Non-thermal sterilization and flavor retention process for wild vegetable pre-prepared dishes

Abstract

This invention discloses a non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes, relating to the field of food processing technology. The process includes: sequentially subjecting the wild vegetable raw materials to acidic plasma-activated water baths and alkaline plasma-activated water baths, with both baths supplemented by ultrasonic treatment; subsequently, acidic plasma-activated water nano-atomization treatment; followed by low-temperature vacuum impregnation and low-temperature vacuum dehydration; after seasoning and mixing, a three-layer edible coating film is formed on the surface, comprising a chitosan layer, a nanocellulose layer, and a chitosan layer containing plant essential oils; finally, modified atmosphere packaging and storage and transportation under cold chain conditions. This invention, through stepwise treatment of acidic activated water sterilization and alkaline activated water enzyme inactivation, combined with atomization supplementary sterilization, flavor impregnation, microcapsule sustained release, and multi-layer coating, improves the microbial safety and flavor quality preservation of pre-prepared wild vegetable dishes without the addition of preservatives.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, and more specifically, to a non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes. Background Technology

[0002] Wild vegetables such as bracken, aralia shoots, and monkey's foot are increasingly being used in prepared food processing due to their unique flavors. However, wild vegetables have a high water content and strong endogenous polyphenol oxidase and peroxidase activity, making them prone to enzymatic browning and softening during processing and storage. Furthermore, the volatile flavor compounds in wild vegetables are heat-sensitive; conventional heat sterilization treatments easily lead to flavor loss, darkening of color, and a mushy texture.

[0003] In existing non-thermal sterilization processes, when using single plasma-activated water immersion treatment, the chemical composition of the immersion medium remains constant during the process. This makes it difficult to simultaneously meet the different chemical environment requirements of efficient sterilization and thorough enzyme inactivation. Typically, this results in sufficient sterilization but insufficient enzyme inactivation, or sufficient enzyme inactivation but limited sterilization efficiency. Furthermore, the immersion method involves prolonged contact between the material and the aqueous phase, which easily leads to the leaching loss of water-soluble amino acids, organic acids, and other flavor components. Regarding the process sequence, existing solutions often sterilize the finished product after seasoning. With flavor substances and sterilization agents in the same system, direct contact between reactive oxygen species and volatile flavor components can easily trigger oxidation reactions, leading to a decline in flavor quality. Therefore, a non-thermal sterilization and flavor preservation process for pre-cooked wild vegetables is proposed to address the above problems. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a non-thermal sterilization and flavor preservation process for pre-prepared wild vegetables. This addresses the problem that the existing plasma-activated water treatment process is difficult to simultaneously achieve efficient sterilization and thorough enzyme inactivation in the processing of pre-prepared wild vegetables, as well as the problems that soaking methods easily cause the loss of water-soluble flavor components and the lack of flavor oxidation caused by sterilization after seasoning.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes, comprising the following steps: S1: The wild vegetable raw materials are subjected to acidic plasma-activated water bath treatment and alkaline plasma-activated water bath treatment sequentially. The acidic plasma-activated water has a pH of 2.8-3.5 and contains hydrogen peroxide and nitrite ions, while the alkaline plasma-activated water has a pH of 8.0-9.0 and contains hydrogen peroxide. The temperature for both bath treatments is 4-8℃. Under acidic conditions, nitrite and peroxynitrite have high permeability to microbial cell membranes to achieve efficient sterilization. Under alkaline conditions, hydrogen peroxide has a selective oxidizing effect on the sulfhydryl groups in the active centers of polyphenol oxidase and peroxidase to inactivate enzymes. The low-temperature environment helps to slow down the decomposition of active species and the metabolism of the materials themselves.

[0006] S2: The semi-finished wild vegetable product processed in step S1 is subjected to low-temperature vacuum impregnation. The impregnation solution contains trehalose, ascorbic acid, citric acid, sodium chloride, and calcium lactate. After impregnation, low-temperature vacuum dehydration is performed. Under vacuum conditions, the impregnation solution is introduced into the pores of the wild vegetable tissue. Trehalose plays a protective role in the cell membrane structure during subsequent dehydration and storage. Ascorbic acid and citric acid provide antioxidant and metal ion chelation effects. Calcium lactate forms crosslinks with pectin to maintain crispness.

[0007] S3: The semi-finished wild vegetable product after dehydration in step S2 is seasoned and mixed to form an edible coating on the surface. The edible coating comprises a chitosan layer, a nanocellulose layer, and a chitosan layer containing plant essential oils. The seasoning step is carried out after sterilization and enzyme inactivation. The seasoning and flavor components do not come into contact with the bactericidal agents to avoid flavor oxidation. In the multi-layer coating structure, the chitosan layer provides basic antibacterial and film-forming properties, the nanocellulose layer improves gas barrier properties, and the outer layer containing plant essential oils provides continuous antibacterial and antioxidant protection.

[0008] S4: The product obtained in step S3 is subjected to modified atmosphere packaging and stored and transported under cold chain conditions of 0–4°C. The low-oxygen, high-carbon dioxide environment inside the modified atmosphere packaging helps inhibit the proliferation of aerobic microorganisms and enzymatic browning, while the cold chain conditions further delay quality deterioration.

[0009] Furthermore, both the acidic plasma-activated water bath treatment and the alkaline plasma-activated water bath treatment in step S1 are supplemented with ultrasonic waves, with an ultrasonic frequency of 20–40 kHz and a power density of 0.3–0.5 W / cm². 2 The ultrasonic waves are applied in pulse mode, and the cavitation effect of the ultrasound accelerates the mass transfer of active species to the material surface to improve processing efficiency. The pulse mode also helps to control temperature rise and reduce mechanical damage.

[0010] The acid plasma activated water immersion treatment time is 3-5 minutes. The acid plasma activated water is prepared by treating deionized water with dielectric barrier discharge plasma, wherein the hydrogen peroxide concentration is 150-250 μM, the nitrite ion concentration is 200-400 μM, and the redox potential is not less than 800 mV.

[0011] The alkaline plasma activated water immersion treatment time is 5-8 minutes. The alkaline plasma activated water is prepared by treating deionized water with dielectric barrier discharge plasma and then adjusting the pH value to 8.0-9.0 with a food-grade phosphate buffer system. The concentration of hydrogen peroxide is 150-250 μM and the concentration of nitrite ions is not higher than 100 μM.

[0012] The specified concentration and potential range ensure bactericidal and enzyme-inactivating effects while avoiding excessive oxidation of plant tissues.

[0013] Furthermore, no rinsing operation is performed between the acidic plasma activated water bath treatment and the alkaline plasma activated water bath treatment in step S1. After the alkaline bath is injected, it automatically neutralizes the residue of the acidic bath on the material surface from the previous step, eliminating the intermediate rinsing step and reducing the total contact time between the material and the water phase, which helps to reduce the leaching loss of water-soluble flavor components.

[0014] Furthermore, after the alkaline plasma-activated water immersion treatment in step S1 and before the low-temperature vacuum impregnation in step S2, the process includes placing the semi-finished wild vegetable product in a sealed chamber for nano-atomization treatment with acidic plasma-activated water. The atomization method is ultrasonic atomization, with droplet size of 5–15 μm, atomization time of 5–8 min, and chamber temperature of 4–8 °C. Micron-sized droplets can penetrate irregular structures such as surface depressions, cut edges, and vascular bundle ends of the material, precisely killing residual microorganisms after immersion treatment and improving sterilization uniformity without prolonging the immersion time.

[0015] Furthermore, the composition of the impregnation solution in step S2, by mass-volume percentage, includes: trehalose 3%–5%, ascorbic acid 0.1%–0.2%, citric acid 0.05%–0.1%, sodium chloride 0.5%–1.0%, calcium lactate 0.1%–0.2%, with the remainder being water and flavor concentrate recovered during the processing of wild vegetables.

[0016] The reuse of flavor concentrate allows water-soluble flavor components such as free amino acids and organic acids lost during processing to re-enter the material structure. The process conditions for low-temperature vacuum impregnation are a vacuum degree of 0.06–0.08 MPa and a temperature of 15–20 °C. After maintaining the vacuum condition for 10–15 minutes, the pressure is restored to normal and the impregnation continues for another 5–10 minutes. The vacuum condition promotes the penetration of the impregnation solution into the pores of the material, and the restoration of normal pressure further promotes the uniform distribution of components.

[0017] Furthermore, flavor microcapsules are added to the impregnation solution. The core material of the flavor microcapsules comprises a concentrated wild vegetable flavor extract and trehalose, while the wall material comprises sodium alginate and chitosan. The amount of microcapsules added to the impregnation solution is 5%–8% by weight / volume, and the particle size of the microcapsules is 200–500 μm. During storage, the microcapsules gradually release the flavor substances from the core material through the slow action of the endogenous enzymes of the wild vegetables on the wall material. Trehalose plays a protective role for the flavor components in the core material, which helps to achieve continuous replenishment of flavor during storage.

[0018] Furthermore, the edible coating in step S3 is formed by a layer-by-layer spraying method. The first layer is a chitosan solution with a mass-volume percentage of 1.0% to 1.5%, the second layer is a nanocellulose suspension with a mass-volume percentage of 0.5% to 1.0%, and the third layer is a chitosan solution containing a mass-volume percentage of 0.1% to 0.2% plant essential oil and 0.3% to 0.5% glycerol. Each layer is dried and cured in hot air at 40 to 45°C after spraying, and the total thickness of the coating is 15 to 30 μm.

[0019] Layer-by-layer spraying allows each layer to cure independently, forming a functional gradient structure. The chitosan layer directly bonds with the material surface, providing basic antibacterial and adhesion properties. The nanocellulose layer fills the micropores in the chitosan membrane to reduce oxygen permeability. The essential oil-containing outer layer continuously releases antibacterial and antioxidant active substances during storage. Glycerin acts as a plasticizer to improve the flexibility of the coating.

[0020] Furthermore, the plant essential oil is wild vegetable essential oil, and the mass ratio of the added nanocellulose to chitosan is 1:2 to 1:3. The wild vegetable essential oil has the same flavor as the main material, avoiding the introduction of external odors. Within the specified mass ratio range, the nanocellulose can effectively improve the density and mechanical strength of the chitosan film without significantly affecting the coating transparency.

[0021] Furthermore, the seasonings used in step S3, based on the weight percentage of the semi-finished wild vegetable product, include: 3%–5% vegetable oil, 1.5%–2.5% salt, 1%–2% white sugar, 0.5%–1.5% spice extract, 0.3%–0.5% yeast extract, and 0.01%–0.02% rosemary extract. Rosemary extract provides natural antioxidant activity to delay the oxidation of vegetable oil, yeast extract enhances the richness of the flavor, and salt and white sugar simultaneously participate in water activity regulation.

[0022] Furthermore, the modified atmosphere packaging described in step S4 uses a high-barrier composite film for packaging, with the gas composition inside the packaging being 1%–3% oxygen, 15%–20% carbon dioxide, and the remainder being nitrogen. The low oxygen concentration inhibits enzymatic browning catalyzed by polyphenol oxidase and the growth of aerobic microorganisms, while the high carbon dioxide concentration delays chlorophyll degradation and further inhibits microbial proliferation. The high-barrier composite film maintains the stability of the gas composition inside the packaging.

[0023] Compared with the prior art, the technical effects and advantages of the present invention are as follows: (1) The acidic plasma activated water bath utilizes the high permeability of nitrite and peroxynitrite to microbial cell membranes under low pH conditions to achieve the main bactericidal function, while the alkaline plasma activated water bath utilizes hydrogen peroxide to selectively oxidize the sulfhydryl groups of polyphenol oxidase and peroxidase active sites under alkaline conditions to achieve the enzyme inactivation function. The two baths are respectively controlled to target the optimal chemical environment for bactericidal and enzyme inactivation, which helps to avoid the problem that the two objectives are difficult to achieve simultaneously when using single activated water treatment. Both baths are supplemented with the cavitation effect of ultrasound to accelerate the mass transfer of active species to the material surface and shorten the treatment time.

[0024] (2) No rinsing operation is performed between the two immersion treatments. After the alkaline bath is injected, the residue of the previous acidic bath on the surface of the material is automatically neutralized, eliminating the intermediate rinsing step and reducing the total contact time between the material and water, which helps to reduce the leaching loss of water-soluble flavor components.

[0025] (3) After alkaline immersion, acidic plasma activated water nano-atomization treatment is added. Micron-sized droplets can penetrate into irregular structures such as depressions, cut edges and vascular bundle ends on the surface of wild vegetables, and accurately kill the microorganisms remaining after immersion treatment, improving the uniformity of sterilization without prolonging the immersion time.

[0026] (4) The impregnation solution contains trehalose, ascorbic acid, citric acid, sodium chloride, and calcium lactate. Under vacuum conditions, these components are introduced into the pores of the wild vegetable tissue. Trehalose helps protect the cell membrane structure during subsequent dehydration and storage, ascorbic acid and citric acid provide antioxidant and metal ion chelation effects, and calcium lactate forms crosslinks with pectin to help maintain crispness. Flavor microcapsules with sodium alginate and chitosan as wall materials are also added to the impregnation solution. The core material encapsulates the concentrated flavor of wild vegetables and trehalose, which gradually release flavor substances during storage with the action of endogenous enzymes, helping to improve the persistence of flavor retention.

[0027] (5) The seasoning and mixing steps are carried out after sterilization, enzyme inactivation and dehydration. The seasoning and its flavor components do not come into contact with any sterilization factors, thus avoiding the oxidation of flavor substances by reactive oxygen species in terms of process sequence.

[0028] (6) After flavoring, a three-layer edible coating is formed on the surface, consisting of a chitosan layer, a nanocellulose layer, and a chitosan layer containing plant essential oils. The chitosan layer provides basic film-forming and antibacterial properties, the nanocellulose layer fills the micropores in the chitosan film to improve gas barrier properties, and the outer layer containing plant essential oils provides continuous antibacterial and antioxidant protection. The three-layer structure together delays the impact of oxygen and water vapor on the quality of the material.

[0029] (7) Modified atmosphere packaging uses a high-barrier composite film and is filled with a mixed gas of 1% to 3% oxygen, 15% to 20% carbon dioxide, and the remainder nitrogen. The low-oxygen environment helps to inhibit the proliferation of aerobic microorganisms and enzymatic browning, while the high-carbon dioxide environment helps to delay chlorophyll degradation. Combined with cold chain storage and transportation conditions, it further maintains product quality. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0032] As attached Figure 1 The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes is shown below, and its specific implementation details are as follows: Example 1

[0033] This embodiment uses bracken fern as the raw material for wild vegetables and provides a non-heat sterilization and flavor preservation process for pre-cooked wild vegetable dishes, including the following steps: S1. After selection and cleaning, the bracken fern raw materials are cut into 4cm segments to obtain wild vegetable raw materials. The wild vegetable raw materials are then subjected to acidic plasma activated water bath treatment and alkaline plasma activated water bath treatment in sequence.

[0034] The preparation method of acidic plasma activated water is as follows: using deionized water as the working medium, a dielectric barrier discharge plasma device is used for discharge treatment with a discharge voltage of 16kV, a frequency of 8kHz, and a treatment time of 18min, to prepare acidic plasma activated water with a pH value of 3.2, a hydrogen peroxide concentration of 210μM, a nitrite ion concentration of 320μM, and a redox potential of 860mV.

[0035] The preparation method of alkaline plasma activated water is as follows: using deionized water as the working medium, a dielectric barrier discharge plasma device is used for discharge treatment with a discharge voltage of 16kV, a frequency of 8kHz, and a treatment time of 8min. Then, the pH value is adjusted to 8.6 with a phosphate buffer system composed of food-grade disodium hydrogen phosphate and potassium dihydrogen phosphate, and alkaline plasma activated water with a hydrogen peroxide concentration of 210μM and a nitrite ion concentration of 75μM is prepared.

[0036] Both acidic plasma-activated water bath treatment and alkaline plasma-activated water bath treatment were supplemented with ultrasonic waves at a frequency of 30 kHz and a power density of 0.4 W / cm². 2 The plasma was applied in a pulsed mode, consisting of 10 seconds of ultrasound followed by a 5-second interval. The temperature for both immersion treatments was 6°C. The acidic plasma-activated water immersion treatment lasted 4 minutes, and the alkaline plasma-activated water immersion treatment lasted 6 minutes. No rinsing was performed between the two immersion treatments.

[0037] S2. The semi-finished wild vegetable product processed in step S1 is placed in a sealed chamber and subjected to nano-atomization treatment with freshly prepared acidic plasma-activated water. The atomization method is ultrasonic atomization, with an ultrasonic atomization power of 25W, a droplet size of 8-12μm, an atomization treatment time of 6min, and a chamber temperature of 6℃.

[0038] S3. The semi-finished wild vegetable product processed in step S2 is subjected to low-temperature vacuum impregnation. The composition of the impregnation solution, by mass-volume percentage, includes: trehalose 4%, ascorbic acid 0.15%, citric acid 0.08%, sodium chloride 0.8%, calcium lactate 0.15%, with the remainder being water and flavor concentrate recovered during the processing of wild vegetables.

[0039] The method for recovering the flavor concentrate is as follows: the water-soluble flavor components dissolved during the washing process are concentrated to 1 / 4 of their original volume using a rotary evaporator at a temperature of 45°C and a vacuum degree of 0.085MPa.

[0040] Flavor microcapsules were also added to the impregnation solution at a weight-volume percentage of 6%. The core material of the flavor microcapsules consisted of the aforementioned wild vegetable flavor concentrate and trehalose, with trehalose accounting for 18% of the core material weight. The wall material consisted of sodium alginate and chitosan.

[0041] The preparation method of flavor microcapsules is as follows: sodium alginate is prepared into an aqueous solution with a mass-volume percentage of 1.8%; flavor concentrate, trehalose and medium-chain triglycerides are mixed in a mass ratio of 75:18:7 and then subjected to high-speed shear homogenization at a speed of 12000 rpm for 4 min to form an O / W type emulsion. Add the emulsion to the sodium alginate solution and stir until homogeneous. Then add the mixture to a 3% (w / v) calcium chloride solution and let it solidify for 15 minutes. After rinsing with sterile deionized water, the mixture was transferred to a 0.4% (w / v) chitosan solution with a pH of 5.2 and stirred for 15 min to adsorb. After rinsing again with sterile deionized water, the product is vacuum dried at 40°C until the surface moisture is removed, thus obtaining flavor microcapsules with a particle size of 280–380 μm.

[0042] The low-temperature vacuum impregnation process conditions were: vacuum degree 0.07 MPa, temperature 18℃, maintaining vacuum for 12 minutes, then restoring to normal pressure and continuing immersion for 8 minutes. After impregnation, low-temperature vacuum dehydration was performed under the following conditions: temperature 48℃, vacuum degree 0.085 MPa, and dehydration time 40 minutes.

[0043] S4. Season and mix the dehydrated wild vegetable semi-finished product from step S3. The seasonings, by weight percentage of the wild vegetable semi-finished product, include: 4% vegetable oil, 2% salt, 1.5% white sugar, 1.0% spice extract, 0.4% yeast extract, and 0.015% rosemary extract, wherein the spice extract is a mixture of garlic powder and ginger powder.

[0044] After seasoning, an edible coating is formed on the surface. The edible coating is formed by layer-by-layer spraying: the first layer is a chitosan solution with a mass-volume percentage of 1.2%, in which chitosan is dissolved in an acetic acid solution with a mass-volume percentage of 1.0%, and the spraying amount is 0.6% of the material mass. After spraying, it is dried in hot air at 42℃ for 1.5 min. The second layer is a nanocellulose suspension with a mass-volume percentage of 0.8%, and the spraying amount is 0.6% of the material mass. After spraying, it is dried in hot air at 42℃ for 1.5 minutes. The third layer is a chitosan solution containing 0.15% by volume of plant essential oil and 0.4% by volume of glycerol. The chitosan content is 1.2% by volume, and the coating amount is 0.6% of the material mass. After spraying, it is dried in hot air at 42℃ for 2 minutes. The total coating thickness is 20–25 μm.

[0045] The plant essential oil is extracted from bracken fern processing byproducts through steam distillation, including old bracken fern leaves and stem bark. The mass ratio of nanocellulose to chitosan is 1:2.5.

[0046] S5. Perform modified atmosphere packaging on the product obtained in step S4. Modified atmosphere packaging uses a PA / EVOH / PE high-barrier composite film, with the gas composition inside the packaging being 2% oxygen, 18% carbon dioxide, and the remainder nitrogen. After packaging, the finished product is stored and transported under a cold chain condition at 2℃.

[0047] The test results of various indicators of the bracken pre-cooked vegetable product prepared in this embodiment after storage at 0-4℃ for 6 months are shown in Table 1. Example 2

[0048] This embodiment uses Aralia elata shoots as the raw material for wild vegetables, and the process steps are basically the same as in Embodiment 1, except that: In step S1, the temperature of the acidic plasma activated water bath treatment is 5°C and the time is 3.5 min, and the temperature of the alkaline plasma activated water bath treatment is 5°C and the time is 5.5 min. No rinsing operation is performed between the two bath treatments.

[0049] The preparation parameters for acidic plasma activated water are: discharge voltage 15kV, frequency 7kHz, treatment time 17min, pH value 3.0, hydrogen peroxide concentration 185μM, nitrite ion concentration 280μM, and redox potential 830mV.

[0050] The preparation parameters for alkaline plasma activated water are: discharge voltage 15kV, frequency 7kHz, treatment time 7min, pH adjusted to 8.4 with phosphate buffer system, hydrogen peroxide concentration 185μM, and nitrite ion concentration 65μM.

[0051] In step S2, the atomization time is 5 min, the chamber temperature is 5℃, and the droplet size is 6~10μm.

[0052] In step S3, the composition of the impregnation solution, by mass-volume percentage, is: trehalose 3.5%, ascorbic acid 0.12%, citric acid 0.06%, sodium chloride 0.6%, calcium lactate 0.12%, with the remainder being water and flavor concentrate recovered during the processing of Aralia elata buds. The amount of flavor microcapsules added is 5.5% by mass-volume percentage, and the microcapsule particle size is 250–350 μm. The low-temperature vacuum impregnation is performed at a vacuum degree of 0.065 MPa and a temperature of 16°C for 11 minutes, followed by restoring to normal pressure and continuing impregnation for another 7 minutes. The low-temperature vacuum dehydration is performed at a temperature of 46°C for 35 minutes.

[0053] In step S4, the plant essential oil is extracted from the processing by-products of Aralia elata buds through steam distillation. In the edible coating, the first layer is a chitosan solution with a mass-volume percentage of 1.1%, the second layer is a nanocellulose suspension with a mass-volume percentage of 0.7%, and the third layer contains a chitosan solution with a mass-volume percentage of 0.12% Aralia elata bud essential oil and 0.35% glycerol, with a chitosan mass-volume percentage of 1.1%. The mass ratio of nanocellulose to chitosan is 1:2.2, and the total coating thickness is 18–22 μm.

[0054] In step S5, the gas composition inside the modified atmosphere packaging is 1.5% oxygen, 16% carbon dioxide, and the remainder nitrogen.

[0055] The test results of various indicators of the pre-cooked Aralia elata sprouts prepared in this embodiment after being stored at 0-4℃ for 6 months are shown in Table 1. Example 3

[0056] This embodiment uses monkey leg as the raw material for wild vegetables, and the process steps are basically the same as in embodiment 1, except that: In step S1, the temperature of the acidic plasma activated water bath treatment is 7°C and the time is 4.5 min, and the temperature of the alkaline plasma activated water bath treatment is 7°C and the time is 7 min. No rinsing operation is performed between the two bath treatments.

[0057] The preparation parameters for acidic plasma activated water are: discharge voltage 17kV, frequency 9kHz, treatment time 19min, pH value 3.4, hydrogen peroxide concentration 235μM, nitrite ion concentration 370μM, and redox potential 880mV.

[0058] The preparation parameters for alkaline plasma activated water are: discharge voltage 17kV, frequency 9kHz, treatment time 9min, pH adjusted to 8.8 with phosphate buffer system, hydrogen peroxide concentration 235μM, and nitrite ion concentration 88μM.

[0059] In step S2, the atomization time is 7 minutes, the chamber temperature is 7°C, and the droplet size is 10–14 μm.

[0060] In step S3, the composition of the impregnation solution, by mass-volume percentage, is: trehalose 4.5%, ascorbic acid 0.18%, citric acid 0.09%, sodium chloride 0.9%, calcium lactate 0.18%, with the remainder being water and flavor concentrate recovered during the monkey leg processing. The amount of flavor microcapsules added is 7% by mass-volume percentage, and the microcapsule particle size is 320–420 μm. The low-temperature vacuum impregnation is performed at a vacuum degree of 0.075 MPa and a temperature of 19°C for 13 minutes, followed by restoring to normal pressure and continuing impregnation for another 9 minutes. The low-temperature vacuum dehydration is performed at a temperature of 49°C for 42 minutes.

[0061] In step S4, the first layer of the edible coating contains a chitosan solution with a mass-volume percentage of 1.4%, the second layer contains a nanocellulose suspension with a mass-volume percentage of 0.9%, and the third layer contains a chitosan solution with a mass-volume percentage of 0.18% plant essential oil and 0.45% glycerol, with a chitosan mass-volume percentage of 1.4%. The mass ratio of nanocellulose to chitosan is 1:2.8, and the total thickness of the coating is 22-28 μm.

[0062] In step S5, the gas composition inside the modified atmosphere packaging is 2.5% oxygen, 20% carbon dioxide, and the remainder nitrogen.

[0063] The test results of various indicators of the pre-cooked monkey leg dish product prepared in this embodiment after being stored at 0-4℃ for 6 months are shown in Table 1.

[0064] Comparative Example 1 The process steps of this comparative example are basically the same as those of Example 1, except that in step S1, only acidic plasma-activated water bath treatment is performed, and alkaline plasma-activated water bath treatment is not performed; the other steps are the same. The test results of various indicators of the prepared bracken fern pre-cooked product after storage at 0-4℃ for 6 months are shown in Table 2.

[0065] Comparative Example 2 The process steps of this comparative example are basically the same as those of Example 1, except that a sterile cold water rinsing operation is added between the acidic plasma activated water bath treatment and the alkaline plasma activated water bath treatment in step S1. The temperature of the sterile cold water used is 6°C, and the rinsing time is 30 seconds. The remaining steps are the same. The test results of various indicators of the prepared bracken fern pre-processed product after storage at 0-4°C for 6 months are shown in Table 2.

[0066] Comparative Example 3 The process steps of this comparative example are basically the same as those of Example 1, except that the nano-atomization treatment in step S2 is omitted, and the process proceeds directly to step S3 after treatment in step S1. The remaining steps are the same. The test results of various indicators of the prepared bracken fern product after storage at 0-4℃ for 6 months are shown in Table 2.

[0067] Comparative Example 4 The process steps of this comparative example are basically the same as those of Example 1, except that in step S4, the edible coating is only coated with a single layer of chitosan solution, the chitosan solution has a mass-volume percentage of 1.2%, the total amount of coating is 1.8% of the material mass, and it is dried in hot air at 42℃ for 5 minutes after spraying, without forming a three-layer structured coating. The remaining steps are the same. The test results of various indicators of the prepared bracken fern product after storage at 0-4℃ for 6 months are shown in Table 2.

[0068] Comparative Example 5 The process steps of this comparative example are basically the same as those of Example 1, except that flavor microcapsules are not added to the impregnation solution in step S3, while the other steps are the same. The test results of various indicators of the prepared bracken fern products after storage at 0-4℃ for 6 months are shown in Table 2.

[0069] Comparative Example 6 The process steps of this comparative example are basically the same as those of Example 1, except that in step S5, ordinary polyethylene film is used for ordinary air packaging, and the gas inside the packaging is natural air. The remaining steps are the same. The test results of various indicators of the prepared bracken fern product after storage at 0-4℃ for 6 months are shown in Table 2.

[0070] Table 1. Quality index test results of products from each example after storage at 0–4°C for 6 months. Table 2. Quality index test results of each comparative product after storage at 0–4℃ for 6 months. The test results in Tables 1 and 2 show that: Examples 1 to 3 employed the complete process of this invention, and the total bacterial count of the products was below 1×10⁻⁶ after 6 months of storage. 3 The CFU / g, polyphenol oxidase activity inhibition rate all reached over 91%, the relative retention rate of volatile flavor substances all reached over 89%, and the hardness retention rate all reached over 87%.

[0071] Comparative Example 1, which omitted the alkaline plasma-activated water bath treatment, showed a decrease in polyphenol oxidase activity inhibition rate of approximately 38 percentage points, a decrease in flavor retention rate of approximately 17 percentage points, and a decrease in hardness retention rate of approximately 17 percentage points compared to Example 1. This indicates that the alkaline activated water bath treatment plays an important role in inactivating endogenous enzymes and maintaining the texture and flavor of the product.

[0072] Comparative Example 2, which added a rinsing operation between two immersions, had a slightly higher total bacterial count than Example 1, and a slightly lower enzyme inactivation effect and flavor retention rate, indicating that omitting the intermediate rinsing step helps maintain the sterilization and enzyme inactivation effects.

[0073] Comparative Example 3, which omitted the nano-atomization treatment, showed an increase in total bacterial count of approximately 1.5 × 10⁻⁶ compared to Example 1. 3 The CFU / g indicates that nano-atomization treatment has a significant effect on the precise elimination of residual microorganisms on the surface.

[0074] Comparative Example 4, which uses only a single-layer chitosan coating, showed a decrease in flavor retention rate of approximately 8 percentage points and a decrease in hardness retention rate of approximately 11 percentage points compared to Example 1. This indicates that the three-layer coating structure is superior to the single-layer coating in delaying quality deterioration.

[0075] Comparative Example 5, without the addition of flavor microcapsules, showed a flavor retention rate that decreased by approximately 7 percentage points compared to Example 1, indicating that the sustained-release effect of flavor microcapsules helps to continuously replenish flavor during storage.

[0076] Comparative Example 6, which used ordinary air packaging, had a total bacterial count that was one order of magnitude higher than that of Example 1, and a flavor retention rate that decreased by about 13 percentage points, indicating that modified atmosphere packaging has a significant effect on inhibiting microbial growth and maintaining flavor.

[0077] The above results indicate that the various process steps of this invention have a synergistic effect, jointly achieving a comprehensive improvement in the microbial safety, enzyme activity inhibition effect, and flavor quality of pre-prepared wild vegetable dishes.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes, characterized in that, Includes the following steps: S1: The wild vegetable raw materials are subjected to acidic plasma activated water bath treatment and alkaline plasma activated water bath treatment in sequence. The acidic plasma activated water has a pH value of 2.8 to 3.5 and contains hydrogen peroxide and nitrite ions. The alkaline plasma activated water has a pH value of 8.0 to 9.0 and contains hydrogen peroxide. The temperature of both bath treatments is 4 to 8°C. S2: The semi-finished wild vegetables processed in step S1 are subjected to low-temperature vacuum impregnation. The impregnation solution contains trehalose, ascorbic acid, citric acid, sodium chloride and calcium lactate. After impregnation, the vegetables are subjected to low-temperature vacuum dehydration. S3: Season and mix the semi-finished wild vegetables after dehydration in step S2. After seasoning, an edible coating is formed on the surface. The edible coating includes a chitosan layer, a nanocellulose layer and a chitosan layer containing plant essential oils. S4: The product obtained in step S3 is packaged with modified atmosphere packaging and stored and transported under cold chain conditions of 0-4℃.

2. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 1, characterized in that: In step S1, both the acidic plasma-activated water bath treatment and the alkaline plasma-activated water bath treatment are supplemented with ultrasonic waves. The ultrasonic frequency is 20–40 kHz, and the power density is 0.3–0.5 W / cm². 2 And applied in a pulse mode; The acid plasma activated water immersion treatment time is 3-5 min. The acid plasma activated water is prepared by treating deionized water with dielectric barrier discharge plasma, wherein the hydrogen peroxide concentration is 150-250 μM, the nitrite ion concentration is 200-400 μM, and the redox potential is not less than 800 mV. The alkaline plasma activated water immersion treatment time is 5-8 minutes. The alkaline plasma activated water is prepared by treating deionized water with dielectric barrier discharge plasma and then adjusting the pH value to 8.0-9.0 with a food-grade phosphate buffer system. The concentration of hydrogen peroxide is 150-250 μM and the concentration of nitrite ions is not higher than 100 μM.

3. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 2, characterized in that: No rinsing operation is performed between the acidic plasma activated water bath treatment and the alkaline plasma activated water bath treatment in step S1.

4. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 1, characterized in that: After the alkaline plasma activated water bath treatment in step S1 and before the low-temperature vacuum impregnation in step S2, the process further includes placing the semi-finished wild vegetable product in a sealed chamber for nano-atomization treatment with acidic plasma activated water. The atomization method is ultrasonic atomization, the droplet size is 5-15 μm, the atomization treatment time is 5-8 min, and the temperature inside the chamber is 4-8℃.

5. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 1, characterized in that: The composition of the impregnation solution in step S2, by mass-volume percentage, includes: trehalose 3%–5%, ascorbic acid 0.1%–0.2%, citric acid 0.05%–0.1%, sodium chloride 0.5%–1.0%, calcium lactate 0.1%–0.2%, with the remainder being water and flavor concentrate recovered during the processing of wild vegetables; the process conditions for low-temperature vacuum impregnation are a vacuum degree of 0.06–0.08 MPa and a temperature of 15–20°C, maintained under vacuum conditions for 10–15 min, then restored to normal pressure and continued to soak for 5–10 min.

6. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 5, characterized in that: The impregnation solution also contains flavor microcapsules. The core material of the flavor microcapsules includes concentrated wild vegetable flavor liquid and trehalose, and the wall material includes sodium alginate and chitosan. The amount of microcapsules added to the impregnation solution is 5% to 8% by mass and volume, and the particle size of the microcapsules is 200 to 500 μm.

7. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 1, characterized in that: The edible coating in step S3 is formed by a layer-by-layer spraying method. The first layer is a chitosan solution with a mass-volume percentage of 1.0% to 1.5%, the second layer is a nanocellulose suspension with a mass-volume percentage of 0.5% to 1.0%, and the third layer is a chitosan solution containing a mass-volume percentage of 0.1% to 0.2% plant essential oil and 0.3% to 0.5% glycerol. Each layer is dried and cured in hot air at 40 to 45°C after spraying, and the total thickness of the coating is 15 to 30 μm.

8. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 7, characterized in that: The plant essential oil is a wild vegetable plant essential oil, and the mass ratio of the added nanocellulose to chitosan is 1:2 to 1:

3.

9. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 1, characterized in that: The seasonings used in step S3, based on the mass percentage of the semi-finished wild vegetable product, include: 3%–5% vegetable oil, 1.5%–2.5% salt, 1%–2% white sugar, 0.5%–1.5% spice extract, 0.3%–0.5% yeast extract, and 0.01%–0.02% rosemary extract.

10. The non-thermal sterilization and flavor preservation process for pre-prepared wild vegetable dishes according to claim 1, characterized in that: The modified atmosphere packaging described in step S4 uses a high-barrier composite film for packaging, and the gas ratio inside the packaging is 1% to 3% oxygen, 15% to 20% carbon dioxide, and the remainder is nitrogen.

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