Method for preserving cooked crayfish through cooperation of plasma activation of lactic acid and radio frequency

Abstract

The invention discloses a method for preserving cooked crayfish through cooperation of plasma activation of lactic acid and radio frequency, and the method comprises the following steps: taking fresh and alive crayfish as a raw material, cleaning, removing heads, and heating in a water bath to obtain the cooked crayfish; preparing plasma activated lactic acid, and cooling to room temperature; soaking and sterilizing the cooked crayfish in the prepared plasma activated lactic acid; fishing out the cooked crayfish after soaking treatment, draining water, sealing and packaging, and performing radio frequency treatment; and refrigerating the cooked crayfish subjected to radio frequency treatment. Compared with single plasma activated lactic acid treatment or radio frequency treatment, the method can effectively inhibit growth and reproduction of microorganisms of the cooked crayfish, delay protein oxidation and quality deterioration, remarkably prolong the shelf life of the product, and has an excellent fresh-keeping effect; meanwhile, the taste and flavor of the product are not affected, and the market competitiveness of the product is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aquatic product preservation, and particularly relates to a method for preserving cooked crayfish by synergistically using plasma-activated lactic acid and radio frequency. Background Art

[0002] Crayfish are deeply loved by consumers because of their high nutritional value and unique flavor. In recent years, cooked crayfish have gradually become a popular choice among young consumers due to their convenience and diverse flavors. Since crayfish have a high protein content and their growth environment is mostly rivers, lakes or swamps, there are a variety of microorganisms in their bodies. There are differences in the microbial flora between cooked crayfish and fresh crayfish. For example, the genus Bacillus can produce heat-resistant spores, which are difficult to be completely inactivated during the cooking process and become specific spoilage bacteria in cooked crayfish. During storage, crayfish are prone to quality deterioration due to problems such as microbial growth, fat oxidation and protein denaturation, shortening the shelf life and restricting the development of the industry. Traditional preservation methods such as low-temperature freezing and chemical preservatives have problems such as limited preservation effect, affecting taste or insufficient safety, and it is difficult to meet the needs of consumers for high-quality crayfish.

[0003] Lactic acid, as a natural organic acid, has a broad-spectrum antibacterial effect, high safety and is easy to obtain, and has been widely used in the field of food preservation. It realizes antibacterial and antiseptic preservation through mechanisms such as adjusting pH, destroying cell membrane permeability, and inhibiting bacterial activity, and at the same time has functions such as flavoring and color protection. However, too high an addition amount of lactic acid will affect the food quality and flavor, so it is necessary to explore new technologies for achieving efficient preservation at a low lactic acid addition amount. In recent years, low-temperature plasma technology and radio frequency technology have received extensive attention in the field of food preservation due to their high efficiency, greenness and safety. Low-temperature plasma technology can activate lactic acid to produce a variety of active substances (such as reactive oxygen species, reactive nitrogen species), significantly enhancing its antibacterial effect; radio frequency technology further enhances the sterilization intensity through thermal effects and electromagnetic effects, while delaying protein oxidation and fat deterioration.

[0004] In the prior art, the invention patent "A Plasma-Activated Lactic Acid Solution with High-Efficiency Bacteriostatic Performance, Its Preparation Method and Application" (CN201910196952.8) discloses a preparation method of plasma-activated lactic acid, but it does not involve the combined application with radio frequency technology, nor does it target the preservation of cooked aquatic products; the invention patent "A Fresh Crawfish Preservation Method by Ultrasonic Coupled Low-Temperature Plasma Activated Water Synergistic with High-Concentration Carbon Dioxide Modified Atmosphere" (CN118266493A) discloses a method for preserving fresh crawfish by ultrasonic coupled low-temperature plasma activated water synergistic with high-concentration CO2 modified atmosphere, but it does not involve the synergistic application of lactic acid and plasma technology; the invention patent "A Fresh Fish Low-Temperature Plasma Cold Sterilization and Preservation Method" (CN117296908A) discloses a technology of plasma-activated water combined with DBD low-temperature plasma cold sterilization treatment, and does not involve the synergistic application of plasma lactic acid and radio frequency. Summary of the Invention

[0005] Object of the Invention: Aiming at the problems existing in the prior art, the present invention provides a method for preserving cooked crawfish by plasma-activated lactic acid synergistic with radio frequency. The present invention aims to provide a preservation technology of plasma-activated lactic acid synergistic with radio frequency, which is used to improve the nutritional quality of cooked crawfish and extend the product shelf life. Cooked crawfish are susceptible to the influence of microbial reproduction during storage, resulting in spoilage. Microbial reproduction will not only decompose nutrients such as proteins and fats, but also produce metabolites with bad flavors, seriously affecting the product quality and significantly shortening its shelf life. By treating cooked crawfish with plasma-activated lactic acid, the plasma-activated lactic acid contains various bacteriostatic and bactericidal components such as H2O2, O3, NO 3- 、NO 2- and organic acids, etc., and further combines with radio frequency technology to achieve an efficient bactericidal effect. After being treated by the method of the present invention, the shelf life of cooked crawfish can be significantly extended, the microbial growth and protein oxidation of cooked crawfish during refrigeration can be significantly delayed, and the quality deterioration can be alleviated.

[0006] Technical Solution: In order to achieve the above object, the method for preserving cooked crawfish by plasma-activated lactic acid synergistic with radio frequency according to the present invention includes the following steps:

[0007] (1) Using live crawfish as raw materials, after cleaning and removing the heads, heating in a water bath to obtain cooked crawfish;

[0008] (2) Preparing plasma-activated lactic acid and cooling it to room temperature;

[0009] (3) Immersing the cooked crawfish in step (1) in the plasma-activated lactic acid prepared in step (2) for sterilization;

[0010] (4) Take out the cooked crayfish after the soaking treatment in step (3), drain the water, seal and package it, and then perform radio frequency treatment;

[0011] (5) Refrigerate the cooked crayfish after the radio frequency treatment in step (4).

[0012] Among them, the water bath heating in step (1) is water bath heating at 90 - 100 °C for 10 - 15 min.

[0013] Among them, the preparation parameters of the plasma-activated lactic acid in step (2): using an atmospheric pressure low-temperature plasma jet device with a system power of 700 - 800 VA, a working frequency of 20 - 30 kHz, the preparation gas is air, the gas flow rate is 20 - 30 L / min, the nozzle is 1 - 10 cm below the liquid level of the lactic acid solution, the lactic acid concentration is 2 - 20 g / L, the volume of the lactic acid solution is 300 - 1000 mL, and the treatment time is 10 - 20 min.

[0014] Furthermore, the lactic acid concentration in step (2) is 2 - 5 g / L.

[0015] Preferably, the lactic acid concentration is 2 g / L.

[0016] Among them, the soaking time of the cooked crayfish in the plasma-activated lactic acid solution in step (3) is 10 - 30 min, and the ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 200 - 300:20 - 30.

[0017] Among them, in step (4), it is sealed and packaged with a polyethylene packaging box and then subjected to radio frequency treatment.

[0018] Among them, the radio frequency treatment parameters in step (4): the plate distance is 50 - 60 mm; the radio frequency time is 5 - 10 min, and the radio frequency power is 3.0 - 3.5 kw.

[0019] Among them, the storage temperature in step (5) is 0 - 10 °C.

[0020] Application of the method for preserving cooked crayfish by plasma-activated lactic acid in cooperation with radio frequency in the present invention in inhibiting the growth and reproduction of microorganisms in cooked crayfish, delaying protein oxidation and quality deterioration, and extending the product shelf life.

[0021] The present invention proposes a new technology for plasma-activated lactic acid and radio frequency preservation of cooked crayfish. The technology produces highly active antibacterial substances through plasma-activated lactic acid, and combines the thermal effect and electromagnetic effect of radio frequency technology to achieve synergistic sterilization and comprehensive preservation. The present invention can not only significantly reduce the total number of colonies in cooked crayfish, delay protein oxidation and fat deterioration, but also effectively maintain its color, taste and flavor, meet consumers' demand for high-quality cooked aquatic products, and has broad application prospects.

[0022] The present invention activates lactic acid through low-temperature plasma to produce a variety of antibacterial active substances (such as active oxygen and active nitrogen). Its permeability and bactericidal effect are significantly better than those of ordinary lactic acid. At the same time, radio frequency technology is a non-thermal sterilization technology that uses high-frequency electromagnetic waves for energy transfer. It effectively kills microorganisms and delays the deterioration of food quality based on thermal and electromagnetic effects, thereby extending the shelf life of food. The present invention combines plasma activation technology with radio frequency sterilization, and introduces lactic acid activation synergism to form a "chemical-physical" multi-target sterilization system. High-efficiency antibacterial activity is achieved at a low lactic acid addition, which makes up for the short action time of plasma-activated water and the difficulty of completely inactivating heat-resistant bacteria (such as Bacillus) by radio frequency treatment alone.

[0023] The present invention proposes for the first time a method for preserving cooked crayfish by combining low-concentration plasma-activated lactic acid with radio frequency. Compared with plasma-activated lactic acid treatment or radio frequency treatment alone, the present invention can significantly and effectively inhibit the growth and reproduction of cooked crayfish microorganisms, delay protein oxidation and quality deterioration, significantly extend the shelf life of the product, and has an excellent preservation effect; at the same time, it will not affect the taste and flavor of the product, thereby enhancing the market competitiveness of the product.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0025] (1) Through the synergistic effect of plasma-activated lactic acid and radio frequency technology, the growth and reproduction of microorganisms in cooked crayfish can be significantly inhibited, while effectively delaying quality deterioration processes such as protein oxidation, ensuring that the product maintains good color, texture and nutritional content during storage, thereby extending the shelf life of the product.

[0026] (2) After plasma-activated lactic acid and radio frequency treatment, the smell and taste of cooked crayfish were not significantly different from those of the untreated group, indicating that this technology will not have an adverse effect on the taste and flavor of the product, and can better preserve its original edible quality, meeting consumers' high requirements for food flavor.

[0027] (3) This technology combines natural preservatives (organic acids) with physical technologies (plasma and radio frequency) to form an efficient and safe preservation method. This technology not only avoids the potential residue problems caused by traditional chemical preservatives but also makes up for the limitations of the insufficient effects of single physical technologies, giving full play to the antibacterial properties of natural preservatives and the high-efficiency sterilization advantages of physical technologies, meeting the requirements of the modern food industry for green, safe, and environmentally friendly characteristics.

[0028] In summary, the plasma-activated lactic acid combined with radio frequency preservation technology provides an innovative solution for the preservation of cooked aquatic products with its efficient, safe, and environmentally friendly characteristics. While improving food quality and extending the shelf life, this technology can better meet consumers' high requirements for food safety and flavor, having important economic value and social benefits, and having broad application prospects in the field of aquatic product processing and preservation. Brief Description of the Drawings

[0029] Figure 1 Shows the changes in the total number of colonies (TVC) of cooked crayfish under different treatments during storage;

[0030] Figure 2 Shows the changes in the content of total volatile basic nitrogen (TVB-N) of cooked crayfish in different treatment groups during storage;

[0031] Figure 3 Is the radar chart of electronic nose analysis of cooked crayfish under different treatments at the initial stage of storage;

[0032] Figure 4 Is the radar chart of electronic tongue analysis of cooked crayfish under different treatments at the initial stage of storage;

[0033] Figure 5 Shows the schematic diagram of the appearance changes of cooked crayfish in different treatment groups during storage;

[0034] Figure 6 Is the schematic diagram of crayfish radio frequency treatment. Detailed Embodiments

[0035] The following further illustrates the present invention in conjunction with the drawings and embodiments.

[0036] The materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial channels without special instructions. The experimental methods without specific conditions in the embodiments usually follow conventional conditions or the conditions recommended by the manufacturer.

[0037] Example 1

[0038] Select fresh crayfish with sound limbs and uniform size, wash them with a soft brush, decapitate them after thorough washing, put the crayfish tails into a sterile homogenization bag, and heat them in a 90°C water bath for 10 minutes to obtain cooked crayfish. Prepare a 2 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generator (PG-1000Z / D). The power of the atmospheric pressure low-temperature plasma jet device system is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 minutes, the volume of the treatment solution is 300 mL, and lactic acid is 2 g / L to prepare plasma-activated lactic acid and cool it to room temperature. The physicochemical parameters of the prepared plasma-activated lactic acid are: pH is 2.26, conductivity is 2578.2 μs / cm, redox potential is 479.8 mv, ozone is 37.2 μmol / L, nitrite is 50.0 mg / L, and nitrate is 611.9 mg / L. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 minutes. The ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After the immersion, take out the cooked crayfish, drain the water, and package and seal them in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6 the radio frequency treatment device shown to perform radio frequency treatment on the sample. The plate distance is 50 mm, the radio frequency power is 3.5 kw, and the radio frequency time is 10 minutes.

[0039] Example 2

[0040] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, decapitate them after thorough cleaning, put the crayfish tails into a sterile homogenization bag, and heat them in a 90 °C water bath for 10 min to obtain cooked crayfish. Prepare a 5 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generator (PG-1000Z / D). The power of the atmospheric pressure low-temperature plasma jet device system is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the volume of the treatment solution is 300 mL, and lactic acid is 5 g / L to prepare plasma-activated lactic acid and cool it to room temperature. The physicochemical parameters of the prepared plasma-activated lactic acid are: pH is 2.18, conductivity is 3016.7 μs / cm, redox potential is 489.6 mv, ozone is 37.5 μmol / L, nitrite is 50.0 mg / L, and nitrate is 725.1 mg / L. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min. The ratio of the volume of the plasma-activated lactic acid solution (mL) to the number of cooked crayfish tails is 300:20. After the immersion, take out the cooked crayfish, drain the water, and package and seal them in a 22×13×4 cm polyethylene box. Subsequently, use the Figure 6 radio frequency treatment device shown to perform radio frequency treatment on the sample, with the plate distance of 50 mm, radio frequency power of 3.5 kw, and radio frequency time of 10 min.

[0041] Example 3

[0042] Select live crayfish with sound limbs and uniform size, clean them with a soft brush, remove the heads after thorough cleaning, put the crayfish tails into a sterile homogenization bag, and heat them in a water bath at 90 °C for 10 min to obtain cooked crayfish. Prepare a 10 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generator (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the treatment solution volume is 300 mL, and lactic acid is 10 g / L. Prepare plasma-activated lactic acid and cool it to room temperature. The physicochemical parameters of the prepared plasma-activated lactic acid are: pH is 2.03, conductivity is 4110.0 μs / cm, redox potential is 495.7 mv, ozone is 38.3 μmol / L, nitrite is 49.8 mg / L, and nitrate is 919.4 mg / L. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min. The ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After soaking, take out the cooked crayfish, drain the water, and package and seal them in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6 the radio frequency treatment device shown in

[0043] Example 4

[0044] Select live crayfish with sound limbs and uniform size, clean them with a soft brush, remove the heads after thorough cleaning, put the crayfish tails into a sterile homogenization bag, and heat them in a water bath at 90 °C for 10 min to obtain cooked crayfish. Prepare a 2 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generator (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the treatment solution volume is 300 mL, and lactic acid is 2 g / L. Prepare plasma-activated lactic acid and cool it to room temperature. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min. The ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After soaking, take out the cooked crayfish, drain the water, and package and seal them in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6The shown radio frequency processing device performs radio frequency processing on the sample. The plate distance is 50 mm, the radio frequency power is 3 kw, and the radio frequency time is 10 min.

[0045] Example 4

[0046] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, remove the heads after thorough washing, put the crayfish tails in a sterile homogenization bag, and heat them in a 90 °C water bath for 10 min to obtain cooked crayfish. Prepare a 2 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generating device (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; using air as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the treatment solution volume is 300 mL, and lactic acid is 2 g / L to prepare plasma-activated lactic acid, and then cool it to room temperature. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min. The ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After the immersion, take out the cooked crayfish, drain the water, and package and seal the film in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6 the shown radio frequency processing device to perform radio frequency processing on the sample. The plate distance is 55 mm, the radio frequency power is 3.5 kw, and the radio frequency time is 10 min.

[0047] Example 5

[0048] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, remove the heads after thorough washing, put the crayfish in a sterile homogenization bag, and heat them in a 90 °C water bath for 10 min to obtain cooked crayfish. Prepare a 2 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generating device (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; using air as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the treatment solution volume is 300 mL, and lactic acid is 2 g / L to prepare plasma-activated lactic acid, and then cool it to room temperature. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min. The ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After the immersion, take out the cooked crayfish, drain the water, and package and seal the film in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6The shown radio frequency processing device performs radio frequency processing on the sample. The plate distance is 55 mm, the radio frequency power is 3 kw, and the radio frequency time is 10 min.

[0049] Example 6

[0050] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, remove the heads after thorough washing, put the crayfish tails in a sterile homogenization bag, and heat them in a 90 °C water bath for 10 min to obtain cooked crayfish. Prepare a 2 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generator (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the treatment solution volume is 300 mL, and lactic acid is 2 g / L to prepare plasma-activated lactic acid, and then cool it to room temperature. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min. The ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After the immersion is completed, take out the cooked crayfish, drain the water, and package and seal the film in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6 The shown radio frequency processing device performs radio frequency processing on the sample. The plate distance is 60 mm, the radio frequency power is 3.5 kw, and the radio frequency time is 10 min.

[0051] Example 7

[0052] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, remove the heads after thorough washing, put the crayfish tails in a sterile homogenization bag, and heat them in a 90 °C water bath for 10 min to obtain cooked crayfish. Prepare a 2 g / L plasma-activated lactic acid solution using an atmospheric pressure cold plasma jet generator (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the treatment solution volume is 300 mL, and lactic acid is 2 g / L to prepare plasma-activated lactic acid, and then cool it to room temperature. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min. The ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After the immersion is completed, take out the cooked crayfish, drain the water, and package and seal the film in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6The shown radio frequency processing device performs radio frequency processing on the sample, with the plate distance being 60 mm, the radio frequency power being 3 kw, and the radio frequency time being 10 min.

[0053] Comparative Example 1

[0054] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, remove the heads after thorough washing, put the crayfish tails in a sterile homogenization bag, place them in a water bath at 90 °C for 10 min to obtain cooked crayfish, and seal and package them in a 22×13×4 cm polyethylene box.

[0055] Comparative Example 2

[0056] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, remove the heads after thorough washing, put the crayfish tails in a sterile homogenization bag, place them in a water bath at 90 °C for 10 min to obtain cooked crayfish. Prepare a 2 g / L plasma-activated lactic acid solution by means of an atmospheric pressure cold plasma jet generating device (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the volume of the treatment solution is 300 mL, and the lactic acid is 2 g / L to prepare plasma-activated lactic acid, and then cool it to room temperature. Immerse the cooked crayfish in the plasma-activated lactic acid for 20 min, and the ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 300:20. After the immersion is over, take out the cooked crayfish, drain the water, and package and seal them in a 22×13×4 cm polyethylene box. No radio frequency treatment is carried out.

[0057] Comparative Example 3

[0058] Select live crayfish with sound limbs and uniform size, wash them with a soft brush, remove the heads after thorough washing, put the crayfish tails in a sterile homogenization bag, place them in a water bath at 90 °C for 10 min to obtain cooked crayfish. Package and seal the cooked crayfish in a 22×13×4 cm polyethylene box. Subsequently, use Figure 6 the shown radio frequency processing device to perform radio frequency processing on the sample, with the plate distance being 50 mm, the radio frequency power being 3.5 kw, and the radio frequency time being 10 min.

[0059] Test Example 1

[0060] Process the sample using different radio frequency parameters according to the method of Example 1, record the temperature of the crayfish during the radio frequency process, and control the product temperature during the radio frequency process to ensure the sterilization effect while not damaging the food quality.

[0061] Table 1 Temperature change of cooked crayfish under different radio frequency processing parameters

[0062]

[0063]

[0064] As shown in Table 1, the plate distance, radio frequency power, and processing time all significantly affect the final temperature of cooked crayfish. The smaller the plate distance, the higher the radio frequency energy transfer efficiency, and the more significant the temperature rise. When the plate distance increases, the electric field strength weakens, and the temperature rise amplitude decreases. For example, when the plate distance is 60nm, the temperature of the crayfish sample after 10 minutes of radio frequency at a power of 3.5kW is only 30.2℃, which may not be sufficient to effectively sterilize. At the same plate distance, when the power is increased from 3.0kW to 3.5kW, the temperature of the crayfish increases significantly. A power of 3.5kW is more likely to reach above 50℃, while the highest temperature of 3.0kW only reaches 28.2℃. The range of 50 - 60℃ is the mild heat treatment interval, which can maximize the retention of the texture, color, and flavor of crayfish, and avoid excessive protein denaturation or water loss caused by high temperature. Considering comprehensively, the plate distance is 50mm, the radio frequency power is 3.5kW, and the radio frequency time is 10 minutes.

[0065] Test Example 2

[0066] In Example 1 and Comparative Examples 1 - 3, different methods were used to preserve cooked crayfish, and relevant indicators were measured during refrigeration. Among them, Example 1 was the PALA + radio frequency group, Comparative Example 1 was the CK group, Comparative Example 2 was the PALA group, and Comparative Example 3 was the radio frequency group.

[0067] Detection of relevant indicators:

[0068] Microbial determination: Refer to the regulations in GB 4789.2 - 2022 "National Food Safety Standard Food Microbiological Examination Total Number of Colonies Determination": Immerse the cooked crayfish sample in 9 - fold 0.85% sterile physiological saline, beat with a homogenizer for 2 minutes, perform 10 - fold serial dilutions on the homogenate, and take 100μL of the appropriate dilution and spread it on PCA plates. Incubate the plates upside - down in an incubator at 36 ± 1℃ for 24 ± 2h, and record the number of colonies.

[0069] Determination of total volatile basic nitrogen (TVB - N): Refer to the microdiffusion method in GB 5009.228 - 2016 "National Food Safety Standard Determination of Total Volatile Basic Nitrogen in Foods".

[0070] Electronic nose analysis: The PEN3 electronic nose was used to analyze the odor of crayfish samples. 3.00 g of crayfish samples were placed in a 20 mL sealed headspace vial, sealed with plastic wrap, and equilibrated at room temperature for 30 min. The detection parameters of the electronic nose were: carrier gas flow rate 300 mL / min; sampling interval time 1 s; cleaning time 80 s; pre-injection time 5 s; sampling time 80 s.

[0071] Electronic tongue analysis: 10 g of the crayfish samples to be tested were taken, deionized water was added according to the solid-liquid ratio of 1:10, homogenized by a homogenizer for 2 min and then filtered, and the filtrate was taken for on-machine analysis. The reference solution was 30 mM KCl and 0.3 mM tartaric acid. The negative electrode cleaning solution was 30% (v / v) ethanol and 100 mM HCl, and the positive electrode cleaning solution was 10 mM KOH, 100 mM KCl and 30% (v / v) ethanol. The detection conditions of the electronic tongue were: sensor cleaning time 6 min; sample determination time 30 s; cleaning time 3 s after the test was completed.

[0072] The total number of colonies of cooked crayfish after different treatments during storage was as Figure 1 shown. Plasma-activated lactic acid (PALA) treatment significantly reduced the microbial content of cooked crayfish on day 0. Compared with the CK group and the single radio frequency group, PALA showed a better cleaning and bacteriostatic effect (P<0.05). The total number of colonies of cooked crayfish in the CK group, the radio frequency treatment group and the PALA treatment group increased rapidly during storage, reaching 8.54 log CFU / g, 8.60 log CFU / g and 6.64 log CFU / g respectively on day 18, all exceeding the spoilage limit. The total number of colonies of the PALA combined with radio frequency group remained at a low level throughout the period, only 4.04 log CFU / g after storage, and especially on day 18, the total number of colonies of the PALA combined with radio frequency group was significantly lower than that of the radio frequency treatment group and the PALA treatment group. This shows that by applying the plasma-activated lactic acid combined with radio frequency of the present invention to the preservation of cooked crayfish, the growth of microorganisms in cooked crayfish can be effectively synergistically inhibited and the shelf life can be extended.

[0073] The TVB-N change of cooked crayfish after different treatments during storage was as Figure 2As shown, TVB-N is an important indicator for evaluating the freshness of cooked crayfish, and its change reflects the degree of microbial activity and protein decomposition. During storage at 4°C, the TVB-N of cooked crayfish in the CK group, radio frequency treatment group, and PALA treatment group showed an upward trend, reaching 38.07 mg / 100 g, 33.86 mg / 100 g, and 23.62 mg / 100 g respectively on the 18th day, all exceeding the spoilage limit. The TVB-N of the PALA combined with radio frequency group after storage was only 8.87 mg / 100 g. This indicates that by applying a plasma-activated lactic acid of the present invention to the preservation of cooked crayfish, it has significant advantages in delaying the protein decomposition of cooked crayfish and maintaining the freshness of the product. Especially on the 18th day, the TVB-N of the PALA combined with radio frequency group was significantly lower than that of the radio frequency treatment group and the PALA treatment group, showing an excellent synergistic effect.

[0074] The electronic nose analysis of cooked crayfish after different treatments at the initial stage of storage is as Figure 3 shown. On the 0th day, the taste characteristics of cooked crayfish samples in different treatment groups were close or even overlapped, indicating that by applying a plasma-activated lactic acid of the present invention to the preservation of cooked crayfish, the original flavor of the product will not be changed.

[0075] The electronic tongue analysis of cooked crayfish after different treatments at the initial stage of storage is as Figure 4 shown. The response values of saltiness and umami are greater than 0, which are the main characteristic tastes of cooked crayfish. The sourness response value of crayfish after PALA treatment is significantly lower than the tasteless point (the taste value of the reference solution, generally 0), indicating that by applying a plasma-activated lactic acid combined with radio frequency of the present invention to the preservation of cooked crayfish tails, the cooked crayfish tails will not be significantly sour and affect the quality.

[0076] The texture changes of cooked crayfish after different treatments during storage are shown in Table 2, mainly including hardness, elasticity, and chewiness. Compared with the untreated group, the effect of single radio frequency treatment on delaying the texture deterioration of cooked crayfish during storage is not significant. The decreasing trends of its hardness, elasticity, and chewiness are similar to those of the control group, indicating that the single radio frequency treatment has limited effect on maintaining the texture characteristics of the product. PALA treatment can delay the texture deterioration of cooked crayfish to a certain extent at the initial stage of storage, but the effect in the later stage of storage is still not significant. In contrast, the PALA combined with radio frequency treatment shows the best effect, and there is no significant change in the texture characteristics before and after storage, which can significantly delay the texture deterioration of cooked crayfish and maintain the taste and quality of the product.

[0077] Table 2 Texture changes of cooked crayfish in different treatment groups during storage

[0078]

[0079]

[0080] Note: Different lowercase letters represent significant differences among different treatment groups at the same storage time, and different uppercase letters represent significant differences of the same treatment at different storage times (P < 0.05).

[0081] The appearance of cooked crayfish after different treatments during storage is as Figure 5 shown. On the 18th day, the crayfish samples in the CK group, PALA treatment group, and radio frequency treatment group all showed characteristics such as blackened whiskers, slightly dull shell color, and local browning. However, the color and texture of the samples in the PALA + radio frequency treatment group were close to those at the initial stage of storage, still maintaining bright color and firm shell and meat.

[0082] Example 8

[0083] Prepare plasma-activated lactic acid solutions (0, 2, 5, 10, and 20 g / L) by using an atmospheric pressure cold plasma jet generating device (PG-1000Z / D). The system power of the atmospheric pressure low-temperature plasma jet device is 800 VA, the working voltage is 220 V, and the working frequency is 20 kHz; air is used as the discharge gas, the working pressure is 0.18 MPa, the gas flow rate is 30 L / min, the probe extends 10 cm below the liquid surface for discharge, the treatment time is 20 min, the volume of the treatment solution is 300 mL, and the lactic acid concentrations are 0, 2, 5, 10, and 20 g / L. Prepare plasma-activated lactic acid and cool it to room temperature. Prepare special nutrient broth media with the treated plasma-activated lactic acid at different concentrations, and mix each medium with a Bacillus subtilis spore suspension of 10 7 CFU / mL in a ratio of 10:1, and place it at 30 °C for 30 days to study the inhibitory effect of plasma-activated lactic acid solutions at different concentrations on spore growth. The results show that the minimum concentration of plasma-activated lactic acid that inhibits spore growth is 10 g / L. The plasma-activated lactic acid in the prior art is for fresh products. Since cooked aquatic products have different dominant spoilage bacteria (heat-resistant spores) due to thermal processing, a higher lactic acid concentration is required to inactivate heat-resistant spores using plasma-activated lactic acid. After combining with radio frequency technology in the present invention, the lactic acid addition amount can also be reduced.

Claims

1. A method for preserving cooked crayfish by plasma-activated lactic acid and radio frequency, characterized in that: The steps include: (1) Using fresh crayfish as raw material, washing and removing the head, and heating in a water bath to obtain cooked crayfish; (2) preparing plasma-activated lactic acid and cooling it to room temperature; (3) placing the cooked crayfish in step (1) in the plasma-activated lactic acid prepared in step (2) for immersion sterilization; (4) taking out the cooked crayfish after the soaking treatment in step (3), draining the water, sealing and packaging, and performing radio frequency treatment; (5) Refrigerate the cooked crayfish after the radio frequency treatment in step (4).

2. The method for preserving cooked crayfish by plasma activated lactic acid and radio frequency according to claim 1, characterized in that: In step (1), the water bath heating is performed at 90-100° C. for 10-15 min.

3. The method for preserving cooked crayfish by plasma activated lactic acid and radio frequency according to claim 1, characterized in that: The preparation parameters of plasma activated lactic acid in step (2) are as follows: an atmospheric pressure low-temperature plasma jet device with a system power of 700-800VA, an operating frequency of 20-30kHz, air as the preparation gas, a gas flow rate of 20-30L / min, a nozzle located 1-10cm below the liquid surface of the lactic acid solution, a lactic acid concentration of 2-20g / L, a lactic acid solution volume of 300-1000mL, and a treatment time of 10-20min.

4. The method for preserving cooked crayfish by plasma activated lactic acid and radio frequency according to claim 1, characterized in that: The lactic acid concentration in step (2) is preferably 2-5 g / L.

5. The method for preserving cooked crayfish by plasma activated lactic acid and radio frequency according to claim 1, characterized in that: In step (3), the soaking time of the cooked crayfish in the plasma-activated lactic acid solution is 10-30 minutes, and the ratio of the volume (mL) of the plasma-activated lactic acid solution to the number of cooked crayfish tails is 200-300:20-30.

6. The method for preserving cooked crayfish by plasma activated lactic acid and radio frequency according to claim 1, characterized in that: In step (4), the product is sealed in a polyethylene box and subjected to radio frequency treatment.

7. The method for preserving cooked crayfish by plasma activated lactic acid and radio frequency according to claim 1, characterized in that: The radio frequency processing parameters in step (4) are as follows: the distance between the electrodes is 50-60 mm; the radio frequency time is 5-10 min; and the radio frequency power is 3.0-3.5 kw.

8. The method for preserving cooked crayfish by plasma activated lactic acid and radio frequency according to claim 1, characterized in that: The storage temperature in step (5) is 0-10°C.

9. An application of the method of plasma activated lactic acid synergistic with radio frequency preservation of cooked crayfish as claimed in claim 1 in inhibiting the growth and reproduction of microorganisms in cooked crayfish, delaying protein oxidation and quality deterioration, and extending the shelf life of the product.

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