Method for activating water-steam superheated sterilization

Abstract

This invention discloses a combined sterilization method using activated water and superheated steam, belonging to the field of food sterilization technology. The method includes the following steps: S1, immersing the food in plasma-activated water for soaking treatment, then removing surface moisture; S2, treating the food with superheated steam, cooling, and completing sterilization. This invention treats the food with plasma-activated water followed by superheated steam treatment. Specifically, it first utilizes reactive oxygen and nitrogen to damage the structure of microorganisms and weaken their tolerance, then further enhances inactivation through superheated steam. While achieving highly efficient sterilization, it also effectively reduces the risk of quality changes such as lipid oxidation and textural deterioration. This sterilization method is applicable to various food systems, including meat, seafood, vegetables, and grains, and has the advantages of high processing efficiency, wide applicability, and good quality preservation.

Description

Technical Field

[0001] This invention relates to the field of food sterilization technology, and in particular to a method for sterilization using activated water and superheated steam. Background Technology

[0002] During processing, storage, transportation, and sales, food is susceptible to microbial contamination and subsequent deterioration of its physicochemical properties, leading to a decline in food quality and even posing food safety risks. Currently, food sterilization technologies are mainly divided into two categories: thermal treatment and non-thermal treatment. Thermal sterilization, such as superheated steam treatment, has advantages such as high heat transfer efficiency, short processing time, and low-oxygen treatment. However, to achieve a high sterilization effect, it is often necessary to increase the processing temperature or extend the processing time, which frequently leads to moisture loss, textural deterioration, and color changes in food. Furthermore, its ability to inactivate some resistant microorganisms is limited, making it difficult to balance sterilization efficiency with quality preservation.

[0003] While non-thermal treatments can reduce damage to food quality to some extent, they suffer from uneven action, weak penetration, and low efficiency in complex foods, making it difficult to fully inactivate resistant microorganisms such as spores. Plasma-activated water, as a novel food sterilization technology, has good application potential in the control of microorganisms on food surfaces due to its rich content of reactive oxygen species and nitrogen species. However, its inactivation effect on resistant microorganisms such as spores is limited, and a tailing effect of significant decrease or even stagnation in the inactivation rate easily occurs during the treatment process, making it difficult to achieve thorough sterilization.

[0004] To improve sterilization efficiency and mitigate the adverse effects of single treatment methods, existing technologies attempt to combine different sterilization methods. However, existing combinations are mostly designed for single food types, lacking universal technical solutions applicable to various food ingredients such as meat, seafood, vegetables, and grains, and failing to balance sterilization efficiency, processing stability, and food quality. Therefore, it is necessary to provide a sterilization method that is highly efficient, widely applicable, and capable of maintaining food quality. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention provides a combined sterilization method using activated water and superheated steam. This sterilization method significantly improves the inactivation effect on microorganisms on food surfaces while effectively mitigating adverse effects on food quality, exhibiting high efficiency, safety, and versatility.

[0006] The technical solution of the present invention is as follows: The first aspect of this invention protects a method for sterilization using activated water and superheated steam, comprising the following steps: S1. After immersing the food in plasma-activated water, remove surface moisture. S2. Then, treat the food with superheated steam, cool it, and complete the sterilization process.

[0007] Preferably, in step S1, the soaking time is 3-5 minutes.

[0008] Preferably, in step S1, the temperature of the plasma-activated water is 20~25℃.

[0009] Preferably, in step S1, the method for preparing plasma-activated water includes the following steps: placing a plasma device in deionized water, introducing a working gas for discharge treatment, and obtaining the plasma-activated water.

[0010] Preferably, the working gas includes at least one of air, oxygen, and nitrogen; And / or, the discharge voltage is 10~30kV; And / or, the discharge frequency is 5~20kHz; And / or, the discharge treatment time is 15~30 min.

[0011] Preferably, in step S2, the steam temperature is 140~180℃.

[0012] Preferably, in step S2, the superheated steam treatment time is 3~10s; And / or, the cooling includes at least one of sterile ice-water bath cooling and air cooling; And / or, the cooling temperature is not higher than 10°C.

[0013] Preferably, the time interval between step S1 and step S2 does not exceed 5 minutes.

[0014] Preferably, the food includes solid food, which includes at least one of meat products, aquatic products, vegetables, and grains.

[0015] The second aspect of this invention protects the application of the activated water-superheated steam combined sterilization method described in the first aspect in the field of food processing.

[0016] The beneficial technical effects of this invention are as follows: This invention combines plasma-activated water treatment with superheated steam treatment to construct a stable synergistic sterilization process, thereby achieving more thorough and stable inactivation of microorganisms on food surfaces. It is particularly effective in killing resistant microorganisms such as spores, significantly improving the inactivation efficiency of microorganisms on food surfaces. The sterilization effect is superior to single treatment methods and random combination treatment methods, effectively overcoming the tailing phenomenon of sudden drop and stagnation in inactivation rate during single treatment processes. Furthermore, while improving the sterilization effect, this invention can effectively reduce the adverse effects of the treatment process on food quality, reducing lipid oxidation, textural deterioration, moisture loss, color abnormalities, and nutrient loss during sterilization. Thus, it better balances sterilization effect and quality maintenance, improving the overall quality of the treated food.

[0017] The sterilization method of the present invention can be widely applied to the surface sterilization of various food raw materials such as meat, aquatic products, vegetables, and grains. It has good versatility and breaks the limitation of existing sterilization solutions that are developed for a single food category.

[0018] Furthermore, the sterilization method of the present invention features short processing time, high efficiency, and mild conditions. Specifically, the plasma-activated water treatment time is short, and the superheated steam treatment time is only in the seconds range. No extreme treatment conditions are required, and it can be implemented under conventional food processing equipment conditions. It has the advantages of low energy consumption, simple operation, and high production efficiency, making it suitable for industrial applications.

[0019] The sterilization method of this invention adopts a physical sterilization method without any additives throughout the process. The plasma-activated water is obtained by activating deionized water, and the superheated steam is a purely physical heat treatment process. No chemical preservatives or chemical sterilizers are introduced, which meets the requirements of green and safe food processing and improves the food safety of the product. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the embodiments.

[0021] A method for sterilization using activated water and superheated steam includes the following steps: S1. After immersing the food in plasma-activated water, remove surface moisture. S2. Then, treat the food with superheated steam, cool it, and complete the sterilization process.

[0022] The sterilization method of this invention involves first treating the water with plasma-activated water, followed by treatment with superheated steam. The plasma-activated water first causes oxidative pre-damage to the microbial cell structure on the food surface, weakening its heat resistance and survival tolerance. It may also disrupt the expression mechanism of heat shock proteins in microorganisms, preventing them from initiating heat protection procedures, thus making them extremely sensitive to subsequent heat treatment. Based on this, superheated steam utilizes a high-temperature and low-oxygen environment to rapidly and deeply inactivate the pre-damaged microorganisms, thereby significantly improving the overall sterilization efficiency and effectively reducing the tailing phenomenon that easily occurs in single-treatment processes.

[0023] It is understood that the order of the two steps in the method of the present invention cannot be changed. For example, the food is first treated with superheated steam and then immersed in plasma-activated water for soaking treatment. This method will destroy the surface structure of the food due to high temperature and cause the microorganisms to enter a dormant state due to heat. This will prevent the plasma-activated water from fully contacting the microorganisms and ultimately cause the synergistic sterilization effect to be completely ineffective.

[0024] In some embodiments, step S2 includes rapid cooling using air cooling or a sterile ice-water bath. The cooling rate is controlled to reduce the core temperature of the food raw material to below 10°C within a short time. Subsequently, it is sealed using sterile packaging equipment and stored at 0-4°C to maintain product quality stability and prevent subsequent secondary contamination and quality deterioration.

[0025] In the following specific embodiments of the present invention, the plasma-activated water is prepared by the following method: deionized water is activated using a plasma device, with air as the working gas, the discharge voltage of the device is adjusted to 20 kV and the discharge frequency to 10 kHz, and the water is continuously activated for 30 min to generate high concentrations of active oxygen, active nitrogen and other oxidizing active substances in the water, thus obtaining plasma-activated water.

[0026] In the following specific embodiments of the present invention, the plate count method is used to detect microbial colonies on the sample surface. The sterilization effect is characterized by the sterilization logarithm (lg CFU / g, logarithmic value of colony count), and the synergistic sterilization effect is characterized by the synergistic value. The calculation formula is as follows: Sterilization logarithm = Initial colony count (lg CFU / g) - Post-treatment colony count (lg CFU / g) Synergy value = Number of sterilization logs from synergistic treatment - Number of sterilization logs from plasma-activated water - Number of sterilization logs from superheated steam A synergy value greater than 0 indicates that there is a synergistic effect between the two treatment methods. The larger the synergy value, the more significant the synergistic effect. All data results are expressed as "mean ± standard deviation".

[0027] The detection methods involved in the following embodiments, comparative examples, and test examples of this invention are as follows: The plate count method was used to detect microbial colonies on the food surface. The results were characterized by 1g CFU / g logarithmic colony count. The overall microbiological testing followed GB 4789.1-2016 "National Food Safety Standard - General Rules for Microbiological Examination of Food". The total colony count was determined according to GB 4789.2-2022. Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus, and Bacillus subtilis were tested according to GB 4789.38-2025, GB 4789.10-2016, GB 4789.30-2025, and GB 4789.14-2014, respectively.

[0028] Among the quality indicators, the hardness of food texture was determined using a texture analyzer; the L* value of color was determined using a CIE L*a*b* color system; the moisture content was determined according to GB 5009.3-2016; and the vitamin C content was determined according to GB 5009.86-2025. All tests were conducted with parallel samples, and the test results are expressed as mean ± standard deviation.

[0029] Example 1: Sterilization of pork surface Fresh pork belly was selected as raw material and aseptically cut into 10-15 pieces as samples, which were then refrigerated at 0-4℃ for later use. A mixed bacterial suspension of *Escherichia coli*, *Staphylococcus aureus*, and *Listeria monocytogenes* was inoculated onto the sample surface using an aseptic coating method, ensuring an initial total bacterial count of 10⁻⁶. 6 ~10 7 The concentration of CFU / g was then set and allowed to stand under sterile conditions for 30 min. The samples were then sterilized using the methods described below.

[0030] Untreated group: The samples were not treated.

[0031] Plasma-activated water group: The sample was completely immersed in plasma-activated water at 25°C for 5 min and then drained using a sterile filter.

[0032] Superheated steam group: The sample was placed in a closed superheated steam treatment device for 8 seconds. The superheated steam temperature was 180℃. After treatment, the sample was rapidly cooled to below 10℃ in a sterile ice water bath.

[0033] Collaborative processing group: The sample was completely immersed in plasma-activated water at 25°C for 5 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 8 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0034] Table 1: Sterilization effect of different treatment methods on pork surface

[0035] The values ​​in rows 3-5 of the table represent the bacterial count after treatment (lg CFU / g). For example, the E. coli count in the plasma-activated water group is 5.91 ± 0.20 (lg CFU / g), which means that the E. coli count in the plasma-activated water group after treatment is 5.91 ± 0.20 (lg CFU / g).

[0036] Table 2: Effects of different treatment methods on pork quality

[0037] As shown in Tables 1 and 2, both plasma-activated water and superheated steam treatment alone can reduce the colony counts of Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes on the surface of pork, but the sterilization effect is limited. After sterilizing the surface of pork using the method of this invention (synergistic treatment group), the colony counts of the three bacteria all decreased to about 1.00 lg CFU / g, the sterilization logarithms were all >5.0, and the synergistic values ​​were all far >0, indicating that plasma-activated water and superheated steam treatment have a significant synergistic effect in the method of this invention, and the combined treatment significantly improves the sterilization effect.

[0038] Different treatment methods all have a certain impact on pork quality. Activated water treatment alone has a relatively small impact on pork quality, while superheated steam treatment alone has a more significant impact on sample firmness, moisture content, and color. In comparison, the synergistic treatment group showed a 54.38% reduction in pork firmness and a 28.14% increase in moisture content compared to superheated steam treatment alone. This indicates that the method of this invention can better balance sterilization effect and quality preservation.

[0039] Example 2: Surface sterilization of fresh shrimp Fresh whiteleg shrimp were selected, deveined, and aseptically processed to serve as samples, which were then refrigerated at 0–4°C for later use. A mixed bacterial suspension of *Escherichia coli*, *Staphylococcus aureus*, and *Listeria monocytogenes* was inoculated onto the sample surface using an aseptic plating method, ensuring an initial total bacterial count of 10⁻⁶. 6 ~10 7 The concentration of CFU / g was then set and allowed to stand under sterile conditions for 30 min. The samples were then sterilized using the methods described below.

[0040] Untreated group: The samples were not treated.

[0041] Plasma-activated water group: The sample was completely immersed in plasma-activated water at 25°C for 3 minutes and then drained using a sterile filter.

[0042] Superheated steam group: The sample was placed in a closed superheated steam treatment device for 5 seconds. The superheated steam temperature was 160℃. After treatment, the sample was rapidly cooled to below 10℃ in a sterile ice water bath.

[0043] Collaborative processing group: The sample was completely immersed in plasma-activated water at 25°C for 3 min, and after sterile filtration, it was immediately (≤1 min) placed in a closed superheated steam treatment device for 5 s. The superheated steam temperature was 160°C. After treatment, it was rapidly cooled to below 10°C in a sterile ice water bath.

[0044] Table 3: Sterilization effect of different treatment methods on the surface of fresh shrimp

[0045] Table 4: Effects of different treatment methods on the quality of fresh shrimp

[0046] As shown in Tables 3 and 4, after sterilizing the surface of fresh shrimp using the method of this invention, the colony counts of the three bacteria all decreased to approximately 1.8 lg CFU / g, and the synergistic values ​​were all >3.4, indicating that the sterilization effect of the method of this invention is significant. The firmness of the fresh shrimp in the synergistic treatment group increased by only 25.58% compared to the untreated group, and the moisture loss was only 3.95%. This demonstrates that the method of this invention can effectively sterilize the surface of fresh shrimp while also effectively maintaining the tenderness and moisture of aquatic products.

[0047] Example 3: Sterilization of green pepper surface Fresh, thin-skinned green peppers were selected, stemmed, and seeded, then aseptically processed and stored at 0–4°C for later use. A mixed bacterial suspension of *Escherichia coli*, *Staphylococcus aureus*, and *Listeria monocytogenes* was inoculated onto the sample surface using an aseptic plating method, ensuring an initial total bacterial count of 10⁻⁶. 6 ~10 7 The concentration of CFU / g was then set and allowed to stand under sterile conditions for 30 min. The samples were then sterilized using the methods described below.

[0048] Untreated group: The samples were not treated.

[0049] Plasma-activated water group: The sample was completely immersed in plasma-activated water at 25°C for 3 minutes and then drained using a sterile filter.

[0050] Superheated steam group: The sample was placed in a closed superheated steam treatment device for 3 seconds. The superheated steam temperature was 140℃. After treatment, it was rapidly cooled to below 10℃ in a sterile ice water bath.

[0051] Collaborative treatment group: The sample was completely immersed in plasma-activated water at 25°C for 3 min. After sterile draining, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 3 s. The superheated steam temperature was 140°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0052] Table 5: Sterilization effect of different treatment methods on the surface of green peppers

[0053] Table 6: Effects of different treatments on the quality of green peppers

[0054] As can be seen from Tables 5 and 6, when the surface of green peppers is sterilized using the method of the present invention, the colony counts of the three bacteria are reduced to about 2.0 1g CFU / g, and the synergistic values ​​are all >3.2. Compared with the untreated group, the green peppers sterilized by the method of the present invention have only a 10.38% decrease in hardness and only a 10% loss of vitamin C, which is far superior to the single superheated steam treatment and can effectively maintain the structure and nutrition of the vegetables.

[0055] Example 4: Sterilization of rice surface Using Bacillus cereus and Bacillus subtilis as indicator bacteria, 10 8 CFU / mL spore suspension; aseptically sprayed onto the surface of rice to achieve an initial total bacterial count of 10. 6 ~10 7 The concentration of CFU / g was then set and allowed to stand under sterile conditions for 30 min. The samples were then sterilized using the methods described below.

[0056] Untreated group: The samples were not treated.

[0057] Plasma-activated water group: The sample was completely immersed in plasma-activated water at 25°C for 5 min and then drained using a sterile filter.

[0058] Superheated steam group: The sample was placed in a closed superheated steam treatment device for 10 seconds. The superheated steam temperature was 180℃. After treatment, the sample was rapidly cooled to below 10℃ in a sterile ice water bath.

[0059] Collaborative treatment group: The sample was completely immersed in plasma-activated water at 25°C for 5 min. After sterile draining, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 10 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0060] Table 7: Sterilization effect of different treatment methods on rice surface

[0061] As shown in Table 7, the method of this invention for sterilizing the surface of rice can effectively inactivate highly resistant spore-forming bacteria, with sterilization logs all > 4.5. This indicates that the sterilization method of this invention can effectively inactivate spores in grains.

[0062] Comparative Example 1: Sterilization of pork surface The sample obtained in Example 1 was sterilized using the following different methods.

[0063] The treatment methods for the untreated group, the plasma-activated water group, and the superheated steam group are the same as those in Example 1.

[0064] Superheated steam + activated water group: The sample was placed in a closed superheated steam treatment device for 8 seconds. The superheated steam temperature was 180℃. After cooling to 10℃, the sample was completely immersed in plasma activated water at 25℃ for 5 minutes.

[0065] Table 8: Sterilization effect of different treatment methods on pork surface

[0066] As can be seen from Table 8, the sterilization effect of treating with superheated steam first and then with activated water is not much different from that of single treatment. The synergistic value shows a slight negative trend, with almost no actual synergistic sterilization effect. The sterilization effect is far worse than that of the method of the present invention.

[0067] The possible reasons are twofold: firstly, after short-term high-temperature steam treatment, the proteins on the surface of the pork may undergo slight denaturation, forming a microstructural barrier that makes it difficult for reactive oxygen and nitrogen substances in the plasma-activated water to penetrate to the microbial attachment sites on the food surface, thus failing to exert their oxidative damage effect; secondly, microorganisms may develop stress tolerance after short-term high-temperature treatment, significantly reducing their sensitivity to the oxidative effect of plasma-activated water. Ultimately, the combined treatment may only result in a simple superposition of the effects of the two individual treatments, or even a weak negative synergy due to the presence of the microbarrier, without any actual synergistic bactericidal value.

[0068] Comparative Example 2: Sterilization of pork surface The sample obtained in Example 1 was sterilized according to the following method.

[0069] The sample was completely immersed in plasma-activated water at 25°C for 5 minutes. After being drained through a sterile filter, it was left to stand for 10 minutes and then placed in a closed superheated steam treatment device for 8 seconds. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0070] Comparative Example 3: Sterilization of pork surface The sample obtained in Example 1 was sterilized according to the following method.

[0071] The sample was completely immersed in plasma-activated water at 25°C for 5 minutes. After being drained through a sterile filter, it was left to stand for 30 minutes and then placed in a closed superheated steam treatment device for 8 seconds. The superheated steam temperature was 180°C. After treatment, it was rapidly cooled to below 10°C in a sterile ice water bath.

[0072] The initial bacterial counts of Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes were the same as in Example 1, and the sterilization logarithms of the plasma-activated water group and the superheated steam group were the same as in Example 1. The sterilization effects of Example 1, Comparative Examples 2 and 3 are shown in the table below.

[0073] Table 9: Sterilization effect of Examples 1, 2, and 3 on pork surface

[0074] As shown in Table 9, compared to Example 1, the sterilization effect was poor when the time interval between the plasma-activated water treatment and the superheated steam treatment steps was too long. Specifically, the sterilization effect at a 30-minute interval was worse than that at a 10-minute interval, indicating that there was almost no actual synergistic effect at this time.

[0075] The speculated reason may be that microorganisms pre-damaged by plasma-activated water gradually complete their cell structure self-repair during room temperature storage, restoring their heat resistance and survival tolerance to initial levels, thus significantly reducing the deep inactivation effect of subsequent superheated steam. Furthermore, in the sterilization method of this invention, it is necessary to control the time window between the plasma-activated water treatment and the superheated steam treatment steps. If the time interval between the two treatment steps is too long, it will negatively impact the final sterilization effect.

[0076] Comparative Example 4: Sterilization of pork surface The sample obtained in Example 1 was sterilized according to the following method.

[0077] The sample was completely immersed in plasma-activated water at 25°C for 5 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 8 s. The superheated steam temperature was 120°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0078] Comparative Example 5: Sterilization of pork surface The sample obtained in Example 1 was sterilized according to the following method.

[0079] The sample was completely immersed in plasma-activated water at 25°C for 5 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 8 s. The superheated steam temperature was 200°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0080] Comparative Example 6: Sterilization of pork surface The sample obtained in Example 1 was sterilized according to the following method.

[0081] The sample was completely immersed in plasma-activated water at 25°C for 5 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 2 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0082] Comparative Example 7: Sterilization of pork surface The sample obtained in Example 1 was sterilized according to the following method.

[0083] The sample was completely immersed in plasma-activated water at 25°C for 5 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 15 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0084] Comparative Example 8: Sterilization of Pork Surface The sample obtained in Example 1 was sterilized according to the following method.

[0085] The sample was completely immersed in plasma-activated water at 25°C for 2 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 8 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0086] Comparative Example 9: Sterilization of Pork Surface The sample obtained in Example 1 was sterilized according to the following method.

[0087] The sample was completely immersed in plasma-activated water at 25°C for 6 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 8 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0088] The initial Escherichia coli count was the same as in Example 1, and the sterilization logs of the plasma-activated water group and the superheated steam group were the same as in Example 1. The sterilization effects of Examples 1 and Comparative Examples 4-9 on Escherichia coli are shown in the table below.

[0089] Table 10: Sterilization effect of Examples 1 and Comparative Examples 4-9 on Escherichia coli on pork surface

[0090] As can be seen from Table 10, the superheated steam temperature in Comparative Example 4 was too low, the superheated steam treatment time in Comparative Example 6 was too short, and the plasma-activated water treatment time in Comparative Example 8 was too short. The sterilization logs all decreased significantly, the sterilization effect was significantly reduced, and there was no quality advantage. They could not meet the sterilization requirements of the food industry.

[0091] As shown in Table 10, Comparative Example 5 had an excessively high superheated steam temperature, and Comparative Example 7 had an excessively long superheated steam treatment time. Although the sterilization effect was slightly improved, the food quality deteriorated severely, with problems such as surface scorching, significant moisture loss, and hardening of texture, rendering them unusable. Comparative Example 9 had an excessively long activated water treatment time, resulting in only a slight improvement in sterilization effect. The sample showed only a slight decrease in moisture content, with no obvious deterioration in texture or scorching. Exceeding the soaking time specified in this scheme did not yield any significant benefit or severe deterioration, thus offering no additional application value.

[0092] Comparative Example 10: Sterilization of Pork Surface The sample obtained in Example 1 was sterilized according to the following method.

[0093] The sample was completely immersed in plasma-activated water at 4°C for 5 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 8 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0094] Comparative Example 11: Sterilization of pork surface The sample obtained in Example 1 was sterilized according to the following method.

[0095] The sample was completely immersed in plasma-activated water at 35°C for 5 min. After being drained through a sterile filter, the sample was immediately (≤1 min) placed in a closed superheated steam treatment device for 8 s. The superheated steam temperature was 180°C. After treatment, the sample was rapidly cooled to below 10°C in a sterile ice water bath.

[0096] The initial bacterial counts of Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes were the same as in Example 1, and the sterilization logs of the plasma-activated water group and the superheated steam group were the same as in Example 1. The sterilization effects of Example 1, Comparative Examples 10 and 11 are shown in the table below.

[0097] Table 11: Sterilization effect of Examples 1, 10, and 11 on pork surface

[0098] As can be seen from Table 11, when the temperature of the plasma-activated water is too low (Comparative Example 10, 4℃) or too high (Comparative Example 11, 35℃), its final killing effect on the three indicator bacteria is significantly worse than that in Example 1.

[0099] The possible reasons are: when the temperature is too low (4℃), the molecular motion rate of reactive oxygen and nitrogen substances in the activated water decreases, and the oxidative damage effect on microbial cells is greatly weakened; when the temperature is too high (35℃), reactive oxygen and nitrogen substances will decompose and become ineffective quickly, and the concentration of active substances in the water will drop sharply, so that their pre-damage effect can hardly be exerted, and the synergistic effect will be greatly reduced.

[0100] Test case For Example 1, the inactivation effect of Escherichia coli on the surface of pork was tested at each time point for plasma-activated water treatment alone (1, 2, 3, 4, 5 min), superheated steam treatment alone (8 s), and synergistic treatment (activated water 1, 2, 3, 4, 5 min + steam 8 s). A tailing effect was defined as a decrease of ≥50% in the logarithmic increment of sterilization at adjacent time points. The improvement effect of the present invention on the tailing effect was quantitatively verified.

[0101] Table 12: Inactivation effect on pork surface at different time points under different treatment methods

[0102] As shown in Table 12, when plasma-activated water treatment is used alone, the peak value of sterilization effect is reached at 2-3 min, with a sterilization logarithmic increment of 0.22-0.23. However, the increment drops sharply to 0.10 at 3-4 min and only 0.09 at 4-5 min, a decrease of ≥56% from the peak value, meeting the criteria for tailing effect and showing a significant tailing effect. This indicates that after 3 min, continuing to extend the activated water treatment time will have almost no improvement in sterilization effect, only achieving limited inactivation, and failing to meet the deep sterilization requirements of the food industry.

[0103] As can be seen from Table 12, when superheated steam is used alone, only a cumulative sterilization log of 1.54 can be achieved, which is a limited sterilization effect. Although there is no basis for judging the tailing effect, single treatment cannot effectively inactivate resistant microorganisms and is prone to causing food quality deterioration.

[0104] As shown in Table 12, with the superheated steam treatment time remaining constant at 8 seconds, the cumulative sterilization logarithm steadily increased with the increase of the plasma-activated water treatment time, gradually rising from 4.17 to 5.74. The increase in sterilization logarithm at adjacent time points remained above 0.27, with no point showing a decrease in the increase of ≥50%, and no tailing effect was observed. Furthermore, the total cumulative sterilization logarithm was far higher than the sum of the two single treatments, achieving a highly significant synergistic effect of 1+1>2. This indicates that the synergistic sterilization method of the present invention can effectively reduce or even eliminate the tailing effect of single plasma-activated water treatment, and combined with superheated steam treatment, achieves continuous and efficient inactivation of microorganisms, solving the technical problems of insufficient inactivation and easy tailing in single sterilization treatments in the prior art.

[0105] In summary, the sterilization method of the present invention has good versatility for various food raw materials such as meat, aquatic products, vegetables, and grains. While achieving efficient inactivation of pathogenic bacteria and spore-forming microorganisms, it can minimize problems such as lipid oxidation, texture deterioration, and nutrient loss in food, thus balancing sterilization efficiency and quality preservation. Moreover, the operation process is simple, and it has prospects for industrial application and promotion value.

[0106] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. An activated water- superheated steam composite sterilization method, characterized by, Includes the following steps: S1. After immersing the food in plasma-activated water, remove surface moisture. S2. Then, treat the food with superheated steam, cool it, and complete the sterilization process.

2. The activated water- superheated steam composite sterilization method according to claim 1, characterized by, In step S1, the soaking time is 3-5 minutes.

3. The activated water-steam superheated composite sterilization method according to claim 1, characterized in that, In step S1, the temperature of the plasma-activated water is 20~25℃.

4. The activated water-superheated steam combined sterilization method according to claim 1, characterized in that, In step S1, the method for preparing plasma-activated water includes the following steps: placing a plasma device in deionized water, introducing a working gas for discharge treatment, and obtaining the plasma-activated water.

5. The activated water-superheated steam combined sterilization method according to claim 4, characterized in that, The working gas includes at least one of air, oxygen, and nitrogen; And / or, the discharge voltage is 10~30kV; And / or, the discharge frequency is 5~20kHz; And / or, the discharge treatment time is 15~30 min.

6. The activated water-superheated steam combined sterilization method according to claim 1, characterized in that, In step S2, the steam temperature is 140~180℃.

7. The activated water-superheated steam combined sterilization method according to claim 1, characterized in that, In step S2, the superheated steam treatment time is 3~10s; And / or, the cooling includes at least one of sterile ice-water bath cooling and air cooling; And / or, the cooling temperature is not higher than 10°C.

8. The activated water-superheated steam combined sterilization method according to claim 1, characterized in that, The time interval between step S1 and step S2 shall not exceed 5 minutes.

9. The activated water-superheated steam combined sterilization method according to claim 1, characterized in that, The food includes solid food, which includes at least one of meat products, aquatic products, vegetables, and grains.

10. The application of the activated water-superheated steam composite sterilization method according to any one of claims 1 to 9 in the field of food processing.

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