Preparation method and application of edible coating preservation material with IPN network structure

Abstract

The invention relates to a preparation method and application of an edible coating preservation material with an IPN network structure. The preparation method comprises the following steps: cooking gelatin particles and acid-base under high pressure, stirring the modified ISF under a water bath condition until the modified ISF is completely dissolved, and adding glycerol as a plasticizer to obtain a solution A for later use; stirring gelatin particles and ultrasonic-assisted laccase modified ISF under a water bath condition until the gelatin particles and the ISF are completely dissolved, and adding glycerol as a plasticizer to obtain a solution B for later use; and mixing the solution A with the cinnamon essential oil under the action of a shearing machine to form the uniform and stable edible coating fresh-keeping material. The raw materials of the prepared edible coating emulsion are food-grade raw materials and have the characteristics of being edible, green and safe, the gelatin raw materials and ISF are derived from bioprocessing by-products and are wide in source and low in price, the application field and research direction of the gelatin and ISF are widened, and the edible coating has a wider application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of edible gelatin preservative coating materials, and in particular to a preparation method and application of an edible coating preservative material with an IPN network structure. Background Art

[0002] With the continuous improvement of socioeconomic levels, public demand for food safety and quality is growing. Food preservation technology, as a key strategy for ensuring food safety and extending food shelf life, has become a research focus in the food industry. Traditional food preservation methods mainly include refrigeration, freezing, and drying. However, these methods can negatively impact food taste, nutritional content, and flavor. Therefore, the search for novel preservation technologies that effectively maintain food quality and offer environmental, safety, and economical advantages has become a key research direction. To meet the growing demand for innovative food preservation technologies, emulsion preservation has been introduced as a promising approach to extend shelf life and maintain food quality. Compared with traditional preservation methods, emulsion preservation technology does not rely on chemical additives and therefore offers significant advantages in maintaining food quality and safety. Furthermore, emulsions (hereinafter referred to as emulsion-based edible films) can encapsulate bioactive ingredients, control the release of preservatives, and optimize sensory properties without the irritation of chemical additives. However, emulsion preservation still presents some challenges. For example, emulsions can experience creaming during storage, leading to reduced stability. Furthermore, pure emulsions can suffer from weak hydrophobicity and poor antimicrobial efficacy, ultimately impairing the preservation effectiveness of emulsion films. Therefore, improving emulsion performance and enhancing the preservation effectiveness of emulsion films are current research hotspots in emulsion preservation technology. Emulsion-based gel membranes offer the advantage of being loaded with oily active ingredients that can provide antimicrobial and antioxidant properties.

[0003] In recent years, the use of latexes incorporating natural active substances and their integration into biopolymer-based films has become an important approach to enhancing the performance of packaging materials. Interpenetrating polymer networks (IPNs) are polymers composed of two or more interpenetrating, cross-linked molecular chains forming a network. Their characteristic is that one material randomly penetrates into another, creating a synergistic effect between the two components in the system, acting as a "forced inclusion" and resulting in superior performance compared to conventional blends. Gelatin (GE) is an excellent material for making protein-based films, exhibiting excellent film-forming properties, biodegradability, and high biosafety. Gelatin is readily available and inexpensive, making it suitable for the production of biodegradable, safe, and nontoxic food packaging films. Cellulose is a natural polymer material, an insoluble, hydrophilic, linear polysaccharide with low density, renewable properties, biodegradability, and biocompatibility. It also possesses advantages such as high modulus and low thermal expansion coefficient.

[0004] Insoluble dietary fiber (IDF) is an anionic polysaccharide primarily composed of cellulose, lignin, and hemicellulose. Unmodified IDF has a compact structure, high degree of polymerization, poor emulsification ability, and a lumpy microstructure, limiting its industrial application. Insoluble soybean fiber (ISF) is a byproduct of soybean processing. When preparing emulsion systems using unmodified ISF, the internal oil droplets aggregate into large particles under the action of van der Waals forces, causing oil precipitation and stratification in the emulsion, resulting in poor stability. Treatment of ISF (with acid, alkali, cooking, ultrasound, enzyme modification, etc.) allows the originally dense ISF to acquire an open linear structure while releasing more hydroxyl groups. This spatial structure and chemical bonds give ISF more functional properties. First, linear ISF and linear gelatin spatially form a gel with an interpenetrating network structure, known as an IPN gel. This interpenetration creates a more compact internal structure, enhancing the gel's strength. Second, the hydroxyl groups released by the ISF form hydrogen bonds with hydroxyl groups on the gelatin, strengthening chemical interactions. Therefore, the modified ISF enhances its interaction with gelatin through physical interpenetration and chemical crosslinking. This structure effectively hinders van der Waals forces between oil droplet molecules, inhibits aggregation of oil droplet particles, and enhances the stability of the oil droplet emulsion. Gelatin is a protein-derived hydrophilic colloid with excellent biocompatibility, biodegradability, and film-forming properties. However, gelatin-based emulsion gel films exhibit poor thermal stability and are prone to internal aggregation of oil droplets, hindering the application of gelatin-based emulsion gels in food preservation at room temperature. Therefore, the development of an edible cling film composed of a gelatin-based emulsion and modified ISF with a unique IPN network structure is an urgent problem. Summary of the Invention

[0005] The present invention aims to provide a method for preparing an edible coating preservative material with an IPN network structure, which has a wide source of raw materials, low cost, simple operation and is degradable, so that the gelatin-based edible film has a broader application prospect.

[0006] The technical solutions of the present invention are as follows: A method for preparing an edible coating preservative material having an IPN network structure, the method comprising the following steps: S1 treated ISF by acid-base treatment and high-pressure cooking to obtain modified ISF; S2: gelatin, modified ISF and water are mixed and stirred in a water bath until the gelatin is completely dissolved to obtain a gelatin mixed solution; Add glycerol to the S3 gelatin mixed solution and mix well to obtain a mixed solution; Adding cinnamon essential oil solution to the S4 mixed solution, shearing and mixing, to obtain a composite gelatin emulsion; The preparation of edible coating preservative materials with IPN network structure was completed.

[0007] Preferably, in the method, the raw materials of the edible coating preservative material include: gelatin 4-6% w / v, glycerin 1-2% v / v, cinnamon essential oil 15-25% v / v, ISF 0-2.5% w / v, and the balance is deionized water; further preferably, gelatin 5% w / v, glycerin 1.5% v / v, cinnamon essential oil 20% v / v, ISF 0-1.5% w / v, and the balance is deionized water.

[0008] Further preferably, the gelatin is animal gelatin with a power of 260-280; and ISF is insoluble soybean fiber.

[0009] Preferably, the acid-base high-pressure cooking modification method in step S1 is to mix the dregs with water in a mass ratio of 1:(15-25), adjust the pH range to 7-14, and perform high-pressure cooking on the dregs under alkaline conditions, and then wash, centrifuge, dry, and sieve to obtain ISF.

[0010] More preferably, the high-pressure cooking conditions are 100-121°C for 10-60 minutes. The alkaline high-pressure cooking treatment destroys the dense structure of the ISF, releasing more hydroxyl groups, improving water holding capacity, emulsification properties, and specific surface area, thereby forming stable Pickering particles.

[0011] Further preferably, after high-pressure cooking, washing, centrifugation, and subsequent treatment with ultrasound-assisted laccase are performed. The ultrasound-assisted laccase treatment involves mixing the centrifuged product with water at a mass ratio of 1:(10-15) to form an ISF suspension, adding laccase (0.3-0.5 U / g), and ultrasonically treating the suspension (20 kHz, 360W, 5-15 min). The modified ISF is then centrifuged, dried, and sieved to obtain the modified ISF. Ultrasonic treatment exposes the hydroxyl groups of the ISF, which are then oxidized by laccase to form quinone-type active groups, enhancing the covalent cross-linking ability with gelatin.

[0012] Preferably, in step S3, the water bath is heated at a temperature of 30-80°C. At this temperature, the triple helical structure of the gelatin chains fully unfolds in the aqueous solution, facilitating mixing with the soybean oil. The soybean oil can fully mix with the triple helical gelatin to form a uniform and stable solution. Preferably, in step S4, the shearing rate is 3000-25000 rpm, and the time is 2-10 min.

[0013] The invention discloses a method for preparing an edible coating fresh-keeping material with an IPN network structure, and uses the composite gelatin emulsion prepared by the method in the edible coating fresh-keeping material.

[0014] Preferably, the composite gelatin emulsion prepared by the method is used in the preservation of sturgeon, and the specific operation is: pre-treating the fresh sturgeon, dividing the fish meat into slices, immersing the fish slices in the composite gelatin emulsion, evenly coating the emulsion on the surface of the sample, and storing.

[0015] Further preferably, the composite gelatin emulsion prepared by the method is used in the preservation of sturgeon, and the specific operation is: pre-treating the fresh sturgeon, dividing the fish meat into slices, immersing the fish slices in the composite gelatin emulsion, evenly coating the emulsion on the surface of the sample, and storing.

[0016] Beneficial effects of the present invention: 1. The present invention discloses a method for preparing an edible preservative coating material. The method comprises gelatin as a raw material, cinnamon essential oil as a hydrophobic component, glycerin as a plasticizer, modified ISF as Pickering particles, and distilled water as a solvent. The edible coating material is obtained by heating and melting the solution and homogenizing it with a shearing machine to form a uniform solution. The edible coating material is then applied to the surface of food to preserve the food.

[0017] 2. Acid-base treatment and high-pressure steaming of ISF physically and chemically open up the fiber structure, releasing hydroxyl groups. This opens up the dense structure and increases the fiber's specific surface area and water-holding capacity. Laccase, a copper-containing polyphenol oxidase, produces only water as a byproduct during catalysis. The synergistic effect of ultrasound and laccase treatment lies in the fact that the microjets and shock waves generated by ultrasonic cavitation can disrupt the aggregated structure of biopolymers, fully exposing hydrophobic groups such as urushiol and increasing the accessibility of laccase catalytic sites. The modified ISF exhibits excellent emulsification and stability. Acting as Pickering particles, it stabilizes the oil phase in emulsions. When formed into a composite system with a viscous solution, the presence of the Pickering particles increases the oil phase content of the emulsion. The modified ISF releases more hydroxyl groups, which form hydrogen bonds between the hydroxyl groups of ISF and gelatin, strengthening the intermolecular bonding within the emulsion. Furthermore, the gelatin and ISF molecular chains interpenetrate and cross-link to form a polymer with an IPN network structure. The IPN structure firmly wraps the hydrophobic molecule - cinnamon essential oil in the polymer network, making the oil droplets dispersed smaller and more evenly inside the gelatin emulsion, enhancing the emulsification properties of the emulsion. At the same time, the small oil droplets reduce their ability to hinder the interaction between proteins, and the fluidity inside the emulsion becomes worse, thereby enhancing the stability of the emulsion.

[0018] 3. The edible coating preservative material prepared by the present invention preserves food, avoiding the harm to the human body caused by the use of chemical preservatives. The IPN structure in the edible coating enhances the water vapor barrier, antibacterial barrier, and antioxidant barrier capabilities of the emulsion gel, and the three barrier properties are stable. Sturgeon meat was preserved using this edible film. The results showed that the edible coating preservative material provided by the present invention can extend the shelf life of sturgeon and has a good preservation effect. The materials selected by the present invention are edible, green, inexpensive and easily available, and the preparation method is simple. At the same time, the present invention can further utilize biological byproduct resources for high value. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 This is a particle size diagram of the coating preservative material emulsion of the present invention; Figure 2 This is a graph showing changes in the emulsification activity index and emulsification stability index of the coating fresh-keeping material of the present invention; Figure 3 This is a graph showing changes in total volatile basic nitrogen during storage of a sample of sturgeon when the preservative coating material of the present invention is applied thereto; Figure 4 This is a graph showing the total bacterial count during the storage of samples of sturgeon when the fresh-keeping material of the present invention is applied. Figure 5 Example 6 Application of the emulsion in the preservation of fruits. DETAILED DESCRIPTION

[0021] The following will be combined with specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] The acid-base autoclave-modified ISF method involves mixing okara and water in a mass ratio of 1:20, adjusting the pH to 8, and autoclaving the okara under alkaline conditions. The resulting ISF is then washed, centrifuged, dried, and sieved to obtain the acid-base autoclave-modified ISF. The autoclave is performed at 150°C for 30 minutes. The method for modifying ISF by acid-base high-pressure cooking and ultrasonic enzymatic hydrolysis is as follows: bean dregs are mixed with water in a mass ratio of 1:20, the pH range is adjusted to 8, and the bean dregs are high-pressure cooked under alkaline conditions (high-pressure cooking conditions are 150ºC, time is 30 min). After washing and centrifugation, they are treated with ultrasonic-assisted laccase before subsequent operations. The ultrasonic-assisted laccase conditions are as follows: the centrifuged product is mixed with water in a mass ratio of 1:12 to form an ISF suspension, laccase (0.4 U / g) is added, and ultrasonic treatment (20 kHz, 360 W, 10 min) is performed. Then, the suspension is centrifuged, dried, and sieved to obtain acid-base high-pressure cooking and ultrasonic enzymatic hydrolysis modified ISF.

[0023] The water bath condition in the Examples and Comparative Examples was 50°C.

[0024] Comparative Example 1 Mix 5% w / v gelatin, 1.5% v / v glycerol, and 60 mL of distilled water in a water bath. Stir until completely dissolved. This is Solution A and is set aside. Add 20% v / v cinnamon essential oil to Solution B. Shear Solution A and Solution B at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion, Solution C. Apply Solution C evenly to the surface of food for preservation. This emulsion is designated E1.

[0025] Example 1 Mix 5% w / v gelatin, 1.5% v / v glycerol, 0.6% acid-base autoclaved modified ISF, and 60 mL of distilled water. Stir in a water bath until completely dissolved. This is Solution A and is set aside. Add 20% v / v cinnamon essential oil to Solution B. Shear the two solutions at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion, Solution C. Apply Solution C evenly to the surface of food for preservation. This emulsion is designated E2.

[0026] Example 2 Mix 5% w / v gelatin, 1.5% v / v glycerol, 0.9% acid-base autoclaved modified ISF, and 60 mL of distilled water. Stir in a water bath until completely dissolved. This is Solution A and is set aside. Add 20% v / v cinnamon essential oil to Solution B. Shear the two solutions at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion, Solution C. Apply Solution C evenly to the surface of food for preservation. This emulsion is designated E3.

[0027] Example 3 Mix 5% w / v gelatin, 1.5% v / v glycerol, 1.2% acid-base autoclaved modified ISF, and 60 mL of distilled water. Stir in a water bath until completely dissolved. This is Solution A and is set aside. Add 20% v / v cinnamon essential oil to Solution B. Shear the two solutions at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion, Solution C. Apply Solution C evenly to the surface of food for preservation. This emulsion is designated E4.

[0028] Example 4 Prepare 5% w / v gelatin, 1.5% v / v glycerol, 1.5% w / v acid-base autoclaved modified ISF, and 60 mL of distilled water. Stir in a water bath until completely dissolved. This is Solution A and is set aside. Add 20% v / v cinnamon essential oil to Solution B. Shear the two solutions at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion, Solution C. Apply Solution C evenly to the surface of food for preservation. This emulsion is designated E5.

[0029] Example 5 Prepare 5% w / v gelatin, 1.5% v / v glycerol, 0.9% w / v ISF modified by acid-base autoclaving and ultrasonic enzymatic hydrolysis, and 60 mL of distilled water. Stir in a water bath until completely dissolved. This is Solution A and is set aside. Add 20% v / v cinnamon essential oil to Solution B. Combine Solution A and Solution B at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion, Solution C. Apply Solution C evenly to the surface of food for preservation. This emulsion is designated E6. Example 6 5% w / v gelatin, 1.5% v / v glycerol, 0.9% w / v ISF modified by acid-base autoclaving and ultrasonic enzymatic hydrolysis, and 60 mL of distilled water were stirred in a water bath until completely dissolved. This is Solution A and is set aside. 20% v / v cinnamon essential oil is Solution B. A 0.05% w / v konjac glucan dispersion was slowly injected into Solution A (50°C). After mixing, the mixture was heated to 75°C. 0.02% sodium bicarbonate was added, stirred for 5 minutes, and then cooled to 50°C. The mixture was then sheared with Solution B at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion, Solution C. Solution C was evenly applied to the surface of food for preservation. This emulsion was designated E7. During the coating process, due to the high water content of the sturgeon meat, the coating did not adhere evenly to the fish meat and the thickness was thin, which may affect the preservation effect of the coating. By constructing an IPN and combining the acetyl / hydroxyl groups of konjac glucomannan, a flexible filling effect is achieved in the network structure, which can block the penetration of water. That is, the SF rigid skeleton combined with the KGM tough network increases the elongation at break from 115% (Example 5) to 350% (Example 6), the tensile strength from 20.05 MPa (Example 6) to 66.57 MPa (Example 6), and the water vapor transmission rate from 6.55×10 -11 g·m -1 ·s -1 ·Pa -1 (Example 6) decreased to 2.14×10 -11 g·m -1 ·s -1 ·Pa -1 (Example 6), the water contact angle increased from 75° (Example 5) to 88° (Example 6), and the water resistance was significantly improved. KGM absorbs water and swells to block the pores. Combined with the hydrophobic quinone group of ISF, it can enhance the adhesion of the coating liquid and form a uniform gel on the surface of the fish meat. It can prevent the film formed by the emulsion from falling off the surface of the fish meat, and effectively play the water vapor barrier, antioxidant barrier, and antibacterial barrier functions of the gel. In addition, using this solution, it was unexpectedly found that the preservation effect was very good during the storage of fruits at a higher temperature (30°C). This may be because this example uses the linear structure of gelatin and ISF to construct an emulsion gel with an IPN network. The IPN network interpenetrates in space to form a more dense structure; at the same time, the chemical cross-linking of the IPN structure is strengthened through hydrogen bonds, hydrophobic interactions and ionic bonds, forming a gel coating with good thermal stability. Using this coating to coat fruits for fresh-keeping can achieve a preservation effect at a higher temperature of 30°C. See for specific results. Figure 5 . Figure 5 The inspection method is as follows: immerse kiwi, citrus, passion fruit, and grapes in the prepared emulsion (select E7 here) at room temperature, apply the emulsion evenly on the surface of the sample, and after the emulsion gel forms a thin film on the surface, place the fruit in a 30-degree environment and observe the changes in the fruit during storage.

[0030] The specific implementation method of using an edible coating preservative material to preserve sturgeon meat is as follows: Comparative Application Example 1 Live fish were slaughtered in the laboratory, and the skin, bones, head, and tail were removed. The dorsal meat was collected and prepared into fish fillets. Untreated fresh fish meat was sampled and packed into sample boxes and stored at 4°C. Samples were collected every other day to observe changes in parameters. The sampling period was 18 days, and the sample was designated R1.

[0031] Application Example 1 Live fish were slaughtered in the laboratory, and the skin, bones, head, and tail were removed. The dorsal flesh was removed and prepared into fish fillets. An emulsion (5% w / v gelatin, 1.5% v / v glycerol, and 60 mL of distilled water) was prepared and stirred in a water bath until completely dissolved. The emulsion was then sheared at 12,000 rpm for 3 minutes to form an emulsion. Fish fillets were immersed in the prepared emulsion at room temperature, and the emulsion was evenly coated on the sample surface. The coated samples were aliquoted into sample boxes and stored at 4°C. Samples were collected every other day for 18 days to observe changes in parameters. Samples were collected over a period of 18 days, and the sample was designated R2.

[0032] Application Example 2 Live fish were slaughtered in the laboratory, and the skin, bones, head, and tail were removed. The dorsal meat was removed and prepared into fish fillets. An emulsion (5% w / v gelatin, 1.5% v / v glycerin, 20% v / v cinnamon essential oil, and 60 mL of distilled water) was prepared and stirred in a water bath until completely dissolved. The mixture was then sheared at 12,000 rpm for 3 minutes to form an emulsion. Fish fillets were immersed in the prepared emulsion at room temperature, evenly coating the surface of the sample. The sample was then stored at 4°C, and samples were taken every other day to observe changes in parameters. The sampling period lasted for 18 days, and the sample was designated R3.

[0033] Application Example 3 Live fish were slaughtered in the laboratory, and the skin, bones, head, and tail were removed. The dorsal flesh was removed and prepared into fish fillets. An emulsion (5% w / v gelatin, 1.5% v / v glycerin, 20% v / v cinnamon essential oil, 0.9% acid-base autoclaved modified ISF, and 60 mL of distilled water) was prepared. The mixture was stirred in a water bath until completely dissolved and then sheared at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion. Fish fillets were immersed in the prepared emulsion at room temperature, allowing the emulsion to evenly coat the surface of the sample. The sample was then stored at 4°C, and samples were taken every other day to observe changes in parameters. The sampling period lasted for 18 days, and this sample was designated R4.

[0034] Application Example 4 Live fish were slaughtered in the laboratory, and the skin, bones, head, and tail were removed. The dorsal flesh was removed and prepared into fish fillets. An emulsion (5% w / v gelatin, 1.5% v / v glycerin, 20% v / v cinnamon essential oil, 0.9% ISF modified by acid-base autoclaving and ultrasonic enzymatic hydrolysis, and 60 mL of distilled water) was prepared. The mixture was stirred in a water bath until completely dissolved and then sheared at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion. Fish fillets were immersed in the prepared emulsion at room temperature, allowing the emulsion to evenly coat the surface of the sample. The sample was then stored at 4°C, with samples collected every other day to observe changes in performance indicators. The sampling period lasted for 18 days, and this sample was designated R5. Application Example 5 Live fish were slaughtered in the laboratory, and the skin, bones, head, and tail were removed. The dorsal meat was removed and prepared into fish nuggets. An emulsion (5% w / v gelatin, 1.5% v / v glycerol, 0.9% w / v ISF modified by acid-base autoclaving and ultrasonic enzymatic hydrolysis, and 60 mL of distilled water) was prepared. Stir in a water bath until completely dissolved (this is Solution A, set aside). 20% v / v cinnamon essential oil was used as Solution B. A 0.05% w / v konjac glucan dispersion was slowly injected into Solution A (50°C). After mixing, the mixture was heated to 75°C. 0.02% sodium bicarbonate was added, stirred for 5 minutes, and then cooled to 50°C. The mixture was then sheared with Solution B at 12,000 rpm for 3 minutes to form a uniform and stable IPN emulsion (Solution C). Immerse the fish fillets in the prepared emulsion at room temperature, coat the sample surface with the emulsion evenly, and store at 4°C. Take samples every other day to observe changes in indicators. The sampling period is 18 days, and the sample is recorded as R6. The present invention prepares the emulsion comparative example 1 (E1) and examples 1-6 (E2-E7) of the edible coating preservative material and characterizes the particle size, emulsification activity index and emulsification stability index during the application of the material in the preservation process of sturgeon meat, and monitors the total volatile basic nitrogen and total colony count of the fish meat.

[0035] 1. Emulsion particle size determination The particle size of the emulsion was measured using a laser particle size analyzer (Master Sizer 3000). The emulsion was added to a particle size plate. Deionized water was used as the dispersant of the emulsion. The parameters were set so that the refractive index was 1.95-0.1.

[0036] The emulsification and stability of the emulsion are closely related to the average particle size and dispersion of the internal solid particles. The average particle size and distribution of IPN emulsion are as follows: Figure 1 As shown. It can be seen that the addition of modified ISF can significantly reduce the particle size of the emulsion, among which the particle size of the E4 group in the acid-base high-pressure cooking modified ISF group is the smallest. This is because the molecular structure of ISF is opened after the modification treatment, and more hydroxyl groups are exposed, so that the molecular chains of GE and ISF are cross-linked to form a network polymer, and a synergistic effect is produced between the two components, which makes the particle size of the emulsion particles gradually decrease. At the same time, smaller particles have fast adsorption kinetics and can be adsorbed more quickly and accurately on the oil-water interface, so that the interface is filled to a greater extent, thereby forming a more stable emulsion. This result shows that the addition of acid-base high-pressure cooking modified ISF can improve the emulsification and stability of gelatin emulsion. Based on this modification, the ISF fiber was further modified by ultrasound-assisted lacquerase, and the particle size results are shown as follows. Figure 1As shown in Group E6, further modification resulted in a smaller emulsion particle size. This is because ultrasound further opens up some molecular groups within the ISF molecular chains. Simultaneously, laccase oxidizes the exposed hydroxyl groups to quinone compounds, which react with gelatin to form covalent bonds, making the emulsion network denser and more stable, further improving the emulsion particle size. Group E7, based on the modification of Group E6, added konjac glucan. The results showed no significant change in emulsion particle size (p>0.05), indicating that the addition of konjac glucan did not alter the IPN network structure formed by gelatin and ISF. Instead, it served as a penetrating material, interpenetrating within the N network and increasing the adsorption sites of the IPN emulsion film. This further enhanced the physical strength and adsorption properties of the emulsion film, broadening its application range.

[0037] 2. Emulsion activity index (EAI) and emulsion stability index (ESI) At 0 and 10 minutes, take 50 μL of the emulsion from 5 mm below the bottom of the cup and dilute it in a tube containing 5 mL of 0.1% SDS solution. Measure the absorbance of the diluted sample at 500 nm. EAI and ESI are calculated using the following formulas:

[0038]

[0039] Where: A 500 is the absorbance at 500 nm; DF is the dilution factor, is the volume fraction of the oil phase (v / v) ( =0.1); C is the protein concentration (g / ml); A0, A 10 is the absorbance value of the emulsion at 0 min and 10 min.

[0040] The emulsification activity index (EAI) and emulsion stability index (ESI) are used to evaluate the emulsification performance of the emulsion and the adsorption capacity of protein at the oil / water interface. Figure 2 As shown, the EAI of group E1 (14.959 m 2 / g) and ESI (117.681%), the EAI and ESI of the emulsion increased significantly after adding modified ISF (p < 0.05). With the increase of ISF concentration, EAI and ESI also increased. At E4, the EAI of the emulsion (26.125 m 2 / g) and ESI (157.186%) reached their highest values. Compared with group E1, the addition of group E4 effectively increased the EAI and ESI of the IPN emulsion by 1.746 times and 1.336 times, respectively. However, when the ISF addition level exceeded the concentration of group E4, the emulsification performance gradually decreased. Specifically, when ISF was modified with ultrasound-assisted laccase after acid-base autoclaving, the EAI and ESI of group E6 were significantly increased. This may be because the ultrasound treatment nanosized the ISF fibers, increasing the specific surface area and exposing more phenolic hydroxyl groups. In addition, the quinone compounds catalyzed by laccase are amphiphilic and can anchor at the oil-water interface, reducing interfacial tension. Simultaneously, the covalently cross-linked network formed can tightly load the oil droplets in the grid, inhibiting droplet aggregation. The results of group E7 also verified the results of particle size. The emulsification and stability of the emulsion are related to the size of the emulsion particles. The smaller the particles, the more uniform the emulsion distribution and the better the emulsification and stability. There was no significant difference between the results of this group and those of group E6. This also shows that the interpenetration of konjac glucan in the emulsion did not change the IPN network structure, and the adsorption sites increased during the interpenetration process did not significantly affect the emulsification and stability of the emulsion.

[0041] 3. Total Volatile Basic Nitrogen (TVB-N) Weigh 10 g of sample into a distillation tube, add 75 ml of water and shake to evenly disperse the sample in the sample solution. Soak for 30 minutes, then add 1 g of magnesium oxide. Immediately connect to a fully automatic Kjeldahl nitrogen analyzer for distillation. Use boric acid solution for absorption, methyl red and bromocresol green as indicators, and titrate with standard hydrochloric acid solution to calculate the TVB-N content.

[0042] Meat is a perishable product. During storage, the action of microorganisms and endogenous enzymes causes changes in its chemical composition. Proteins continuously decompose, producing ammonia and other alkaline nitrogen-containing substances such as amines. Total volatile basic nitrogen (TVB-N) is often used as a biomarker for protein and amine degradation. Higher TVB-N values ​​indicate a more severe degree of fish spoilage. Figure 3The changes in TVB-N values ​​of sturgeon meat treated with different coatings during storage are shown. All samples showed an increase in TVB-N values ​​over time, with the fastest increase in the control group (R1), followed by the R2 group, and the slowest increase in the R4 and R5 groups. On day 8, TVB-N values ​​in the R1 and R2 groups were 21.96 mg / 100 g and 20.05 mg / 100 g, respectively, exceeding the Chinese national standard for freshwater fish (20 mg / 100 g). However, TVB-N values ​​in the R3, R4, and R5 groups were 16.53 mg / 100 g, 14.05 mg / 100 g, and 12.37 mg / 100 g, respectively. This indicates that the addition of essential oils and the different modification methods significantly (p < 0.05) mitigated the increase in TVB-N values. Comparisons of groups R3 and R4 revealed that the emulsion coating with ISF significantly (p<0.05) inhibited the increase in TVB-N values ​​compared to group R3. Comparisons of groups R4 and R5 revealed that ultrasound-assisted laccase modification was more effective than acid-base autoclaving alone, resulting in a slower increase in TVB-N values. This is because ultrasound-assisted laccase modification of ISF and gelatin forms a denser network, exhibiting lower oxygen and moisture permeability, slowing lipid oxidation in fish meat and the growth of aerobic bacteria. Furthermore, the dense network structure impedes the diffusion of spoilage metabolites (such as ammonia and hydrogen sulfide). Comparing the R6 group with the R5 group, the addition of konjac glucan slightly reduced the TVB-N value of the sample, but the change was not significant. This is because konjac glucan provides adsorption sites during the interpenetration process, enhancing the adsorption of the emulsion film and allowing the film to better adsorb on the sample surface. However, due to its nature as an interpenetrating material, the emulsion film's ability to block spoilage metabolites was not significantly enhanced, and it did not participate in blocking the diffusion of spoilage metabolites. Therefore, the TVB-N value of this group did not show a significant improvement compared to the R5 group. In summary, IPN emulsion-loaded essential oil coatings can inhibit the increase in TVB-N values ​​and can be used to extend the shelf life of fish.

[0043] 4. Total viable count (TVC) Aseptically remove 225 g of sturgeon sample and homogenize it in a centrifuge tube containing 0.85% NaCl buffer. Then perform a decimal gradient dilution. Select the appropriate dilution and evenly spread 0.1 mL of the dilution on the surface of plate count agar (PCA). Repeat 3 times for each group. Culture in a constant temperature incubator for 72 h. Calculate the TVC value and the result is log 10 Measured in CFU / g.

[0044] The number of microorganisms is one of the important basic indicators for evaluating the quality and safety of fish meat. Since fish meat contains various nutrients, it will promote the growth of microorganisms. When the total number of colonies in fish meat reaches 7 log10 CFU / g, the fish meat reaches the maximum edible range. In order to evaluate the effect of IPN emulsion on the restriction of fish meat microorganisms, the TVC value of refrigerated sturgeon fillets was measured, such as Figure 4 The initial TVC value of fresh fish meat was 3.83±0.16 log 10 CFU / g, indicating that the fish used in this experiment was of high quality. With the extension of storage time, the TVC values ​​of each group showed an upward trend, among which the colony growth rate of group R1 was the fastest, with 7.24 log on the eighth day. 10 CFU / g; R2 group reached 8.02 log on the 10th day 10 CFU / g; R3 group reached 7.21 log on the 10th day 10 CFU / g; R4 group reached 7.02 log on the 16th day 10 CFU / g; R5 group reached 7.02 log on the 18th day 10 CFU / g. The R3 and R4 groups extended the shelf life of the fish by 2 and 8 days, respectively, and the R5 group extended it by 10 days. The main function of the coating is to prevent the fish from contacting with oxygen in the air, thereby inhibiting the oxidative decomposition of proteins and the growth of microorganisms in the fish. The two groups with added essential oils were able to extend the shelf life of the fish mainly because cinnamon essential oil has a strong antibacterial effect, which inhibits the growth of microorganisms in the fish. The preservation effect of the R4 group was better than that of the R3 group because the essential oil is highly volatile. In the R4 group, the modified ISF and gelatin formed an IPN network structure, which firmly loaded the essential oil in the network structure, making it difficult for the essential oil to evaporate, thereby greatly preserving the effect of the essential oil. At the same time, the surface of the IPN network structure emulsion membrane is smooth and compact, with small and evenly distributed pores, making the emulsion membrane difficult to be destroyed on the surface of the fish, better blocking the contact between the fish and oxygen. Since the R3 group does not have this structure, the R4 group is better than the R3 group. The R5 group performed better than the R4 group because, based on the essential oil loading in the R4 group, the R5 group formed quinone compounds. These compounds can oxidize the -SH groups of bacterial membrane proteins, causing their death and inhibiting bacterial growth. Furthermore, the IPN network formed by covalent and hydrogen bonding between the modified ISF and gelatin is more stable, effectively delaying the volatilization of the essential oil, thereby inhibiting microbial growth and effectively extending the storage time of the fish. The R6 group showed a slightly lower TVC than the R5 group. This is because the enhanced adsorption of the emulsion film makes it less likely to fall off the sample surface during storage, slightly delaying microbial growth. However, in the emulsion film, the stability of the IPN network and the synergistic effect of the antibacterial components of the essential oil inhibit microbial growth. Therefore, there was no significant difference in the TVC values ​​between the R6 and R5 groups.

[0045] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an edible coating preservative material having an IPN network structure, characterized in that: The preparation method comprises the following steps: S1 treated ISF by acid-base high-pressure cooking and ultrasound-assisted laccase treatment to obtain modified ISF; S2: gelatin, modified ISF and water are mixed and stirred in a water bath until the gelatin is completely dissolved to obtain a gelatin mixed solution; Add glycerol to the S3 gelatin mixed solution and mix well to obtain a mixed solution; Adding cinnamon essential oil solution to the S4 mixed solution, shearing and mixing, to obtain a composite gelatin emulsion; The preparation of edible coating preservative materials with IPN network structure was completed.

2. The method for preparing the edible coating fresh-keeping material having an IPN network structure according to claim 1, characterized in that: In the method, the raw materials of the edible coating preservative material include: gelatin 4-6% w / v, glycerin 1-2% v / v, cinnamon essential oil 15-25% v / v, ISF 0-2.5% w / v, and the balance is deionized water; preferably, gelatin 5% w / v, glycerin 1.5% v / v, cinnamon essential oil 20% v / v, ISF 0-1.5% w / v, and the balance is deionized water.

3. The method for preparing the edible coating fresh-keeping material having an IPN network structure according to claim 2, characterized in that: The gelatin is animal gelatin with a power of 260-280; ISF is insoluble soybean fiber.

4. The method for preparing the edible coating fresh-keeping material having an IPN network structure according to claim 1, characterized in that: In the step S1, the acid-base high-pressure cooking modification method comprises mixing bean dregs with water in a mass ratio of 1:(15-25), adjusting the pH range to 7-14, and high-pressure cooking the bean dregs under alkaline conditions, followed by washing, centrifugation, drying, and sieving to obtain ISF.

5. The method for preparing the edible coating fresh-keeping material having an IPN network structure according to claim 4, characterized in that: The high pressure cooking conditions are 100-121°C and the time is 10-60 min.

6. The method for preparing the edible coating fresh-keeping material having an IPN network structure according to claim 5, characterized in that: After high-pressure cooking, the product is washed and centrifuged, and then subjected to ultrasound-assisted laccase treatment before subsequent operations. The ultrasound-assisted laccase treatment conditions are as follows: the centrifuged product is mixed with water at a mass ratio of 1: (10-15) to form an ISF suspension, 0.3-0.5 U / g of laccase is added, ultrasonic treatment is performed, and then centrifugation, drying, and sieving are performed to obtain modified ISF.

7. The method for preparing the edible coating fresh-keeping material having an IPN network structure according to claim 4, characterized in that: In step S2, the water bath heating temperature is 30-80°C.

8. The method for preparing the edible coating fresh-keeping material having an IPN network structure according to claim 1, characterized in that: In step S4, the shearing rate is 3000-25000 rpm, and the time is 2-10 min.

9. The method for preparing the edible coating preservative material having an IPN network structure according to any one of claims 1 to 8, characterized in that: The composite gelatin emulsion prepared by the method is used in edible coating fresh-keeping materials.

10. The use according to claim 9, characterized in that: The composite gelatin emulsion prepared by the method is used in the preservation of sturgeons. The specific operation is: pre-treating fresh sturgeons, cutting the fish meat into slices, immersing the fish slices in the composite gelatin emulsion, evenly coating the emulsion on the sample surface, and storing.

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