Triploid oncorhynchus mykiss cold storage and preservation method by combining plant extract with low-temperature plasma technology

Abstract

The invention provides a triploid rainbow trout refrigeration and fresh-keeping method by combining plant extracts with a low-temperature plasma technology, and belongs to the technical field of rainbow trout refrigeration and fresh-keeping. Hawthorn, pericarpium citri reticulatae and fried semen raphani are mixed according to the mass ratio of 2: 1: 2 to prepare a composite plant fresh-keeping agent; according to a sequence of soaking for 20 minutes with plasma activated water, soaking for 10 minutes with a composite plant preservative, and then carrying out dielectric barrier discharge treatment for 2 minutes, a flavonoid compound and organic acid are used for removing strong oxidizing substances generated by plasma treatment, and an anti-oxidation protection layer is formed; the soaking time of the composite plant preservative is dynamically adjusted according to the thiobarbituric acid value, and the technical problem that the preservation effect is reduced due to the fact that low-temperature plasma treatment accelerates lipid oxidation of the triploid rainbow trout is solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of rainbow trout cold storage preservation, and specifically relates to a triploid rainbow trout cold storage preservation method combining plant extracts and low-temperature plasma technology. BACKGROUND

[0002] As a cold-water fish with high protein and low cholesterol, triploid rainbow trout is mainly farmed in the western mountainous areas, while the consumption market is concentrated in the eastern regions, requiring long-distance transportation and cold storage preservation. Traditional cold storage preservation methods use low-temperature plasma dielectric barrier discharge technology or plasma-activated water treatment to generate active oxygen and active nitrogen and other strong oxidizing substances to attack microbial nucleic acids and proteins for sterilization, which has been widely applied in the field of fruit and vegetable, meat and aquatic product preservation. However, the strong oxidizing substances such as hydroxyl radicals and hydrogen peroxide generated by low-temperature plasma treatment accelerate the oxidative degradation of polyunsaturated fatty acids in triploid rainbow trout during sterilization, leading to a rapid increase in thiobarbituric acid value and the generation of off-flavors, reducing the preservation effect. Direct treatment by dielectric barrier discharge also has the problem of uneven treatment due to irregular sample surface, with some areas being over-treated and some areas being under-treated. That is, the existing technology has the technical problem of low-temperature plasma treatment accelerating the lipid oxidation of triploid rainbow trout, resulting in a decline in preservation effect. SUMMARY

[0003] Therefore, the present application provides a triploid rainbow trout cold storage preservation method combining plant extracts and low-temperature plasma technology, which can solve the technical problem of low-temperature plasma treatment accelerating the lipid oxidation of triploid rainbow trout, resulting in a decline in preservation effect in the prior art.

[0004] The present application is implemented as follows: The present application provides a triploid rainbow trout cold storage preservation method combining plant extracts and low-temperature plasma technology, which mixes hawthorn, dried tangerine or orange peel and fried Semen Raphani according to a mass ratio to prepare a composite plant preservative, uses an atmospheric cold plasma treatment device to treat distilled water to prepare plasma-activated water, cuts triploid rainbow trout after removing the internal organs and fish skin into fish blocks of consistent specifications, soaks the fish blocks in the plasma-activated water according to a liquid-to-material ratio, then adds the composite plant preservative for soaking, places the soaked triploid rainbow trout in a dielectric barrier discharge device for treatment, measures the first thiobarbituric acid value of the treated triploid rainbow trout and adjusts the soaking time of the composite plant preservative according to the first thiobarbituric acid value, seals the treated triploid rainbow trout in a sterile homogenization bag, and stores it in a cold storage environment and regularly measures the preservation indicators; the strong oxidizing substances generated by plasma treatment are removed by flavonoids and organic acids in the composite plant preservative.

[0005] The mass ratio of the hawthorn, dried tangerine or orange peel and fried Semen Raphani is 2:1:2, which is determined by comparing the thiobarbituric acid value and total bacterial count value on the 8th day after treatment.

[0006] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0007] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0008] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0009] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0010] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0011] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0012] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0013] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0014] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0015] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0016] The preparation steps of the composite plant preservative include: soaking the plant material in distilled water at a mass-volume ratio of 1:10 for 10 minutes, and determining the total flavonoid content and total phenol content in the extraction liquid under different conditions.

[0017] The measurement frequency is determined every 3 days or every 2 days by analyzing the changing trends of preservation indicators at different time points.

[0018] The preservation indicators include total bacterial count, volatile basic nitrogen, and dithiobarbituric acid. When the total bacterial count exceeds [a certain value], [the following parameters are considered]. Discontinue storage when CFU / g or volatile basic nitrogen value exceeds 20 mg / 100g.

[0019] The plasma-activated water is used within 30 minutes of preparation to avoid rapid decay of strong oxidizing substances such as hydroxyl radicals and hydrogen peroxide.

[0020] This invention prepares a compound plant preservative by mixing hawthorn, dried tangerine peel, and stir-fried radish seeds in a mass ratio of 2:1:2. After soaking in plasma-activated water, the mixture is then soaked in the compound plant preservative before being treated with dielectric barrier discharge (DPD). Flavonoids and organic acids remove strong oxidizing substances such as hydroxyl radicals and hydrogen peroxide generated during plasma treatment, forming an antioxidant protective layer within the fish tissue. The flavonoids in the compound plant preservative have the ability to scavenge free radicals, the organic acids inhibit microbial growth by lowering the pH value, and the polyphenols protect proteins, mitigating oxidative damage caused by DPD. The initial soaking in plasma-activated water ensures uniform contact of the active substances across the entire sample surface due to the fluidity of the liquid, overcoming the unevenness problem of direct DPD treatment. The subsequent soaking in the compound plant preservative neutralizes any remaining strong oxidizing substances. In summary, this invention solves the technical problem of accelerated lipid oxidation in triploid rainbow trout due to low-temperature plasma treatment, which leads to a decrease in preservation effectiveness, by neutralizing the strong oxidizing substances generated during plasma treatment and forming an antioxidant protective layer. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method of the present invention.

[0022] Figure 2 This graph shows the changes in TVC values ​​of triploid rainbow trout during storage.

[0023] Figure 3 A graph showing the changes in TVB-N values ​​of triploid rainbow trout during storage.

[0024] Figure 4 This graph shows the changes in TBA values ​​of triploid rainbow trout during storage.

[0025] Figure 5 Radar image of triploid rainbow trout during storage.

[0026] Figure 6 Radar image of taste perception in triploid rainbow trout during storage. Detailed Implementation

[0027] 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.

[0028] like Figure 1 The diagram shown is a flowchart of a method for cold storage and preservation of triploid rainbow trout using plant extracts combined with low-temperature plasma technology, provided by this invention. This method includes the following steps:

[0029] S01. Mix hawthorn, dried tangerine peel and stir-fried radish seeds in a mass ratio of 2:1:2, soak in a mixture of materials and distilled water at a mass-volume ratio of 1:10 for 10 minutes, boil and filter, then concentrate by rotary evaporation to 1g / mL, autoclave and cool to room temperature to obtain a compound plant preservative.

[0030] S02. 900mL of distilled water was treated using an atmospheric cold plasma treatment device. The power was set to 750W, the voltage to 5kV, the compressed air pressure to 0.18MPa, and the gas flow rate to 30L / min. The nozzle of the spray gun was placed 15mm below the liquid surface and discharged for 5 minutes to prepare plasma-activated water.

[0031] S03. After removing the internal organs and skin of the triploid rainbow trout, cut them into fish pieces of the same size. Soak them in the plasma-activated water prepared in step S02 at a liquid-to-material ratio of 5:1 for 20 minutes, and then soak them in the compound plant preservative prepared in step S01 for 10 minutes.

[0032] S04. Place the soaked triploid rainbow trout in a dielectric barrier discharge device for treatment. Set the voltage to 70kV, the frequency to 80Hz, the electrode spacing to 80 to 90mm, and the treatment time to 2 minutes.

[0033] S05. Determine the first thiobarbituric acid value of the treated triploid rainbow trout. When the first thiobarbituric acid value exceeds 0.3 mg / kg, increase the soaking time of the compound plant preservative to 15 minutes. When the first thiobarbituric acid value is lower than 0.2 mg / kg, shorten the soaking time of the compound plant preservative to 8 minutes.

[0034] S06. After processing, the triploid rainbow trout are placed in sterile homogenization bags, sealed, and stored in a refrigerated environment at 4°C. The total bacterial count, volatile basic nitrogen, and second thiobarbituric acid value are measured every 3 days. Storage is stopped when the total bacterial count exceeds the first threshold or the volatile basic nitrogen value exceeds the second threshold.

[0035] The frequency of measurement mentioned above, or every 3 days, can also be measured every 2 days.

[0036] The combined treatment of compound plant preservatives with dielectric barrier discharge and plasma-activated water produces a synergistic preservation effect. The flavonoids and organic acids in the compound plant preservatives inhibit microbial growth and scavenge free radicals generated by plasma treatment, reducing lipid oxidation rates. The strong oxidizing substances in dielectric barrier discharge and plasma-activated water disrupt microbial structures, while the antioxidant components of the compound plant preservatives protect fish tissue from oxidative damage. The combination of these two technologies achieves both antibacterial and antioxidant effects. After the combined treatment of these three technologies, the total bacterial count of triploid rainbow trout remained below the first threshold on day 11 of storage, the volatile basic nitrogen value remained at a low level, the second thiobarbituric acid value increased slowly, and the shelf life was extended to over 12 days.

[0037] Texture parameters, including hardness, cohesion, elasticity, and chewiness, reflect the taste quality of triploid rainbow trout. Fish treated with dielectric barrier discharge exhibits higher hardness and cohesion but lower elasticity and chewiness. Fish treated with a compound plant preservative shows better elasticity and chewiness but slightly lower hardness. Fish treated with a combination of compound plant preservative and dielectric barrier discharge demonstrates superior hardness, elasticity, and chewiness compared to either treatment alone. Plasma treatment causes mild protein cross-linking, affecting texture. The polyphenols in the compound plant preservative protect proteins, mitigating oxidative damage caused by dielectric barrier discharge and maintaining the fish's good texture properties.

[0038] Furthermore, flavor is a comprehensive sensory experience constructed by taste and smell, including odor and taste characteristics, reflecting the flavor quality of triploid rainbow trout. Plasma treatment causes mild cross-linking of proteins, affecting odor and taste characteristics. Polyphenols in the compound plant preservative have a protective effect on proteins, reducing oxidative damage to proteins caused by dielectric barrier discharge. The combined treatment of these three technologies maintains the good flavor characteristics of the fish.

[0039] This method achieves multiple objectives—antibacterial activity, antioxidant effects, and maintenance of texture and flavor characteristics—by optimizing the processing sequence and parameter control. First, plasma-activated water immersion ensures uniform contact of active substances across the entire sample surface using liquid fluidity, overcoming the unevenness issues inherent in direct dielectric barrier discharge treatment. Then, immersion in a compound plant preservative immediately forms an antioxidant protective layer after plasma treatment, neutralizing residual strong oxidizing substances and preventing excessive oxidation of lipids and proteins. Finally, dielectric barrier discharge treatment further enhances the surface sterilization effect. The synergistic effect of these three technologies significantly extends the cold storage shelf life of triploid rainbow trout, providing technical support for high-quality storage of aquatic products.

[0040] The specific implementation methods of the above steps are described in detail below.

[0041] In step S01, the rotary evaporation concentration process is controlled at a temperature of 60 to 70°C and a vacuum degree of 0.08 to 0.09 MPa, with a concentration time of approximately 40 to 60 minutes. The flavonoids and organic acids in the compound plant preservative have the ability to scavenge free radicals. Hawthorn is rich in pectin, amino acids, and vitamin C; dried tangerine peel contains flavonoids such as hesperidin, tangeretin, and senna; and the extract from roasted radish seeds has an inhibitory effect on spoilage bacteria.

[0042] The mass ratio of hawthorn, dried tangerine peel, and stir-fried radish seeds in step S01, 2:1:2, was determined through the following experiment. Several triploid rainbow trout samples were soaked in plant extracts with different mass ratios and then refrigerated at 4℃. The thiobarbituric acid value and total bacterial count were measured every two days. Experimental data showed that when the mass ratio was 1:1:1, the thiobarbituric acid value reached 0.48 mg / kg and the total bacterial count reached 5.87 lg CFU / g on day 8; when the mass ratio was 2:1:2, the thiobarbituric acid value was 0.32 mg / kg and the total bacterial count was 4.95 lg CFU / g on day 8; when the mass ratio was 3:1:3, the thiobarbituric acid value was 0.30 mg / kg and the total bacterial count was 4.89 lg CFU / g on day 8; and when the mass ratio was 2:1:1, the thiobarbituric acid value was 0.39 mg / kg and the total bacterial count was 5.23 lg CFU / g on day 8. Based on a comprehensive analysis of the antioxidant and antibacterial effects, a mass ratio of 2:1:2 maintained a low thiobarbituric acid value while effectively controlling the total bacterial count. Furthermore, increasing the proportion of hawthorn and roasted radish seeds did not significantly improve the results. Therefore, the optimal mass ratio was determined to be 2:1:2.

[0043] The mass-to-volume ratio of material to distilled water (1:10) and the soaking time (10 minutes) in step S01 were determined through the following experiments. The mass ratio of hawthorn, dried tangerine peel, and stir-fried radish seeds was fixed at 2:1:2. Extraction was performed using mass-to-volume ratios of 1:5, 1:10, and 1:15, with soaking times set to 5 minutes, 10 minutes, and 15 minutes, respectively. The total flavonoid and total phenolic content in the extracts were measured after extraction. Experimental data showed that when soaked for 10 minutes at a mass-to-volume ratio of 1:5, the total flavonoid content was 1.23 mg / mL and the total phenolic content was 2.87 mg / mL; when soaked for 10 minutes at a mass-to-volume ratio of 1:10, the total flavonoid content was 0.98 mg / mL and the total phenolic content was 2.31 mg / mL; and when soaked for 10 minutes at a mass-to-volume ratio of 1:15, the total flavonoid content was 0.67 mg / mL and the total phenolic content was 1.54 mg / mL. When soaked at a mass-to-volume ratio of 1:10 for 5 minutes, the total flavonoid content was 0.65 mg / mL and the total phenol content was 1.48 mg / mL. When soaked at a mass-to-volume ratio of 1:10 for 15 minutes, the total flavonoid content was 1.05 mg / mL and the total phenol content was 2.45 mg / mL. Considering extraction efficiency and subsequent concentration costs, a mass-to-volume ratio of 1:10 for 10 minutes yielded a high content of active ingredients while avoiding excessive energy consumption during the concentration process; therefore, this was determined to be the optimal parameter.

[0044] The rotary evaporation temperature (60-70℃) and vacuum degree (0.09-0.10MPa) in step S01 were determined through the following experiments. Several portions of the extract obtained in step S01 were taken and concentrated by rotary evaporation under different temperatures and vacuum degrees. The retention rates of the active ingredients after concentration were measured. Experimental data showed that at 50℃ and 0.09MPa, the concentration time was 80 minutes, with a total flavonoid retention rate of 92% and a total phenol retention rate of 89%; at 60℃ and 0.09MPa, the concentration time was 55 minutes, with a total flavonoid retention rate of 94% and a total phenol retention rate of 91%; at 70℃ and 0.10MPa, the concentration time was 45 minutes, with a total flavonoid retention rate of 93% and a total phenol retention rate of 90%; and at 80℃ and 0.10MPa, the concentration time was 35 minutes, with a total flavonoid retention rate of 86% and a total phenol retention rate of 83%. The optimal parameter range is determined to be 60 to 70°C, which ensures both concentration efficiency and high retention of active ingredients, and 0.09 to 0.10 MPa, which provides a moderate evaporation rate.

[0045] The preparation parameters for plasma-activated water in step S02 were determined through the following experiments. Plasma-activated water was prepared using power of 500W, 750W, and 1000W, voltage of 3kV, 5kV, and 7kV, nozzle-to-liquid-surface distance of 10mm, 15mm, and 20mm, and treatment times of 3 minutes, 5 minutes, and 7 minutes, respectively. The concentration of reactive oxygen species and pH value were measured. Experimental data showed that when treated for 5 minutes at 500W power, 3kV voltage, 15mm distance, and 5 minutes, the reactive oxygen species concentration was 35μmol / L and the pH value was 3.8; when treated for 5 minutes at 750W power, 5kV voltage, and 15mm distance, the reactive oxygen species concentration was 68μmol / L and the pH value was 3.2; and when treated for 5 minutes at 1000W power, 7kV voltage, and 15mm distance, the reactive oxygen species concentration was 87μmol / L and the pH value was 2.9. With a power of 750W, a voltage of 5kV, and a distance of 10mm, the water temperature rose to 38℃ after 5 minutes of treatment. At a distance of 15mm, the water temperature rose to 24℃, and at a distance of 20mm, the reactive oxygen species concentration decreased to 52μmol / L. With the same power of 750W, a voltage of 5kV, and a distance of 15mm, the reactive oxygen species concentration was 45μmol / L after 3 minutes of treatment, and 72μmol / L after 7 minutes, but the water temperature rose to 31℃. Considering both reactive oxygen species concentration and water temperature control, the optimal parameter combination is 750W power, 5kV voltage, 15mm distance, and 5 minutes of treatment time.

[0046] The parameter for placing the spray gun nozzle 15mm below the liquid surface in step S02 is derived from the above experimental data analysis. At a distance of 10mm, the water temperature rises too quickly, affecting the stability of the active substance. At a distance of 20mm, the concentration of the active substance decreases significantly. At a distance of 15mm, the concentration of active oxygen species can be guaranteed to reach 68μmol / L, while the water temperature can be controlled at 24℃, which is the optimal distance.

[0047] The soaking time in plasma-activated water (20 minutes) and the soaking time in the compound plant preservative (10 minutes) in step S03 were determined through the following experiment. Several triploid rainbow trout samples were taken and soaked in plasma-activated water for 10 minutes, 20 minutes, and 30 minutes, respectively, followed by soaking in the compound plant preservative for 5 minutes, 10 minutes, and 15 minutes. The total bacterial count and thiobarbituric acid value were measured on the second day after treatment. The experimental data showed that after soaking in plasma-activated water for 10 minutes and then in the compound plant preservative for 10 minutes, the total bacterial count was 4.321 g CFU / g and the thiobarbituric acid value was 0.26 mg / kg. After soaking in plasma-activated water for 20 minutes and then in the compound plant preservative for 10 minutes, the total bacterial count was 3.871 g CFU / g and the thiobarbituric acid value was 0.21 mg / kg. After soaking in plasma-activated water for 30 minutes and then in the compound plant preservative for 10 minutes, the total bacterial count was 3.751 g CFU / g and the thiobarbituric acid value was 0.31 mg / kg. After soaking in plasma-activated water for 20 minutes and then in the compound plant preservative for 5 minutes, the thiobarbituric acid value was 0.29 mg / kg. After soaking for 15 minutes, the water absorption rate of the fish meat reached 12%, affecting its texture. Therefore, the optimal combination was determined to be soaking in plasma-activated water for 20 minutes and in the compound plant preservative for 10 minutes.

[0048] The liquid-to-solid ratio of 5:1 in step S03 was determined through the following experiment. With a fixed soaking time of 20 minutes in plasma-activated water and 10 minutes in the compound plant preservative, soaking treatments were performed using liquid-to-solid ratios of 3:1, 5:1, and 7:1, respectively. The total bacterial count and water absorption rate of the fish were measured on the second day after treatment. Experimental data showed that at a liquid-to-solid ratio of 3:1, some areas of the fish pieces were not completely submerged, resulting in uneven treatment, with a total bacterial count of 4.58 lg CFU / g. At a liquid-to-solid ratio of 5:1, the fish pieces were completely submerged and treated evenly, with a total bacterial count of 3.87 lg CFU / g and a water absorption rate of 6.2%. At a liquid-to-solid ratio of 7:1, the total bacterial count was 3.81 lg CFU / g and the water absorption rate was 6.5%. Considering both treatment uniformity and solution volume, a liquid-to-solid ratio of 5:1 ensured complete submersion of the fish pieces while avoiding excessive waste of solution, and was therefore determined as the optimal parameter.

[0049] The voltage (70kV), frequency (80Hz), electrode spacing (80-90mm), and treatment time (2 minutes) of the dielectric barrier discharge device in step S04 were determined through the following experiments. Triploid rainbow trout were treated with voltages of 50kV, 70kV, and 90kV, frequencies of 60Hz, 80Hz, and 100Hz, electrode spacings of 60mm, 80mm, and 100mm, and treatment times of 1 minute, 2 minutes, and 3 minutes, respectively. The total bacterial count and thiobarbituric acid value were measured on the second day after treatment. Experimental data show that after 2 minutes of treatment at 50kV, 60Hz, and 80mm spacing, the total bacterial count was 4.65 lg CFU / g and the thiobarbituric acid value was 0.25 mg / kg. After 2 minutes of treatment at 70kV, 80Hz, and 80mm spacing, the total bacterial count was 3.52 lg CFU / g and the thiobarbituric acid value was 0.35 mg / kg. After 2 minutes of treatment at 90kV, 100Hz, and 80mm spacing, the total bacterial count was 3.21 lg CFU / g and the thiobarbituric acid value was 0.58 mg / kg. Local overheating occurred at 70kV, 80Hz, and 60mm spacing. At a spacing of 100mm, the discharge efficiency decreased and the total bacterial count was 4.12 lg CFU / g. After 1 minute of treatment at 70kV, 80Hz, and 80mm spacing, the total bacterial count was 4.01 lg CFU / g, and after 3 minutes of treatment, the thiobarbituric acid value increased to 0.49 mg / kg. The optimal parameter combination for considering both antibacterial effect and lipid oxidation control is 70kV voltage, 80Hz frequency, 80 to 90mm electrode spacing, and 2 minutes treatment time.

[0050] The threshold values ​​of 0.2 mg / kg and 0.3 mg / kg for the first thiobarbituric acid value in step S05 were determined through the following experiments. Several triploid rainbow trout samples treated in step S04 were taken, and their thiobarbituric acid values ​​were measured to be in the range of 0.15 to 0.42 mg / kg. Samples with thiobarbituric acid values ​​in the range of 0.15 to 0.20 mg / kg were treated with the original compound plant preservative for 10 minutes and then refrigerated. On the 8th day, the average thiobarbituric acid value was 0.38 mg / kg. Samples with thiobarbituric acid values ​​in the range of 0.20 to 0.30 mg / kg were treated with the original soaking time and then refrigerated. On the 8th day, the average thiobarbituric acid value was 0.43 mg / kg. Samples with thiobarbituric acid values ​​ranging from 0.30 to 0.42 mg / kg were treated with a compound plant preservative for 10, 12, and 15 minutes, respectively, followed by refrigeration. On day 8, the thiobarbituric acid values ​​were 0.51 mg / kg, 0.47 mg / kg, and 0.41 mg / kg, respectively. Experimental data showed that when the initial thiobarbituric acid value was below 0.2 mg / kg, lipid oxidation was relatively mild. Shortening the soaking time to 8 minutes resulted in a thiobarbituric acid value of 0.39 mg / kg on day 8, saving on the amount of compound plant preservative while maintaining good preservation effects. When the initial thiobarbituric acid value exceeded 0.3 mg / kg, the lipid oxidation rate was rapid. Increasing the soaking time to 15 minutes controlled the thiobarbituric acid value below 0.45 mg / kg on day 8. Therefore, 0.2 mg / kg and 0.3 mg / kg were determined as the threshold values ​​for adjusting the soaking time of the compound plant preservative.

[0051] The adjusted soaking times of 8 minutes and 15 minutes for the compound plant preservative in step S05 are derived from the above experimental data analysis. When the first thiobarbituric acid value is below 0.2 mg / kg, shortening it to 8 minutes can meet the antioxidant requirements while avoiding excessive soaking that could affect the texture. When the first thiobarbituric acid value exceeds 0.3 mg / kg, extending it to 15 minutes provides stronger antioxidant protection.

[0052] In step S06, the first threshold and the second threshold are respectively CFU / g and 20mg / 100g. The first threshold is derived from GB2733-2015 National Food Safety Standard for Fresh and Frozen Aquatic Animal Products, which sets limits on the total bacterial count of aquatic products. Exceeding these limits... CFU / g indicates that the product has been severely contaminated by microorganisms and is no longer suitable for consumption. The second threshold comes from the aquatic product freshness evaluation standard; a volatile basic nitrogen value exceeding 20 mg / 100g indicates that the protein has decomposed significantly and the product has spoiled.

[0053] The frequency of measuring preservation indicators every 3 days in step S06 was determined through the following experiment. Triploid rainbow trout samples that had undergone complete treatment were refrigerated at 4°C, and the total bacterial count, volatile basic nitrogen (VBN) value, and dithiobarbituric acid (DBA) value were measured on days 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, and 14. Experimental data showed that the total bacterial count increased little from 3.52 lg CFU / g to 3.89 lg CFU / g from days 1 to 3; it rapidly increased to 4.67 lg CFU / g from days 3 to 6; it increased to 5.35 lg CFU / g from days 6 to 9; and it increased to 5.98 lg CFU / g from days 9 to 12. The VBN value remained below 8 mg / 100g for the first 6 days, increased to 12 mg / 100g from days 6 to 9, and increased to 16 mg / 100g from days 9 to 12. The dithiobarbituric acid value increased relatively gradually throughout the storage period, rising from 0.21 mg / kg to 0.48 mg / kg. Analysis of the experimental data revealed that measuring every 3 days allowed for timely monitoring of quality changes while avoiding sample consumption and operational costs associated with frequent measurements; therefore, the measurement frequency was determined to be every 3 days.

[0054] Due to the influence of some environmental factors, such as the stability of storage temperature and the variability of microbial content in the storage environment, the frequency can be increased to every 2 days.

[0055] The plasma-activated water in step S02 is a functionalized liquid rich in active oxygen, active nitrogen, and metastable substances, formed by treating an aqueous solution with low-temperature plasma. The distance between the spray nozzle and the liquid surface directly affects the transfer efficiency of the active substances. Too close a distance will cause the water temperature to rise, affecting the stability of the active substances; too far a distance will reduce the concentration of the active substances. The plasma-activated water should be used within 30 minutes after preparation to ensure the concentration of active substances and avoid the rapid decay of strong oxidizing substances such as hydroxyl radicals and hydrogen peroxide.

[0056] Step S03 employs a sequential treatment process: first soaking in plasma-activated water, then soaking in a compound plant preservative. The fluidity and uniformity of the plasma-activated water overcome the uneven treatment caused by the irregular surface of the sample when directly treated with dielectric barrier discharge. The active substances in the plasma-activated water have a destructive effect on the cell membranes and cell walls of microorganisms. The flavonoids and organic acids in the compound plant preservative penetrate into the fish tissue during soaking, forming an antioxidant protective layer. A liquid-to-material ratio of 5:1 ensures the fish pieces are completely submerged. Too short a soaking time affects the penetration of active substances, while too long a soaking time causes the fish to absorb water and swell, affecting its texture.

[0057] The dielectric barrier discharge treatment in step S04 is a method of generating non-equilibrium plasma by isolating electrodes with an insulating dielectric layer and applying high-frequency, high-voltage alternating current to ionize the gas. The hydroxyl radicals, hydrogen peroxide, reactive oxygen species, and reactive nitrogen species generated during the discharge process attack the nucleic acids and proteins of microorganisms, causing them to denature and become inactive, thus achieving a sterilization effect. The electrode spacing is controlled within the range of 80 to 90 mm to ensure discharge intensity and uniformity; too small a spacing will lead to localized overheating, while too large a spacing will reduce discharge efficiency. A treatment time of 2 minutes is a balance point between antibacterial effect and avoiding excessive oxidation; excessive time will accelerate the oxidative degradation of polyunsaturated fatty acids in triploid rainbow trout.

[0058] The first thiobarbituric acid value in step S05 reflects the degree of lipid oxidation and is a key indicator for evaluating the quality of triploid rainbow trout. The strong oxidizing substances generated by dielectric barrier discharge and plasma-activated water treatment accelerate the oxidation of polyunsaturated fatty acids, leading to a rapid increase in thiobarbituric acid value and the production of off-flavors. By dynamically adjusting the soaking time of the compound plant preservative by monitoring the first thiobarbituric acid value, the antioxidant components in the compound plant preservative neutralize excess reactive oxygen species, preventing excessive lipid oxidation. When the first thiobarbituric acid value exceeds 0.3 mg / kg, it indicates a rapid lipid oxidation rate, requiring an increased soaking time with the compound plant preservative to provide more antioxidant protection. When the first thiobarbituric acid value is below 0.2 mg / kg, it indicates a milder degree of oxidation, requiring a shorter soaking time with the compound plant preservative to avoid over-soaking and affecting the texture of the fish flesh.

[0059] The total bacterial count in step S06 reflects the degree of microbial contamination, while the volatile basic nitrogen value reflects the degree of protein degradation. During refrigeration, the endogenous enzymes and microorganisms in triploid rainbow trout cause protein degradation into alkaline nitrogenous substances such as ammonia and amines, and the volatile basic nitrogen value increases with prolonged storage time. A total bacterial count exceeding the first threshold indicates that the product is severely contaminated with microorganisms and is no longer suitable for consumption, while a volatile basic nitrogen value exceeding the second threshold indicates that a large amount of protein has decomposed. Measure preservation indicators every 3 days to promptly monitor the quality changes of triploid rainbow trout. A refrigeration temperature of 4℃ inhibits microbial growth and enzyme activity, extending shelf life.

[0060] Specifically, the principle of this invention is as follows: Low-temperature plasma treatment sterilizes microorganisms by generating hydroxyl radicals, hydrogen peroxide, reactive oxygen species, and reactive nitrogen species that attack their nucleic acids and proteins. However, these strong oxidizing substances simultaneously attack the polyunsaturated fatty acids in triploid rainbow trout, triggering lipid peroxidation and generating oxidation products such as malondialdehyde, leading to increased thiobarbituric acid levels and off-flavors. This invention employs a strategy of immediately soaking the fish in a compound plant preservative after plasma treatment. Vitamin C and flavonoids in hawthorn act as electron donors to neutralize hydroxyl radicals and hydrogen peroxide. Hesperidin and tangeretin in dried tangerine peel block the lipid peroxidation chain reaction through hydrogen donation. Sulforaphane in stir-fried radish seeds has a destructive effect on microbial cell membranes, enhancing the antibacterial effect. A mass ratio of 2:1:2 was experimentally optimized to ensure the best synergistic ratio of flavonoids and organic acids. A soaking time of 10 minutes allows the antioxidant components to fully penetrate the fish tissue. A 20-minute immersion time in plasma-activated water ensures the active substances' ability to disrupt microbial cell membranes, while a 2-minute dielectric barrier discharge treatment balances antibacterial effects with the avoidance of excessive oxidation. When the thiobarbituric acid value exceeds 0.3 mg / kg, the immersion time with the compound plant preservative is increased to 15 minutes to provide stronger antioxidant protection. When the thiobarbituric acid value is below 0.2 mg / kg, the immersion time is shortened to 8 minutes to avoid excessive immersion affecting texture, thus achieving dynamic regulation of lipid oxidation rate to maintain the stable quality of triploid rainbow trout.

[0061] The following provides a specific embodiment 1 of the present invention, and the specific implementation of each step in this embodiment 1 is described in detail below.

[0062] The specific implementation of step S01 involves mixing hawthorn, dried tangerine peel, and stir-fried radish seeds in a mass ratio of 2:1:2, soaking them in a mixture of materials and distilled water at a mass-to-volume ratio of 1:10 for 10 minutes, boiling, filtering, and then rotary evaporating to concentrate the mixture to 1. The compound plant preservative was obtained by autoclaving and cooling to room temperature. The temperature and vacuum level were controlled at 60-70℃ and 0.09-0.10 MPa respectively during the rotary evaporation concentration process, with a concentration time of approximately 40-60 minutes. The expression for the total active ingredient concentration of the compound plant preservative is as follows:

[0063] ;

[0064] In the formula, This represents the total active ingredient concentration of the compound plant preservative, expressed in units of... ; For hawthorn quality, the unit is... ; For the quality of dried tangerine peel, the unit is... ; The unit for measuring the quality of stir-fried radish seeds is... ; The content of active ingredients per unit mass of hawthorn is expressed in units of... The experimentally measured value was 3.2. ; The active ingredient content per unit mass of dried tangerine peel, in units of... The experimentally measured value was 4.8. ; The content of active ingredients per unit mass of stir-fried radish seeds is expressed in units of... The experimentally measured value was 2.9. ; This is the standard quality parameter, with a value of 1. ; This is the initial extraction volume, in units of... ; This is the standard volume parameter, with a value of 1. ; This is the concentration ratio, which defaults to 10. Among them, The method of obtaining the sample is to take 5 hawthorn samples. The rutin standard curve method was used to measure the rutin standard curve using a UV spectrophotometer at 510 nm. The absorbance was measured at a specific wavelength, and the total flavonoid content was calculated based on the standard curve. and The determination method and same.

[0065] The specific implementation of step S02 is to use an atmospheric cold plasma treatment device to process 900 Distilled water is treated with the following settings: power 750W, voltage 5KV, compressed air pressure 0.18MPa, gas flow rate 30L / min, and the spray nozzle positioned 15 cm below the liquid surface. Plasma-activated water is prepared by discharging for 5 minutes. The formula for calculating the concentration of reactive oxygen species in plasma-activated water is as follows:

[0066] ;

[0067] In the formula, This represents the concentration of reactive oxygen species, in units of... ; This refers to the plasma processing power, measured in W. The standard power parameter is 1W. Processing time, in units of ; This is the standard time parameter, with a value of 1. ; The energy conversion coefficient is 0.012, and the experimentally fitted value is 0.012. ; The volume of water is expressed in units of 1000 liters. ; The distance between the spray gun nozzle and the liquid surface, in units of The value is 15 ; This is the temperature decay coefficient, with an empirical value of 0.035; The value represents the increase in water temperature, expressed in °C. It is obtained in real time by measuring the water temperature with a thermometer with an accuracy of 0.1 °C before and after plasma treatment and calculating the difference.

[0068] The specific implementation of step S03 involves removing the internal organs and skin from triploid rainbow trout, cutting them into uniformly sized pieces, and soaking them in the plasma-activated water prepared in step S02 at a liquid-to-material ratio of 5:1 for 20 minutes. Following this, the compound plant preservative prepared in step S01 is added and soaked for 10 minutes. The formula for calculating the penetration depth of the active substances is as follows:

[0069] ;

[0070] In the formula, The depth of penetration of the active substance, in units of ; The effective diffusion coefficient is expressed in units of 1000 ppm. The value was determined to be 0.15 using Fick's second law experiment. ; The standard diffusion coefficient parameter has a value of 1. ; Soaking time, in units of ; The permeation resistance coefficient has an empirical value of 1.2. The standard concentration parameter has a value of 1. ; This is the concentration conversion factor, with a value of 1000, used to convert... Convert to A comparable value; For reference concentration, the value is 50. ; This is the standard length parameter, with a value of 1. .in, The determination method is to use the diffusion cell method, where the compound plant preservative is placed on one side of the diffusion cell and the triploid rainbow trout tissue is placed on the other side. The concentration of active ingredients on the receiving side is measured every 5 minutes, and the diffusion coefficient is fitted according to Fick's second law.

[0071] The specific implementation of step S04 involves placing the soaked triploid rainbow trout in a dielectric barrier discharge device for treatment. The device is set with a voltage of 70 kV, a pressure of 5 kV, a compressed air pressure of 0.18 MPa, and a gas flow rate of 30 L / min. The nozzle is positioned 15 cm below the liquid surface. Plasma-activated water is prepared by discharge for 5 minutes. The sterilization efficiency expression of dielectric barrier discharge is as follows:

[0072] ;

[0073] In the formula, is the dielectric barrier discharge sterilization efficiency, which is a dimensionless parameter; The applied voltage is measured in kV. The standard voltage parameter is 1KV. Discharge frequency, unit: ; This is the standard frequency parameter, with a value of 1. ; Processing time, in units of ; The distance between the plates is 1 / 2 oz. ; This is the standard distance parameter, with a value of 1. ; This is the normalized impedance parameter, with an empirical value of 1000.

[0074] The specific implementation of step S05 involves measuring the primary thiobarbituric acid (LTA) value of the treated triploid rainbow trout. When the LTA value exceeds 0.3... At that time, increase the soaking time of the compound plant preservative to 15 minutes, and when the first thiobarbituric acid value is below 0.2... At the same time, shorten the soaking time of the compound plant preservative to 8 minutes. The formula for calculating the adjusted soaking time is as follows:

[0075] ;

[0076] In the formula, The adjusted soaking time for the compound plant preservative is expressed in units of... ; This is the initial soaking time, with a value of 10. ; The adjustment factor is empirically set at 0.5; The first thiobarbituric acid value, in units of The determination was performed using the thiobarbituric acid colorimetric method. The intermediate threshold is set to 0.25. The value is 0.2 and 0.3 The arithmetic mean of two adjusted thresholds; The standard thiobarbituric acid value parameter is set to 1. .in, The determination method involves taking 10 samples of triploid rainbow trout. The mixture was homogenized, extracted with trichloroacetic acid solution, filtered, and the filtrate was mixed with thiobarbituric acid reagent. The mixture was boiled in a water bath for 15 minutes, then cooled and heated at 532°C. The absorbance was measured at the specified wavelength, and the thiobarbituric acid value was calculated based on the standard curve.

[0077] The specific implementation of step S06 involves sealing the treated triploid rainbow trout in sterile homogenizing bags and storing them at 4°C. The total bacterial count, volatile basic nitrogen, and second thiobarbituric acid levels are measured every 3 days. Storage is stopped when the total bacterial count exceeds a first threshold or the volatile basic nitrogen exceeds a second threshold. The shelf-life prediction model expression is as follows:

[0078] ;

[0079] In the formula, To predict shelf life, the unit is... ; The threshold for total bacterial count is set to a value of [value to be filled in]. ; This is the initial total bacterial count, in units of... The determination was made by plate counting method; The standard colony count parameter has a value of [value missing]. ; The rate constant is 0.35, and the experimentally fitted value is 0.35. The standard rate parameter has a value of 1. ; The activation energy is set to 52000. ; This is the gas constant, with a value of 8.314. ; Absolute temperature, unit: The calculation method is 273.15 plus the temperature in Celsius. Among them, The determination method involves taking 25g of triploid rainbow trout samples. Join 225 Homogenize in sterile physiological saline, perform serial dilutions, spread on plate counting agar, and incubate at 36°C for 48 hours to count colonies.

[0080] The synergistic preservation effect of compound plant preservatives and plasma technology is quantified by a synergistic factor, which is calculated using the following formula:

[0081] ;

[0082] In the formula, is the synergistic factor, and is a dimensionless parameter; The efficiency of plasma-activated water treatment is a dimensionless parameter, and the calculation method is as follows: ,in This represents the total bacterial count in the untreated control group, in units of... , This represents the total bacterial count after plasma-activated water treatment, in units of... ; The treatment efficiency of the compound plant preservative is a dimensionless parameter, and the calculation method is as follows: ,in The absorbance of DPPH free radicals is the value of the blank control group. To determine the DPPH free radical absorbance after adding the compound plant preservative, the absorbance was measured using 517... Measurements were taken using an ultraviolet spectrophotometer at the specified wavelength. The synergistic enhancement coefficient has an empirical value of 0.3.

[0083] To better understand and implement this invention, the following is a specific application scenario of this invention, Example 2: Example

[0084] In optimizing the cold storage and preservation technology for triploid rainbow trout, a technical team addressed the problems of short shelf life and rapid quality deterioration associated with traditional preservation methods by applying the composite preservation technology of this invention. The team purchased 15 kg of fresh triploid rainbow trout from a breeding farm, with an average weight of 2.5 kg. After transporting the triploid rainbow trout to the processing workshop, the internal organs and skin were immediately removed on a sterile operating table, and the trout were cut into pieces measuring 80 mm in length, 60 mm in width, and 15 mm in thickness, yielding approximately 200 sample pieces.

[0085] The technical team first prepared the compound plant preservative according to the method of this invention. 200g of hawthorn, 100g of dried tangerine peel, and 200g of stir-fried radish seeds were weighed and mixed in a mass ratio of 2:1:2. 5000mL of distilled water was added, and the mixture was soaked at room temperature for 10 minutes. Then, it was transferred to a stainless steel pot and heated to boiling, continuing to boil for 15 minutes. The boiled mixture was filtered through four layers of gauze to remove solid residue. The filtrate was transferred to a rotary evaporator, and the water bath temperature was set to 65℃ and the vacuum degree to 0.095MPa. After rotary evaporation and concentration for 50 minutes, 500mL of concentrated solution was obtained. The concentrated solution was diluted to a 500mL volumetric flask to obtain a compound plant preservative with a concentration of 1g / mL. The compound plant preservative was transferred to an autoclave and sterilized at 121℃ and 0.1MPa for 20 minutes. After sterilization, it was cooled to room temperature for later use.

[0086] The technical team used an atmospheric cold plasma treatment device to prepare plasma-activated water. 900 mL of distilled water was placed in a 1500 mL glass container, and the device was set to 750 W power, 5 KV voltage, 0.18 MPa compressed air pressure, and 30 L / min gas flow rate. The nozzle was placed 15 mm below the liquid surface for discharge treatment, which lasted 5 minutes. During the treatment, a pH meter was used to monitor the pH changes. At the end of the treatment, the pH dropped to 3.2, and the concentration of reactive oxygen species was measured at 68 μmol / L, while the water temperature rose to 24 °C. The plasma-activated water was immediately used for subsequent soaking treatments after preparation, ensuring it was used within 30 minutes to maintain the concentration of active substances.

[0087] Two hundred triploid rainbow trout pieces were randomly divided into eight groups of 25 pieces each. The technical team used a liquid-to-material ratio of 5:1 for soaking treatment, that is, 1000 mL of soaking solution for every 5 kg of fish pieces. The treatment plan is shown in Table 1.

[0088] Table 1 Treatment schemes for different treatment groups

[0089]

[0090] For groups requiring plasma-activated water treatment, immerse the fish pieces in the plasma-activated water for the appropriate time, gently stirring every 5 minutes to ensure even treatment. After soaking in the plasma-activated water, drain the surface water from the fish pieces, then add the compound plant preservative and soak for 10 minutes. After soaking, remove the fish pieces and drain the surface liquid for about 2 minutes.

[0091] The technical team placed the soaked fish pieces into a dielectric barrier discharge device for further processing, setting the voltage to 70KV and the frequency to 80. The electrode spacing was 85mm. Fish pieces were placed on an insulating dielectric layer, ensuring a uniform distance between the fish piece surface and the upper electrode. The dielectric barrier discharge treatment lasted 2 minutes. Uniform discharge was observed during the treatment, with no localized overheating or arcing. Immediately after treatment, the first thiobarbituric acid value of the fish pieces was measured using spectrophotometry. The results showed that the thiobarbituric acid values ​​of different fish pieces ranged from 0.18 to 0.35 mg / kg.

[0092] Based on the test results, the technical team analyzed the first thiobarbituric acid value. Twelve fish pieces had thiobarbituric acid values ​​below 0.2 mg / kg, with an average of 0.17 mg / kg. These fish pieces were retreated with an 8-minute soaking time in the compound plant preservative. Eight other fish pieces had thiobarbituric acid values ​​exceeding 0.3 mg / kg, with an average of 0.33 mg / kg. These fish pieces were retreated with a 15-minute soaking time in the compound plant preservative. The remaining fish pieces had thiobarbituric acid values ​​between 0.2 and 0.3 mg / kg, and the original 10-minute soaking time was maintained. After adjusting the soaking time, the retreated fish pieces underwent a second dielectric barrier discharge treatment for 2 minutes.

[0093] All processed triploid rainbow trout fillets were placed into sterile homogenization bags, with 3 fillets (approximately 150g) per bag. The bags were vacuum-sealed and stored in a 4°C refrigerator. The technical team developed a detailed quality monitoring plan, taking samples on days 2, 5, 8, 11, and 14 of storage to determine the total bacterial count, volatile basic nitrogen, and dithiobarbituric acid levels. Figure 2 As shown, the total bacterial count was determined using the plate count method. 10g of fish sample was added to 90mL of sterile physiological saline to prepare a homogenate, which was then serially diluted and spread onto plate counting agar. After incubation at 36℃ for 48 hours, the colonies were counted. The volatile basic nitrogen value was determined using the micro-diffusion method. 10g of fish sample was added to 75mL of water for extraction for 30 minutes. After filtration, 1mL of the extract was placed in the outer chamber of a diffusion dish. Boric acid absorption solution was added to the inner chamber, and saturated potassium carbonate solution was added to the outer chamber. The dish was sealed and diffused for 2 hours. The volatile basic nitrogen value was calculated by titration with hydrochloric acid standard solution. Figure 3 As shown, the second thiobarbituric acid value was determined by spectrophotometry. 10g of fish meat sample was added to trichloroacetic acid solution for extraction and filtration. After the filtrate reacted with thiobarbituric acid reagent, the absorbance was measured at a wavelength of 532nm. The thiobarbituric acid value was calculated according to the standard curve.

[0094] Results measured on the second day of storage showed that the total bacterial count in the CK group was 4.23. The total bacterial count in the PAW + plant extract + DBD group was 3.52. The differences between the two groups were significant. Volatile basic nitrogen (VBI) values ​​showed a concentration of 6.8 mg / 100g in the control group (CK) and 4.5 mg / 100g in the PAW + plant extract + DBD group. Dithiobarbituric acid (DBI) values ​​showed a concentration of 0.22 mg / kg in the CK group and 0.21 mg / kg in the PAW + plant extract + DBD group. On the 5th day of storage, the total bacterial count in the CK group reached 5.67. The PAW + plant extract + DBD group had a value of 3.89. Volatile basic nitrogen (VBN) levels were measured at 11.2 mg / 100g in the control group (CK) and 6.3 mg / 100g in the PAW + plant extract + DBD group. Dithiobarbituric acid (DBA) levels were measured at 0.31 mg / kg in the CK group and 0.28 mg / kg in the PAW + plant extract + DBD group.

[0095] like Figures 2-4 As shown, the results measured on the 8th day of storage indicated that the total bacterial count in the CK group had exceeded the first threshold. Reached 6.45 The PAW + plant extract + DBD group had a value of 4.67. Still below the limit. Volatile basic nitrogen (VB) determination showed the CK group at 18.6 mg / 100g, close to the second threshold of 20 mg / 100g, while the PAW + plant extract + DBD group was 9.2 mg / 100g. Second thiobarbituric acid (THB) determination showed the CK group at 0.46 mg / kg, and the PAW + plant extract + DBD group at 0.35 mg / kg. Results on day 11 of storage showed the PAW + plant extract + DBD group had a total bacterial count of 5.35. The volatile basic nitrogen value was 12.8 mg / 100g, and the dithiobarbituric acid value was 0.41 mg / kg; all three indicators did not exceed the limits. Results from the 14th day of storage showed that the total bacterial count in the PAW + plant extract + DBD group was 5.98. The levels were still below the first threshold, the volatile basic nitrogen value of 16.3 mg / 100g was below the second threshold, and the second thiobarbituric acid value of 0.48 mg / kg was close to the odor generation threshold. Based on a comprehensive analysis of the trends in these indicators, the technical team determined that the triploid rainbow trout treated with the compound method could have a shelf life of over 12 days under refrigerated conditions at 4°C.

[0096] The technical team conducted flavor characteristic measurements on the fish meat on days 2, 8, and 14 of storage. The fish meat was cut into rectangular samples of 20mm × 20mm × 10mm. An electronic nose was used to measure odor characteristics, and an electronic tongue was used to measure taste characteristics. The results are as follows: Figures 5-6 As shown, where Figure 5 and Figure 6 Because it contains a lot of content, the font size will be small, but even without considering that... Figure 5 and Figure 6 In this case, it will not affect the understanding of the entire plan.

[0097] The electronic nose system has 10 sensors: W1C (sensitive to aromatic compounds), W5S (sensitive to nitrogen oxides), W3C (sensitive to ammonia and aromatic compounds), W6S (sensitive to hydrides), W5C (sensitive to short-chain alkanes and aromatic compounds), W1S (sensitive to methane), W1W (sensitive to sulfides), W2S (sensitive to ethanol), W2W (sensitive to aromatic compounds and organosulfur compounds), and W3S (sensitive to alkanes). Figure 5 It can be seen that the odor profile of the CK group changed most significantly with the extension of storage time, indicating that its spoilage process was faster and the composition and intensity of volatile odor substances changed significantly. In contrast, all treatment groups delayed the odor deterioration process to varying degrees, especially the PAW & plant & DBD combined treatment group, which performed better in maintaining odor stability.

[0098] Based on the morphological changes observed in the radar charts, differences in some sensor responses were already apparent between the treatment groups and the control group by day 2 of storage. By day 8, the odor profile of the control group had further expanded, particularly showing a significant increase in sensor responses reflecting putrefactive gases such as sulfides, ammonia, and alcohols / aldehydes, indicating accelerated protein degradation and lipid oxidation product accumulation. By day 14 of storage, the odor profile of the control group exhibited typical putrefactive characteristics, indicating that the samples had entered a severe putrefactive stage. Among the single treatment groups, the plant extract treatment showed some effectiveness in inhibiting nitrogenous compounds and sulfides, possibly related to the antioxidant and antibacterial effects of the phenols and flavonoids it contained. The PAW, plant, and DBD combined treatment group maintained low levels in most sensor response values, namely W1C 0.4283, W5S 10.97396667, W3C 0.6157, W6S 1.076133333, W5C 0.8437, W1S 6.2524, W1W1 2.84253333, W2S 4.4767, W2W1 1.16716667, and W3S 1.149866667. In particular, it significantly outperformed other treatment groups in key spoilage indicators such as W5S, W1W, and W2W, indicating that this combined treatment can effectively inhibit the formation of typical spoilage odors such as sulfur-containing, nitrogen-containing, and organic sulfide-containing compounds in the later stages of storage. The mechanism may be that polyphenols and flavonoids in plant extracts delay lipid oxidation and protein degradation through antioxidant effects, PAW inhibits microbial growth through reactive oxygen species, and DBD works together through surface modification and microbial inactivation. The three work together to form a multi-layered odor protection barrier.

[0099] The electronic tongue system has eight sensors: salty, sour, bitter, astringent, umami, bitter aftertaste, astringent aftertaste, and umami richness. Figure 6It can be seen that with the extension of storage time, the taste characteristics of the CK group showed a significant deterioration trend, mainly manifested as a decrease in umami response and an increase in unpleasant taste responses such as bitterness and sourness. All treatment groups delayed the above changes to varying degrees, among which the PAW & plant & DBD combined treatment group showed a better effect in maintaining taste balance.

[0100] In the early stages of storage, the acidity value of the PAW treatment group was higher than that of the CK group during both the early and middle stages of storage, while the saltiness value remained relatively stable. The DBD treatment had a significant effect on maintaining umami and its richness, especially in the later stages, where its umami value remained significantly higher than that of the CK. The plant extract treatment group showed outstanding performance in suppressing bitterness and astringency, with its bitterness and astringency values ​​significantly lower than those of the CK throughout the entire storage period. This may be related to the adsorption or masking effect of active ingredients such as polyphenols in the plant extract on flavor substances. The combined treatments showed synergistic or additive effects on most indicators, especially the PAW & plant & DBD combined treatment group. On day fourteen, the values ​​were -10.74 for sourness, -0.13 for bitterness, -4.243333333 for astringency, 0.58 for bitter aftertaste, -0.4 for astringency aftertaste, 6.22 for umami, 1.25 for umami richness, and 10.33 for saltiness. The group maintained high umami and richness values ​​while effectively inhibiting the increase of bitterness and astringency, indicating that the three treatments have an advantage in maintaining the overall flavor balance.

[0101] The technical team also conducted electronic tongue tests. Acidity values ​​below -13, salinity values ​​below -6, and all others below 0 were considered imperceptible. Therefore, on the fourteenth day, the PAW & plant & DBD compound treatment group only had a slight sour and bitter aftertaste, but the umami and richness of umami could still be perceived.

[0102] The technical team measured the textural properties of the fish meat on days 2, 5, 8, 11, and 14 of storage. The measured indicators included hardness, elasticity, chewiness, and adhesiveness. The fish meat was cut into rectangular samples of 20mm × 20mm × 10mm and measured using a texture analyzer equipped with a P / 5N cylindrical probe. The test speed was 1mm / s, the deformation rate was 30%, and the trigger force was 0.15N. The measurement results are shown in Table 2.

[0103] Table 2. Changes in textural parameters of triploid rainbow trout during cold storage.

[0104] As shown in Table 2, the textural parameters of all treatment groups decreased with prolonged storage time, which is consistent with the general pattern of protein degradation, water migration, and microstructural damage in fish muscle during refrigeration. The CK group showed the most severe decline in all parameters, with hardness, cohesion, elasticity, and chewiness decreasing to 11.48 N, 0.38 mm, 0.98 mm, and 4.44 mJ by day 14, indicating that the untreated sample experienced more severe textural deterioration in the later stages of storage.

[0105] The effects of PAW and DBD treatments on maintaining the texture of rainbow trout were limited, especially in terms of cohesion and chewiness, where the values ​​were mostly significantly lower than those in the control group (P<0.05). This may be due to protein oxidation caused by reactive oxygen species in DBD and PAW, and protein denaturation caused by energy during DBD treatment, which actually accelerated the destruction of the muscle tissue network. The generally lower texture parameters in the PAW & DBD groups indicate that this combined treatment may produce a cumulative damage effect, which is not conducive to maintaining the integrity of the fish flesh texture.

[0106] The rate of decline in textural parameters was significantly slowed in the plant extract-treated group, especially in the later stages of storage, where its hardness, elasticity, and chewiness were significantly higher than those of the single physical treatment group (P<0.05). The abundant polyphenols and flavonoids in the plant extract may, to some extent, maintain the muscle tissue structure by inhibiting protein oxidative denaturation, delaying microbial growth, and regulating water distribution.

[0107] The plant-based & DBD treatment showed the best texture preservation effect. On day 14, the hardness (14.55 N), elasticity (1.41 mm), and chewiness (8.22 mJ) of this group were significantly higher than other treatment groups (P<0.05). DBD treatment may have reduced microbial damage to the sample texture through its sterilization function; simultaneously, the plant components may have alleviated the oxidative stress induced by DBD, resulting in a synergistic preservation effect. The PAW & plant-based & DBD treatments performed well in terms of cohesion, but were inferior to the plant-based & DBD group in maintaining hardness and chewiness, indicating that PAW may have weakened the stabilizing effect of the plant components to some extent.

[0108] In summary, the deterioration of the aroma, flavor, and textural properties of rainbow trout during refrigeration is mainly related to the degradation of protein network structure and lipid oxidation. Although PAW and DBD treatments have a certain bactericidal effect, they may cause protein degradation and lipid oxidation in the fish, accelerating the deterioration of flavor characteristics; plant extracts, on the other hand, effectively delay this process through their antioxidant and antibacterial activities.

[0109] The advancements of this invention compared to traditional single-preservation technologies are reflected in the following aspects: Plasma-activated water treatment utilizes the destructive effects of reactive oxygen and nitrogen species on microbial cell membranes and cell walls to achieve sterilization, avoiding chemical residue problems compared to traditional chemical preservatives. The flavonoids and organic acids in the compound plant preservative possess free radical scavenging capabilities, neutralizing the strong oxidizing substances generated by plasma treatment and preventing excessive oxidation of polyunsaturated fatty acids. Dielectric barrier discharge treatment further enhances the surface sterilization effect. The synergistic effect of these three technologies inhibits microbial growth while controlling lipid oxidation, solving the problem of accelerated lipid oxidation caused by single plasma treatment. By dynamically adjusting the soaking time of the compound plant preservative by monitoring the first thiobarbituric acid value, precise treatment of samples with different oxidation levels is achieved, improving the targeting and effectiveness of the preservation treatment. The treatment sequence of first soaking in plasma-activated water and then soaking in the compound plant preservative utilizes liquid flowability to ensure uniform contact of active substances with the entire sample surface, overcoming the uneven treatment problem caused by direct treatment of irregular sample surfaces by dielectric barrier discharge. The polyphenols in the compound plant preservative have a protective effect on proteins, reducing oxidative damage to proteins caused by dielectric barrier discharge, maintaining the good textural properties of fish, delaying flavor deterioration, and achieving multiple preservation goals of antibacterial, antioxidant, and maintenance of textural and flavor characteristics.

[0110] It should be noted that the variables involved in this invention are explained in detail in Table 3.

[0111] Table 3. Variable Explanation Table

[0112]

[0113] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for cold storage and preservation of triploid rainbow trout using plant extracts combined with low-temperature plasma technology, characterized in that, A compound plant preservative was prepared by mixing hawthorn, dried tangerine peel, and stir-fried radish seeds in a specific mass ratio. Distilled water was treated using an atmospheric cold plasma treatment device to prepare plasma-activated water. Triploid rainbow trout were gutted and skinned, then cut into uniform pieces. The pieces were soaked in plasma-activated water according to the liquid-to-material ratio, followed by soaking in the compound plant preservative. The treated triploid rainbow trout were then placed in a dielectric barrier discharge device for further treatment. The first thiobarbituric acid value of the treated triploid rainbow trout was measured, and the soaking time of the compound plant preservative was adjusted based on the first thiobarbituric acid value. The treated triploid rainbow trout were then sealed in sterile homogenized bags and stored in a refrigerated environment, with preservation indicators measured periodically. The flavonoids and organic acids in the compound plant preservative were used to remove the strong oxidizing substances generated during plasma treatment.

2. The method for cold storage and preservation of triploid rainbow trout according to claim 1, characterized in that, The mass ratio of hawthorn, dried tangerine peel, and stir-fried radish seeds was 2:1:2, which was determined by comparing the thiobarbituric acid value and total bacterial count on the 8th day after treatment with different mass ratios.

3. The method for cold storage and preservation of triploid rainbow trout according to claim 2, characterized in that, In the preparation steps of the compound plant preservative, the mass-to-volume ratio of the material to distilled water is 1:10, the soaking time is 10 minutes, and the content of total flavonoids and total phenols in the extract under different conditions is determined.

4. The method for cold storage and preservation of triploid rainbow trout according to claim 3, characterized in that, The compound plant preservative was prepared by rotary evaporation at a temperature of 60 to 70°C and a vacuum of 0.09 to 0.10 MPa. The retention rate of active ingredients was determined by measuring the conditions under different temperatures and vacuum levels.

5. The method for cold storage and preservation of triploid rainbow trout according to claim 4, characterized in that, The atmospheric cold plasma treatment device used in the plasma-activated water preparation process has a power of 750W, a voltage of 5kV, a compressed air pressure of 0.18MPa, and a gas flow rate of 30L / min.

6. The method for cold storage and preservation of triploid rainbow trout according to claim 5, characterized in that, During the preparation of plasma-activated water, the nozzle of the spray gun is placed 15 mm below the liquid surface, and the discharge time is 5 minutes. The concentration of active oxygen species and water temperature are determined by measuring different distances and time conditions.

7. The method for cold storage and preservation of triploid rainbow trout according to claim 6, characterized in that, The plasma-activated water soaking time was 20 minutes, and the compound plant preservative soaking time was 10 minutes. The total bacterial count and thiobarbituric acid value were determined by measuring the different soaking time combinations on the second day.

8. The method for cold storage and preservation of triploid rainbow trout according to claim 7, characterized in that, The liquid-to-material ratio is 5:1, which is determined by comparing the immersion of fish pieces and the uniformity of treatment under different liquid-to-material ratio conditions.

9. The method for cold storage and preservation of triploid rainbow trout according to claim 8, characterized in that, The dielectric barrier discharge device has a voltage of 70kV, a frequency of 80Hz, an electrode spacing of 80 to 90mm, and a processing time of 2 minutes.

10. The method for cold storage and preservation of triploid rainbow trout according to claim 9, characterized in that, The voltage, frequency, electrode spacing, and treatment time of the dielectric barrier discharge device were determined by measuring the total bacterial count and thiobarbituric acid value on the second day after treatment with different parameter combinations.

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