Method for preserving cold water fish by using plasma-activated water in combination with vacuum pre-cooling

Abstract

The application provides a preservation method for cold water fish by plasma-activated water in cooperation with vacuum precooling, and relates to the technical field of aquatic food processing. The method comprises the following steps: placing fresh cold water fish pieces in plasma-activated water for soaking, then transferring the fish pieces to a vacuum environment for cooling treatment, controlling the vacuum degree, rapidly reducing the center temperature of the fish pieces from 16-19 DEG C to 0-4 DEG C, and then packaging and storing. The application realizes the double preservation effect of "first inhibiting bacteria and locking freshness, and then rapidly shaping" by the broad-spectrum bacteriostasis and antioxidant properties of plasma-activated water and the rapid cooling advantage of vacuum precooling. The application does not need to add chemical preservatives, can effectively delay the denaturation of fish protein, fat oxidation and color deterioration, greatly prolongs the cold storage shelf life of cold water fish, and is green, safe, efficient and suitable for the large-scale processing and cold chain preservation of cold water fish.

Description

Technical Field

[0001] This invention relates to the field of aquatic food processing technology, and in particular to a method for preserving cold-water fish using plasma-activated water in conjunction with vacuum precooling. Background Technology

[0002] Cold-water fish are a high-quality and distinctive aquaculture category in my country, mainly including rainbow trout, lenok, wrasse, and pike. Their flesh is tender, high in protein, low in fat, and rich in unsaturated fatty acids, making them nutritionally superior to conventional freshwater fish in both taste and texture. They are highly favored by consumers and are also core products in aquatic product processing, fresh food cold chain sales, and export trade, demonstrating significant economic value. Rainbow trout, in particular, is a typical cold-water economic fish species farmed on a large scale in my country. It boasts advantages such as rapid growth, tender flesh, few intramuscular bones, and high nutritional value, holding an important position in freshwater aquaculture and the high-end fresh food market.

[0003] However, rainbow trout has a high water content, soft muscle tissue, and strong endogenous enzyme activity. After slaughter and processing, the fish loses its immune protection, and its surface is extremely susceptible to the adhesion of a large number of putrefactive microorganisms. At the same time, biochemical reactions such as lipid oxidation and protein degradation occur rapidly, resulting in putrefaction phenomena such as sticky meat, dark color, deterioration of flavor, and increased volatile basic nitrogen in a short period of time. This greatly limits the storage and transportation radius and shelf life of rainbow trout, and seriously restricts its industrial processing and market promotion.

[0004] Currently, the preservation and processing of cold-water fish in China still relies mainly on traditional preservation technologies, including chilled storage, low-temperature freezing, chemical preservation, and vacuum cooling. Vacuum cooling, as a novel physical pre-cooling process, utilizes a low-pressure environment to rapidly cool the food, shortening the time the fish remains at high temperatures and effectively mitigating quality deterioration. It offers significant advantages over traditional pre-cooling methods. However, this technology only provides cooling and lacks active antibacterial and antioxidant capabilities. It is difficult to eliminate low-temperature-resistant spoilage bacteria on the surface of the fish and cannot inhibit lipid oxidation and protein degradation, making subsequent storage prone to spoilage and limiting its preservation effect. Plasma-activated water is an emerging green non-thermal preservation technology, rich in various highly active oxygen and nitrogen substances. It can broadly inhibit bacteria, suppress enzyme activity, and delay fish deterioration, while also offering advantages such as safety, no residue, and minimal damage to the food. However, single plasma-activated water immersion treatment suffers from delayed cooling, untimely microbial control at high temperatures, and an inability to rapidly pre-cool and set the fish, resulting in insufficient preservation stability.

[0005] Therefore, there is an urgent need to develop a composite preservation method that combines rapid cooling, long-lasting antibacterial effect, antioxidant and anti-deterioration properties, and is green and safe, in order to overcome the shortcomings of existing cold-water fish preservation technologies, such as slow cooling rate, poor antibacterial effect, and easy deterioration of quality. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preserving cold-water fish using plasma-activated water in conjunction with vacuum precooling.

[0007] In a first aspect, the present invention provides a method for preserving cold-water fish using plasma-activated water in conjunction with vacuum precooling, comprising the following steps:

[0008] (1) Preparation of plasma-activated water: Water is placed in a plasma-activated water generator for discharge treatment to obtain plasma-activated water;

[0009] (2) Raw material pretreatment: The cold-water fish raw materials are soaked in plasma-activated water;

[0010] (3) Vacuum cooling treatment: The cold-water fish raw material soaked in step (2) is placed in a vacuum environment for cooling treatment. During the cooling treatment, the center temperature of the cold-water fish raw material soaked in step (2) drops from the initial temperature to the target temperature.

[0011] (4) Storage: Package the cold-water fish raw materials processed in step (3) and store them in a refrigerated environment.

[0012] Optionally, the cold-water fish includes rainbow trout; the rainbow trout includes fish chunks.

[0013] Optionally, the discharge treatment time in step (1) is > 15 min.

[0014] Optionally, the discharge voltage during plasma-activated water preparation in step (1) is 350~420V.

[0015] Optionally, the soaking time in step (2) is 3 to 8 minutes; the mass ratio of the cold-water fish raw material to the plasma-activated water is (1:1) to (1:3).

[0016] Optionally, the absolute pressure of the vacuum environment in step (3) is 0.1~1.0 kPa.

[0017] Optionally, the initial temperature in step (3) is 16~19℃; the target temperature is 0~4℃.

[0018] Optionally, the cooling process in step (3) takes 10 to 30 minutes.

[0019] Optionally, the vacuum cooling process in step (3) is carried out in a vacuum chamber containing a sterilization device, which is positioned above the cold-water fish raw material and sterilizes the cold-water fish raw material during the cooling process; the sterilization device includes an excimer lamp.

[0020] Optionally, the temperature of the refrigeration environment in step (4) is 0~4℃.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The preservation method provided by the present invention organically combines plasma-activated water immersion pretreatment with vacuum precooling process in a sequential manner, utilizing the hydroxyl radicals (·OH) and superoxide anions (·O2) abundant in plasma-activated water. - ), hydrogen peroxide (H2O2) and nitrite (NO2) - It uses a variety of highly reactive reactive oxygen species (RONS) to perform broad-spectrum sterilization and enzyme activity inhibition on the surface and shallow tissues of fish pieces before cooling. At the same time, it uses a vacuum low-pressure environment to achieve rapid cooling of the core temperature of the fish pieces from 16~19℃ to 0~4℃. This overcomes the inherent defects of single technologies that "only cool down without inhibiting bacteria" or "only inhibit bacteria but not cool down", and forms a synergistic preservation effect of "first inhibiting bacteria and locking in freshness, then rapidly shaping".

[0023] (2) The preservation method provided by the present invention, by setting up sterilization devices such as excimer lamps in the vacuum cooling chamber, continuously irradiates and sterilizes the fish pieces and the surrounding environment during the vacuum cooling process, effectively preventing secondary pollution of the fish pieces during the transfer from the soaking process to the cooling process, and making up for the lack of active antibacterial function in conventional vacuum cooling equipment.

[0024] (3) The preservation method provided by the present invention further optimizes and reduces the final temperature of vacuum precooling from the conventional 4°C to 0°C, which significantly slows down the denaturation rate of myofibril protein in fish pieces during cold storage, effectively inhibits the conversion of non-flowing water to free water, and makes the hardness of fish pieces decrease by only 13.3% during the 12-day storage period, while the hardness of untreated fish pieces decreases by as much as 50.2%, which greatly improves the preservation effect of the water-holding and texture properties of fish meat.

[0025] (4) The preservation method provided by the present invention effectively delays the oxidation process of myoglobin and lipid oxidation in fish meat by combining the antioxidant effect of plasma-activated water with the dual protection of vacuum low temperature environment. The total color difference ΔE* of the fish pieces in the co-treatment group is only 8.4 during the 12-day storage period, which is much lower than 13.2 in the untreated group and 10.1 in the single activated water treatment group, which significantly improves the color stability of cold water fish during storage.

[0026] (5) The preservation method provided by the present invention, through the superposition effect of plasma-activated water antibacterial effect and vacuum pre-cooling rapid cooling, makes the total number of fish colonies significantly lower than that of the single treatment group throughout the storage process. The sample treated to 0℃ showed the smallest increase in total number of colonies after 12 days of storage, effectively breaking through the technical bottleneck of traditional ice-fresh refrigeration reaching the critical value of microbial spoilage (6Log CFU / g) after a few days, and greatly extending the cold storage shelf life of cold-water fish.

[0027] (6) The preservation method provided by the present invention uses only pure water to prepare activated water through plasma discharge as the preservation medium throughout the process. No chemical preservatives or antioxidants need to be added. There are no harmful chemical residues in the process. At the same time, it avoids the mechanical damage to the myofiber cell structure caused by ice crystal formation in the traditional freezing process. It preserves the natural freshness, tenderness, nutritional quality and food safety of cold-water fish to the greatest extent. It is in line with the development trend of green and clean aquatic product processing and has good prospects for industrialization. Attached Figure Description

[0028] Figure 1 The graph shows the effect of different pre-cooling methods on the texture of fish fillets in Examples 1 to 4 of this invention. Different letters in the graph indicate significant differences between groups of different cooling methods (P<0.05).

[0029] Figure 2 The graphs show the effects of different precooling methods on the color of fish pieces in Examples 1 to 4 of this invention.

[0030] Figure 3 The graph shows the effect of different precooling methods on the moisture distribution characteristics of fish pieces in Examples 1 to 4 of this invention; wherein, Figure 3 In the figure, A represents the trend of moisture distribution changes in uncooled fish pieces during storage; Figure 3 In the figure, B represents the trend of moisture distribution changes in fish pieces after plasma-activated water pre-cooling during storage; Figure 3 C in the figure represents the trend of moisture distribution changes in fish pieces that have undergone plasma-activated water and vacuum pre-cooling to 4°C during storage. Figure 3 D in the figure represents the trend of moisture distribution changes in fish pieces that have undergone plasma-activated water and vacuum pre-cooling to 0°C during storage.

[0031] Figure 4 The graph shows the effect of different precooling methods on the total bacterial count of fish pieces in Examples 1 to 4 of this invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art to which this invention pertains.

[0033] This invention provides a method for preserving cold-water fish using plasma-activated water in conjunction with vacuum precooling, comprising the following steps:

[0034] (1) Preparation of plasma-activated water: Water is placed in a plasma-activated water generator for discharge treatment to obtain plasma-activated water;

[0035] (2) Raw material pretreatment: The cold-water fish raw materials are soaked in plasma-activated water;

[0036] (3) Vacuum cooling treatment: The cold-water fish raw material soaked in step (2) is placed in a vacuum environment for cooling treatment. During the cooling treatment, the center temperature of the cold-water fish raw material soaked in step (2) drops from the initial temperature to the target temperature.

[0037] (4) Storage: Package the cold-water fish raw materials processed in step (3) and store them in a refrigerated environment.

[0038] In fact, this invention achieves a dual preservation effect of "first inhibiting bacteria and locking in freshness, then rapidly shaping" by combining the broad-spectrum antibacterial and antioxidant properties of plasma-activated water with the rapid cooling advantage of vacuum precooling. Furthermore, a sterilization device is introduced into the vacuum environment to construct a multi-layered protection system. This invention requires no chemical preservatives, effectively delaying protein denaturation, fat oxidation, and color deterioration in fish, significantly extending the refrigerated shelf life of cold-water fish. The process is green, safe, and highly efficient, suitable for large-scale processing and cold chain preservation of cold-water fish.

[0039] In some embodiments, the cold-water fish used include rainbow trout; the rainbow trout used includes fish chunks.

[0040] In some embodiments, the selected fish piece is 5*5*5cm from the back of the fish. 3 Specifically, the shape and size of the rainbow trout pieces can be adjusted according to actual needs.

[0041] In some embodiments, the discharge process performed in step (1) takes >15 min.

[0042] In some embodiments, the discharge voltage used in step (2) for plasma-activated water preparation is 350~420V.

[0043] Specifically, plasma-activated water is produced by discharging distilled water in a plasma-activated water device for 15 minutes; the plasma-activated water used is prepared as an ice-water mixture.

[0044] In some embodiments, the soaking time in step (2) is 3 to 8 minutes; the mass ratio of the cold-water fish raw material to the plasma-activated water is (1:1) to (1:3).

[0045] Specifically, the soaking time for cold-water fish pieces in plasma-activated water is set to 3 min, 5 min, 7 min, and 9 min, with 5 min being the preferred setting.

[0046] Specifically, the mass ratio of the cold-water fish raw material to the plasma-activated water is set as 1:1, 1:2, and 1:3, preferably 1:3.

[0047] In some embodiments, the absolute pressure of the vacuum environment used in step (3) is 0.1~1.0 kPa.

[0048] Specifically, the absolute pressure setting of the vacuum environment is set to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 kPa, preferably 0.1 kPa.

[0049] In some embodiments, the initial temperature used in step (3) is 16~19°C; the target temperature used is 0~4°C.

[0050] Specifically, the target temperature set is such as 0°C, 2°C, and 4°C, preferably 0°C.

[0051] In some embodiments, the cooling process in step (3) takes 10 to 30 minutes.

[0052] Specifically, the time to reduce the center temperature of the fish pieces to the target temperature is set to 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30 minutes, preferably 10 to 15 minutes, and more preferably 10.4 to 14.2 minutes.

[0053] In some embodiments, the vacuum cooling process used in step (3) is carried out in a vacuum chamber containing a sterilization device, which is located above the cold-water fish raw material and sterilizes the cold-water fish raw material during the cooling process; the sterilization device used includes an excimer lamp.

[0054] In some embodiments, the temperature of the refrigerated environment used in step (4) is 0~4°C.

[0055] The vacuum cooling equipment used in the specific embodiments of this invention includes core components such as a vacuum chamber, a vacuum pump, a condenser, an evaporator, a control panel, and thermocouple probes. The plasma-activated water generator is a conventional dielectric barrier discharge or high-voltage pulse discharge device. Unless otherwise specified, all reagents and materials used are commercially available products in the art.

[0056] Example 1 (Plasma-activated water group)

[0057] This embodiment 1 provides a method for preserving cold-water fish using plasma-activated water precooling, comprising the following steps:

[0058] (1) Preparation of plasma-activated water: Place distilled water in the water tank of the plasma-activated water generator, introduce working gas (air or oxygen) into the device, adjust the gas flow rate to 1.0~2.0L / min, turn on the high voltage electrode power supply, and process for more than 15 minutes under the condition of discharge voltage of 350~420V to obtain plasma-activated water for later use.

[0059] (2) Raw material pretreatment: Take freshly slaughtered rainbow trout, remove the head, tail and internal organs, take the back muscle and cut it into fish pieces with a size of 5cm×5cm×5cm. The initial core temperature of the fish pieces is 16~19℃. Immediately place the fish pieces into the low-temperature plasma activated water prepared in step (1) for soaking. The mass ratio of fish pieces to activated water is 1:3 and the soaking time is 5min.

[0060] (3) Storage: The fish pieces processed in step (2) are packaged in sterile bags and stored in a refrigerated environment at 4°C.

[0061] Example 2 (Plasma-activated water + vacuum precooling to 4°C group)

[0062] This embodiment 2 provides a method for preserving cold-water fish using plasma-activated water combined with vacuum precooling, including the following steps:

[0063] (1) Preparation of plasma-activated water: Place distilled water in the water tank of the plasma-activated water generator, introduce working gas (air or oxygen) into the device, adjust the gas flow rate to 1.0~2.0L / min, turn on the high voltage electrode power supply, and process for more than 15 minutes under the condition of discharge voltage of 350~420V to obtain plasma-activated water for later use.

[0064] (2) Raw material pretreatment: Take freshly slaughtered rainbow trout, remove the head, tail and internal organs, take the back muscle and cut it into fish pieces with a size of 5cm×5cm×5cm. The initial core temperature of the fish pieces is 16~19℃. Immediately place the fish pieces into the plasma-activated water prepared in step (1) for soaking. The mass ratio of fish pieces to activated water is 1:3 and the soaking time is 5min.

[0065] (3) Vacuum cooling treatment: Take out the fish pieces soaked in step (2) and transfer them to the vacuum chamber of the vacuum cooling equipment. Place an excimer lamp above the fish pieces in the vacuum chamber. Start the vacuum pump and control the vacuum degree to 0.1 kPa. Turn on the excimer lamp to irradiate and sterilize the fish pieces, while simultaneously performing vacuum cooling treatment until the center temperature of the fish pieces drops to 4°C. The cooling treatment time is 15 min.

[0066] (4) Storage: The fish pieces processed in step (3) are packaged in sterile bags and stored in a refrigerated environment at 4°C.

[0067] Example 3 (Plasma-activated water + vacuum precooling to 0°C group)

[0068] This embodiment 3 provides a method for preserving cold-water fish by plasma-activated water combined with vacuum pre-cooling. The difference from embodiment 1 is that in step (3), when vacuum cooling is performed, the temperature at the center of the fish piece drops to 0°C.

[0069] Example 4 (Untreated group)

[0070] This embodiment 4 provides a method for preserving cold-water fish, including: without any pre-cooling and sterilization operations, directly taking freshly slaughtered rainbow trout, removing the head, tail, and internal organs, taking the back muscle, cutting it into fish pieces with a size of 5cm×5cm×5cm, and storing it in an environment of 4℃.

[0071] The impact of different cooling methods on the quality of rainbow trout fillets

[0072] (1) Measurement method

[0073] Rainbow trout fillet samples obtained from Examples 1, 2, 3, and 4 were collected on days 0, 3, 6, 9, and 12 of the storage period for texture analysis. Before measurement, the fish fillets were cut into 1*1*1 cm pieces and stabilized at room temperature for 1 hour. Then, a texture analyzer equipped with a P / 50 probe was used for measurement, with the following parameters set: trigger force 2 g, test distance 10 mm, test speed 1 mm / s, post-test speed 1 mm / s, and compression ratio 30%. Each sample was measured in parallel five times, and the average value was taken.

[0074] (2) Measurement results

[0075] Changes in texture data of fish fillets treated with four different precooling methods during storage are as follows: Figure 1 As shown, the hardness of rainbow trout fillets treated with four different pre-cooling methods showed a continuous decreasing trend with the extension of storage time. This is completely consistent with the quality deterioration pattern of increased endogenous protease activity, myofibril protein degradation, and damage to muscle fiber structure during refrigeration. However, there were extremely significant differences in the effect of different pre-cooling methods on maintaining the hardness of the fillets. The decrease in hardness from largest to smallest was as follows: untreated group > plasma-activated water group > plasma-activated water + vacuum pre-cooling to 4℃ group > plasma-activated water + vacuum pre-cooling to 0℃ group.

[0076] The untreated group showed the greatest decrease in fish fillet hardness and the fastest rate of quality deterioration. Initially (day 0), there was no significant difference between the untreated group and the other three groups. After 3 days of storage, the hardness dropped to 304.47g, a significant decrease. After 12 days, the hardness was only 180.51g, a 50.2% decrease from the initial value. This indicates that the untreated rainbow trout fillets experienced the fastest rate of myofiber structure destruction and the most severe hardness loss during refrigeration, making long-term preservation impossible. The plasma-activated water single treatment group significantly delayed the decrease in fish fillet hardness, showing better preservation than the untreated group, with only a 31.4% decrease in hardness over 12 days. The results indicate that the highly reactive oxygen and nitrogen substances in the plasma-activated water effectively inhibit the growth of spoilage microorganisms on the fish surface, while reducing the activity of endogenous proteases and decreasing the degradation of myofibril proteins, thereby delaying the deterioration of fish hardness.

[0077] The combined treatment of plasma-activated water and vacuum precooling further improved the hardness retention, with lower final precooling temperatures resulting in better preservation. The plasma-activated water + vacuum precooling to 0℃ group showed only a 13.3% decrease in hardness over 12 days. Different precooling methods significantly regulate the hardness changes of rainbow trout fillets during cold storage. The synergistic treatment of plasma-activated water + vacuum precooling to 0℃, through the antibacterial and enzyme-inhibiting effects of plasma-activated water combined with the low-temperature preservation effect of rapid vacuum cooling, maximizes the inhibition of damage to the muscle fiber structure of the fish, delays the decrease in hardness, and achieves long-term preservation of the textural properties of rainbow trout fillets. This is the optimal precooling technology solution for fresh rainbow trout preservation and cold chain transportation, providing scientific and technical support for the cold-water fish preservation and processing industry.

[0078] The effect of different cooling methods on the color of rainbow trout fillets

[0079] (1) Measurement method

[0080] Rainbow trout fillet samples obtained from Examples 1, 2, 3, and 4 were collected on days 0, 3, 6, 9, and 12 of the storage period for color measurement. A colorimeter was used to measure the color of the fish meat. The fish meat samples were placed flat on a clean, colorless surface, and the measurement was performed in a dark, colorless background environment. Five different measurement points were randomly selected for each sample, avoiding the raised and recessed areas of muscle fiber texture and areas with minor congestion. The brightness value (L*), redness value (a*), and yellowness value (b*) were measured, and ΔE* was calculated using the following formula:

[0081]

[0082] Among them, L0*, a0*, and b0* are standard sample parameter values, that is, the color values ​​of fresh fish meat that has not undergone any treatment and has not been oxidized on day 0.

[0083] (2) Measurement results

[0084] The measurement results are as follows Figure 2 The figure shows the trend of color difference changes in rainbow trout fillets during storage under four different precooling methods. During storage, the total color difference ΔE* continuously increased with the number of storage days, with the untreated group showing the largest increase, reaching 5.3 after 3 days and 13.2 after 12 days, indicating the fastest rate of oxidative browning and color deterioration. Plasma-activated water treatment alone effectively inhibited the increase in color difference, with ΔE* consistently lower than the untreated group at the same storage days, decreasing to 4.9 after 3 days and only 10.1 after 12 days, representing reductions of 7.5% and 23.5% respectively compared to the untreated group. This delayed myoglobin oxidation and browning through antioxidant effects. The combined treatment of plasma-activated water and vacuum precooling further improved color difference control, with lower precooling temperatures showing more significant effects. The plasma-activated water + 4℃ vacuum pre-cooling group had a ΔE* of only 4.1 after 3 days, while the plasma-activated water + 0℃ vacuum pre-cooling group had a ΔE* as low as 3.6 after 3 days, which was 22.6% and 32.1% lower than the untreated group, respectively. The ΔE* of the 4℃ pre-cooling group after 12 days was only 8.4, which was much lower than other groups, and could maintain the color and quality of the fish meat for a long time.

[0085] Effects of different precooling methods on moisture distribution of rainbow trout fillets

[0086] (1) Measurement method

[0087] Rainbow trout fillet samples obtained from Examples 1, 2, 3, and 4 were collected on days 0, 3, 6, 9, and 12 of the storage period for moisture distribution determination. The measurements were performed using a MesoMR21-040V high-performance two-dimensional nuclear magnetic resonance (NMR) analyzer. The refrigerated fish samples were cut into 1.0cm × 1.0cm × 1.0cm pieces and placed in 15mm sample cuvettes for testing at 25°C. The instrument was calibrated using Q-FID mode and standards. Subsequently, the T1 and T2 spin-spin relaxation times were measured using a CPMG pulse sequence with the following parameters: measurement temperature 32°C; sampling frequency 200 kHz; repetition wait time 3000 ms; echo count 8000; echo time 0.20 ms. The T2 relaxation time of the fish fillet was obtained by inverting the data using synchronous iterative reconstruction technology.

[0088] (2) Measurement results

[0089] The measurement results are as follows Figure 3 As shown in the figure. During the 0-12 day storage period, the moisture distribution of the fish meat in all treatment groups showed a consistent pattern of deterioration. T represents free water. 22 The water content (T) of fish meat continues to rise, and the water that is not easily moved (T) is the main component of the fish meat. 21 The amount of strongly bound water (T) that is continuously reduced and tightly bound to proteins decreases. 2b The temperature gradually increases. This change indicates that the myofibril protein in the fish meat denatures during storage, reducing the protein's ability to bind water. The water that was originally stored in the myofibril network that is not easily moved is continuously released and converted into free water. As a result, the water-holding capacity of the fish meat continues to decline, and the freshness of the meat gradually deteriorates.

[0090] like Figure 3 In group A, the untreated control group showed the fastest rate of deterioration in the moisture structure of the fish meat, with T being the highest after 12 days of storage. 22 The increase reached 86.6%, T 21 The decrease was 6.76%, T 2b The increase was 46.9%, and the proportion of free water at the end of storage was significantly higher than in other treatments, indicating the highest risk of water loss. For example... Figure 3 In sample B, immersion in plasma-activated water alone effectively mitigated the trend of moisture deterioration, with all three indicators showing a decrease in variation. This demonstrates that plasma-activated water can improve the binding state between proteins and water, reduce the precipitation of free water, and thus provide basic preservation effects. Figure 3 C and Figure 3 In section D, the combined use of plasma-activated water soaking and vacuum precooling processes produces a synergistic preservation effect, with a significantly better effect on stabilizing the moisture distribution of fish meat than single activated water treatment. Specifically, lowering the precooling temperature to 0℃ resulted in the optimal preservation effect across all groups, with this group achieving the best T value after 12 days of storage. 22 It increased by only 12.2% from the initial value, T21 It only decreased by 1.11%, T 2b The increase was only 11.9%, with the lowest variation in moisture distribution. Vacuum precooling slows down the denaturation of myofibril proteins. The rapid cooling characteristic of vacuum, combined with the regulatory effect of plasma-activated water on the hydrophilic groups of proteins, effectively locks in moisture within the muscle fibers, delaying the decline in the water-holding capacity of the fish during storage. Based on comprehensive moisture distribution data, plasma-activated water immersion combined with vacuum precooling to 0℃ is the optimal treatment process. This can stabilize the moisture content of the fish during long-term storage, delaying deterioration of meat quality and extending the shelf life of the fish.

[0091] Effects of different precooling methods on total bacterial count in rainbow trout fillets

[0092] (1) Measurement method

[0093] Rainbow trout fillet samples obtained from Examples 1, 2, 3, and 4 were collected on days 0, 3, 6, 9, and 12 of the storage period for total bacterial count determination. The determination was performed according to Chinese National Standard GB 4789.2-2022, "National Food Safety Standard - Microbiological Examination of Food - Determination of Total Colony Count". 25g of fish meat sample was weighed and mixed with 225mL of sterile physiological saline. After homogenization, the sample was diluted in a 10-fold gradient, and 1-3 suitable dilutions were selected. The diluted solutions were then spread on plate counting agar and incubated at 30±1℃ for 72 hours before counting. Results are expressed as log CFU / g. Each sample was measured in triplicate, and the average value was taken.

[0094] (2) Measurement results

[0095] The measurement results are from Figure 4 The change curve of total bacterial count (Log CFU / g) in fish meat during the storage period is shown. The total bacterial count in fish meat of each experimental group continued to increase with the extension of storage days, but the inhibitory effect of different treatments on microbial proliferation was significantly different.

[0096] At the initial storage stage (0 days), the total bacterial count of all four groups of samples was at a similarly low level (approximately 4.2–4.4 Log CFU / g), representing the initial basic microbial content of fresh fish. The untreated control group exhibited the fastest growth rate of total bacterial count throughout the storage period, reaching 6.32 Log CFU / g (the critical value for microbial spoilage of fish) on day 3. Microorganisms proliferated rapidly without inhibition, resulting in the shortest shelf life for the fish. The samples treated only with plasma-activated water showed a significantly lower increase in total bacterial count compared to the untreated group, demonstrating that plasma-activated water itself possesses antibacterial activity, capable of killing and inhibiting microorganisms attached to the surface of the fish, effectively delaying bacterial proliferation. However, relying solely on activated water treatment without the support of a low-temperature environment limits its antibacterial ability. Combining activated water soaking with vacuum pre-cooling creates a synergistic preservation effect. The total bacterial count of the two combined treatment groups was consistently lower than that of the single activated water treatment group, and the lower the final vacuum pre-cooling temperature, the stronger the antibacterial effect.

[0097] In summary, the above measurement results show that the synergistic treatment method of plasma-activated water immersion combined with vacuum pre-cooling to 0°C used in Example 3 of this invention maintains hardness (hardness decrease of only 13.3% after 12 days), stabilizes color (ΔE* of only 8.2 after 12 days), and maintains moisture content (T). 22 The method exhibits significantly better performance than other embodiments in terms of both a 12.2% increase in bacterial count and antibacterial effect (lowest total bacterial count throughout the process), making it the optimal implementation of this invention. This process can significantly extend the shelf life of cold-water fish and has promising prospects for industrial application.

[0098] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for preserving cold-water fish using plasma-activated water in conjunction with vacuum precooling, characterized in that, Includes the following steps: (1) Preparation of plasma-activated water: Water is placed in a plasma-activated water generator for discharge treatment to obtain plasma-activated water; (2) Raw material pretreatment: The cold-water fish raw materials are soaked in plasma-activated water; (3) Vacuum cooling treatment: The cold-water fish raw material soaked in step (2) is placed in a vacuum environment for cooling treatment. During the cooling treatment, the center temperature of the cold-water fish raw material soaked in step (2) drops from the initial temperature to the target temperature. (4) Storage: Package the cold-water fish raw materials processed in step (3) and store them in a refrigerated environment.

2. The method according to claim 1, characterized in that, The cold-water fish includes rainbow trout; the rainbow trout includes fish chunks.

3. The method according to claim 1, characterized in that, The discharge treatment time in step (1) is >15 min.

4. The method according to claim 1, characterized in that, The discharge voltage for plasma-activated water preparation in step (1) is 350~420V.

5. The method according to claim 1, characterized in that, The soaking time in step (2) is 3 to 8 minutes; the mass ratio of the cold-water fish raw material to the plasma-activated water is (1:1) to (1:3).

6. The method according to claim 1, characterized in that, The absolute pressure of the vacuum environment described in step (3) is 0.1~1.0 kPa.

7. The method according to claim 1, characterized in that, The initial temperature in step (3) is 16~19℃; the target temperature is 0~4℃.

8. The method according to claim 1, characterized in that, The cooling process in step (3) takes 10 to 30 minutes.

9. The method according to claim 1, characterized in that, The vacuum cooling process described in step (3) is carried out in a vacuum chamber containing a sterilization device, which is positioned above the cold-water fish raw material and sterilizes the cold-water fish raw material during the cooling process; the sterilization device includes an excimer lamp.

10. The method according to claim 1, characterized in that, The temperature of the refrigeration environment in step (4) is 0~4℃.

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