Preparation method of antibacterial and antioxidant hydrophobic film and application thereof in fish ball preservation

Abstract

The application relates to a preparation method of an antibacterial and antioxidant hydrophobic film, which comprises the following steps: S1, dispersing a brown alga polyphenol / nano-cellulose compound in water to obtain a brown alga polyphenol / nano-cellulose compound suspension; S2, mixing the brown alga polyphenol / nano-cellulose compound suspension with cinnamon essential oil, performing homogenization and ultrasonic treatment to obtain a Pickering emulsion; S3, mixing and stirring the Pickering emulsion and a sodium alginate casting solution to obtain an active casting solution, and performing drying and calcium chloride crosslinking to obtain the antibacterial and antioxidant hydrophobic film. The compound formed by the high-density hydrogen bond and the pi-pi aromatic stacking synergistic interaction between the brown alga polyphenol and the nano-cellulose can more effectively stabilize the Pickering emulsion; the Pickering emulsion introduced into the sodium alginate film matrix can form a continuous and dense three-dimensional network, so that the mechanical performance, the barrier performance and the functional activity of the antibacterial and antioxidant hydrophobic film are simultaneously improved, and the shelf life of perishable aquatic products such as fish balls is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, and in particular to a method for preparing an antibacterial, antioxidant, and hydrophobic film and its application in fish ball preservation. Background Technology

[0002] Sodium alginate is widely used as a food packaging substrate due to its excellent film-forming properties, biocompatibility, and biodegradability. However, sodium alginate films alone have drawbacks such as insufficient mechanical strength, poor wet stability, weak water vapor barrier properties, and a lack of antibacterial and antioxidant functions, making it difficult to meet the preservation requirements of high-protein and perishable aquatic products such as fish balls.

[0003] To improve the performance of sodium alginate membranes, active ingredients such as plant essential oils are usually added to the sodium alginate casting solution to prepare composite membranes. This method is simple and low-cost, but due to direct blending, the binding force between the active ingredients and the membrane matrix is ​​poor, and burst release loss is likely to occur during storage and use, making it difficult to achieve long-term preservation. At the same time, the active ingredients have poor stability and are easily damaged by factors such as heat and light.

[0004] Pickering emulsions, as emulsion systems stabilized by solid particles, possess advantages such as high stability, good biocompatibility, and controllable release of active ingredients, making them a research hotspot in food packaging materials in recent years. However, current research on the use of Pickering emulsions for modifying sodium alginate membranes is relatively limited. This is mainly because the screening and design of stabilizing particles, the regulation and stabilization of the emulsion interface, and the compatibility of the emulsion with the membrane matrix all require precise control, resulting in high technical barriers. Therefore, existing Pickering emulsion-modified sodium alginate membranes struggle to achieve a good balance between mechanical properties, barrier properties, and functional activity, and their practical application results remain unsatisfactory.

[0005] Therefore, it is necessary to further improve the existing Pickering emulsion-modified sodium alginate membrane. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for preparing an antibacterial, antioxidant, and hydrophobic membrane and its application in fish ball preservation.

[0007] The technical solution adopted in this invention is as follows: This invention provides a method for preparing an antibacterial, antioxidant, and hydrophobic membrane, comprising the following steps: S1. Disperse the brown algae polyphenol / nanocellulose complex in water to obtain a brown algae polyphenol / nanocellulose complex suspension. S2. The brown algae polyphenol / nanocellulose complex suspension is mixed with cinnamon essential oil, homogenized and sonicated to obtain Pickering emulsion; S3. The Pickering emulsion and sodium alginate casting solution are mixed and stirred to obtain an active casting solution, which is then dried and crosslinked with calcium chloride to obtain the antibacterial, antioxidant, and hydrophobic membrane.

[0008] Preferably, in step S1, the mass ratio of nanocellulose to brown algae polyphenols in the brown algae polyphenol / nanocellulose composite is 1:0.05~0.15.

[0009] Preferably, in step S1, the concentration of the brown algae polyphenol / nanocellulose complex suspension is 0.5~1% w / v.

[0010] Preferably, in step S2, the volume ratio of the brown algae polyphenol / nanocellulose complex suspension to the cinnamon essential oil is 1:1.

[0011] Preferably, in step S3, the amount of Pickering emulsion added is not less than 5% of the volume of the sodium alginate membrane liquid.

[0012] Preferably, the amount of Pickering emulsion added is 10-15% of the volume of the sodium alginate membrane liquid.

[0013] Preferably, in step S3, after the calcium chloride crosslinking, the step further includes fumigation treatment with octadecylamine.

[0014] Another aspect of the present invention provides the application of an antibacterial, antioxidant, and hydrophobic membrane prepared by the method described in any of the above technical solutions in the preservation of fish balls.

[0015] The beneficial effects of this invention are: (1) The method for preparing the antibacterial and antioxidant hydrophobic membrane of the present invention utilizes the multivalent strong interaction formed by the high-density hydrogen bonds and π-π aromatic stacking between brown algae polyphenols and nanocellulose to construct a structurally stable complex, which can more effectively stabilize Pickering emulsion; the introduction of the Pickering emulsion into the sodium alginate membrane matrix can form a continuous and dense three-dimensional network, thereby simultaneously improving the mechanical properties, barrier properties and functional activities of the antibacterial and antioxidant hydrophobic membrane.

[0016] (2) The antibacterial and antioxidant hydrophobic membrane prepared by the method of the present invention has excellent mechanical properties, barrier properties and antibacterial and antioxidant activities. It can effectively extend the shelf life to 16 days by inhibiting lipid oxidation and microbial reproduction, delaying protein degradation, maintaining the water holding capacity, gel strength and texture of fish balls during the 4℃ cold storage preservation of perishable aquatic products such as fish balls. Attached Figure Description

[0017] Figure 1The mechanical and light blocking properties of different films in Example 1 are shown, where A is tensile strength TS, B is elongation at break EAB, C is light transmittance, and D is macroscopic performance. Figure 2 The surface properties of different films in Example 1 are characterized, where A is the contact angle WCA and B is the SEM image; Figure 3 Thermogravimetric analysis of different membranes in Example 1 is shown. A is the thermogravimetric curve TG before membrane fumigation, B is the thermogravimetric curve TG after membrane fumigation, C is the derivative thermogravimetric curve DTG before membrane fumigation, and D is the derivative thermogravimetric curve DTG after membrane fumigation. Figure 4 The Fourier transform infrared spectra of different membranes in Example 1 are shown, where A represents the membrane before fumigation and B represents the membrane after fumigation. Figure 5 The antioxidant and antibacterial activities of different membranes in Example 1 were tested, where A represents DPPH free radical scavenging ability and B represents antibacterial performance. Figure 6 The color changes of fish balls wrapped in different films in Example 2 are shown, where A represents the appearance change and B represents the whiteness change. Figure 7 The pH and water-holding capacity changes of fish balls wrapped with different membranes in Example 2 are shown, where A is pH and B is water-holding capacity. Figure 8 The changes in volatile basic nitrogen (TVB-N) and thiobarbituric acid (TBA) values ​​of fish balls coated with different membranes in Example 2 are shown in Figure 2. In this figure, A represents TVB-N and B represents TBA. Figure 9 The textural properties of fish balls wrapped in different membranes in Example 2 are shown, where A represents strength, B represents elasticity, C represents cohesiveness, and D represents chewiness. Figure 10 The changes in gel strength and microbial growth of fish balls wrapped in different membranes in Example 2 are shown. A represents gel strength, and B represents the plate colony growth count (day 16). Detailed Implementation

[0018] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0019] This invention provides a method for preparing an antibacterial, antioxidant, and hydrophobic membrane, comprising the following steps: S1. Disperse the brown algae polyphenol / nanocellulose complex in water to obtain a brown algae polyphenol / nanocellulose complex suspension. S2. Mix the brown algae polyphenol / nanocellulose complex suspension with cinnamon essential oil, homogenize and sonicate to obtain Pickering emulsion; S3. The Pickering emulsion and sodium alginate casting solution are mixed and stirred to obtain an active casting solution. After drying and cross-linking with calcium chloride, an antibacterial, antioxidant, and hydrophobic membrane is obtained.

[0020] Through extensive experimental verification, the inventors discovered that the abundant phenolic hydroxyl groups on the highly polymerized brown algae polyphenol molecular chains can form a dense hydrogen bond network with nanocellulose. Simultaneously, π-π stacking of aromatic rings between brown algae polyphenol molecules occurs, and the two synergistically construct a stable complex with strong multivalent interactions. Compared to simple polyphenols (such as tea polyphenols), whose hydrogen bond sites are relatively dispersed and intermolecular interactions are weaker, the brown algae polyphenol / nanocellulose complex of this invention, due to its strong multivalent interactions, exhibits higher crystallinity, thermal stability, and interfacial activity, enabling more effective adsorption at the oil-water interface, thus obtaining a more stable Pickering emulsion. When this Pickering emulsion is introduced into a sodium alginate membrane matrix, the brown algae polyphenol / nanocellulose complex can further crosslink with sodium alginate through hydrogen bonds, forming a continuous and dense three-dimensional network structure within the membrane, significantly improving the mechanical and barrier properties of the antibacterial, antioxidant, and hydrophobic membrane. Furthermore, the sustained-release properties of the Pickering emulsion allow the antibacterial and antioxidant activities of cinnamon oil and brown algae polyphenols to be exerted for a long period.

[0021] The present invention does not impose any particular limitation on the raw material composition of the sodium alginate casting solution. For example, the raw material composition includes sodium alginate, glycerol and water. The concentration of sodium alginate can be 1~3% w / v and the concentration of glycerol can be 0.1~0.5% w / v.

[0022] In a preferred embodiment, in step S1, the mass ratio of nanocellulose to brown algae polyphenols in the brown algae polyphenol / nanocellulose composite is 1:0.05~0.15. This invention, by controlling the mass ratio of nanocellulose to brown algae polyphenols in the composite, facilitates the formation of a high-density multi-point hydrogen bond network and intermolecular aromatic stacking, while simultaneously endowing the composite with a suitable interfacial hydrophilic-hydrophobic balance, thereby obtaining a Pickering emulsion with excellent stability. For example, the mass ratio of nanocellulose to brown algae polyphenols can be 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, etc.

[0023] In a preferred embodiment, in step S1, the concentration of the brown algae polyphenol / nanocellulose complex suspension is 0.5% to 1% w / v. For example, the concentration of the brown algae polyphenol / nanocellulose complex suspension can be 0.5% w / v, 0.6% w / v, 0.7% w / v, 0.8% w / v, 0.9% w / v, 1% w / v, etc.

[0024] In a preferred embodiment, in step S2, the volume ratio of the brown algae polyphenol / nanocellulose complex suspension to cinnamon essential oil is 1:1. This invention does not impose particular limitations on the homogenization and sonication conditions after mixing the two components. For example, the homogenization rotation speed can be 5000~8000 rpm, and the homogenization time can be 1~3 min; the sonication power can be 300~600 W, and the sonication time can be 1~3 min.

[0025] In a preferred embodiment, in step S3, the amount of Pickering emulsion added is not less than 5% of the volume of the sodium alginate membrane liquid. If the amount of Pickering emulsion added is too low, the brown algae polyphenol / nanocellulose complex (where nanocellulose serves as the main framework) will have difficulty forming a continuous and uniform three-dimensional cross-linked network with the sodium alginate membrane matrix, resulting in insufficient improvement in the mechanical and barrier properties of the antibacterial, antioxidant, and hydrophobic membrane; at the same time, the loading of brown algae polyphenols and cinnamon essential oil is insufficient, failing to effectively exert antibacterial and antioxidant effects, resulting in poor preservation effect of the antibacterial, antioxidant, and hydrophobic membrane.

[0026] In a preferred embodiment, the amount of Pickering emulsion added is 10-15% of the sodium alginate membrane liquid volume. This invention selects the Pickering emulsion addition amount within the above range so that the resulting antibacterial, antioxidant, and hydrophobic membrane simultaneously possesses excellent mechanical properties, barrier properties, and antibacterial and antioxidant activity, meeting the requirements for long-term preservation of high-protein, perishable aquatic products such as fish balls. For example, the amount of Pickering emulsion added can be 10%, 11%, 12%, 13%, 14%, 15% of the sodium alginate membrane liquid volume, etc.

[0027] In a preferred embodiment, step S3 further includes a fumigation treatment with octadecylamine after calcium chloride crosslinking. In this invention, octadecylamine fumigation is performed after calcium chloride crosslinking. The octadecylamine volatilizes upon heating and deposits on the membrane surface, forming a low surface energy monolayer through the interaction of amino groups with hydroxyl groups on the membrane surface, thereby further improving the membrane's hydrophobicity and physical barrier properties. This invention does not particularly limit the calcium chloride crosslinking; for example, a calcium chloride solution with a concentration of 0.5~2 wt% can be used for immersion.

[0028] Another aspect of the present invention provides the application of an antibacterial, antioxidant, and hydrophobic membrane prepared by any of the above-mentioned technical solutions in the preservation of fish balls. The antibacterial, antioxidant, and hydrophobic membrane prepared by the method of the present invention can form a stable and dense film layer on the surface of fish balls, exerting a physical barrier effect. At the same time, the continuously released cinnamon essential oil and brown algae polyphenols can synergistically inhibit lipid oxidation and microbial reproduction, delay protein degradation, maintain the water-holding capacity and textural properties of fish balls, and significantly extend the refrigerated shelf life.

[0029] Example 1 (1) Preparation of an antibacterial, antioxidant, and hydrophobic membrane (SA / PE membrane), including the following steps: S1. Nanocellulose (NC) and brown algae polyphenols (Fucol type) were added to ultrapure water at a mass ratio of 1:0.1 and reacted at 30℃, pH 4.0~4.2, and 800 rpm for 24 h. After the reaction was completed, the mixture was freeze-dried to obtain a brown algae polyphenol / nanocellulose complex (NC-Fu). 0.07 g of NC-Fu was dispersed in 10 mL of ultrapure water to obtain a brown algae polyphenol / nanocellulose complex suspension.

[0030] S2. Mix the brown algae polyphenol / nanocellulose complex suspension with cinnamon essential oil at a volume ratio of 1:1, homogenize at 7000 rpm for 2 min, and then sonicate at 450 W for 2 min to obtain Pickering emulsion.

[0031] S3. Dissolve 0.4 g of sodium alginate in 20 mL of ultrapure water (60℃ water bath), and then add 0.04 g of glycerol to obtain sodium alginate casting solution. Take 1 mL, 2 mL, and 3 mL of the above Pickering emulsion and add them to the sodium alginate casting solution, respectively. Stir for 30 min to obtain three active casting solutions. Pour them into 100 mm × 100 mm × 10 mm polytetrafluoroethylene molds and dry them in a constant temperature and humidity chamber at 26℃ and 50% humidity for 48 h. Remove the film, soak it in 1 wt% calcium chloride solution for 5 min, take it out and dry it to obtain three antibacterial, antioxidant and hydrophobic films, named SA / PE5 (addition amount 5%), SA / PE10 (addition amount 10%) and SA / PE15 (addition amount 15%) according to the amount of Pickering emulsion added.

[0032] (2) Preparation of sodium alginate membrane (SA membrane): Dissolve 0.4 g sodium alginate in 20 mL of ultrapure water (60℃ water bath), then add 0.04 g glycerol and stir for 30 min to obtain sodium alginate casting solution. The subsequent molding, drying and calcium chloride crosslinking steps are the same as those of the above SA / PE membrane to obtain SA membrane.

[0033] (3) Octadecylamine fumigation: The SA / PE5, SA / PE10, SA / PE15 antibacterial and antioxidant hydrophobic membranes and pure SA membranes prepared above are placed together with octadecylamine solid in a sealed container and heated at 80°C for 3 h to obtain SA / PE5-f, SA / PE10-f, SA / PE15-f and SA-f membranes.

[0034] The physicochemical properties of the membranes prepared above were analyzed, and the results are recorded in Table 1 and... Figures 1-5 .

[0035] 1. Basic properties of membranes Test method: Film thickness was measured using a micrometer screw gauge. Eight different locations were randomly selected for testing, and the average value was taken as the overall thickness of the film.

[0036] For the determination of water content (WC) and water solubility (WS), the membrane sample was cut into 20 mm × 20 mm squares and weighed (W0). After drying in an oven at 105 °C for 24 h, it was weighed again (W1). The dried membrane sample was then placed in a vial containing 15 mL of water and shaken in a water bath at 26 °C for 24 h. The insoluble matter was collected and dried again at 105 °C for 24 h, then weighed (W2). The formulas for calculating WC and WS are as follows:

[0037]

[0038] To determine the water vapor transmission coefficient (WVP), add 7 mL of ultrapure water to a 10 mL vial, place the membrane sample flat on the mouth of the vial and seal it, then weigh the total mass. After placing it in a constant temperature incubator at 30℃ for 24 h, weigh it again and calculate the mass loss. The formula for calculating WVP is as follows:

[0039] In the formula, ΔM is the mass loss (g), d is the film thickness (mm), and A is the area of ​​the vial opening (m²). 2 ), t is the time interval (h), and ΔP is the atmospheric pressure difference across the membrane (4247 Pa at 30℃). The results are recorded in Table 1.

[0040] As shown in Table 1, the membrane thickness gradually increases with the increase of Pickering emulsion addition. The SA membrane thickness is approximately 44 μm, while the SA / PE15 membrane (high essential oil content) increases to approximately 59 μm. This is because the Pickering emulsion alters the internal microstructure of the membrane. The deposition of a hydrophobic molecular layer on the membrane surface after octadecylamine fumigation treatment, and the relaxation of molecular chains due to heat treatment, further increase the thickness.

[0041] The wetted carbon (WC) of the SA membrane was 18.67±1.79%. The WC of the SA / PE membrane decreased after the addition of Pickering emulsion, mainly due to the formation of a dense three-dimensional network between nanocellulose and sodium alginate, and the hydrophobic microdomains of cinnamon essential oil hindering water permeation. The WC of the SA / PE-f membrane and SA-f membrane decreased significantly after fumigation with octadecylamine, due to free water evaporation and structural densification. The water-soluble solids (WS) of the SA membrane was 13.53±0.78%. The WS of the SA / PE membrane decreased after the addition of Pickering emulsion, mainly due to the cross-linked network enhancing the membrane structural integrity and the hydrophobic regions of essential oil delaying dissolution. The WS of the SA / PE-f membrane and SA-f membrane decreased significantly after fumigation treatment, mainly because octadecylamine formed a dense hydrophobic layer on the membrane surface, inhibiting water contact.

[0042] Compared to SA membranes, the WVP of SA / PE membranes with added Pickering emulsion is reduced, and the decrease trend is upward with increasing emulsion content. The mechanism is that nanocellulose and sodium alginate form a dense network, which hinders water vapor diffusion; the phenolic hydroxyl groups of brown algae polyphenols shield the hydrophilic groups of sodium alginate through hydrogen bonding, reducing hygroscopicity. After fumigation treatment with octadecylamine, the WVP can be further reduced, which is attributed to the formation of a hydrophobic layer on the membrane surface by octadecylamine, which enhances the barrier properties.

[0043] Table 1. Basic properties of membranes from different samples

[0044] Note: Different letters indicate significant differences (p<0.05). 2. Mechanical properties, UV and visible light blocking properties of the membrane Test method: Tensile strength (TS) and elongation at break (EAB) were determined using a food texture analyzer. The film sample was cut into strips of 60 mm × 20 mm and placed in the analyzer. The stretching rate was set to 0.5 mm / s. The formulas for calculating TS and EAB are as follows:

[0045]

[0046] In the formula, F max d is the maximum tension (N), d is the film thickness (mm), w is the film width (mm), L1 is the length at break (mm), and L0 is the original length (mm).

[0047] The transmittance and transparency of the membrane were measured using a UV-Vis spectrophotometer. The membrane sample was cut into 20 mm × 10 mm pieces and attached to one side of a quartz cuvette. The absorbance was measured in the wavelength range of 200–800 nm, and the results were recorded. Figure 1 .

[0048] like Figure 1 As shown in (A~B), compared with SA film, SA / PE film with appropriate addition of Pickering emulsion can improve mechanical properties; after fumigation treatment, water evaporation weakens the plasticizing effect, and octadecylamine interferes with the hydrogen bond network, resulting in a decrease in both TS and EAB. Figure 1 (C) The SA film has a transmittance of >60% in the visible light region and limited light blocking ability. As the amount of Pickering emulsion added increases, the transmittance decreases significantly and the opacity of the film gradually increases. This is because the interaction between nanocellulose and sodium alginate matrix and the formation of multiphase heterogeneous interfaces by emulsion droplets create a dense light scattering path. Figure 1 (D) The fumigation treatment causes octadecylamine to deposit and form an additional light barrier layer, which further improves the light blocking performance, while the film color turns yellow.

[0049] 3. Contact angle and SEM image analysis of the membrane Test method: The water contact angle of the membrane was measured using a contact angle meter. The membrane was flattened and placed on a platform. Ultrapure water was loaded into a syringe, and a 5 μL droplet was added to the membrane. The changes in the droplet were observed and recorded using a camera.

[0050] The microstructure of the film surface was observed using field emission scanning electron microscopy. The film sample was cut into strips of 10 mm × 5 mm, fixed with conductive tape, and sputter-coated with gold for 3 minutes before observation. Results were recorded in [document name missing]. Figure 2 .

[0051] like Figure 2 As shown in (A), the SA membrane is hydrophilic with a water contact angle of approximately 77°. The contact angle increases after adding Pickering emulsion, mainly due to the hydrophobic properties of cinnamon oil reducing the membrane surface free energy; however, the material as a whole remains hydrophilic (water contact angle < 90°). After octadecylamine fumigation treatment, a dense hydrophobic layer forms on the membrane surface, significantly increasing the water contact angle and noticeably improving the hydrophobic properties. Figure 2 As shown in (B), the SA membrane surface is dense and smooth. After adding Pickering emulsion, the SA / PE membrane surface still remains dense, uniform, and smooth. This is because the Pickering emulsion and sodium alginate molecules form a tighter network structure through hydrogen bonding or electrostatic interaction. The SA / PE membrane surface exhibits non-uniformity after fumigation, mainly due to high-temperature water loss and the adhesion of octadecylamine to the membrane surface.

[0052] 4. Thermogravimetric analysis of membranes Test method: The thermal stability of the membrane was analyzed using a simultaneous thermal analyzer. The heating rate was 10℃ / min, and the temperature was increased from 20℃ to 600℃ in a nitrogen atmosphere. The results were recorded. Figure 3 .

[0053] like Figure 3 As shown, thermal degradation occurs in three stages: below 150℃, adsorbed and bound water evaporate, resulting in low weight loss, consistent with the moisture content results; 220–400℃ is the main degradation stage of sodium alginate and nanocellulose molecular chains; and from 400–600℃, weight loss slows down, leaving inorganic components or highly thermally stable organic matter. SA / PE membranes with added Pickering emulsion exhibit greater total mass loss and lower thermal stability because the emulsion oil phase completely decomposes at 200–500℃, and its products catalyze and accelerate polymer chain breakage. The mass loss of the membrane further increases after octadecylamine fumigation treatment, due to the high-temperature decomposition and volatilization of octadecylamine itself.

[0054] 5. ATR-FTIR analysis of the membrane Test method: A Nicolet AVATAR 360 FTIR spectrometer with attenuated total reflectance ATR was used, with a scan wavenumber range of 4000–400 cm⁻¹. - ¹, characterizing the interactions of components within the membrane. Results are recorded in Figure 4 .

[0055] like Figure 4 As shown, all membrane samples were within the range of 4000–400 cm⁻¹. - ¹The band spectra are similar, but the intensity and position of the characteristic peaks differ significantly, indicating that the addition of Pickering emulsion alters the chemical structure of the sodium alginate matrix. The samples exhibit similar spectra at 3400–3200 cm⁻¹. - The strong, broad absorption band at ¹ corresponds to the OH stretching vibration. The addition of the emulsion resulted in a red shift and broadening of this peak, indicating enhanced hydrogen bonding between sodium alginate and the brown algal polyphenol / nanocellulose complex; located at approximately 2920 cm⁻¹. - The absorption peak ¹ mainly originates from the symmetric and asymmetric stretching vibrations of the methylene and methine groups in the sugar ring; 1600 cm⁻¹ - ¹, 1410 cm - ¹ represents sodium alginate - COO - The characteristic double peak. After fumigation with octadecylamine, the OH stretching vibration peak was further enhanced and broadened, reaching 920 cm⁻¹. - The appearance of a new absorption peak near the membrane indicates that the fumigation not only resulted in physical adhesion but also altered the chemical structure of the membrane surface.

[0056] 6. Analysis of the membrane's antioxidant capacity and antibacterial properties Test method: The antioxidant performance of the membrane was evaluated using a DPPH free radical scavenging assay. 50 mg of the membrane sample was immersed in 4 mL of 0.1 mM DPPH ethanol solution and reacted for 30 min in the dark. The absorbance was then measured at 517 nm using a microplate reader. The DPPH free radical scavenging activity was calculated using the following formula:

[0057] In the formula, Ac is the absorbance of the DPPH solution without a membrane, and As is the absorbance of the DPPH solution with a membrane.

[0058] Antibacterial performance analysis: 100 mL of LB solid medium was dissolved and cooled to room temperature; then the cultured Staphylococcus aureus and Escherichia coli were diluted to 10... 5 CFU, add 1 mL of diluted bacterial suspension to dissolved LB solid medium, gently shake to mix, pour into disposable petri dishes, and after solidification, attach a 1 cm diameter film to the petri dish. Incubate at 37 °C for 18–24 h, and measure the diameter of the inhibition zone. Results are recorded in [document name missing]. Figure 5 .

[0059] like Figure 5 As shown in (A), the SA membrane lacks antioxidant capacity due to the absence of highly effective active antioxidant components. To address this, brown algae polyphenols (rich in phenolic hydroxyl groups, which can act as electron / hydrogen donors and efficiently scavenge DPPH, hydroxyl radicals, and superoxide anions) and cinnamon essential oil (containing cinnamaldehyde and eugenol, possessing free radical scavenging and antibacterial effects) were introduced. These two ingredients may produce synergistic or additive effects at different stages of oxidation, constructing a more complete antioxidant defense system. However, the membrane's antioxidant capacity decreased after fumigation treatment. This was due to several reasons: the densification of the membrane structure limited the migration and replenishment of internal antioxidant components to the surface and hindered the escape of oxidation products; simultaneously, heating promoted the volatilization and thermal oxidative decomposition of cinnamaldehyde, eugenol, etc., reducing their effective concentration and activity.

[0060] like Figure 5 As shown in (B), the SA membrane showed no inhibition zone against either *Escherichia coli* or *Staphylococcus aureus*, consistent with its structural characteristics lacking antibacterial active ingredients. When the Pickering emulsion concentration was 5%, the SA / PE membrane showed no clearly visible inhibition zone; however, when the concentration was increased to 10% and 15%, the SA / PE membrane exhibited significant and clear inhibition zones against both bacteria, and the antibacterial effect increased with increasing concentration. This indicates that controlling the emulsion concentration can effectively impart antibacterial function to the sodium alginate membrane. After fumigation with octadecylamine, the antibacterial activity of the SA / PE membrane still followed the above pattern, indicating that the fumigation treatment did not alter the antibacterial mechanism and dose-dependent effect of cinnamon essential oil.

[0061] Example 2: The Preservative Effect of Antibacterial, Antioxidant, and Hydrophobic Film on Fish Balls Fish ball processing: After freezing fresh fish balls, samples with no significant differences in size and color were selected and divided into three groups. These groups were then wrapped with SA film, SA / PE10 film, and SA / PE10-f film, respectively. The packaged fish ball samples were then stored in a 4°C constant temperature refrigerator. Samples were taken on days 0, 4, 8, 12, and 16 of the storage period, and the changes in various quality indicators of the fish balls during storage were systematically analyzed. The results were recorded in [document name missing]. Figures 6-10 .

[0062] 1. Analysis of fish ball color changes Test method: The L, a, and b values ​​of all fish ball samples were measured using a colorimeter, and the whiteness of the fish balls was calculated using the following formula: Whiteness =

[0063] In the formula, L represents the brightness of the fish ball, a represents the red-green value of the fish ball, and b represents the yellow-blue value of the fish ball. The results are recorded in... Figure 6 .

[0064] like Figure 6 As shown, the appearance and color difference of the fish balls were good in the early stage of storage, and the whiteness did not change significantly.

[0065] 2. Analysis of pH and water-holding capacity of fish balls Test method: pH determination: Take 1 g of fish balls, grind them, dissolve them in 10 mL of ultrapure water and homogenize for 1 min, then centrifuge at 5000 rpm for 20 min. Measure the pH value of the supernatant using a pH meter.

[0066] Water-holding capacity determination: Weigh 2 g of fish balls, wrap them in filter paper, and place them in a centrifuge tube. Centrifuge at 4℃ and 8500 rpm for 10 min. After centrifugation, remove the sample, remove excess water, and weigh it again. Water-holding capacity is expressed as the percentage of water mass retained by the sample, and the calculation formula is:

[0067] In the formula: The mass of the sample before centrifugation. This represents the sample mass after centrifugation. Results are recorded in [the relevant section]. Figure 7 .

[0068] like Figure 7As shown in (A), the pH values ​​of the three groups of fish balls were all between 7.0 and 7.2 during the initial storage period, indicating a slightly alkaline environment. Initially, the pH values ​​of all groups decreased due to the production of organic acids from microbial fermentation. As storage prolonged, psychrophilic putrefactive bacteria decomposed proteins and amino acids, generating alkaline nitrogenous compounds such as ammonia and trimethylamine, causing the pH value to rise continuously from its low point. When the pH exceeded 7.4-7.6, putrefactive characteristics such as ammonia odor and fishy smell appeared. After 16 days, the pH of the SA group reached approximately 8.6, significantly higher than that of the SA / PE10 group (7.9) and the SA / PE10-f group (7.7). This difference was mainly attributed to the antibacterial effect of the active ingredients (such as cinnamaldehyde) in the cinnamon oil loaded in the Pickering emulsion, which inhibited the growth and metabolism of putrefactive microorganisms, delayed protein decomposition and the generation of alkaline nitrogenous compounds, thereby slowing down the pH rise and maintaining the storage stability of the fish balls.

[0069] like Figure 7 As shown in (B), the fish balls treated with the SA / PE10-f membrane exhibited significantly better water retention: compared to the SA group (10.37% water loss) and the SA / PE10 group (10.67%), the SA / PE10-f group showed a water loss rate of only about 6.67% during the same storage period. This is because the long-chain alkyl hydrophobic properties of octadecylamine create an effective physical barrier for the fish balls, inhibiting water migration and loss, thereby better maintaining water content and textural properties. Therefore, under ice or cold storage conditions, SA / PE10-f membrane treatment can more effectively maintain the moisture stability of fish balls.

[0070] 3. Analysis of volatile basic nitrogen (TVB-N) and thiobarbituric acid (TBA) values ​​in fish balls Test method: TVB-N determination: The experimental procedure is based on the national standard GB 5009.228-2016, and the specific operation is as follows: (1) Weigh 1 g of fish balls from different groups, cut them into pieces, and immerse them in the distillation tube of a Kjeldahl nitrogen analyzer containing 75 mL of ultrapure water.

[0071] (2) Clean, preheat and test the instrument, and measure the sample blank.

[0072] (3) Add 1 g of magnesium oxide to the sample, start measuring the fish ball sample and record the data.

[0073] (4) Calculate TVB-N according to the following formula:

[0074] In the formula, V1 and V2 are the volumes (mL) of hydrochloric acid consumed by the sample group and the blank group, respectively, c is the concentration of the hydrochloric acid standard solution (mol / L), 14 is the mass of nitrogen equivalent to titrating 1 mL of hydrochloric acid (g / mol), and m is the mass of the fish ball (g).

[0075] For TBA determination, 5 g of fish ball sample was mixed with 25 mL of 7.5 wt% trichloroacetic acid solution and homogenized for 2 min. The mixture was filtered using qualitative filter paper. 5 mL of the filtrate was mixed with 5 mL of 0.02 mol / L 2-thiobarbituric acid solution and incubated in a boiling water bath for 40 min. After cooling, the mixture was centrifuged at 4℃ and 8500 rpm for 10 min, and the supernatant was collected. The absorbance at 532 nm and 600 nm was measured.

[0076] Thiobarbituric acid value is calculated using the following formula:

[0077] In the formula, m is the mass of the fish ball (g), and D (532 nm) and D (600 nm) represent the absorbance of the sample at 532 nm and 600 nm, respectively. The results are recorded in... Figure 8 .

[0078] like Figure 8 As shown in (A), the initial TVB-N of the fish balls was 10.59 mg / 100g. During storage, TVB-N increased in all groups, but the differences were significant: from day 8, the TVB-N in the SA group was significantly higher than that in the SA / PE10 and SA / PE10-f groups, and the increase was greater; the SA group experienced a rapid increase in TVB-N due to its inability to inhibit spoilage, while the SA / PE10 and SA / PE10-f groups showed slower increases. On day 16, the SA group was completely spoiled, with TVB-N reaching 65.67 mg / 100g, far exceeding that of the SA / PE10 group (32.26) and the SA / PE10-f group (25.72). The results indicate that the SA / PE10 membrane containing Pickering emulsion indirectly maintains TVB-N stability by forming a dense physical barrier that reduces water evaporation and oxygen contact. The SA / PE10-f group further underwent fumigation with octadecylamine to construct a hydrophobic layer on the membrane surface, enhancing barrier performance and delaying TVB-N accumulation. In addition, the cinnamon oil in Pickering emulsion acts as a natural antibacterial agent, which can inhibit putrefactive microorganisms such as Listeria and reduce the generation of volatile nitrogenous substances.

[0079] like Figure 8(B) shows that the initial TBA value was 0.96 ± 0.07 mg MDA / kg. With prolonged storage, TBA levels increased in all groups: the SA group showed the most significant increase, followed by the SA / PE10 group, and the SA / PE10-f group showed the least. The coating containing Pickering emulsion formed a dense interfacial barrier, reducing water evaporation and oxygen permeation, and inhibiting oxidation reactions. The SA / PE10-f group further constructed a hydrophobic interfacial layer through octadecylamine fumigation, enhancing physical barrier properties and more effectively delaying TBA accumulation. Furthermore, brown algae polyphenols and cinnamon essential oil may have a synergistic effect in their antioxidant mechanisms, acting on different stages of lipid oxidation (such as scavenging free radicals, chelating metal ions, and inhibiting oxidase activity), constructing a more complete antioxidant defense system while reducing the indirect promotion of lipid oxidation by microbial metabolism.

[0080] 4. Texture analysis of fish balls Test method: Texture determination: The middle portion of each fish ball was taken and approached by a P / 50 probe of a food texture analyzer at a speed of 1 mm / s. The shape variable was set to 50%. Three parallel tests were performed on each fish ball to obtain its hardness and elasticity data. Results were recorded in [document name missing]. Figure 9 .

[0081] like Figure 9 As shown, during storage, the increase in hardness of the SA / PE10-f group was significantly lower than that of the SA / PE10 group and the SA group; in terms of elasticity, cohesiveness, and chewiness, the decrease in hardness of the SA / PE10-f group was also lower than that of the other two groups. This is mainly due to the effective inhibition of moisture loss by the composite barrier formed by the fumigation process and Pickering emulsion. Octadecylamine constructs a hydrophobic barrier on the membrane surface through fumigation, slowing down moisture migration and loss, and maintaining moisture distribution and textural stability. In addition, brown algae polyphenols and cinnamon essential oil play a synergistic role in the antioxidant mechanism (scavenging free radicals, chelating metal ions, inhibiting oxidases, etc.), reducing the damage to the protein network caused by lipid oxidation and microbial metabolism. Therefore, the fish balls in the SA / PE10 group and the SA / PE10-f group are superior to the SA group in terms of hardness, elasticity, cohesiveness, and chewiness, and are closer to the fresh state.

[0082] 5. Analysis of fish ball gel strength and microbial growth Test method: Determination of gel strength: Fish ball samples were cut into cylinders with a height and diameter of 15 mm, and the gel strength was tested by puncture test of the fish balls at room temperature using a texture analyzer.

[0083] Determination of microbial growth: The determination of total bacterial count refers to GB 4789.2-2016, and the specific method is as follows: Take 5 g of fish balls and 45 mL of sterile physiological saline in a sterile homogenizing bag, homogenize the fish balls into a paste using a homogenizer, and dilute with sterile physiological saline to a concentration of 10.- ²、10 - ³、10 -4 10 -5 10 -6 Diluted solutions were prepared; 100 μL of each dilution was spread onto nutrient agar plates, with each dilution replicated three times; after incubation at 37 °C for 48 ± 2 h, plates with colony counts ranging from 30 CFU to 300 CFU were selected for counting. Results were recorded on [the relevant documentation]. Figure 10 .

[0084] like Figure 10 As shown in (A), the gel strength of all fish balls decreased with prolonged storage time, primarily due to protein degradation and denaturation. The SA group showed the fastest decline, with a decrease of approximately 34% after 16 days. In contrast, the decline in the SA / PE10 and SA / PE10-f groups was significantly slower than that of the SA group. This is because the added antioxidants (such as Fucol-type brown algae polyphenols) in the emulsion enhanced antioxidant capacity, inhibiting protein and lipid oxidation at its source and slowing down gel strength deterioration. The SA / PE10-f group also benefited from the introduction of an octadecylamine hydrophobic layer, further blocking adverse external factors and better maintaining gel strength.

[0085] like Figure 10 As shown in (B), the total number of microorganisms in the SA / PE10 group and the SA / PE10-f group was significantly lower than that in the SA group throughout the storage period, indicating the best antibacterial effect. The main putrefactive bacteria included Pseudomonas, Shewanella (which produces volatile sulfides causing a fishy odor), lactic acid bacteria, Enterobacteriaceae (such as Escherichia coli), and potentially pathogenic bacteria such as Staphylococcus aureus and Listeria monocytogenes. Mechanistically, cinnamaldehyde in cinnamon essential oil, due to its hydrophobic properties, preferentially dissolves and accumulates in the lipid bilayer of bacterial cell membranes, disrupting membrane integrity and order.

[0086] In summary, this invention discovers that brown algae polyphenols and nanocellulose can form a structurally stable composite system through high-density hydrogen bonding and aromatic stacking. This composite system is used to stabilize Pickering emulsion as an active additive for sodium alginate membranes, providing a solution to the problems of poor mechanical strength, weak barrier properties, and lack of antibacterial and antioxidant functions in single sodium alginate membranes. It avoids the safety hazards of traditional chemical preservatives and the disadvantages of ordinary emulsions, such as poor stability and uncontrollable release of active ingredients. Furthermore, this invention also finds that when the amount of Pickering emulsion added is 10% of the volume of the sodium alginate casting liquid, the prepared antibacterial, antioxidant, and hydrophobic membrane can significantly inhibit lipid oxidation, microbial growth, and protein degradation of fish balls during refrigeration, greatly reducing the accumulation of TVB-N and TBA, while maintaining good gel strength and water retention. This results in a significantly different preservation effect compared to unmodified membranes or membranes with low addition amounts.

[0087] Furthermore, this invention also provides a comprehensive research method for systematically evaluating the application of Pickering emulsion-modified sodium alginate membranes in aquatic product preservation. This method includes: analysis of membrane physicochemical properties (thickness, water content, water solubility, water vapor transmission coefficient) → mechanical and optical performance testing (tensile strength, elongation at break, light transmittance) → surface property characterization (contact angle, SEM microstructure) → thermal stability and chemical structure analysis (thermogravimetric analysis, ATR-FTIR) → evaluation of antioxidant and antibacterial activity (DPPH scavenging, inhibition zone) → verification of aquatic product preservation effects (color, pH, water holding capacity, TVB-N, TBA, texture, gel strength, total microbial count). This research pathway provides a theoretical basis and experimental evidence for the development of novel food packaging films and their application in food preservation.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing an antibacterial, antioxidant, and hydrophobic membrane, characterized in that, Includes the following steps: S1. Disperse the brown algae polyphenol / nanocellulose complex in water to obtain a brown algae polyphenol / nanocellulose complex suspension. S2. The brown algae polyphenol / nanocellulose complex suspension is mixed with cinnamon essential oil, homogenized and sonicated to obtain Pickering emulsion; S3. The Pickering emulsion and sodium alginate casting solution are mixed and stirred to obtain an active casting solution, which is then dried and crosslinked with calcium chloride to obtain the antibacterial, antioxidant, and hydrophobic membrane.

2. The method for preparing the antibacterial, antioxidant, and hydrophobic membrane as described in claim 1, characterized in that, In step S1, the mass ratio of nanocellulose to brown algae polyphenols in the brown algae polyphenol / nanocellulose composite is 1:0.05~0.

15.

3. The method for preparing the antibacterial, antioxidant, and hydrophobic membrane as described in claim 1, characterized in that, In step S1, the concentration of the brown algae polyphenol / nanocellulose complex suspension is 0.5~1% w / v.

4. The method for preparing the antibacterial, antioxidant, and hydrophobic membrane as described in claim 1, characterized in that, In step S2, the volume ratio of the brown algae polyphenol / nanocellulose complex suspension to the cinnamon essential oil is 1:

1.

5. The method for preparing the antibacterial, antioxidant, and hydrophobic membrane as described in claim 1, characterized in that, In step S3, the amount of Pickering emulsion added is not less than 5% of the volume of the sodium alginate membrane liquid.

6. The method for preparing the antibacterial, antioxidant, and hydrophobic membrane as described in claim 5, characterized in that, The amount of Pickering emulsion added is 10-15% of the volume of the sodium alginate membrane liquid.

7. The method for preparing the antibacterial, antioxidant, and hydrophobic membrane as described in claim 1, characterized in that, In step S3, after the calcium chloride crosslinking, the step of fumigation with octadecylamine is further included.

8. The application of an antibacterial, antioxidant, and hydrophobic membrane prepared by any one of claims 1-7 in the preservation of fish balls.

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