ASBAVA / PVA composite film, preparation method and application of ASBAVA / PVA composite film in fruit preservation

Abstract

The invention discloses an ASBAVA / PVA composite film and a preparation method and application thereof in fruit preservation, and the preparation method comprises the following steps: mixing vanillin and absolute ethyl alcohol, stirring until the vanillin is completely dissolved, adding aminated mesoporous silica, continuously stirring, centrifugally washing for 3-4 times by using ethyl alcohol after the reaction is completed, and carrying out vacuum drying at 45 DEG C for 8 hours to obtain a yellow powdery product, namely ASBAVA; pVA, glycerin, deionized water and ASBAVA are mixed and stirred at the temperature of 80 DEG C to prepare uniform membrane liquid, and defoaming is carried out; and after the bubbles are completely removed, scraping the film, and removing the solvent to obtain the ASBAVA / PVA antibacterial composite film. The invention designs and develops an efficient antibacterial composite film ASBAVA / PVA with pH response release based on bacteria proliferation induced environmental acidification and acid response characteristics of imine bonds, by utilizing nucleophilic characteristics of amino groups on the surface of aminated mesoporous silica and by constructing an intelligent antibacterial strategy dominated by the imine bonds. The defects that a coupling type antibacterial agent is large in adding amount, poor in antibacterial property and incapable of responding to the change of the surrounding environment are overcome.

Description

Technical Field

[0001] This invention belongs to the field of preservation technology, specifically relating to an ASBAVA / PVA composite film, its preparation method, and its application in fruit preservation. Background Technology

[0002] PVA, a typical biodegradable polymer, is considered a top candidate to replace petroleum-based plastics for food preservation due to its excellent film-forming properties, barrier properties, and high flexibility. However, the presence of numerous hydrophilic hydroxyl groups (-OH) in the PVA molecule causes films or products made from PVA to swell and degrade in humid environments or when in contact with water, limiting the application of PVA materials in high-humidity environments. Furthermore, the lack of antibacterial properties in PVA significantly restricts its development in healthcare and food packaging. Therefore, antibacterial and hydrophobic modification of PVA to endow it with superior antibacterial and hydrophobic properties is of great significance.

[0003] Currently, leveraging the high specific area and unique surface structure of porous nanomaterials to composite PVA substrates with porous nanomaterials that adsorb antibacterial agents has become an effective strategy for solving this problem. Mesoporous silica is a typical representative of porous nanomaterials. It can form nanoscale rough structures on the material surface, increasing surface roughness. This rough structure allows water droplets to form spherical shapes on the surface, reducing the contact area between the droplets and the surface, thereby improving the hydrophobicity of the material. Simultaneously, the low surface energy of mesoporous silica also makes the material surface more hydrophobic. Furthermore, the abundant pore structure on the surface of mesoporous silica and its ease of modification and grafting make it demonstrate great potential in the development of antibacterial composite materials.

[0004] Currently, there are no reports on the preparation of ASBAVA / PVA composite films. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of the embodiments of the present invention and to briefly describe some preferred embodiments.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing ASBAVA / PVA composite films.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing an ASBAVA / PVA composite film, comprising, Vanillin and anhydrous ethanol were mixed and stirred until vanillin was completely dissolved. Aminated mesoporous silica was added and stirring was continued. After the reaction was complete, the mixture was washed 3-4 times by centrifugation with ethanol and dried under vacuum at 45°C for 8 h to obtain a yellow powder product, which is ASBAVA. PVA, glycerin, deionized water and ASBAVA are mixed and stirred at 80°C to prepare a uniform film solution for defoaming. After defoaming is complete, the film is scraped off to remove the solvent, resulting in an ASBAVA / PVA antibacterial composite film.

[0009] In a preferred embodiment of the preparation method described in this invention, the method for preparing the aminated mesoporous silica includes: Mesoporous silica and 3-aminopropyltriethoxysilane were added to a single-necked flask containing dry toluene. The mixture was refluxed and stirred at 80-90°C for 12-24 h. After the reaction was complete and cooled to room temperature, the mixture was washed 2-3 times with dry toluene and then dried under vacuum to obtain aminated mesoporous silica.

[0010] In a preferred embodiment of the preparation method described in this invention, the ratio of mesoporous silica, 3-aminopropyltriethoxysilane, and dry toluene is 1.0~2.0 g: 1.0~1.3 g: 40 mL.

[0011] In a preferred embodiment of the preparation method described in this invention, the ratio of vanillin, anhydrous ethanol, and aminated mesoporous silica is 1.0~2.0 g: 20 mL: 2 g.

[0012] As a preferred embodiment of the preparation method described in this invention, the ratio of PVA, glycerol, deionized water and ASBAVA is 8g:2g:70ml:(0.8~3.3)g.

[0013] In a preferred embodiment of the preparation method described in this invention, the ratio of PVA, glycerol, deionized water and ASBAVA is 8g:2g:70ml:1.6g.

[0014] Another objective of this invention is to overcome the shortcomings of the prior art and provide an ASBAVA / PVA composite film.

[0015] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of ASBAVA / PVA composite film in fruit preservation, wherein the fruits include blueberries and cherry tomatoes.

[0016] Beneficial effects of this invention: (1) Based on the acid response characteristics of bacterial proliferation-induced environmental acidification and imine bonds, this invention utilizes the nucleophilic properties of amino groups on the surface of aminated mesoporous silica to design and develop a highly efficient antibacterial composite film ASBAVA / PVA with pH-responsive release by constructing an intelligent antibacterial strategy dominated by imine bonds; it solves the defects of coupling antibacterial agents, such as large addition amount, poor antibacterial properties and inability to respond to changes in the surrounding environment.

[0017] (2) This invention systematically studies the antibacterial properties, barrier properties, thermal stability, optical properties and mechanical properties of ASBAVA / PVA materials. Using blueberries and cherry tomatoes as research models, and combining existing antibacterial packaging antibacterial theories, it explores the antibacterial and freshness preservation mechanism of silicon-based antibacterial modified PVA packaging materials, providing a reference for the development of new green biodegradable antibacterial food packaging materials.

[0018] (3) The silicon-based antibacterial agent ASBAVA of the present invention does not cause agglomeration or reduce the crystallinity of PVA material at an addition amount of 2 wt%, and even increases the crystallinity of PVA material at an addition amount of 1 wt%. The thermal stability test results show that the addition of silicon-based antibacterial agent ASBAVA will reduce the antibacterial activity. The thermal degradation rate (T5) of the ASBAVA / PVA composite membrane is lower than that of the pure PVA membrane during the PVA chain decomposition stage. This may be a result of the interaction between PVA and the antibacterial agent ASBAVA. These studies indicate that the addition of ASBAVA reduces the T5% of the composite membrane but also decreases the PVA chain thermal decomposition rate, ensuring that the functionality of the composite membrane is not lost in daily use. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a synthetic route diagram of ASBAVA in an embodiment of the present invention.

[0020] Figure 2 The infrared spectra of SBA, ASBA, and ASBAVA are shown in the embodiments of the present invention.

[0021] Figure 3 The above are XPS data plots of ASBAVA in this embodiment of the invention, where a is the total spectrum and b is the C1s spectrum.

[0022] Figure 4The XRD patterns of VA, AL, SBA, ASBA, and ASBAVA are shown in the embodiments of the present invention.

[0023] Figure 5 ASBAVA in the embodiments of the present invention 13 C SSNMR spectrum.

[0024] Figure 6 This is a diagram showing the antibacterial test results of ASBAVA against E. coli and S. aureus in an embodiment of the present invention.

[0025] Figure 7 The image shows the infrared spectrum of the ASBAVA / PVA composite film in an embodiment of the present invention.

[0026] Figure 8 The images show the XRD patterns of PVA and ASBAVA / PVA composite films in the embodiments of the present invention.

[0027] Figure 9 The diagram shows the synthesis and release mechanism and stability in the embodiments of the present invention, where a represents the synthesis and release mechanism of ASBAVA, and b represents the stability of the imine bonds in the ASBAVA / PVA composite membrane in aqueous solutions at different pH values.

[0028] Figure 10 This is a water vapor transmission rate diagram of PVA and ASBAVA / PVA composite films in the embodiments of the present invention.

[0029] Figure 11 This is a contact angle diagram of PVA and ASBAVA / PVA composite films in an embodiment of the present invention.

[0030] Figure 12 This is a transmittance diagram of PVA and ASBAVA / PVA composite films in an embodiment of the present invention.

[0031] Figure 13 This is an antibacterial diagram of PVA and ASBAVA / PVA composite films in an embodiment of the present invention.

[0032] Figure 14 The graphs show the TG and DTG curves of PVA and ASBAVA / PVA composite films in the embodiments of the present invention.

[0033] Figure 15 The images shown are of fruits stored using PVA film, ASBAVA / PVA composite film, and no film treatment, respectively, according to embodiments of the present invention. In these images, a represents blueberries and b represents cherry tomatoes.

[0034] Figure 16The image shows the weight loss rate of fruits stored under PVA film, ASBAVA / PVA composite film, and no film treatment in this embodiment of the invention, where a represents blueberries and b represents cherry tomatoes.

[0035] Figure 17 The diagram shows the spoilage rate of fruits stored with PVA film, ASBAVA / PVA composite film, and no film treatment in the embodiments of the present invention, where a represents blueberries and b represents cherry tomatoes.

[0036] Figure 18 The graph shows the soluble solids content of fruits stored using PVA film, ASBAVA / PVA composite film, and no film treatment in the embodiments of the present invention. In the graph, a represents blueberries and b represents cherry tomatoes. Detailed Implementation

[0037] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0038] All raw materials used in this invention are common commercially available products; Kirby-Bauer assay: Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus were used as research subjects. 100 μL of laboratory-prepared cryopreserved solutions of the two bacterial strains were added to 5 mL of TSB liquid medium and incubated at 37 ℃ with shaking for 12 h. The bacterial concentration was then adjusted to 10⁸ CFU / mL with sterile PBS buffer. 10 mL of TSB solid medium, sterilized at 121 ℃ for 15 min, was cooled to 60 ℃ and poured into a 90 mm diameter sterile petri dish, then placed in a stable laminar flow hood for cooling and solidification. 100 μL of the solution was then adjusted to 10⁸ CFU / mL with sterile PBS buffer. 8 After evenly spreading the CFU / mL bacterial suspension onto a plate, place the sample to be tested flat on the culture medium coated with the bacterial suspension (if the sample curls, gently press the sample with a sterile paper pad). Invert the plate and incubate at 37 ℃ for 24 h. Measure the diameter of the inhibition zone using calipers. Each experiment was performed in triplicate.

[0039] WVP test: WVP was tested according to the literature method, with some modifications. The membrane was sealed in a vial (5.0 cm in diameter, RH1 = 0%) containing 3.0 g of anhydrous CaCl2, and then placed in a desiccator containing saturated K2SO4 solution (RH2 = 97%). Subsequently, the desiccator was placed in a circulating oven at 25°C, and the weight of the vial was measured every 2 hours until the vial reached a constant weight.

[0040] WVP (g·cm / cm) 2 After plotting ·s·Pa) as a time function, according to: In the formula, ΔM (g) is the weight increase of the test cup, d (m) is the average film thickness, P is the saturated vapor pressure, and S (m 2 ) represents the exposed membrane area, and T(s) represents the recording time.

[0041] CA Test: The static water contact angle of a 3 mL water droplet on the film surface was recorded using a digital microscope. The average of the three static water contact angle measurements was taken.

[0042] Weight Loss Rate Test: Weigh the samples every 3 days. Based on the 0-day period, calculate the sample weight loss rate using the following formula: In the formula, m0(g) is the mass of blueberries stored at room temperature on day 0, and m n (g) represents the mass of blueberries stored at room temperature for n days.

[0043] Corruption Rate Test (Decay Rate): Observe the surface condition of blueberries every 3 days. If mold appears on the surface, the fruit is considered rotten. Calculate the rot rate using the following formula: In the formula, N is the total number of blueberries in each group, and Nn is the total number of rotten blueberries on the nth day of storage at room temperature.

[0044] Determination of Soluble Solid Content: The measurements were performed using a portable digital refractometer.

[0045] Example 1 (1) Amination of mesoporous silica Commercial mesoporous silica (SBA, 2.0 g, 32.89 mmol) and 3-aminopropyltriethoxysilane (APTES, 1.3 g, 5.92 mmol) were added to a single-necked flask containing 40 mL of dry toluene, maintaining a molar ratio of APTES to SBA of 0.18. The mixture was refluxed and stirred at 90 °C for 24 h. After the reaction was complete and cooled to room temperature, the mixture was washed 2–3 times with dry toluene and then dried under vacuum at 35 °C for 10 h to obtain aminated mesoporous silica, named ASBA. (2) Synthesis of silicon-based antibacterial agent ASBAVA Vanillin (VA, 2.0 g, 13.14 mmol) and 20 mL of anhydrous ethanol were added to a 100 mL beaker. The mixture was stirred at room temperature until the vanillin was completely dissolved. Then, 2 g of ASBA was added and stirring continued for 4 h, ensuring a VA to ASBA mass ratio of 1:1. After the reaction was complete, the mixture was washed 3-4 times by centrifugation with ethanol and dried under vacuum at 45 °C for 8 h to obtain a yellow powder product, named ASBAVA. The synthetic route is shown below. Figure 1 .

[0046] (3) Structural characterization of antibacterial agent ASBAVA Figure 2 Infrared spectra of SBA, ASBA, and ASBAVA. Spectra at 1080 and 798 cm⁻¹. -1 The absorption vibration peaks correspond to the stretching / bending vibration peaks of Si-O-Si in mesoporous silica. ASBA and ASBAVA spectra at 2980 cm⁻¹ -1 The new peak appearing at 720 cm⁻¹ is the tensile vibration peak of the methylene group after the introduction of a silane coupling agent into aminated mesoporous silica. -1 The weak peak appearing at [a certain point] is the out-of-plane rocking vibration peak of the primary amine group -NH2. Unlike ASBA, ASBAVA shows peaks at 1594 and 1637 cm⁻¹. -1 Two new peaks appeared at the spectrum. The former was caused by the C=C skeleton vibration of the benzene ring, and the latter was attributed to the C=N in the Schiff base structure. The characteristic chemical bonds of the target molecule were both reflected in the spectrum.

[0047] The changes in chemical structure during the interaction between VA and ASBA were analyzed using XPS. Figure 3 (a) is the wide XPS scan spectrum of ASBAVA. Figure 3 (b) shows the high-resolution XPS scan spectrum of C1s. Figure 3 (a) shows that the Si peak is centered at 154.08 (Si 2s) and 103.12 eV (Si 2p), while the XPS signal of O1s is centered at a binding energy of 532.30 eV. Figure 3 (a) XPS spectroscopy confirmed that ASBAVA contains a silica structure. Meanwhile, in Figure 3 (b) In the C1s spectrum, the peak at 284.80 eV is attributed to the aromatic ring of VA. The peak at 286.90 eV corresponds to the presence of C=N+.

[0048] Figure 4 This is the XRD diffraction pattern of ASBAVA. AL represents the peak of the aluminum sample disk in the XRD test. Figure 4It can be seen that the obvious diffraction peaks at 2θ = 12.7, 26.3, 26.7, and 28.7 ° are characteristic peaks of VA; the broad peak at 2θ = 20.0 ° is caused by SBA. Diffraction interference is characteristic of low-crystallinity SBA, and the peak shape of SBA and ASBA does not change significantly, indicating that amino modification has not changed the crystal structure of mesoporous silica. Obvious characteristic diffraction peaks of VA can be observed at 2θ = 12.7, 26.3, 26.7, and 28.7 °.

[0049] To further confirm the construction of the amino-silica and vanillin-modified imine structure, the ASBAVA sample was subjected to... 13 C SSNMR test. Figure 5 For ASBAVA 13 The C SSNMR spectrum shows a characteristic peak involving carbon in the imine bond at around 165 ppm. Figure 5 The distribution of all other carbon atoms in the chemical structure was clearly identified through numerical identification. Based on the above characterization results, it was confirmed that the antibacterial agent ASBAVA has been successfully synthesized.

[0050] The antibacterial activity of ASBAVA against E. coli and S. aureus was determined using the Kirby-Bauer method. Table 1 shows the diameter of the inhibition zone of ASBAVA against the two bacterial species. Figure 6 This is a graph showing the antibacterial test results of ASBAVA against two bacterial species.

[0051] Table 1

[0052] from Figure 6 As can be seen, ASBAVA exhibits antibacterial activity against both types of bacteria. ASBAVA releases vanillin through the hydrolysis of imine bonds, which comes into contact with the bacteria and forms a transparent inhibition zone around the ASBAVA disc. The inhibition zone diameter is measured, and the antibacterial effect is judged as follows: inhibition zone diameter >20 mm is extremely sensitive, 15-20 mm is highly sensitive, 10-15 mm is moderately sensitive, and inhibition zone <10 mm is lowly sensitive. ASBAVA has an inhibition zone diameter greater than 20 mm against both types of bacteria, which is considered extremely sensitive.

[0053] Example 2 (1) Preparation of ASBAVA / PVA antibacterial composite film PVA, glycerin, deionized water, and ASBAVA were added to a 250 mL three-necked flask according to the formula in Table 4.2. The mixture was mechanically stirred at 80 °C to form a homogeneous film solution. The film solution in the three-necked flask was then transferred to a 250 mL beaker and defoamed using a vacuum drying oven. After defoaming was complete, a hot-scalpel-and-wire coating machine was used to coat the film on a flat glass plate. Finally, the glass plate carrying the film was placed horizontally in a 40 °C forced-air dryer overnight to remove the solvent, resulting in an ASBAVA / PVA antibacterial composite film.

[0054] Table 2 Formulations of PVA and its composite films ASBAVA / PVA

[0055] Antimicrobial composite films with ASBAVA mass fractions of 1%, 2%, 3%, and 4% are denoted as 1wt%ASBAVA / PVA, 2wt%ASBAVA / PVA, 3wt%ASBAVA / PVA, and 4wt%ASBAVA / PVA, respectively.

[0056] (2) Analysis of ATR-FTIR measurement results ATR-FTIR spectra of pure PVA films and ASBAVA / PVA films are as follows: Figure 7 As shown, all films except the PVA film exhibit a series of characteristic wavelengths of ASBAVA. The abundant hydroxyl groups in PVA molecules can form intramolecular and intermolecular hydrogen bonds, contributing to the formation of a continuous and dense structure in the film. Furthermore, the characteristic peaks of PVA—3274 (-OH), 2947 (CH), 1422 (CO), and 1092 cm⁻¹ (COC)—are present in all films. Moreover, with increasing ASBAVA content, the OH vibrational band (3274 cm⁻¹) exhibits a blue shift, indicating an intermolecular hydrogen bond interaction between ASBAVA and PVA. The formation of hydrogen bonds lowers the vibrational frequency of the Si-O-Si absorption peak, which is beneficial for the dispersion of ASBAVA in the PVA film, improving its physical and mechanical properties. This demonstrates the good compatibility between PVA and ASBAVA.

[0057] (3) Analysis of XRD measurement results To investigate the effect of ASBAVA on the crystallization of PVA materials, XRD analysis was performed on ASBAVA / PVA films with different ASBAVA contents. The test results are as follows: Figure 8 As shown.

[0058] like Figure 8As shown, 2θ = 19.3, 38.4, 44.5, 64.9, and 78.1 can be observed in all membranes. The diffraction peaks at 2θ = 19.3 ° are attributed to the crystallization of the PVA(101) crystal plane, while the diffraction peaks at 38.4, 44.5, 64.9, 78.1 and 82.3 ° are attributed to the aluminum sample disk. The absence of a distinct silica peak in the film indicates that mesoporous silica is uniformly distributed throughout the PVA matrix. Meanwhile, characteristic peaks of vanillin were observed in the 2–4 wt% concentration, but not at 1 wt%, likely due to the low amount of ASBAVA encapsulated within the PVA film, further confirming the uniform distribution of mesoporous silica within the PVA matrix. Furthermore, with increasing ASBAVA content in the ASBAVA / PVA film, the diffraction peak at 2θ = 19.3 ° becomes both broad and narrow, indicating that the crystallinity of the film decreases with increasing ASBAVA content. The crystallinity of the composite film affects its mechanical strength; decreased crystallinity is often accompanied by weakened mechanical properties. The decrease in composite film crystallinity also alters the film's barrier properties. At 1 wt%, due to heterogeneous nucleation, the composite film exhibits increased crystallinity and decreased grain size, resulting in a higher tensile strength than the PVA film.

[0059] (4) Analysis of pH response release measurement results To verify the sensitivity of imine bonds to acidic environments, we placed the prepared ASBAVA / PVA composite membranes in buffer solutions at 23°C with pH values ​​of 4, 5, 6, and 7, respectively, and used ATR-FTIR to study the ASBAVA bonds. Stability of the imine bond.

[0060] Figure 9 To illustrate the synthesis and release mechanism of imine bonds in ASBAVA, Figure 9(b) shows the ATR-FTIR spectra of the ASBAVA / PVA composite membrane after contact with water for 4 days at different pH levels. Figure 9 (b) It can be seen that, compared to a neutral environment (pH 7), when the membrane was exposed to an acidic environment (pH 4, 5, 6) for 4 days, the imine absorption band weakened, and at 1562 cm⁻¹... -1 A new vibrational peak appeared at 1562 cm⁻¹, mainly due to the weakening of the imine absorption peak caused by the hydrolysis of the imine bond under acidic conditions. -1 The new peak at 1562 cm⁻¹ is attributed to the protonation of the ASBAVA amino group following the hydrolysis of the imine bond. Simultaneously, with increasing solution acidity, the peak at 1562 cm⁻¹... -1The more pronounced the peak, the more this indicates that the hydrolysis of imine bonds in ASBAVA / PVA is affected by the pH value of the surrounding environment.

[0061] (5) Analysis of WVP measurement results WVP is an important factor in evaluating film quality. Low WVP is sometimes detrimental to the storage of certain self-ripening fruits and vegetables, such as bananas and blueberries.

[0062] Introducing nanoparticles into the matrix is ​​an effective strategy for improving matrix barrier properties. The WVP test results of ASBAVA / PVA films with different ASBAVA addition amounts are shown below. Figure 10 As shown. By Figure 10 It can be seen that the WVP of PVA film is the lowest, at only 0.9226 × 10⁻⁶. - 12 g·cm / cm 2 While the WVP of the ASBAVA / PVA film gradually increases with increasing ASBAVA content, reaching 4 wt% at which point its WVP increases by 444.0% compared to the PVA film, this is likely because the resistance of the PVA film to water vapor transport primarily depends on the crystalline phase within the membrane. The addition of ASBAVA leads to the formation of "interfacial voids" at the particle / polymer matrix interface, providing a preferential pathway for water molecules to permeate and migrate. Furthermore, the aggregation of ASBAVA also reduces the crystallinity of the PVA film. This significantly improves the barrier properties of the PVA film, endowing the ASBAVA / PVA composite membrane with excellent water vapor permeability.

[0063] (6) Analysis of CA measurement results The wettability of thin films is an important factor in evaluating their application value. To assess the effect of ASBAVA content on the wettability of ASBAVA / PVA films, the surface properties were evaluated using the CA method. The results are as follows: Figure 11 As shown.

[0064] Depend on Figure 11It can be seen that, compared with PVA film, the CA value of 2 wt% ASBAVA / PVA increased by 113%. Furthermore, the CA value showed a trend of first increasing and then decreasing with increasing ASBAVA content. This may be because when the ASBAVA content is less than 2 wt%, the uniform distribution of ASBAVA in PVA imparts a rough hydrophobic surface structure to the ASBAVA / PVA film. In addition, the hydroxyl groups on the ASBAVA surface and the hydrophobic groups of VA also play important roles. However, with further increases in ASBAVA content, ASBAVA aggregates, vanillin permeates to the film surface, and the surface structure of the ASBAVA / PVA film is damaged, leading to a decrease in the hydrophobicity of the composite film. However, overall, it is still superior to the unmodified PVA film.

[0065] Example 3 Analysis of UV-Vis measurement results: Ultraviolet (UV) radiation is one of the factors that cause food spoilage. The UV-shielding properties and opacity of films are key factors in preventing food from oxidizing and spoiling during storage and transportation. Figure 12 This image shows the UV-Vis spectra of PVA and ASBAVA / PVA composite films. UV wavelength range: 200-400 nm; Visible wavelength range: 400-760 nm. Figure 12 As shown, the transmittance of all ASBAVA / PVA composite films is much lower than that of PVA films, especially in the UV region with wavelengths ranging from 200 to 400 nm. ASBAVA / PVA composite films almost completely absorb UV light. In the visible light range, compared to the 86.98% transmittance of PVA films, the transmittance of ASBAVA / PVA films decreases from 36.9% to 1.2% as the amount of ASBVA added increases. This means that ASBAVA / PVA films not only possess excellent UV shielding capabilities but also a certain degree of transparency.

[0066] The significant decrease in UV transmittance of ASBAVA / PVA films is likely due to the combined effect of the abundant benzene rings in VA and SBA. The presence of numerous benzene rings enhances the n→π* transition, while the addition of SBA weakens the transmittance of the UV-Vis film. Similar to the UV region, the visible light region exhibits the same pattern, which may be a result of the refraction and diffraction of light by silica.

[0067] Example 4 Analysis of the results of the antibacterial test of the composite membrane: The antibacterial activity of composite materials can usually be evaluated by the strength of their ability to inhibit microbial growth. Table 3 and Figure 13The results of antibacterial experiments on E. coli and S. aureus using ASBAVA / PVA composite films with different addition amounts.

[0068] Table 3. Diameter of the inhibition zone of PVA and its composite film ASBAVA / PVA

[0069] Depend on Figure 13 It can be seen that neither the PVA film nor the ASBAVA / PVA film with an addition of 1 wt% inhibited the growth of the two tested bacteria. This is because, at low addition levels, ASBAVA is encapsulated within the PVA film, preventing the hydrolysis of ASBAVA imine bonds and thus preventing the release of VA from the ASBAVA pores, resulting in the loss of its antibacterial activity. With increasing ASBAVA dosage, ASBAVA disrupts the film's crystal structure, making ASBAVA more easily exposed and reducing the difficulty of ASBAVA imine bond hydrolysis, thereby allowing the ASBAVA / PVA film to exhibit antibacterial activity (ASBAVA / PVA film with an addition of 2 wt% showed antibacterial activity). The film exhibited antibacterial activity against E. coli and S. aureus (with inhibition zone diameter of 21 mm for both). Furthermore, with increasing addition, ASBAVA tended to aggregate, directly exposing it to a slightly acidic environment, which facilitated the release of VA. The released VA directly acted on the cell membranes of Escherichia coli and Staphylococcus aureus, leading to bacterial cell membrane damage, osmotic imbalance, leakage of cell components, and ultimately bacterial death. The antibacterial activity of the film was also enhanced accordingly.

[0070] Example 5 Analysis of thermal stability test results: To investigate the effect of ASBAVA addition on the thermal stability of composite membranes, TGA tests were performed on composite membranes with different ASBAVA addition amounts.

[0071] Figure 14 The TG and DTG curves are for PVA and ASBAVA / PVA composite films. Figure 14As shown in b, the thermal weight loss of PVA roughly goes through three stages. The first stage, from 30 to 140 °C, is mainly due to moisture evaporation from the film; the second stage, from 208 to 407 °C, is mainly due to the disintegration of the PVA chains; and the third stage, from 415 to 500 °C, is mainly due to the decomposition of the PVA backbone. Compared to PVA films, ASBAVA-containing composite films exhibit four thermal weight loss stages. The first stage, from 30 to 101 °C, is related to moisture evaporation from the film; the second stage, from 101 to 218 °C, is related to the loss of glycerol and the carbonization of vanillin; the third stage, from 218 to 366 °C, is related to the decomposition of the PVA chains; and the fourth stage, from 370 to 580 °C, is mainly due to the disintegration of the PVA chains. It is worth noting that during the PVA chain decomposition stage, the thermal degradation rate of ASBAVA / PVA composite films with an addition amount of 1 wt% to 4 wt% was lower than that of pure PVA films. This may be because the interaction between PVA and ASBAVA reduced the thermal degradation rate of the film.

[0072] The above studies show that the addition of ASBAVA reduces the T5% of the composite membrane, but reduces the PVA chain decomposition rate of the composite membrane, ensuring that the functionality of the composite membrane is not lost in daily use scenarios.

[0073] Example 6 (1) Treatment of blueberries and cherry tomatoes with ASBAVA / PVA antibacterial composite film: First, the collected blueberries and cherry tomatoes were selected, with only fresh blueberries and cherry tomatoes of healthy skin and uniform size chosen for the preservation test. All tested blueberries and cherry tomatoes were soaked in distilled water for 2 minutes and then air-dried. Subsequently, the blueberries and cherry tomatoes were packaged separately using antibacterial composite film, PVA film, and no film, and were named the experimental group, PVA group, and control group, respectively.

[0074] All samples were stored in a constant temperature and humidity environment of 25°C and 75% RH for 12 days.

[0075] (2) Analysis of the appearance of blueberries and cherry tomatoes Figure 15 The images show the appearance changes of blueberries and cherry tomatoes at different time points during storage, comparing the control group, PVA-treated group, and experimental group. Figure 15It was found that both the blueberry control group and the PVA group showed significant mold growth after 9 days of storage. The cherry tomato control group also showed significant mold growth after 9 days of storage, while the PVA group showed significant rot. However, the experimental groups of blueberries and cherry tomatoes did not show significant changes in appearance throughout the entire storage period. This indicates that the ASBAVA / PVA antibacterial composite film can effectively inhibit the proliferation of fungi and bacterial pathogens on the surface of blueberries and cherry tomatoes, effectively preventing rot and mold growth throughout the entire storage period, thus preserving the commercial value of blueberries and cherry tomatoes.

[0076] (3) Analysis of weight loss rate measurement results Weight loss rate and spoilage rate are key indicators for evaluating the preservation performance of composite films.

[0077] Figure 16 The figure shows the changes in weight loss rate of blueberries and cherry tomatoes during storage. As can be seen from the figure, with the extension of the storage time, the weight loss rate of blueberries in the control group, PVA group and experimental group all increased. The weight loss rate of blueberries and cherry tomatoes reached its peak at a storage time of 12 days (blueberry: control group: 48.7%, PVA group: 28.6%, experimental group: 35.6%; cherry tomatoes: control group: 20.0%, PVA group: 13.0%, experimental group: 16.0%).

[0078] It is noteworthy that throughout the storage period, the weight loss rates of blueberries and cherry tomatoes in the control group, PVA group, and experimental group were ranked as follows: control group > experimental group > PVA group. The reason why the weight loss rates of the experimental group and PVA group were lower than those of the control group is mainly due to the barrier effect of the packaging film, which inhibited the transpiration of blueberries and cherry tomatoes, thus reducing their weight loss rate. The reason why the weight loss rate of the experimental group was lower than that of the PVA group is mainly attributed to the fact that the addition of ASBAVA formed "interfacial voids" at the PVA matrix interface, providing a preferential pathway for water molecules to permeate and migrate. At the same time, at this addition level, ASBAVA reduced the crystallinity of the composite film, resulting in a higher weight loss rate in the experimental group than in the PVA group. This indicates that the ASBAVA / PVA antibacterial composite film can achieve a certain weight retention rate of packaged food while also achieving a certain permeability, preventing bacterial growth caused by humidity and other factors.

[0079] (4) Analysis of the results of the corruption rate measurement Of particular concern is that ethylene gas promotes the softening and rotting of blueberries and cherry tomatoes, and is one of the important factors contributing to fruit spoilage. The high barrier properties of PVA film will limit the emission of ethylene gas inside the packaging.

[0080] Figure 17The change in the spoilage rate of blueberries and cherry tomatoes during storage. (Source: [Insert Source Here]) Figure 17 The changes in spoilage rates of blueberries and cherry tomatoes during storage revealed that the experimental group showed no spoilage or mold growth throughout the entire storage period. In contrast, both the PVA group and the control group showed spoilage or mold growth on day 9, with the spoilage rate peaking on day 12 (blueberry: control group: 33.3%, PVA group: 20.0%; cherry tomatoes: control group: 25.0%, PVA group: 12.5%). This is because the blank group was directly exposed to the external environment without the composite film providing a barrier protection for the fruit, allowing fungal and bacterial pathogens to directly erode the fruit. Although the PVA group had a PVA film providing a barrier protection, the PVA film lacked antibacterial activity, and its dense structure limited the exchange of atmosphere between the inside and outside of the film, failing to inhibit the proliferation of fungal and bacterial pathogens. The addition of ASBAVA in the experimental group improved the crystallinity of the film, giving the composite film not only certain moisturizing properties and excellent antibacterial properties but also improving the PVA film's ability to retain moisture. The gas permeability of the substrate inhibits the infection of fungal and bacterial pathogens, thus better preserving the fruit of blueberries and cherry tomatoes.

[0081] (5) Analysis of soluble solids determination results Soluble solids in fruits and vegetables generally refer to the total amount of solid substances that can dissolve in water. This indicator is often used to assess the sweetness and taste of fruits and vegetables and is one of the important indicators for measuring the maturity and quality of fruits and vegetables.

[0082] Figure 18 The changes in soluble solids content of blueberries and cherry tomatoes under untreated, PVA film, and ASBAVA / PVA composite film treatments were investigated. Figure 18a shows that the soluble solids content of the blueberry control group, PVA group, and experimental group all showed a decreasing trend. This is because the respiration of blueberries consumes nutrients within the fruit, leading to a decrease in soluble solids content. At a storage time span of 12 days, the soluble solids content of the control group, PVA group, and experimental group reached the lowest levels (control group: 9.5%, PVA group: 10.2%, experimental group: 11.5%).

[0083] Throughout the storage period, the soluble solids content in the experimental group decreased relatively gradually, followed by the PVA group, and finally the control group. This may be attributed to the different atmospheric environments within the packaging films of the blank group, PVA group, and experimental group affecting the blueberry respiration process and thus causing different soluble solids contents. In conclusion, compared with the control group and PVA group, ASBAVA / PVA film can maintain the flavor of blueberries for a longer period of time and delay the consumption of nutrients in the blueberry fruit.

[0084] Depend on Figure 18As shown in b, the soluble solids content of cherry tomatoes in the control group, PVA group, and experimental group all showed a trend of first increasing and then decreasing. This is because as the storage time increases, the cherry tomatoes progress from ripening to decay. During ripening, polysaccharides hydrolyze to produce sucrose and fructose, providing sweetness to the fruit. However, as the storage time further increases, the respiration of the fruit consumes nutrients, resulting in a decrease in the soluble solids content. At a storage time of 12 days, the soluble solids content of the control group, PVA group, and experimental group reached the lowest level (control group: 7.55%, PVA group: 6.32%, experimental group: 5.72%). Throughout the storage period, the decrease in soluble solids content was relatively gradual in the experimental group, followed by the PVA group, and finally the control group. This indicates that compared to the control group and PVA group, the experimental group was able to maintain the flavor of the cherry tomatoes for a longer period and delay the consumption of nutrients in the fruit. In conclusion, the ASBAVA / PVA antibacterial composite film can maintain the flavor of fruit for a longer period of time, delay the consumption of nutrients in the fruit, and has good preservation application value.

[0085] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for preparing an ASBAVA / PVA composite film, characterized in that: include, Vanillin and anhydrous ethanol were mixed and stirred until vanillin was completely dissolved. Aminated mesoporous silica was added and stirring was continued. After the reaction was complete, the mixture was washed 3-4 times by centrifugation with ethanol and dried under vacuum at 45°C for 8 h to obtain a yellow powder product, which is ASBAVA. PVA, glycerin, deionized water and ASBAVA are mixed and stirred at 80°C to prepare a uniform film solution for defoaming. After defoaming is complete, the film is scraped off to remove the solvent, resulting in an ASBAVA / PVA antibacterial composite film.

2. The preparation method according to claim 1, characterized in that: The method for preparing the aminated mesoporous silica includes, Mesoporous silica and 3-aminopropyltriethoxysilane were added to a single-necked flask containing dry toluene. The mixture was refluxed and stirred at 80-90°C for 12-24 h. After the reaction was complete and cooled to room temperature, the mixture was washed 2-3 times with dry toluene and then dried under vacuum to obtain aminated mesoporous silica.

3. The preparation method according to claim 2, characterized in that: The ratio of mesoporous silica, 3-aminopropyltriethoxysilane, and dry toluene is 1.0~2.0 g: 1.0~1.3 g: 40 mL.

4. The preparation method according to claim 1, characterized in that: The ratio of vanillin, anhydrous ethanol, and aminated mesoporous silica is 1.0~2.0 g: 20 mL: 2 g.

5. The preparation method according to claim 1, characterized in that: The ratio of PVA, glycerin, deionized water and ASBAVA is 8g:2g:70ml:(0.8~3.3)g.

6. The preparation method according to claim 5, characterized in that: The ratio of PVA, glycerin, deionized water and ASBAVA is 8g:2g:70ml:1.6g.

7. The ASBAVA / PVA composite film prepared by any one of the preparation methods described in claims 1 to 6.

8. The application of the ASBAVA / PVA composite film as described in claim 7 in fruit preservation.

9. The application as described in claim 8, characterized in that: The fruits include blueberries and cherry tomatoes.

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