A method for locking freshness and toughening of fish fillets

Abstract

The present application relates to a kind of fish slice fresh-keeping toughening deployment method, which is sequentially prepared by fish slice pretreatment, composite fresh-keeping toughening deployment liquid, ultrasonic assisted infiltration, gradient wet heat protein shaping and vacuum deep cold storage process. The deployment liquid is compounded by edible salt, white granulated sugar, trehalose, composite phosphate, composite toughening regulator, crosslinking accelerator, natural antioxidant and bacteriostatic agent. After low-temperature ultrasonic infiltration of fish slice, wet heat pre-hardening, gradient cooling rearrangement, ice water quenching and repeated shaping are used in a step-by-step process, and protein structure solidification is completed under constant pressure. Through the synergistic effect of functional components and multiple processes, the present application can significantly reduce the thawing juice loss rate of fish slice, improve water holding capacity and texture toughness, inhibit fat oxidation and microbial reproduction, and keep the fish meat elastic and tough without being dry and tasteless. The present application effectively solves the technical defects of existing fish slice fresh-keeping and toughening.

Description

Technical Field

[0001] This invention belongs to the field of aquatic product processing, preservation, and meat quality improvement technology, and specifically relates to a method for preserving and strengthening fish fillets. Background Technology

[0002] Fish fillets are a popular seafood product, known for their rich nutrition, convenient preparation, and delicious flavor. However, fish fillets have a high water content and a fragile myofibril protein structure. During freezing, thawing, and long-term low-temperature storage, internal ice crystals can easily puncture muscle cells and muscle fiber networks, causing significant juice loss. This results in loose, brittle meat with a dry texture and a marked decrease in toughness and chewiness. Simultaneously, fish fat is prone to oxidative rancidity, and microorganisms easily grow on the surface, accelerating quality deterioration and shortening shelf life.

[0003] Existing fish fillet preservation and toughening technologies have many obvious defects: conventionally, plant colloids and polysaccharides are used as toughening and water-retaining components, which can easily cause the fish fillets to become sticky and mask the original flavor of the fish; some technologies use nano-inorganic oxide modification, which raises concerns about the food safety compliance of nanomaterials and limits their industrial application; traditional single brine or ordinary phosphate soaking can only achieve slight water absorption and weight gain, and cannot reconstruct the protein structure at the microscopic level, resulting in poor toughening and water-locking effects, and the quality deteriorates significantly after freezing.

[0004] Therefore, it is necessary to develop a method for preserving and strengthening fish fillets, which can significantly improve the toughness, firmness and water retention of fish fillets, and also have good antioxidant and antibacterial preservation effects. Summary of the Invention

[0005] This invention provides a method for preparing fish fillets to lock in freshness and enhance their firmness, thereby solving the aforementioned technical problems.

[0006] Technical solution:

[0007] A method for preparing fish fillets to lock in freshness and enhance firmness, characterized by comprising the following steps:

[0008] (1) Fish fillet pretreatment: Remove the scales, bones and internal organs from the fresh fish, clean it and cut it into uniform thin slices with a thickness of 2-3mm, drain the surface water and set aside.

[0009] Cutting the fish fillets into uniform 2-3mm slices ensures even and consistent penetration of the subsequent preparation solution. Draining the surface free water avoids diluting the compound freshness-locking and toughening preparation solution, maintains a stable concentration of effective components, and provides a uniform and stable substrate for subsequent soaking and protein setting processes, ensuring the consistency and stability of the overall process effect.

[0010] (2) Preparation of compound freshness-locking and toughening preparation solution: According to the mass fraction, add 1.5-2.5 parts of edible salt, 2.5-3.5 parts of white sugar, 0.5-1 parts of trehalose, 0.15-0.29 parts of compound phosphate, 0.4-0.9 parts of compound toughening regulator, 0.03-0.08 parts of cross-linking promoter, 0.09-0.22 parts of natural antioxidant, and 0.015-0.045 parts of antibacterial agent to 93.5-95.5 parts of purified water, stir and disperse until completely dissolved, adjust the pH value of the preparation solution to 6.8-7.0, and obtain compound freshness-locking and toughening preparation solution;

[0011] Using edible salt and white sugar to regulate osmotic pressure promotes the penetration of effective components and imparts basic flavor, using trehalose to form a hydration film to protect proteins and enhance freeze resistance, using complex phosphates to dissociate proteins, improve water retention, and chelate metal ions, using complex toughening regulators to activate cross-linking sites, fill protein gaps, and stabilize the system pH, using cross-linking promoters to catalyze protein cross-linking and reduce cross-linking resistance, using natural antioxidants to scavenge free radicals and reduce oxidation products, and using antibacterial agents to inhibit the growth of bacteria and fungi, adjusting the pH to 6.8-7.0 matches the stable range of fish meat proteins. Each component individually exerts water-locking, toughening, antioxidant, and antibacterial effects. When combined, they synergistically form a dense and stable three-dimensional protein network, while blocking oxidation and microbial contamination pathways, providing a comprehensive preservation and toughening effect without masking the original flavor of the fish meat.

[0012] The compound phosphate is composed of sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate in a mass ratio of 4:2:1. This compound phosphate combines the triple effects of water retention, protein dissociation, and metal ion chelation, and has a more comprehensive effect than single phosphate. It can maximize the water retention and protein stability of fish fillets, while avoiding the astringent taste caused by excessive addition of single phosphate.

[0013] The composite toughening regulator is composed of food-grade magnesium oxide, tricalcium phosphate, and magnesium lactate in a mass ratio of 3:2:2. In this ratio, magnesium oxide provides active magnesium ions, tricalcium phosphate provides filling and reinforcement, and magnesium lactate plays a pH buffering role. Each of the three can improve the firmness of the fish fillet on its own. When combined, they can synergistically and gently reconstruct the structure of fish protein, which can enhance the toughness of the fish fillet without producing a sticky feeling.

[0014] The cross-linking promoter is composed of transglutaminase and L-cysteine ​​hydrochloride in a mass ratio of 2:1. Transglutaminase, as the main cross-linking agent, can catalyze cross-linking between protein molecules, while L-cysteine ​​hydrochloride, as a co-cross-linking agent, can open protein disulfide bonds and reduce cross-linking resistance. The two are combined in a 2:1 ratio to synergistically optimize the cross-linking rate and protein structural stability, rapidly strengthen the protein network structure, and significantly improve the toughness and chewing performance of fish fillets.

[0015] The natural antioxidant is composed of rosemary extract and sodium vitamin C in a mass ratio of 1.5:1. Rosemary extract can effectively scavenge free radicals of fat oxidation, while sodium vitamin C can quickly reduce oxidation intermediates. Both have antioxidant effects on their own, and the 1.5:1 combination has a synergistic effect, resulting in a better antioxidant effect than the single component. It can effectively inhibit the oxidation and rancidity of fish fat and maintain the good color and flavor of fish fillets.

[0016] The antibacterial agent is composed of ε-polylysine hydrochloride and natamycin in a mass ratio of 1:1. ε-polylysine hydrochloride can inhibit bacterial reproduction, and natamycin can inhibit fungal growth. The antibacterial spectra of the two are complementary when used alone. When combined in a 1:1 ratio, they achieve broad-spectrum, highly effective, and low-dose antibacterial activity, which can extend the product's shelf life.

[0017] (3) Ultrasonic assisted soaking treatment: Mix the pretreated fish fillets with the compound freshness-locking and toughening preparation liquid at a mass ratio of 1:2-3. First, soak them at a low temperature of 4-8℃ for 50-60 minutes, then use ultrasonic treatment with a power of 200-300W and a frequency of 20-40kHz for 10-20 minutes, and continue to soak them at 4-8℃ for 30-40 minutes. Take out the fish fillets and drain the excess liquid on the surface.

[0018] Low temperature of 4-8℃ can avoid thermal denaturation of fish protein. The cavitation effect generated by ultrasound can open the gaps between muscle fibers, greatly improving the penetration rate and uniformity of the preparation solution. Through the three-step immersion process of "standing, ultrasound and then standing again", the functional components in the preparation solution can be fully adsorbed and penetrated, synergistically improving the effect and uniformity of freshness-locking and toughening treatment.

[0019] (4) Protein setting treatment: After draining, the fish fillets are laid out in a single layer and pre-hardened in a humid heat steam environment of 41-43℃ and relative humidity ≥90% for 6-8 minutes. Then, the temperature is reduced to 35-37℃ at a rate of 0.8-1.2℃ / min and kept at a constant temperature for 18-22 minutes to allow protein molecule rearrangement. During the constant temperature process, 360-370nm UVA ultraviolet light is turned on for double-sided irradiation from the top and bottom, with a power density of 5-15mW / cm² and an irradiation distance of 15-20cm. Finally, the fish fillets are immediately transferred to an ice water bath of 0-2℃ for 3-5 minutes to cool. Step (4) is repeated 2 to 3 times. The fish fillets are then removed and the surface moisture is dried. The air pressure is maintained at 0.09-0.11MPa throughout the process.

[0020] Moist heat pre-hardening allows for moderate denaturation and initial shaping of the protein. Gradient cooling ensures orderly rearrangement of the protein and prevents structural instability. Ice-water bath quenching rapidly solidifies the protein network. Constant pressure ensures uniform heat transfer. This process alone can stabilize the protein structure. When combined with composite toughening regulators and cross-linking promoters, the protein network constructed by the mixture can be solidified again. Repeating this process 2-3 times can further enhance network stability, completely solving the problems of looseness, dryness, and water leakage after fish fillets are frozen.

[0021] During the isothermal protein molecular rearrangement stage at 35-37℃, 365nm UVA ultraviolet light irradiation is introduced. The photon energy of this wavelength can match the excitation energy of tyrosine residues in fish myofibril protein. Without damaging the protein backbone, it can excite tyrosine to form free radicals and combine with each other to form stable dityrosine covalent bonds. Together with the isopeptide bonds catalyzed by glutamine transaminase and the metal ion bridges provided by the composite toughening regulator, it forms a triple dense cross-linking network. At the same time, the magnesium and calcium ions in the composite toughening regulator can act as natural photosensitizing cofactors to improve the efficiency of photocross-linking. In addition, the rosemary extract and sodium vitamin C in the formula can eliminate trace amounts of reactive oxygen species generated by light irradiation and prevent the fish meat from oxidizing and deteriorating.

[0022] (5) Post-processing and storage: The shaped fish fillets are vacuum-packed with a vacuum degree controlled at -0.08 to -0.09 MPa and stored at a low temperature below -18℃.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. This invention constructs a stable protein water-holding network through the synergistic construction of compound phosphate and trehalose, combined with low-temperature ultrasonic-assisted penetration and gradient protein shaping process, which can effectively protect the myofibril protein structure and reduce the puncture damage to muscle cells caused by frozen ice crystals. Compared with the traditional single phosphate treatment process, the loss rate of thawed fish fillets is greatly reduced, the water-holding capacity is significantly improved, and the freshness-locking stability and long-lasting effect are better.

[0025] 2. This invention uses a composite toughening regulator, a cross-linking promoter, and a gradient wet heat protein setting process to work synergistically to promote the orderly rearrangement and stable cross-linking and solidification of myofibril proteins, which greatly improves the hardness, elasticity, toughness and chewiness of fish fillets. It solves the defects of traditional fish fillets that are loose, brittle and dry in taste from the root, and has no sticky taste, thus preserving the natural texture of fish to the greatest extent.

[0026] 3. The present invention takes the compound freshness-locking and toughening preparation liquid, ultrasonic-assisted immersion, and gradient moist heat protein shaping as the core links. The three links work together to enhance the effect and are indispensable. This invention comprehensively solves the multiple technical defects of the existing technology, such as poor water-locking effect, weak toughening ability, rapid oxidation and pollution, and distorted taste.

[0027] 4. This invention utilizes a gradient moist heat protein shaping process, employing a step-by-step process of moist heat pre-hardening, gradient cooling rearrangement, and ice water quenching solidification. The shaping is repeated 2-3 times under constant pressure, which denatures, rearranges, and solidifies myofibril proteins, firmly locking the three-dimensional protein network constructed by the toughening and cross-linking components in the preparation solution. This prevents subsequent protein structure collapse and textural deterioration. This process, highly synergistic with composite toughening regulators and cross-linking promoters, can completely solve the core problem of deteriorated texture and loss of toughness after freezing traditional fish fillets, significantly improving the stability and durability of the fish fillet texture. Detailed Implementation

[0028] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0029] Example 1

[0030] A method for preparing fish fillets to lock in freshness and enhance firmness, characterized by comprising the following steps:

[0031] (1) Fish fillet pretreatment: Remove the scales, bones and internal organs from the fresh fish, clean it and cut it into uniform thin slices with a thickness of 2-3mm, drain the surface water and set aside.

[0032] (2) Preparation of compound freshness-locking and toughening preparation solution: According to the mass parts, 1.5 parts of edible salt, 2.5 parts of white sugar, 0.5 parts of trehalose, 0.15 parts of compound phosphate, 0.4 parts of compound toughening regulator, 0.03 parts of cross-linking promoter, 0.09 parts of natural antioxidant and 0.015 parts of antibacterial agent are added to 93.5 parts of purified water, stirred and dispersed until completely dissolved, and the pH value of the preparation solution is adjusted to 6.8 to obtain the compound freshness-locking and toughening preparation solution;

[0033] The composite phosphate is composed of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a mass ratio of 4:2:1.

[0034] The composite toughening modifier is composed of food-grade magnesium oxide, tricalcium phosphate and magnesium lactate in a mass ratio of 3:2:2.

[0035] The cross-linking accelerator is composed of glutamine transaminase and L-cysteine ​​hydrochloride in a mass ratio of 2:1;

[0036] The natural antioxidant is composed of rosemary extract and sodium vitamin C in a mass ratio of 1.5:1.

[0037] The antibacterial agent is composed of ε-polylysine hydrochloride and natamycin in a mass ratio of 1:1.

[0038] (3) Ultrasonic assisted soaking treatment: The pre-treated fish fillets are mixed with the compound freshness-locking and toughening preparation liquid at a mass ratio of 1:2. First, they are soaked at a low temperature of 4℃ for 50 minutes, then treated with ultrasonic waves at a power of 200W and a frequency of 20kHz for 10 minutes, and then soaked at a low temperature of 4℃ for 30 minutes. The fish fillets are then removed and the excess liquid on the surface is drained.

[0039] (4) Protein setting treatment: After draining, the fish fillets are laid out in a single layer and placed in a humid heat steam environment of 41℃ and 95% relative humidity for 6 minutes to pre-harden. Then, the temperature is reduced to 35℃ at a rate of 0.8℃ / min and kept at a constant temperature for 18 minutes to allow protein molecules to rearrange. During the constant temperature process, 360nm UVA ultraviolet light is turned on for double-sided irradiation with a power density of 5mW / cm² and an irradiation distance of 15cm. Finally, the fish fillets are immediately transferred to a 0℃ ice water bath for 3 minutes to cool. Step (4) is repeated twice and the fish fillets are then removed and the surface moisture is dried. The air pressure is maintained at 0.09MPa throughout the process.

[0040] (5) Post-processing and storage: The shaped fish fillets are vacuum-packed with a vacuum degree controlled at -0.08MPa and stored at a low temperature below -18℃.

[0041] Example 2

[0042] A method for preparing fish fillets to lock in freshness and enhance firmness, characterized by comprising the following steps:

[0043] (1) Fish fillet pretreatment: Remove the scales, bones and internal organs from the fresh fish, clean it and cut it into uniform thin slices with a thickness of 3mm. Drain the surface water and set aside.

[0044] (2) Preparation of compound freshness-locking and toughening preparation solution: According to the mass parts, 2.5 parts of edible salt, 3.5 parts of white sugar, 1 part of trehalose, 0.29 parts of compound phosphate, 0.9 parts of compound toughening regulator, 0.08 parts of cross-linking promoter, 0.22 parts of natural antioxidant and 0.045 parts of antibacterial agent are added to 95.5 parts of purified water, stirred and dispersed until completely dissolved, and the pH value of the preparation solution is adjusted to 7.0 to obtain compound freshness-locking and toughening preparation solution;

[0045] The composite phosphate is composed of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a mass ratio of 4:2:1.

[0046] The composite toughening modifier is composed of food-grade magnesium oxide, tricalcium phosphate and magnesium lactate in a mass ratio of 3:2:2.

[0047] The cross-linking accelerator is composed of glutamine transaminase and L-cysteine ​​hydrochloride in a mass ratio of 2:1;

[0048] The natural antioxidant is composed of rosemary extract and sodium vitamin C in a mass ratio of 1.5:1.

[0049] The antibacterial agent is composed of ε-polylysine hydrochloride and natamycin in a mass ratio of 1:1.

[0050] (3) Ultrasonic assisted soaking treatment: The pretreated fish fillets are mixed with the compound freshness-locking and toughening preparation liquid at a mass ratio of 1:3. First, they are soaked at a low temperature of 8℃ for 60 minutes, then treated with ultrasonic waves at a power of 300W and a frequency of 40kHz for 20 minutes, and then soaked at 8℃ for 40 minutes. The fish fillets are then removed and the excess liquid on the surface is drained.

[0051] (4) Protein setting treatment: After draining, the fish fillets are laid out in a single layer and pre-hardened in a humid heat steam environment of 43℃ and 97% relative humidity for 8 minutes. Then, the temperature is reduced to 37℃ at a rate of 1.2℃ / min and kept at a constant temperature for 22 minutes to allow protein molecules to rearrange. During the constant temperature process, 370nm UVA ultraviolet light is turned on for double-sided irradiation with a power density of 15mW / cm² and an irradiation distance of 20cm. Finally, the fillets are immediately transferred to a 2℃ ice water bath for 5 minutes to cool. Step (4) is repeated 3 times and the fillets are then removed and the surface moisture is dried. The air pressure is maintained at 0.11MPa throughout the process.

[0052] (5) Post-processing and storage: The shaped fish fillets are vacuum-packed with a vacuum degree controlled at -0.09MPa and stored at a low temperature below -18℃.

[0053] Example 3

[0054] A method for preparing fish fillets to lock in freshness and enhance firmness, characterized by comprising the following steps:

[0055] (1) Fish fillet pretreatment: Remove the scales, bones and internal organs from the fresh fish, clean it and cut it into uniform thin slices with a thickness of 2mm. Drain the surface water and set aside.

[0056] (2) Preparation of compound freshness-locking and toughening preparation solution: According to the mass parts, 2 parts of edible salt, 3 parts of white sugar, 0.8 parts of trehalose, 0.2 parts of compound phosphate, 0.7 parts of compound toughening regulator, 0.06 parts of cross-linking promoter, 0.16 parts of natural antioxidant and 0.03 parts of antibacterial agent are added to 94 parts of purified water, stirred and dispersed until completely dissolved, and the pH value of the preparation solution is adjusted to 7.0 to obtain compound freshness-locking and toughening preparation solution;

[0057] The composite phosphate is composed of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a mass ratio of 4:2:1.

[0058] The composite toughening modifier is composed of food-grade magnesium oxide, tricalcium phosphate and magnesium lactate in a mass ratio of 3:2:2.

[0059] The cross-linking accelerator is composed of glutamine transaminase and L-cysteine ​​hydrochloride in a mass ratio of 2:1;

[0060] The natural antioxidant is composed of rosemary extract and sodium vitamin C in a mass ratio of 1.5:1.

[0061] The antibacterial agent is composed of ε-polylysine hydrochloride and natamycin in a mass ratio of 1:1.

[0062] (3) Ultrasonic assisted soaking treatment: The pretreated fish fillets are mixed with the compound freshness-locking and toughening preparation liquid at a mass ratio of 1:2.5. First, they are soaked at a low temperature of 6℃ for 55 minutes, then treated with ultrasonic waves at a power of 260W and a frequency of 30kHz for 15 minutes, and then soaked at a low temperature of 6℃ for 37 minutes. The fish fillets are then removed and the excess liquid on the surface is drained.

[0063] (4) Protein setting treatment: After draining, the fish fillets are laid out in a single layer and pre-hardened in a humid steam environment of 42℃ and 90% relative humidity for 7 minutes. Then, the temperature is reduced to 36℃ at a rate of 1℃ / min and kept at a constant temperature for 20 minutes to allow protein molecules to rearrange. During the constant temperature process, 365nm UVA ultraviolet light is turned on for double-sided irradiation with a power density of 10mW / cm² and an irradiation distance of 17cm. Finally, the fish fillets are immediately transferred to a 1℃ ice water bath for 4 minutes to cool. Step (4) is repeated 3 times and the fish fillets are then removed and the surface moisture is dried. The air pressure is kept at 0.1MPa throughout the process.

[0064] (5) Post-processing and storage: The shaped fish fillets are vacuum-packed with a vacuum degree controlled at -0.09MPa and stored at a low temperature below -18℃.

[0065] Comparative Example 1

[0066] The fish fillets are soaked in traditional single phosphate without ultrasound assistance or protein setting.

[0067] Comparative Example 2

[0068] Compared to Example 3, which omits the compound toughening regulator in the compound freshness-locking and toughening preparation liquid, everything else is the same as in Example 3.

[0069] Comparative Example 3

[0070] Compared to the deletion of step (4) protein shaping process in Example 3, everything else is the same as in Example 3.

[0071] Comparative Example 4

[0072] Compared to Example 3, step (4) of the protein shaping process was deleted, which included "during the constant temperature insulation process, 365nm UVA ultraviolet light was turned on for double-sided irradiation from the top and bottom, with a power density of 10mW / cm² and an irradiation distance of 17cm". The rest was consistent with the Example 3.

[0073] Implementation verification

[0074] The tilapia fillets prepared using the methods of Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to the following verification.

[0075] I. Detection Methods

[0076] (1) Thawing juice loss rate: Referring to GB / T 30891-2014 "Methods for Thawing Aquatic Products", take fish fillet samples that have been frozen for 7 days, thaw them naturally to a core temperature of 0-4℃, blot off the surface free moisture with filter paper, weigh them, and calculate as follows:

[0077] Thawing juice loss rate (%) = (mass before thawing - mass after thawing) / mass before thawing × 100%;

[0078] (2) Water retention: Weigh 10.0g of fish fillet sample into a centrifuge tube, centrifuge at 4℃ and 8000r / min for 15min, discard the centrifuged liquid and weigh it, and calculate as follows:

[0079] Water-holding capacity (%) = (mass after centrifugation / mass before centrifugation) × 100%;

[0080] (3) Texture properties: The texture instrument was used in TPA mode, with a probe P / 50; the speed before the test was 2 mm / s, the test speed was 1 mm / s, the speed after the test was 2 mm / s, and the compression ratio was 50%; the test was performed in parallel for 6 times and the average value was taken; the shear toughness was measured in shear mode of the texture instrument, with a probe HDP / BS, the test speed was 1 mm / s, the shear depth was 10 mm, and the unit was N·mm.

[0081] (4) Peroxide value (POV): Refer to GB 5009.227-2016 "National Food Safety Standard - Determination of Peroxide Value in Food" to determine the degree of fat oxidation in fish fillets, unit g / 100g;

[0082] (5) Total bacterial count: Refer to GB 4789.2-2022 "National Food Safety Standard for Microbiological Examination of Food - Determination of Total Bacterial Count" to determine the total bacterial count of fish fillets after 7 days of frozen storage, in units of lg (CFU / g);

[0083] (6) Sensory evaluation: A professional evaluation team of 10 people will be formed to score the meat based on four dimensions: color (2 points), smell (2 points), meat texture (3 points), and taste (3 points). The total score is 10 points, and the higher the score, the better the quality.

[0084] II. Summary of Experimental Data

[0085]

[0086] III. Analysis of Experimental Results

[0087] (1) The thawing juice loss rate of Examples 1-3 was significantly lower than that of the comparative examples, and the water retention capacity was significantly higher than that of the comparative examples. The experimental results show that the stable water-retaining network constructed by the composite phosphate and trehalose of the present invention can effectively reduce the damage to muscle cells caused by ice crystals during freezing, reduce the juice loss rate from the source, and has an outstanding water-locking and preservation effect.

[0088] (2) The hardness, elasticity, toughness, and chewiness of the fish fillets in the examples were significantly higher than those in the comparative examples. The test results show that the composite toughening regulator of the present invention can reconstruct the myofibril protein structure, and the cross-linking promoter strengthens the cross-linking between protein molecules. Combined with the gradient wet heat protein setting process, it effectively improves the firmness and chewiness of the fish fillets, and completely solves the industry pain point of traditional fish fillets being tough and brittle.

[0089] (3) The peroxide value and total bacterial count of the fish fillets in the examples were significantly lower than those in the comparative examples. The test results show that the natural antioxidant of the present invention can effectively inhibit the oxidative rancidity of fish fat, and the compound antibacterial agent can block the reproduction of microorganisms, significantly delay the deterioration of fish fillet quality, and greatly extend the shelf life of the product.

[0090] (4) In Comparative Example 2, the lack of the composite toughening regulator resulted in a significant decrease in the texture and water-holding capacity of the fish fillets; in Comparative Example 3, the protein setting step was omitted, and the protein structure could not be stably solidified, leading to a significant deterioration in product quality; in Comparative Example 1, which used the traditional process, all indicators were at the worst level. The experimental results demonstrate that the synergistic system of the composite freshness-locking and toughening preparation liquid, ultrasonic-assisted immersion, and gradient moist heat protein setting is the core key to achieving freshness-locking, toughening, and preservation of fish fillets, with the three components working synergistically.

[0091] (5) After removing the UVA ultraviolet irradiation step in Comparative Example 4, the shear toughness of the fish fillets decreased significantly, the loss rate of thawed juice increased significantly, and the total number of colonies increased. This proves that 360-370nm UVA ultraviolet irradiation can produce a significant synergistic effect with the gradient wet heat protein shaping process and the composite functional component system, and is one of the key technical means to further improve product quality.

[0092] (6) The sensory scores of the fish fillets in the example were significantly higher than those in the other pairs. The product has a bright color, no fishy or odor, and a firm and elastic texture. It retains the original flavor of the fish and does not have the stickiness caused by traditional processing, resulting in a better eating experience.

[0093] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing fish fillets to lock in freshness and enhance firmness, characterized in that, Includes the following steps: (1) Fish fillet pretreatment: Remove the scales, bones and internal organs from the fresh fish, clean it and cut it into uniform thin slices with a thickness of 2-3mm, drain the surface water and set aside. (2) Preparation of compound freshness-locking and toughening preparation solution: According to the mass fraction, add 1.5-2.5 parts of edible salt, 2.5-3.5 parts of white sugar, 0.5-1 parts of trehalose, 0.15-0.29 parts of compound phosphate, 0.4-0.9 parts of compound toughening regulator, 0.03-0.08 parts of cross-linking promoter, 0.09-0.22 parts of natural antioxidant, and 0.015-0.045 parts of antibacterial agent to 93.5-95.5 parts of purified water, stir and disperse until completely dissolved, adjust the pH value of the preparation solution to 6.8-7.0, and obtain compound freshness-locking and toughening preparation solution; (3) Ultrasonic assisted soaking treatment: Mix the pretreated fish fillets with the compound freshness-locking and toughening preparation liquid at a mass ratio of 1:2-3. First, soak them at a low temperature of 4-8℃ for 50-60 minutes, then use ultrasonic treatment with a power of 200-300W and a frequency of 20-40kHz for 10-20 minutes, and continue to soak them at 4-8℃ for 30-40 minutes. Take out the fish fillets and drain the excess liquid on the surface. (4) Protein setting treatment: After draining, lay the fish fillets in a single layer and place them in a humid and hot steam environment of 41-43℃ and relative humidity ≥90% for 6-8 minutes to pre-harden. Then, cool them down to 35-37℃ at a rate of 0.8-1.2℃ / min and keep them at a constant temperature for 18-22 minutes to allow protein molecules to rearrange. Finally, immediately transfer them to an ice water bath of 0-2℃ to cool for 3-5 minutes. Repeat step (4) 2 to 3 times and then take them out and pat them dry.

2. The method for preserving freshness and enhancing the firmness of fish fillets according to claim 1, characterized in that, The composite phosphate in step (2) is composed of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a mass ratio of 4:2:

1.

3. The method for preserving freshness and enhancing the firmness of fish fillets according to claim 1, characterized in that, The composite toughening regulator mentioned in step (2) is composed of food-grade magnesium oxide, tricalcium phosphate and magnesium lactate in a mass ratio of 3:2:

2.

4. The method for preserving freshness and enhancing the firmness of fish fillets according to claim 1, characterized in that, The cross-linking promoter mentioned in step (2) is a mixture of glutamine transaminase and L-cysteine ​​hydrochloride in a mass ratio of 2:

1.

5. The method for preserving freshness and enhancing the firmness of fish fillets according to claim 1, characterized in that, The natural antioxidant mentioned in step (2) is a mixture of rosemary extract and sodium vitamin C in a mass ratio of 1.5:

1.

6. The method for preserving freshness and enhancing the firmness of fish fillets according to claim 1, characterized in that, The antibacterial agent described in step (2) is a mixture of ε-polylysine hydrochloride and natamycin in a mass ratio of 1:

1.

7. The method for preparing fish fillets to lock in freshness and enhance firmness according to claim 1, characterized in that, In step (4), the gradient cooling rate is 1℃ / min, the molecular rearrangement constant temperature is 36℃, the holding time is 20min, and the fish fillets being processed are tilapia fillets.

8. The method for preparing fish fillets to lock in freshness and enhance firmness according to claim 1, characterized in that, Step (4) is performed while maintaining an absolute pressure of 0.09-0.11 MPa.

9. The method for preserving freshness and enhancing the firmness of fish fillets according to claim 1, characterized in that, After step (4), the following will also be executed: (5) Post-processing and storage: The shaped fish fillets are vacuum-packed with a vacuum degree controlled at -0.08 to -0.09 MPa and stored at a low temperature below -18℃.

10. The method for preparing fish fillets to lock in freshness and enhance firmness according to claim 1, characterized in that, During the isothermal incubation process of protein shaping treatment in step (4), 360-370nm UVA ultraviolet light is turned on for double-sided irradiation from the top and bottom, with a power density of 5-15mW / cm² and an irradiation distance of 15-20cm.

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