Intelligent collaborative preservative film for ice-fresh fish transportation and preparation method thereof

Abstract

This invention relates to the field of food packaging and preservation technology, and discloses an intelligent collaborative preservation film for transporting chilled fish and its preparation method, comprising the following components by mass: 10-20 parts fish scale collagen, 20-30 parts fish skin gelatin, 10-18 parts sodium caseinate, 5-12 parts pectin, 0.5-2 parts blueberry anthocyanins, 1-3 parts citrus extract, 5-10 parts glycerin, 5-10 parts sodium alginate, and 0.1-0.5 parts nano zinc oxide. The technical problem to be solved by this invention is to provide an intelligent synergistic preservation film for the transportation of chilled fish and its preparation method. It constructs a sodium caseinate-pectin dual-substrate system and builds an integrated preservation mechanism with three functions: physical protection, active preservation, and intelligent indication. The components form a quadruple synergistic effect of double cross-linking, polyelectrolyte composite, antibacterial, and antioxidant properties. It has excellent mechanical strength and barrier properties. At 4°C, it can extend the shelf life of chilled fish from 5 days to 12 days. Moreover, the raw material cost is low and it is completely biodegradable. It is suitable for long-distance cold chain transportation and preservation of chilled fish and has broad industrialization prospects.

Description

Technical Field

[0001] This invention relates to the field of food packaging and preservation technology, specifically to an intelligent collaborative preservation film for transporting chilled fish and its preparation method. Background Technology

[0002] Freshly chilled fish refers to fish that has been rapidly cooled after being caught, bringing its body temperature close to 0°C and circulating under low-temperature conditions. It is highly favored by consumers due to its high freshness, excellent meat quality, and complete preservation of nutrients. However, after a fish dies, its body undergoes a series of rapid biochemical changes, including muscle rigor mortis and thawing, protein denaturation, and lipid oxidation and rancidity. Simultaneously, putrefactive microorganisms such as Pseudomonas and Escherichia coli proliferate rapidly, resulting in a shelf life of only 5-6 days under conventional refrigeration conditions at 0-4°C. This severely limits the long-distance cold chain transportation and cross-regional market circulation of freshly chilled fish.

[0003] To extend the shelf life of chilled fish, researchers have developed various preservation technologies, including low-temperature refrigeration, modified atmosphere packaging, coating preservation, ozone treatment, and irradiation sterilization. Among these, active packaging technology has become a research hotspot in the food packaging field because it can actively inhibit microbial growth, delay food oxidation and spoilage, and indicate food freshness in real time. Active packaging constructs a preservation system integrating physical protection, active preservation, and intelligent indication by adding functional ingredients such as antibacterial agents, antioxidants, and freshness indicators to packaging materials, thereby achieving dynamic monitoring and active control of food quality.

[0004] However, after in-depth research and analysis of existing technologies, it has been found that existing active packaging materials for chilled fish still have many technical defects and industrialization challenges, as follows: In existing technologies, synthetic polymer materials such as polyethylene and polypropylene are inexpensive but cannot be biodegraded, which easily causes white pollution. Bio-based materials are mostly based on chitosan, resulting in serious technological homogenization.

[0005] Prior Art 1: Chinese Patent CN105154795A (A Chitosan-Based Antibacterial Preservative Film, Applicant: Jiangnan University, Publication Date: 2015.12.16) discloses a chitosan-based antibacterial preservative film, using chitosan as the main film-forming substrate and adding nano-silver as an antibacterial agent. The defects of this patent are: ① The application of chitosan substrate in the field of chilled fish preservation is too widespread, lacking technological innovation; ② It only has a single antibacterial function, without antioxidant and intelligent indicator functions; ③ Nano-silver is subject to regulatory restrictions (GB 9685-2016 has not yet approved nano-silver as an additive for food contact materials) and biosafety controversies. The preservative film disclosed in this patent extends the shelf life of chilled fish to 7 days at 4℃, with an extension rate of only 40%, and the raw material cost is as high as 12-15 yuan / kg of film. Studies have shown that the oxygen barrier properties of chitosan membranes are significantly lower than those of sodium caseinate-based materials. The study of NaOH / Urea-Compatible Chitosan / Carboxymethylcellulose Films (Molecules, 2026, 30(4): 2279) recorded an oxygen permeability of 5.21 × 10⁻⁶ for pure chitosan membranes. -4 g / (m²·s), while the oxygen permeability of the sodium caseinate-pectin dual-substrate system of the present invention is only 48.5±3.8 cc / (m²·day·atm), and the barrier performance is improved by 48%.

[0006] Prior art 2: Chinese patent CN108530792A (A gelatin-based composite food preservation film, applicant: South China University of Technology, publication date 2018.09.14) uses a gelatin-tea polyphenol system, with a water vapor transmission rate of 500-600 g / (m²·24h), significantly higher than the 258±15 g / (m²·24h) of this invention. "Research Progress of Chitosan Food Preservation Film" (Polymer Bulletin, 2004, 6: 68-72) points out that single chitosan substrates suffer from insufficient intermolecular hydrogen bond density, making it difficult to simultaneously achieve both mechanical strength and barrier properties.

[0007] Prior art 3: Chinese patent CN112011517A discloses a polyethylene-chitosan composite food preservation film, which uses polyethylene and chitosan as a composite. The defects of this patent are: ① Polyethylene is not biodegradable, causing white pollution; ② The composite process is complex and costly (18-20 yuan / kg film), which is not conducive to large-scale industrialization; ③ The interfacial bonding between the chitosan layer and the polyethylene layer is weak, making it easy to delaminate and resulting in a short service life.

[0008] The active ingredients have poor stability, making it difficult to achieve long-term preservation.

[0009] In existing technologies, natural antioxidants and antibacterial agents such as vitamin E and tea polyphenols are easily affected by environmental factors such as light, heat, and oxygen, and thus quickly become ineffective.

[0010] Existing technology 4: Chinese patent CN107759710A (Gelatin-Vitamin E Preservative Film, Applicant: Ocean University of China, Publication Date: 2018.03.06) shows that the antioxidant properties of Vitamin E decrease by 65% ​​after 5 days of storage. A study in the Journal of Food Engineering, 2020, 269:109812 confirmed that unencapsulated Vitamin E experiences a 60% loss rate within 2 weeks in active packaging. This invention stabilizes blueberry anthocyanins using citrus extracts, extending their half-life from 3-5 days to 8-12 days. The study "Anthocyanin Stability Research" (Douban.com, 2025) shows that flavonoids can increase the stability of anthocyanin molecules by 2.3 times through π-π stacking interactions.

[0011] Prior art 5: Chinese patent CN109053980A discloses a gelatin-based preservation film with added tea polyphenols. The defects of this patent are: ① Tea polyphenols are easily oxidized and degraded in an alkaline environment (where the pH increases during fish spoilage), resulting in a 55% performance degradation after 7 days of shelf life; ② Tea polyphenols have poor compatibility with the gelatin substrate, easily leading to phase separation and causing discoloration on the film surface; ③ It only has antioxidant functions and lacks antibacterial and intelligent indicator functions. The preservation film disclosed in this patent extends the shelf life of chilled fish to 7.5 days at 4℃, an extension rate of only 50%.

[0012] Its single function cannot meet multiple preservation needs.

[0013] In existing technologies, packaging materials mostly have only one function, such as antibacterial or anti-oxidation, which cannot simultaneously meet the multiple needs of preserving chilled fish.

[0014] Prior Art 6: Chinese Patent CN104387633A discloses a nano-silver antibacterial preservation film, which only possesses antibacterial function. The defects of this patent are: ① It only has antibacterial function, lacking antioxidant and intelligent indicator functions; ② Nano-silver is subject to regulatory restrictions and biosafety controversies; ③ Its antibacterial spectrum is narrow, with an inhibition rate of only 75% against Pseudomonas, failing to effectively inhibit the main spoilage bacteria of chilled fish. The preservation film disclosed in this patent extends the shelf life of chilled fish to 6.5 days at 4℃, an extension rate of only 30%.

[0015] Prior Art 7: Chinese Patent CN106479055A discloses a phytic acid antioxidant preservation film, which only possesses antioxidant function. The defects of this patent are: ① It only has antioxidant function, lacking antibacterial and intelligent indicator functions; ② Phytic acid has poor compatibility with the substrate, easily migrating to the food surface and affecting the food flavor; ③ Its antioxidant performance is limited, with a DPPH free radical scavenging rate of only 65%, failing to effectively delay the oxidation of fish fat. The preservation film disclosed in this patent extends the shelf life of chilled fish to 6 days at 4℃, an extension rate of only 20%.

[0016] It lacks an intuitive freshness indicator.

[0017] In existing technologies, packaging materials often lack intuitive freshness indicators, making it difficult for consumers and logistics personnel to quickly determine the freshness of chilled fish, which poses a food safety hazard.

[0018] Existing technology 8: Chinese patent CN108893429A (Anthocyanin smart label, applicant: Zhejiang University, publication date 2018.11.27) adopts an independent sticker design, and the anthocyanin half-life is only 3-5 days. "Research progress on anthocyanin-loaded aquatic product freshness indicator film" (Food and Machinery, 2025, 41(12):25-32) points out that free anthocyanins have a blurred color change in the pH range of 6.0-8.5, while the present invention achieves a clear color gradient from pH 6.0 (red) to 8.5 (dark blue) through the "citrus extract-anthocyanin" composite system.

[0019] Prior Art 9: Chinese Patent CN109865617A discloses a composite membrane with added pH indicator, but the defects of this patent are: ① Using synthetic dye as pH indicator poses a biosafety problem; ② The color change range is narrow (pH 7.0-8.0), which cannot cover the entire process of fish spoilage (first-grade freshness pH 6.0-7.0, second-grade freshness pH 7.0-8.5); ③ Synthetic dye has poor compatibility with the substrate and is easy to migrate to the food surface.

[0020] Antimicrobial agents face regulatory risks, limiting their industrialization and promotion. In existing technologies, some antibacterial agents, such as nano-silver, have good antibacterial effects, but there are regulatory restrictions on their use and controversies regarding their biosafety, which are not conducive to large-scale industrialization and promotion.

[0021] Prior Art 10: Chinese Patent CN105111435A discloses a nano-silver antibacterial preservation film. The defects of this patent are: ① GB 9685-2016 has not yet approved nano-silver as a food contact material additive, and its use is subject to regulatory restrictions; ② There are controversies regarding the biosafety of nano-silver, and long-term intake may pose potential risks to human health; ③ The antibacterial spectrum is narrow, with an inhibition rate of only 78% against Pseudomonas, failing to effectively inhibit the main spoilage bacteria of chilled fish; ④ Nano-silver is expensive (approximately 800 yuan / kg), with raw material costs as high as 15-18 yuan / kg of film, resulting in a low cost-effectiveness ratio. The preservation film disclosed in this patent extends the shelf life of chilled fish to 7 days at 4℃, but the extension rate is only 40%.

[0022] Prior Art 11: Chinese Patent CN107090080A discloses a food preservation film with added quaternary ammonium salt antibacterial agents. The defects of this patent are: ① Quaternary ammonium salt antibacterial agents are subject to regulatory restrictions, with GB 9685-2016 specifying strict migration limits; ② The antibacterial spectrum is narrow, with an inhibition rate of only 72% against Pseudomonas aeruginosa; ③ The antibacterial agent easily migrates to the food surface, affecting the food flavor. Summary of the Invention

[0023] The technical problem to be solved by this invention is to provide an intelligent synergistic preservation film for the transportation of chilled fish and its preparation method. It constructs a sodium caseinate-pectin dual-substrate system, creating an integrated preservation mechanism with three functions: physical protection, active preservation, and intelligent indication. The components form a quadruple synergistic effect of double cross-linking, polyelectrolyte composite, antibacterial, and antioxidant properties. It exhibits excellent mechanical strength and barrier properties, extending the shelf life of chilled fish from 5 days to 12 days at 4°C. Furthermore, it has low raw material costs, is fully biodegradable, and is regulatory compliant, making it suitable for long-distance cold chain transportation and preservation of chilled fish, with broad industrialization prospects.

[0024] The present invention achieves its objective by employing the following technical solution: A smart collaborative preservation film for transporting chilled fish, comprising: Fish scale collagen 10-20 parts, fish skin gelatin 20-30 parts, sodium caseinate 10-18 parts, pectin 5-12 parts, blueberry anthocyanins 0.5-2 parts, citrus extract 1-3 parts, glycerin 5-10 parts, sodium alginate 5-10 parts, nano zinc oxide 0.1-0.5 parts.

[0025] Based on the concept of high-value utilization of by-products in the food industry, an intelligent synergistic preservation system integrating physical protection, active preservation, and intelligent indication was constructed. Each raw material individually performs a specific function, while simultaneously forming multiple synergistic effects through intermolecular interactions, achieving a preservation effect of 1+1>2. The roles and synergistic mechanisms of each component are as follows: Fish scale collagen: The molecular chain contains a large number of glycine-proline-hydroxyproline repeating sequences, forming a unique triple helix structure. It can form a stable interpenetrating polymer network with fish skin gelatin molecular chains through hydrogen bonds and hydrophobic interactions, providing excellent mechanical strength and film-forming properties for the plastic wrap. The hydrophilic amino acids in its molecules can form hydrogen bonds with water molecules, precisely regulating the water vapor permeability of the plastic wrap, maintaining a suitable humidity and gas exchange environment inside the packaging, and preventing the fish from dehydrating or getting damp.

[0026] Fish skin gelatin: It synergistically constructs an interpenetrating polymer network with fish scale collagen, further enhancing the mechanical strength and flexibility of the membrane; the carboxyl and amino groups in the molecular chain can form a complex with sodium caseinate through hydrophobic interactions, improving the barrier properties of the membrane; at the same time, it has good emulsifying properties, which can promote the uniform dispersion of nano zinc oxide and citrus extract in the substrate and avoid the performance degradation caused by the aggregation of functional components.

[0027] Sodium caseinate: The phosphoserine residues in the molecular chain can form a stable cross-linked structure with calcium ions, improving the mechanical strength and oxygen barrier properties of the membrane. Its oxygen permeability is 40-50% lower than that of traditional chitosan, which can more effectively inhibit the growth of aerobic putrefactive bacteria. With an isoelectric point of pH 4.6, when fish spoilage releases alkaline substances such as ammonia and trimethylamine, causing the pH to rise, the molecular chain unfolds and forms a complex with flavonoids in citrus extracts, significantly enhancing antioxidant properties. It can also form a polyelectrolyte complex with pectin through electrostatic interaction, further optimizing the membrane's density and structural stability.

[0028] Pectin: The carboxyl groups of galacturonic acid residues in the molecular chain can form an "egg-box structure" crosslink with calcium ions, and synergistically construct a double crosslinking network with sodium alginate, significantly improving the barrier properties and structural stability of the plastic wrap; the polyelectrolyte complex formed with sodium caseinate can further improve the mechanical strength and thermal stability of the film; at the same time, it has certain antibacterial properties, forming an antibacterial synergistic system with nano zinc oxide and citrus extract.

[0029] Blueberry anthocyanins: As a natural pH indicator, the hydroxyl structure in the molecule is highly sensitive to pH changes. It is red under acidic conditions and gradually turns blue-purple as the pH increases. It can intuitively indicate the pH change during the spoilage of fish and make a visual judgment of the freshness of chilled fish. At the same time, it has certain antioxidant properties and can work synergistically with citrus extracts to scavenge free radicals and delay the oxidation of fat in fish.

[0030] Citrus extract: Rich in flavonoids such as hesperidin and naringin, and essential oil components such as limonene and linalool. Flavonoids can effectively scavenge free radicals and delay the oxidation and rancidity of fish fat, while essential oil components can destroy bacterial cell membranes and exert broad-spectrum antibacterial effects. It forms an antibacterial synergy with nano zinc oxide and an antioxidant synergy with blueberry anthocyanins. At the same time, it can stabilize the molecular structure of blueberry anthocyanins, delay their degradation, and extend the effective period of the smart indicator function.

[0031] Glycerin: As a plasticizer, it can insert between polymer molecular chains, weaken intermolecular forces, increase chain segment mobility, effectively improve the flexibility and extensibility of plastic wrap, prevent the film from cracking due to vibration and folding during transportation, and at the same time, it does not affect the other core properties of the film.

[0032] Sodium alginate: It works synergistically with pectin to form a double "egg carton structure" cross-linking through calcium ions, constructing a dense three-dimensional network structure, which significantly reduces the water vapor permeability of plastic wrap and improves its barrier properties; at the same time, it has certain antibacterial properties and can synergistically enhance the overall antibacterial effect of plastic wrap.

[0033] Nano zinc oxide: As an inorganic antibacterial agent, it exerts a broad-spectrum antibacterial effect by releasing zinc ions to disrupt the integrity of bacterial cell membranes and inhibit the activity of enzymes within bacteria. After surface modification with silane coupling agents, its dispersibility and compatibility with polymer matrices are significantly improved, preventing aggregation. It forms a synergistic antibacterial effect with citrus extract. After zinc ions disrupt the bacterial cell membrane, they promote the penetration of essential oil components in citrus extract into the bacterial cells, further enhancing the antibacterial effect, with a synergistic effect of 20-25%.

[0034] The core synergistic effect is reflected in four aspects: Dual cross-linking synergistic effect: Pectin and sodium alginate form a dual "egg carton structure" through calcium ions, while sodium caseinate forms additional cross-linking points with calcium ions through phosphoserine residues. The three work synergistically to form a dense three-dimensional network structure, reducing the water vapor permeability of the plastic wrap from 600-800 g / (m²·24h) of a single substrate film to 180-350 g / (m²·24h), and improving the barrier performance by 40-50%. Synergistic effect of polyelectrolyte complex: Sodium caseinate is negatively charged at pH>4.6, and forms a ternary polyelectrolyte complex with negatively charged pectin under the action of calcium ions, which significantly improves the mechanical strength and thermal stability of the plastic wrap, and increases the tensile strength from 25-30 MPa of single substrate film to 35-45 MPa. Synergistic antibacterial effect: The zinc ions released by nano zinc oxide disrupt bacterial cell membranes and promote the penetration of essential oil components in citrus extract into bacterial cells. The synergistic effect of the two increases the antibacterial rate by 20-25% compared to the single component, and the antibacterial rate against the three major putrefactive bacteria is ≥90%. Synergistic antioxidant effect: Flavonoids in citrus extracts form a synergistic antioxidant network with blueberry anthocyanins, which together scavenge free radicals and delay the oxidation of fish fat. At the same time, this network can stabilize the molecular structure of blueberry anthocyanins, extending their half-life from 3-5 days to 8-12 days and prolonging the effective period of the smart indicator function.

[0035] As a further limitation of this technical solution, the molecular weight of the fish scale collagen is 5-10 kDa, the gel strength of the fish skin gelatin is 200-300 Bloom, the protein content of the sodium caseinate is not less than 90%, and the degree of esterification of the pectin is 65-75%.

[0036] As a further limitation of this technical solution, the purity of the blueberry anthocyanins is not less than 95%; the total content of flavonoids in the citrus extract is not less than 40%, of which the content of hesperidin is not less than 15% and the content of naringin is not less than 10%.

[0037] As a further limitation of this technical solution, the nano zinc oxide has a particle size of 20-50 nm and its surface is modified with a silane coupling agent.

[0038] As a further limitation of this technical solution, the performance indicators are as follows: water vapor transmission rate 180-350 g / (m²·24h), tensile strength 35-45 MPa, elongation at break 65-85%; inhibition rate against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa not less than 90%, DPPH free radical scavenging rate 85-90%; pH response color change range is pH 6.0-8.5, with the color gradually changing from red to blue-purple as the pH increases.

[0039] A method for preparing an intelligent collaborative preservation film for transporting chilled fish includes the following steps: S1: Prepare the substrate solution by dissolving the fish scale collagen, the fish skin gelatin, and the sodium caseinate in deionized water and stirring at 55±2℃ and 250-350rpm for 2-3 hours to obtain a substrate solution with a mass concentration of 3-5%. After stirring, filter through a 100-mesh filter to remove insoluble matter. S2: Add the blueberry anthocyanins, the citrus extract, and the glycerin to the substrate solution obtained in S1, and stir at 250-350 rpm for 20-30 minutes to ensure that the functional components are evenly dispersed. S3: Add the sodium alginate, the pectin, and the nano zinc oxide to the mixture obtained in S2, and ultrasonically disperse it for 25-35 minutes at 25±5℃ with a power of 200-300W and a frequency of 35-45kHz to form a cross-linked mixture. S4: Cast the cross-linked mixture obtained in S3 into a film, control the casting thickness to be 0.07-0.09 mm, and dry it for 20-28 hours at 30-40℃ and 40-60% relative humidity to obtain the intelligent synergistic preservation film.

[0040] As a further limitation of this technical solution, the fish scale collagen is derived from fish scales, a by-product of fish processing; the fish skin gelatin is derived from fish skin, a by-product of fish processing; the sodium caseinate is derived from whey, a by-product of dairy processing; and the pectin and the citrus extract are derived from citrus peel, a by-product of fruit and vegetable processing.

[0041] As a further limitation of this technical solution, in S4, a food-grade stainless steel casting roller is used for casting film formation, the roller temperature is 25±3℃, the rotation speed is 5 r / min, and the casting thickness is adjusted to 0.08±0.01 mm by a scraper. The drying process uses a three-stage hot air drying oven with a temperature gradient of 30℃→40℃→30℃, a relative humidity of 40-60%, and a total drying time of 20-28 hours. After drying, the plastic wrap is wound up by silicone guide rollers with a winding tension of 5 N, and then cut into preset specifications by a CNC cutting machine.

[0042] Compared with related technologies, the intelligent collaborative preservation film for transporting chilled fish and its preparation method provided by the present invention have the following beneficial effects: (1) Realize the synergistic high-value utilization of multi-source food industry by-products: Using fish scales and skins (by-products of aquatic product processing), whey (by-products of dairy product processing), and citrus peels (by-products of fruit and vegetable processing) as the main raw material sources, the raw material cost is only 5-8 yuan / kg film, which is 10-15% lower than traditional chitosan-based preservation film. At the same time, it solves the problem of food industry by-product accumulation and environmental pollution, and has significant economic and social benefits. Every year, my country produces about 3 million tons of fish processing by-products, about 5 million tons of whey by-products, and about 10 million tons of citrus processing by-products. This invention provides a new way for the resource utilization of these by-products.

[0043] (2) The innovative film-forming system is the first of its kind, with significant technological novelty: The first "sodium caseinate-pectin" dual-substrate system is used to replace the traditional chitosan substrate, which has good technological novelty in the field of smart preservation film for chilled fish; the search results show that the technical solution of sodium caseinate and pectin compound for smart preservation film for chilled fish has not been reported, and the technology is novel and creative.

[0044] (3) Significant synergistic effects and excellent preservation performance: Through the synergistic effects of double cross-linking between components, polyelectrolyte composite, antibacterial and antioxidant properties, the mechanical properties, barrier properties, antibacterial properties and antioxidant properties of the preservation film are significantly improved. At 4℃, the shelf life of chilled fish can be extended from 5 days to 12 days, with an extension rate of 140%. The preservation effect is significantly better than that of traditional PE preservation bags (extending by 1 day, with an extension rate of 20%) and ordinary chitosan film (extending by 3 days, with an extension rate of 60%).

[0045] (4) Excellent overall performance, suitable for the transportation needs of chilled fish: the tensile strength of the plastic wrap is 35-45 MPa and the elongation at break is 65-85%, which meets the mechanical strength requirements during transportation. It is vibration resistant and fold resistant; the water vapor transmission rate is 180-350 g / (m²·24h), which can effectively prevent the fish from dehydrating and external pollutants from entering; at the same time, it has excellent antibacterial and antioxidant properties and intelligent freshness indication function, realizing dynamic monitoring of the quality of chilled fish.

[0046] (5) Regulatory friendly and safe and reliable: All raw materials are natural or biodegradable materials, and no ingredients such as nano silver are used that are subject to regulatory restrictions and safety controversies. Nano zinc oxide has been approved for use as a food contact material additive in GB 9685-2016, and the amount added in this invention is far below the maximum usage. Sodium caseinate, pectin, citrus extract, blueberry anthocyanins and other ingredients are all natural food ingredients with no regulatory risks and are safe and reliable to use.

[0047] (6) Environmentally friendly and in line with the concept of green and sustainable development: The food preservation film is made of biodegradable bio-based materials, which can be completely degraded in the natural environment and will not cause white pollution; at the same time, it realizes the resource recycling of by-products of the food industry, which is in line with the national green, low-carbon and sustainable development industrial policy.

[0048] (7) The preparation process is simple and easy to industrialize and scale up production: The preparation process adopts the casting film method, which does not require expensive production equipment. After optimization, the core process parameters can be adapted to industrial production. Roller casting and hot air drying are used to replace the template casting and room temperature drying in the laboratory, which greatly improves the production efficiency. The product quality of the film is stable and can meet the needs of large-scale markets. At the same time, the food preservation film can be made into composite bags, cut films and other specifications, which are suitable for various packaging methods such as vacuum skin packaging of fresh fish and ordinary sealed packaging, and have high application flexibility. Detailed Implementation

[0049] The present invention will be further described below with reference to the embodiments.

[0050] A smart collaborative preservation film for transporting chilled fish and its preparation method, comprising: Fish scale collagen 10-20 parts, fish skin gelatin 20-30 parts, sodium caseinate 10-18 parts, pectin 5-12 parts, blueberry anthocyanins 0.5-2 parts, citrus extract 1-3 parts, glycerin 5-10 parts, sodium alginate 5-10 parts, nano zinc oxide 0.1-0.5 parts.

[0051] The weight ratio of fish scale collagen to fish skin gelatin is 1:(1.0-3.0), the weight ratio of sodium caseinate to pectin is 1:(0.3-1.2), and the weight ratio of sodium alginate to pectin is 1:(0.5-2.4) to ensure that the synergistic effect among the components is maximized.

[0052] A dense interpenetrating polymer network structure is formed by combining sodium caseinate with pectin and crosslinking sodium alginate.

[0053] The fish scale collagen has a molecular weight of 5-10 kDa and is prepared by decalcification, defatting, and enzymatic hydrolysis pretreatment. It exhibits excellent film-forming properties and biocompatibility.

[0054] The fish skin gelatin has a gel strength of 200-300 Bloom, good film-forming properties and flexibility, and can form a stable interpenetrating polymer network with fish scale collagen.

[0055] The sodium caseinate has a protein content of not less than 90%, excellent oxygen barrier properties, and good compounding effect with pectin.

[0056] The pectin has an esterification degree of 65-75% and excellent cross-linking properties, and can form a double cross-linking network with sodium alginate.

[0057] The blueberry anthocyanins are derived from wild blueberries and have a purity of no less than 95%; they have high pH response sensitivity and stable color development.

[0058] The citrus extract contains a total content of flavonoids of not less than 40%, of which hesperidin content is not less than 15% and naringin content is not less than 10%, exhibiting synergistic antioxidant and antibacterial properties.

[0059] The nano zinc oxide has a particle size of 20-50 nm, and its surface is modified with a silane coupling agent, resulting in good dispersibility and stable antibacterial properties.

[0060] Sodium alginate: food grade, purity ≥95%, excellent cross-linking properties, and synergistically enhances the structural stability of the membrane with pectin.

[0061] The preservation film prepared by this invention possesses excellent comprehensive performance, with the following performance indicators: water vapor transmission rate of 180-350 g / (m²·24h), tensile strength of 35-45 MPa, and elongation at break of 65-85%; its antibacterial rate against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa is not less than 90%, and its DPPH free radical scavenging rate is 85-90%; the pH-responsive color change range is pH 6.0-8.5, with the color gradually changing from red to blue-purple as the pH increases. It can visually indicate pH changes during the spoilage process of fish.

[0062] A method for preparing an intelligent collaborative preservation film for transporting chilled fish includes the following steps: S1: Prepare the substrate solution by dissolving the fish scale collagen, the fish skin gelatin, and the sodium caseinate in deionized water and stirring at 55±2℃ and 250-350rpm for 2-3 hours to obtain a substrate solution with a mass concentration of 3-5%. After stirring, filter through a 100-mesh filter to remove insoluble matter and avoid film surface defects. S2: Add the blueberry anthocyanin, the citrus extract, and the glycerin to the substrate solution obtained in S1, and stir at 250-350 rpm for 20-30 minutes to disperse the functional ingredients evenly in the substrate solution; All raw materials in this invention are derived from by-products of the food industry, realizing the synergistic high-value utilization of by-products from the aquatic, dairy, and fruit and vegetable industries: fish scale collagen and fish skin gelatin are derived from fish scales and fish skin by-products of fish processing; sodium caseinate is derived from whey by-products of dairy processing; and pectin and citrus extract are derived from citrus peel by-products of fruit and vegetable processing. The raw materials are widely available and inexpensive, while solving the problem of resource utilization of by-products from the food industry.

[0063] The preparation method of the fish scale collagen includes: Decalcification: After cleaning and degreasing the fish scales, decalcify them with 0.5 mol / L HCl solution for 24 hours; Degreasing: Wash with water until neutral, then degrease with 95% ethanol for 4 hours; Enzymatic hydrolysis: After defatting and drying, 0.5% (w / w) alkaline protease was added and enzymatically hydrolyzed at 50℃ for 3 hours. The supernatant was collected by centrifugation, and the pH was adjusted to 4.5 to induce isoelectric precipitation of collagen. The collagen was then freeze-dried to obtain the fish scale collagen with a molecular weight of 8 kDa and a moisture content of ≤5%.

[0064] The preparation method of the fish skin gelatin includes: Clean the fish skin thoroughly, removing any remaining fish meat and scales; Degreased with 95% ethanol at a ratio of 1:8 (w / v) for 4 hours, then dried and decalcified with 0.5 mol / L HCl solution for 12 hours; After washing with water until neutral, the gelatin was extracted with hot water at 60℃ for 8 hours. The supernatant was collected by centrifugation, decolorized by passing through a diatomaceous earth column, and freeze-dried to obtain the fish skin gelatin powder with a gel strength of 250 Bloom and a moisture content of ≤12%.

[0065] The preparation method of the nano zinc oxide includes: Dissolve zinc acetate in water, add sodium hydroxide solution to adjust the pH to 9-10, and stir the reaction at 60-80℃ for 2 hours; After centrifugation and washing, the precipitate was dispersed in a silane coupling agent solution, stirred at room temperature for 4 hours, and dried to obtain modified nano zinc oxide.

[0066] S3: Add the sodium alginate, pectin and nano zinc oxide to the mixture obtained in S2, and ultrasonically disperse it for 25-35 minutes at 25±5℃ with a power of 200-300W and a frequency of 35-45kHz. Use the ultrasonic action to promote the cross-linking of each component to form a cross-linked mixture. S4: Cast the cross-linked mixture obtained in S3 into a film, control the casting thickness to be 0.07-0.09 mm, and dry it for 20-28 hours at 30-40 ℃ and 40-60% relative humidity to obtain the intelligent synergistic preservation film.

[0067] In step S4, a food-grade stainless steel casting roller is used for casting film formation. The roller temperature is 25±3℃, the rotation speed is 5 r / min, and the casting thickness is adjusted to 0.08±0.01 mm by a scraper. To solve the problems of template sticking and low efficiency in laboratory casting, a three-stage hot air drying oven is used for drying, with a temperature gradient of 30℃→40℃→30℃, relative humidity of 40-60%, and a total drying time of 20-28 hours. Compared with room temperature natural drying, the efficiency is improved by 3-4 times, and the flatness and mechanical properties of the film are more stable.

[0068] After drying, the cling film is wound up by silicone guide rollers with a winding tension of 5 N, and then cut into preset sizes by a CNC cutting machine. The CNC cutting machine then cuts the film into preset sizes such as 30cm×50cm and 50cm×100cm to meet practical application needs.

[0069] An application of a preservation film in the transportation and preservation of chilled fish involves making the film into a composite bag with an easy-tear opening. The bag body is embossed with breathable micropores with a diameter of 0.01 mm and a density of 5 pores / cm², ensuring both the airtightness of the packaging and allowing for moderate gas exchange. The chilled fish is wrapped in a vacuum skin packaging method, adhering to the surface of the fish, reducing gaps inside the packaging, and inhibiting the growth of microorganisms. This preservation film can be used under actual transportation conditions of temperature fluctuations and vibration impacts in cold chain transportation at 0-8℃. It does not swell when in continuous contact with ice water and does not crack in low-temperature environments. It can extend the shelf life of chilled fish from 5 days to more than 12 days, and its preservation effect is significantly better than that of traditional PE preservation bags and ordinary chitosan films.

[0070] Table 1 shows a comparison of the main performance indicators of the present invention with those of the prior art: Table 1. Comparison of the performance of the present invention with existing technologies. Note: Shelf life extension rate = (Shelf life of this invention - shelf life of blank control group) / shelf life of blank control group × 100%, and the shelf life of blank control group (naked packaging) is 5 days.

[0071] As can be seen from Table 1, the present invention is significantly superior to the prior art in terms of mechanical properties, barrier properties, antibacterial properties, antioxidant properties, intelligent indication function, shelf life extension rate, and cost-effectiveness.

[0072] This invention provides a special preservation film for transporting chilled fish, which uses food industry by-products as the main raw material, is low in cost, biodegradable, has multiple functions that work synergistically, and also features intelligent freshness indication. It not only solves the problem of preserving chilled fish during long-distance transportation, but also realizes the high-value utilization of food industry by-products, combining economic, social, and environmental benefits, and has significant industrial application value.

[0073] Example 1: The preferred formula for the intelligent synergistic food preservation film consists of the following ingredients in parts by weight: 15 parts fish scale collagen, 25 parts fish skin gelatin, 14 parts sodium caseinate, 8 parts pectin, 1 part blueberry anthocyanin, 2.5 parts citrus extract, 7 parts glycerin, 6 parts sodium alginate, and 0.4 parts nano zinc oxide.

[0074] Specifications of each raw material: Fish scale collagen molecular weight 8 kDa, fish skin gel strength 250 Bloom, sodium caseinate protein content 92%, pectin esterification degree 70%; blueberry anthocyanin purity 98%, derived from wild blueberries; citrus extract flavonoid content 40%, hesperidin 20%, naringin 12%, moisture ≤5%; nano zinc oxide particle size 30 nm, surface modified with KH-570 silane coupling agent; glycerin food grade, purity ≥99.5%, density 1.26 g / mL; sodium alginate food grade, purity ≥95%.

[0075] Example 2: The intelligent synergistic food preservation film was prepared according to the formula of Example 1, using the preparation method of the present invention. Specific steps included: S1: Dissolve 15 parts fish scale collagen, 25 parts fish skin gelatin and 14 parts sodium caseinate in 800 mL of deionized water, stir at 55℃ and 300 rpm for 2.5 h to obtain a substrate solution with a mass concentration of 4%, and filter it through a 100-mesh filter. S2: Add 1 part blueberry anthocyanin, 2.5 parts citrus extract and 7 parts glycerin to the base solution, stir at 300 rpm for 30 minutes to ensure uniform dispersion of the functional ingredients; S3: Add 6 parts sodium alginate, 8 parts pectin and 0.4 parts modified nano zinc oxide, and ultrasonically disperse at 250 W power and 40 kHz frequency for 30 minutes at 25±3℃. S4: Pour the cross-linked mixture onto a food-grade stainless steel casting roller, adjust the scraper to make the casting thickness 0.08mm, roller temperature 25℃, rotation speed 5 r / min, dry in a three-stage hot air drying oven (30℃→40℃→30℃, relative humidity 45%) for 7 hours, then wind it up with silicone guide rollers (tension 5 N) and CNC cut it to 30cm×50cm specifications to obtain the intelligent collaborative food preservation film.

[0076] Example 3: Performance testing of the intelligent collaborative food preservation film: Core performance tests were conducted on the food preservation film prepared in Example 2. All test methods followed national standards. The test results are as follows: Mechanical properties: Tested according to GB / T 1040.3-2006, the tensile strength is 40 MPa and the elongation at break is 78%, which meets the mechanical strength requirements for the transportation of chilled fish. Water vapor transmission rate: Tested according to GB / T 1037-1988, the water vapor transmission rate is 260 g / (m²·24h), which shows excellent barrier performance; Antibacterial performance: According to GB / T 21510-2008, the inhibition zone method was used for testing. The inhibition zone diameter was 17 mm for Escherichia coli (ATCC 25922) with an inhibition rate of 93%; the inhibition zone diameter was 19 mm for Staphylococcus aureus (ATCC 25923) with an inhibition rate of 96%; and the inhibition zone diameter was 15 mm for Pseudomonas aeruginosa (ATCC 15442) with an inhibition rate of 91%. The inhibition rate of the three major bacteria was ≥90%. Antioxidant performance: Tested using the DPPH free radical scavenging method, the DPPH free radical scavenging rate was 86%, indicating excellent antioxidant performance; pH response performance: The plastic wrap was soaked in buffer solutions of different pH values ​​and equilibrated at 25°C for 30 min. The results showed that the plastic wrap was red at pH 6.0, purple-red at pH 6.5, purple at pH 7.0, blue-purple at pH 7.5, blue at pH 8.0, and dark blue at pH 8.5. The plastic wrap showed high sensitivity and color differentiation.

[0077] Example 4: To verify the synergistic effect, a controlled experiment was designed to verify the antibacterial and antioxidant synergistic effect of the food preservation film of the present invention. The control group consisted of the substrate and a combination of single / dual functional ingredients, while the experimental group consisted of the complete formulation of Example 1. The antibacterial rate and DPPH free radical scavenging rate were tested, and the results are shown in Table 2. Table 2. Comparison results of antibacterial rate and DPPH free radical scavenging rate. The test results show that the antibacterial rate and DPPH free radical scavenging rate of the experimental group were significantly higher than those of the control groups, indicating that the citrus extract and nano zinc oxide form a significant antibacterial synergistic effect, with a synergistic effect of about 20-25%; the citrus extract and blueberry anthocyanins form a significant antioxidant synergistic effect, with a synergistic effect of about 25-35%. The multiple synergistic effects of this invention are significant.

[0078] Example 5: A trial of fresh fish preservation was conducted using tilapia from the same batch. After slaughtering and processing, the fish were divided into four groups of 10 fish each, with each fish weighing approximately 500 g. Different packaging methods were used, and the fish were refrigerated at 4°C to simulate the cold chain transportation conditions for fresh fish. Shelf life and core quality indicators were tested, and the results are as follows: Shelf life: Blank group (naked packaging) had a shelf life of 5 days, control group 1 (PE preservation bag) had a shelf life of 6 days, control group 2 (ordinary chitosan film) had a shelf life of 8 days, and experimental group (the preservation film of this invention) had a shelf life of 12 days. The experimental group extended the shelf life of chilled fish by 7 days, an extension rate of 140%. Sensory evaluation: After 12 days of storage, the experimental group scored 6.0 points (secondary freshness), while control group 1 scored 3.5 points and control group 2 scored 4.5 points, both of which were close to spoilage. Total bacterial count: After 12 days of storage, the control group >1.0×10⁻⁶. 8 CFU / g, control group 1 3.2×10 7 CFU / g, control group 26.3×10 6 CFU / g, experimental group 1.5×10 6 CFU / g, the total number of colonies in the experimental group was significantly lower than that in other groups; TVB-N value: After 12 days of storage, the blank group was >30 mg / 100 g, the control group was 123.0 mg / 100 g, the experimental group was 219.5 mg / 100 g, and the experimental group was 15.8 mg / 100 g. The experimental group was still within the range of secondary freshness. TBARS values: After 12 days of storage, the blank group had >2.0 mg MDA / kg, control group 1 had 1.25 mg MDA / kg, control group 2 had 1.00 mg MDA / kg, and the experimental group had 0.73 mg MDA / kg. The degree of lipid oxidation in the experimental group was significantly lower than that in other groups.

[0079] Meanwhile, the color changes of the plastic wrap in the experimental group were observed: red to purple after 0-6 days of storage, corresponding to first-grade freshness of the fish; blue-purple to blue after 9-12 days of storage, corresponding to second-grade freshness of the fish; and dark blue after 15 days of storage, corresponding to spoilage of the fish. The color change of the film showed a good correlation with the freshness of the fish, and could intuitively indicate the freshness of the chilled fish.

[0080] Example 6: The effectiveness of the extreme formulation was verified by film-making and core performance testing of the extreme ratios within the formulation range of this invention. The results showed that the preservation films prepared by the four extreme ratios all achieved antibacterial rates of ≥90% against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa, DPPH free radical scavenging rates of ≥85%, tensile strength of ≥35 MPa, and water vapor transmission rate of ≤350 g / (m²·24h), thus demonstrating the effectiveness of the formulation range of this invention.

[0081] Determining the optimal parameters: The optimal addition range for each component was determined through single-factor experiments. Sodium caseinate addition amount: 10-18 parts, preferably 14 parts. Experimental results show that when the sodium caseinate addition amount is less than 10 parts, the film-forming properties and mechanical strength are insufficient, while when it is more than 18 parts, the cost increases and the improvement in barrier performance is limited.

[0082] Pectin addition: 5-12 parts, preferably 8 parts. Experimental results show that when the pectin addition is less than 5 parts, insufficient cross-linking leads to poor barrier performance, while when it is more than 12 parts, excessive cross-linking leads to brittle membrane.

[0083] Citrus extract addition amount: 1-3 parts, preferably 2.5 parts. Experimental results show that when the citrus extract addition amount is less than 1 part, the antibacterial and antioxidant properties are insufficient, while when it is more than 3 parts, the mechanical properties decrease and the cost increases.

[0084] The amount of nano-zinc oxide added is 0.1-0.5 parts, preferably 0.4 parts. Experimental results show that when the amount of nano-zinc oxide added is less than 0.2 parts, the antibacterial performance is insufficient, and when it is more than 0.5 parts, the mechanical properties decrease and there may be safety risks.

[0085] Blueberry anthocyanin addition amount: 0.5-2 parts, preferably 1 part. Experimental results show that when the blueberry anthocyanin addition amount is less than 0.5 parts, the color change is not obvious, and when it is more than 2 parts, the cost increases and the improvement in antioxidant performance is limited.

[0086] Sodium alginate addition amount: 5-10 parts, preferably 6 parts. Experimental results show that when the sodium alginate addition amount is less than 5 parts, insufficient cross-linking leads to poor barrier performance, while when it is more than 10 parts, excessive cross-linking leads to membrane brittleness.

[0087] The intelligent collaborative preservation film for transporting chilled fish based on food industry by-products of this invention has broad prospects for industrial application and market value, mainly reflected in the following aspects: In line with the industry trend of resource utilization of by-products in the food industry: my country's aquatic product, dairy product, and fruit and vegetable processing industries generate a large number of by-products that have not yet been fully utilized at high value. This invention provides a new way to utilize these by-products, which can promote the development of the circular economy in related industries and has significant economic and social benefits.

[0088] Solving the Preservation Pain Points of Long-Distance Transportation of Fresh Fish: With the improvement of residents' living standards, the market demand for high-quality fresh fish continues to increase. However, the short shelf life is the core pain point restricting the cross-regional circulation of fresh fish. The preservation film of this invention can extend the shelf life of fresh fish to 12 days, meet the needs of long-distance cold chain transportation, and promote the market expansion of the fresh fish industry.

[0089] The product boasts a high cost-performance ratio and strong market competitiveness: its raw material cost is 10-15% lower than that of traditional chitosan-based food preservation film, and its preservation effect is significantly better than that of traditional PE food preservation bags and ordinary chitosan film. It also features intelligent freshness indication function. The product is cost-effective and can quickly replace existing traditional food preservation materials, with huge market demand potential.

[0090] The preparation process is simple and the industrialization threshold is low: the preparation process adopts the mature casting film formation method, which does not require expensive special equipment. Existing food packaging film manufacturers only need to make minor adjustments to the process parameters to achieve mass production. The industrialization threshold is low and it is easy to promote quickly.

[0091] It aligns with national policies on green and sustainable development: This invention enables the recycling of by-products from the food industry, and the cling film is completely biodegradable, producing no white pollution. It fits the national "dual carbon" goals and green, low-carbon, and sustainable development industrial policies, and can obtain relevant industrial policy support.

[0092] Highly innovative technology with high patent protection value: The first-ever "sodium caseinate-pectin" dual-substrate system for intelligent preservation film of chilled fish has significant technological novelty and creativity, clear patent protection scope, and can effectively prevent competitors from imitating it, forming a core technology barrier for the enterprise.

[0093] In summary, the intelligent collaborative preservation film of this invention has the advantages of low raw material cost, excellent preservation performance, comprehensive functions, environmental friendliness, and ease of industrialization. It can effectively solve the preservation problem of long-distance transportation of chilled fish, and at the same time realize the high-value utilization of food industry by-products. It has important industrial application value and broad market prospects in the field of food packaging and preservation.

[0094] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A smart collaborative preservation film for transporting chilled fish, characterized in that, Including components by parts by weight: Fish scale collagen 10-20 parts, fish skin gelatin 20-30 parts, sodium caseinate 10-18 parts, pectin 5-12 parts, blueberry anthocyanins 0.5-2 parts, citrus extract 1-3 parts, glycerin 5-10 parts, sodium alginate 5-10 parts, nano zinc oxide 0.1-0.5 parts.

2. The intelligent collaborative preservation film for transporting chilled fish according to claim 1, characterized in that: The fish scale collagen has a molecular weight of 5-10 kDa, the fish skin gelatin has a gel strength of 200-300 Bloom, the sodium caseinate has a protein content of not less than 90%, and the pectin has an esterification degree of 65-75%.

3. The intelligent collaborative preservation film for transporting chilled fish according to claim 1, characterized in that: The purity of the blueberry anthocyanins is not less than 95%; the total content of the citrus extract is not less than 40%, of which the content of hesperidin is not less than 15% and the content of naringin is not less than 10%.

4. The intelligent collaborative preservation film for transporting chilled fish according to claim 1, characterized in that: The nano zinc oxide has a particle size of 20-50 nm and its surface is modified with a silane coupling agent.

5. The intelligent collaborative preservation film for transporting chilled fish according to claim 1, characterized in that: The performance indicators are as follows: water vapor transmission rate 180-350 g / (m²·24h), tensile strength 35-45 MPa, elongation at break 65-85%; the inhibition rate against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa is not less than 90%, the DPPH free radical scavenging rate is 85-90%; the pH response color change range is pH 6.0-8.5, and the color gradually changes from red to blue-purple as the pH increases.

6. A method for preparing the intelligent collaborative preservation film for transporting chilled fish according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Prepare the substrate solution by dissolving the fish scale collagen, the fish skin gelatin, and the sodium caseinate in deionized water and stirring at 55±2℃ and 250-350rpm for 2-3 hours to obtain a substrate solution with a mass concentration of 3-5%. After stirring, filter through a 100-mesh filter to remove insoluble matter. S2: Add the blueberry anthocyanins, the citrus extract, and the glycerin to the substrate solution obtained in S1, and stir at 250-350 rpm for 20-30 minutes to ensure that the functional components are evenly dispersed. S3: Add the sodium alginate, pectin, and nano zinc oxide to the mixture obtained in S2, and ultrasonically disperse it for 25-35 minutes at 25±5℃ with a power of 200-300 W and a frequency of 35-45 kHz to form a cross-linked mixture; S4: Cast the cross-linked mixture obtained in S3 into a film, control the casting thickness to be 0.07-0.09 mm, and dry it for 20-28 hours at 30-40 ℃ and 40-60% relative humidity to obtain the intelligent synergistic preservation film.

7. The method for preparing an intelligent collaborative preservation film for transporting chilled fish according to claim 6, characterized in that: The fish scale collagen is derived from fish scales, a byproduct of fish processing; the fish skin gelatin is derived from fish skin, a byproduct of fish processing; the sodium caseinate is derived from whey, a byproduct of dairy processing; and the pectin and citrus extract are derived from citrus peel, a byproduct of fruit and vegetable processing.

8. The method for preparing an intelligent collaborative preservation film for transporting chilled fish according to claim 6, characterized in that: In step S4, a food-grade stainless steel casting roller is used for casting film formation. The roller temperature is 25±3 ℃, the rotation speed is 5 r / min, and the casting thickness is adjusted to 0.08±0.01 mm by a scraper. The drying process uses a three-stage hot air drying oven with a temperature gradient of 30℃→40℃→30℃, a relative humidity of 40-60%, and a total drying time of 20-28 hours. After drying, the plastic wrap is wound up by silicone guide rollers with a winding tension of 5 N, and then cut into preset specifications by a CNC cutting machine.

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