A preservation composite film, its preparation method, and its application in fruit and vegetable preservation.

Abstract

This invention provides a food preservation composite film, its preparation method, and its application in fruit and vegetable preservation, belonging to the field of food preservation technology. It is prepared from raw materials comprising the following mass ratio: chitosan: rosin acid: paraffin wax: beeswax = (100~200): (1~1.5): (1~1.5): (1~1.5); the resulting food preservation composite film has high moisture resistance and high air permeability, and its WVTR can be reduced to 167.64 g / (m³). 2 (day), with air permeability comparable to PE film. The preservation composite film of the present invention can effectively maintain the quality of citrus, reduce post-harvest losses of citrus, and improve the preservation effect of citrus. It is of great significance for expanding the application market of chitosan-based preservation coating film and further replacing PE preservation bags in the post-harvest production of citrus and other fruits and vegetables.

Description

Technical Field

[0001] This invention belongs to the field of food preservation technology, specifically relating to a preservation composite film, its preparation method, and its use in fruit and vegetable preservation. Background Technology

[0002] Citrus fruits hold a vital position in global agriculture, being among the most widely cultivated fruit crops. However, post-harvest citrus fruits suffer from alterations in quality and reduced value due to mechanical damage, microbial infection, and physiological metabolism. The main quality changes in post-harvest citrus include spoilage, nutrient loss, flavor degradation, and changes in appearance and color. Besides economic losses, these quality deteriorations can also negatively impact consumer health. Therefore, developing more suitable and effective methods for storing, transporting, and preserving citrus is crucial for minimizing post-harvest losses.

[0003] Penicillium mold is the most common postharvest disease of citrus, mainly caused by *Penicillium fingernail* and *Penicillium italicum*. It invades through the citrus peel or wounds, producing numerous spores that disperse into the surrounding air. High humidity, poor ventilation, and improper handling exacerbate infection. Citrus fruits with mechanical damage are highly susceptible to infection by pathogens, and if left uncontrolled, these diseases can spread rapidly, leading to significant losses. Furthermore, ingesting citrus fruits infected with Penicillium mold can also harm human health. Moisture loss is another major cause of postharvest losses in citrus, and this loss is related to factors such as temperature and humidity. During storage, transpiration and metabolic activities within the citrus fruit cause water loss, resulting in wrinkled peels, reduced palatability, nutrient loss, and diminished flavor. Simultaneously, increased respiration and physiological activity accelerate the consumption of water and nutrients within the fruit, promoting senescence and shortening its storage life. Therefore, reducing the incidence of Penicillium mold during postharvest storage and maintaining fruit moisture content are crucial for citrus preservation.

[0004] Common preservation techniques for citrus fruits include physical preservation, chemical preservation, and coating preservation. Among these, the most widely used post-harvest preservation method is to first use chemical sterilization followed by physical preservation. Physical preservation most commonly uses PE (petroleum-based) wrapping, but PE film is a petroleum-based non-degradable plastic with poor environmental friendliness. Furthermore, PE film is mostly used for single-fruit bagging of citrus fruits, which is limited by factors such as irregular fruit shape and the thinness of the film, making automation difficult and labor-intensive. In addition, PE film cannot adhere to the natural microporous structure of the citrus peel to form a protective film, resulting in insufficient performance in buffering mechanical damage such as compression and impact.

[0005] Compared to "chemical + physical" preservation methods, coating preservation is greener and safer. The components of coating preservatives are often biodegradable substances, such as polysaccharides, proteins, and lipids, including chitosan, zein, propolis, pectin, starch, CMC, and oregano oil. These are safe, pollution-free, widely available, and inexpensive. Among these, chitosan, with its excellent film-forming properties, natural broad-spectrum antibacterial ability, and good biocompatibility, has become an ideal base material for preparing coating preservatives and has received widespread attention in the field of fruit and vegetable preservation. Compared to PE films, chitosan films are applied evenly to fruits through soaking, spraying, or coating methods, and then dried to form a film. This coating preservation method can be automated, reducing labor costs. Furthermore, chitosan films can conform to the natural microporous structure of citrus peel to form a dense, adherent protective layer, better buffering mechanical damage from compression and collisions, and reducing post-harvest physical damage.

[0006] However, chitosan membranes have strong hydrophilicity and excessively high gas barrier properties, making them unsuitable for the post-harvest physiological and metabolic needs of citrus fruits. Furthermore, their insufficient mechanical strength and limited antibacterial effect as a single system fail to comprehensively address issues such as water loss and rot during citrus storage. Therefore, it is necessary to modify and optimize chitosan membranes to develop a chitosan-based preservative coating with high moisture barrier properties, high air permeability, and good antibacterial properties. This would effectively reduce the rot rate of citrus fruits and vegetables during post-harvest storage and maintain fruit moisture content, which is of great significance for expanding the application market of chitosan-based preservative coatings. Summary of the Invention

[0007] The purpose of this invention is to provide a preservation composite film, its preparation method, and its use in the preservation of fruits and vegetables.

[0008] This invention provides a food preservation composite film, which is prepared from raw materials comprising the following mass ratio: chitosan: rosin acid: paraffin wax: beeswax = (100~200): (1~1.5): (1~1.5): (1~1.5).

[0009] Furthermore, it is prepared from raw materials comprising the following mass ratio: chitosan: rosin acid: paraffin: beeswax = (120~180) : (1~1.5) : (1~1.5) : (1~1.5).

[0010] Furthermore, it is prepared from raw materials comprising the following mass ratio: chitosan: rosin acid: paraffin: beeswax = 150: 1.25: 1.5: 1.

[0011] Furthermore, it also includes preservatives and bactericides for raw fruits and vegetables.

[0012] Furthermore, the fruit and vegetable preservative and bactericide includes at least one of natamycin, imazalil, thiamethoxam, and calcium propionate.

[0013] This invention also provides a method for preparing a food preservation composite film, comprising the following steps: (1) Preparation of chitosan solution: Chitosan is dissolved in an aqueous solution of organic acid, plasticizer is added, and the mixture is mixed evenly to obtain chitosan solution. Impurities are removed and the solution is ready for use. (2) Preparation of chitosan / rosin acid / paraffin / beeswax composite film solution: Rosin acid was dissolved in an organic solvent and emulsified with an emulsifier to obtain rosin acid emulsion; paraffin wax and beeswax were weighed and emulsified with an emulsifier to obtain wax emulsion; then the rosin acid emulsion and wax emulsion were mixed, and then mixed with chitosan solution and adjusted to a fixed volume to obtain chitosan / rosin acid / paraffin / beeswax composite film solution; (3) Dry the chitosan / rosin acid / paraffin / beeswax composite film liquid into a film to obtain the chitosan / rosin acid / paraffin / beeswax composite film; The chitosan solution has a mass concentration of 1.0% to 2.0%; the rosin acid emulsion has a mass concentration of 1.0% to 1.5%; and in the wax emulsion, the paraffin wax and beeswax each have a mass concentration of 1.0% to 1.5%.

[0014] Further, the chitosan solution has a mass concentration of 1.2% to 1.8%; the rosin acid emulsion has a mass concentration of 1.0% to 1.5%; and in the mixed emulsion of paraffin wax and beeswax, the mass concentration of paraffin wax is 1.0% to 1.5% and the mass concentration of beeswax is 1.0% to 1.5%.

[0015] Further, the chitosan solution has a mass concentration of 1.5%; the rosin acid emulsion has a mass concentration of 1.25%; and in the mixed emulsion of paraffin wax and beeswax, the mass concentration of paraffin wax is 1.5% and the mass concentration of beeswax is 1.0%.

[0016] Furthermore, the preparation method of the preservation composite film also includes the following steps: adding a fruit and vegetable preservation bactericide to the chitosan / rosin acid / paraffin / beeswax composite film liquid to obtain a chitosan / rosin acid / paraffin / beeswax / bactericide composite film liquid, and then drying the chitosan / rosin acid / paraffin / beeswax / bactericide composite film liquid to form a film, thus obtaining the chitosan / rosin acid / paraffin / beeswax / bactericide composite film.

[0017] Further, the fruit and vegetable preservative fungicide includes at least one of imazalil, natamycin, prochloraz, and calcium propionate; the concentration of imazalil in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 2~100 μg / L; the concentration of natamycin in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 3~300 mg / L; the concentration of prochloraz in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 4~10 mg / L; and the concentration of calcium propionate in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 8~30 mg / L.

[0018] Further, the organic acid aqueous solution includes at least one of acetic acid, lactic acid, citric acid, and malic acid; the plasticizer includes at least one of glycerol, propylene glycol, 1,3-butanediol, sorbitol, and mannitol; and the emulsifier includes at least one of Tween-80, Span-60, Tween-20, polyethylene glycol, Span-80, and monoglyceride.

[0019] This invention also provides the use of preservation composite film in the preservation of citrus fruits.

[0020] The present invention has achieved the following beneficial effects: This invention utilizes a compound of rosin acid, paraffin wax, beeswax, and chitosan to prepare a food preservation composite film with high moisture resistance and high air permeability. Experiments show that the composite food preservation film prepared with a mass ratio of chitosan, rosin acid, paraffin wax, and beeswax of (100~200):(1~1.5):(1~1.5):(1~1.5) significantly improves moisture resistance and air permeability compared to a single chitosan film. Among these, the composite film obtained with a mass ratio of chitosan, rosin acid, paraffin wax, and beeswax of 150:1.25:1.5:1 exhibits the best moisture resistance, with a water vapor transmission rate of 164.64 g / (m²). 2 (day), the water vapor permeability of the chitosan membrane was reduced by 78.3%.

[0021] This invention further adds a fruit and vegetable bactericide to the chitosan / rosin acid / paraffin / beeswax composite film liquid to obtain a preservation composite film with high moisture resistance, high air permeability, and excellent antibacterial properties. Specifically, the addition of the bactericide imazalil to the chitosan / rosin acid / paraffin / beeswax composite film significantly inhibits the growth and reproduction of Penicillium fingering on citrus fruits, resulting in a rot rate of only 26.98±2.75% after 35 days of storage.

[0022] The chitosan / rosin acid / paraffin / beeswax / bactericide composite film of this invention can effectively reduce the weight loss rate, rot rate, and respiration rate of citrus fruits, delay the decrease in firmness, maintain the TSS content and peel brightness index of citrus fruits, effectively cover the stomata of citrus peel, significantly improve the smoothness of citrus peel, effectively inhibit respiration and material exchange through citrus peel, maintain the weight of citrus fruits, reduce the growth and reproduction of microorganisms on citrus peel, and have excellent preservation effect; among them, the chitosan / rosin acid / paraffin / beeswax / imidazolium composite film has a better preservation effect.

[0023] The composite preservation film of this invention possesses high moisture resistance, high air permeability, and excellent antibacterial properties, effectively maintaining the quality of citrus fruits, reducing post-harvest losses, and improving preservation. Furthermore, compared to PE film, this composite preservation film, while meeting high moisture resistance and air permeability requirements, eliminates the need for additional sterilization steps. The composite preservation film itself possesses antibacterial properties and is environmentally friendly and cost-effective. Simultaneously, it conforms to the natural microporous structure of the citrus peel, forming a dense and adherent protective layer that better buffers against mechanical damage from compression and collisions, reducing post-harvest physical damage. This invention is of great significance for expanding the application market of chitosan-based preservation coatings and further replacing PE preservation bags in the post-harvest production of citrus and other fruits and vegetables.

[0024] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0025] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0026] Figure 1 The water vapor transmission rate (p < 0.05) of composite membranes prepared by mixing PE membranes, CS membranes (chitosan membranes prepared from a 1.5% chitosan solution), esters (thymol essential oil, vanillin, rosin, monoglycerides, sucrose esters, palm wax, paraffin wax, beeswax, sodium phytate), organic acids (rosin acid, lauric acid, stearic acid, phytic acid, oleic acid, gallic acid, salicylic acid, anhydrous gallic acid, palmitic acid, vanillic acid, palmitate), polysaccharides (gum arabic), amino acids (phenylalanine, tyrosine, isoleucine), nanocompounds (nano SiO2, nano TiO2), proteins (zein, gelatin), and polymers (polyhydroxybutyrate (PHB), polyvinyl alcohol) with a 1.5% chitosan solution.

[0027] Figure 2 The water vapor transmission rate of chitosan (CS) membranes, chitosan / paraffin (CS-P) composite membranes, chitosan / rosin acid (CS-A) composite membranes, chitosan / beeswax (CS-B) composite membranes, chitosan / paraffin / beeswax (CS-PB) composite membranes, chitosan / rosin acid / beeswax (CS-AB) composite membranes, chitosan / rosin acid / paraffin (CS-AP) composite membranes, and chitosan / rosin acid / paraffin / beeswax (CS-APB) composite membranes.

[0028] Figure 3 The effects of different concentrations of paraffin, rosin acid, and beeswax on the water vapor transmission rate of the CS membrane are as follows: A is the effect of different concentrations of paraffin on the water vapor transmission rate of the CS membrane; B is the effect of different concentrations of rosin acid on the water vapor transmission rate of the CS membrane; C is the effect of different concentrations of beeswax on the water vapor transmission rate of the CS membrane, p < 0.05.

[0029] Figure 4 These are scanning electron microscope (SEM) images of the CS membrane and the CS-APB composite membrane: A, B, and C are SEM images of the CS membrane; D and E are SEM images of the CS-APB composite membrane.

[0030] Figure 5 The effects of different membranes on the growth of Penicillium digitatum are as follows: A is the control group; B is the CS membrane; C is the chitosan-rosin acid-paraffin-beeswax-natamycin (CS-APB-N) composite membrane; and D is the chitosan-rosin acid-paraffin-beeswax-imidazol (CS-APB-I) composite membrane.

[0031] Figure 6 The images show the changes and states of lesion index in citrus after in vitro inoculation with Penicillium digitatum: A shows the changes in lesion index in the control group, CS-APB-N composite film group, and CS-APB-I composite film group after in vitro inoculation with Penicillium digitatum; B shows the state of citrus at 0 and 6 days after inoculation with Penicillium digitatum: a, b, and c show the state of citrus in the control group, CS-APB-N composite film group, and CS-APB-I composite film group at 0 days, and d, e, and f show the state of citrus in the control group, CS-APB-N composite film group, and CS-APB-I composite film group at 6 days, respectively.

[0032] Figure 7 The effects of different membranes on the rot rate of citrus during storage are shown in Figure A: the condition of citrus in the control group, CS-APB-N composite membrane group, and CS-APB-I composite membrane group on day 0 and day 35; and Figure B: the rot rate of citrus in the control group, CS-APB-N composite membrane group, and CS-APB-I composite membrane group at different storage times (d is the number of days).

[0033] Figure 8 The hardness of citrus fruits in the control group, CS-APB-N composite film group, and CS-APB-I composite film group at different storage times (d is the number of days) is compared.

[0034] Figure 9 The effects of different films on the surface brightness of citrus: A is the appearance of citrus in the control group, CS-APB-I composite film group, and CS-APB-N composite film group at the end of storage; B is the peel brightness index of citrus in the control group, CS-APB-I composite film group, and CS-APB-N composite film group at different storage times (d is the number of days), p < 0.05.

[0035] Figure 10 These are scanning electron microscope (SEM) images of citrus peels treated with different membranes: A, B, and C are SEM images of citrus peels treated with the control group; D, E, and F are SEM images of citrus peels treated with the CS-APB-I composite membrane.

[0036] Figure 11 The respiration rates of citrus fruits in the control group, CS-APB-N composite membrane group, and CS-APB-I composite membrane group at different storage times (d represents days) are shown.

[0037] Figure 12 The weight loss rate of citrus fruits in the control group, CS-APB-N composite film group, and CS-APB-I composite film group at different storage times (d is the number of days).

[0038] Figure 13 The soluble solids content of citrus fruits in the control group, CS-APB-N composite membrane group, and CS-APB-I composite membrane group at different storage times (d is the number of days) is shown.

[0039] Figure 14 The V of citrus fruits in the control group, CS-APB-N composite membrane group, and CS-APB-I composite membrane group are... C content.

[0040] Figure 15 The titratable acid content of citrus fruits in the control group, CS-APB-N composite membrane group, and CS-APB-I composite membrane group is shown. Detailed Implementation

[0041] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0042] In a specific embodiment of the present invention, v / v is the volume of the substance relative to the chitosan solution.

[0043] Example 1: Preparation of food preservation composite film (1) Preparation of chitosan solution: Chitosan was dissolved in 1% acetic acid aqueous solution, 1% (v / v) glycerol was added, stirred at room temperature for 4h, and degassed by ultrasonication to obtain a chitosan solution with a mass concentration of 1.5%. Impurities were removed and it was used for later use, denoted as CS. (2) Preparation of chitosan / rosin acid / paraffin / beeswax composite film liquid: Rosin acid was dissolved in 95% alcohol under a water bath heating environment at 65℃ (the ratio of rosin acid to alcohol was 1:1 (g:ml)). After the rosin acid was completely dissolved, 0.1% (v / v) emulsifier Tween-80 was added for emulsification. The emulsification was carried out until the emulsion was a uniform emulsion with no obvious oil droplets or particles suspended or separated into layers, and the rosin acid emulsion was obtained with a mass concentration of 1.25%. Weigh paraffin wax and beeswax into a beaker. Add the composite emulsifier (composed of Tween-80 and Span-60 in a mass ratio of 1:1) at a ratio of 4:1 (total mass of beeswax and paraffin wax to composite emulsifier). Emulsify in a 95°C water bath until the emulsion is a uniform emulsion with no obvious oil droplets or particles suspended or separated. This yields a wax emulsion with mass concentrations of 1.5% paraffin wax and 1.0% beeswax. The rosin acid emulsion and wax emulsion were mixed at a ratio of 1% of the volume of the chitosan solution, and then mixed with the chitosan solution and brought to a final volume. The mixture was sonicated for 20 minutes and magnetically stirred for 10 minutes before use. The resulting composite membrane solution was denoted as CS-APB. In the CS-APB composite membrane solution, the mass ratio of chitosan:rosin acid:paraffin:beeswax is 150:1.25:1.5:1.

[0044] (3) Preparation of chitosan / rosin acid / paraffin / beeswax / antibacterial agent composite membrane solution: Natamycin (3mg / L) or imidazolium (2μg / L) were added to the CS-APB membrane solution to obtain composite membrane solutions, namely CS-APB-N and CS-APB-I.

[0045] (4) Preparation of membranes: 15 mL of CS, CS-APB, CS-APB-N and CS-APB-I were respectively taken by casting method and poured into a float glass plate with a diameter of 13 cm. The membranes were dried in a forced-air drying oven (55℃, 5h) to obtain CS membrane, CS-APB composite membrane, CS-APB-N composite membrane and CS-APB-I composite membrane. The membranes were stored in a desiccator at 26℃ and 50% relative humidity for 24h for later use.

[0046] Example 2: Preparation of food preservation composite film Referring to Example 1, the only difference is that the mass concentrations of chitosan, rosin acid, paraffin wax, and beeswax are different, as shown in Table 1.

[0047] Table 1. Mass concentrations of chitosan, rosin acid, paraffin wax, and beeswax in Example 2. Example 1: Evaluation of the film-forming properties, moisture barrier properties, and air permeability of chitosan membranes. 1. Experimental Methods (1) Determination of water vapor transmission rate (WVTR): The water vapor transmission rate of the sample was measured according to GB / T 1037-2021 Test method for water vapor transmission of plastic films and sheets - cup method. The film was cut into 33.48cm pieces. 2 For a uniform circular sample, use a micrometer to randomly select five points on the sample for thickness measurement, and calculate the average value as the thickness of the circular sample. Add an appropriate amount of ultrapure water to six permeation cups, place the sample after thickness measurement into the permeation cups and fix it in place. Set the temperature to 25℃ and the relative humidity to 50%, and measure for 24 hours according to the instrument operation mode. Perform three parallel measurements for each sample, and take the average value of the results.

[0048] (2) Determination of carbon dioxide permeability: The oxygen permeability of the sample was measured by the pressure difference method of the gas permeability test method for plastic film and sheet according to GB / T 1038-2000. The film was cut into 33.48 cm pieces. 2 For a uniform circular sample, five points were randomly selected using a micrometer to measure the thickness, and the average value was calculated as the thickness of the circular sample. After the thickness test, vacuum grease was evenly applied to the lower test chamber, and the sample was placed between the upper and lower test chambers and clamped. The test conditions were 25℃ and 50% relative humidity. The vacuum pump was turned on, and the lower test chamber was evacuated for 12 hours. After the vacuum level decreased and remained stable for 3 hours, the lower test chamber was closed, and carbon dioxide was introduced into the high-pressure chamber (upper chamber) at a certain pressure, ensuring a constant pressure difference across the sample. The gas would then permeate from the high-pressure side to the low-pressure side under the influence of the pressure gradient. By monitoring the pressure on the low-pressure side, the oxygen permeation rate of the tested sample was determined. Three parallel tests were performed for each sample membrane, and the average value was taken.

[0049] 2. Experimental Results Table 2 shows the comparison of chitosan solutions with different mass concentrations through multiple film-forming experiments. When the mass concentration of chitosan solution is less than 1.2%, the film has high viscosity and is prone to adhesion, making it difficult to remove it completely from the float glass plate. When the mass concentration of chitosan is greater than 1.5% and less than 3.0%, the film's adhesion decreases, the film-forming properties are good, and it is easier to remove it completely from the float glass plate.

[0050] Table 2 Evaluation of film-forming properties and adhesion of chitosan films with different concentrations The chitosan membrane prepared with 1.5% CS was used in the following experiment, denoted as 1.5% CS.

[0051] As shown in Table 3, the WVTR of 1.5% CS is 752.13 ± 17.21 g / (m²). 2 •day), the WVTR of the PE film is 12.92±0.57g / (m 2 The CO2 permeability of the chitosan membrane is 2.56 ± 1.44 (cm²), indicating that the moisture barrier properties of the chitosan membrane are inferior to those of the PE membrane. 3 / m 2 (24h·0.1MPa) The CO2 permeability of the PE membrane was relatively high, exceeding the instrument's measurement range, indicating that the chitosan membrane had poor air permeability. Better air permeability helps reduce anaerobic respiration in fruits and vegetables, while poor air permeability of the chitosan membrane is detrimental to their storage. The experimental results show that the moisture barrier and air permeability of the chitosan membrane are both worse than those of the PE membrane. Therefore, improvements to the chitosan membrane are needed to enhance its moisture barrier and air permeability.

[0052] Table 3. Moisture barrier properties and air permeability of chitosan film and PE film Experimental Example 2: Improvement of the moisture barrier properties of chitosan membranes 1. Experimental Methods (1) Effect of different types of substances on moisture barrier performance: Different composite films were prepared by mixing esters (thymol essential oil, vanillin, rosin, monoglyceride, sucrose ester, palm wax, paraffin, beeswax, sodium phytate) with a mass concentration of 1%, organic acids (rosin acid, lauric acid, stearic acid, phytic acid, oleic acid, gallic acid, salicylic acid, anhydrous gallic acid, palmitic acid, vanillic acid, palmitate), polysaccharides (gum arabic), amino acids (phenylalanine, tyrosine, isoleucine), nano compounds (nano SiO2, nano TiO2), proteins (zein, gelatin) and polymers (polyhydroxybutyrate (PHB), polyvinyl alcohol) with a mass concentration of 1.5% CS; the mixing ratio was 1% (v / v).

[0053] (2) Screening of moisture barrier material combination: Referring to (1), different composite membranes were prepared, namely chitosan (CS) membrane, chitosan / paraffin (CS-P) composite membrane, chitosan / rosin acid (CS-A) composite membrane, chitosan / beeswax (CS-B) composite membrane, chitosan / paraffin / beeswax (CS-PB) composite membrane, chitosan / rosin acid / beeswax (CS-AB) composite membrane, chitosan / rosin acid / paraffin (CS-AP) composite membrane, and chitosan / rosin acid / paraffin / beeswax (CS-APB) composite membrane.

[0054] (3) Effect of different mass concentrations of rosin acid, paraffin wax and beeswax on the moisture barrier properties of composite membranes: Different composite membranes were prepared by mixing rosin acid, paraffin wax and beeswax with CS at a mass concentration of 1.5% at different mass concentrations (0%, 0.5%, 0.75%, 1%, 1.25% and 1.5%) with CS at a mass concentration of 1.5%, and the WVTR of each composite membrane was measured.

[0055] (4) Multi-factor orthogonal experiment: The moisture-blocking substances rosin acid, paraffin wax, beeswax and chitosan were used as four factors, and the different mass concentrations of each moisture-blocking substance were used as three levels. An orthogonal experiment was designed to obtain nine composite membrane solutions with different mass concentrations of rosin acid, paraffin wax, beeswax and chitosan. The membranes were dried and the WVTR of each composite membrane was measured to obtain the optimal ratio of different moisture-blocking substances to chitosan.

[0056] 2. Experimental Results like Figure 1 As shown, the WVTR of the chitosan-organic acid-wax composite membrane decreased significantly, and the addition of rosin acid, paraffin wax, and beeswax had a more significant effect on reducing the WVTR of the chitosan membrane. Specifically, the WVTR of the chitosan membrane was 752.13 ± 17.21 g / (m²). 2 The WVTR of the CS / rosin acid composite membrane was 545.06 ± 13.6 g / (m²). 2 The WVTR of the CS / paraffin composite membrane was 559.69 ± 14.45 g / (m²). 2 The WVTR of the CS / beeswax composite film was 431.86 ± 21.90 g / (m²). 2 (day). Compared to chitosan film, the average water vapor resistance (WVTR) of the composite films after adding rosin acid, paraffin wax, and beeswax decreased significantly, by 27.53%, 25.59%, and 42.58%, respectively. The decrease in WVTR was most pronounced after adding beeswax, indicating that rosin acid, paraffin wax, and beeswax have a significant impact on improving the moisture barrier properties of chitosan film. However, it still lags behind PE food preservation film in some aspects.

[0057] like Figure 2As shown, when 1% (v / v) of rosin acid, paraffin, and beeswax (mass concentration of 1%) are simultaneously added to chitosan, the resulting composite membrane exhibits the lowest WVTR, at 304.26 ± 25.99 g / (m²). 2 Compared with CS membrane, CS-P composite membrane, CS-A composite membrane and CS-B composite membrane, the average WVTR was reduced by 61.22%, 44.96%, 44.18% and 29.55% respectively. This shows that blending rosin acid, paraffin wax and beeswax with CS can significantly improve the moisture barrier performance of CS membrane.

[0058] like Figure 3 As shown in Figure A, the WVTR of the composite membrane decreases with increasing paraffin concentration. The decrease is most significant when the paraffin concentration exceeds 1.0%. While the WVTR continues to decrease gradually within the range of 1.0% to 1.5%, the effect of increasing paraffin concentration on the rate of decrease is no longer significant. The WVTR reaches its lowest value at 1.5%, at 512.18 ± 27.0 g / (m³). 2 (day), compared to chitosan membrane, it reduced by 34.71%. For example... Figure 3 As shown in Figure B, the WVTR of the composite membrane decreases continuously with the increase of rosin acid concentration. The WVTR is lowest when the rosin acid concentration is 1.5%, at 532.31 ± 5.12 g / (m³). 2 (day), compared to chitosan membrane, it reduced by 31.61%. For example... Figure 3 As shown in Figure C, when the mass concentration of beeswax is greater than 1.0%, the WVTR of the composite membrane is significantly reduced, and the composite membrane has the lowest WVTR, which is 409.73 ± 5.44 g / (m²). 2 (day), compared to chitosan membrane, it reduced by 47.77%.

[0059] As shown in Tables 4 and 5, the composite membranes in all experimental groups exhibited excellent moisture barrier properties, with a WVTR of less than 240 g / (m²). 2 •day); When the mass concentrations of chitosan, rosin acid, paraffin wax, and beeswax were 1.5%, the resulting composite membrane exhibited the lowest WVTR, at 167.64 g / (m²). 2 ·day), compared to chitosan membrane, the WVTR of CS-APB composite membrane was reduced by 78.3%.

[0060] Table 4 Factors and Levels Table 5 Results of the orthogonal experiment Experiment 3: Evaluation of air permeability of 1.5% CS membrane, CS-APB composite membrane, and PE membrane. 1. Experimental Methods (1) Determination of carbon dioxide permeability: Refer to Experimental Example 1.

[0061] (2) Observation of the ultrastructure of the membrane: The surface structure of the membrane was observed using a JEOL JEM-6390LV scanning electron microscope. Before the test, the membrane was kept dry and cut into 1cm×1cm squares. The membrane sample was fixed on a copper stage with conductive adhesive and sputtered with gold for 20 minutes on a JEOL JFC-1600 ion sputtering instrument. The chitosan membrane and the composite membrane were observed and photographed under a scanning electron microscope.

[0062] 2. Experimental Results As shown in Table 6, the carbon dioxide permeability of the 1.5% CS membrane is 2.56 ± 1.44 (cm²). 3 / m 2 (24h·0.1MPa), the carbon dioxide permeability of the CS-APB composite membrane, like that of the PE membrane, exceeded the measurement range, making it impossible to obtain a specific value. For example... Figure 4 As shown in the SEM images, at 100x magnification, the CS membrane surface is smooth, while the CS-APB membrane surface is uneven. Further magnification of the CS membrane to 300x reveals a smooth and dense surface. Even at 5000x magnification, the surface of the single CS membrane remains smooth without cracks or penetrating pores. However, at 300x magnification, the CS-APB composite membrane exhibits obvious fractures and cracks. This indicates the presence of pores on the CS-APB composite membrane surface. These pores allow some gas to permeate the composite membrane, resulting in a higher gas permeability. The experimental results demonstrate that the CS-APB composite membrane significantly improves gas permeability compared to the CS membrane, achieving permeability comparable to the PE membrane.

[0063] Table 6. CO2 permeability of the membrane Experiment Example 4: Improvement of the antibacterial properties of chitosan membranes 1. Experimental Methods (1) Four fungicides commonly used for fruit and vegetable preservation, namely natamycin, imazalil, imazalil and calcium propionate, were selected. By screening the minimum inhibitory concentration (MIC) of the fungicides, the fungicides with good inhibitory effect on Penicillium digitatum were obtained. The fungicides with the best antibacterial performance were used to optimize the antibacterial performance of CS-APB composite membrane.

[0064] (2) Determination of the minimum inhibitory concentration (MIC) of the bactericide: Natamycin was dissolved in dimethyl sulfoxide, while imazalil, prochlorazine, and calcium propionate were dissolved in distilled water. The dissolved drugs were diluted to different concentrations, and 10 µL of each drug solution was mixed with 1 mL of PDA medium in a 48-well plate. After the medium solidified, 10 µL of each solution with a concentration of 1×10⁻⁶ was taken out. 6 A suspension of wild-type Penicillium finger spores (CFU / mL) was dropped onto a culture medium and incubated in a constant temperature incubator at 26±2℃ for 3 days. Colony growth was observed, and the minimum inhibitory concentration (MIC) values ​​of each drug for each strain were obtained.

[0065] 2. Experimental Results As shown in Table 7, the MIC screening results for fungicides revealed that imazalil had the lowest MIC against Penicillium digitatum (2 μg / L), while natamycin and prochloraz had MICs of 3 mg / L and 4.5 mg / L, respectively. Calcium propionate had a relatively high MIC, exceeding 10 mg / L. Therefore, CS-APB-I and CS-APB-N composite membranes were prepared by combining 2 μg / L imazalil and 3 mg / L natamycin with the CS-APB membrane solution.

[0066] Table 7 Minimum Inhibitory Concentrations of Bactericides Experiment 5: Evaluation of the inhibitory effects of CS membrane, CS-APB-N composite membrane, and CS-APB-I composite membrane on the growth of Penicillium fingering and their control effects on citrus Penicillium disease under artificial inoculation conditions. 1. Experimental Methods (1) Evaluation of antibacterial activity of composite membranes: The growth rate method was used. The prepared CS membrane, CS-APB-N composite membrane and CS-APB-I composite membrane were cut into circular pieces with a diameter of 4 cm. After sterilization under UV lamp for 1 h (30 min on both sides), they were attached to the center of PDA medium. Then, the purified Penicillium finger culture dish was taken, and a 5 mm diameter mycelial cake was punched at the edge of the colony with a punch. The mycelial side was attached to the center of the circular membrane, and the culture dish was sealed with sealing film. Plates without any film were used as the control group. Each treatment was set up in triplicate. The culture was incubated in a constant temperature incubator at 26℃ for 3 days. The colony diameter of the pathogen was measured by cross-sectional method every 12 h.

[0067] (2) In vitro inoculation experiment of *Penicillium fingertips* on citrus: 45 physiologically healthy, undamaged, and similarly shaped fresh citrus fruits were selected and divided into three groups. The citrus fruits were treated with water, CS-APB-N, and CS-APB-I coating solutions, respectively. A sterilized 5mm diameter punch was used to make holes at the equatorial region of the citrus peel, one at the front and one at the back. 10μL of a pre-prepared solution with a concentration of 1×10⁻⁶ was then used. 6A CFU / mL suspension of Penicillium finger spores was injected into pre-drilled holes in the citrus peel. After the spore suspension was absorbed, the citrus was stored in a temperature-controlled environment, and the incidence rate and lesion diameter were recorded.

[0068] 2. Experimental Results Depend on Figure 5 As can be seen, after 72 hours of incubation, obvious *Penicillium fingeringense* colonies appeared in the control group, with an average colony diameter of 21 mm. The growth rate of *Penicillium fingeringense* colonies on the CS membrane was significantly lower than that in the control group, but an expansion of the colony growth area was observed. No colonies grew on either the CS-APB-N composite membrane or the CS-APB-I composite membrane, meaning the colony growth was limited to the mycelial cake and did not spread across the composite membrane. This indicates that the composite membrane treatment had a good inhibitory effect on *Penicillium fingeringense*.

[0069] The results of the composite membrane treatment for in vitro inoculation of citrus with Penicillium finger are as follows: Figure 6 As shown in the results, until the end of the observation period, no lesions appeared on citrus treated with CS-APB-I coating after inoculation with Penicillium digitatum suspension, indicating that imazalil has a significant control effect against Penicillium digitatum. Compared with the control group, the coating treatment with added natamycin can reduce and delay the onset of Penicillium digitatum on citrus and can inhibit the growth and reproduction of Penicillium digitatum on citrus to a certain extent, but the effect is significantly less than that of the CS-APB-I composite film treatment group. This indicates that imazalil is more effective in inhibiting the infection of Penicillium digitatum on citrus. Figure 6 A).

[0070] like Figure 6 As shown in Figure B, compared with the control group citrus, the growth of Penicillium fingering on the peel of citrus treated with CS-APB-I and CS-APB-N was inhibited. However, the inhibitory effect of CS-APB-N on the growth of Penicillium fingering on the peel of citrus was significantly less than that of CS-APB-I.

[0071] Considering that different usage environments can affect the antibacterial effect of the antibacterial agent, in order to achieve a better antibacterial effect of the CS-APB-N composite film on the fruit peel surface, the concentration of natamycin was increased to 0.3 g / L during the subsequent preparation of the CS-APB-N coating solution.

[0072] The above experimental results show that both CS-APB-N composite membrane and CS-APB-I composite membrane can significantly inhibit the growth and reproduction of Penicillium digitatum, especially the CS-APB-I composite membrane has a more significant inhibitory effect on the growth and reproduction of Penicillium digitatum.

[0073] Experiment 6: Effects of CS-APB-I composite film and CS-APB-N composite film on citrus decay rate 1. Experimental Methods Citrus coating treatment: Select citrus fruits with no mechanical damage and good physiological condition, soak them in a 5% sodium hypochlorite solution for 3 minutes for preliminary sterilization; after sterilization, rinse with clean water and air dry for later use; divide the treated citrus fruits into CS-APB-I composite film group, CS-APB-N composite film group, and control group. Soak the citrus fruits in the corresponding film solution for 5 minutes (the control group was soaked in clean water), take them out and air dry, and put the treated citrus fruits into breathable PE preservation bags and store them at room temperature (24±2℃, 50±10%RH) for 35 days; each treatment group has 3 replicates, with 30 fruits in each replicate.

[0074] Every 7 days, the number of rotten citrus fruits in each group is counted until the citrus fruits lose their storage value. The rot rate is calculated according to formula (1): rot rate % = (number of rotten fruits / total number of fruits) × 100……(1).

[0075] 2. Experimental Results like Figure 7 As shown, the control group had the highest citrus decay rate, with the number of decayed fruits being approximately half of the total stored quantity, reaching 47.62±4.76% at the end of storage. Compared to the control group, the CS-APB-I composite film group and the CS-APB-N composite film group showed a significant reduction in the number of decayed fruits and a significantly lower decay rate. During the first 14 days of storage, the citrus decay rates in both the CS-APB-I and CS-APB-N composite film groups were low, with no significant difference between the two groups. From day 21 to 35 of storage, the citrus decay rate in the CS-APB-N composite film group began to increase, exceeding that of the CS-APB-I composite film group, but remained lower than that of the control group. At the end of storage (day 35), the decay rates of the CS-APB-I and CS-APB-N composite film groups were 26.98±2.75% and 30.15±2.75%, respectively. Experimental results show that CS-APB-N composite film and CS-APB-I composite film can effectively reduce the occurrence of citrus rot, with CS-APB-I composite film showing better results.

[0076] Experimental Example 7: Effects of CS-APB-I and CS-APB-N composite films on the firmness of citrus fruits. 1. Experimental Methods The experiment was conducted based on Example 6. Every 14 days, 9 citrus fruits in good physiological condition were randomly selected from each group (3 fruits in each replicate). After sampling, the change in the hardness value of the citrus peel was measured: three points were randomly selected at the equatorial part of the citrus fruit, and the hardness was measured using a handheld hardness tester. The average value of the measurement results was taken.

[0077] 2. Experimental Results The firmness of citrus fruits largely determines their taste and texture, making it a very important indicator of citrus quality. For example... Figure 8 As shown, compared to day 0, the firmness of citrus fruits in the control group, CS-APB-I composite film group, and CS-APB-N composite film group all decreased during storage. The control group showed a more significant decrease in firmness, exhibiting a trend of initial decrease followed by an increase, reaching its lowest point on day 14 and rebounding sharply on day 28. This was because the citrus fruits in the control group suffered severe water loss, resulting in dried-out peels. The firmness of citrus fruits in both the CS-APB-I and CS-APB-N composite film groups showed a continuous decrease, but the rate of decrease was relatively slow. After day 14, the rate of decrease in firmness increased, with the CS-APB-N composite film group showing a more significant decrease in firmness than the CS-APB-I treatment group. No peak firmness change was observed in either the CS-APB-I or CS-APB-N composite film groups during the 28-day period.

[0078] Experimental results show that CS-APB-N composite film and CS-APB-I composite film can effectively reduce changes in the firmness of citrus fruits and delay the decrease in firmness, with CS-APB-I composite film showing better results.

[0079] Experimental Example 8: Effects of CS-APB-I and CS-APB-N composite films on the surface gloss of citrus fruits. 1. Experimental Methods The experiment was conducted based on Example 6. Every 14 days, nine citrus fruits in good physiological condition were randomly selected from each treatment group (three in each replicate). After sampling, the changes in the brightness value of the citrus peel were measured: four different points were randomly selected on each citrus fruit, and the measurements were taken using a 3nh spectrophotometer. The results were analyzed using the Lab colorimetric system.

[0080] 2. Experimental Results like Figure 9 As shown in Figure B, compared to day 0, after 28 days of storage, the color of the citrus peel in all three groups decreased to varying degrees. The CS-APB-I and CS-APB-N composite film groups showed less decrease in peel brightness, and the change was more gradual. The brightness index of the control group decreased from 61.65±1.21 to 59.68±1.08. The brightness indices of the citrus peel in the CS-APB-N and CS-APB-I composite film groups were higher than those in the control group during storage. Figure 9 As can be seen from A, the citrus peels in the control group lacked luster and showed some wilting, while the citrus peels in the CS-APB-I composite film group and the CS-APB-N composite film group had stronger luster, were more plump, and did not show any wilting.

[0081] Experimental results show that CS-APB-N composite film and CS-APB-I composite film can reduce the decrease in brightness of citrus peel and maintain the gloss of fruit surface; among them, CS-APB-I composite film has a better effect.

[0082] Experimental Example 9: Effects of CS-APB-I Composite Film on the Micromorphology of Citrus Peel 1. Experimental Methods The experiment was conducted based on Example 6. After freeze-drying the citrus peel, the citrus was kept dry, and the surface structure of the citrus peel was observed using a JEOL JEM-6390LV scanning electron microscope. The citrus peels of the control group and the CS-APB-I composite film group were cut into 1cm×1cm squares, the film samples were fixed on a copper stage with conductive adhesive, sputtered with gold for 20 min on a JEOL JFC-1600 ion sputtering instrument, and then observed under a scanning electron microscope (SEM).

[0083] 2. Experimental Results Figure 10 As shown, at 100x magnification, the citrus peel of the control group showed more pores and a slightly uneven surface. At 300x and 1000x magnification, numerous fungal hyphae were observed on the peel surface. The citrus peel of the CS-APB-I composite film group showed a smoother surface at 100x magnification, with larger areas of film liquid coverage visible. At 300x and 1000x magnification, the pores of the citrus peel were completely covered by the film liquid, and no fungal hyphae were observed. Furthermore, at 300x and 1000x magnification, the citrus peel of the control group appeared microscopically rougher, while the citrus peel of the CS-APB-I composite film group showed significantly improved smoothness. This indicates that the composite film effectively fills the pores in the citrus peel, improves its smoothness, and inhibits the growth and reproduction of pathogenic microorganisms on the citrus peel.

[0084] Experiment 10: Effects of CS-APB-I and CS-APB-N composite membranes on the respiration rate of citrus fruits. 1. Experimental Methods The experiment was conducted based on Example 6. The respiration rate of citrus was measured using an FT-GX20 fruit and vegetable respiration analyzer. Five healthy citrus fruits were randomly selected from the replicates of each treatment group. The respiration rate of the citrus fruits was measured on storage days 0, 14, and 28, with a measurement duration of 20 minutes. The respiration rate of the citrus fruits was calculated according to formula (2), with the unit of respiration rate being mg·h⁻¹. -1 •kg -1 FW indicates; Respiration rate = (carbon dioxide concentration × (container volume - fruit volume) × 44) / (22.4 × sealing time × fruit mass) × 273 / (273 + 25) …… (2).

[0085] 2. Experimental Results like Figure 11 As shown, the respiration rate of citrus in the control group did not change significantly, while the respiration rates of citrus in the CS-APB-I composite membrane group and the CS-APB-N composite membrane group decreased significantly on day 14, reaching 21556.47±1966.96 (mg·h⁻¹). -1 ·kg -1 ·FW), 20215.82±2626.9 (mg·h -1 ·k g-1 The respiration rate (FW) of citrus fruits decreased by one-third compared to day 0. At day 28, an increase in respiration rate was observed in all groups, especially in the CS-APB-I and CS-APB-N composite membrane groups. However, throughout the entire storage period, the respiration rate of citrus fruits in the CS-APB-I and CS-APB-N composite membrane groups remained lower than that in the control group. The experimental results indicate that the CS-APB-N and CS-APB-I composite membranes can reduce the respiration rate of citrus fruits, which is beneficial for reducing the consumption of nutrients and maintaining the quality of citrus fruits.

[0086] Experimental Example 11: Effects of CS-APB-I and CS-APB-N composite membranes on the weight loss rate of citrus fruits. 1. Experimental Methods The experiment was conducted based on Experiment Example 6. Determination of weight loss rate: After the treatment, the initial weight was recorded. Every 7 days, the unrotten fruit was weighed, and the weight loss rate of the citrus was calculated according to formula (3). Weight loss rate % = (m0 - m) x ) / m0×100; m0—the mass of the fruit in 0 days; m x —The quality of the fruit on day X… (3).

[0087] 2. Experimental Results During the storage of citrus fruits, the weight of the fruit will decrease due to respiration and water evaporation. The weight loss rate of citrus fruits can reflect the intensity of physiological metabolism and the degree of water loss during storage.

[0088] like Figure 12As shown, on day 7, the weight loss rate of citrus fruits in the three groups increased significantly: 4.45±0.37% in the control group, 3.91±0.57% in the CS-APB-N composite film group, and 3.11±0.49% in the CS-APB-I composite film group. However, during the subsequent storage period, the weight loss rate of the CS-APB-I and CS-APB-N composite film groups increased more slowly, consistently lower than that of the control group. Furthermore, the weight loss rate of the control group increased more significantly with prolonged storage. At day 35, the weight loss rates of citrus fruits in the control group, CS-APB-N composite film group, and CS-APB-I composite film group were 12.23±0.80%, 8.42±0.60%, and 7.85±0.96%, respectively. The experimental results indicate that CS-APB-I and CS-APB-N composite films can effectively reduce the weight loss of citrus fruits during storage.

[0089] Experimental Example 12: Effects of CS-APB-I and CS-APB-N composite films on citrus quality indicators 1. Experimental Methods The experiment was conducted based on Experiment 6.

[0090] (1) Determination of soluble solids content: Mixed juice was taken from 3 fruits, with 3 replicates per group. The mixture was centrifuged at 4℃ and 6000r / min for 15min, and 200μL of supernatant was taken. The soluble solids content (%) in the citrus was determined using a digital display saccharimeter.

[0091] (2) At the end of the 35-day storage period, nine healthy citrus fruits were randomly selected from each group, and the levels of vitamin V in the fruits were measured. C Content: After juicing the fruit, filter it with gauze, take 10g of juice, dilute it to 100mL with 20g / L oxalic acid solution, extract for 10min and then filter; take 10mL of filtrate and titrate it with 0.1g / L 2,6-dichlorophenolindophenol solution until the filtrate turns pink and does not change color within 30s; at this time, record the volume of 2,6-dichlorophenolindophenol solution consumed, calculate the Vc content in the juice according to formula (4), and the result is expressed as mg / 100g.

[0092] Vitamin C content (mg / 100g) = (v1-v0)×v×ρ / v s ×m×100…(4; In the formula: v1—volume of 2,6-dichlorophenolindophenol solution consumed in titrating the filtrate / mL; v0—volume of 2,6-dichlorophenolindophenol solution consumed in titrating oxalic acid / mL; v—total volume of juice after dilution / mL; ρ—mass concentration of ascorbic acid equivalent to a unit volume of 2,6-dichlorophenolindophenol solution / (mg / mL); v s —Volume of filtrate used for titration / mL; m —Mass of fruit juice weighed / g.

[0093] (3) Determination of titratable acid content: The sodium hydroxide titration method (refer to GB / T8210-2011) is used. 5 mL of filtered juice is pipetted into a 50 mL volumetric flask and diluted to the mark. 10 mL of diluted juice is then pipetted in, and 2-3 drops of phenolphthalein are added. The solution is titrated with a standardized sodium hydroxide solution until a faint red color persists for 30 seconds. The titration is repeated three times. Titratable acid content % = v × c × (v1 - v0) / (v s ×m)×100%…(5;In the formula: v—total volume of sample solution (mL); v s — Volume of extract used for titration (mL); c — Concentration of NaOH titrant (mol / L); v1 — Volume of NaOH solution consumed in titration of extract (mL); v0 — Volume of NaOH solution consumed in titration of distilled water (mL); m — Mass of sample used for determination (g).

[0094] (4) Sensory evaluation of citrus: After storage, 15 citrus fruits with normal physiological condition were randomly selected from different treatment groups, cut evenly, and 10 students were randomly selected to conduct sensory evaluation; the sensory evaluation criteria of citrus fruits are shown in Table 8 below.

[0095] Table 8 Sensory Evaluation Criteria for Citrus (5) Data processing: Data processing and plotting were performed using Origin 2019. The results are expressed as mean ± standard deviation. SPSS 21.0 software was used to perform one-way ANOVA on the experimental data. The least significant number (LSD) test was applied to test the significance of differences (P<0.05). Different letters indicate significant differences.

[0096] 2. Experimental Results The soluble solids (TSS) content of citrus fruits is closely related to their flavor, and changes in TSS can also reflect changes in the quality of citrus fruits. For example... Figure 13As shown, during the 28-day storage period, the TSS content of citrus fruits in all treatment groups showed an increasing trend. The control group showed the most significant increase in TSS content, rising from 12.60±0.34% on day 0 to 13.81±0.47% on day 28. On day 28, the TSS contents of the CS-APB-I composite film group and the CS-APB-N composite film group were 12.90±0.36% and 13.00±0.57%, respectively. When the TSS content increases to a certain level, it gradually decreases due to the consumption of nutrients by the fruit's physiological metabolic activities. The rate of increase in TSS content in the control group was significantly higher than that in the CS-APB-I and CS-APB-N composite film groups. The experimental results indicate that the CS-APB-I and CS-APB-N composite films can delay the increase in TSS content in citrus fruits.

[0097] V C It has antioxidant properties, which can reduce the free radical content in fruits and delay the senescence of citrus fruits. C Vitamin C content is an important nutritional indicator for citrus fruits. During post-harvest storage, citrus fruits lose vitamin C through oxidation. C The content will gradually decrease. For example... Figure 14 As shown, in the three groups of citrus fruits, the V in the control group was... C The lowest content was 4.97±0.05 mg / 100g; the V content of citrus fruits in the CS-APB-I composite membrane group and the CS-APB-N composite membrane group was... C The content was higher than that of the control group, at 5.17 mg / 100g and 5.44 ± 0.05 mg / 100g, respectively. The experimental results indicate that CS-APB-I composite membrane and CS-APB-N composite membrane can reduce the intensity of oxidation in citrus and inhibit V... C The content decreased.

[0098] Titratable acids in citrus fruits are mainly organic acids. The content of organic acids is closely related to the flavor of citrus fruits. Organic acids also participate in respiration and gluconeogenesis. Therefore, the content of organic acids can reflect the strength of fruit metabolic activities. Figure 15 As shown, the control group of citrus fruits had the lowest organic acid (TA) content, at 0.199±0.008%; the TA contents of the CS-APB-I composite membrane group and the CS-APB-N composite membrane group were 0.258±0.008% and 0.263±0.004%, respectively. The experimental results indicate that the CS-APB-I and CS-APB-N composite membranes can reduce the respiration of citrus fruits, helping to maintain the organic acid content inside the fruit and thus preserving its flavor.

[0099] As shown in Table 9, the sensory evaluation results indicate that, compared with the control group, the citrus fruits in the CS-APB-I composite film group and the CS-APB-N composite film group showed less change in appearance and were able to better maintain their plump and glossy appearance. They also had more moisture and more pronounced flavor, indicating that the CS-APB-I composite film and the CS-APB-N composite film can better preserve the flavor and moisture of the fruit.

[0100] Table 9 Sensory evaluation results of citrus fruits In summary, the composite membrane prepared by rosin acid, paraffin wax, beeswax, and chitosan through screening experiments shows that it possesses high moisture resistance and high air permeability. Furthermore, the composite membrane obtained when the mass ratio of chitosan, rosin acid, paraffin wax, and beeswax is 150:1.25:1.5:1 exhibits the best moisture resistance, with a water vapor permeability of 164.64 g / (m²). 2 The water vapor permeability of the CS-APB-I composite film was reduced by 78.3% compared to that of the chitosan film. Screening experiments were conducted to determine the minimum inhibitory concentrations (MICs) of common fungicides against *Penicillium digitatum*, with imazalil showing the lowest MIC at 2 μg / L. In the antibacterial experiment, the CS-APB-I composite film also exhibited the best antibacterial effect, significantly inhibiting the growth and reproduction of *Penicillium digitatum*. Furthermore, in the test of the composite film's effect on citrus preservation, both the CS-APB-N and CS-APB-I composite films effectively reduced the weight loss, decay rate, and respiration rate of citrus, delayed the decrease in firmness, maintained the TSS content and peel brightness index of citrus, and effectively covered the stomata of the citrus peel, significantly improving the smoothness of the peel, effectively inhibiting respiration and material exchange through the peel, maintaining the weight of the citrus, and reducing the growth and reproduction of microorganisms on the peel. Among them, the CS-APB-I composite film showed superior citrus preservation effect. This invention produces a composite preservation film with high moisture resistance and high air permeability by compounding chitosan, rosin acid, paraffin wax, and beeswax. By adding a bactericide to this film, a composite preservation film with high moisture resistance, high air permeability, and high antibacterial properties can be obtained, which has excellent preservation effect on citrus fruits and is of great significance for expanding the application market of chitosan-based preservation coatings.

Claims

1. A food preservation composite film, characterized in that, It is prepared from raw materials in the following mass ratio: chitosan: rosin acid: paraffin: beeswax = (100~200): (1~1.5): (1~1.5): (1~1.5).

2. The food preservation composite film according to claim 1, characterized in that, It is prepared from raw materials in the following mass ratio: chitosan: rosin acid: paraffin: beeswax = (120~180): (1~1.5): (1~1.5): (1~1.5).

3. The food preservation composite film according to claim 2, characterized in that, It is prepared from raw materials in the following mass ratio: chitosan: rosin acid: paraffin: beeswax = 150: 1.25: 1.5:

1.

4. The food preservation composite film according to any one of claims 1 to 3, characterized in that, It also includes preservatives and bactericides for raw fruits and vegetables.

5. The food preservation composite film according to claim 4, characterized in that, The fruit and vegetable preservative and bactericide includes at least one of natamycin, imazalil, and calcium propionate.

6. The method for preparing the food preservation composite film according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Preparation of chitosan solution: Chitosan is dissolved in an aqueous solution of organic acid, plasticizer is added, and the mixture is stirred evenly to obtain chitosan solution. Impurities are removed and the solution is ready for use. (2) Preparation of chitosan / rosin acid / paraffin / beeswax composite film solution: Rosin acid was dissolved in an organic solvent and emulsified with an emulsifier to obtain rosin acid emulsion; paraffin wax and beeswax were weighed and emulsified with an emulsifier to obtain wax emulsion; then the rosin acid emulsion and wax emulsion were mixed, and then mixed with chitosan solution and adjusted to a fixed volume to obtain chitosan / rosin acid / paraffin / beeswax composite film solution; (3) Dry the chitosan / rosin acid / paraffin / beeswax composite film liquid into a film to obtain the chitosan / rosin acid / paraffin / beeswax composite film; The chitosan solution has a mass concentration of 1.0% to 2.0%; the rosin acid emulsion has a mass concentration of 1.0% to 1.5%; and in the wax emulsion, the paraffin wax and beeswax each have a mass concentration of 1.0% to 1.5%.

7. The preparation method according to claim 6, characterized in that, It also includes the following steps: Based on the chitosan / rosin acid / paraffin / beeswax composite film liquid, a fruit and vegetable preservative and bactericide is added to obtain a chitosan / rosin acid / paraffin / beeswax / bactericide composite film liquid. The chitosan / rosin acid / paraffin / beeswax / bactericide composite film liquid is then dried into a film to obtain the chitosan / rosin acid / paraffin / beeswax / bactericide composite film.

8. The preparation method according to claim 7, characterized in that, The fruit and vegetable preservative fungicide includes at least one of imazalil, natamycin, prochloraz, and calcium propionate; the concentration of imazalil in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 2~100 μg / L; the concentration of natamycin in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 3~300 mg / L; the concentration of prochloraz in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 4~10 mg / L; and the concentration of calcium propionate in the chitosan / rosin acid / paraffin / beeswax / fungicide composite film solution is 8~30 mg / L.

9. The preparation method according to any one of claims 6 to 8, characterized in that, The organic acid aqueous solution includes at least one of acetic acid, lactic acid, citric acid, and malic acid; the plasticizer includes at least one of glycerol, propylene glycol, 1,3-butanediol, sorbitol, and mannitol; and the emulsifier includes at least one of Tween-80, Span-60, Tween-20, polyethylene glycol, Span-80, and monoglyceride.

10. The use of the preservation composite film according to any one of claims 1 to 5 in the preservation of citrus fruits.

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