Preparation and application of composite plant extract slow-release preservative for targeted inhibition of putrefying bacteria in aquatic products

Abstract

The invention discloses a preparation method of a composite plant extract slow-release preservative for targeted inhibition of putrefying bacteria of aquatic products, which comprises the following steps: selecting plant extract, tea polyphenol, vitamin E and water-soluble chitosan, compounding, adding sodium hyaluronate, homogenizing, finally adjusting the pH value, adding a stabilizer to form a preservative solution, and freeze-drying to obtain the preservative. Plant extracts of origanum vulgare, clove and the like can damage a microbial film structure and a metabolic function in a targeted manner and cover gram positive / negative bacteria and fungi; the tea polyphenol and the vitamin E scavenge free radicals and inhibit the activity of lipoxygenase through redox cycle, and block the oxidation chain reaction of lipid and protein; the water-soluble chitosan and the plant polyphenol can form a pH-responsive slow-release film, so that the invasion of oxygen and microorganisms is physically blocked, and active ingredients are intelligently released in a putrefying microenvironment (the pH is reduced), so that'on-demand bacteriostasis' is realized; the preservative disclosed by the invention can effectively protect the color, luster and texture quality of aquatic products through multi-mechanism synergistic antibiosis.

Description

Technical Field

[0001] The present invention belongs to the technical field of aquatic product preservation, and relates to a natural composite preservative for targeted inhibition of aquatic product spoilage bacteria prepared from plant extracts as raw materials, and a method for applying the same in the storage and preservation of aquatic products, and more particularly to the preparation and application of a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria. Background Art

[0002] Aquatic products have high nutritional value because they are rich in high-quality protein and unsaturated fatty acids. However, they are extremely susceptible to microbial contamination and endogenous enzyme action during storage and transportation, leading to spoilage, economic losses and food safety risks. Currently, commonly used preservation technologies mainly rely on low-temperature refrigeration, chemical preservatives (such as nitrites and benzoates) and physical treatments (such as irradiation). The low-temperature cold chain is costly and difficult to cover the entire process. Chemical preservatives have the risk of residual toxicity and drug resistance, and physical preservation technology can easily have a negative impact on the quality structure of aquatic products. Therefore, as consumers' demand for natural and safe food increases, the development of new, efficient and non-toxic biological preservatives has become an urgent need in the industry.

[0003] Plant extracts are rich in active ingredients such as polyphenols, flavonoids, and organic acids, and have broad-spectrum antibacterial and antioxidant properties. In recent years, they have been gradually applied to the field of food preservation. For example, rosemary extract can delay lipid oxidation by scavenging free radicals, and tea polyphenols show significant inhibitory effects on common spoilage bacteria in aquatic products (such as Pseudomonas and Shewanella). However, single plant extracts have problems such as narrow antibacterial spectrum, high effective concentration, and insufficient stability. In addition, there may be antagonistic effects between different active ingredients, which limits their practical application.

[0004] Compounding different plant extracts and utilizing the synergistic effects between components to enhance the freshness-keeping properties of food is currently the main research direction in the field of food preservation. For example, patent CN116616335A discloses a preservative for crab sticks, as well as a preparation method and a method of use. The preservative that can be used for crab stick preservation is prepared by compounding trehalose, tea polyphenols, protamine, lysine, and modified Houttuynia cordata stem and leaf extracts. This patent applies the preservative to crab stick preservation and has excellent antibacterial effects on the four dominant bacterial communities in crab sticks. It can effectively inhibit the growth of common bacteria in crab sticks and extend the shelf life. However, this method only relies on the correlation between the components to improve the antibacterial properties of the preservative, which may result in limited overall preservation effect. Patent CN 116616334A discloses a composite biological preservative for aquatic products and a preservation method thereof. The preservative is prepared by mixing water-soluble chitosan, lentil lectin, tea polyphenols, and sodium alginate, then mixing with an antibacterial agent and a composite plant extract, and homogenizing. While this preservative forms a protective film on the surface of aquatic products, blocking air and preventing oxidation, effectively inhibiting the growth of psychrophilic Pseudomonas, Escherichia coli, and Staphylococcus aureus, and effectively maintaining the texture of fish meat and extending its shelf life, this method, however, lacks encapsulation and sustained-release technology, resulting in rapid loss of active ingredients from the surface of the aquatic product, making it impossible to achieve pH-responsive, long-lasting release. This method, in particular, suffers from uneven penetration and insufficient penetration depth for large, bulky, or high-fat aquatic products. Patent CN 119498394A discloses a preservative for fresh tilapia chunks and its preparation method. The preservative is prepared using a three-layer structure using an electrostatic deposition technique, using natural plant extracts, modified biopolysaccharides, organic acids, natural antimicrobial peptides, humectants, and deionized water as raw materials. The preservative incorporates multiple active ingredients, including natural plant extracts, modified biopolysaccharides, organic acids, and natural antimicrobial peptides. These ingredients synergistically inhibit microbial growth and enzymatic degradation during storage, delaying spoilage and significantly extending the shelf life of the tilapia chunks, maintaining their freshness and nutritional value. However, this method also merely involves combining the antimicrobial properties of various ingredients (such as trehalose and protamine) and fails to effectively combat spoilage bacteria in aquatic products. Summary of the Invention

[0005] [Technical Issues]

[0006] Traditional aquatic product preservation technologies face bottlenecks such as high risk of chemical preservative residues, narrow antimicrobial spectrum of single plant extracts, and high physical preservation costs. Furthermore, it is difficult to simultaneously inhibit multiple spoilage pathways, including microbial proliferation, lipid oxidation, and enzymatic spoilage. Due to their high moisture and protein content, aquatic products are susceptible to colonization by spoilage bacteria such as Pseudomonas during storage, leading to lipid peroxidation, protein degradation, and accumulation of odorous substances, shortening shelf life and reducing sensory quality. Existing technologies often rely on a single antibacterial or antioxidant mechanism, making it impossible to achieve full-chain control of spoilage pathways. Furthermore, the safety of chemical additives and the industrial compatibility of physical preservation methods urgently need to be improved.

[0007] [Technical solution]

[0008] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a preparation and application of a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria. Through the synergistic enhancement of multiple components and the design of a targeted delivery system, the problems of limited antibacterial activity, chemical residue risks and insufficient control of aquatic product spoilage mechanisms in the prior art are solved, thereby achieving an efficient, green and multifunctional preservation effect.

[0009] The present invention first provides a method for preparing a composite plant extract sustained-release preservative for targeted inhibition of spoilage bacteria in aquatic products, comprising the following steps:

[0010] (1) Preparation of plant extracts: The plant raw materials were crushed through a 40-mesh sieve, added with ethanol solution, and subjected to ultrasonic-assisted extraction, followed by concentration and freeze-drying to obtain plant extract powder;

[0011] (2) Raw material compounding: dissolving the plant extract powder, tea polyphenols, vitamin E and water-soluble chitosan obtained in step (1) in deionized water and homogenizing to form a uniform solution;

[0012] (3) Pretreatment of embedded sustained-release material: Sodium hyaluronate was dissolved in deionized water and stirred at 40-50°C until completely dissolved to form a premixed solution;

[0013] (4) Mixing treatment: mixing the homogeneous solution of step (2) with the premixed solution of step (3), and homogenizing to obtain a mixed solution;

[0014] (5) Stabilization treatment: adjust the pH of the mixed solution to 4.5-5.5, add sodium alginate as a stabilizer, and filter after ultrasonic dispersion to obtain a transparent and stable preservative solution. After freeze-drying, crush the solution to obtain a powdered preservative.

[0015] In one embodiment of the present invention, the plant raw material in step (1) is any one or more of oregano, cloves, thyme, lemon and cinnamon.

[0016] In one embodiment of the present invention, the ethanol solution in step (1) is a 60% ethanol solution, and the material-liquid ratio of the crushed plant material to the ethanol solution is 1:20-3:10.

[0017] In one embodiment of the present invention, the ultrasonic frequency during the ultrasonic-assisted extraction in step (1) is 20-50 kHz, the extraction temperature is 25-50° C., and the extraction time is 20-30 min.

[0018] In one embodiment of the present invention, the concentration in step (1) is a reduced pressure concentration, and the concentration is performed until the solid content is ≥20%, and the freeze-drying process is first freezing at -80°C for 1-2 hours and then freezing at -50°C for 24-36 hours.

[0019] In one embodiment of the present invention, the plant extract powder in step (2) is any one of oregano extract powder, clove extract powder, thyme extract powder, lemon extract powder and cinnamon extract powder, or a mixture of several of them.

[0020] In one embodiment of the present invention, the plant extract powder in step (2) includes oregano extract powder and clove extract powder, and the homogeneous solution includes, by weight percentage, 1-5% oregano extract, 1-2% clove extract, 0.3-2% tea polyphenols, 0.5-2.5% vitamin E, 0.02-4.2% water-soluble chitosan, and the balance is deionized water.

[0021] In one embodiment of the present invention, the plant extract powder described in step (2) includes thyme extract powder and cinnamon extract powder. Calculated by mass percentage, the homogeneous solution includes 1-6% thyme extract, 2-8% cinnamon extract, 1-5% lemon extract, 0.02-5% tea polyphenols, 0.5-1.5% vitamin E, 3-6% water-soluble chitosan, and the balance is deionized water.

[0022] In one embodiment of the present invention, the plant extract powder in step (2) includes oregano extract powder, clove extract powder and thyme extract powder, and the homogenous solution includes, by mass percentage, 0.5-3% oregano extract, 1-7% clove extract, 0.3-1.6% thyme extract, 0.08-2% tea polyphenols, 0.03-1.05% vitamin E, 2-7% water-soluble chitosan, and the balance is deionized water.

[0023] In one embodiment of the present invention, the water-soluble chitosan is carboxymethyl chitosan, and the molecular weight of the carboxymethyl chitosan is 20 to 40 kDa.

[0024] In one embodiment of the present invention, in step (2), the homogenization temperature is 25-40° C., the homogenization speed is 8000-12000 rpm, and the homogenization time is 5-10 min.

[0025] In one embodiment of the present invention, in step (3), the mass concentration of sodium hyaluronate in the premix is ​​5-10%.

[0026] In one embodiment of the present invention, in step (4), the volume ratio of the homogeneous solution to the premixed solution is (4:1) to (8:1).

[0027] In one embodiment of the present invention, in step (4), the homogenization temperature is 25-40° C., the homogenization speed is 8000-12000 rpm, and the homogenization time is 5-10 min.

[0028] In one embodiment of the present invention, in step (5), a citric acid / sodium citrate buffer system is used to adjust the pH, wherein the citric acid / sodium citrate buffer system consists of citric acid and sodium citrate with a concentration of 0.05-0.1% (w / v).

[0029] In one embodiment of the present invention, in step (5), the amount of sodium alginate added is 0.1 to 0.5% of the mass of the mixed solution.

[0030] In one embodiment of the present invention, in step (5), the power of ultrasonic dispersion is 300 W, the time is 10 min, and a microfiltration membrane is used for filtration, and the pore size of the microfiltration membrane is 0.22 μm.

[0031] In one embodiment of the present invention, the freeze-drying includes pre-freezing the fresh-keeping liquid and then placing it in a vacuum freeze dryer for vacuum freezing. The pre-freezing temperature is -80°C and the pre-freezing time is 2 hours. The vacuum freezing is carried out by drying for 24 hours at -50°C and a vacuum degree of ≤10Pa until the water content is ≤5%. After freeze-drying, the fresh-keeping liquid is crushed with a mortar or a grinder and passed through a 40-mesh sieve to obtain a powdered preservative.

[0032] The present invention also provides a preservative prepared according to the method.

[0033] The invention also discloses an application of the preservative in preserving aquatic products.

[0034] In one embodiment of the present invention, the application includes soaking the pretreated aquatic product in a preservative liquid in which the preservative is redissolved, so that the preservative liquid covers the surface of the aquatic product, and then putting the treated aquatic product into a food-grade packaging bag, expelling the air in the bag and heat sealing it, and refrigerating it at 4°C±1°C.

[0035] In one embodiment of the present invention, the soaking time is 10 to 30 minutes, and the oxygen transmission rate of the food-grade packaging bag is ≤5 cm 3 / m 2 ·24h.

[0036] In one embodiment of the present invention, the soaking in the preservative liquid may be supplemented by vacuum impregnation (-0.08 MPa, with ventilation every 2 minutes).

[0037] In one embodiment of the present invention, when the aquatic product is a high-fat or high-water fish (such as salmon or squid), ultrasonic assisted immersion (frequency 40 kHz, power 150 W, time 2 min) is used during soaking in the preservative liquid to promote the penetration of the active ingredient to 1-2 mm below the skin to enhance film formation.

[0038] In one embodiment of the present invention, the pretreatment method of aquatic products is to remove the head, tail and internal organs of fresh aquatic products (such as marine fish), and rinse them with sterile water three times to remove surface mucus and blood stains; cutting standardization: cutting the aquatic products into pieces or segments, controlling the length to ≤5 cm to ensure uniform penetration of subsequent preservatives; surface draining: placing them in a draining sieve and letting them stand for 10-15 minutes to make the surface moisture content ≤5% (weight ratio).

[0039] Beneficial effects:

[0040] (1) The present invention selects plant extracts such as oregano and cloves and natural components such as tea polyphenols to construct a multi-dimensional preservation system, wherein plant extracts such as oregano and cloves can target and destroy the structure and metabolic function of microbial membranes, covering Gram-positive / negative bacteria and fungi; tea polyphenols and vitamin E remove free radicals and inhibit the activity of lipoxygenase through redox cycles, blocking the lipid and protein oxidation chain reaction; water-soluble chitosan and plant polyphenols will form a pH-responsive sustained-release film, physically blocking the invasion of oxygen and microorganisms, and intelligently releasing active ingredients in the corruption microenvironment (pH decreases), achieving "on-demand antibacterial"; the preservative of the present invention can effectively protect the color and texture quality of aquatic products through multi-mechanism synergistic antibacterial.

[0041] (2) The present invention first compounds plant extracts, tea polyphenols, vitamin E and water-soluble chitosan, then adds sodium hyaluronate for homogenization, constructs a pH-sensitive composite film, and finally adds a stabilizer to stabilize the solution. This method can effectively improve the dispersibility of sodium hyaluronate, and the prepared preservative has better antibacterial properties and sustained-release antibacterial effects.

[0042] (3) The all-natural ingredients used in this invention avoid the risk of chemical residues and are compatible with conventional processes such as spraying, soaking, or glazing. This eliminates the need for complex equipment modifications, significantly reducing cold chain dependence and processing costs. Furthermore, aldehydes mask the fishy odor and enhance sensory quality. This invention breaks through the single-target limitations of traditional technologies and provides an innovative solution for the green and efficient preservation of aquatic products.

[0043] (4) The present invention breaks through the limitations of traditional preservation technology such as single target, high residue and high cost through the combination of natural components, multi-mechanism synergy and dynamic response technology, and realizes the full chain control of spoilage microorganisms, oxidative deterioration and enzymatic degradation of aquatic products, providing an innovative solution for green, efficient and sustainable aquatic product preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The color results of scallops during the preservation process in Examples 1 to 5 and Comparative Example 1 are as follows;

[0045] Figure 2 The color results of tilapia during the preservation process in Examples 6-7 and Comparative Example 2 are as follows;

[0046] Figure 3 The results of texture analysis of scallops during the preservation process in Examples 1 to 5 and Comparative Example 1 are as follows;

[0047] Figure 4 The results of microbial analysis during the preservation of scallops in Examples 1 to 5 and Comparative Example 1 are as follows;

[0048] Figure 5 The microbial analysis results of the aquatic products of Examples 8-9 and Comparative Examples 2-5 are as follows;

[0049] Figure 6 The microbial analysis results of the aquatic products of Examples 6-7, Comparative Examples 2 and Comparative Examples 6-7;

[0050] Figure 7 The microbial analysis results of the aquatic products of Example 6 and Comparative Example 11;

[0051] Figure 8 The microbial analysis results of the aquatic products of Example 6 and Comparative Examples 12-13 are shown;

[0052] Figure 9 The microbial analysis results of the aquatic products of Example 10 and Comparative Example 8;

[0053] Figure 10 The microbial analysis results of the aquatic products of Example 11 and Comparative Example 9 are shown;

[0054] Figure 11 These are the microbial analysis results of the aquatic products of Example 12 and Comparative Example 10. DETAILED DESCRIPTION

[0055] The following describes preferred embodiments of the present invention. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0056] The test methods used in the following examples are:

[0057] 1. Texture Testing Method: Cut the preservative-soaked sample into chunks and perform a full texture test using a texture analyzer. Specific parameters: spherical probe P / 5s; pre-test speed: 2 mm / sec; test speed: 2 mm / sec; post-test speed: 2 mm / sec; trigger force: 5g; compression: 50%; and interval between probe measurements: 5s.

[0058] 2. Color detection method: Cut the sample soaked in preservative into blocks and use a colorimeter to measure the L* (brightness value), a* (redness value) and b* (yellowness value) of the fish meat.

[0059] Example 1

[0060] A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria comprises the following steps:

[0061] (1) Plant extraction: The oregano plant material was crushed and passed through a 40-mesh sieve. A 60% ethanol solution was added at a solid-liquid ratio of 1:10. Ultrasonic-assisted extraction (40 kHz, 30 min) was performed at 50°C. After filtration, the extraction was repeated once. The filtrates after the two extractions were combined and concentrated under reduced pressure to a solid content of ≥20%. The mixture was pre-frozen (-80°C, 2 h) and then freeze-dried (-50°C, 24 h) to obtain a plant extract powder.

[0062] (2) Compounding: 1.5% oregano extract, 0.5% tea polyphenols, 0.05% vitamin E, and 1.5% 20 kDa water-soluble chitosan were dissolved in deionized water according to mass percentage, and homogenized at 25°C for 5 min (8000 rpm) to form a uniform solution;

[0063] (3) Pretreatment of embedded sustained-release material: Sodium hyaluronate was dissolved in deionized water and stirred at 40-50°C until completely dissolved to form a premixed solution with a mass concentration of 5%;

[0064] (4) Mixing: The homogenous solution of step (2) and the premixed solution of step (3) were mixed in a volume ratio of 6:1, and homogenized at 30° C. and 8000 rpm to form a homogenous solution;

[0065] (5) Stabilization treatment: The pH was adjusted to 4.5 (citric acid / sodium citrate buffer system), 0.3% sodium alginate was added as a stabilizer, and a transparent and stable preservative solution was obtained by ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm).

[0066] (6) Freeze-drying

[0067] Pre-freezing: Pour the transparent and stable preservative liquid into a shallow dish with a thickness of 0.5 cm. Place it in a -80℃ refrigerator and pre-freeze for 2 hours to form a solid frozen block.

[0068] Freeze drying: Transfer the frozen block to a freeze dryer and dry it at -50°C and vacuum ≤10Pa for 24 hours until the water content is ≤5%.

[0069] Crushing and sieving: The dried solid is crushed with a mortar or grinder, and passed through a 40-mesh sieve to obtain a powdered preservative.

[0070] Application of preservative liquid in scallop preservation:

[0071] S1. Raw material pretreatment: commercially available scallop meat was cleaned to remove surface mucus, thawed at room temperature, cut into pieces (diameter ≤ 3 cm), and drained until the surface moisture was ≤ 5%;

[0072] S2, soaking: immerse the scallop pieces in a preservative solution (4°C) so that the preservative solution completely covers the scallop pieces for 10 min, supplemented by vacuum impregnation (-0.08 MPa, with ventilation every 2 min). The preservative solution is prepared by redissolving the preservative and water in a mass ratio of 1:6.

[0073] S3. Packaging: Take out the scallop pieces from step S2, drain them, put them into high-barrier aluminum foil bags, and vacuum heat-seal them.

[0074] S4. Freezing: Quickly freeze the packaged scallop pieces at -18°C and store at -18°C.

[0075] Example 2

[0076] The difference between Example 2 and Example 1 is that the oregano plant raw material in step (1) is replaced by a clove plant raw material, the oregano extract in step (2) is replaced by a clove extract, and the raw material ratio in step (2) is: 1.2% clove extract, 3% water-soluble chitosan, 1% tea polyphenols, 0.05% vitamin E, and the rest is deionized water; the mass concentration of the premix in step (3) is 7%.

[0077] A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria comprises the following steps:

[0078] (1) Plant extraction: The oregano plant material was crushed and passed through a 40-mesh sieve. A 60% ethanol solution was added at a solid-liquid ratio of 1:10. Ultrasonic-assisted extraction (40 kHz, 30 min) was performed at 50°C. After filtration, the extraction was repeated once. The filtrates after the two extractions were combined and concentrated under reduced pressure to a solid content of ≥20%. The mixture was pre-frozen (-80°C, 2 h) and then freeze-dried (-50°C, 24 h) to obtain a plant extract powder.

[0079] (2) Compounding: Dissolve 1.2% of clove extract, 3% of 20 kDa water-soluble chitosan, 1% of tea polyphenols, and 0.05% of vitamin E in deionized water according to mass percentage, and homogenize at 25°C (8000 rpm) to form a uniform solution;

[0080] (3) Pretreatment of embedded sustained-release material: Sodium hyaluronate was dissolved in deionized water and stirred at 40-50°C until completely dissolved to form a premixed solution with a mass concentration of 7%;

[0081] (4) Mixing: The homogenous solution of step (2) and the premixed solution of step (3) were mixed in a ratio of 6:1, and homogenized at 30° C. and 8000 rpm to form a homogenous solution;

[0082] (5) Stabilization treatment: The pH was adjusted to 4.5 (citric acid / sodium citrate buffer system), 0.3% sodium alginate was added as a stabilizer, and a transparent and stable preservative solution was obtained by ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm).

[0083] (6) Freeze-drying

[0084] Pre-freezing: Pour the transparent and stable preservative liquid into a shallow dish with a thickness of 0.5 cm. Place it in a -80℃ refrigerator and pre-freeze for 2 hours to form a solid frozen block.

[0085] Vacuum drying: Transfer the frozen block to a freeze dryer and dry it at -50°C and vacuum ≤10Pa for 24 hours until the water content is ≤5%.

[0086] Crushing and sieving: The dried solid is crushed with a mortar or grinder, and passed through a 40-mesh sieve to obtain a powdered preservative.

[0087] Example 3

[0088] The difference between Example 3 and Example 1 is that the oregano plant raw material in step (1) is replaced by cinnamon plant raw material, the oregano extract in step (2) is replaced by cinnamon extract, and the raw material ratio in step (2) is: cinnamon extract 1.0%, water-soluble chitosan 1.5%, tea polyphenols 0.8%, vitamin E 0.3%, and the rest is deionized water; the mass concentration of the premix in step (3) is 9%, and the ratio in step (4) is 7:1.

[0089] A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria comprises the following steps:

[0090] (1) Plant extraction: The oregano plant material was crushed and passed through a 40-mesh sieve. A 60% ethanol solution was added at a solid-liquid ratio of 1:10. Ultrasonic-assisted extraction (40 kHz, 30 min) was performed at 50°C. After filtration, the extraction was repeated once. The filtrates after the two extractions were combined and concentrated under reduced pressure to a solid content of ≥20%. The mixture was pre-frozen (-80°C, 2 h) and then freeze-dried (-50°C, 24 h) to obtain a plant extract powder.

[0091] (2) Compounding: 1.0% cinnamon extract, 1.5% 20 kDa water-soluble chitosan, 0.8% tea polyphenols, and 0.3% vitamin E were dissolved in deionized water according to mass percentage, and homogenized at 25°C (8000 rpm) to form a uniform solution;

[0092] (3) Pretreatment of embedded sustained-release material: Sodium hyaluronate was dissolved in deionized water and stirred at 40-50°C until completely dissolved to form a premixed solution with a mass concentration of 9%;

[0093] (4) Mixing: The homogenous solution of step (2) and the premixed solution of step (3) were mixed in a ratio of 7:1, and homogenized at 25° C. and 8000 rpm to form a homogenous solution;

[0094] (5) Stabilization treatment: The pH was adjusted to 4.5 (citric acid / sodium citrate buffer system), 0.5% sodium alginate was added as a stabilizer, and a transparent and stable preservative solution was obtained by ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm).

[0095] (6) Freeze-drying

[0096] Pre-freezing: Pour the transparent and stable preservative liquid into a shallow dish with a thickness of 0.5 cm. Place it in a -80℃ refrigerator and pre-freeze for 2 hours to form a solid frozen block.

[0097] Vacuum drying: Transfer the frozen block to a freeze dryer and dry it at -50°C and vacuum ≤10Pa for 24 hours until the water content is ≤5%.

[0098] Crushing and sieving: The dried solid is crushed with a mortar or grinder, and passed through a 40-mesh sieve to obtain a powdered preservative.

[0099] Example 4

[0100] The difference between Example 4 and Example 1 is that the oregano plant raw material in step (1) is replaced by thyme plant raw material, the oregano extract in step (2) is replaced by thyme extract, and the raw material ratio in step (2) is: thyme extract 1.8%, water-soluble chitosan 0.7%, tea polyphenols 1.0%, vitamin E 0.5%, and the rest is deionized water; the mass concentration of the premix in step (3) is 10%, and the ratio in step (4) is 5:1.

[0101] A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria comprises the following steps:

[0102] (1) Plant extraction: The oregano plant material was crushed and passed through a 40-mesh sieve. A 60% ethanol solution was added at a solid-liquid ratio of 1:10. Ultrasonic-assisted extraction (40 kHz, 30 min) was performed at 50°C. After filtration, the extraction was repeated once. The filtrates after the two extractions were combined and concentrated under reduced pressure to a solid content of ≥20%. The mixture was pre-frozen (-80°C, 2 h) and then freeze-dried (-50°C, 24 h) to obtain a plant extract powder.

[0103] (2) Compounding: 1.8% thyme extract, 0.7% 20 kDa water-soluble chitosan, 1.0% tea polyphenols, and 0.5% vitamin E were dissolved in deionized water according to mass percentage, and homogenized at 25° C. (speed 8000 rpm) to form a uniform solution;

[0104] (3) Pretreatment of embedded sustained-release material: Sodium hyaluronate was dissolved in deionized water and stirred at 40-50°C until completely dissolved to form a premixed solution with a mass concentration of 10%;

[0105] (4) Mixing: The homogenous solution of step (2) and the premixed solution of step (3) were mixed in a ratio of 5:1, and homogenized at 25° C. and 8000 rpm to form a homogenous solution;

[0106] (5) Stabilization treatment: The pH was adjusted to 4.5 (citric acid / sodium citrate buffer system), 0.4% sodium alginate was added as a stabilizer, and a transparent and stable preservative solution was obtained by ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm).

[0107] (6) Freeze-drying

[0108] Prefreezing: Pour the stabilized homogeneous solution into a shallow dish with a thickness of 0.5 cm, and prefreeze it in a -80°C refrigerator for 2 hours to form a solid frozen block.

[0109] Vacuum drying: Transfer the frozen block to a freeze dryer and dry it at -50°C and vacuum ≤10Pa for 24 hours until the water content is ≤5%.

[0110] Crushing and sieving: The dried solid is crushed with a mortar or grinder, and passed through a 40-mesh sieve to obtain a powdered preservative.

[0111] Example 5

[0112] The difference between Example 5 and Example 1 is that the oregano plant raw material in step (1) is replaced by lemon plant raw material, the oregano extract in step (2) is replaced by lemon extract, and the raw material ratio in step (2) is: 1.3% lemon extract, 0.7% 20kDa water-soluble chitosan, 1.1% tea polyphenols, 0.4% vitamin E, and the rest is deionized water; the mass concentration of the premix in step (3) is 10%.

[0113] A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria comprises the following steps:

[0114] (1) Plant extraction: The oregano plant material was crushed and passed through a 40-mesh sieve. A 60% ethanol solution was added at a solid-liquid ratio of 1:10. Ultrasonic-assisted extraction (40 kHz, 30 min) was performed at 50°C. After filtration, the extraction was repeated once. The filtrates after the two extractions were combined and concentrated under reduced pressure to a solid content of ≥20%. The mixture was pre-frozen (-80°C, 2 h) and then freeze-dried (-50°C, 24 h) to obtain a plant extract powder.

[0115] (2) Compounding: 1.3% lemon extract, 0.7% 20 kDa water-soluble chitosan, 1.1% tea polyphenols, and 0.4% vitamin E were dissolved in deionized water according to mass percentage, and homogenized at 25°C (8000 rpm) to form a uniform solution;

[0116] (3) Pretreatment of embedded sustained-release materials: Sodium hyaluronate was dissolved in deionized water and stirred at 40°C until completely dissolved to form a premixed solution with a mass concentration of 10%;

[0117] (4) Mixing: The homogenous solution of step (2) and the premixed solution of step (3) were mixed in a ratio of 6:1, and homogenized at 25° C. and 8000 rpm to form a homogenous solution;

[0118] (5) Stabilization treatment: The pH was adjusted to 4.5 (citric acid / sodium citrate buffer system), 0.15% sodium alginate was added as a stabilizer, and a transparent and stable preservative solution was obtained by ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm).

[0119] (6) Freeze-drying

[0120] Prefreezing: Pour the stabilized homogeneous solution into a shallow dish with a thickness of 0.5 cm, and prefreeze it in a -80°C refrigerator for 2 hours to form a solid frozen block.

[0121] Vacuum drying: Transfer the frozen block to a freeze dryer and dry it at -50°C and vacuum ≤10Pa for 24 hours until the water content is ≤5%.

[0122] Crushing and sieving: The dried solid is crushed with a mortar or grinder, and passed through a 40-mesh sieve to obtain a powdered preservative.

[0123] Example 6

[0124] A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria comprises the following steps:

[0125] (1) Plant Extraction: Cinnamon and clove plant materials were pulverized and passed through a 40-mesh sieve, and ultrasonic-assisted ethanol extraction was performed to prepare cinnamon extract powder and clove extract powder, respectively. The preparation methods of cinnamon and clove extract powders were the same as those in Example 1.

[0126] (2) Compounding: 1.0% cinnamon extract, 1.5% clove extract, 3% 20 kDa water-soluble chitosan, 0.5% tea polyphenols, and 0.5% vitamin E were dissolved in deionized water according to mass percentage, and homogenized at 25°C (8000 rpm) to form a uniform solution;

[0127] (3) Pretreatment of embedded sustained-release materials: Sodium hyaluronate was dissolved in deionized water and stirred at 40°C until completely dissolved to form a premixed solution with a mass concentration of 10%;

[0128] (4) Mixing: The homogenous solution of step (2) and the premixed solution of step (3) were mixed in a ratio of 6:1, and homogenized at 25° C. and 8000 rpm to form a homogenous solution;

[0129] (5) Stabilization treatment: The pH was adjusted to 4.5 (citric acid / sodium citrate buffer system), 0.2% sodium alginate was added as a stabilizer, and a transparent and stable preservative solution was obtained by ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm).

[0130] (6) Freeze-drying

[0131] Prefreezing: Pour the stabilized homogeneous solution into a shallow dish with a thickness of 0.5 cm, and prefreeze it in a -80°C refrigerator for 2 hours to form a solid frozen block.

[0132] Vacuum drying: Transfer the frozen block to a freeze dryer and dry it at -50°C and vacuum ≤10Pa for 24 hours until the water content is ≤5%.

[0133] Crushing and sieving: The dried solid is crushed with a mortar or grinder, and passed through a 40-mesh sieve to obtain a powdered preservative.

[0134] Application of preservative liquid in tilapia preservation:

[0135] S1. Raw material pretreatment

[0136] Commercially available boneless and boneless tilapia was washed to remove surface mucus, thawed at room temperature, cut into segments (length ≤ 5 cm), and drained until the surface moisture was ≤ 5%.

[0137] S2, soaking preservative solution: tilapia pieces are immersed in the preservative solution (4 ℃), it is fast to ensure that the preservative solution completely submerges tilapia, soak time 10min, assisted by vacuum impregnation (-0.08MPa, 2min ventilation interval), and the preservative solution is prepared by redissolving the preservative and water in a mass ratio of 1:6;

[0138] S3, packaging: take out the tilapia pieces from step (2), drain them, put them into high-barrier aluminum foil bags, and vacuum heat-seal them.

[0139] S4. Freezing: Quickly freeze the packaged tilapia pieces at -18°C and store at -18°C.

[0140] Example 7

[0141] The difference between Example 7 and Example 6 is that the proportions of the components in step (2) are different. The raw materials and proportions in step (2) of Example 7 are: cinnamon extract 1.0%, clove extract 1.0%, tea polyphenols 0.8%, chitosan 4%, and vitamin E 0.7%.

[0142] Example 8

[0143] The difference between Example 8 and Example 6 is that the proportions of the components in step (2) are different. The raw materials and proportions in step (2) of Example 8 are: cinnamon extract 1.0%, tea polyphenols 0.8%, chitosan 4%, and vitamin E 0.7%.

[0144] Example 9

[0145] The difference between Example 9 and Example 6 is that the proportions of the components in step (2) are different. The raw materials and proportions in step (2) of Example 7 are: clove extract 1.0%, tea polyphenols 0.8%, chitosan 4%, and vitamin E 0.7%.

[0146] Example 10

[0147] A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of aquatic product spoilage bacteria comprises the following steps:

[0148] (1) Plant Extraction: Cinnamon and clove plant materials were pulverized and passed through a 40-mesh sieve, and ultrasonic-assisted ethanol extraction was performed to prepare cinnamon extract powder and clove extract powder, respectively. The preparation methods of cinnamon and clove extract powders were the same as those in Example 1.

[0149] (2) Compounding: 1.0% cinnamon extract, 1.5% clove extract, 3% 20 kDa water-soluble chitosan, 0.5% tea polyphenols, and 0.5% vitamin E were dissolved in deionized water according to mass percentage, and homogenized at 25°C (8000 rpm) to form a uniform solution;

[0150] (3) Pretreatment of embedded sustained-release materials: Sodium hyaluronate was dissolved in deionized water and stirred at 40°C until completely dissolved to form a premixed solution with a mass concentration of 10%;

[0151] (4) Mixing: The homogenous solution of step (2) and the premixed solution of step (3) were mixed in a ratio of 6:1, and homogenized at 25° C. and 8000 rpm to form a homogenous solution;

[0152] (5) Stabilization treatment: The pH was adjusted to 4.5 (citric acid / sodium citrate buffer system), 0.2% sodium alginate was added as a stabilizer, and a transparent and stable preservative solution was obtained by ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm).

[0153] (6) Freeze-drying

[0154] Prefreezing: Pour the stabilized homogeneous solution into a shallow dish with a thickness of 0.5 cm, and prefreeze it in a -80°C refrigerator for 2 hours to form a solid frozen block.

[0155] Vacuum drying: Transfer the frozen block to a freeze dryer and dry it at -50°C and vacuum ≤10Pa for 24 hours until the water content is ≤5%.

[0156] Crushing and sieving: The dried solid is crushed with a mortar or grinder, and passed through a 40-mesh sieve to obtain a powdered preservative.

[0157] Application of preservative liquid in the preservation of golden pomfret:

[0158] S1. Raw material pretreatment

[0159] Commercially available boneless and boneless golden pomfret was washed to remove surface mucus, thawed at room temperature, cut into segments (length ≤ 5 cm), and drained until the surface moisture was ≤ 5%.

[0160] S2, soaking in preservative solution: immerse the tilapia pieces in preservative solution (4°C) to ensure that the preservative solution completely submerges the golden pomfret pieces. The soaking time is 10 min, supplemented by vacuum impregnation (-0.08 MPa, with ventilation every 2 min). The preservative solution is prepared by re-dissolving the preservative and water in a mass ratio of 1:6.

[0161] S3. Packaging: Take out the golden pomfret pieces from step (2), drain them, put them into high-barrier aluminum foil bags, and vacuum heat-seal them.

[0162] S4. Freezing: Quickly freeze the packaged golden pomfret pieces at -18°C and store at -18°C.

[0163] Example 11

[0164] The difference between Example 11 and Example 10 is that the preparation method of the preservative is the same, but the application of the preservative liquid is different.

[0165] Application of preservative liquid in preserving silver carp:

[0166] S1. Raw material pretreatment

[0167] Commercially available boneless and boneless silver carp was cleaned to remove surface mucus, thawed at room temperature, cut into sections (length ≤ 5 cm), and drained until the surface moisture was ≤ 5%.

[0168] S2. Soaking in preservative solution: immerse the silver carp pieces in preservative solution (4° C.), ensuring that the preservative solution completely submerges the silver carp pieces, for 10 min, supplemented by vacuum impregnation (-0.08 MPa, with ventilation every 2 min), wherein the preservative solution is prepared by reconstituted preservative and water in a mass ratio of 1:6;

[0169] S3, packaging: take out the silver carp pieces from step (2), drain them, put them into high-barrier aluminum foil bags, and vacuum heat-seal them.

[0170] S4. Freezing: Quickly freeze the packaged silver carp pieces at -18°C and store at -18°C.

[0171] Example 12

[0172] The difference between Example 12 and Example 10 is that the preparation method of the preservative is the same, but the application of the preservative liquid is different.

[0173] Application of preservative liquid in sea bass preservation:

[0174] S1. Raw material pretreatment

[0175] Commercially available boneless and scabbard-free sea bass was cleaned to remove surface mucus, thawed at room temperature, cut into segments (length ≤ 5 cm), and drained until the surface moisture was ≤ 5%.

[0176] S2. Soaking in preservative solution: Immerse the sea bass pieces in preservative solution (4° C.), ensuring that the preservative solution completely submerges the sea bass pieces, for 10 min, supplemented by vacuum impregnation (-0.08 MPa, with ventilation every 2 min). The preservative solution is prepared by reconstituting the preservative and water in a mass ratio of 1:6.

[0177] S3. Packaging: Take out the sea bass pieces from step (2), drain them, put them into high-barrier aluminum foil bags, and vacuum heat-seal them.

[0178] S4. Freezing: Quickly freeze the packaged sea bass pieces at -18°C and store at -18°C.

[0179] Comparative Example 1

[0180] The difference between Comparative Example 1 and Example 1 is that, when preserving the scallops, deionized water is used instead of the preservative liquid for soaking.

[0181] Comparative Example 2

[0182] The difference between Comparative Example 1 and Example 6 is that, when preserving the tilapia, deionized water is used instead of the preservative liquid for soaking.

[0183] Comparative Example 3

[0184] The difference between Comparative Example 3 and Example 8 is that when the tilapia is preserved, the plant extract used in step (2) is pepper extract.

[0185] Comparative Example 4

[0186] The difference between Comparative Example 4 and Example 8 is that when the tilapia is preserved, the plant extract used in step (2) is anise extract.

[0187] Comparative Example 5

[0188] The difference between Comparative Example 5 and Example 8 is that when the tilapia is preserved, the plant extract used in step (2) is dried ginger extract.

[0189] Comparative Example 6

[0190] The difference between Comparative Example 6 and Example 6 is that when preserving tilapia, the plant extracts used in step (2) are cinnamon extract and dried ginger extract, wherein the amount of cinnamon extract is 1.0% and the amount of dried ginger extract is 1.0%.

[0191] Comparative Example 7

[0192] The difference between Comparative Example 7 and Example 6 is that when the tilapia is preserved, the plant extracts used in step (2) are 1.0% thyme extract and 1.0% dried ginger extract.

[0193] Comparative Example 8

[0194] The difference between Comparative Example 8 and Example 10 is that, when preserving the golden pomfret, deionized water is used instead of the preservative liquid for soaking.

[0195] Comparative Example 9

[0196] The difference between Comparison 9 and Example 11 is that, when preserving the silver carp, deionized water is used instead of the preservative liquid for soaking.

[0197] Comparative Example 10

[0198] The difference between Comparative Example 10 and Example 12 is that, when preserving the sea bass, deionized water is used instead of the preservative liquid for soaking.

[0199] Comparative Example 11

[0200] The difference between Comparative Example 11 and Example 6 is that when preserving tilapia, 10% sodium hyaluronate solution and 0.2% sodium alginate are directly added to the solution of step (2), the pH is adjusted to 4.5 (citric acid / sodium citrate buffer system), and ultrasonic dispersion (power 300 W, time 10 min) and microfiltration (pore size 0.22 μm) are performed to obtain a transparent and stable preservative solution.

[0201] Comparative Example 12

[0202] The difference between Comparative Example 12 and Example 6 is that when preserving tilapia, the sodium hyaluronate in step (3) is replaced with sodium carboxymethyl cellulose (molecular weight 100kDa).

[0203] Comparative Example 13

[0204] The difference between Comparative Example 13 and Example 6 is that when preserving tilapia, the sodium hyaluronate in step (3) is replaced with polyvinyl alcohol (molecular weight 200kDa).

[0205] In this invention, plant extracts serve as core functional components to achieve freshness preservation of aquatic products through the following multi-dimensional mechanisms:

[0206] 1. Multi-target antibacterial effect

[0207] 1.1 Membrane structure destruction: Carvacrol in oregano and thymol in thyme insert into the lipid bilayer of microbial cell membrane through hydrophobic interaction, increasing membrane permeability and causing intracellular ion leakage (such as K + , ATP);

[0208] 1.2 Metabolic interference: Eugenol in cloves blocks energy metabolism by inhibiting bacterial ATP synthase activity, while cinnamaldehyde in cinnamon covalently modifies the sulfhydryl groups (-SH) of microbial proteins, interfering with enzyme function and DNA replication;

[0209] 1.3 Quorum sensing inhibition: Citral in lemon can downregulate the quorum sensing signal molecules (such as AHLs) of spoilage bacteria (such as Pseudomonas) and inhibit biofilm formation.

[0210] 2. Synergistic Antioxidant Network

[0211] 2.1 Free radical scavenging: The phenolic hydroxyl groups of tea polyphenols and the chroman ring of vitamin E synergistically scavenge free radicals (such as OH, O2 - ·);

[0212] 2.2 Oxidase inhibition: Plant polyphenols (such as eugenol) can inhibit oxidases by chelating metal ions (Fe 2+ / Cu 2+ ), inhibiting the activities of lipoxygenase (LOX) and myeloperoxidase (MPO), blocking the lipid peroxidation chain reaction;

[0213] 2.3 Redox cycle: Vitamin E regenerates the oxidation products of tea polyphenols, forming a continuous antioxidant cycle and prolonging the action time of the active ingredients.

[0214] 3. Physical barriers and functional regulation

[0215] 3.1 Film formation and sustained release: Water-soluble chitosan forms a dense edible film through electrostatic compounding of the positive amino groups with the negatively charged groups of plant polyphenols, reducing oxygen permeability. At the same time, the membrane structure undergoes protonation response in the corruption microenvironment (pH decrease), accelerating the targeted release of active ingredients.

[0216] 3.2 Moisture and quality maintenance: The chitosan-polyphenol composite film combines with fish protein through hydrogen bonds, reducing juice loss and maintaining the water holding capacity of the muscle, delaying the texture deterioration caused by protein denaturation; 3.3 Odor masking: Plant aldehydes (such as citral and cinnamaldehyde) adsorb volatile sulfides (such as trimethylamine) through hydrophobic effects, and at the same time undergo nucleophilic addition reactions with fishy odor precursors (such as trimethylamine oxide), reducing the perception of odor.

[0217] The color analysis results of the aquatic products of Examples 1 to 5 and Comparative Example 1 are as follows: Figure 1 The brightness (L*) of Examples 1 to 5 is higher than that of Comparative Example 1 (corresponding to Figure 1 With increasing time, the brightness (L*) of Examples 1 and 2 reached the highest values ​​on the tenth day, at 78 and 74.09, respectively, while that of Comparative Example 1 was the lowest, remaining at the lowest value from day 0 to day 10. The redness (a*) values ​​of Examples 1-5 and Comparative Example 1 were all negative, and the redness (a*) value of Comparative Example 1 was higher than that of the Examples within ten days, indicating that the Comparative Examples were less greenish than the Examples.

[0218] The color analysis results of the aquatic products of Examples 6-7 and Comparative Example 2 are as follows: Figure 2 As shown. Except for the 0th day, the brightness (L*) of Examples 6-7 is higher than that of Comparative Example 2 starting from the 3rd day. As time increases, on the sixth day, the brightness (L*) of Example 6 and Example 7 is the highest. Starting from the sixth day, the redness value (a*) of Comparative Example 2 is greater than that of Examples 6 and 7. The yellowness value (b*) of Examples 6 and 7 is greater than that of the Comparative Example within 0-12 days. The technical solution of the present invention can effectively protect the color of fresh-frozen seafood products. The preservative solutions of Examples 8 to 9 each contain only one plant extract. Although they can also achieve the effect of preservation, their preservation effect is significantly worse than that of Examples 6 to 7.

[0219] The texture analysis results of the fresh scallop products of Examples 1-5 and Comparative Example 1 are as follows: Figure 3 As shown. Hardness indicates the force required for the sample to reach a certain deformation. With the change of storage time, at the same storage time, the values ​​of various texture indicators of experimental groups 1-5 are higher than or closer to the initial values, while the value of the indicator of experimental group 1 drops significantly. Springiness refers to the ability of food to return to its original shape after being compressed. High elasticity indicates better recovery. During the ten-day storage period, the elasticity retention rate of Example 1 is as high as more than 80%, which is much higher than that of Comparative Example 1. Resilience indicates the ability of food to quickly return to its original shape. High resilience indicates better elastic recovery. Examples 1-5 all maintain good recovery, while the recovery of the comparative example decreases by ≥25%. This shows that the technical solution of the present invention can slow down the deterioration of the texture characteristics of aquatic products. In particular, Example 1 has a better texture maintenance effect on the freshness of scallops.

[0220] The microbial analysis results of the aquatic products of Examples 1-5 and Comparative Example 1 are as follows: Figure 4 As shown, in the first seven days of storage, the microbial content of the examples was significantly lower than that of the comparative examples. On the tenth day, the content of Example 1 was the lowest, significantly less than that of the comparative examples. The microbial analysis results of the aquatic products of Examples 8-9 and Comparative Examples 2-5 are shown in FIG. Figure 5 As the storage time increases, the microbial content of the example group within 36 hours is significantly lower than that of the comparative example group. The microbial analysis results of the aquatic products of Examples 6-7, Comparative Examples 2 and Comparative Examples 6-7 are shown as follows: Figure 6 As shown in the figure, as the storage time increases, the microbial content of the example group after 6 hours is significantly lower than that of the comparative example group. In particular, the microbial content of Example 6 is the lowest after 36 hours of storage, and its preservation effect is the best, indicating that the technical solution of the present invention can significantly slow down the growth of microorganisms during the storage of aquatic products. The microbial analysis results of Examples 10-12 and Comparative Examples 8-10 are shown in the figure. Figure 9-11As shown in the graph, during the 36-hour storage, the microbial content of the examples was much lower than that of the comparative examples, indicating that the technical solution of the present invention can significantly slow down the growth of microorganisms in different aquatic products during storage.

[0221] The microbial analysis results of the aquatic products of Example 6 and Comparative Example 11 are as follows: Figure 7 As shown in the results, during the 36-hour storage, the microbial content in the examples was much lower than that in the control examples, indicating that the "pretreatment of embedded sustained-release materials-step homogenization" process in the original method is the core to ensure the effect of the preservative, and verifies the necessity of premixing treatment to improve the dispersibility of sodium hyaluronate and cooperate with chitosan to form a functional film.

[0222] The microbial analysis results of the aquatic products of Example 6 and Comparative Examples 12-13 are as follows: Figure 8 As shown in the results, during the 36-hour storage, the microbial content of the examples was much lower than that of the control examples, indicating that when sodium hyaluronate is used as an embedding material, its molecular structure is significantly more compatible with aquatic products than traditional materials such as sodium carboxymethyl cellulose and polyvinyl alcohol. It can also improve the penetration depth and membrane stability of the preservative, providing a better material choice for preserving aquatic products.

[0223] The embodiments provided above are not intended to limit the scope of the present invention, nor are the steps described to limit their execution order. Any obvious improvements to the present invention made by those skilled in the art in combination with existing common knowledge shall fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a composite plant extract sustained-release preservative for targeted inhibition of spoilage bacteria in aquatic products, characterized in that: The following steps are involved: (1) Preparation of plant extracts: The plant raw materials were crushed through a 40-mesh sieve, added with ethanol solution, and subjected to ultrasonic-assisted extraction, followed by concentration and freeze-drying to obtain plant extract powder; (2) Raw material compounding: dissolving the plant extract powder, tea polyphenols, vitamin E and water-soluble chitosan obtained in step (1) in deionized water and homogenizing to form a uniform solution; (3) Pretreatment of embedded sustained-release material: Sodium hyaluronate was dissolved in deionized water and stirred at 40-50°C until completely dissolved to form a premixed solution; (4) Mixing treatment: mixing the homogeneous solution of step (2) with the premixed solution of step (3), and homogenizing to obtain a mixed solution; (5) Stabilization treatment: adjust the pH of the mixed solution obtained in step (4) to 4.5-5.5, add sodium alginate as a stabilizer, and filter after ultrasonic dispersion to obtain a transparent and stable preservative solution, freeze-dry and crush to obtain a powdered preservative.

2. The preparation method according to claim 1, characterized in that The plant raw material described in step (1) is any one or more of oregano, cloves, thyme, lemon and cinnamon, the material-liquid ratio of the crushed plant raw material to the ethanol solution is 1:20-3:10, the ultrasonic frequency during ultrasonic-assisted extraction is 20-50kHz, the extraction temperature is 25-50°C, and the extraction time is 20-30min. The concentration is concentrated under reduced pressure until the solid content is ≥20%, and the freeze-drying process is first frozen at -80°C for 1-2h and then frozen at -50°C for 24-36h.

3. The preparation method according to claim 1, characterized in that The plant extract powder in step (2) is any one of oregano extract powder, clove extract powder, thyme extract powder, lemon extract powder and cinnamon extract powder, or a mixture of several of them.

4. The preparation method according to claim 1, characterized in that The plant extract powder in step (2) includes oregano extract powder and clove extract powder. Calculated by weight percentage, the homogeneous solution includes 1-5% oregano extract, 1-2% clove extract, 0.3-2% tea polyphenols, 0.5-2.5% vitamin E, 0.02-4.2% water-soluble chitosan, and the balance is deionized water.

5. The preparation method according to claim 1, characterized in that The water-soluble chitosan is carboxymethyl chitosan, and the molecular weight of the carboxymethyl chitosan is 20-40 kDa.

6. The preparation method according to claim 1, characterized in that The mass concentration of sodium hyaluronate in the premixed solution in step (3) is 5-10%. In step (4), the volume ratio of the homogeneous solution to the premixed solution is (4:1)-(8:1).

7. The preparation method according to claim 1, characterized in that In step (5), the amount of sodium alginate added is 0.1 to 0.5% of the mass of the mixed solution.

8. The preparation method according to claim 1, characterized in that In step (5), the power of ultrasonic dispersion is 300W, the time is 10 minutes, and the filtration is carried out using a microfiltration membrane with a pore size of 0.22 μm. The freeze-drying comprises pre-freezing the fresh-keeping liquid and then placing it in a vacuum freeze dryer for vacuum freezing. The pre-freezing temperature is -80°C and the pre-freezing time is 2 hours. The vacuum freezing is carried out at -50°C and a vacuum degree of ≤10Pa for 24 hours until the water content is ≤5%. After freeze-drying, the fresh-keeping liquid is crushed with a mortar or a grinder and passed through a 40-mesh sieve to obtain a powdered preservative.

9. The preservative prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the preservative according to claim 9 in preserving aquatic products.

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