effect concentration system ( Figure 3 Concentrate.

[0017] Start pump 1, and the material enters the first-effect heating chamber (80℃) from the temporary storage tank. When a certain liquid level is reached, start pump 2 and the material enters the second-effect heating chamber (65-68℃). The material falls into the second-effect evaporation chamber and is sent to the third-effect heating chamber (50-55℃) by pump 3. The material falls into the third-effect evaporation chamber and is returned to the temporary storage tank by pump 4. Turn on the cooling water inlet and outlet pumps, and observe the control valves through the sight glass of the cooling water tower to maintain cooling water balance. Once the material is running normally and the liquid levels in each effect are balanced, then turn on the vacuum pump (note that the cooling water should be turned on).

[0018] Once the vacuum reaches -0.086 MPa for the first effect and -0.09 MPa for the second effect, open the steam valve (note: steam drainage). As the temperature rises, you can see the material moving, separating, and rotating through the sight glass of each effect. Take a sample from the return port of the material and check that the concentration is qualified. Then close the return valve and discharge the material to the pre-filling storage tank to obtain concentrated asparagus juice with a soluble solids content of 18-65°Brix. (6) Degassing, sterilization, and filling: The concentrated liquid will be degassed before formal sterilization. The principle is to remove moisture and other gaseous components by reducing the saturated vapor pressure of water vapor in the material under vacuum conditions. It mainly removes moisture, carbon dioxide and other gaseous components from the material, effectively prevents material oxidation, better maintains color and flavor, reduces filling bubbles, enhances stability, and extends product shelf life; UHT ultra-high temperature instantaneous sterilization is used (the system used is such as...) Figure 2 As shown in the image, the sterilization process can kill almost all microorganisms, including pathogens, resulting in a very low risk to food safety. Combined with aseptic filling, this effectively ensures product quality.

[0019] Example 2: 2.1 Optimization of Gradient Heat Treatment Conditions The difference between the preparation process steps in Example 1 and the gradient heat treatment conditions in step (1) is shown in Table 1 below. The remaining steps are the same as in Example 1.

[0020] Table 1. Effects of gradient heat treatment conditions on the asparagus juice index Example Gradient heat treatment conditions Rutin retention rate % Asparagine loss rate % 2 105℃ / 15min 63.5 45.2 3 100℃ / 15min 71.9 29.4 4 95℃ / 15min 82.7 14.5 5 90℃ / 15min 82.73 14.3

[0021] As shown in Table 1, the higher the temperature, the greater the loss of rutin. Excessively high temperatures significantly increase the loss of asparagine through Maillard reactions and thermal degradation. The optimal processing temperature range is 90-95℃. Given that 95℃ provides better sterilization of microorganisms and ensures product quality and safety, 95℃ was chosen for heat treatment.

[0022] 2.2 Component Optimization in Compound Enzyme Preparations The difference between the preparation process steps in Example 1 and the one in Example 2 is the type of enzyme in the compound enzyme preparation, as shown in Table 2 below. The other steps are the same as in Example 1.

[0023] Table 2. Effects of enzyme types in compound enzyme preparations on asparagus juice indicators. Example pectinase amylase Cellulase hemicellulase protease Rutin retention rate % Asparagine loss rate % 6 √ √ √ √ √ 82.7 16.5 7 √ 45.1 38.7 8 √ √ 59.1 35.7 9 √ √ √ 72.4 32.7 10 √ √ √ √ 75.2 30.5

[0024] As shown in Table 2, the composite enzyme preparation with pectinase, cellulase, and hemicellulase as the core can achieve the most thorough cell wall disruption through the synergistic effect of these three enzymes, thereby maximizing the release of rutin. Amylase can reduce the viscosity of the turbid juice, providing a better working space for other enzymes. Protease, as a targeted enzyme, can hydrolyze the protein bound to rutin, releasing the "bound rutin" into "free rutin." Therefore, the use of composite enzyme preparations can maximize the extraction of rutin from the slurry.

[0025] Pectinase, cellulase, and hemicellulase do not recognize or break down asparagine molecules, making their use safe and beneficial, and they are the mainstays of enzymatic extraction. Asparagus contains a certain amount of amylase; adding amylase hydrolyzes starch to produce a large amount of reducing sugars. In the subsequent concentration stage, these hydrolyzed small sugar molecules are more easily removed along with other impurities, or more easily separated from asparagine in the separation step, thus reducing the risk of Maillard reaction during the final product processing. It protects asparagine by "cleaning up" a potential reactant. The problem with proteases is that they indiscriminately attack all peptide bonds. If a protein chain contains an asparagine residue, this residue may be released when the protein is hydrolyzed by the protease, but it is also very likely to be further degraded or converted into other amino acids under the catalysis of the enzyme.

[0026] The difference between the preparation process steps in Example 1 and the steps in Example 2 is the ratio of enzymes in the compound enzyme preparation, as shown in Table 3 below. The remaining steps are the same as in Example 1.

[0027] Table 3. Effect of enzyme ratio in compound enzyme preparation on asparagus juice index. Example pectinase‰ amylase‰ Cellulase‰ hemicellulase‰ protease‰ Rutin retention rate % Asparagine loss rate % 11 0.4 0.1 0.1 0.1 0.1 42.1 24.6 12 0.1 0.1 0.4 0.1 0.1 25.1 25.4 13 0.1 0.1 0.1 0.4 0.1 15.3 25.6 14 0.1 0.4 0.1 0.1 0.1 0.8 23.8 15 0.1 0.1 0.1 0.1 0.4 0.8 39.5 16 0.1 0.1 0.1 0.1 0 0.5 15.1

[0028] As shown in Table 3, the use of compound enzyme preparations can retain functional components such as rutin and asparagine to the greatest extent.

[0029] 2.3 Optimization of Enzymatic Hydrolysis Temperature The difference between the preparation process steps in Example 1 and that in Example 2 is the temperature of enzymatic hydrolysis, as shown in Table 4 below. All other steps are the same as in Example 1.

[0030] Table 4. Effect of enzymatic hydrolysis temperature on the properties of asparagus juice. Example Temperature ℃ Rutin retention rate % Asparagine loss rate % 17 30 20.6 30.5 18 40 40.9 25.6 19 60 23.1 32.5

[0031] As shown in Table 4, lower temperatures reduce the enzyme's reaction rate by a certain percentage or even more, increasing the risk of contamination. Within a fixed processing time, low temperatures can lead to insufficient extraction and a decrease in the yield of rutin and asparagine. Conversely, excessively high temperatures can damage the enzyme's three-dimensional structure, causing permanent and irreversible loss of enzyme activity. This prevents effective cell wall breaking, preventing the release of rutin and asparagine residues and resulting in very low yields. Excessively high temperatures also increase energy consumption, leading to potentially fatal consequences.

[0032] 2.4 Optimization of Enzymatic Hydrolysis Time The difference between the preparation process steps in Example 1 and the enzymatic hydrolysis time is shown in Table 5 below. The remaining steps are the same as in Example 1.

[0033] Table 5. Effect of enzymatic hydrolysis time on the indicators of asparagus juice. Example Enzymatic hydrolysis time Rutin retention rate % Asparagine loss rate % 20 1h 50.3 30.2 21 1.5h 70.6 20.6 22 2.5h 82.4 21.9 23 3h 81.1 35.5

[0034] As shown in Table 5, within the optimal temperature range of 1.5H-2.5H, the highest substrate concentration (cell wall, etc.) leads to the fastest enzymatic hydrolysis rate in the initial stage. As time progresses, the available substrate decreases, the reaction rate gradually declines, and eventually reaches equilibrium. Extending the hydrolysis time then produces almost no further effect. Excessive hydrolysis time means decreased equipment utilization, increased energy consumption, and reduced production capacity, significantly harming economic efficiency.

[0035] Comparative Example The specific steps for preparing concentrated asparagus juice using traditional methods are as follows: (1) After the raw materials have been inspected and sorted, they should be crushed in time, made into a pulp, and the juice collected after juicing. (2) Pasteurize the juice, control the sterilization temperature in the range of 85℃-95℃, and adjust the discharge temperature in the range of 50℃-55℃ before feeding it into the enzymatic hydrolysis tank; (3) Add 0.4‰ pectinase (60,000 units of enzyme activity) and enzymatically hydrolyze for 1.5-2 hours; (4) After enzymatic hydrolysis, separate the food into plates; (5) The separated liquid is poured into a temporary storage tank before concentration and waits for concentration; (6) Perform low-temperature triple-effect falling film concentration, and pump the concentrated liquid into a pre-sterilization storage tank; (7) Perform UHT ultra-high temperature instantaneous sterilization, and then fill the product after sterilization.

[0036] Traditional asparagus juice processing technology has the following technical defects: low efficiency of single enzymatic hydrolysis, incomplete degradation of pectin and cellulose (residual rate >15%), high temperature treatment (>100℃) leads to a loss rate of more than 40% of heat-sensitive functional components (such as rutin and asparagine), turbidity is still higher than 50 NTU after conventional centrifugation, requiring repeated filtration, serious membrane fouling, and ultrafiltration membrane flux decay rate of up to 30% / batch.

[0037] Other aspects are the same as in Example 1. Table 6 Experimental Data index Embodiment 1 of the present invention Comparative Example Clear juice yield 89.2±1.8% 71.6±2.3% Rutin retention rate 82.7±2.1% 63.5±3.4% Membrane flux decay rate / batch 8.7% 30.2% Turbidity (NTU) 1.8±0.3 12.5±2.1

[0038] As shown in Table 6, the process employs gradient heat treatment, five-element complex enzymatic hydrolysis, two-stage centrifugation, enzyme inactivation-ultrafiltration coupling, and low-temperature concentration to achieve high retention rates and efficient clarification of asparagus functional components. Specifically, the combination of a specially formulated complex enzyme preparation with a 50kDa ultrafiltration membrane reduces membrane fouling by 60% while maintaining clarification effectiveness. The concentrated asparagus juice produced by this process achieves a rutin retention rate of 82.7% and a turbidity of <2 NTU, demonstrating significant technical advantages and economic benefits.

[0039] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. All equivalent changes and modifications made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. A process for the preparation of a concentrated clear juice of asparagus, characterized in that, The method comprises the following steps: (1) heat treatment: taking asparagus juice, adopting gradient heat treatment, the specific process is 90-95℃ tube heating, then holding for 15 minutes, and then rapidly cooling to 55℃ at a rate of 15-25℃ / min; (2) enzyme hydrolysis: adding a compound enzyme preparation, mixing uniformly, and then hydrolyzing at 30-60℃ for 1.5-2.5h; The compound enzyme preparation is prepared by mixing at least two of pectinase, amylase, cellulase, hemicellulase and protease, wherein the amount of any one of the pectinase, amylase, cellulase, hemicellulase and protease is 0.1‰-0.4‰ of the volume fraction of the asparagus juice; (3) pasteurization, enzyme inactivation and ultrafiltration: inactivating the enzyme at 70-100℃ for 10-20s, filtering through a 50kDa ultrafiltration membrane to obtain a filtrate; (4) centrifugation: taking the filtrate and performing horizontal centrifugation at 8000rpm, then performing disc centrifugation at 12000rpm, and taking the supernatant; (5) concentration: the supernatant is subjected to low-temperature three-effect concentration to obtain asparagus concentrated clear juice, and the soluble solid content of the asparagus concentrated clear juice is 18-65°Brix, wherein the temperature gradient of the low-temperature three-effect concentration is 65-75℃→55-65℃→45-55℃; (6) degassing, sterilization and canning: the asparagus concentrated clear juice after concentration is subjected to degassing treatment, then subjected to UHT ultra-high temperature instantaneous sterilization, canned to obtain the product asparagus concentrated clear juice.

2. The preparation process of claim 1, wherein, In the (1), the soluble solid content of the asparagus juice is 9°Brix, and the cooling rate of the gradient heat treatment is 20℃ / min.

3. The preparation process of claim 1, wherein, In the (2), the cellulase is C1+Cx compound type; the activity of the pectinase is ≥30000U / g; the amylase is a 50℃-resistant type; the cellulase is C1+Cx compound type; the hemicellulase is dominated by xylanase; and the protease is neutral protease.

4. The preparation process of claim 1, wherein, In the (3), the transmembrane pressure of the ultrafiltration membrane is 0.4-0.6MPa.

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