A bio-based active packaging film with fresh-keeping and volatile flavor regulating functions, and a preparation method and application thereof

Abstract

The application discloses a kind of biological base active packaging film with fresh-keeping and volatile flavor control function and its preparation method and application, belong to food packaging material technical field.The biological base particle / protein co-stable Pickering emulsion is constructed, natural volatile active oil phase is embedded, then the emulsion is introduced into protein film-forming system, and film is prepared by mixing, defoaming, casting, drying.The biological base particle of the application synchronously stabilizes emulsion interface, enhances protein film network, effectively solves the defect that volatile active oil phase is directly added and easily phase separation, volatile loss;Emulsion droplet in film as active depot can long-acting release active component, give film barrier, antibacterial, antioxidant performance, both can delay fruit and vegetable, aquatic product moisture loss, oxidation and microbial spoilage, also can control food volatile flavor during storage, realize fresh-keeping and flavor synergic control, can be used for various perishable food green packaging.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials technology, specifically relating to a bio-based active packaging film with preservation and volatile flavor regulation functions, its preparation method, and its application. Background Technology

[0002] With increasingly stringent requirements for food safety and environmental protection, food packaging materials not only need to provide basic enclosure and barrier functions, but also need to slow down microbial growth, oxidative deterioration, moisture migration, and flavor degradation during food storage. While traditional petroleum-based plastic packaging materials offer good processing and barrier properties, their non-renewable source makes them difficult to degrade naturally after disposal, easily causing environmental pollution. Therefore, developing bio-based packaging materials that are renewable, environmentally friendly, and possess active preservation functions is of great significance.

[0003] Plant proteins, polysaccharides, and other natural polymers are renewable, biodegradable, and relatively safe, making them important raw materials for preparing bio-based food packaging films. Among them, plant proteins possess excellent film-forming ability, forming continuous membrane networks through intermolecular interactions. However, single-protein membranes typically suffer from strong hydrophilicity, insufficient wet stability, limited mechanical properties, and weak water vapor barrier properties, restricting their application in packaging high-moisture, easily oxidized, and perishable foods.

[0004] To impart antibacterial, antioxidant, and preservation functions to packaging films, existing technologies often incorporate natural active ingredients such as plant essential oils and terpenoids into the film-forming system. However, these active oil phases are typically highly hydrophobic, volatile, and lack stability, exhibiting poor compatibility with hydrophilic protein membrane matrices. Direct addition to the film-forming solution can easily lead to problems such as oil droplet aggregation, phase separation, migration, rapid evaporation, or burst release, thereby disrupting the uniformity and continuity of the membrane structure and reducing its mechanical properties, barrier properties, and long-term preservation effect.

[0005] Pickering emulsions, formed by the adsorption of solid particles at the oil-water interface, can achieve stable dispersion of hydrophobic active components without relying on traditional small-molecule surfactants. Preparing a natural volatile active oil phase into a Pickering emulsion helps improve its dispersion stability in a hydrophilic membrane matrix, allowing the emulsion droplets to act as reservoirs of active components within the membrane, thereby enhancing the retention and slow release of active ingredients.

[0006] However, existing bio-based active packaging films mainly focus on antibacterial, antioxidant, barrier, and mechanical property enhancement, with insufficient attention paid to the regulation of volatile flavor components during food storage. For perishable foods such as aquatic products, fruits, and vegetables, storage not only leads to deterioration in appearance, texture, and microbial spoilage, but also to a decline in flavor quality due to the production of undesirable volatile substances caused by lipid oxidation, protein degradation, and microbial metabolism. Therefore, developing a packaging film material that combines bio-based origin, active preservation, and volatile flavor regulation functions has significant application value. Summary of the Invention

[0007] The first technical problem solved by this invention is to provide a method for preparing a bio-based active packaging film with preservation and volatile flavor regulation functions. This method utilizes bio-based nanoparticles and plant proteins to stabilize a natural volatile active oil phase, allowing the hydrophobic and volatile active components to be stably dispersed in the form of Pickering emulsion droplets, thus improving its compatibility with the protein-based film matrix. The second technical problem solved by this invention is to provide a bio-based active packaging film with preservation and volatile flavor regulation functions. This bio-based active packaging film can delay moisture loss, tissue softening, oxidative deterioration, and microbial spoilage during food storage, and is suitable for active preservation packaging of aquatic products, fruits and vegetables, and other perishable foods. The third technical problem solved by this invention is to provide the application of this bio-based active packaging film in food preservation and volatile flavor regulation.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a bio-based active packaging film with preservation and volatile flavor regulation functions includes the following steps:

[0010] 1) Microcrystalline cellulose was treated with sodium hydroxide solution, washed until neutral and dried; then the alkali-treated microcrystalline cellulose was dispersed in dimethyl sulfoxide for pretreatment, filtered and washed; then hydrolyzed using a mixed acid system of hydrochloric acid, sulfuric acid and water, and after adding water to terminate the reaction, centrifugation and dialysis, a suspension of spherical cellulose nanocrystals was obtained.

[0011] 2) Dissolve soy protein isolate in water and adjust the pH to prepare an SPI solution;

[0012] 3) Mix the spherical cellulose nanocrystal suspension obtained in step 1) with the SPI solution obtained in step 2) to prepare the SCNC / SPI composite dispersion;

[0013] 4) Using the SCNC / SPI composite dispersion obtained in step 3) as the aqueous phase and limonene as the oil phase, a Pickering emulsion was prepared by shear emulsification and ultrasonic treatment.

[0014] 5) Prepare a film-forming solution for the SPI matrix, and add the SCNC suspension obtained in step 1) and the Pickering emulsion obtained in step 4) to it, and mix them to obtain a composite film-forming solution;

[0015] 6) After degassing the composite film-forming liquid obtained in step 5), the liquid is cast, dried and equilibrated to obtain a bio-based active packaging film.

[0016] Further, in step 1), the mass-to-volume ratio of the microcrystalline cellulose to the sodium hydroxide solution is 1g:5-15mL, the concentration of the sodium hydroxide solution is 3-8mol / L, the alkali treatment temperature is 60-90℃, and the treatment time is 2-5h; the dimethyl sulfoxide treatment temperature is 60-90℃, and the treatment time is 2-5h; the volume ratio of hydrochloric acid, sulfuric acid, and water in the mixed acid system is 1:2-4:5-8, the hydrolysis temperature is 50-75℃, and the hydrolysis time is 5-10h; and the dispersion is dialyzed until the pH is 5-6.

[0017] Further, in step 2), the SPI solution has a mass percentage concentration of 3-8%, a pH of 9-11, and a dissolution temperature of 35-55℃.

[0018] Further, in step 3), the mass percentage concentration of the SCNC suspension is 0.5-2%, and the mass ratio of SCNC to SPI is 3:1 to 1:3.

[0019] Further, in step 4), the volume fraction of limonene in the Pickering emulsion is 10-20%; the shear emulsification speed is 8000-15000 r / min, and the shear emulsification time is 1-5 min; the ultrasonic treatment power is 200-500 W, and the ultrasonic treatment time is 1-5 min.

[0020] Further, in step 5), the mass-volume percentage concentration of the film-forming solution of the SPI matrix is ​​3-8%.

[0021] Further, in step 5), in the composite film-forming solution, the amount of SCNC added in the SCNC suspension is 0.3-1.2 wt%, and the amount of Pickering emulsion added is 3-12 wt%, and the added amounts are all based on the total mass of the composite film-forming solution.

[0022] Further, in step 6), the composite film-forming liquid is degassed under vacuum for 25-30 minutes and then cast onto a polytetrafluoroethylene plate, dried at 40°C for 5 hours, and then equilibrated at 25°C and 58% relative humidity for 48 hours after peeling.

[0023] Furthermore, the bio-based active packaging film prepared by the method described above, which has the functions of preservation and volatile flavor regulation, yields a bio-based active packaging film.

[0024] Furthermore, the application of the aforementioned bio-based active packaging film in food preservation and volatile flavor control.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] (1) This invention utilizes bio-based nanoparticles and plant proteins to stabilize the natural volatile active oil phase, so that the hydrophobic and volatile active components are stably dispersed in the form of Pickering emulsion droplets, which improves the compatibility between them and the protein base membrane matrix and reduces phase separation, migration, rapid volatilization and burst release problems.

[0027] (2) The Pickering emulsion microdroplets in this invention serve as a reservoir of active components in the membrane, which is beneficial for the retention and continuous release of the natural volatile active oil phase, thereby enabling the packaging film to continuously exert its antibacterial, antioxidant and preservation effects.

[0028] (3) The bio-based active packaging film obtained by the present invention can delay moisture loss, tissue softening, oxidative deterioration and microbial spoilage during food storage, and is suitable for active preservation packaging of aquatic products, fruits and vegetables and other perishable foods.

[0029] (4) This invention utilizes the aroma properties and slow release characteristics of natural volatile active oil phases to enable the packaging film to participate in the regulation of volatile flavor composition during food storage, thereby achieving the integration of food preservation and volatile flavor regulation. Attached Figure Description

[0030] Figure 1 These are optical microscope images of limonene Pickering emulsions prepared by aqueous phase with different SCNC and SPI ratios at different storage times in this application.

[0031] Figure 2 This is a particle size distribution diagram of limonene Pickering emulsions prepared by aqueous phase with different SCNC and SPI ratios in this application.

[0032] Figure 3 This is a low-temperature scanning electron microscope image of the SCNC / SPI co-stabilized limonene Pickering emulsion of this application;

[0033] Figure 4 Tensile stress-strain curves of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application;

[0034] Figure 5 The ultraviolet-visible transmittance diagrams are for the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application.

[0035] Figure 6The water vapor transmission rate diagrams are for the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application.

[0036] Figure 7 The water contact angle diagrams are for the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application.

[0037] Figure 8 These are photographs and atomic force microscope images of the cross-sectional morphology, surface morphology, appearance, and packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application.

[0038] Figure 9 The diagram shows the antibacterial properties of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application against Escherichia coli and Staphylococcus aureus.

[0039] Figure 10 The graphs show the DPPH radical scavenging rate and ABTS radical scavenging rate of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application.

[0040] Figure 11 The images show the changes in appearance of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application when used for strawberry preservation.

[0041] Figure 12 The images show the changes in appearance of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application when used for banana preservation.

[0042] Figure 13 The graph shows the changes in hardness and weight loss rate of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application during the preservation of strawberries and bananas.

[0043] Figure 14 The images show the changes in appearance of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 of this application when used for salmon preservation.

[0044] Figure 15 Clustering heatmaps of volatile flavor compounds in the blank group of this application and the salmon samples treated in Example 1 during storage;

[0045] Figure 16 The VIP values ​​and relative abundance heatmaps of key volatile flavor compounds in the blank group and the salmon samples treated in Example 1 during storage are shown. Detailed Implementation

[0046] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0047] The method for preparing a bio-based active packaging film with preservation and volatile flavor regulation functions in this application includes the preparation of SCNC suspension, the preparation of SCNC / SPI co-stabilized limonene Pickering emulsion, the preparation of film matrix forming solution, the preparation of mixed film forming solution, and film formation by casting. In the Pickering emulsion, the aqueous phase is formed by the composite of SCNC and SPI, and the oil phase is limonene; the film matrix forming solution is a film forming solution of SPI matrix; the SCNC suspension, limonene Pickering emulsion, and film matrix forming solution are mixed in a certain proportion to obtain a mixed film forming solution, and finally, the bio-based active packaging film is obtained by casting.

[0048] The SPI powder used in these embodiments of the invention is soy protein isolate, purchased from Yuan Ye Company, specification BR; the microcrystalline cellulose used is purchased from Shanghai Testing, specification column chromatography grade, conforming to FCC standards. Unless otherwise specified, all other reagents used in these embodiments of the invention are conventional commercially available products.

[0049] In the following examples, the preparation process of the SCNC suspension is as follows:

[0050] (1) Weigh 30g of microcrystalline cellulose and add it to 250mL of 5mol / L sodium hydroxide solution, and treat it at 80℃ for 3h. After treatment, wash the obtained sample with deionized water until neutral and dry it.

[0051] (2) Disperse the dried sample in 250 mL of dimethyl sulfoxide and treat it in a water bath at 80 °C for 3 h. After treatment, filter and wash with deionized water.

[0052] (3) The pretreated sample was subjected to mixed acid hydrolysis treatment. The mixed acid was prepared by hydrochloric acid, sulfuric acid and deionized water in a volume ratio of 1:3:6. The volume mass ratio of acid solution to microcrystalline cellulose was 25.7 mL / g. The hydrolysis temperature was 65℃ and the hydrolysis time was 8h.

[0053] (4) After hydrolysis, a large amount of deionized water was added to terminate the reaction. Then, the resulting suspension was centrifuged at 10,000 r / min at room temperature until a colloidal suspension was obtained. Finally, the resulting colloidal suspension was placed in a dialysis bag with a molecular weight cutoff of 10,000 Da for dialysis until the pH of the dispersion was 5-6, thus obtaining the SCNC suspension.

[0054] The preparation process of SCNC / SPI co-stabilized limonene Pickering emulsion is as follows:

[0055] (1) Weigh SPI powder and disperse it in deionized water to prepare an SPI solution with a mass percentage concentration of 5%, and adjust the pH to 10. Stir the solution at 45℃ and 600r / min until the SPI is completely dissolved.

[0056] (2) Dilute the SCNC suspension with ultrapure water to a mass percentage concentration of 1%, and mix the SCNC suspension with the SPI solution according to the mass ratio of SCNC to SPI of 1:2. Stir at 500 r / min for 20 min to obtain the SCNC / SPI composite dispersion.

[0057] (3) Using SCNC / SPI composite dispersion as the aqueous phase and limonene as the oil phase, the volume fraction of limonene was controlled to be 15%. Limonene was slowly added dropwise to the composite dispersion, and then homogenized for 2 min at 12000 r / min using a high-speed shear emulsifier to obtain a crude emulsion.

[0058] (4) The mixture was then ultrasonically treated at 300W for 3 minutes using an ultrasonic cell disruptor to obtain SCNC / SPI co-stabilized limonene Pickering emulsion.

[0059] Example 1

[0060] A method for preparing a bio-based active packaging film with preservation and volatile flavor regulation functions includes the following steps:

[0061] 1) Preparation of membrane matrix film-forming solution: Weigh SPI powder and dissolve it in deionized water to prepare an SPI film-forming solution with a mass-volume percentage concentration of 5.0%, and fully hydrate it to obtain the SPI matrix film-forming solution.

[0062] 2) Preparation of SCNC composite film-forming solution: Add SCNC suspension to the film-forming solution of SPI matrix obtained in step 1), so that the amount of SCNC added is 0.75 wt% of the total mass of the mixed film-forming solution, and stir to mix evenly.

[0063] 3) Preparation of mixed film-forming solution: Slowly add SCNC / SPI co-stabilized limonene Pickering emulsion to the film-forming solution obtained in step 2), so that the amount of Pickering emulsion added is 5 wt% of the total mass of the mixed film-forming solution, and add deionized water to keep the total mass of the mixed film-forming solution consistent.

[0064] 4) Mixing uniformly: Stir the mixture obtained in step 3) at 45℃ and 400-600r / min for 5-10min to obtain the mixed film-forming liquid.

[0065] 5) Degassing: Vacuum degas the mixed film-forming solution obtained in step 4) for 25-30 minutes.

[0066] 6) Film preparation: Take about 10g of the mixed film-forming solution obtained in step 5) and pour it into a polytetrafluoroethylene plate using the casting method. Place it in a 40℃ hot air circulating oven to dry for 5 hours. Then peel off the film and equilibrate it for 48 hours at 25℃ and 58% relative humidity to obtain a bio-based active packaging film.

[0067] Example 2

[0068] The difference from Example 1 is that in step 3), the amount of SCNC / SPI co-stabilized limonene Pickering emulsion added is adjusted to 10 wt% of the total mass of the mixed film-forming solution to obtain a bio-based active packaging film.

[0069] Comparative Example 1

[0070] A method for preparing an SPI-based packaging film includes the following steps:

[0071] 1) Preparation of membrane matrix film-forming solution: Weigh SPI powder and dissolve it in deionized water to prepare an SPI film-forming solution with a mass-volume percentage concentration of 5.0%, and fully hydrate it to obtain the SPI matrix film-forming solution.

[0072] 2) Degassing: Vacuum degas the film-forming solution obtained in step 1) for 25-30 minutes.

[0073] 3) Film preparation: Take about 10g of the film-forming solution obtained in step 2) and pour it into a polytetrafluoroethylene plate using the casting method. Place it in a 40℃ hot air circulating oven to dry for 5 hours. Then peel off the film and equilibrate it for 48 hours at 25℃ and 58% relative humidity to obtain the SPI-based packaging film.

[0074] Comparative Example 2

[0075] A method for preparing an SPI-based packaging film with added SCNC, comprising the following steps:

[0076] 1) Preparation of membrane matrix film-forming solution: Weigh SPI powder and dissolve it in deionized water to prepare an SPI film-forming solution with a mass-volume percentage concentration of 5.0%, and fully hydrate it to obtain the SPI matrix film-forming solution.

[0077] 2) Preparation of film-forming solution: Add SCNC suspension to the film-forming solution of SPI matrix obtained in step 1), so that the amount of SCNC added is 0.75 wt% of the total mass of the film-forming solution, and stir to mix evenly.

[0078] 3) Degassing: Vacuum degas the film-forming solution obtained in step 2) for 25-30 minutes.

[0079] 4) Film preparation: Take about 10g of the film-forming solution obtained in step 3) and pour it into a polytetrafluoroethylene plate using the casting method. Place it in a 40℃ hot air circulating oven to dry for 5 hours. Then peel off the film and equilibrate it for 48 hours at 25℃ and 58% relative humidity to obtain the SPI-based packaging film with added SCNC.

[0080] Comparative Example 3

[0081] A method for preparing an SPI-based active packaging film with added limonene Pickering emulsion includes the following steps:

[0082] 1) Preparation of membrane matrix film-forming solution: Weigh SPI powder and dissolve it in deionized water to prepare an SPI film-forming solution with a mass-volume percentage concentration of 5.0%, and fully hydrate it to obtain the SPI matrix film-forming solution.

[0083] 2) Preparation of mixed film-forming solution: Slowly add SCNC / SPI co-stabilized limonene Pickering emulsion to the film-forming solution of the SPI matrix obtained in step 1), so that the amount of Pickering emulsion added is 5 wt% of the total mass of the film-forming solution, and add deionized water to keep the total mass of the film-forming solution consistent.

[0084] 3) Mixing evenly: Stir the mixture obtained in step 2) at 45℃ and 400-600r / min for 5-10min to obtain the mixed film-forming liquid.

[0085] 4) Degassing: Vacuum degas the mixed film-forming solution obtained in step 3) for 25-30 minutes.

[0086] 5) Film preparation: Take about 10g of the mixed film-forming liquid obtained in step 4) and pour it into a polytetrafluoroethylene plate by casting. Place it in a 40℃ hot air circulating oven to dry for 5h. Then peel off the film and equilibrate it for 48h at 25℃ and 58% relative humidity to obtain the SPI-based active packaging film with added limonene Pickering emulsion.

[0087] The packaging films prepared in Examples 1-2 and Comparative Examples 1-3 were subjected to performance tests.

[0088] In the following performance tests, Comparative Example 1 corresponds to the SPI-based packaging film, Comparative Example 2 corresponds to the SPI+SCNC packaging film, Comparative Example 3 corresponds to the SPI+EM-M packaging film, Example 1 corresponds to the SPI+SCNC+EM-M bio-based active packaging film, and Example 2 corresponds to the SPI+SCNC+EM-H bio-based active packaging film. Here, EM-M indicates a Pickering emulsion addition of 5 wt%, and EM-H indicates a Pickering emulsion addition of 10 wt%.

[0089] 1. Optical microscopic observation of limonene Pickering emulsion

[0090] The optical microscopy observation procedure for limonene Pickering emulsions was as follows: Limonene Pickering emulsions with SCNC and SPI ratios of 3:1, 2:1, 1:1, 1:2, and 1:3 were prepared. Samples of the prepared emulsions were taken after 1, 7, and 15 days of storage. Small amounts of emulsion were pipetted onto glass slides, covered with coverslips, and observed under an optical microscope. The same magnification and imaging conditions were maintained throughout the observation process. The morphology, size, dispersion state, and aggregation or co-drip phenomena of the droplets in the different emulsion samples were recorded. Results are as follows: Figure 1 As shown.

[0091] Depend on Figure 1 It was found that different SCNC to SPI ratios significantly affected the droplet morphology and storage stability of limonene Pickering emulsions. When the SCNC to SPI ratios were 3:1 and 2:1, the emulsion droplets were large and unevenly distributed; with prolonged storage, the droplets further increased in size and showed significant aggregation. At a ratio of 1:1, the droplet size decreased somewhat, but some droplet coarsening still occurred after storage. At a ratio of 1:2, the emulsion droplets were small and relatively uniformly distributed, maintaining good dispersion even after 15 days of storage. At a ratio of 1:3, the droplet size increased again, and local aggregation occurred. These results indicate that a 1:2 SCNC to SPI ratio is more conducive to the formation of stable limonene Pickering emulsions.

[0092] 2. Limonene Pickering emulsion particle size distribution test

[0093] The particle size distribution test procedure for limonene Pickering emulsions was as follows: Limonene Pickering emulsion samples prepared with different SCNC and SPI blending ratios were taken, and the droplet diameters were statistically analyzed using microscopic image analysis or particle size analysis methods. Multiple fields of view were randomly selected for each sample, and the droplet diameters were measured. The proportion of droplets within different particle size ranges was statistically analyzed, and the mean particle size and standard deviation were calculated. The results are as follows: Figure 2 As shown.

[0094] Depend on Figure 2It was found that the particle size distribution of the limonene Pickering emulsion changed significantly with the change in the SCNC to SPI blending ratio. At a blending ratio of 3:1, the average particle size was 19.19 ± 5.07 μm; at 2:1, it was 12.78 ± 2.30 μm; at 1:1, it was 9.12 ± 2.32 μm; at 1:2, the average particle size decreased to 3.07 ± 0.83 μm; and at 1:3, it increased to 6.56 ± 1.56 μm. The results indicate that the emulsion droplet size was smallest and the distribution was most concentrated when SCNC and SPI were blended at a 1:2 ratio, suggesting that this ratio allows for more effective synergistic stabilization of the limonene oil phase.

[0095] 3. Low-temperature scanning electron microscopy observation of limonene Pickering emulsion

[0096] The cryogenic scanning electron microscopy (CEM) observation process of limonene Pickering emulsion was as follows: A limonene Pickering emulsion sample prepared by mixing SCNC and SPI at a ratio of 1:2 was subjected to rapid cryo-fixation to stabilize the emulsion's microstructure. Subsequently, fracture and surface treatment were performed at low temperature, followed by gold sputtering. The treated sample was then observed under a cryogenic scanning electron microscope, and the surface morphology of the emulsion droplets, the interface coverage, and the continuous phase network structure around the droplets were recorded. The results are as follows: Figure 3 As shown.

[0097] Depend on Figure 3 It can be seen that the droplets in the SCNC / SPI co-stabilized limonene Pickering emulsion maintain a relatively complete spherical morphology, and a relatively continuous covering structure can be observed on the droplet surface. In the magnified local images, granular covering features and a network-like support structure around the droplets are visible. These results indicate that SCNC and SPI jointly participate in the construction of the oil-water interface layer and form a certain spatial support network in the continuous phase, thereby limiting droplet migration and aggregation and improving emulsion stability.

[0098] 4. Mechanical performance testing

[0099] The mechanical property testing process was as follows: Tensile properties were tested on the packaging films prepared in Examples 1-2 and Comparative Examples 1-3. Before testing, the film samples were equilibrated under constant temperature and humidity conditions, and then cut into strips of uniform size, ensuring smooth edges and no obvious gaps or cracks. A universal testing machine was used for tensile testing. The samples were vertically fixed between upper and lower clamps, ensuring the sample centerline was aligned with the tensile direction. After setting the initial clamping distance and tensile speed, the test began, and the stress-strain changes during the tensile process were recorded until the sample broke. Each group of samples was tested at least three times, and the average value was used for analysis. The results are as follows: Figure 4 As shown.

[0100] Depend on Figure 4 It can be seen that the pure SPI membrane prepared in Comparative Example 1 has certain film-forming properties, but its tensile strength is low. In Comparative Example 2, the addition of SCNC significantly improved the tensile strength of the packaging membrane, indicating that SCNC can act as a rigid reinforcing phase to improve the load-bearing capacity of the protein membrane network. In Comparative Example 3, the addition of only limonene Pickering emulsion increased the membrane's tensile strain, indicating that emulsion droplets can act as a flexible dispersed phase to improve the membrane's extensibility. In Example 1, the simultaneous addition of SCNC and an appropriate amount of limonene Pickering emulsion resulted in the highest tensile strength of the membrane while maintaining good deformability, indicating that the reinforcing effect of SCNC and the flexible regulation effect of emulsion droplets can synergistically improve the membrane's mechanical properties. In Example 2, further increasing the emulsion addition improved the membrane's extensibility, but decreased its tensile strength, indicating that excessive emulsion can cause some disturbance to the continuous membrane network.

[0101] 5. Ultraviolet-Visible Light Transmittance Test

[0102] The UV-Vis transmittance testing procedure was as follows: The packaging films prepared in Examples 1-2 and Comparative Examples 1-3 were cut to suitable test sizes, ensuring the film sample surface was flat and free of obvious creases and damage. The transmittance of the film samples was tested using a UV-Vis spectrophotometer in the wavelength range of 200-800 nm, with air or blank samples used as references. The film samples were fixed in a sample holder, and the transmittance changes at different wavelengths were scanned and recorded. Each group of samples was tested at least three times, and the average value was used for analysis. The results are as follows: Figure 5 As shown.

[0103] Depend on Figure 5 It can be seen that all groups of packaging films exhibited low transmittance in the short-wave ultraviolet region, indicating that the SPI base film itself has a certain ultraviolet shielding capability. Compared with Comparative Example 1, the transmittance of the packaging films prepared in Comparative Example 2, Comparative Example 3, and the Examples decreased to varying degrees in both the UVA and visible light regions. The addition of SCNC can increase the internal interface and light scattering path of the film, and the introduction of limonene Pickering emulsion microdroplets further enhances the light scattering and light-blocking effect. The packaging films prepared in Examples 1 and 2 showed stronger light-blocking capabilities, with Example 2 showing a further decrease in transmittance due to the higher emulsion addition. The results indicate that the combined introduction of SCNC and limonene Pickering emulsion can improve the ultraviolet shielding and light-blocking performance of the packaging film.

[0104] 6. Water vapor barrier performance test

[0105] The water vapor barrier performance test procedure was as follows: The packaging films prepared in Examples 1-2 and Comparative Examples 1-3 were cut to suitable test sizes, ensuring that the film sample surface was flat and free of obvious creases, holes, and damage. A water vapor transmission rate tester was used to test the film samples. Before testing, the samples were fixed in the test chamber, ensuring a good seal at the edges to prevent edge leakage during the test. The test conditions were set at 38℃ and 90% relative humidity. During the test, the amount of water vapor passing through the film sample per unit time was recorded, and the water vapor transmission rate was calculated. Each group of samples was tested repeatedly, and the average value was used for analysis. The results are as follows: Figure 6 As shown.

[0106] Depend on Figure 6 It can be seen that the pure SPI membrane prepared in Comparative Example 1 has the highest water vapor permeability, indicating that the single SPI membrane matrix has many water migration channels and weak water vapor barrier ability. In Comparative Example 3, the water vapor permeability decreased after the addition of limonene Pickering emulsion, indicating that the hydrophobic oil phase and emulsion droplets can hinder water migration to a certain extent. In Comparative Example 2, the water vapor permeability further decreased after the addition of SCNC, indicating that SCNC can improve the barrier performance of the packaging film by filling the micropores in the membrane, increasing the membrane structure density, and extending the water vapor diffusion path. In Example 1, the water vapor permeability was lowest after the simultaneous addition of SCNC and an appropriate amount of limonene Pickering emulsion, indicating that the SCNC-reinforced network and the hydrophobic interface of the emulsion can synergistically limit water migration. In Example 2, the water vapor permeability increased compared to Example 1 after further increasing the amount of emulsion added, indicating that excessive emulsion may cause local phase separation, oil phase migration, or interface inhomogeneity, thereby weakening the continuity and barrier performance of the membrane network.

[0107] 7. Water contact angle test

[0108] The water contact angle test procedure was as follows: The packaging films prepared in Examples 1-2 and Comparative Examples 1-3 were cut into flat small pieces and fixed on a clean glass slide, ensuring the test surface was flat. A contact angle meter was used for testing. Approximately 5 μL of deionized water was added to the film surface using a micro-syringe, and the morphology of the water droplet on the film surface was recorded. The water contact angle was calculated using the instrument software. Each sample was tested at least three times at different locations, and the average value was used for analysis. The results are as follows: Figure 7 As shown.

[0109] Depend on Figure 7It can be seen that the water contact angle of the pure SPI membrane prepared in Comparative Example 1 is 53.69°, indicating that its surface has strong hydrophilicity. After adding limonene Pickering emulsion to Comparative Example 3, the water contact angle increased to 60.31°, indicating that the introduction of the hydrophobic oil phase improved the hydrophobicity of the membrane surface. After adding SCNC to Comparative Example 2, the water contact angle increased to 74.61°, indicating that SCNC can improve the membrane network density and change the exposure state of surface polar groups. The water contact angles of Examples 1 and 2 reached 79.14° and 83.15°, respectively, indicating that the synergistic effect of SCNC and limonene Pickering emulsion can further reduce the wettability of the membrane surface and improve the hydrophobicity of the packaging film.

[0110] 8. Observation of microstructure, appearance and surface morphology

[0111] The observation process for microstructure, appearance, and surface morphology was as follows: The packaging films prepared in Examples 1-2 and Comparative Examples 1-3 were observed using cross-sectional scanning electron microscopy (SEM), surface scanning electron microscopy (SEM), appearance photography, and atomic force microscopy (AFM). For cross-sectional observation, the film samples were frozen and fractured in liquid nitrogen. The fractured surface was fixed on a sample stage and sputter-coated with gold, then observed under a scanning electron microscope. For surface observation, the film samples were cut to appropriate sizes and fixed on a sample stage. After sputter-coating with gold, the surface morphology was observed. For appearance observation, the film samples were photographed under the same background and lighting conditions, and their transparency, color, and integrity were compared. For AFM testing, the film samples were fixed on a flat substrate, and the film surface was scanned using a tapping mode to obtain two-dimensional and three-dimensional surface morphology images, and the surface roughness was calculated. The results are as follows: Figure 8 As shown.

[0112] Depend on Figure 8It can be seen that the pure SPI membrane prepared in Comparative Example 1 has pores, local collapses, and discontinuous regions in its cross-section, indicating that single protein membranes are prone to structural defects during the drying process. In Comparative Example 2, after adding SCNC, the membrane cross-section and surface are more flat and continuous, indicating that SCNC can improve the membrane structure density through filling and network support. In Comparative Example 3, after adding limonene Pickering emulsion, cracks or local discontinuous structures appear in the membrane cross-section, and a certain number of pores or droplet traces are visible on the surface, indicating that the introduction of emulsion droplets alone can affect the continuity of the protein matrix. In Example 1, after simultaneously adding SCNC and an appropriate amount of limonene Pickering emulsion, the membrane cross-section is more continuous and uniform, and surface defects are reduced, indicating that SCNC can improve the dispersion of emulsion droplets in the membrane matrix and maintain membrane structural stability. In Example 2, the higher emulsion addition amount results in more pores or depressions in the membrane cross-section and surface, indicating that excessive emulsion increases local phase separation and interfacial inhomogeneity. The results from atomic force microscopy were consistent with those from scanning electron microscopy. The surface roughness of Example 1 was lower than that of Comparative Example 3, which only added emulsion, while the surface roughness of Example 2 was significantly increased.

[0113] 9. Antibacterial performance test

[0114] The antibacterial performance testing process was as follows: The antibacterial performance of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 was evaluated using the inhibition zone method. *Escherichia coli* and *Staphylococcus aureus* were selected as test strains. The strains were inoculated into liquid culture medium and cultured at 37°C until the logarithmic growth phase. The concentration of the bacterial suspension was adjusted to approximately 10. 7 CFU / mL. Sterile LB agar medium was poured into sterile petri dishes. After cooling and solidification, an appropriate amount of bacterial suspension was evenly spread onto the surface of the medium. Then, the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 were cut into circular pieces of uniform diameter and placed on the surface of the culture medium coated with bacterial suspension. The petri dishes were incubated at 37°C for 24 hours. After incubation, the formation of a transparent inhibition zone around each film was observed, and the diameter of the inhibition zone was measured. Each group of samples was tested repeatedly, and the average value was used for analysis. The results are as follows: Figure 9 As shown.

[0115] Depend on Figure 9It can be seen that the packaging films prepared in Comparative Examples 1 and 2 have weak inhibitory effects on Escherichia coli and Staphylococcus aureus, and no obvious inhibition zone appears around the film, indicating that the direct antibacterial ability of the SPI membrane matrix and SCNC-reinforced membrane itself is limited. In Comparative Example 3, after adding limonene Pickering emulsion, a clear inhibition zone appeared around the film, indicating that the limonene active oil phase is the main source of the antibacterial effect of the packaging film. In Examples 1 and 2, the simultaneous introduction of SCNC and limonene Pickering emulsion showed inhibitory effects on both test bacteria, with Example 2 showing a more significant antibacterial effect due to the higher amount of Pickering emulsion added. These results indicate that limonene Pickering emulsion can impart antibacterial function to the packaging film, while the SCNC-reinforced network helps to stably disperse emulsion droplets in the membrane matrix, thus providing a structural basis for the sustained exertion of the active ingredients.

[0116] 10. Antioxidant performance test

[0117] The antioxidant performance testing process was as follows: The antioxidant performance of the packaging films prepared in Examples 1-2 and Comparative Examples 1-3 was evaluated using DPPH and ABTS free radical scavenging experiments. Each group of film samples was cut into small pieces of the same mass or area and added to the corresponding free radical solution, reacting for a certain time under light-protected conditions. After the reaction, the absorbance of the reaction solution was measured using a UV-Vis spectrophotometer, and the free radical scavenging rate was calculated based on the absorbance of the blank group and the sample group. Each group of samples was tested at least three times, and the average value was used for analysis. The results are as follows: Figure 10 As shown.

[0118] Depend on Figure 10 It can be seen that the DPPH and ABTS free radical scavenging rates of Comparative Examples 1 and 2 are relatively low, indicating that the SPI membrane and SCNC reinforced membrane themselves have limited antioxidant capacity. In Comparative Example 3, the addition of limonene Pickering emulsion significantly improved the free radical scavenging rate, indicating that the limonene active oil phase is the main source of improved antioxidant performance of the packaging film. In Example 1, the antioxidant performance was further improved after the simultaneous addition of SCNC and limonene Pickering emulsion. In Example 2, due to the higher emulsion addition amount, the DPPH and ABTS free radical scavenging rates were the highest, indicating that increasing the amount of limonene Pickering emulsion can enhance the free radical scavenging ability of the packaging film.

[0119] 11. Strawberry preservation performance test

[0120] The strawberry preservation performance test process was as follows: Fresh strawberries with similar maturity, size, and color, and no obvious mechanical damage were selected and randomly divided into different treatment groups. The samples were packaged using the packaging films prepared in Comparative Example 1, Comparative Example 2, and Example 1, respectively. A polyethylene film-packaged group and an unpackaged blank group were also set up as controls. All groups of strawberries were stored under the same storage conditions. During storage, photos were taken periodically using the same photographic equipment, under the same lighting conditions, and at the same shooting angle and distance to record changes in the appearance of the strawberries, including water loss, wrinkling, darkening of color, softening, mold, and rotting. The results are as follows: Figure 11 As shown.

[0121] Depend on Figure 11 It can be seen that with prolonged storage, the strawberries in the control group showed significant dehydration, darkening of color, and rotting. The polyethylene film group and the treatment group in Comparative Example 1 could delay the deterioration of strawberry appearance to some extent, but significant softening and spoilage still occurred in the later stages. The treatment group in Comparative Example 2, due to its increased membrane density, had a certain delaying effect on strawberry dehydration and appearance deterioration. The strawberries in the treatment group in Example 1 maintained good appearance integrity in the later stages of storage, indicating that the SCNC-enhanced network and the active components of the limonene Pickering emulsion can work together to provide barrier protection and active preservation, thereby delaying the deterioration of strawberry quality.

[0122] 12. Banana preservation performance test

[0123] The banana preservation performance test process was as follows: Fresh bananas with similar maturity, size, and color, and no obvious mechanical damage were selected and randomly divided into different treatment groups. The samples were packaged using the packaging films prepared in Comparative Example 1, Comparative Example 2, and Example 1, respectively. A polyethylene film-packaged group and an unpackaged blank group were also set up as controls. All bananas were stored under the same storage conditions, and photographs were taken and recorded on days 0, 4, 6, 8, and 10 to observe changes in appearance such as browning, black spots, softening, rotting, and shrinkage due to water loss. The results are as follows: Figure 12 As shown.

[0124] Depend on Figure 12 It was found that the control group of bananas rapidly developed browning, black spots, and peel deterioration during storage. The polyethylene film group and the treatment group in Comparative Example 1 were able to delay some of the appearance changes, but significant browning still occurred in the later stages of storage. The treatment group in Comparative Example 2 showed better appearance retention than Comparative Example 1, indicating that the barrier effect of the SCNC reinforced film is beneficial in slowing down the decline in banana quality. The bananas in the treatment group in Example 1 maintained relatively good peel color and integrity in the later stages of storage, indicating that the bio-based active packaging film can delay banana browning and spoilage through barrier protection, antioxidant effects, and the release of active oil phases.

[0125] 13. Fruit and vegetable firmness and weight loss rate test

[0126] The testing process for fruit and vegetable firmness and weight loss rate was as follows: During the storage of strawberries and bananas, the firmness and weight loss rate of samples from each treatment group were measured periodically. For the weight loss rate test, the initial mass of the samples and the mass at different storage times were recorded, and the weight loss rate was calculated based on the mass change. For the firmness test, a texture analyzer was used to test the samples. Multiple locations were selected for each sample for measurement, and the maximum pressure value or firmness value was recorded, and the average value was calculated. By comparing the firmness retention and weight loss rate changes of different treatment groups during storage, the effect of packaging film on delaying the deterioration of fruit and vegetable texture and moisture loss was evaluated. The results are as follows: Figure 13 As shown.

[0127] Depend on Figure 13 It can be seen that with the extension of storage time, the firmness of strawberries and bananas gradually decreased, and the weight loss rate gradually increased. The control group showed the fastest decrease in firmness and the highest weight loss rate, indicating that the quality deterioration of fruits and vegetables was most obvious under unpackaged treatment. The polyethylene film group and the comparative treatment group were able to slow down the decrease in firmness and weight loss to a certain extent. The treatment group in Example 1 maintained high firmness and low weight loss rate in the later stage of storage, indicating that the bio-based active packaging film can effectively reduce water migration, delay tissue softening, and maintain the storage quality of fruits and vegetables.

[0128] 14. Salmon preservation performance test

[0129] The salmon preservation performance test process was as follows: Fresh salmon samples of similar size, thickness, and appearance were selected and randomly divided into different treatment groups. The salmon samples were packaged using the packaging films prepared in Comparative Example 1, Comparative Example 2, and Example 1, respectively. A polyethylene film-packaged group and an unpackaged blank group were also set up as controls. All salmon samples were stored under the same refrigeration conditions, and photographs were taken and recorded on days 0, 3, 6, and 9 to observe color changes, tissue integrity, surface moisture status, and signs of spoilage. The results are as follows: Figure 14 As shown.

[0130] Depend on Figure 14 It can be seen that the salmon in the blank group gradually darkened in color and decreased in tissue integrity during refrigeration, showing significant quality deterioration in the later stages of storage. The polyethylene film group and the treatment group of Comparative Example 1 could delay the appearance deterioration to some extent, but color fading or tissue quality deterioration still occurred in the later stages. The treatment group of Comparative Example 2 had a certain effect on maintaining the appearance quality of salmon. The salmon in the treatment group of Example 1 maintained a good orange-red appearance and tissue integrity in the later stages of storage, indicating that the bio-based active packaging film can effectively delay the decline in appearance quality of aquatic products during refrigeration.

[0131] 15. Analysis of volatile flavor compounds in salmon

[0132] The analysis process for volatile flavor compounds in salmon was as follows: After salmon was stored for a set time, representative samples from the blank group and the treatment group of Example 1 were taken for the determination of volatile flavor compounds. 2.5g of minced salmon sample was weighed and placed in a 20mL headspace vial, and 1.25μg of 2-octanol was added as an internal standard. The vial was immediately sealed and equilibrated at 60℃ for 30min. After equilibration, volatile compounds were extracted using headspace extraction for 30min and analyzed using gas chromatography-mass spectrometry (GC-MS). Volatile compounds were identified by mass spectrometry deconvolution and library comparison, and relative quantification was performed using the internal standard method. Cluster analysis was performed on the volatile compounds detected in different treatment groups and at different storage times, and the results are shown below. Figure 15 As shown.

[0133] Depend on Figure 15 It was found that the composition of volatile flavor compounds in salmon samples from different treatment groups differed significantly during storage. The composition of volatile compounds in the control group changed considerably with prolonged storage, indicating that the salmon underwent significant flavor degradation during refrigeration. In the treatment group of Example 1, volatile components related to limonene and related terpenes remained at high levels, indicating that the limonene Pickering emulsion can act as a reservoir of volatile active components in the film, continuously influencing the volatile flavor composition of the salmon samples during storage. The results show that this bio-based active packaging film can not only delay the deterioration of salmon quality but also regulate its volatile flavor composition during storage.

[0134] 16. Screening of key volatile flavor compounds

[0135] The screening process for key volatile flavor compounds was as follows: Based on the volatile flavor compound data of salmon obtained by gas chromatography-mass spectrometry (GC-MS), multivariate statistical analysis was performed on samples from different treatment groups. Partial least squares discriminant analysis was used to screen volatile compounds that contributed significantly to the differences between sample groups, and the variable projection importance value of each volatile compound was calculated. Compounds with a variable projection importance value greater than 1 were typically considered important volatile flavor compounds distinguishing different treatment groups. Furthermore, the relative abundance heatmap was used to analyze the variation patterns of key volatile flavor compounds under different treatment groups and different storage times. The results are as follows: Figure 16 As shown.

[0136] Depend on Figure 16It was found that the key volatile flavor compounds in salmon samples from different treatment groups showed significant differences. In the treatment group of Example 1, limonene and its related terpenes had relatively high abundances and made a significant contribution to the differences between sample groups, indicating that the bio-based active packaging film can regulate the volatile flavor composition of salmon during storage by retaining and releasing the active limonene oil phase. In the blank group, some volatile compounds related to storage deterioration had relatively high abundances, indicating that complex volatile substances are more likely to accumulate in the unpackaged group. These results further demonstrate that the bio-based active packaging film prepared in this application can achieve a synergistic effect of food preservation and volatile flavor regulation.

[0137] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a bio-based active packaging film with preservation and volatile flavor regulation functions, characterized in that: Includes the following steps: 1) Add microcrystalline cellulose to sodium hydroxide solution for alkaline treatment, wash until neutral and dry; The alkali-treated microcrystalline cellulose was then pretreated by dispersing it in dimethyl sulfoxide, followed by filtration and washing. Hydrolysis was then carried out using a mixed acid system consisting of hydrochloric acid, sulfuric acid, and water. After terminating the reaction with water, centrifugation, and dialysis, a suspension of spherical cellulose nanocrystals was obtained. 2) Dissolve soy protein isolate in water and adjust the pH to prepare an SPI solution; 3) Mix the spherical cellulose nanocrystal suspension obtained in step 1) with the SPI solution obtained in step 2) to prepare the SCNC / SPI composite dispersion; 4) Using the SCNC / SPI composite dispersion obtained in step 3) as the aqueous phase and limonene as the oil phase, a Pickering emulsion was prepared by shear emulsification and ultrasonic treatment. 5) Prepare a film-forming solution for the SPI matrix, and add the SCNC suspension obtained in step 1) and the Pickering emulsion obtained in step 4) to it, and mix them to obtain a composite film-forming solution; 6) After degassing the composite film-forming liquid obtained in step 5), the liquid is cast, dried and equilibrated to obtain a bio-based active packaging film.

2. The method for preparing the bio-based active packaging film with preservation and volatile flavor regulation functions according to claim 1, characterized in that: In step 1), the mass-to-volume ratio of microcrystalline cellulose to sodium hydroxide solution is 1g:5-15mL, the concentration of sodium hydroxide solution is 3-8mol / L, the alkali treatment temperature is 60-90℃, and the treatment time is 2-5h; the dimethyl sulfoxide treatment temperature is 60-90℃, and the treatment time is 2-5h; the volume ratio of hydrochloric acid, sulfuric acid, and water in the mixed acid system is 1:2-4:5-8, the hydrolysis temperature is 50-75℃, and the hydrolysis time is 5-10h; dialyzing is performed until the pH of the dispersion is 5-6.

3. The method for preparing the bio-based active packaging film with preservation and volatile flavor regulation functions according to claim 1, characterized in that: In step 2), the SPI solution has a mass percentage concentration of 3-8%, a pH of 9-11, and a dissolution temperature of 35-55℃.

4. The method for preparing the bio-based active packaging film with preservation and volatile flavor regulation functions according to claim 1, characterized in that: In step 3), the mass percentage concentration of the SCNC suspension is 0.5-2%, and the mass ratio of SCNC to SPI is 3~1:1~3.

5. The method for preparing the bio-based active packaging film with preservation and volatile flavor regulation functions according to claim 1, characterized in that: In step 4), the volume fraction of limonene in the Pickering emulsion is 10-20%; the shear emulsification speed is 8000-15000 r / min, and the shear emulsification time is 1-5 min; the ultrasonic treatment power is 200-500 W, and the ultrasonic treatment time is 1-5 min.

6. The method for preparing the bio-based active packaging film with preservation and volatile flavor regulation functions according to claim 1, characterized in that: In step 5), the mass-volume percentage concentration of the film-forming solution of the SPI matrix is ​​3-8%.

7. The method for preparing the bio-based active packaging film with preservation and volatile flavor regulation functions according to claim 1, characterized in that: In step 5), the amount of SCNC added to the composite film-forming solution is 0.3-1.2 wt% in the SCNC suspension and 3-12 wt% in the Pickering emulsion. The amounts added are based on the total mass of the composite film-forming solution.

8. The method for preparing the bio-based active packaging film with preservation and volatile flavor regulation functions according to claim 1, characterized in that: In step 6), the composite film-forming liquid is degassed under vacuum for 25-30 minutes and then cast onto a polytetrafluoroethylene plate. It is dried at 40°C for 5 hours and then peeled off and equilibrated at 25°C and 58% relative humidity for 48 hours.

9. The bio-based active packaging film prepared by the method of any one of claims 1-8, which has the functions of preservation and volatile flavor regulation.

10. The application of the bio-based active packaging film according to claim 9 in food preservation and volatile flavor control.

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