Watermelon juice sterilization process based on HPP technology

Abstract

The present application relates to the technical field of ultra-high pressure processing, in particular to a watermelon juice sterilization process based on HPP technology: low-temperature juicing of watermelons, collection of watermelon juice, pumping of the watermelon juice into the lower cavity of a piston-isolated autoclave, pressure maintaining treatment by supercritical carbon dioxide, and obtaining of watermelon juice intermediates; injection of degassed pure water into the upper cavity of the piston-isolated autoclave, pressure increase by HPP technology, chelation of polyphenols in the watermelon juice intermediates, and obtaining of high-pressure watermelon juice. The present application uses the polyphenols of watermelons as natural ligands, and under ultra-high pressure, irreversible coordination chelation occurs with the enzyme active center, solving the difficult problem of enzymatic browning in watermelon juice processing, and pre-acidification of carbon dioxide, ultra-high pressure complexation are integrated in the same autoclave and completed in stages, avoiding the risk of pollution, and the gas-liquid mass transfer efficiency is improved by orders of magnitude, presenting the fresh watermelon pure melon aroma and high nutrient retention rate.

Description

Technical Field

[0001] This invention relates to the field of ultra-high pressure processing technology, specifically to a watermelon juice sterilization process based on HPP technology. Background Technology

[0002] HPP technology, or ultra-high pressure processing technology, refers to a novel food processing technology that uses ultra-high hydrostatic pressure on food under mild temperature conditions. This process disrupts the cell membrane structure of microorganisms, inhibits enzyme activity, and destroys their genetic material, achieving non-thermal sterilization and enzyme inactivation while preserving the original color, flavor, nutrients, and heat-sensitive substances of the food to the greatest extent possible. It is characterized by high sterilization efficiency, no chemical additives, and excellent nutrient retention. The watermelon juice sterilization process based on HPP technology uses HPP ultra-high pressure processing as the core sterilization method. Combined with the physicochemical properties of watermelon juice, it kills pathogenic bacteria and spoilage microorganisms in watermelon juice and inactivates browning enzymes such as polyphenol oxidase by controlling key parameters such as pressure, holding time, and pressurization method at room temperature. This achieves safe preservation and extended shelf life of watermelon juice through non-thermal sterilization, avoiding the vitamin loss, flavor deterioration, and darkening of color caused by traditional heat sterilization.

[0003] First, while traditional heat sterilization can effectively inactivate enzymes, high-temperature treatment inevitably destroys heat-sensitive functional active ingredients in watermelon juice, such as vitamin C and lycopene, causing the watermelon juice to lose the natural flavor and nutritional value that freshly squeezed watermelon juice should have. Second, the inactivation of enzymes by ultra-high pressure technology alone is often not thorough enough. During the sales period, polyphenol oxidase and peroxidase are prone to reactivation, triggering enzymatic browning reactions, resulting in darker juice color, deterioration of flavor, and difficulty in ensuring stability. In addition, in order to inhibit oxidative browning, existing technologies often require the addition of chemical antioxidants such as ascorbic acid, which destroys the purity of flavor.

[0004] Therefore, the present invention provides a watermelon juice sterilization process based on HPP technology to solve the aforementioned related technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a watermelon juice sterilization process based on HPP technology. Using a piston-isolated high-pressure autoclave, supercritical carbon dioxide is injected into the watermelon juice in the form of microbubbles through a microporous membrane in the lower chamber. Its high permeability and solvation effect disrupt microbial cell membranes, while hydration generates carbonic acid, acidifying the system and activating the coordination activity of endogenous polyphenols. Subsequently, water is injected into the upper chamber to increase the pressure, inducing hydrophobic collapse and conformational exposure of the chlorogenic acid and other endogenous polyphenols abundant in the watermelon juice. These polyphenols are then directed to the copper ion active center of polyphenol oxidase to form chelates and block the heme active pocket entrance of peroxidase, achieving irreversible inactivation of the enzyme. A two-stage depressurization process, first slow and then rapid, causes the carbon dioxide to explode, resulting in secondary cold sterilization.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A watermelon juice sterilization process based on HPP technology, the process comprising the following steps: Watermelon juice is extracted at low temperature, and the juice is collected. The juice is then pumped into the lower chamber of a piston-isolated high-pressure autoclave, where supercritical carbon dioxide is introduced for pressure treatment to obtain a watermelon juice intermediate. Deaerated pure water is injected into the upper chamber of a piston-isolated high-pressure autoclave, and the pressure is increased using HPP technology to chelate the polyphenols in the watermelon juice intermediate, thereby obtaining high-pressure watermelon juice. The watermelon suspension is formed by multiple stages of depressurization. The watermelon suspension is then refined and aseptically filled and stored.

[0007] The watermelon is juiced at low temperature, specifically as follows: Watermelons are placed in an environment of 4℃ and pressed using a screw press. The initial watermelon juice is filtered through a 200-mesh vibrating screen to remove residual seed shells and coarse fibers, thus obtaining watermelon juice.

[0008] Furthermore, the pumping of watermelon juice into the lower chamber of the piston-isolated autoclave includes: Pump watermelon juice into the lower chamber of the piston-isolated autoclave through a sterile pipeline until the lower chamber is full and juice overflows from the outlet. Confirm that there is no residual air in the headspace and close the feed valve and discharge valve. Degassed pure water is added to the upper chamber of the autoclave, and the lower chamber is pressurized by the piston to 0.45-0.55 MPa to form a balanced lower chamber of the autoclave.

[0009] At this point, the watermelon juice is in a controlled initial back pressure state, slightly higher than normal pressure, which helps maintain stability when carbon dioxide is subsequently introduced.

[0010] Furthermore, the pressure holding process involving the introduction of supercritical carbon dioxide includes: Carbon dioxide is pressurized and heated to 40-42°C to bring it to a supercritical state, thus obtaining supercritical carbon dioxide. Supercritical carbon dioxide was introduced into the lower chamber of a high-pressure reactor using a microporous membrane disperser to stabilize the pressure in the lower chamber at 19.9–20.1 MPa. After all the supercritical carbon dioxide was injected, the inlet valve was closed and the mixture was allowed to stand for 5–8 minutes to obtain the watermelon juice intermediate.

[0011] Among them, a small portion of degassed pure water can be discharged by finely adjusting the pressure relief valve in the upper chamber, so that the piston moves slightly upward and the pressure is stabilized at 19.9-20.1 MPa, and the amount of supercritical carbon dioxide introduced is 3.5% of the mass of watermelon juice.

[0012] This pressure-holding process allows the dissolved supercritical carbon dioxide to reach a distribution equilibrium in the watermelon juice, completing the hydration and acidification reactions. At the end of the pressure-holding stage, when the pH value stabilizes in the range of 4.35 to 4.45, it indicates that the acidification process has reached its end.

[0013] Furthermore, degassed pure water is injected into the upper chamber of the piston-isolated autoclave, and pressurization is achieved using HPP technology, including: After confirming that the inlet valve of the lower chamber is closed and sealed properly, degassed pure water is injected into the upper chamber of the piston-isolated autoclave. As the volume of the upper chamber increases, the free piston is pushed downward smoothly, causing the pressure in the lower chamber containing the watermelon juice intermediate to rise to 580-585 MPa. The temperature of the watermelon juice intermediate is controlled at 38-40℃ and maintained for 4 minutes to obtain high-pressure watermelon juice, with the pressure increase rate controlled at 3 MPa / s.

[0014] At this point, the phenolic hydroxyl groups of the endogenous polyphenols in watermelon juice undergo enhanced deprotonation, resulting in hydrophobic collapse of the molecules. The phenolic hydroxyl groups, originally encased in the hydration layer, are directionally exposed and coordinate with copper ions at the active site of polyphenol oxidase, occupying the catalytic site. Simultaneously, polyphenol molecules adsorb at the entrance of the peroxidase active pocket through hydrophobic interactions and hydrogen bonds, forming steric hindrance and preventing the substrate from approaching the heme active site. High pressure synergistically promotes the relaxation of the enzyme protein's tertiary structure and locks in a denatured conformation, resulting in the irreversible loss of enzyme activity.

[0015] Furthermore, the specific steps for forming the watermelon suspension are as follows: The lower chamber containing high-pressure watermelon juice is depressurized linearly to the node pressure, with the depressurization rate controlled at 4.5 MPa / s. When the pressure is reduced to the node pressure, the pressure relief valve is fully opened to reduce the pressure to 0.1 MPa, resulting in a watermelon suspension. The node pressure is set to 8 MPa.

[0016] Furthermore, the purification of the watermelon suspension includes: The watermelon suspension was maintained at 35–37°C and allowed to settle naturally for 8–12 minutes to obtain layered watermelon juice. The layered watermelon juice was then centrifuged to separate the layers, and the supernatant was collected.

[0017] The layered watermelon juice is separated by centrifugation as follows: start the disc centrifuge, rinse it with sterile water beforehand and run it idle at the set speed of 3000 r / min, and pump the layered watermelon juice into the feed inlet.

[0018] Furthermore, the purification of the watermelon suspension also includes: The centrifuged liquid was filtered through a 0.5μm ceramic membrane to obtain watermelon filtrate. The watermelon filtrate was then cooled to 4–6℃ to obtain low-temperature watermelon juice.

[0019] Furthermore, the aseptic filling and storage of the refined watermelon suspension specifically involves: Low-temperature watermelon juice is poured into sterile bottles through a sterile filter and filled with nitrogen gas, then stored at 4°C.

[0020] Compared with the prior art, the beneficial effects of the present invention are: This invention utilizes a piston-isolated autoclave. In the lower chamber, supercritical carbon dioxide is injected into watermelon juice in the form of microbubbles through a microporous membrane. Its high permeability and solvation effect disrupt microbial cell membranes, while hydration generates carbonic acid, acidifying the system and activating the coordination activity of endogenous polyphenols. Subsequently, water is injected into the upper chamber to increase the pressure, inducing hydrophobic collapse and conformational exposure of the chlorogenic acid and other endogenous polyphenols abundant in the watermelon juice. These polyphenols then directionally coordinate with the copper ion active center of polyphenol oxidase to form chelates and block the heme active pocket entrance of peroxidase, achieving irreversible inactivation of the enzyme. A two-stage depressurization process, first slow and then rapid, causes the carbon dioxide to explode, resulting in secondary cold sterilization.

[0021] This invention utilizes watermelon polyphenols as natural ligands, which undergo irreversible coordination chelation with enzyme active centers under ultra-high pressure, solving the thorny problem of enzymatic browning in watermelon juice processing. Furthermore, carbon dioxide pre-acidification and ultra-high pressure complexation are integrated into the same reactor and completed in stages, avoiding the risk of contamination and increasing the gas-liquid mass transfer efficiency by orders of magnitude, resulting in the pure melon aroma and high nutrient retention of freshly squeezed watermelon. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart of the watermelon juice sterilization process based on HPP technology according to the present invention. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In this embodiment, unless otherwise specified, all raw materials are conventional commercially available products. The average pore size of the microporous membrane disperser is 0.2 μm, and the membrane contact area is 0.05 m² per liter of watermelon juice. 2.

[0026] Example 1 like Figure 1 As shown, a watermelon juice sterilization process based on HPP technology includes the following steps: Watermelon juice is extracted at low temperature, and the juice is collected. The juice is then pumped into the lower chamber of a piston-isolated high-pressure autoclave, where supercritical carbon dioxide is introduced for pressure treatment to obtain a watermelon juice intermediate. Deaerated pure water is injected into the upper chamber of a piston-isolated high-pressure autoclave, and the pressure is increased using HPP technology to chelate the polyphenols in the watermelon juice intermediate, thereby obtaining high-pressure watermelon juice. The watermelon suspension is formed by multiple stages of depressurization. The watermelon suspension is then refined and aseptically filled and stored.

[0027] The watermelon is juiced at low temperature, specifically as follows: Watermelons are placed in an environment of 4℃ and pressed using a screw press. The initial watermelon juice is filtered through a 200-mesh vibrating screen to remove residual seed shells and coarse fibers, thus obtaining watermelon juice.

[0028] Furthermore, the pumping of watermelon juice into the lower chamber of the piston-isolated autoclave includes: Pump watermelon juice into the lower chamber of the piston-isolated autoclave through a sterile pipeline until the lower chamber is full and juice overflows from the outlet. Confirm that there is no residual air in the headspace and close the feed valve and discharge valve. Degassed pure water is added to the upper chamber of the autoclave, and the lower chamber is pressurized to 0.45 MPa by a piston to form a balanced lower chamber of the autoclave.

[0029] At this point, the watermelon juice is in a controlled initial back pressure state, slightly higher than normal pressure, which helps maintain stability when carbon dioxide is subsequently introduced.

[0030] Furthermore, the pressure holding process involving the introduction of supercritical carbon dioxide includes: Carbon dioxide is pressurized and heated to 40°C to bring it to a supercritical state, thus obtaining supercritical carbon dioxide. Supercritical carbon dioxide was introduced into the lower chamber of a high-pressure reactor using a microporous membrane disperser to stabilize the pressure in the lower chamber at 19.9 MPa. After all the supercritical carbon dioxide was injected, the inlet valve was closed and the mixture was allowed to stand for 5 minutes to obtain the watermelon juice intermediate.

[0031] Among them, a small portion of degassed pure water can be discharged by finely adjusting the pressure relief valve in the upper chamber, so that the piston moves slightly upward to stabilize the pressure at 19.9 MPa, and the amount of supercritical carbon dioxide introduced is 3.5% of the mass of watermelon juice.

[0032] This pressure-holding process allows the dissolved supercritical carbon dioxide to reach a distribution equilibrium in the watermelon juice, completing the hydration and acidification reactions. At the end of the pressure-holding stage, when the pH value stabilizes within the range of 4.35, it indicates that the acidification process has reached its end.

[0033] Furthermore, degassed pure water is injected into the upper chamber of the piston-isolated autoclave, and pressurization is achieved using HPP technology, including: After confirming that the inlet valve of the lower chamber is closed and sealed properly, degassed pure water is injected into the upper chamber of the piston-isolated autoclave. As the volume of the upper chamber increases, the free piston is pushed downward smoothly, causing the pressure in the lower chamber containing the watermelon juice intermediate to rise to 580 MPa. The temperature of the watermelon juice intermediate is controlled at 38°C and maintained for 4 minutes to obtain high-pressure watermelon juice, with the pressure increase rate controlled at 3 MPa / s.

[0034] At this point, the phenolic hydroxyl groups of the endogenous polyphenols in watermelon juice undergo enhanced deprotonation, resulting in hydrophobic collapse of the molecules. The phenolic hydroxyl groups, originally encased in the hydration layer, are directionally exposed and coordinate with copper ions at the active site of polyphenol oxidase, occupying the catalytic site. Simultaneously, polyphenol molecules adsorb at the entrance of the peroxidase active pocket through hydrophobic interactions and hydrogen bonds, forming steric hindrance and preventing the substrate from approaching the heme active site. High pressure synergistically promotes the relaxation of the enzyme protein's tertiary structure and locks in a denatured conformation, resulting in the irreversible loss of enzyme activity.

[0035] Furthermore, the specific steps for forming the watermelon suspension are as follows: The lower chamber containing high-pressure watermelon juice is depressurized linearly to the node pressure, with the depressurization rate controlled at 4.5 MPa / s. When the pressure is reduced to the node pressure, the pressure relief valve is fully opened to reduce the pressure to 0.1 MPa, resulting in a watermelon suspension. The node pressure is set to 8 MPa.

[0036] Furthermore, the purification of the watermelon suspension includes: The watermelon suspension was kept at 35°C and allowed to settle naturally for 8 minutes to obtain layered watermelon juice. The layered watermelon juice was then centrifuged to separate the layers, and the supernatant was collected.

[0037] The layered watermelon juice is separated by centrifugation as follows: start the disc centrifuge, rinse it with sterile water beforehand and run it idle at the set speed of 3000 r / min, and pump the layered watermelon juice into the feed inlet.

[0038] Furthermore, the purification of the watermelon suspension also includes: The centrifuged liquid was filtered through a 0.5μm ceramic membrane to obtain watermelon filtrate. The watermelon filtrate was then cooled to 4℃ to obtain low-temperature watermelon juice.

[0039] Furthermore, the aseptic filling and storage of the refined watermelon suspension specifically involves: Low-temperature watermelon juice was passed through a sterile filter into sterile bottles and filled with nitrogen gas, then stored at 4°C. Example 2 The preparation process of the watermelon juice sterilization process based on HPP technology provided in this embodiment is basically the same as that in Example 1. The main difference between the two lies in the specific composition and ratio of the raw materials used. The specific composition of the raw materials used in this embodiment is as follows: The process includes the following steps: Watermelon juice is extracted at low temperature, and the juice is collected. The juice is then pumped into the lower chamber of a piston-isolated high-pressure autoclave, where supercritical carbon dioxide is introduced for pressure treatment to obtain a watermelon juice intermediate. Deaerated pure water is injected into the upper chamber of a piston-isolated high-pressure autoclave, and the pressure is increased using HPP technology to chelate the polyphenols in the watermelon juice intermediate, thereby obtaining high-pressure watermelon juice. The watermelon suspension is formed by multiple stages of depressurization. The watermelon suspension is then refined and aseptically filled and stored.

[0040] The watermelon is juiced at low temperature, specifically as follows: Watermelons are placed in an environment of 4℃ and pressed using a screw press. The initial watermelon juice is filtered through a 200-mesh vibrating screen to remove residual seed shells and coarse fibers, thus obtaining watermelon juice.

[0041] Furthermore, the pumping of watermelon juice into the lower chamber of the piston-isolated autoclave includes: Pump watermelon juice into the lower chamber of the piston-isolated autoclave through a sterile pipeline until the lower chamber is full and juice overflows from the outlet. Confirm that there is no residual air in the headspace and close the feed valve and discharge valve. Degassed pure water is added to the upper chamber of the autoclave, and the lower chamber is pressurized to 0.55 MPa by a piston to form a balanced lower chamber of the autoclave.

[0042] At this point, the watermelon juice is in a controlled initial back pressure state, slightly higher than normal pressure, which helps maintain stability when carbon dioxide is subsequently introduced.

[0043] Furthermore, the pressure holding process involving the introduction of supercritical carbon dioxide includes: Carbon dioxide is pressurized and heated to 42°C to bring it to a supercritical state, thus obtaining supercritical carbon dioxide. Supercritical carbon dioxide was introduced into the lower chamber of a high-pressure reactor using a microporous membrane disperser to stabilize the pressure in the lower chamber at 20.1 MPa. After all the supercritical carbon dioxide was injected, the inlet valve was closed and the mixture was allowed to stand for 8 minutes to obtain the watermelon juice intermediate.

[0044] Among them, a small portion of degassed pure water can be discharged by finely adjusting the pressure relief valve in the upper chamber, so that the piston moves slightly upward to stabilize the pressure at 20.1 MPa, and the amount of supercritical carbon dioxide introduced is 3.5% of the mass of watermelon juice.

[0045] This pressure-holding process allows the dissolved supercritical carbon dioxide to reach a distribution equilibrium in the watermelon juice, completing the hydration and acidification reactions. At the end of the pressure-holding stage, when the pH value stabilizes within the range of 4.45, it indicates that the acidification process has reached its end.

[0046] Furthermore, degassed pure water is injected into the upper chamber of the piston-isolated autoclave, and pressurization is achieved using HPP technology, including: After confirming that the inlet valve of the lower chamber is closed and sealed properly, degassed pure water is injected into the upper chamber of the piston-isolated autoclave. As the volume of the upper chamber increases, the free piston is pushed downward smoothly, causing the pressure in the lower chamber containing the watermelon juice intermediate to rise to 585 MPa. The temperature of the watermelon juice intermediate is controlled at 40℃ and maintained for 4 minutes to obtain high-pressure watermelon juice, with the pressure increase rate controlled at 3 MPa / s.

[0047] At this point, the phenolic hydroxyl groups of the endogenous polyphenols in watermelon juice undergo enhanced deprotonation, resulting in hydrophobic collapse of the molecules. The phenolic hydroxyl groups, originally encased in the hydration layer, are directionally exposed and coordinate with copper ions at the active site of polyphenol oxidase, occupying the catalytic site. Simultaneously, polyphenol molecules adsorb at the entrance of the peroxidase active pocket through hydrophobic interactions and hydrogen bonds, forming steric hindrance and preventing the substrate from approaching the heme active site. High pressure synergistically promotes the relaxation of the enzyme protein's tertiary structure and locks in a denatured conformation, resulting in the irreversible loss of enzyme activity.

[0048] Furthermore, the specific steps for forming the watermelon suspension are as follows: The lower chamber containing high-pressure watermelon juice is depressurized linearly to the node pressure, with the depressurization rate controlled at 4.5 MPa / s. When the pressure is reduced to the node pressure, the pressure relief valve is fully opened to reduce the pressure to 0.1 MPa, resulting in a watermelon suspension. The node pressure is set to 8 MPa.

[0049] Furthermore, the purification of the watermelon suspension includes: The watermelon suspension was kept at 37°C and allowed to settle naturally for 12 minutes to obtain layered watermelon juice. The layered watermelon juice was then centrifuged to separate the layers, and the supernatant was collected.

[0050] The layered watermelon juice is separated by centrifugation as follows: start the disc centrifuge, rinse it with sterile water beforehand and run it idle at the set speed of 3000 r / min, and pump the layered watermelon juice into the feed inlet.

[0051] Furthermore, the purification of the watermelon suspension also includes: The centrifuged liquid was filtered through a 0.5μm ceramic membrane to obtain watermelon filtrate. The watermelon filtrate was then cooled to 6℃ to obtain low-temperature watermelon juice.

[0052] Furthermore, the aseptic filling and storage of the refined watermelon suspension specifically involves: Low-temperature watermelon juice is poured into sterile bottles through a sterile filter and filled with nitrogen gas, then stored at 4°C.

[0053] Example 3 The preparation process of the watermelon juice sterilization process based on HPP technology provided in this embodiment is basically the same as that in Example 1. The main difference between the two lies in the specific composition and ratio of the raw materials used. The specific composition of the raw materials used in this embodiment is as follows: The process includes the following steps: Watermelon juice is extracted at low temperature, and the juice is collected. The juice is then pumped into the lower chamber of a piston-isolated high-pressure autoclave, where supercritical carbon dioxide is introduced for pressure treatment to obtain a watermelon juice intermediate. Deaerated pure water is injected into the upper chamber of a piston-isolated high-pressure autoclave, and the pressure is increased using HPP technology to chelate the polyphenols in the watermelon juice intermediate, thereby obtaining high-pressure watermelon juice. The watermelon suspension is formed by multiple stages of depressurization. The watermelon suspension is then refined and aseptically filled and stored.

[0054] The watermelon is juiced at low temperature, specifically as follows: Watermelons are placed in an environment of 4℃ and pressed using a screw press. The initial watermelon juice is filtered through a 200-mesh vibrating screen to remove residual seed shells and coarse fibers, thus obtaining watermelon juice.

[0055] Furthermore, the pumping of watermelon juice into the lower chamber of the piston-isolated autoclave includes: Pump watermelon juice into the lower chamber of the piston-isolated autoclave through a sterile pipeline until the lower chamber is full and juice overflows from the outlet. Confirm that there is no residual air in the headspace and close the feed valve and discharge valve. Degassed pure water is added to the upper chamber of the autoclave, and the lower chamber is pressurized to 0.5 MPa by a piston to form a balanced lower chamber of the autoclave.

[0056] At this point, the watermelon juice is in a controlled initial back pressure state, slightly higher than normal pressure, which helps maintain stability when carbon dioxide is subsequently introduced.

[0057] Furthermore, the pressure holding process involving the introduction of supercritical carbon dioxide includes: Carbon dioxide is pressurized and heated to 40-42°C to bring it to a supercritical state, thus obtaining supercritical carbon dioxide. Supercritical carbon dioxide was introduced into the lower chamber of a high-pressure reactor using a microporous membrane disperser to stabilize the pressure in the lower chamber at 20 MPa. After all the supercritical carbon dioxide was injected, the inlet valve was closed and the mixture was allowed to stand for 6 minutes to obtain the watermelon juice intermediate.

[0058] Among them, a small portion of degassed pure water can be discharged by finely adjusting the pressure relief valve in the upper chamber, so that the piston moves slightly upward to stabilize the pressure at 20MPa, and the amount of supercritical carbon dioxide introduced is 3.5% of the mass of watermelon juice.

[0059] This pressure-holding process allows the dissolved supercritical carbon dioxide to reach a distribution equilibrium in the watermelon juice, completing the hydration and acidification reactions. At the end of the pressure-holding stage, when the pH value stabilizes within the range of 4.4, it indicates that the acidification process has reached its end.

[0060] Furthermore, degassed pure water is injected into the upper chamber of the piston-isolated autoclave, and pressurization is achieved using HPP technology, including: After confirming that the inlet valve of the lower chamber is closed and sealed properly, degassed pure water is injected into the upper chamber of the piston-isolated autoclave. As the volume of the upper chamber increases, the free piston is pushed downward smoothly, causing the pressure in the lower chamber containing the watermelon juice intermediate to rise to 583 MPa. The temperature of the watermelon juice intermediate is controlled at 39°C and maintained for 4 minutes to obtain high-pressure watermelon juice, with the pressure increase rate controlled at 3 MPa / s.

[0061] At this point, the phenolic hydroxyl groups of the endogenous polyphenols in watermelon juice undergo enhanced deprotonation, resulting in hydrophobic collapse of the molecules. The phenolic hydroxyl groups, originally encased in the hydration layer, are directionally exposed and coordinate with copper ions at the active site of polyphenol oxidase, occupying the catalytic site. Simultaneously, polyphenol molecules adsorb at the entrance of the peroxidase active pocket through hydrophobic interactions and hydrogen bonds, forming steric hindrance and preventing the substrate from approaching the heme active site. High pressure synergistically promotes the relaxation of the enzyme protein's tertiary structure and locks in a denatured conformation, resulting in the irreversible loss of enzyme activity.

[0062] Furthermore, the specific steps for forming the watermelon suspension are as follows: The lower chamber containing high-pressure watermelon juice is depressurized linearly to the node pressure, with the depressurization rate controlled at 4.5 MPa / s. When the pressure is reduced to the node pressure, the pressure relief valve is fully opened to reduce the pressure to 0.1 MPa, resulting in a watermelon suspension. The node pressure is set to 8 MPa.

[0063] Furthermore, the purification of the watermelon suspension includes: The watermelon suspension was kept at 36°C and allowed to settle naturally for 10 minutes to obtain layered watermelon juice. The layered watermelon juice was then centrifuged to separate the layers, and the supernatant was collected.

[0064] The layered watermelon juice is separated by centrifugation as follows: start the disc centrifuge, rinse it with sterile water beforehand and run it idle at the set speed of 3000 r / min, and pump the layered watermelon juice into the feed inlet.

[0065] Furthermore, the purification of the watermelon suspension also includes: The centrifuged liquid was filtered through a 0.5μm ceramic membrane to obtain watermelon filtrate. The watermelon filtrate was then cooled to 5℃ to obtain low-temperature watermelon juice.

[0066] Furthermore, the aseptic filling and storage of the refined watermelon suspension specifically involves: Low-temperature watermelon juice is poured into sterile bottles through a sterile filter and filled with nitrogen gas, then stored at 4°C.

[0067] Comparative Example 1: The watermelon juice sterilization process based on HPP technology provided in this embodiment is largely the same as that in Example 1. The main difference is that only HPP technology is used for sterilization in this embodiment.

[0068] Comparative Example 2: The watermelon juice sterilization process based on HPP technology provided in this embodiment adopts pasteurization, which is existing technology and will not be described in detail here.

[0069] Comparative Example 3: The watermelon juice sterilization process based on HPP technology provided in this embodiment uses high-pressure carbon dioxide technology for sterilization, which is existing technology and will not be described in detail here.

[0070] Effect test The watermelon juice sterilization processes based on HPP technology in Examples 1-3 of this invention are referred to as Experimental Examples 1-3; the watermelon juice sterilization processes based on HPP technology in Comparative Examples 1-3 are referred to as Comparative Examples 1-3; and then the performance of each group of watermelon juice sterilization processes based on HPP technology in equal amounts is tested.

[0071] Security testing: SPF-grade KM mice, half male and half female, were selected and administered the corresponding watermelon juice samples by gavage at a dose of 5000 mg / kg·bw. The mice were observed for 14 consecutive days, and the mortality rate, weight change, and organ pathological abnormalities were recorded to determine the acute toxicity of the samples. All mice in the test groups showed no death, no symptoms of poisoning, no organ pathological damage, and their weight all showed a normal growth trend.

[0072] The tests were conducted in accordance with GB / T31121-2014 "Fruit and Vegetable Juices and Their Beverages" and GB15193.3-2014 "National Food Safety Standard Acute Oral Toxicity Test". The test subjects were Examples 1-3 and Comparative Examples 1-3. Each group was tested in parallel 3 times and the average value was taken.

[0073] Enzyme activity inhibition performance test: PPO enzyme activity was determined by the catechol colorimetric method and POD enzyme activity was determined by the guaiacol method. The residual enzyme activity rate was calculated. The lower the residual rate, the better the enzyme activity inhibition effect, which can directly reflect the anti-browning ability of watermelon juice. The data results are detailed in Table 1. Table 1: Enzyme Activity Inhibition Performance Table

[0074] Pasteurization can significantly inactivate enzymes through heat, resulting in the lowest PPO / POD residual rate; HPP alone has a very poor inactivation effect on POD.

[0075] Sterilization performance test: To determine the total bacterial count and mold / yeast count of the sample, the unit is CFU / mL. Please refer to Table 2: Table 2: Data on sterilization performance

[0076] The synergistic sterilization process in the example resulted in a lower number of microorganisms, which was superior to single HPP and pasteurization. While single HPP and pasteurization were effective, the residual microorganisms were slightly higher than in the example. High-pressure CO2 sterilization alone was incomplete, resulting in a significantly higher residual amount of microorganisms. The synergistic process of this invention has higher sterilization efficiency and stronger sterilization stability.

[0077] Nutritional retention performance: Vitamin C content was determined by 2,6-dichlorophenolindophenol titration, and total polyphenol content was determined by the Folin-phenol colorimetric method. Nutrient retention rates were calculated. Detailed data are shown in Table 3. Table 3: Nutritional Retention Performance Table

[0078] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0079] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A watermelon juice sterilization process based on HPP technology, characterized in that: The process includes the following steps: Watermelon juice is extracted at low temperature, and the juice is collected. The juice is then pumped into the lower chamber of a piston-isolated high-pressure autoclave, where supercritical carbon dioxide is introduced for pressure treatment to obtain a watermelon juice intermediate. Deaerated pure water is injected into the upper chamber of a piston-isolated high-pressure autoclave, and the pressure is increased using HPP technology to chelate the polyphenols in the watermelon juice intermediate, thereby obtaining high-pressure watermelon juice. The watermelon suspension is formed by multiple stages of depressurization. The watermelon suspension is then refined and aseptically filled and stored.

2. The watermelon juice sterilization process based on HPP technology according to claim 1, characterized in that: The process of pumping watermelon juice into the lower chamber of a piston-isolated autoclave includes: Pump the watermelon juice into the lower chamber of the piston-isolated autoclave through a sterile pipeline until the lower chamber is full, then close the feed valve and discharge valve. Degassed pure water is added to the upper chamber of the autoclave, and the lower chamber is pressurized by the piston to 0.45-0.55 MPa to form a balanced lower chamber of the autoclave.

3. The watermelon juice sterilization process based on HPP technology according to claim 1, characterized in that: The pressure holding process involving the introduction of supercritical carbon dioxide includes: Carbon dioxide is pressurized and heated to 40-42°C to bring it to a supercritical state, thus obtaining supercritical carbon dioxide. Supercritical carbon dioxide was introduced into the lower chamber of a high-pressure reactor using a microporous membrane disperser to stabilize the pressure in the lower chamber at 19.9–20.1 MPa. After all the supercritical carbon dioxide was injected, the inlet valve was closed and the mixture was allowed to stand for 5–8 minutes to obtain the watermelon juice intermediate.

4. The watermelon juice sterilization process based on HPP technology according to claim 1, characterized in that: The injection of degassed pure water into the upper chamber of the piston-isolated autoclave employs HPP technology for pressurization, including: Deaerated pure water is injected into the upper chamber of the piston-isolated high-pressure reactor to raise the pressure in the lower chamber containing the watermelon juice intermediate to 580-585 MPa. The temperature of the watermelon juice intermediate is controlled at 38-40℃ to obtain high-pressure watermelon juice.

5. The watermelon juice sterilization process based on HPP technology according to claim 4, characterized in that: The specific steps for forming the watermelon suspension are as follows: The pressure in the lower chamber containing high-pressure watermelon juice is reduced linearly to the node pressure. When the pressure is reduced to the node pressure, the pressure relief valve is fully opened to reduce the pressure to 0.1 MPa, thus obtaining a watermelon suspension.

6. The watermelon juice sterilization process based on HPP technology according to claim 5, characterized in that: The purification of the watermelon suspension includes: The watermelon suspension was maintained at 35–37°C and allowed to settle naturally for 8–12 minutes to obtain layered watermelon juice. The layered watermelon juice was then centrifuged to separate the layers, and the supernatant was collected.

7. The watermelon juice sterilization process based on HPP technology according to claim 6, characterized in that: The purification of the watermelon suspension also includes: The centrifuged liquid is filtered through a ceramic membrane to obtain watermelon filtrate. The watermelon filtrate is then cooled to 4–6°C to obtain low-temperature watermelon juice.

8. The watermelon juice sterilization process based on HPP technology according to claim 7, characterized in that: The process of aseptically filling and storing the refined watermelon suspension specifically involves: Low-temperature watermelon juice is poured into sterile bottles through a sterile filter and filled with nitrogen gas for storage at low temperature.

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