Edible fungus freshness indicating type antibacterial composite packaging film and preparation method and application thereof

Abstract

The present application relates to the technical field of intelligent packaging and food quality detection, and particularly relates to a fresh degree indicating antibacterial composite packaging film for edible fungi, a preparation method and application thereof; the antibacterial peptide in the composite packaging film is self-assembled and wrapped by sodium bicarbonate and calcium chloride to form a calcium carbonate-antibacterial peptide compound, which can be released in a corrupt acidic environment and has high food safety, and the calcium carbonate-antibacterial peptide compound is integrated into the composite packaging film, so that more extensive application can be achieved and the practicality is high; the composite packaging film further comprises cactus anthocyanin as a pH sensitive indicator, so that the deterioration process can be monitored visually, and therefore, the composite packaging film can not only determine the deterioration process of fresh edible fungi in the packaging, which is convenient for users, but also can effectively inhibit the corruption of the packaged goods through the release of the antibacterial peptide.

Description

Technical Field

[0001] This invention relates to the fields of intelligent packaging and food quality testing technology, and in particular to an antibacterial composite packaging film for indicating the freshness of edible fungi, its preparation method, and its application. Background Technology

[0002] The edible mushroom market primarily sells fresh mushrooms. In recent years, consumers have placed higher demands on the quality of fresh edible mushrooms. Therefore, quality control during the logistics and storage of edible mushrooms has attracted widespread attention. Fresh mushrooms undergo rapid metabolism after harvesting, resulting in quick nutrient depletion. With extended storage and transportation periods, they are prone to spoilage and deterioration. High levels of moisture evaporation and respiration are the most significant indicators of this deterioration process. Freshness is a crucial indicator of the value of edible mushrooms. In the context of e-commerce logistics, the adoption of appropriate quality monitoring technologies and improvements to the preservation and distribution models for edible mushrooms are essential for enhancing the quality of cross-regional, long-distance logistics and storage, extending shelf life, and reducing spoilage and preserving the quality of edible mushrooms.

[0003] To extend the shelf life of fresh mushrooms, numerous preservation technologies have been reported, such as irradiation preservation, modified atmosphere storage, magnetic field preservation, chemical preservation (1-methylcyclopropene, amino acids, chlorine dioxide, and compound preservatives, etc.), ozone preservation, acidic electrolyzed water and plasma-activated water preservation, plant extract preservation, microbial preservative preservation, and antagonistic bacteria preservation. However, these preservation technologies still face many problems when applied to fresh edible fungi: ① They are not suitable for large-scale batch processing; ② The investment cost in processing equipment is high; ③ Due to the special morphological structure of edible fungi, the uniformity of liquid preservatives applied through spraying, impregnation, and fumigation is greatly reduced; ④ The most widely used chemical preservatives have been questioned due to safety concerns, while the effective components and mechanisms of action of some biological preservatives are still unclear. Currently, there is an urgent need for efficient, safe, and low-cost preservation monitoring and packaging technologies suitable for the logistics, storage, and transportation of fresh edible fungi to reduce post-harvest losses and improve economic efficiency.

[0004] pH changes frequently occur during the post-harvest storage and transportation of edible fungi. On the one hand, typical physiological changes such as aging and respiration after harvest often lead to spoilage; on the other hand, they are susceptible to bacterial and fungal infection, causing sugar fermentation that produces organic acids, aldehydes, ketones, and CO2, resulting in a decrease in pH and the formation of putrid flavors. Addressing the practical needs of large-volume storage and transportation of fresh edible fungi at the production site and the requirement for timely distribution, developing indicator labels based on the pH change characteristics of edible fungi and integrating them into packaging materials can enable timely monitoring of freshness, reducing spoilage and improving economic efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide an antibacterial composite packaging film for indicating the freshness of edible fungi, its preparation method, and its application. This invention applies the composite packaging film to the storage and transportation of edible fungi, enabling not only the monitoring of changes in freshness and a direct understanding and judgment of storage and transportation quality, but also timely response to spoilage and deterioration within the packaging. This, to a certain extent, delays the spoilage of the edible fungi inside the packaging and reduces economic losses.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing an antibacterial composite packaging film for edible fungi freshness indication, comprising the following steps:

[0008] (1) Mix the antimicrobial peptide solution, CaCl2 aqueous solution and NaHCO3 aqueous solution to obtain a mixed solution;

[0009] (2) The mixed solution is subjected to a polymerization reaction, and the precipitate is the antimicrobial peptide-CaCO3 complex;

[0010] (3) The antimicrobial peptide-CaCO3 complex is mixed with tributyl citrate and monoglyceride to obtain material A;

[0011] (4) Mix PE resin with material A and granulate to obtain modified masterbatch;

[0012] (5) Mix the modified masterbatch with PE resin and prepare PE composite packaging film B using a blown film machine;

[0013] (6) Mix sodium alginate aqueous solution, cactus anthocyanins and plasticizer, and disperse by ultrasonication to obtain active film solution C;

[0014] (7) After one side of the packaging film B is treated with cold plasma, an active film liquid C is sprayed onto it to obtain an antibacterial composite packaging film for indicating the freshness of edible fungi.

[0015] Preferably, the solvent of the antimicrobial peptide solution in step (1) is an ethanol solution; the mass ratio of the antimicrobial peptide to the ethanol solution is 1:8 to 12; the ethanol solution is prepared by mixing anhydrous ethanol and water at a mass ratio of 1:2 to 3, with a pH value of 9 to 10.

[0016] Preferably, the mass ratio of antimicrobial peptide, CaCl2 and NaHCO3 in the mixed solution of step (2) is 1-33:200-250:460-500.

[0017] Preferably, the specific process of the polymerization reaction in step (2) is as follows: the mixed solution is first kept at 4°C for 2 minutes, and then kept at 7-9°C for 3-5 minutes until the temperature is raised to 21-27°C, and the reaction is continued for 3 minutes to complete the polymerization reaction; the reaction is stirred throughout the process, the stirring speed is 80-200 rpm, and the stirring time is 2-5 minutes.

[0018] Preferably, in step (3), the mass ratio of the antimicrobial peptide-CaCO3 complex to tributyl citrate and monoglyceride is 0.8-1.2:0.4-0.6:0.08-0.12.

[0019] Preferably, in step (4), the mass ratio of PE resin to material A is 90-100:2-6.

[0020] Preferably, the mass ratio of modified masterbatch to PE resin in step (5) is 1:1.8 to 2.4.

[0021] Preferably, in step (6), the mass ratio of sodium alginate aqueous solution, cactus anthocyanin and plasticizer is 100-105:0.8-12:0.08-1.2.

[0022] The present invention also provides an antibacterial composite packaging film for edible fungi freshness indicator prepared by the above preparation method.

[0023] The present invention also provides an application of the aforementioned edible fungus freshness indicator antibacterial composite packaging film in monitoring the freshness of edible fungi or extending the shelf life of edible fungi.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The cactus anthocyanins in this invention have a high proportion of acylated anthocyanins and are more stable than those from other sources. They exhibit different colors with changes in pH value, showing obvious color changes in buffer solutions with pH 3 to 10. They have advantages such as color stability and safety and non-toxicity, and can be used as pH-sensitive indicators to achieve visual color monitoring of the deterioration process. In the process of spoilage of fresh edible fungi, they can determine the deterioration process of fresh edible fungi in packaging, which is convenient for practitioners.

[0026] The antimicrobial peptides in this invention exhibit thermal stability, maintaining their activity even at high temperatures. They also demonstrate strong resistance to high ionic strength and both high and low pH values. Furthermore, the antimicrobial peptides possess a degree of hydrophobicity; the reaction of NaHCO3 and CaCl2 to form CaCO3 facilitates the encapsulation of the antimicrobial peptides, further protecting them with a CaCO3 shell. This reduces the adverse effects on the antimicrobial peptides during subsequent granulation and promotes the sustained release of the antimicrobial peptides during preservation applications.

[0027] Post-harvest deterioration of edible fungi involves vigorous respiration and significant water transpiration, making them prone to cap opening, dehydration, morphological changes, browning, loss of nutrients and flavor, and microbial infection. During logistics and storage, this manifests as significant water transpiration, tissue rancidity, and the release of large amounts of CO2 through vigorous respiration. Inside the packaging, the edible fungi tissue comes into contact with the inner active film. As water is released through transpiration and the pH value decreases due to tissue rancidity, the carboxyl groups of sodium alginate in the active film tend to protonate, causing the sodium alginate molecular chains to further contract. This creates voids in the active film. As the CO2 concentration within the packaging's micro-atmosphere increases, the indicator label changes from light green to orange-yellow, and further to light red and even red as rancidity worsens. In this way, the obvious and distinguishable color changes can intuitively indicate the changes in freshness of fresh edible fungi during logistics and storage. As the deterioration process gradually intensifies, the pores of the active membrane further increase and even partially degrade. The evaporation of water vapor and the effect of rancidity trigger the disintegration of the antimicrobial peptide-CaCO3 complex, releasing the antimicrobial peptide, producing an antimicrobial effect, inhibiting the spread of spoilage, and reducing losses.

[0028] The advantages of this invention are that, in response to the storage and transportation needs of fresh edible fungi, a composite packaging film has been developed that can not only monitor changes in the quality of fresh edible fungi but also respond promptly to spoilage and deterioration. It has indication, monitoring, and early warning label functions, and can release antimicrobial peptides to inhibit bacteria, prevent spoilage, and extend the shelf life of fresh mushrooms when they deteriorate. Attached Figure Description

[0029] Figure 1 The graph shows the response of cactus anthocyanins to pH (3.0–10.0) in Experiment Example 1.

[0030] Figure 2 The visible light absorption spectra of cactus anthocyanins in Experiment Example 1 under different pH conditions;

[0031] Figure 3 Fourier transform infrared spectra of different composite packaging films in Experiment Example 2;

[0032] Figure 4 This is a schematic diagram of the thermal stability (TG-DSC) analysis of different composite packaging films in Experiment Example 3;

[0033] Figure 5 This is a graph showing the color response of the composite packaging film to shiitake mushrooms during storage in Experiment Example 4.

[0034] Figure 6 This is a scanning electron microscope image of the composite packaging film in Experiment Example 5. Detailed Implementation

[0035] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Materials and equipment used in the embodiments of the present invention

[0037] PE resin: PE (2426K), purchased from Maoming Branch of China Petroleum & Chemical Corporation.

[0038] Low-temperature ultrafine pulverizing equipment: SQW-6A low-temperature ultrafine pulverizer, purchased from Jinan Yichen Chaowei Pulverizing Technology Co., Ltd.

[0039] Twin-screw extrusion granulation equipment: SY-6217 twin-screw extrusion granulator, purchased from Dongguan Jiutong Machinery Co., Ltd.

[0040] Film blowing equipment: SY-6218-Z-18 / 28 film blowing machine, Dongguan Jiutong Machinery Co., Ltd.

[0041] Cold plasma treatment equipment: HD-1A type cold plasma treatment instrument, Jiangsu Changzhou Zhongke Changtai Plasma Technology Co., Ltd.

[0042] The cactus anthocyanins used in the following experiments are prepared using the following steps:

[0043] (1) Wash and chop the fresh cactus, put it in an ultra-low temperature freezer at -80℃ for 72 hours, then freeze-dry it at -60℃ for 45 hours and grind it into 120 mesh powder for later use.

[0044] (2) Prepare 500 mL of 75% ethanol solution and adjust its pH to 3 with 1 mol / L hydrochloric acid. Extract 20 g of cactus powder at 4°C for 24 h under light-protected conditions to obtain the extract.

[0045] (3) The extract was vacuum filtered, the filtrate was rotary evaporated at 50°C for 1 hour, and finally cooled to room temperature to obtain an extract of cactus anthocyanins with a soluble solids mass concentration of 128.2 g / L.

[0046] Example 1

[0047] A freshness indicator antibacterial composite packaging film for edible fungi, the preparation method of which includes the following steps:

[0048] 1. Preparation of antimicrobial peptide-CaCO3 complex

[0049] (1) Deionized water was dissolved in anhydrous ethanol at a volume ratio of 1 / 3 under pH 9.1 conditions to prepare a 10% (g / g) antimicrobial peptide solution.

[0050] (2) Add CaCl2 aqueous solution and NaHCO3 aqueous solution to the antimicrobial peptide solution in step (1) in sequence, and stir at 600 rpm for 15 min to prepare a mixed solution. The mass ratio of the total mass of antimicrobial peptide, CaCl2 and NaHCO3 to the solvent in the mixed solution is 15:100; wherein the mass ratio of antimicrobial peptide, CaCl2 and NaHCO3 is 1:200:460.

[0051] (3) The mixed solution in step (3) is subjected to polymerization reaction through a staged heating process: temperature is controlled at 4℃ and stirred at 200rpm for 2 minutes; temperature is increased to 8℃ and stirred at 160rpm for 3 minutes; temperature is increased to 16℃ and stirred at 100rpm for 5 minutes; temperature is increased to 24℃ and stirred at 80rpm for 3 minutes, and then left to stand at room temperature. A precipitate appears, and there is no fluid disturbance on the liquid surface.

[0052] (4) Collect the precipitate, wash it with deionized water, centrifuge it, remove the supernatant, repeat the operation 3 times to obtain the antimicrobial peptide-CaCO3 complex freeze-dried for later use.

[0053] 2. The antimicrobial peptide-CaCO3 complex was pulverized to 15μm at low temperature.

[0054] 3. Mix antimicrobial peptides - CaCO3: tributyl citrate: monoglyceride, with a mass ratio of 1:0.5:0.1, and stir evenly to obtain material A;

[0055] 4. Add PE resin and material A at a mass ratio of 96:4 into a twin-screw extruder, blend and granulate to obtain a modified masterbatch with a diameter of 3mm.

[0056] The settings for the twin-screw extruder are: 155℃ in the die zone, 160℃ in zone 5, 175℃ in zone 4, 180℃ in zone 3, 170℃ in zone 2, and 160℃ in zone 1, with a screw speed of 50 r / min.

[0057] 5. The modified masterbatch and PE resin are mixed at different mass ratios of 1:2. After preparing PE composite packaging film using a blown film machine, the inner side of the film is treated with a cold plasma treatment device for 5 minutes to obtain packaging film B.

[0058] The blown film machine was set with the following parameters: film head temperature: 155℃, die head gap: 0.8mm, blow-up ratio: 2.5:1, traction speed: 10m / min, and final film thickness: 30μm.

[0059] The settings for the cold plasma treatment equipment are: Ar as carrier gas, radio frequency power supply, power 200W, background vacuum 15Pa, and discharge vacuum 40Pa.

[0060] 6. Dissolve 2.5g of sodium alginate in 100g of deionized water and heat and stir at 90℃ for 30min to fully dissolve it, so as to obtain sodium alginate aqueous solution; add 1g of glycerol as plasticizer to sodium alginate aqueous solution, add cactus anthocyanin at 4% by mass of sodium alginate aqueous solution, and ultrasonically disperse to prepare active film liquid C as indicator label.

[0061] 7. Spray active film liquid C onto the inside of packaging film B, dry at 60°C and store for later use to obtain the composite packaging film of the present invention, which can not only monitor the quality changes of fresh edible fungi but also respond promptly to spoilage and deterioration.

[0062] Example 2

[0063] A freshness indicator antibacterial composite packaging film for edible fungi, the preparation method of which includes the following steps:

[0064] 1. Preparation of antimicrobial peptide-CaCO3 complex

[0065] (1) Deionized water was dissolved in anhydrous ethanol at a volume ratio of 1 / 3 under pH 9.1 conditions to prepare a 10% (g / g) antimicrobial peptide solution.

[0066] (2) Add CaCl2 solution and NaHCO3 solution to the antimicrobial peptide solution in step (1) in sequence, and stir at 600 rpm for 15 min to prepare a mixed solution. The mass ratio of the total mass of antimicrobial peptide, CaCl2 and NaHCO3 to the mass of solvent in the mixed solution is 9:100; wherein the mass ratio of antimicrobial peptide, CaCl2 and NaHCO3 is 33:250:500.

[0067] (3) The mixed solution in step (3) is subjected to polymerization reaction through a staged heating process: temperature is controlled at 4℃ and stirred at 200rpm for 2 minutes; temperature is increased to 8℃ and stirred at 160rpm for 3 minutes; temperature is increased to 16℃ and stirred at 100rpm for 5 minutes; temperature is increased to 24℃ and stirred at 80rpm for 3 minutes, and then left to stand at room temperature. A precipitate appears, and there is no fluid disturbance on the liquid surface.

[0068] (4) Collect the precipitate, wash it with deionized water, centrifuge it, remove the supernatant, repeat the operation 3 times to obtain the antimicrobial peptide-CaCO3 complex freeze-dried for later use.

[0069] 2. The antimicrobial peptide-CaCO3 complex was pulverized to 15μm using low-temperature ultrafine grinding.

[0070] 3. Mix antimicrobial peptides - CaCO3: tributyl citrate: monoglyceride, with a mass ratio of 1:0.5:0.1, and stir evenly to obtain material A;

[0071] 4. Add PE resin and material A at a mass ratio of 96:4 into a twin-screw extruder, blend and granulate to obtain a modified masterbatch with a diameter of 3mm.

[0072] The settings for the twin-screw extruder are: 155℃ in the die zone, 160℃ in zone 5, 175℃ in zone 4, 180℃ in zone 3, 170℃ in zone 2, and 160℃ in zone 1, with a screw speed of 50 r / min.

[0073] 5. The modified masterbatch and PE resin are mixed at different mass ratios of 1:2. After preparing PE composite packaging film using a blown film machine, the inner side of the film is treated with cold plasma for 5 minutes to obtain packaging film B.

[0074] The blown film machine was set with the following parameters: film head temperature: 155℃, die head gap: 0.8mm, blow-up ratio: 2.5:1, traction speed: 10m / min, and final film thickness: 30μm.

[0075] The settings for the cold plasma treatment equipment are: Ar as carrier gas, radio frequency power supply, power 200W, background vacuum 15Pa, and discharge vacuum 40Pa.

[0076] 6. Dissolve 2.5g of sodium alginate in 100g of deionized water and heat and stir at 90℃ for 30min to fully dissolve it, so as to obtain sodium alginate aqueous solution; add 1g of glycerol as plasticizer to sodium alginate aqueous solution, add cactus anthocyanin at 4% by mass of sodium alginate aqueous solution, and ultrasonically disperse to prepare active film liquid C as indicator label.

[0077] 7. Spray active film liquid C onto the inside of packaging film B, dry at 60°C and store for later use to obtain the composite packaging film of the present invention, which can not only monitor the quality changes of fresh edible fungi but also respond promptly to spoilage and deterioration.

[0078] Comparative Example 1

[0079] No antimicrobial peptides or cactus anthocyanins were added to the raw materials, and the remaining steps were the same as in Example 1.

[0080] Experimental Example 1

[0081] Color rendering effect of cactus anthocyanins

[0082] Prepare a buffer solution with a pH of 3.0–10.0 using 0.1 mol / L HCl and 0.1 mol / L NaOH. Add 0.2 mL of the cactus anthocyanin from Example 1 to the above buffer solution, mix thoroughly, and let stand for 30 min. Record the color development of the buffer solution by taking a photograph (see [link to sample]). Figure 1 The absorbance of the solution at 400-700 nm was measured using a UV spectrophotometer.

[0083] The results are as follows Figure 2 As shown, with increasing pH, the solution color changes sequentially from red to pink (pH = 3.0–5.0), orange (pH = 6.0), light green (pH = 7.0), green (pH = 8.0–9.0), and dark green (pH = 10.0). This indicates that cactus anthocyanins have good pH-responsive characteristics. Figure 2 As can be seen, the visible light absorption spectrum of cactus anthocyanins differs under different pH conditions. When pH = 3.0, the maximum absorption peak of the indicator in the visible light region is at 425 nm; when pH = 5.0–6.0, the absorption peak intensity at 230 nm decreases sharply and undergoes a red shift; when pH = 8.0, the absorption peak intensity at 225 nm increases sharply; when pH = 9.0, the wavelength of the maximum absorption peak shifts to the right, corresponding to a wavelength of 615 nm; when pH = 4.0, 7.0, and 10.0, the absorption peak almost disappears. Therefore, the color change of cactus anthocyanins is significant, making them suitable as pH-sensitive indicators.

[0084] Experiment Example 2

[0085] Fourier transform infrared (FT-IR) analysis of the composite packaging film described in this invention

[0086] The absorption spectrum of the composite packaging film with the inner label markings was measured using a Fourier transform infrared spectrometer, with a scanning range of 650–4000 cm⁻¹. -1 .

[0087] The results are as follows Figure 3 As shown, except for 783cm -1 In addition, no new peaks appeared in the composite packaging films of Comparative Example 1 and Examples 1 and 2, and the main peaks were basically the same, but the peak intensities at different wavenumbers were slightly different. With the addition of cactus anthocyanins, 3437 cm⁻¹ -1 The peak gradually shifts to the left (in Examples 1 and 2, the peaks shift to 3435 cm⁻¹, respectively). -1 and 3432cm -1 (The peak shifts at this point), which is an absorption peak belonging to the stretching vibration of the hydroxyl group. Example 1 shows the absorption peaks at 2586-2929 cm⁻¹. -1 The peak band changes at 2929 cm⁻¹. -1 One peak shifted 2930cm. -1 This is related to the tensile vibration of the methylene group (-CH2). The composite packaging film of Example 1 at 2353 cm⁻¹... -1 The peak intensity decreased at 1632 cm⁻¹. -1 The leftward shift of the peak at 1040 cm⁻¹ may be related to the stretching vibration of C=C in the membrane. Example 1: Composite packaging film at 1040 cm⁻¹ -1The absorption peak at the point gradually shifted to the left and the peak intensity weakened, which may be due to the stretching vibration of CO. Therefore, the addition of cactus anthocyanins did not cause any change in the structure of the composite packaging film.

[0088] Experimental Example 3

[0089] Thermal stability (TG-DSC) analysis of the composite packaging film described in this invention

[0090] Thermogravimetric analysis (TGA) was performed to evaluate the thermal stability of the composite packaging film with the indicated label position. 10 mg of sample was weighed in a thermogravimetric microbalance and heated at a rate of 20 °C / min within a temperature range of 30–600 °C, using nitrogen as the cooling medium at a flow rate of 20 mL / min.

[0091] like Figure 4 As shown, the mass loss of Comparative Example 1 can be divided into four stages: the first stage is within the range of 25–150°C, mainly due to the loss of free and bound water in the indicator label; furthermore, the weight loss of Comparative Example 1 is higher than that of the composite packaging film of Examples 1–2. The second and third stages are within the ranges of 150–290°C and 290–360°C, respectively, in which the mass loss rate decreases rapidly. The fourth stage is above 360°C, where the decreasing trend of the mass loss rate slows down significantly. The weight loss of Examples 1 and 2 can be divided into three stages: 25–160°C (mainly caused by moisture loss), 160–375°C (mainly due to the oxidative decomposition of substances in the indicator label components), and 375–500°C (carbonization decomposition of other substances). Among the three samples, Comparative Example 1 has the highest mass loss rate at 500°C, at 9.92%; followed by Example 2 at 6.78%; while Example 1 has the lowest mass loss rate, at only 5.26%. It can be seen that the addition of cactus anthocyanins inhibits thermal degradation and improves stability.

[0092] Experiment Example 4

[0093] Freshness monitoring and preservation performance testing of shiitake mushrooms

[0094] Shiitake mushrooms were stored at 4℃ and (85±5)% relative humidity for 12 days, and the color changes of the corresponding composite packaging film were observed.

[0095] The results are as follows Figure 5 As shown in Examples 1 and 2, with the extension of storage time and the accelerated deterioration of fresh shiitake mushrooms after harvest, compared with Comparative Example 1, the composite packaging film in Examples 1 and 2 showed a significant color change as the pH of the fresh shiitake mushrooms changed, gradually changing from green and light green to orange-yellow, with the color intensity gradually deepening, eventually turning brownish-yellow and even red. This demonstrates that the composite packaging film loaded with cactus anthocyanins exhibits good responsiveness and shows potential application value.

[0096] Experimental Example 5

[0097] SEM scanning electron microscopy analysis of the composite packaging film of the present invention

[0098] The composite packaging film with the indicator label position sprayed in Example 1 was cut, and the surface microstructure of the cut composite packaging film was observed and photographed using a scanning electron microscope. Specifically, after drying the 1cm×1cm sample film, gold sputtering was performed on its surface with an accelerating voltage of 15KV and a magnification of 10K.

[0099] SEM images primarily reflect the interface morphology and microstructure of the composite system, as shown in the following figures. Figure 6 As shown, the packaging film B treated with cold plasma technology is tightly bonded to the active film liquid C, with no obvious separation between layers, indicating good compatibility of the composite film.

[0100] Experimental Example 6

[0101] Microbial experiments

[0102] The antibacterial performance was tested using a liquid culture method to investigate its inhibitory effects on Staphylococcus aureus, Escherichia coli, Pseudomonas fluorescens, and Bacillus subtilis.

[0103] Different bacterial strains were inoculated into nutrient broth and cultured at their respective optimal temperatures and 150 rpm for 24 hours. The broth was then diluted with culture medium to prepare 10... 8 CFU / mL bacterial suspension. Take 10cm×10cm composite packaging film with the indicated label position sprayed on it as described in Examples 1-2 and Comparative Example 1, dissolve it in water with pH=5 and soak for 20min. Add 100μL of soaking solution and 100μL of bacterial solution to a 96-well plate. Measure the initial absorbance of the mixed solution at 600nm using an ELISA reader. After incubation at the corresponding temperature of the bacterial strain for 24h, measure the initial absorbance at 600nm again. Use the culture medium as a blank control. Each experiment is repeated 3 times and the average value is taken. The results are listed in Table 1.

[0104] The inhibition rate (IR%) of the thin film is calculated as follows:

[0105] IR (%) = (A 24 -A0) / A blank ×100%

[0106] In the formula: A0 is the absorbance value of the initial mixed solution at 600 nm, A 24 A represents the absorbance of the solution at 600 nm after 24 hours of reaction. blank The absorbance value of the blank control solution at 600 nm is shown.

[0107] Table 1 Antibacterial properties of composite packaging films

[0108]

[0109] The results are shown in Table 1. After adding antimicrobial peptides and cactus anthocyanins, the composite packaging film of this invention exhibited good antimicrobial properties, with inhibition rates of over 89% against all four bacterial strains, demonstrating a significant inhibitory effect on bacterial growth. This is mainly due to the transpiration of water vapor and tissue acidification triggering the disintegration of the antimicrobial peptide-CaCO3 complex within the packaging, releasing the antimicrobial peptides to produce an antibacterial effect. This alleviates post-harvest spoilage and other quality deterioration of shiitake mushrooms, extending their post-harvest shelf life.

[0110] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing an antibacterial composite packaging film for indicating the freshness of edible fungi, characterized in that, Includes the following steps: (1) Mix the antimicrobial peptide solution, CaCl2 aqueous solution, and NaHCO3 aqueous solution to obtain a mixed solution; (2) The mixed solution is subjected to a polymerization reaction, and the precipitate is the antimicrobial peptide-CaCO3 complex; (3) The antimicrobial peptide-CaCO3 complex is mixed with tributyl citrate and monoglyceride to obtain material A; (4) Mix PE resin with material A and granulate to obtain modified masterbatch; (5) Mix the modified masterbatch with PE resin and prepare PE composite packaging film B using a blown film machine; (6) Sodium alginate aqueous solution, cactus anthocyanin and plasticizer are mixed and ultrasonically dispersed to obtain active film solution C; (7) After one side of the packaging film B is treated with cold plasma, an active film liquid C is sprayed onto it to obtain an antibacterial composite packaging film for indicating the freshness of edible fungi. The solvent for the antimicrobial peptide solution in step (1) is an ethanol solution; the mass ratio of the antimicrobial peptide to the ethanol solution is 1:8~12; the ethanol solution is prepared by mixing anhydrous ethanol and water at a mass ratio of 1:2~3, with a pH value of 9~10. The mass ratio of antimicrobial peptide, CaCl2 and NaHCO3 in the mixed solution of step (2) is 1~33:200~250:460~500; In step (3), the mass ratio of the antimicrobial peptide-CaCO3 complex to tributyl citrate and monoglyceride is 0.8~1.2:0.4~0.6:0.08~0.

12. In step (4), the mass ratio of PE resin to material A is 90~100:2~6; In step (5), the mass ratio of modified masterbatch to PE resin is 1:1.8~2.4; In step (6), the mass ratio of sodium alginate aqueous solution, cactus anthocyanin and plasticizer is 100~105:0.8~12:0.08~1.

2.

2. The preparation method according to claim 1, characterized in that, The specific process of the polymerization reaction in step (2) is as follows: the mixed solution is first kept at 4°C for 2 minutes, and then kept at 7~9°C for 3~5 minutes until the temperature is raised to 21~27°C. The reaction is continued for 3 minutes, and the polymerization reaction is completed. The reaction is stirred throughout, with a stirring speed of 80~200 rpm and a stirring time of 2~5 minutes.

3. An antibacterial composite packaging film for edible fungi freshness indicator prepared by the preparation method described in claim 1 or 2.

4. The application of the edible fungus freshness indicator antibacterial composite packaging film as described in claim 3 in monitoring the freshness of edible fungi or extending the shelf life of edible fungi.

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