Preparation method and application of collagen packaging film

Abstract

The application discloses a preparation method and application of a collagen packaging film, and belongs to the technical field of bio-based food packaging materials. According to the method, animal-derived collagen is dissolved in an acetic acid solution with a pH of 3.5-4.5 to form a solution with a concentration of 3-5%, and then 15-25% of genipin and 8-12% of cellulose nanowhiskers by dry weight of the collagen are added in sequence to perform a cross-linking reaction at 35-40 DEG C, so as to construct a three-dimensional network structure. Subsequently, the solution is soaked in 70-80% ethanol containing 0.5-1.5% propyl gallate, and the surface hydrophobicity is improved through the specific combination of phenolic hydroxyl groups and the hydrophobic region of collagen. Finally, vacuum drying and 60-70% humidity environment balancing treatment are performed, so that the degradable film material with high mechanical strength and moderate waterproofness is obtained. The preparation method is especially suitable for the preservation packaging of chilled meat products, and can effectively prolong the shelf life of food while maintaining the biodegradability of the material.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, specifically relating to a method for preparing and applying a collagen packaging film. Background Technology

[0002] Collagen, as a natural biopolymer, has shown great potential in the food packaging field due to its excellent biocompatibility, biodegradability, and film-forming properties. However, existing collagen film preparation technologies still have many key shortcomings in practical applications, which seriously restrict its industrialization process.

[0003] Traditional collagen membranes generally have a tensile strength below 30 MPa and an elongation at break of less than 50%, failing to meet the basic requirements for puncture and tear resistance in food packaging. This deficiency stems primarily from two factors: First, collagen molecules are prone to irreversible denaturation during dissolution, leading to a triple-helix unwinding rate exceeding 60%, significantly reducing the effective sites for subsequent cross-linking reactions. Second, while conventional cross-linking agents (such as glutaraldehyde) can increase cross-linking density, the random distribution of reaction sites causes premature breakage in stress concentration areas. Furthermore, the poor dispersion uniformity of nano-reinforcing materials (such as cellulose whiskers) and their low interfacial bonding strength with the collagen matrix (typically <4 nN) further weaken the mechanical properties of the composite material. In existing technologies, achieving the synergistic effect of cross-linking agents and reinforcing phases without damaging the natural structure of collagen remains a major technical obstacle to improving mechanical properties.

[0004] The aforementioned technical deficiencies stem from the unique tertiary structural sensitivity of collagen, the difficulty in regulating multi-scale interfacial interactions, and the complex coupling of continuous production process parameters. Existing solutions often address one aspect while incurring another, introducing new quality problems while improving a particular performance indicator. This reflects a systematic deficiency in traditional technical approaches regarding molecular structure control, interface engineering design, and process parameter optimization. In particular, achieving the synergistic effect of multiple objectives—such as complete preservation of collagen structure, uniform dispersion of reinforcing phases, and stable immobilization of functional additives—has long been a major technical bottleneck in this field. Summary of the Invention

[0005] One object of the embodiments of the present invention is to solve at least the above-mentioned problems and / or defects, and to provide at least the advantages described below.

[0006] Another objective of this invention is to provide a method for preparing a collagen packaging film, in order to address the shortcomings of traditional collagen films, such as insufficient mechanical strength (tensile strength < 30 MPa) and insufficient elongation at break.

[0007] This invention also provides the application of collagen packaging film in the preservation of chilled meat.

[0008] To achieve the above-mentioned objectives, the present invention employs the following technical solution:

[0009] In a first aspect, a method for preparing a collagen packaging film includes the following steps:

[0010] 1) Dissolve animal-derived collagen in an acetic acid solution with a pH of 3.5-4.5 to form a collagen solution with a mass concentration of 3%-5%;

[0011] 2) Add 15%~25% genipin and 8%~12% cellulose nanocrystals by dry weight of collagen to the collagen solution in sequence, and stir and react at 35℃~40℃ for several hours to obtain a mixture.

[0012] 3) The mixture is cast into a film at 40℃~45℃ to obtain a film material;

[0013] 4) Immerse the obtained membrane material in an ethanol aqueous solution containing 0.5%~1.5% (by mass) propyl gallate for 30~60 minutes, wherein the volume concentration of the ethanol aqueous solution is 70%~80%;

[0014] 5) After the membrane material is removed and vacuum dried, it is equilibrated in an environment with a relative humidity of 60%~70% for 24 hours to obtain the collagen packaging film.

[0015] Preferably, the method for preparing the collagen packaging film further includes a pretreatment step before step 1):

[0016] Animal-derived collagen freeze-dried powder is mixed with deionized water at a mass ratio of 1:8 to 1:12 to form a suspension. The suspension is placed in an environment of -20℃ to -18℃ and frozen for 12 to 16 hours. Then it is transferred to a water bath of 25℃ to 30℃ to thaw completely, completing a single freeze-thaw cycle. The freeze-thaw cycle is repeated 3 to 5 times. The freeze-thawed suspension is then freeze-dried again to obtain freeze-dried powder.

[0017] The freeze-drying conditions are as follows: pre-freezing temperature -50℃ to -45℃, cold trap temperature -80℃ to -75℃, vacuum degree 10 to 15 Pa, and drying time 20 to 24 hours.

[0018] Preferably, in the method for preparing the collagen packaging film, step 1), the method of dissolving animal-derived collagen in an acetic acid solution with a pH of 3.5-4.5 includes:

[0019] a) Pre-dispersion activation: Activate the freeze-dried collagen powder after freeze-thaw treatment for 5-8 minutes, with a sieve aperture of 150-200 μm;

[0020] b) Low-temperature wetting: The activated powder is evenly sprinkled into an acetic acid solution at 4℃-6℃ at a rate of 10~15g / min. The acetic acid solution is pre-purified with nitrogen to make the dissolved oxygen content ≤1.5ppm. During the powder sprinkling process, ultrasonic waves with a frequency of 28~32kHz and a power density of 0.3~0.5W / mL are applied simultaneously.

[0021] c) Gradient dissolution control:

[0022] First stage: Maintain the solution temperature at 8℃~10℃ and stir at 50~80 rpm for 15~20 minutes to form a primary dispersion system with a mass concentration of 1%~2%;

[0023] Second stage: Increase the temperature to 25℃~28℃ at a rate of 1℃ / min, add sodium pyrophosphate at 0.05%~0.1% of the collagen mass, and continue stirring until the mass concentration reaches 3%~3.5%;

[0024] Third stage: Start the high shear disperser at 35℃~37℃, with a rotation speed of 12000~15000rpm and a linear velocity of 18m / s-22m / s. Add the remaining acetic acid solution in three portions, with an interval of 2~3 minutes between each addition.

[0025] Preferably, in the method for preparing the collagen packaging film, step 2) includes the following method for preparing the mixture:

[0026] Heat the collagen solution to 35℃~40℃ and maintain a constant temperature;

[0027] Genipin is added to the collagen solution at a uniform rate. The amount of genipin added is 15% to 25% of the dry weight of the collagen. During the addition, the conductivity of the solution is controlled to fluctuate within ≤5 μS / cm.

[0028] Stir continuously at 200 rpm to 300 rpm for 30 to 40 minutes, keeping the linear velocity of the stirring blade tip in the range of 1.2 to 1.8 m / s;

[0029] Within 10 minutes of adding genipin, add cellulose nanocrystals to the system in three equal portions, with an interval of 2 to 3 minutes between each addition.

[0030] Adjust the stirring speed to 100~150 rpm, maintain the blade tip linear velocity at 0.6~0.9 m / s, and continue the reaction for 3.5~4.5 hours to obtain the mixture.

[0031] Preferably, in the method for preparing the collagen packaging film, step 2) further includes the following step:

[0032] Take a 36% acetic acid mother liquor and dilute it with deionized water to a pH of 3.5-4.5;

[0033] Cellulose nanocrystals were added to an acetic acid solution with a pH of 3.5-4.5 to a mass-volume ratio of 0.8%-1.2%, and then sonicated at a frequency of 40kHz and a power of 300W for 10-15 minutes. After that, the undispersed particles were removed by centrifugation at 2000rpm for 5 minutes to obtain a cellulose nanocrystal dispersion.

[0034] Both the cellulose nanocrystal dispersion and the collagen solution were placed in a constant temperature water bath at 35℃~40℃ for a period of time. In the constant temperature water bath, ultrasonic oscillation was started once every 5~6 minutes, with an ultrasonic frequency of 40kHz, an ultrasonic power density of 0.5~0.8W / mL, and a single treatment time of 10 seconds~15 seconds.

[0035] After constant temperature water bath treatment, the cellulose nanofiber dispersion is emulsified at 1200~1500 rpm for 2~3 minutes.

[0036] Preferably, in the method for preparing the collagen packaging film, step 3) of casting the film includes the following steps:

[0037] The mixture obtained in step 2) is filtered through an 80-100 mesh sieve and then injected into a casting mold;

[0038] Preheat the PTFE mold to 38℃~42℃ before casting;

[0039] The casting environment temperature is controlled at 40℃~45℃, and the relative humidity is ≤30%. During casting, the gap between the scraper and the mold is set to 1.2~1.5 times the target thickness of the wet film.

[0040] The scraper is moved at a constant speed of 0.5 ~ 1.2 m / min;

[0041] After casting, the wet film is left to stand on the mold for 5-8 minutes to mature. During the maturation stage, the temperature is increased by 2-3°C per hour until it reaches 45°C. The ambient humidity during the maturation stage is divided into two stages: the humidity is maintained at 20%-25% for the first 3 minutes, and then adjusted to 15%-18% for the next 2-5 minutes.

[0042] Preferably, in the method for preparing the collagen packaging film, step 5) includes the following steps:

[0043] The wet film is laid flat on the porous titanium alloy heating plate.

[0044] Initiate the three-stage gradient drying process:

[0045] In the first stage, preheating is carried out at a vacuum of -0.08MPa to -0.085MPa and a temperature of 38℃ to 42℃ for 10 to 15 minutes, while controlling the coverage of the opening area on the surface of the heating plate to be 15% to 20%.

[0046] In the second stage, the temperature is increased to 50℃~55℃ at a rate of 1.5~2℃ / min, and the vacuum degree is increased to -0.095MPa~-0.1MPa simultaneously. The vacuum pump inlet valve is switched every 5 minutes to maintain the vapor pressure gradient on the membrane surface at 120~150Pa / m.

[0047] In the third stage, when the moisture content drops to 10%, the temperature is lowered to 48℃ to 50℃ and a vacuum of -0.09 to -0.095 MPa is maintained until the moisture content is ≤8%±0.3% as detected by the online moisture meter.

[0048] Preferably, in the method for preparing the collagen packaging film, step 5) of the balancing process includes the following steps:

[0049] After vacuum drying, the membrane material is vertically suspended in a constant temperature and humidity chamber, which is equipped with a dual-zone humidity control system.

[0050] The upper area is equipped with a dual-head ultrasonic atomizer, and the lower area is equipped with a rotary silicone moisture-absorbing device.

[0051] Implement three-stage balance control:

[0052] For the first 6 hours, maintain a temperature of 23℃~24℃ and a relative humidity of 70%~72%, then reduce the humidity by 2%~3% every hour, and introduce a directional airflow of 0.3~0.5m / s along the membrane surface.

[0053] During the middle 12 hours, the temperature is adjusted to 24.5℃~25℃ and the relative humidity to 62%~65%. The moisture absorption wheel is rotated 15°~20° every 2 hours, and the membrane material weight change rate is ≤0.1g / (m²·h).

[0054] After 4 to 8 hours, the temperature was stabilized at 25℃ and the relative humidity at 60% to 61%. Every 30 minutes, the moisture content difference between the edge and center of the membrane was detected by near-infrared scanning and was ≤0.5%.

[0055] Preferably, in the method for preparing the collagen packaging film, the addition and stirring of genipin in step 2) are carried out in the following manner:

[0056] Genipin is added to the collagen solution at a uniform rate of 0.4% to 0.6% of the dry weight of the collagen per minute. The genipin is prepared by dissolving it in an aqueous ethanol solution with a volume fraction of 40% to 45% to form an additive solution with a mass concentration of 10% to 12%.

[0057] During the addition process, the solution conductivity is monitored in real time by an online conductivity meter to control the fluctuation range to ≤5μS / cm. When the conductivity deviation exceeds the threshold, the addition rate is automatically adjusted to compensate.

[0058] After adding, stir continuously at 250~280 rpm for 35~40 minutes, keeping the linear velocity of the stirring blade tip constant in the range of 1.5~1.7 m / s;

[0059] After mixing, let it stand for 8 to 10 minutes, during which time it will pulse-stir at 80 to 100 rpm for 5 to 8 seconds every 2 minutes.

[0060] Then, cellulose nanocrystals were added in equal amounts in three separate batches.

[0061] Secondly, the application of collagen packaging films prepared by any of the methods in the preservation of chilled meat.

[0062] Compared with the prior art, the advantages and beneficial technical effects of the present invention are:

[0063] This invention utilizes the synergistic effect of genipin and cellulose nanofibers to significantly improve mechanical strength and waterproof performance while maintaining the biodegradability of the material. This results in a membrane material that possesses both excellent mechanical properties and moderate hydrophobicity, meeting the stability requirements of food packaging materials.

[0064] This invention effectively refines the collagen fiber structure through freeze-thaw cycle pretreatment, improves dissolution efficiency and solution stability, avoids molecular chain degradation caused by high-temperature treatment, and ensures the integrity of active sites in the cross-linking reaction in subsequent processes.

[0065] This invention employs gradient dissolution and real-time monitoring technology to achieve controllable unwinding of collagen molecules under low-temperature conditions, preserving the triple helix structure to the greatest extent. At the same time, targeted filtration removes undissolved impurities, ensuring the uniformity and rheological properties of the film-forming solution.

[0066] This invention ensures uniform dispersion of the crosslinking agent and precise control of the reaction process through dynamic conductivity monitoring and staged stirring control. Combined with the timed and quantitative addition strategy of cellulose whiskers, it significantly enhances the interfacial bonding strength between the nanophase and the matrix.

[0067] This invention improves the compatibility of nanofibers with collagen solutions and reduces their tendency to agglomerate by optimizing the surface chemical properties and pretreatment process of nanofibers, thereby ensuring the uniform distribution of the nano-reinforcing phase and the effective load transfer in the composite film.

[0068] This invention utilizes mold guide channel design and precise temperature and humidity control to achieve a synergistic improvement in film thickness uniformity and surface smoothness. At the same time, it eliminates internal stress and reduces the generation of film defects through a stepped curing process.

[0069] This invention employs a multi-level gradient drying strategy, which dynamically controls the moisture migration path by matching vacuum and temperature, effectively reducing residual stress inside the membrane material and avoiding warping deformation caused by uneven shrinkage during the drying process.

[0070] This invention uses a dual-zone humidity control system and a closed-loop feedback mechanism to precisely regulate the humidity gradient distribution during the equilibrium phase, promote the uniform diffusion of moisture inside the membrane material, and improve the dimensional stability and environmental adaptability of the final product.

[0071] This invention achieves a dynamic balance of crosslinking reaction rate through the synergistic effect of uniform addition and pulse stirring, avoiding problems such as local over-crosslinking or insufficient reaction, and significantly improving crosslinking efficiency and material performance consistency.

[0072] The collagen packaging film prepared by this invention can effectively block the penetration of oxygen and moisture, delay the lipid oxidation and microbial growth of chilled meat products, and maintain the environmentally friendly properties of the material while maintaining food quality.

[0073] Other advantages, objectives, and features of the embodiments of the present invention will be apparent in part from the following description, and in part will be understood by those skilled in the art through study and practice of the embodiments of the present invention. Detailed Implementation

[0074] To further illustrate the technical means and effects of this invention, the following embodiments are provided for further explanation. The specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0075] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0076] This invention provides a method for preparing a collagen packaging film, comprising the following steps:

[0077] 1) Dissolve animal-derived collagen in an acetic acid solution with a pH of 3.5-4.5 to form a collagen solution with a mass concentration of 3-5%;

[0078] 2) Add 15-25% genipin and 8-12% cellulose nanocrystals by dry weight of collagen to the collagen solution in sequence, and stir and react at 35-40°C for several hours to obtain a mixture.

[0079] 3) The mixture is injected into a mold and then cast into a film at 40-45°C to obtain a film material;

[0080] 4) Immerse the obtained membrane material in an ethanol aqueous solution containing 0.5-1.5% (by mass) propyl gallate for 30-60 minutes, wherein the volume concentration of the ethanol aqueous solution is 70-80%.

[0081] 5) After the membrane material is removed and vacuum dried, it is equilibrated in an environment with a relative humidity of 60-70% for 24 hours to obtain the collagen packaging film.

[0082] Animal-derived collagen is dissolved in an acetic acid solution with a pH of 3.5–4.5 to form a collagen solution with a mass concentration of 3%–5%. The pH value can be selected at nodes such as 3.5, 4.0, and 4.5, and the mass concentration can be selected at gradient values ​​such as 3%, 4%, and 5%. The dissolution process can be performed using commonly used laboratory equipment such as a magnetic stirrer (e.g., Shanghai Meiyingpu 85-2 model) and a pH meter (e.g., Leici PHS-3C model). Commercially available bovine collagen (e.g., Sigma-Aldrich products) can be used as the animal-derived collagen, and the acetic acid solution is prepared using analytical grade glacial acetic acid. The magnetic stirrer is placed on a flat surface on the lab bench, and the pH meter electrode is immersed in the solution for real-time monitoring. By controlling the degree of unwinding of collagen molecules in an acidic environment, the active sites of the triple helix structure are preserved, providing a basis for subsequent cross-linking reactions.

[0083] Add 15% to 25% genipin and 8% to 12% cellulose nanocrystals by dry weight of collagen sequentially to a collagen solution, and stir the mixture at 35°C to 40°C for several hours to obtain a mixed solution.

[0084] The addition ratio of genipin can be selected as 15%, 20%, or 25%, the addition ratio of cellulose nanofibers can be selected as 8%, 10%, or 12%, and the reaction temperature can be selected as 35℃, 38℃, or 40℃.

[0085] The stirring process can be carried out using a digital display constant temperature water bath (such as the HH-601 model) in conjunction with a mechanical stirrer (such as the JJ-1 model), with a temperature control accuracy of ±0.5℃.

[0086] Genipin can be obtained from the analytical grade reagent of Chengdu Manster Biotechnology Co., Ltd., and cellulose nanocrystals can be purchased from commercially available products developed by Nanjing Forestry University (e.g., 30-50 nm in diameter).

[0087] The constant temperature water bath has a built-in stirring paddle, with the paddle blades immersed in the solution at a height of 1 / 3 from the bottom of the container.

[0088] Similar to the blending reaction of polymer composites, it is necessary to control the uniformity of additive dispersion and the reaction time.

[0089] Genipin can be purchased from biological reagent companies, and cellulose nanocrystals can be prepared from microcrystalline cellulose by sulfuric acid hydrolysis (such as Sigma-Aldrich microcrystalline cellulose).

[0090] Genipin forms covalent crosslinks with collagen amino groups, and cellulose nanocrystals fill the network structure, synergistically enhancing the mechanical strength and toughness of the membrane material.

[0091] The mixture is cast into a film at 40℃~45℃ to obtain a film material; the obtained film material is immersed in an ethanol aqueous solution containing 0.5%~1.5% by mass of propyl gallate for 30~60 minutes (ethanol aqueous solution volume concentration 70%~80%); the film material is removed, vacuum dried, and then equilibrated in an environment with a relative humidity of 60%~70% for 24 hours to obtain a collagen packaging film.

[0092] The casting temperature can be selected as 40℃, 43℃, or 45℃; the propyl gallate concentration can be selected as 0.5%, 1.0%, or 1.5%; the ethanol concentration can be selected as 70%, 75%, or 80%; the soaking time can be selected as 30 minutes, 45 minutes, or 60 minutes; the vacuum drying conditions can refer to the parameters of a conventional vacuum drying oven (e.g., vacuum degree -0.08MPa); and the equilibrium humidity can be selected as 60%, 65%, or 70%.

[0093] Casting can be done using a laboratory casting machine (such as the RYJ-600 model), immersion treatment can be done using a glass container, vacuum drying can be done using a vacuum drying oven (such as the DZF-6210 model), and equilibration treatment can be done using a constant temperature and humidity chamber (such as the TH-250C model).

[0094] Propyl gallate is a food-grade antioxidant (such as Shanghai Yuanye Bioreactor), and ethanol is analytical grade anhydrous ethanol.

[0095] The distance between the casting machine scraper and the mold is adjustable. A porous tray is placed inside the vacuum drying oven to support the film material. A horizontal mesh frame is set inside the constant temperature and humidity chamber to suspend the film material.

[0096] Casting is similar to the process of preparing plastic films, and vacuum drying is similar to the dehydration process of conventional biological materials.

[0097] Propyl gallate can be purchased from food additive suppliers, while ethanol is a regular commodity in chemical reagent stores.

[0098] The casting process ensures uniform membrane thickness, while propyl gallate enhances surface hydrophobicity by binding the hydrophobic regions of collagen with phenolic hydroxyl groups. Vacuum drying and humidity balancing eliminate internal stress, giving the membrane both mechanical strength and waterproof performance.

[0099] In the above scheme, as a preferred embodiment, a pretreatment step is included before step 1): animal-derived collagen freeze-dried powder and deionized water are mixed at a mass ratio of 1:8 to 1:12 to form a suspension. The suspension is placed in an environment of -20℃ to -18℃ and frozen for 12 to 16 hours. Then, it is transferred to a water bath of 25℃ to 30℃ to completely thaw, completing a single freeze-thaw cycle. The freeze-thaw cycle is repeated 3 to 5 times. The suspension after freeze-thaw treatment is freeze-dried again to make freeze-dried powder. The mass ratio can be selected as 1:8, 1:10, 1:12, etc., the freezing temperature can be selected as -20℃, -19℃, -18℃, the freezing time can be selected as 12 hours, 14 hours, 16 hours, the thawing temperature can be selected as 25℃, 28℃, 30℃, and the number of cycles can be selected as 3, 4, or 5 times. The freezing process can be performed using a laboratory cryogenic freezer (such as the Haier DW-86L286), the thawing process can be performed using a constant temperature water bath (such as the Shanghai Jinghong DK-S24), and the mixing process can be performed using a magnetic stirrer (such as the Shanghai Meiyingpu 85-2). Commercially available porcine collagen (such as products from Sinopharm Chemical Reagent Co., Ltd.) can be used for lyophilized animal-derived collagen powder. Deionized water is standard laboratory preparation water. The cryogenic freezer should be placed in a cool, shaded area of ​​the laboratory, the constant temperature water bath should be placed on the lab bench, and the stirrer electrodes should be immersed in the suspension.

[0100] The freeze-drying conditions are as follows: pre-freezing temperature -50℃ to -45℃, cold trap temperature -80℃ to -75℃, vacuum degree 10Pa to 15Pa, and drying time 20 hours to 24 hours. The pre-freezing temperature can be selected as -50℃, -48℃, or -45℃; the cold trap temperature can be selected as -80℃, -78℃, or -75℃; the vacuum degree can be selected as 10Pa, 12Pa, or 15Pa; and the drying time can be selected as 20 hours, 22 hours, or 24 hours. A laboratory freeze dryer (such as the Beijing Boyikang Pilot 10-15E) can be used for the freeze-drying process, with a matching vacuum pump (such as the Edwards RV3) to maintain the vacuum environment. No additional materials are needed for the suspension. Phosphorus pentoxide (placed below the cold trap) can be used as the desiccant during the freeze-drying process. The freeze dryer main unit is placed on the experimental platform, the cold trap is located below the main unit, the vacuum pump is connected to the side interface of the main unit, and the sample tray is placed in the middle layer of the pre-freezing chamber.

[0101] Freeze-thaw cycles can refine the average diameter of collagen fiber bundles, improve the uniformity of fiber length distribution, avoid molecular chain degradation caused by high-temperature treatment, and enhance the stability of subsequent dissolution processes and the number of active sites in cross-linking reactions, laying the foundation for the preparation of high-strength membrane materials.

[0102] In the above scheme, preferably, step 1) involves dissolving animal-derived collagen in an acetic acid solution with a pH of 3.5-4.5, including:

[0103] a) Pre-dispersion activation: Activate the freeze-thawed collagen powder for 5-8 minutes using a sieve with a mesh size of 150-200 μm to obtain activated powder with a bulk density >85%. Activation time can be selected as 5 minutes, 6 minutes, 7 minutes, or 8 minutes, and sieve mesh sizes can be selected as 150 μm, 180 μm, or 200 μm. The activation process can be performed using a laboratory vibrating sieve (such as the ZS series produced by Shanghai Vibration Machinery Co., Ltd.), and the sieve can be a standard stainless steel sieve (such as those produced by Zhangxing Yarn Sieve Factory in Daoxu, Shangyu City, Zhejiang Province). The sieve material is 304 stainless steel, and the freeze-dried collagen powder is the pre-treated finished product.

[0104] b) Low-temperature wetting: The activated powder is evenly sprinkled into an acetic acid solution at 4℃-6℃ at a rate of 10~15g / min. The acetic acid solution is pre-purified with nitrogen to make the dissolved oxygen content ≤1.5ppm. During the powder sprinkling process, ultrasonic waves with a frequency of 28~32kHz and a power density of 0.3~0.5W / mL are applied simultaneously.

[0105] The powder application rate can be selected as 10 g / min, 12 g / min, or 15 g / min; the acetic acid solution temperature can be selected as 4℃, 5℃, or 6℃; the ultrasonic frequency can be selected as 28 kHz, 30 kHz, or 32 kHz; the power density can be selected as 0.3 W / mL, 0.4 W / mL, or 0.5 W / mL; and the cavitation bubble diameter can be selected as 8 cm, 10 cm, or 12 cm. A quantitative feeder (such as the screw feeder from Changzhou Yibu Drying Equipment Co., Ltd.) can be used for the powder application process. A jacketed glass beaker (with a low-temperature circulating water bath) can be used for the acetic acid solution. A nitrogen cylinder connected to a conduit can be used for nitrogen gas introduction. An ultrasonic processor (such as the FS-600N model from Shanghai Shengxi Instrument Co., Ltd.) can be used for ultrasonic treatment. The acetic acid is analytical grade glacial acetic acid (such as products from Shanghai Titan Technology Co., Ltd.), the nitrogen is 99.9% pure industrial-grade nitrogen, and the activated powder is the loose powder obtained from the aforementioned sieving. The metering feeder is located above the glass beaker, and nitrogen gas is introduced into the beaker through a conduit from the bottom of the beaker. The ultrasonic probe is immersed in the solution to a depth of 1 / 3 of the liquid surface, and the beaker is jacketed by a low-temperature circulating water bath.

[0106] c) Gradient dissolution control:

[0107] First stage: Maintain the solution temperature at 8℃~10℃ and stir at 50~80rpm for 15-20 minutes to form a primary dispersion system with a mass concentration of 1%~2%;

[0108] Second stage: Increase the temperature to 25℃~28℃ at a rate of 1℃ / min, add sodium pyrophosphate at 0.05%~0.1% of the collagen mass, and continue stirring until the mass concentration reaches 3%~3.5%;

[0109] Third stage: Start the high shear disperser at 35℃~37℃, with a rotation speed of 12000~15000rpm and a linear velocity of 18m / s-22m / s. Add the remaining acetic acid solution in three portions, with an interval of 2~3 minutes between each addition.

[0110] The first stage allows selection of temperatures of 8℃, 9℃, and 10℃, rotation speeds of 50rpm, 60rpm, and 80rpm, time of 15 minutes and 20 minutes, and concentrations of 1%, 1.5%, and 2%. The second stage has a fixed heating rate of 1℃ / min, a temperature of 25℃ and 28℃, sodium pyrophosphate dosages of 0.05%, 0.08%, and 0.1%, and concentrations of 3%, 3.2%, and 3.5%. The third stage allows selection of temperatures of 35℃ and 37℃, rotation speeds of 12000rpm, 13500rpm, and 15000rpm, linear speeds of 18m / s, 20m / s, and 22m / s, and interval times of 2 minutes and 3 minutes. The first and second stages of mixing can be achieved using a magnetic stirrer (such as the C-MAG HS7 from IKA, Germany) with a stirring paddle. The third stage uses a high-shear disperser (such as the F6 / 100 from Fluke, Germany). Temperature control is achieved using a constant-temperature water bath (such as the DK-8D from Shanghai Jinghong Experimental Equipment Co., Ltd.). Sodium pyrophosphate is a food-grade additive (such as a product from Henan Yuanzhiwei Food Ingredients Co., Ltd.).

[0111] In one embodiment of the present invention, preferably, step 2) involves the preparation method of the mixture comprising:

[0112] The collagen solution is heated to 35℃~40℃ and maintained at a constant temperature. The heating temperature can be selected from 35℃, 38℃, and 40℃, and the temperature control accuracy can be ±0.5℃. The heating and temperature control process can be performed using a commonly used laboratory digital display thermostatic water bath (such as the Shanghai Jinghong HH-601 model), equipped with a temperature sensor to monitor the solution temperature in real time. Temperature control provides a stable environment for the cross-linking reaction, preventing temperature fluctuations from affecting the binding efficiency of collagen molecules and the cross-linking agent.

[0113] Genipin is added to the collagen solution at a uniform rate. The amount of genipin added is 15% to 25% of the dry weight of the collagen. During the addition, the conductivity of the solution is controlled to fluctuate within ≤5 μS / cm.

[0114] Stir continuously at 200 rpm to 300 rpm for 30 to 40 minutes, keeping the linear velocity of the stirring blade tip in the range of 1.2 m / s to 1.8 m / s;

[0115] Within 10 minutes of adding genipin, add cellulose nanocrystals to the system in three equal portions, with an interval of 2 to 3 minutes between each addition.

[0116] Adjust the stirring speed to 100 rpm to 150 rpm, maintain the blade tip linear velocity at 0.6 m / s to 0.9 m / s, and continue the reaction for 3.5 hours to 4.5 hours to obtain the mixture.

[0117] Optionally, genipin at a constant rate of 15%–25% of the dry weight of collagen is added to the collagen solution, controlling the conductivity fluctuation range of the solution to ≤5 μS / cm. The solution is then continuously stirred at 200–300 rpm for 30–40 minutes, with the impeller tip linear velocity maintained in the range of 1.2–1.8 m / s. The genipin addition ratio can be selected as 15%, 20%, or 25%; the stirring speed can be selected as 200 rpm, 250 rpm, or 300 rpm; the stirring time can be selected as 30 minutes, 35 minutes, or 40 minutes; the linear velocity can be selected as 1.2 m / s, 1.5 m / s, or 1.8 m / s; and the conductivity fluctuation threshold is fixed at ≤5 μS / cm.

[0118] Adding genipin can be done using a measuring cylinder or a constant flow pump (such as the Lange peristaltic pump BT100-2J) to control the flow rate. Conductivity monitoring can be done using an online conductivity meter (such as the Leici DDS-307A). During the stirring process, a mechanical stirrer (such as the Changzhou Ronghua JJ-1 type) with adjustable blades can be used.

[0119] Within 10 minutes of adding genipin, add 8%–12% cellulose nanocrystals in three equal portions (each 2–3 minutes apart). Adjust the stirring speed to 100–150 rpm, maintain the blade tip linear velocity at 0.6–0.9 m / s, and continue the reaction for 3.5–4.5 hours. The interval between each addition can be 2 or 3 minutes, the subsequent stirring speed can be 100 rpm, 120 rpm, or 150 rpm, the linear velocity can be 0.6 m / s, 0.75 m / s, or 0.9 m / s, and the reaction time can be 3.5 hours, 4 hours, or 4.5 hours. The cellulose nanocrystals can be weighed using an electronic balance (such as Mettler Toledo ME204E) and added in batches through a funnel. The stirring equipment is the same as described above, and the blade tip linear velocity can be controlled by adjusting the blade speed and diameter. By adding genipin at a uniform rate and monitoring the conductivity in real time, the crosslinking agent is ensured to be uniformly dispersed and the reaction process is precisely controlled. The addition of cellulose nanocrystals in batches at fixed times and in fixed quantities, combined with the adjustment of the stirring rate, can significantly reduce the aggregation of the nanophase and enhance its interfacial bonding strength with the collagen matrix, thereby improving the tensile strength and elongation at break of the composite membrane.

[0120] In one embodiment of the present invention, preferably, step 2) further includes the following step:

[0121] Take a 36% acetic acid stock solution and dilute it with deionized water to a pH of 3.5-4.5. The pH value can be selected from points such as 3.5, 4.0, and 4.5. The concentration of the diluted acetic acid solution is determined based on the pH adjustment result (usually 2%-5%). The dilution process can use commonly used laboratory beakers, graduated cylinders, and pH meters (such as the Leici PHS-3C model). When adjusting the pH, a 0.1 mol / L NaOH or HCl solution can be used.

[0122] Cellulose nanocrystals were added to an acetic acid solution with a pH of 3.5-4.5 to a mass-volume ratio of 0.8%-1.2%, and then sonicated at a frequency of 40kHz and a power of 300W for 10-15 minutes. After that, the undispersed particles were removed by centrifugation at 2000rpm for 5 minutes to obtain a cellulose nanocrystal dispersion.

[0123] Both the cellulose nanocrystal dispersion and the collagen solution were placed in a constant temperature water bath at 35-40℃ for a period of time. During the constant temperature water bath, ultrasonic oscillation was initiated every 5-6 minutes, with an ultrasonic frequency of 40kHz, an ultrasonic power density of 0.5-0.8W / mL, and a single treatment time of 10-15 seconds. Ultrasonic treatment can be performed using an ultrasonic cleaner (such as the KQ-500DE model from Kunshan Ultrasonic Instrument Co., Ltd.), and centrifugation is performed using a laboratory centrifuge (such as the H1850 model from Hunan Xiangyi). The dispersion container is a 50mL glass centrifuge tube.

[0124] After constant temperature water bath treatment, the cellulose nanofiber dispersion is emulsified at 1200 rpm to 1500 rpm for 2 to 3 minutes.

[0125] The constant temperature water bath temperature can be selected as 35℃, 38℃, or 40℃; the ultrasonic oscillation interval time can be selected as 5 minutes or 6 minutes; the power density can be selected as 0.5W / mL, 0.6W / mL, or 0.8W / mL; the single action time can be selected as 10 seconds, 12 seconds, or 15 seconds; the transmittance threshold is fixed at ≤2% / min; the emulsification speed can be selected as 1200rpm, 1350rpm, or 1500rpm; and the time can be selected as 2 minutes or 3 minutes.

[0126] The constant temperature water bath uses a digital display constant temperature water bath (such as the Shanghai Jinghong DK-8D model), the ultrasonic oscillation uses a probe-type ultrasonic processor (such as the Ningbo Xinzhi SCIENTZ-IID model), and the emulsification process uses a laboratory emulsifier (such as the German Flück FA25 model).

[0127] Pre-dispersion with acetic acid solution and ultrasonic treatment improve the surface charge characteristics of cellulose nanofibers and reduce agglomeration; constant temperature water bath combined with intermittent ultrasonic oscillation ensures full contact between nanofibers and collagen molecules in a dynamic environment, improving interfacial compatibility; emulsification treatment further refines the size of the dispersed phase, so that the nanofibers are evenly distributed in the collagen matrix, thereby enhancing the mechanical properties and structural stability of the composite membrane.

[0128] In one embodiment of the present invention, preferably, step 3) of casting the film includes the following steps:

[0129] The mixture obtained in step 2) is filtered through an 80-100 mesh sieve and then injected into a casting mold. The sieve mesh size can be selected as 80, 90, or 100 mesh, and the mold preheating temperature can be selected as 38℃, 40℃, or 42℃. The filtration process can use a laboratory standard sieve (such as those from Zhejiang Shangyu Huafeng Sieve Factory) in conjunction with a funnel. The casting mold can be made of PTFE material with a surface roughness Ra0.8μm~Ra1.6μm (such as those customized by Shanghai Plastics Products Factory No. 3). A constant temperature drying oven (such as Shanghai Jinghong DHG-9070A) can be used for preheating. The sieve material is stainless steel, and the PTFE mold is made of commercially available corrosion-resistant material.

[0130] The casting mold is made of polytetrafluoroethylene with a surface roughness of Ra0.8μm~Ra1.6μm, and radial guide grooves with a depth of 0.05mm~0.08mm are engraved on the working surface of the mold.

[0131] Before casting, preheat the PTFE mold to 38℃~42℃ and maintain the temperature gradient between the working surface of the mold and the air contact surface ≤2℃.

[0132] The casting environment temperature is controlled at 40℃~45℃, and the relative humidity is ≤30%. During casting, the gap between the scraper and the mold is set to 1.2 to 1.5 times the target thickness of the wet film.

[0133] The scraper is moved at a uniform speed of 0.5 m / min to 1.2 m / min during the casting process, and the surface temperature fluctuation of the liquid film is monitored in real time by an infrared thermometer, which is ≤ ±0.5℃.

[0134] After casting, the wet film is left to stand on the mold for 5 to 8 minutes to mature. During the maturation stage, the temperature is increased by 2 to 3 degrees Celsius per hour until it reaches 45 degrees Celsius. The ambient humidity during the maturation stage is divided into two stages: the humidity is maintained at 20% to 25% for the first 3 minutes, and then adjusted to 15% to 18% for the next 2 to 5 minutes.

[0135] The casting environment temperature is controlled at 40℃~45℃, and the relative humidity is ≤30%. During casting, the gap between the squeegee and the mold is set to 1.2~1.5 times the target wet film thickness. The squeegee is moved at a uniform casting speed of 0.5~1.2m / min. The ambient temperature can be selected as 40℃, 43℃, or 45℃, the relative humidity threshold is fixed at ≤30%, the squeegee gap ratio can be selected as 1.2 times, 1.3 times, or 1.5 times, and the casting speed can be selected as 0.5m / min, 0.8m / min, or 1.2m / min.

[0136] After casting, the wet film is left to stand and mature on the mold for 5-8 minutes. The standing time can be selected as 5 minutes, 6 minutes, or 8 minutes. The heating rate is fixed at 2℃~3℃ / hour, and the final temperature is fixed at 45℃. The humidity can be selected as 20%, 23%, or 25% in the first stage and 15%, 16%, or 18% in the second stage.

[0137] The filtration process removes impurities to ensure film uniformity, while preheating the mold and controlling the temperature of the casting environment reduces solution viscosity fluctuations. The doctor blade parameter control enables precise regulation of wet film thickness. The stepped curing process gradually promotes collagen molecule cross-linking and releases internal stress through temperature and humidity gradient changes, reducing film shrinkage, deformation, and surface defects, ultimately obtaining a film substrate with uniform thickness and a smooth surface.

[0138] In one embodiment of the present invention, preferably, step 5) includes the following steps:

[0139] A wet film is laid flat on a porous titanium alloy heating plate, the heating plate having a surface roughness of Ra 0.4 μm to Ra 0.6 μm, a pore diameter of 0.5 mm to 0.8 mm, and a pore spacing of 4 mm to 6 mm arranged in a hexagonal pattern;

[0140] Initiate the three-stage gradient drying process:

[0141] The first stage involves preheating for 10 to 15 minutes at a vacuum of -0.08 MPa to -0.085 MPa and a temperature of 38°C to 42°C, while controlling the coverage of the opening area on the heating plate surface to be 15% to 20%.

[0142] In the second stage, the temperature is increased from 1.5℃ / min to 2℃ / min to 50℃ to 55℃, while the vacuum level is increased to -0.095MPa to -0.1MPa. The vacuum pump inlet valve is switched every 5 minutes (open for 3 minutes / closed for 2 minutes) to maintain the vapor pressure gradient on the membrane surface at 120Pa / m to 150Pa / m.

[0143] In the third stage, when the moisture content drops to 10%, the temperature is lowered to 48℃ to 50℃ while maintaining a vacuum of -0.09MPa to -0.095MPa until the online moisture meter detects a moisture content of ≤8%±0.3%. In the first stage, the vacuum level can be selected as -0.08MPa, -0.083MPa, or -0.085MPa; the temperature can be selected as 38℃, 40℃, or 42℃; and the time can be selected as 10 minutes, 12 minutes, or 15 minutes. In the second stage, the heating rate can be selected as 1.5℃ / min or 1.8℃ / min. The speed is 2℃ / min, the target temperature can be selected as 50℃, 53℃, or 55℃, the vacuum degree can be selected as -0.095MPa, -0.098MPa, or -0.1MPa, and the vapor pressure gradient can be selected as 120Pa / m, 135Pa / m, or 150Pa / m; the third-stage cooling temperature can be selected as 48℃, 49℃, or 50℃, the vacuum degree can be selected as -0.09MPa, -0.093MPa, or -0.095MPa, and the water content threshold is fixed at ≤8%±0.3%.

[0144] A 5mm to 8mm thermal insulation gap is provided between the porous titanium alloy heating plate and the inner wall of the vacuum chamber, ensuring that the temperature of the chamber's cold wall is always 2°C to 3°C higher than the dew point temperature. The thermal insulation gap can be selected as 5mm, 6mm, or 8mm, and the cold wall temperature can be selected as 2°C, 2.5°C, or 3°C higher than the dew point temperature.

[0145] The porous titanium alloy heating plate promotes the evaporation of moisture at the bottom of the membrane material through its open structure. The gradient drying process guides the moisture to migrate evenly from the inside to the outside by controlling the vacuum and temperature in stages, avoiding uneven shrinkage of the membrane material caused by local overheating. The insulation gap and cold wall temperature control prevent condensate from dripping and contaminating the membrane material, while reducing heat loss and ensuring that the drying process is efficient and stable, ultimately obtaining a collagen packaging film with low internal stress and good dimensional stability.

[0146] In one embodiment of the present invention, preferably, the balancing process in step 5) includes the following steps:

[0147] After vacuum drying, the membrane material is vertically suspended in a constant temperature and humidity chamber, which is equipped with a dual-zone humidity control system.

[0148] The upper area is equipped with a dual-head ultrasonic atomizer, and the lower area is equipped with a rotary silicone moisture-absorbing device; the ultrasonic atomizer power can be selected as 300W or 400W, and the silicone moisture-absorbing device filling amount can be configured according to 10%-15% of the box volume (such as 5kg or 8kg).

[0149] Implement three-stage balance control:

[0150] For the first 6 hours, maintain a temperature of 23℃~24℃ and a relative humidity of 70%~72%, and reduce the humidity by 2%~3% per hour. Introduce directional airflow at 0.3~0.5m / s along the membrane surface. The temperature can be selected as 23℃, 23.5℃, or 24℃, the initial humidity can be selected as 70%, 71%, or 72%, the hourly humidity reduction can be selected as 2%, 2.5%, or 3%, and the airflow speed can be selected as 0.3m / s, 0.4m / s, or 0.5m / s.

[0151] During the middle 12 hours, the temperature is adjusted to 24.5℃~25℃ and the relative humidity to 62%~65%. The moisture absorption wheel is rotated 15°~20° every 2 hours, and the membrane material weight change rate is ≤0.1g / (m²·h).

[0152] After 4 to 8 hours, the temperature was stabilized at 25℃ and the relative humidity at 60% to 61%. Every 30 minutes, the moisture content difference between the edge and center of the membrane was detected by near-infrared scanning and was ≤0.5%.

[0153] The intermediate stage temperature can be selected as 24.5℃, 24.8℃, or 25℃, the humidity can be selected as 62%, 63%, or 65%, and the rotation angle of the moisture absorption wheel can be selected as 15°, 18°, or 20°; the final stage time can be selected as 4 hours, 6 hours, or 8 hours, and the moisture content difference threshold is fixed at ≤0.5%.

[0154] The dual-zone humidity control system precisely regulates the humidity gradient at different stages through a dynamic balance between atomized humidification and silica gel moisture absorption; three-stage temperature and airflow control promotes uniform diffusion of moisture inside the membrane material, avoiding excessive differences in moisture content between the edges and the center; timed rotating moisture-absorbing wheels and real-time weight monitoring ensure a stable moisture migration rate, ultimately improving the dimensional stability and environmental adaptability of the membrane material, providing performance assurance for subsequent practical applications.

[0155] In one embodiment of the present invention, preferably, the addition and stirring of genipin in step 2) is carried out in the following manner:

[0156] Genipin is added to the collagen solution at a uniform rate of 0.4% to 0.6% of the dry weight of the collagen per minute. The genipin is dissolved in an aqueous ethanol solution with a volume fraction of 40% to 45% to form an additive solution with a mass concentration of 10% to 12%. The addition rate can be selected as 0.4% / minute, 0.5% / minute, or 0.6% / minute, the ethanol volume fraction can be selected as 40%, 42%, or 45%, and the genipin mass concentration can be selected as 10%, 11%, or 12%.

[0157] During the addition process, the solution conductivity is monitored in real time by an online conductivity meter to control the fluctuation range to ≤5μS / cm. When the conductivity deviation exceeds the threshold, the addition rate is automatically adjusted to compensate.

[0158] After adding the additive, stir continuously at 250~280 rpm for 35~40 minutes, keeping the linear velocity of the stirring blade constant in the range of 1.5~1.7 m / s. The stirring speed can be selected as 250 rpm, 260 rpm, or 280 rpm, the stirring time can be selected as 35 minutes, 38 minutes, or 40 minutes, the linear velocity can be selected as 1.5 m / s, 1.6 m / s, or 1.7 m / s, and the conductivity fluctuation threshold is fixed at ≤5 μS / cm.

[0159] After mixing, let it stand for 8 to 10 minutes, during which time pulse mixing at 80 to 100 rpm for 5 to 8 seconds every 2 minutes.

[0160] Then, cellulose nanocrystals were added in equal amounts in three separate batches.

[0161] The settling time can be selected as 8 minutes, 9 minutes, or 10 minutes; the pulse stirring speed can be selected as 80 rpm, 90 rpm, or 100 rpm; the single pulse duration can be selected as 5 seconds, 6 seconds, or 8 seconds; and the number of additions is fixed at three, with an interval of 2-3 minutes between each addition.

[0162] Genipin is added at a uniform rate and its conductivity is adjusted in real time to avoid uneven cross-linking caused by local overconcentration. Pulsed stirring breaks the diffusion layer during the static stage, promoting full contact between unreacted genipin and collagen molecules, while preventing precipitation of cellulose nanofibers due to prolonged static standing. Staged stirring control ensures a uniform cross-linking reaction rate, improves cross-linking efficiency and material performance consistency, and lays the foundation for the uniform dispersion of nanofibers in the future.

[0163] The present invention also provides the application of collagen packaging film obtained by any of the preparation methods in the preservation of chilled meat.

[0164] To enable those skilled in the art to better understand the technical solution of the present invention, the following embodiments are provided for further illustration:

[0165] Example 1

[0166] A method for preparing a collagen packaging film, comprising:

[0167] Animal-derived collagen freeze-dried powder was mixed with deionized water at a mass ratio of 1:8 to form a suspension. The suspension was frozen at -20°C for 16 hours, then thawed in a 25°C water bath. This freeze-thaw cycle was repeated three times. After freezing and thawing, the suspension was pre-frozen at -50°C, then freeze-dried in a cold trap at -80°C under a vacuum of 10 Pa for 24 hours to obtain freeze-dried powder with fiber bundle diameters of 10–20 μm and a free amino content of 0.30 mmol / g. The freeze-dried powder was activated for 8 minutes in a vibrating sieve with an amplitude of 2 mm and a frequency of 25 Hz. After removing aggregates larger than 200 μm, a nitrogen-protected acetic acid solution (pH 3.5) at 4°C was added at a rate of 10 g / min, while simultaneously applying 30 kHz focused ultrasound to generate cavitation bubbles with a diameter of 10 cm. After stirring at 8℃ to form a 1.5% primary dispersion, the temperature was increased to 28℃ at 1℃ / min, 0.1% sodium pyrophosphate was added, and the anchor-type stirring paddle (linear speed 1.0m / s) was switched to form a 3.2% solution. Finally, acetic acid was added in three portions at 37℃ and 15000rpm to a final concentration of 4.8%. Dynamic light scattering monitoring showed D90=320nm, and the solution was then filtered through a 50μm nylon membrane for cross-flow filtration.

[0168] The collagen solution was heated to 38°C, and 20% genipin (dissolved in 42% ethanol) was added at a rate of 0.5% / min, with conductivity fluctuations ≤3μS / cm. The mixture was stirred at 250 rpm (blade tip linear velocity 1.6 m / s) for 35 minutes. Subsequently, 10% cellulose nanocrystals (diameter 30 nm, length 1000 nm, carboxyl content 1.4 mmol / g, dispersed in acetic acid at pH 3.8 and ultrasonically treated for 12 minutes) were added in three batches, and the reaction was continued for 4 hours at 120 rpm. The mixture was then injected into a 1.2 μm Ra PTFE mold (drainage groove depth 0.06 mm), preheated to 40°C, and a 0.2 mm wet film was cast at a speed of 0.8 m / min. During the curing stage, the humidity was 24% for the first 3 minutes and 17% for the last 5 minutes.

[0169] The wet membrane was laid flat on a titanium alloy heating plate with a pore size of 0.6 mm and subjected to three-stage vacuum drying (preheating at -0.085 MPa / 40℃ for 12 minutes → gradient heating at -0.1 MPa / 53℃ → final drying at -0.093 MPa / 50℃) until the moisture content was 7.5%. After drying, the membrane was suspended in a constant humidity chamber with 70% humidity / 0.4 m / s airflow for the first 6 hours, 64% humidity for the middle 12 hours with the moisture absorption wheel rotating 18° every 2 hours, and 60% humidity for the last 6 hours. Near-infrared monitoring showed a moisture content difference of ≤0.3%. Finally, the membrane was immersed in a 1.0% propyl gallate solution in 75% ethanol for 45 minutes, and then equilibrated for 24 hours to obtain the finished product.

[0170] This embodiment preserves the triple helix structure of collagen through freeze-thaw cycles and gradient dissolution, providing sufficient active sites for subsequent cross-linking. Genipin and cellulose nanocrystals are added in stages to form a covalent-hydrogen bond dual network, synergistically enhancing mechanical strength. Propyl gallate binds to the hydrophobic regions of collagen through phenolic hydroxyl groups to construct a surface hydrophobic layer. The casting and guiding groove design combined with gradient drying eliminates internal stress, giving the membrane material high mechanical strength (tensile strength > 45 MPa), moderate hydrophobicity (contact angle > 85°), and controllable degradation (degradation rate > 90% after 180 days). The various process parameters are systematically optimized to form a positive coupling effect, breaking through the performance bottleneck of traditional collagen membranes.

[0171] Example 2: Application of collagen membrane in the preservation of chilled mutton

[0172] 1. Sample preparation

[0173] Take freshly slaughtered mutton hind leg meat (pH 5.8-6.2), cut it into 100g±2g pieces, and wipe the surface dry of blood;

[0174] Experimental group: The meat pieces were completely wrapped with the collagen membrane (0.2 mm thick, 88° contact angle) prepared in Example 1 to form a sealed package;

[0175] Control group: Conventional packaging using commercially available PE cling film (0.02mm thickness);

[0176] All samples were stored in a cold storage at 4℃±0.5℃ with a relative humidity of 85%±3%.

[0177] 2. Preservation parameter detection

[0178] Total bacterial count: Samples were taken every 5 days and determined according to GB 4789.2-2016;

[0179] Volatile basic nitrogen (TVB-N): Tested according to GB 5009.228-2016;

[0180] Juice loss rate: calculated by weighing method (weight difference before and after storage / initial weight × 100%).

[0181] Sensory evaluation: The evaluation is conducted by a professional panel of 10 people based on three criteria: color, smell, and elasticity (out of 9 points).

[0182] The results are shown in Table 1: Table 1

[0183] detection indicators Storage time (days) experimental group control group Total bacterial count 5 <![CDATA[3.2×10 4 CFU / g]]> <![CDATA[1.5×10 5 CFU / g]]> Total bacterial count 10 <![CDATA[8.7×10 4 CFU / g]]> <![CDATA[3.8×10 7 CFU / g]]> TVB-N value 5 12.3 mg / 100g 18.6 mg / 100g TVB-N value 10 18.9 mg / 100g 35.2 mg / 100g Juice loss rate 10 3.8% 9.5% Sensory rating 10 8.5 points (elasticity remains >80%) 4.2 points (Slippery surface)

[0184] In this embodiment, propyl gallate in the membrane material releases phenolic hydroxyl groups, which disrupts the integrity of microbial cell membranes and prolongs the proliferation delay period of putrefactive bacteria such as Escherichia coli by 48 hours.

[0185] The membrane in this embodiment has low oxygen permeability (OTR < 10 cm). 3 m 2 (day) inhibited lipid oxidation, and malondialdehyde content decreased by 65% ​​compared with the control group;

[0186] In this embodiment, the moisturizing properties of collagen work synergistically with the nanofiber network to increase the water-holding capacity of muscle cells by 40% and reduce fluid loss.

[0187] In this embodiment, the gas selective permeability is: CO2 permeability (5000-6000 cm⁻¹). 3 / m 2 • day) Promotes spontaneous modified atmosphere in meat products and inhibits the growth of anaerobic bacteria.

[0188] During the 15-day storage period, the mutton in the experimental group maintained its bright red color (α value > 14), produced no putrid odor, and the total bacterial count remained below 10. 5 CFU / g (national standard safety limit), extending shelf life by 7-9 days compared to traditional PE films. The film material is completely biodegradable after fulfilling its preservation function (weight loss rate >95% after 30 days of soil burial), with no risk of microplastic residue.

[0189] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the embodiments of the present invention. Other modifications can be readily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the embodiments of the present invention are not limited to the specific details.

Claims

1. A method for preparing a collagen packaging film, characterized in that, Includes the following steps: 1) Dissolve animal-derived collagen in an acetic acid solution with a pH of 3.5-4.5 to form a collagen solution with a mass concentration of 3%-5%; 2) Add 15%~25% genipin and 8%~12% cellulose nanocrystals, accounting for 15%~25% of the dry weight of collagen, to the collagen solution in sequence, and stir and react at 35℃~40℃ for several hours to obtain a mixture. The preparation method of the mixture in step 2) includes: Heat the collagen solution to 35℃~40℃ and maintain a constant temperature; Genipin is added to the collagen solution at a uniform rate. The amount of genipin added is 15% to 25% of the dry weight of the collagen. During the addition, the conductivity of the solution is controlled to fluctuate within ≤5 μS / cm. Stir continuously at 200 rpm to 300 rpm for 30 to 40 minutes, keeping the linear velocity of the stirring blade tip in the range of 1.2 to 1.8 m / s; Within 10 minutes of adding genipin, add equal amounts of cellulose nanocrystal dispersion to the system in three separate additions, with an interval of 2 to 3 minutes between each addition. Adjust the stirring speed to 100~150 rpm, maintain the blade tip linear velocity at 0.6~0.9 m / s, and continue the reaction for 3.5~4.5 hours to obtain the mixture. 3) The mixture is cast into a film at 40℃~45℃ to obtain a film material; 4) Immerse the obtained membrane material in an ethanol aqueous solution containing 0.5%~1.5% (by mass) propyl gallate for 30~60 minutes, wherein the volume concentration of the ethanol aqueous solution is 70%~80%; 5) After the membrane material is removed and vacuum dried, it is equilibrated in an environment with a relative humidity of 60%~70% for 24 hours to obtain the collagen packaging film; Step 2) further includes the following step: take a 36% acetic acid mother liquor and dilute it with deionized water to a pH of 3.5-4.5; Cellulose nanocrystals were added to an acetic acid solution with a pH of 3.5-4.5 at a mass-to-volume ratio of 0.8%-1.2%, and then sonicated at a frequency of 40kHz and a power of 300W for 10-15 minutes. After that, the undispersed particles were removed by centrifugation at 2000rpm for 5 minutes to obtain a cellulose nanocrystal dispersion. Both the cellulose nanocrystal dispersion and the collagen solution were placed in a constant temperature water bath at 35℃~40℃ for a period of time. In the constant temperature water bath, ultrasonic oscillation was started once every 5~6 minutes, with an ultrasonic frequency of 40kHz, an ultrasonic power density of 0.5~0.8W / mL, and a single treatment time of 10 seconds~15 seconds. After constant temperature water bath treatment, the cellulose nanofiber dispersion is emulsified at 1200~1500 rpm for 2~3 minutes.

2. The method for preparing the collagen packaging film as described in claim 1, characterized in that, A preprocessing step is included before step 1): Animal-derived collagen freeze-dried powder is mixed with deionized water at a mass ratio of 1:8 to 1:12 to form a suspension. The suspension is placed in an environment of -20℃ to -18℃ and frozen for 12 to 16 hours. Then it is transferred to a water bath of 25℃ to 30℃ to thaw completely, completing a single freeze-thaw cycle. The freeze-thaw cycle is repeated 3 to 5 times. The freeze-thawed suspension is then freeze-dried again to obtain freeze-dried powder. The freeze-drying conditions are as follows: pre-freezing temperature -50℃ to -45℃, cold trap temperature -80℃ to -75℃, vacuum degree 10 to 15 Pa, and drying time 20 to 24 hours.

3. The method for preparing the collagen packaging film as described in claim 2, characterized in that, Step 1), the method of dissolving animal-derived collagen in an acetic acid solution with a pH of 3.5-4.5 includes: a) Pre-dispersion activation: Activate the freeze-dried collagen powder after freeze-thaw treatment for 5-8 minutes, with a sieve aperture of 150-200μm; b) Low-temperature wetting: The activated powder is evenly sprinkled into an acetic acid solution at 4℃-6℃ at a rate of 10~15g / min. The acetic acid solution is pre-purified with nitrogen to make the dissolved oxygen content ≤1.5ppm. During the powder sprinkling process, ultrasonic waves with a frequency of 28~32kHz and a power density of 0.3~0.5W / mL are applied simultaneously. c) Gradient dissolution control: First stage: Maintain the solution temperature at 8℃~10℃ and stir at 50~80 rpm for 15~20 minutes to form a primary dispersion system with a mass concentration of 1%~2%; Second stage: Increase the temperature to 25℃~28℃ at a rate of 1℃ / min, add sodium pyrophosphate at 0.05%~0.1% of the collagen mass, and continue stirring until the mass concentration reaches 3%~3.5%; Third stage: Start the high shear disperser at 35℃~37℃, with a rotation speed of 12000~15000rpm and a linear velocity of 18m / s-22m / s. Add the remaining acetic acid solution in three portions, with an interval of 2~3 minutes between each addition.

4. The method for preparing the collagen packaging film as described in claim 1, characterized in that, Step 3) involves casting the film, which includes the following steps: The mixture obtained in step 2) is filtered through an 80-100 mesh sieve and then injected into a casting mold; Preheat the PTFE mold to 38℃~42℃ before casting; The casting environment temperature is controlled at 40℃~45℃, and the relative humidity is ≤30%. During casting, the gap between the scraper and the mold is set to 1.2~1.5 times the target thickness of the wet film. The scraper is moved at a constant speed of 0.5~1.2m / min. After casting, the wet film is left to stand on the mold for 5-8 minutes to mature. During the maturation stage, the temperature is increased by 2-3°C per hour until it reaches 45°C. The ambient humidity during the maturation stage is divided into two stages: the humidity is maintained at 20%-25% for the first 3 minutes, and then adjusted to 15%-18% for the next 2-5 minutes.

5. The method for preparing the collagen packaging film as described in claim 1, characterized in that, In step 5), the vacuum drying includes the following steps: The wet film is laid flat on the porous titanium alloy heating plate. Initiate the three-stage gradient drying process: In the first stage, preheating is carried out at a vacuum of -0.08MPa to -0.085MPa and a temperature of 38℃ to 42℃ for 10 to 15 minutes, while controlling the coverage of the opening area on the surface of the heating plate to be 15% to 20%. In the second stage, the temperature is increased to 50℃~55℃ at a rate of 1.5~2℃ / min, and the vacuum level is simultaneously increased to -0.095MPa~-0.1MPa. The vacuum pump inlet valve is switched every 5 minutes. In the third stage, when the moisture content drops to 10%, the temperature is lowered to 48℃ to 50℃ and a vacuum of -0.09 to -0.095 MPa is maintained until the moisture content is ≤8%±0.3% as detected by the online moisture meter.

6. The method for preparing the collagen packaging film as described in claim 1, characterized in that, Step 5) involves the following balancing steps: After vacuum drying, the membrane material is vertically suspended in a constant temperature and humidity chamber, which is equipped with a dual-zone humidity control system. The upper area is equipped with a dual-head ultrasonic atomizer, and the lower area is equipped with a rotary silicone moisture-absorbing device. Implement three-stage balance control: For the first 6 hours, maintain a temperature of 23℃~24℃ and a relative humidity of 70%~72%, then reduce the humidity by 2%~3% every hour, and introduce a directional airflow of 0.3~0.5m / s along the membrane surface. During the middle 12 hours, the temperature is adjusted to 24.5℃~25℃ and the relative humidity to 62%~65%. The moisture absorption wheel is rotated 15°~20° every 2 hours, and the membrane material weight change rate is ≤0.1g / (m²·h). The temperature stabilized at 25°C and relative humidity at 60% to 61% for the next 4 to 8 hours.

7. The method for preparing the collagen packaging film as described in claim 3, characterized in that, Step 2) The addition and mixing of genipin shall be carried out as follows: Genipin is added to the collagen solution at a uniform rate of 0.4% to 0.6% of the dry weight of the collagen per minute. The genipin is prepared by dissolving it in an aqueous ethanol solution with a volume fraction of 40% to 45% to form an additive solution with a mass concentration of 10% to 12%. During the addition process, the solution conductivity is monitored in real time by an online conductivity meter to control the fluctuation range to ≤5μS / cm. When the conductivity deviation exceeds the threshold, the addition rate is automatically adjusted to compensate. After adding, stir continuously at 250~280 rpm for 35~40 minutes, keeping the linear velocity of the stirring blade tip constant in the range of 1.5~1.7 m / s; After mixing, let it stand for 8 to 10 minutes, during which time it will pulse-stir at 80 to 100 rpm for 5 to 8 seconds every 2 minutes. Then, cellulose nanocrystals were added in equal amounts in three separate batches.

8. The application of the collagen packaging film obtained by any one of the preparation methods of claims 1 to 7 in the preservation of chilled meat.