Edible preservative film based on emulsion-entrapped and its preparation method and application

Abstract

The application belongs to the technical field of fresh-keeping materials, and relates to an edible fresh-keeping film based on emulsion embedding as well as a preparation method and application thereof, and comprises the following steps: 1) preparation of an essential oil emulsion; mixing protein, a polysaccharide stabilizer and water to obtain an aqueous solution, wherein the mass ratio of the protein and the polysaccharide stabilizer is 1-5:1; the mass fraction of the protein in the aqueous solution is 1.5%; essential oil is added to the aqueous solution, and shearing is performed to obtain the essential oil emulsion; the essential oil accounts for 40%-60% of the volume of the essential oil emulsion; 2) preparation of a sodium alginate-based essential oil emulsion film; the essential oil emulsion is taken, and a plasticizer and a film-forming material are added, and stirring is performed for 10 min-60 min to obtain the emulsion film. The edible fresh-keeping film based on emulsion embedding as well as the preparation method and application thereof provided by the application have good stability, good water solubility, environmental protection safety, can inhibit the respiration of fruits and vegetables, slow down the consumption of nutrients, inhibit the browning of fruits and vegetables, and are used for realizing efficient fresh-keeping.

Description

Technical Field

[0001] This invention belongs to the field of preservation materials technology, and relates to an edible preservation film based on emulsion encapsulation, its preparation method and application. Background Technology

[0002] The food industry currently mainly uses physical methods (modified atmosphere packaging, irradiation), chemical methods, and biological methods to control post-harvest diseases of fruits and vegetables and maintain their quality. Physical preservation technology requires large-scale instruments, has extremely high equipment requirements, and is complex to operate. In addition, it is easily restricted by location and environmental conditions and is not suitable for large-scale promotion. Chemical preservation is a relatively traditional preservation method. It is widely used because it can reduce respiration intensity, reduce the consumption of nutrients, thereby delaying fruit aging, preventing decay and sterilization, and increasing storage period. Moreover, it is inexpensive and has become an important means of post-harvest storage for many fruits. In chemical preservation technology, active ingredients can be released through direct action, slow release, or fumigation to achieve the effect of preservation and antibacterial action. Chemical preservation has the following advantages: (1) low equipment investment; (2) energy saving; (3) low operating cost; (4) simple and easy to implement.

[0003] Significant progress has been made in chemical preservation, and chemical preservation technology has been widely applied in the preservation of many fruits. However, with the rapid development of agricultural production and the abundance of agricultural products, more and more agricultural products require rapid, low-energy, low-cost, and localized preservation in post-harvest storage and distribution. This has created a promising market and application prospect for chemical preservatives. However, their use presents many hidden dangers. For example, the toxicity of chemical preservative residues in fruits and vegetables poses a potential danger to human health, which has become a concern for the entire society. Currently, many chemical fungicides previously used for post-harvest treatment of fruits and vegetables have been banned, such as benomyl, carbendazim, and biguanide salts. Furthermore, long-term use of fungicides in a particular area can lead to the development of drug-resistant strains, thereby reducing the effectiveness of control. As a result, the dosage and chemical residue levels of chemical fungicides are greatly increased, further threatening human health. Food quality and safety are receiving increasing attention from society with the rapid development of science and technology, and more and more people hope to have easier access to nutritious, fresh, and higher-quality food. Therefore, there is an urgent need to seek new, non-toxic, and highly effective anti-corrosion technologies to gradually replace the use of chemical fungicides on harvested fruits and vegetables.

[0004] Biological preservation technology is widely recognized as one of the most promising high-tech advancements of the 21st century in the field of fruit preservation. Using biological preservatives for fruit preservation offers advantages such as relatively easy control of conditions, low cost, and minimal pollution, making it a technology with enormous development potential. Biological preservation technology primarily utilizes microbial cells or their metabolites, natural biological (plant and animal) extracts, or other bioengineering methods to inhibit harmful microorganisms, slow down the natural ripening process of fruits, reduce post-harvest decay rates, maintain good sensory quality and nutritional components, leave no residue, and increase product added value. Among these, plant-derived biological preservatives have advantages such as wide availability, low cost, and promising application prospects, leading numerous researchers to explore the effects of plant-derived preservative components on fruit preservation.

[0005] Plant essential oils are a general term for a class of aromatic, oily liquids widely found in plants. They are secondary metabolites composed of terpenes and phenols with broad-spectrum antibacterial properties. The US FDA classifies plant essential oils as "generally recognized as safe" (GRAS). Phenolic compounds play a major role in their antibacterial activity.

[0006] However, the complexity of chemical components in plants, and the extreme instability of some active ingredients to heat and humidity, mean that environmental factors have a significant impact on these active components. Coating preservation is a storage method that involves dipping, spraying, or brushing a pre-prepared coating solution onto the surface of the fruit, acting individually on each fruit. The raw material for coating preservation is a film with a certain preservative effect, which is edible and can effectively prevent microbial infection, thereby inhibiting the respiration of fruits and vegetables and slowing down nutrient consumption. Furthermore, the materials used in coating preservation are various environmentally friendly materials derived from various biological sources, which can rapidly degrade in the environment, reducing environmental burden and pollution. Due to its simple operation, non-toxicity, hygiene, safety, and low cost, this method has become a research hotspot in the field of fruit and vegetable preservation technology in recent years.

[0007] Commercially available natural preservatives are generally water-soluble or oil-soluble. These substances need to come into contact with fruits, vegetables, or microorganisms to exert their antioxidant or antibacterial activities. Using coatings for fruit and vegetable preservation inevitably presents the problem of active ingredients not migrating, leading to excessive addition and the overuse of bioactive additives. Excessive addition can indirectly harm human health, a concern that has been extensively reported and confirmed. Plant essential oils, due to their small molecule and volatile nature, can protect fruits and vegetables through various methods (fumigation and contact), significantly reducing their usage. However, most biomolecular coating materials are water-soluble, and plant essential oils cannot integrate with these substances, resulting in a significant reduction in their efficacy. Encapsulation can effectively solve the problem of plant essential oils' incompatibility with water; however, existing encapsulation technologies such as emulsions and microcapsules require large amounts of surfactants or organic reagents for stabilization and solidification, as well as significant amounts of water as a solvent. This not only causes environmental pollution and resource waste but also poses a certain degree of damage to human health and ecosystems. Summary of the Invention

[0008] To address the technical problems of volatility, irritation, and water insolubility in existing encapsulation methods, the present invention aims to provide an edible preservation film based on emulsion encapsulation, its preparation method, and its application. This film exhibits good stability, good water solubility, and is environmentally friendly and safe. It can inhibit the respiration of fruits and vegetables, slow down nutrient consumption, and inhibit browning of fruits and vegetables, thereby achieving efficient preservation.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0011] 1) Preparation of essential oil emulsions

[0012] 1.1) A protein, a polysaccharide stabilizer, and water are mixed to obtain an aqueous solution, wherein the mass ratio of the protein to the polysaccharide stabilizer is 1 to 5:1; and the mass fraction of the protein in the aqueous solution is 1.5%.

[0013] 1.2) Add essential oil to the aqueous solution of step 1.1) and shear to obtain an essential oil emulsion; the essential oil accounts for 40% to 60% of the volume of the essential oil emulsion;

[0014] 2) Preparation of sodium alginate-based essential oil emulsion film

[0015] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 10 min to 60 min to obtain an emulsion-like plastic wrap.

[0016] In step 1.2), the shearing speed is 7000 r / min to 23000 r / min, and the shearing time is 1 min to 5 min.

[0017] Furthermore, the protein is soy protein isolate, whey protein isolate, zein, gelatin, or wheat protein isolate.

[0018] Furthermore, the essential oil is peppermint essential oil, tea tree essential oil, lavender essential oil, thyme essential oil, oregano essential oil, ginger essential oil, or sweet orange essential oil.

[0019] Furthermore, the polysaccharide stabilizer is chitosan quaternary ammonium salt, gum arabic, konjac glucomannan, chitosan, or sodium carboxymethyl cellulose.

[0020] Furthermore, in step 2), the ratio of essential oil emulsion, plasticizer, and film-forming material is 0.1g~25g:0.1g~25g:0.1ml~50mL.

[0021] Furthermore, the plasticizer is glycerol, ethylene glycol, sorbitol, mannitol, urea, monosaccharide, disaccharide, or oligosaccharide.

[0022] Furthermore, the film-forming material is pectin, konjac glucomannan, sodium alginate, gum arabic, carrageenan, polylactose, or gelatin.

[0023] The food preservation film prepared by the method for preparing an edible food preservation film based on emulsion encapsulation is described above.

[0024] Application of an emulsion film as described in improving the antibacterial rate of Aspergillus niger, Aspergillus ochraceus, and Penicillium esculentum.

[0025] The beneficial effects of this invention are:

[0026] This invention uses peppermint essential oil as an antibacterial agent, soy protein isolate as an emulsifier, and chitosan quaternary ammonium salt as a stabilizer. High-speed shearing is used to form a high internal phase essential oil emulsion, which is more stable than ordinary essential oil emulsions, maintaining its properties even after 75 days of storage. It solves the problems of essential oil volatility, irritation, and water insolubility. The essential oil emulsion is mixed with sodium alginate film solution to prepare a bioactive essential oil emulsion film. This film is applied evenly to the surface of fruits and vegetables using a dipping method. This edible film effectively prevents microbial infection, reduces water evaporation, thereby inhibiting respiration, slowing nutrient consumption, and inhibiting browning. Furthermore, the coating material is made from various bio-based environmentally friendly materials that can rapidly degrade in the environment, reducing environmental burden and pollution. Attached Figure Description

[0027] Figure 1 The inhibitory effects of different types of essential oils on four common pathogenic fungi;

[0028] Figure 2 Changes in lesion diameter of four common pathogenic fungi after different essential oil treatments

[0029] Figure 3 Micrographs of peppermint essential oil emulsion and its stability after 75 days of storage;

[0030] Figure 4 CLSM image of peppermint essential oil emulsion;

[0031] Figure 5 Release curves of peppermint essential oil at different temperatures;

[0032] Figure 6 Release curves of different peppermint essential oil emulsions at different temperatures;

[0033] Figure 7 AFM image of the emulsion;

[0034] Figure 8 Image of the contact angle of peppermint essential oil emulsion;

[0035] Figure 9 X-ray diffraction pattern of peppermint essential oil emulsion;

[0036] Figure 10 Image of sodium alginate / peppermint oil emulsion film;

[0037] Figure 11 SEM image of sodium alginate / peppermint oil emulsion film;

[0038] Figure 12 AFM image of sodium alginate / peppermint oil emulsion film;

[0039] Figure 13 The growth of Aspergillus carbonisata on PDA medium after 14 days of culture;

[0040] Figure 14 The change in colony diameter of Aspergillus carbonisata after 14 days of cultivation;

[0041] Figure 15 The effect of peppermint essential oil emulsion film on the antibacterial activity of Aspergillus charcoalis on grape fruits infected with Aspergillus charcoalis. Detailed Implementation

[0042] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] Sodium alginate (SA) is a byproduct of extracting iodine and mannitol from brown algae such as kelp or Sargassum. It is a natural polysaccharide widely recognized as a non-toxic, biodegradable, and environmentally friendly packaging material, commonly prepared into films using solution casting and applied in food packaging. Studies have shown that sodium alginate has good biocompatibility, and its composite films, combined with natural active substances, can improve the quality and freshness of food during storage. The numerous beneficial properties of sodium alginate films make them highly promising for applications in food packaging and packaging materials. Using sodium alginate films to package food effectively blocks gas exchange between the packaged food and the air, preventing the loss of moisture and nutrients. Applying a composite preservative solution of sodium alginate to the food surface forms a unique protective layer, which is highly effective in preserving food, maintaining its quality, and significantly extending the shelf life of certain foods. Sodium alginate-based film-forming solutions have extremely strong hydrophilicity, while plant essential oils, due to their inherent physical properties, cannot be evenly distributed within the solution. This means that the network structure of sodium alginate macromolecules cannot encapsulate the plant essential oils to provide them with performance support and chemical protection.

[0044] Soy protein isolate (SPI), as an amphiphilic substance (lipophilic and hydrophilic), is an excellent emulsifier and is commonly used to make emulsions for applications in the food, pharmaceutical, and cosmetic industries. However, in the food industry, the microenvironment of food, whether acidic or alkaline, or containing enzymes or other substances, affects its stability, limiting the application of SPI. Therefore, selecting suitable stabilizers to enhance its emulsifying properties has been a focus of research. Using polysaccharides as stabilizers to enhance the stability of protein emulsions has attracted attention because polysaccharides are widely available, highly hydrophilic, and commonly used as thickeners and stabilizers in the food industry. Appropriate addition of polysaccharides can significantly improve the physicochemical stability and functionality of emulsions. O / W systems prepared using SPI can significantly improve the water solubility of plant essential oils, thereby broadening their applications.

[0045] Peppermint essential oil has excellent antibacterial and toxin-degrading effects. After 14 days of fumigation inhibition and degradation tests, it was found that peppermint essential oil had significantly better inhibitory effects on Aspergillus carbonarius, Aspergillus ocraceus, Aspergillus niger, and Penicillium expansum, as well as a significantly better degradation effect on ochratoxin (OTA) standards than other essential oil products. It can be added as a highly effective bioactive ingredient to prepare fruit and vegetable coating preservation products with antibacterial properties.

[0046] In this invention, the principle of protein emulsion formation is as follows: Soy protein isolate (SPI) emulsifies immiscible oil and water phases into a relatively stable emulsion, forming a thin film at the oil / water interface to reduce surface tension. During this process, the presence of SPI transforms nonpolar hydrophobic oil droplets into charged colloidal particles, increasing surface area and surface energy. Due to the interaction of polarity and surface energy, the charged oil droplets adsorb counterions or polar water molecules from the water, forming a colloidal double layer that prevents collisions between oil droplets, allowing them to remain stable in the water for a longer period.

[0047] This invention relates to a method for preparing an edible preservative film based on emulsion encapsulation, which comprises two main steps.

[0048] 1) Preparation of essential oil emulsions

[0049] 1.1) The protein, polysaccharide stabilizer, and water are mixed to obtain an aqueous solution.

[0050] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 7000 r / min to 23000 r / min for 1 to 5 min to obtain an essential oil emulsion.

[0051] In step 1.1) of this invention, the mass fraction of protein in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 1 to 5:1.

[0052] In step 1.2 of this invention, the essential oil accounts for 40% to 60% of the volume of the essential oil emulsion.

[0053] The protein of this invention is soy protein isolate, whey protein isolate, zein, gelatin or wheat protein isolate.

[0054] The essential oils of this invention are peppermint essential oil, tea tree essential oil, lavender essential oil, thyme essential oil, oregano essential oil, ginger essential oil, or sweet orange essential oil.

[0055] The polysaccharide stabilizer of this invention is chitosan quaternary ammonium salt, gum arabic, konjac glucomannan, chitosan, or sodium carboxymethyl cellulose.

[0056] 2) Preparation of sodium alginate-based essential oil emulsion film

[0057] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 10 min to 60 min to obtain an emulsion-like plastic wrap.

[0058] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 0.1g~25g:0.1g~25g:0.1ml~50mL.

[0059] A further preferred embodiment is that the ratio of essential oil emulsion, plasticizer, and film-forming material is 2.5g~7.5g:2.5g~7.5g:2.5ml~15mL.

[0060] The plasticizers of this invention are glycerol, ethylene glycol, sorbitol, mannitol, urea, monosaccharides, disaccharides, or oligosaccharides.

[0061] The film-forming materials of this invention are pectin, konjac glucomannan, sodium alginate, gum arabic, carrageenan, polylactose, or gelatin.

[0062] The emulsion film prepared by this invention is edible and can effectively prevent microbial infection, reduce water evaporation, thereby inhibiting the respiration of fruits and vegetables, slowing down the consumption of nutrients, and inhibiting the browning of fruits and vegetables. In addition, the materials used for coating preservation are environmentally friendly materials from various biological sources, which can not only degrade quickly in the environment, but also reduce the environmental burden and pollution.

[0063] The application of the emulsion film prepared by this invention in improving the antibacterial rate of Aspergillus niger, Aspergillus ochraceus, and Penicillium extended.

[0064] The following specific examples illustrate the preparation and performance advantages of the edible preservation coating prepared according to the present invention.

[0065] Example 1

[0066] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0067] 1) Preparation of essential oil emulsions

[0068] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0069] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0070] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 1:1. Essential oil comprises 60% of the essential oil emulsion volume.

[0071] Based on a 1L essential oil emulsion, the volume of the essential oil is 600mL, the volume of the aqueous solution is 400mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 6mg, and the amount of polysaccharide stabilizer is 6mg.

[0072] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0073] 2) Preparation of sodium alginate-based essential oil emulsion film

[0074] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0075] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 5g:2.5g:2.5mL.

[0076] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0077] Example 2

[0078] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0079] 1) Preparation of essential oil emulsions

[0080] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0081] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0082] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 2:1. Essential oil comprises 60% of the essential oil emulsion volume.

[0083] Based on a 1L essential oil emulsion, the volume of the essential oil is 600mL, the volume of the aqueous solution is 400mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 6mg, and the amount of polysaccharide stabilizer is 6mg.

[0084] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0085] 2) Preparation of sodium alginate-based essential oil emulsion film

[0086] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0087] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 5g:2.5g:2.5mL.

[0088] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0089] Example 3

[0090] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0091] 1) Preparation of essential oil emulsions

[0092] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0093] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0094] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 5:1. Essential oil comprises 60% of the essential oil emulsion volume.

[0095] Based on a 1L essential oil emulsion, the volume of the essential oil is 600mL, the volume of the aqueous solution is 400mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 6mg, and the amount of polysaccharide stabilizer is 6mg.

[0096] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0097] 2) Preparation of sodium alginate-based essential oil emulsion film

[0098] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0099] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 5g:2.5g:2.5mL.

[0100] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0101] Example 4

[0102] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0103] 1) Preparation of essential oil emulsions

[0104] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0105] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0106] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 1:1. Essential oil comprises 50% of the essential oil emulsion volume.

[0107] Based on a 1L essential oil emulsion, the volume of the essential oil is 500mL, the volume of the aqueous solution is 500mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 7.5mg, and the amount of polysaccharide stabilizer is 7.5mg.

[0108] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0109] 2) Preparation of sodium alginate-based essential oil emulsion film

[0110] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0111] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 5g:2.5g:2.5mL.

[0112] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0113] Example 5

[0114] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0115] 1) Preparation of essential oil emulsions

[0116] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0117] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0118] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 1:1. Essential oil comprises 40% of the essential oil emulsion volume.

[0119] Based on a 1L essential oil emulsion, the volume of the essential oil is 400mL, the volume of the aqueous solution is 600mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 9mg, and the amount of polysaccharide stabilizer is 9mg.

[0120] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0121] 2) Preparation of sodium alginate-based essential oil emulsion film

[0122] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0123] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 5g:2.5g:2.5mL.

[0124] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0125] Example 6

[0126] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0127] 1) Preparation of essential oil emulsions

[0128] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0129] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0130] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 1:1. Essential oil comprises 60% of the essential oil emulsion volume.

[0131] Based on a 1L essential oil emulsion, the volume of the essential oil is 600mL, the volume of the aqueous solution is 400mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 6mg, and the amount of polysaccharide stabilizer is 6mg.

[0132] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0133] 2) Preparation of sodium alginate-based essential oil emulsion film

[0134] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0135] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 2.5g:3g:3mL.

[0136] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0137] Example 7

[0138] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0139] 1) Preparation of essential oil emulsions

[0140] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0141] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0142] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 1:1. Essential oil comprises 60% of the essential oil emulsion volume.

[0143] Based on a 1L essential oil emulsion, the volume of the essential oil is 600mL, the volume of the aqueous solution is 400mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 6mg, and the amount of polysaccharide stabilizer is 6mg.

[0144] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0145] 2) Preparation of sodium alginate-based essential oil emulsion film

[0146] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0147] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 5g:3g:3mL.

[0148] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0149] Example 8

[0150] In this embodiment, the method for preparing an edible preservative film based on emulsion encapsulation includes the following steps:

[0151] 1) Preparation of essential oil emulsions

[0152] 1.1) Prepare an aqueous solution of the protein and polysaccharide stabilizers;

[0153] 1.2) Add essential oil to the aqueous solution in step 1.1) and shear at 12000 r / min for 2 min to obtain essential oil emulsion.

[0154] In this embodiment, the protein mass fraction in the aqueous solution is 1.5%, and the mass ratio of protein to polysaccharide stabilizer is 1:1. Essential oil comprises 60% of the essential oil emulsion volume.

[0155] Based on a 1L essential oil emulsion, the volume of the essential oil is 600mL, the volume of the aqueous solution is 400mL, the mass fraction of the protein is 1.5%, then the amount of protein added is 6mg, and the amount of polysaccharide stabilizer is 6mg.

[0156] In this embodiment, the protein is soy protein isolate, the essential oil is peppermint oil, and the polysaccharide stabilizer is chitosan quaternary ammonium salt.

[0157] 2) Preparation of sodium alginate-based essential oil emulsion film

[0158] Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 30 minutes to obtain an emulsion-like plastic wrap.

[0159] In step 2) of this invention, the ratio of essential oil emulsion, plasticizer and film-forming material is 7.5g:3g:3mL.

[0160] The plasticizer is glycerol, and the film-forming material is sodium alginate.

[0161] Furthermore, the performance of the edible preservation film prepared in the above embodiments was experimentally verified.

[0162] Experiment 1: Determination of the antibacterial effect of essential oils

[0163] Samples: Peppermint essential oil (PMO), Tea tree essential oil (TTO), Lavender essential oil (LO).

[0164] The fumigation inhibition effects of peppermint oil (PMO), tea tree oil (TTO), and lavender oil (LO) on Aspergillus carbonarius, Aspergillus niger, Aspergillus ochraceus, and Penicillium expansum after 14 days, and their colony growth curves, are shown in the figure. Figure 1 and Figure 2 As shown.

[0165] See Figure 1 and Figure 2 Compared with the other two essential oils, peppermint oil (PMO) exhibited strong fumigation activity against the experimental pathogens. At a concentration of 2.5 μL / plate, it completely inhibited the growth of *Aspergillus charcoalii* after 14 days. The inhibition rates against *Aspergillus niger*, *Aspergillus ochraceus*, and *Penicillium expansum* were as high as 95.53%, 97.23%, and 96.76%, respectively.

[0166] Experiment 2: Stability Study of Peppermint Essential Oil Emulsion

[0167] sample:

[0168] Control group: Pure soy protein isolate emulsion prepared according to step 1) of Example 1, denoted as SPI.

[0169] Experimental Group 1: The essential oil emulsion prepared in step 1) of Example 1, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 1:1, is designated as PE-11.

[0170] Experimental Group 2: The essential oil emulsion prepared in step 1) of Example 2, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 2:1, is designated as PE-21.

[0171] Experimental Group 3: The essential oil emulsion prepared in step 1) of Example 3 has a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 5:1, and is designated as PE-51.

[0172] The specific experimental process is as follows:

[0173] The above four samples were photographed, observed under a microscope, and their particle size was measured. The results are as follows: Figure 3 As shown, Figure A is pure SPI, Figure B is PE-11, Figure C is PE-21, and Figure D is PE-51.

[0174] See Figure 3 The emulsion prepared from pure soy protein isolate (SPI) quickly showed stratification (Figure A), and essential oils were clearly exuded from the emulsion. In contrast, the three groups with added HACC showed relatively stable results, and the particle size distribution curve of the essential oil emulsion shifted towards smaller particle sizes as the HACC content increased. This is because when soy protein isolate (SPI) is dispersed in water, it forms insoluble aggregates or precipitates. These macroscopic aggregates combine with oil under intense mechanical shear forces to form small emulsions. The emulsifying ability of soy protein isolate (SPI) largely depends on spontaneous interactions, such as hydrogen bonds and covalent bonds, electrostatic interactions, and hydrophobic interactions. Meanwhile, the essential oil emulsion formed in experimental group 1 (PE-11) maintained good stability even after 75 days of storage.

[0175] from Figure 3 It is known that the emulsion droplets formed by pure soy protein isolate (SPI) are relatively large (average particle size 1356 nm), non-uniform in size, and have a thin interfacial layer. It does not exhibit resistance to flocculation and aggregation, thus the emulsion system is highly unstable. The main peaks of droplet size distribution, from smallest to largest, are SPI-60%, PE-51-60%, PE-21-60%, and PE-11-60%. The increase in droplet size is due to the inability of the droplets to be completely covered by the stabilizer. Proteins fold their hydrophobic groups to achieve system equilibrium and stability. The addition of polysaccharides enhances the steric hindrance effect of the system.

[0176] Furthermore, the CLSM image of the essential oil emulsion prepared by the SPI-HACC proteoglycan system was measured, and the results are as follows: Figure 4 As shown.

[0177] Figure 4In the diagram, A1 to D1 represent the SPI group, A2 to D2 represent the PE-11 group, A3 to D3 represent the PE-21 group, and A4 to D4 represent the PE-51 group. Subscript 1 indicates the corresponding essential oil emulsion CLSM image, subscript 2 indicates the corresponding essential oil emulsion stained with Nile Red (red area) CLSM image, subscript 3 indicates the corresponding essential oil emulsion stained with Nile Blue (green area) CLSM image, and subscript 4 indicates the superposition of the CLSM image stained with Nile Red (red area) and the CLSM image stained with Nile Blue (green area).

[0178] See Figure 4 The essential oil emulsion prepared from pure soy protein isolate (SPI) exhibited widespread clumping and insoluble aggregation, with significant essential oil spillage (first row A1–D1). In the group with added low concentrations of HACC (fourth row A4–D4), the droplet average size was larger and the particle size distribution was severely uneven, accompanied by localized aggregation, which greatly reduced the stability of the emulsion. When the mass ratio of SPI to HACC was 2:1, a small amount of essential oil spillage occurred (third row A3–D3). When the mass ratio of SPI to HACC was 1:1, the droplets were densely distributed, and red and green fluorescence were clearly visible inside and at the edges of the emulsion, respectively, with no essential oil spillage (second row A2–D2). This indicates that the optimal mass ratio of SPI to HACC is 1:1.

[0179] Experiment 3: Determination of the sustained-release performance of peppermint essential oil emulsion

[0180] Weight loss rate curves of peppermint oil (PMO) at 4℃ and 25℃.

[0181] Control group: pure peppermint essential oil, denoted as PMO.

[0182] Experimental Group 1: The essential oil emulsion prepared in step 1) of Example 1, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 1:1, is designated as PE-11.

[0183] Experimental Group 2: The essential oil emulsion prepared in step 1) of Example 2, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 2:1, is designated as PE-21.

[0184] Experimental Group 3: The essential oil emulsion prepared in step 1) of Example 3 has a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 5:1, and is designated as PE-51.

[0185] The experimental procedure is as follows:

[0186] On day 0, 30g of PMO (actual essential oil content of 30g) and 30g of PE-11, 30g of PE-21, and 30g of PE-51 (actual essential oil content of 18g) were weighed from the above samples respectively.

[0187] Then, 30g of PMO was placed at 4℃ and 25℃ for 30 days respectively, and the weight of PMO was measured daily. The results are as follows. Figure 5 As shown.

[0188] The weight loss rate of the three essential oil emulsions (PE-11, PE-21, and PE-51) was measured over time at 4℃ and 25℃. The results are as follows: Figure 6 As shown.

[0189] from Figure 5 As can be seen, at 4℃ and 25℃, the unencapsulated PMO exhibited significant weight loss with increasing storage time; at this point, the essential oil release curve progressed relatively quickly. At 25℃, the PMO had completely evaporated by day 8. Even at a low temperature of 4℃, PMO was undetectable after 10 days.

[0190] See Figure 6 The essential oil release rate in the encapsulated essential oil emulsions (PE-11, PE-21, and PE-51) was relatively slow. At day 30, the retention rates at 4°C were 82.70% (PE-11), 82.17% (PE-21), and 80.03% (PE-51), respectively, while at 25°C, the retention rates were 79.20% (PE-11), 78.73% (PE-21), and 75.90% (PE-51), respectively. Therefore, the comparison of retention rates at different temperatures shows that PE-11 had the best controlled-release effect. This also indicates that the protein-polysaccharide emulsion system prepared using soy protein isolate and chitosan quaternary ammonium salt has a certain controlling effect on the release of essential oils.

[0191] Experiment 4: Surface structure of peppermint essential oil emulsion

[0192] AFM obtains surface morphology information of a sample by using the weak interaction force (atomic force) between the probe and the sample. A three-dimensional AFM image is obtained based on the height of the aqueous solution sample relative to a reference plane.

[0193] sample:

[0194] Experimental Group 1: The aqueous solution obtained in step 1.1) of Example 1, denoted as w-11.

[0195] Experimental Group 2: The aqueous solution obtained in step 1.1) of Example 2 is denoted as w-21.

[0196] Experimental Group 3: The aqueous solution obtained in step 1.1) of Example 3 is denoted as w-51.

[0197] Experimental Group 4: The essential oil emulsion prepared in step 1) of Example 1, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 1:1, is designated as PE-11.

[0198] Experimental Group 5: The essential oil emulsion prepared in step 1) of Example 2, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 2:1, is designated as PE-21.

[0199] Experimental Group 6: The essential oil emulsion prepared in step 1) of Example 3, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 5:1, is designated as PE-51.

[0200] Experimental method: The above samples were taken, and the surface morphology of the six groups of samples was obtained using existing testing methods. The results are as follows. Figure 7 As shown, A represents experimental group 1, B represents experimental group 2, C represents experimental group 3, D represents experimental group 4, E represents experimental group 5, and F represents experimental group 6. The roughness parameters of the six groups of samples were obtained simultaneously, including the root mean square roughness (Rm). q ) and average roughness (R a The results are shown in Table 1.

[0201] See Figure 7 The surface of pure chitosan quaternary ammonium salt exhibits slight irregularities. After adding soy protein isolate, the surface morphology of the complex changes significantly. When the ratio of soy protein isolate to chitosan quaternary ammonium salt is 1:1 (w-11), the surface of the complex is the smoothest and has the least roughness. As the proportion of chitosan quaternary ammonium salt decreases, the complex becomes increasingly rough. This microscopic phenomenon is consistent with the macroscopic behavior of the aqueous system.

[0202] See Table 1, roughness parameters (R) a and R q This can quantitatively reflect changes in the surface morphology of the composite membrane. As the proportion of chitosan quaternary ammonium salt increases, R... q The value increased from 20.65 to 47.60, R a The value increased from 16.10 to 39.03. The change in roughness parameters is because, while the soy protein isolate content remained constant, the overall content of the system increased with the increase of chitosan quaternary ammonium salt, ultimately leading to an increase in the system's roughness-related parameters. The opposite trend between the change in roughness parameters and the change in the surface smoothness of the aqueous system may be related to the chemical interaction between soy protein isolate and chitosan quaternary ammonium salt.

[0203] However, after being prepared into an essential oil emulsion, as the HACC concentration increases, R... q The value decreased from 22.5 to 11.24, R a The value decreased from 16.00 to 5.50. The roughness parameter of the emulsion showed an opposite trend to that of the aqueous system, which is related to the electrostatic interaction between SPI and HACC, hydrogen bonding, volume exclusion effect, and molecular chain entanglement.

[0204] Table 1. Roughness parameters of the emulsion

[0205]

[0206] Experiment 5: Contact Angle Measurement of Peppermint Essential Oil Emulsion

[0207] The interfacial wettability of particles is an important indicator for evaluating the emulsification of solid particles. The wettability of particles can be determined by measuring the contact angle (θ) of solid particles to evaluate their emulsification ability.

[0208] sample:

[0209] Experimental Group 1: The aqueous solution obtained in step 1.1) of Example 1, denoted as w-11.

[0210] Experimental Group 2: The aqueous solution obtained in step 1.1) of Example 2 is denoted as w-21.

[0211] Experimental Group 3: The aqueous solution obtained in step 1.1) of Example 3 is denoted as w-51.

[0212] Experimental Group 4: The essential oil emulsion prepared in step 1) of Example 1, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 1:1, is designated as PE-11.

[0213] Experimental Group 5: The essential oil emulsion prepared in step 1) of Example 2, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 2:1, is designated as PE-21.

[0214] Experimental Group 6: The essential oil emulsion prepared in step 1) of Example 3, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 5:1, is designated as PE-51.

[0215] The experimental procedure was as follows: For the above six groups of samples, their contact angles were measured, and the results were as follows: Figure 8 As shown, 8A, 8B, and 8C are the contact angles of w-11, w-21, and w-51, respectively; Figure 8 D, 8E, and 8F represent the interfacial wettability of emulsions prepared using PE-11, PE-21, and PE-51, respectively.

[0216] See Figure 8 The contact angles of w-11, w-21 and w-51 were 83.85, 84.3 and 79.1, respectively. The contact angle of the aqueous solution was significantly higher than that of pure soy protein isolate (SPI) (60.5). However, there was no significant difference in the contact angle values ​​of different aqueous systems. It can be seen that the interaction between HACC and SPI improved the hydrophobicity of the aqueous composite system.

[0217] Emulsions (PE-11, PE-21, and PE-51) were prepared using different aqueous phase systems, and their interfacial wettability was measured. The contact angles of PE-11, PE-21, and PE-51 were 102.45°, 109.75°, and 112.4°, respectively. Since the hydrophobicity of emulsions can be classified as "hydrophobic" or "hydrophilic" based on contact angles θ>90° and θ<90°, and all emulsions had contact angles higher than 90°, this indicates that all emulsions are hydrophobic. Simultaneously, the contact angle of the emulsions decreased with increasing HACC content, with PE-11 exhibiting the lowest interfacial wettability. This may be due to stronger intermolecular hydrogen bonds between soy protein isolate (SPI) and HACC at this ratio, making the system more hydrophilic.

[0218] Experiment 6: X-ray diffraction of peppermint essential oil emulsion

[0219] XRD analysis can reveal the structure of the phase and the state of the elements. If sharp diffraction peaks appear in the spectrum, it is crystallization diffraction, which is closely related to the crystal structure and amorphous regions of the sample.

[0220] X-rays possess wave characteristics, being electromagnetic waves with wavelengths ranging from tens to hundreds of picometers, and exhibit diffraction capabilities. When a beam of monochromatic X-rays is incident on a crystal, because crystals are composed of unit cells with atoms arranged in a regular pattern, the interatomic distances are on the same order of magnitude as the wavelength of the incident X-rays. Therefore, the X-rays scattered by different atoms interfere with each other, producing strong X-ray diffraction in certain specific directions. The spatial distribution and intensity of the diffracted rays are closely related to the crystal structure, and the diffraction pattern produced by each crystal reflects the atomic distribution pattern within that crystal. This is the basic principle of X-ray diffraction. XRD, also known as X-ray diffraction instrument, can be used to measure the crystallinity of materials, and since crystallinity directly affects the properties of materials, the measurement of this index is particularly important.

[0221] sample:

[0222] Comparative Group 1: An aqueous solution of pure chitosan quaternary ammonium salt and water, with a mass fraction of 1.5%. This is denoted as HACC.

[0223] Control group 2: Aqueous solution of pure soy protein isolate and water, with a mass fraction of 1.5%, denoted as SPI.

[0224] Experimental Group 1: The aqueous solution obtained in step 1.1) of Example 1, with a mass ratio of soy protein isolate to chitosan quaternary ammonium salt of 1:1, is denoted as w-11.

[0225] Experimental Group 2: The aqueous solution obtained in step 1.1) of Example 2, with a mass ratio of soy protein isolate to chitosan quaternary ammonium salt of 2:1, is denoted as w-21.

[0226] Experimental Group 3: The aqueous solution obtained in step 1.1) of Example 3 has a mass ratio of soy protein isolate to chitosan quaternary ammonium salt of 5:1, denoted as w-51.

[0227] Experimental Group 4: The essential oil emulsion prepared in step 1) of Example 1, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 1:1, is designated as PE-11.

[0228] Experimental Group 5: The essential oil emulsion prepared in step 1) of Example 2, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 2:1, is designated as PE-21.

[0229] Experimental Group 6: The essential oil emulsion prepared in step 1) of Example 3, with a mass ratio of soy protein isolate (SPI) and chitosan quaternary ammonium salt (HACC) of 5:1, is designated as PE-51.

[0230] Experimental procedure: X-rays were used to test the spectra of the above 8 groups of samples, and the results are as follows. Figure 9 As shown.

[0231] from Figure 9 As can be seen, pure soy protein isolate (SPI) exhibits an amorphous hump. The diffraction peak of pure HACC is located around 2θ = 20.62°, and the crystallinity of pure HACC is 20.62% according to the peak-splitting method based on X-ray diffraction curve fitting.

[0232] When soy protein isolate of the same concentration is combined with chitosan quaternary ammonium salts (w-11, w-21, w-51) of different concentrations, the diffraction peaks shift to around 2θ = 21.2° and tend towards amorphous. This is because there is a strong interaction between HACC and SPI in the composite, which disrupts the original crystal structure of HACC, causing some diffraction peaks to disappear. This further proves that the two substances in the composite membrane have good compatibility. When w-11, w-21, and w-51 are used to encapsulate essential oils, their relative crystallinity is found to be 17.10%, 17.02%, and 16.42%, respectively. The crystallinity of the emulsion is closely related to its mechanical properties; the higher the crystallinity, the better the strength. As the HACC content increases, the crystallinity of the emulsion generally decreases, and the strength continuously weakens.

[0233] Experiment 7: Emulsion Film Characterization

[0234] sample:

[0235] Control group: 3g of glycerol and 3mL of sodium alginate were mixed and then PDA medium was added to make up the volume to 100mL.

[0236] Experimental Group 1: 2.5g of essential oil emulsion, 3g of glycerol, and 3mL of sodium alginate were mixed, and then PDA culture medium was added to make up the volume to 100mL.

[0237] Experimental group 2: 5g of essential oil emulsion, 3g of glycerol and 3mL of sodium alginate were mixed and then PDA culture medium was added to make up the volume to 100mL.

[0238] Experimental group 3: 7.5g of essential oil emulsion, 3g of glycerol and 3mL of sodium alginate were mixed and then PDA culture medium was added to make up the volume to 100mL.

[0239] See Figure 10 The above-mentioned emulsion films were coated onto a transparent plate for observation. As the concentration of the essential oil emulsion increased, the emulsion film became rougher. Note: Figure 10 The label is a laboratory mark and is unrelated to the morphology of the emulsion film.

[0240] The microstructure of sodium alginate-based emulsion films with different emulsion contents was observed using SEM (scanning electron microscopy). The results are as follows: Figure 11 As shown, A is the control group, B is experimental group 1, C is experimental group 2, and D is experimental group 3.

[0241] The microstructure of sodium alginate-based emulsion films with different emulsion contents was observed using AFM (atomic force microscopy). The results are as follows: Figure 12 As shown, where: A is the control group, B is experimental group 1, C is experimental group 2, and D is experimental group 3.

[0242] See Figure 11 The membrane surface formed by pure sodium alginate is relatively smooth and flat. Figure 11 A) The addition of emulsion caused a distinct spherical structure to appear on the surface of the emulsion film, and this structure increased with increasing emulsion content (7.5g corresponds to...). Figure 11 D) The emulsion aggregates in sodium alginate to form irregular, spherical clusters.

[0243] See Figure 12 The AFM images were consistent with those of SEM. The heights of the pure sodium alginate membrane and the emulsion membrane of 2.5g essential oil emulsion were 17nm and 17nm, respectively. Figure 12 A) and 8.4nm ( Figure 12 B), and the surface material is evenly distributed;

[0244] The film thickness of the 5.0g and 7.5g essential oil emulsions increased by 84.4nm respectively. Figure 12 C) and 103.6nm ( Figure 12 D) At the same time, as the concentration of the essential oil emulsion increases, the irregularity of the emulsion film increases, indicating that the emulsion film has a better effect when the amount of essential oil emulsion added is low.

[0245] In addition, the tensile strength (TS), elongation at break (EB), and water vapor transmission rate (WVP) of the emulsion film obtained in experimental group 1 were measured according to existing detection methods, and the results are shown in Table 2.

[0246] Table 2 Tensile strength, elongation at break, and water vapor transmission rate of sodium alginate / peppermint oil emulsion film

[0247] TS (MPa) EB (%) <![CDATA[WVP(×10 -10 g·m -1 ·s -1 ·Pa -1 )]]> SA-PE-11 <![CDATA[80.48±0.010 a ]]> <![CDATA[45.37±2.193 a ]]> <![CDATA[2.582±0.016 a ]]>

[0248] Experiment 8: Effect of emulsion film on the growth of Aspergillus carbonisata mycelia (in vitro)

[0249] Sample: 2.5g of essential oil emulsion, 3g of glycerol, and 3mL of sodium alginate were mixed to obtain an emulsion film.

[0250] The experimental procedure was as follows: 0, 1, 2, 4, 6.25, and 8 mL of emulsion film were taken, and then the volume was increased to 100 mL with PDA medium to obtain mediums with different peppermint oil contents (0, 0.25 μL / mL, 0.5 μL / mL, 1.0 μL / mL, 1.5 μL / mL, and 2.0 μL / mL). The inhibitory effects on the mycelial growth of *Aspergillus charcoalis* were then analyzed, and the results are shown in the figure below. Figure 13 and Figure 14 As shown.

[0251] See Figure 13 The colony diameter of *Aspergillus charcoalis* decreased with increasing peppermint oil emulsion content in the film-forming solution. After one day of incubation in a fungal incubator, no *Aspergillus charcoalis* hyphae growth was observed in the film-forming solution containing 2 μL / mL peppermint oil emulsion. Furthermore, the film-forming solution containing 2 μL / mL peppermint oil emulsion showed the best inhibitory effect on *Aspergillus charcoalis* hyphae growth on day 14 of incubation.

[0252] Depend on Figure 14 It can be seen that on day 14, the membrane solution containing 2 μL / mL peppermint oil emulsion achieved a 100% inhibition rate on the growth of Aspergillus charcoalis mycelia, which is higher than that of low concentration peppermint oil emulsion.

[0253] Experiment 9: In vivo antibacterial effect of emulsion film on Aspergillus carbonisata

[0254] The antibacterial effect of emulsion film on Kyoho grape berries infected with Aspergillus carbonisata was investigated, and the experimental procedure is as follows.

[0255] The Kyoho grapes were randomly divided into six equal groups of six, and each group was treated according to the following methods.

[0256] Group 1 (Group A): Blank group, untreated grapes (positive control, naturally diseased).

[0257] Group 2 (Group B): Inoculated with 5 μL of Aspergillus charcoalis, without coating treatment.

[0258] Group 3 (Group C): After treatment with 5 μL of Aspergillus charcoalis, a pure sodium alginate film was coated (the pure sodium alginate film does not contain essential oil emulsion, but is made by mixing 3g of glycerol and 3mL of sodium alginate to form an emulsion film, and the volume was made up to 100mL with PDA medium).

[0259] Group 4 (Group D): After treatment with 5 μL of Aspergillus charcoalis, an emulsion film containing 2.0 μL / mL essential oil was applied (first, 2.5 g of essential oil emulsion, 3 g of glycerol and 3 mL of sodium alginate were mixed to obtain an emulsion film; then 8 mL of the emulsion film was taken and the volume was made up to 100 mL with PDA medium).

[0260] Group 5 (Group E): After treatment with 5 μL of Aspergillus charcoalis, an emulsion film containing 4.0 μL / mL essential oil was applied (first, 2.5 g of essential oil emulsion, 3 g of glycerol and 3 mL of sodium alginate were mixed to obtain an emulsion film; then 16 mL of the emulsion film was taken and the volume was made up to 100 mL with PDA medium).

[0261] Group 6 (Group F): After treatment with 5 μL of Aspergillus charcoalis, an emulsion film containing 6.0 μL / mL essential oil was applied (first, 2.5 g of essential oil emulsion, 3 g of glycerol and 3 mL of sodium alginate were mixed to obtain an emulsion film; then 24 mL of the emulsion film was taken and the volume was made up to 100 mL with PDA medium).

[0262] Then, the changes in the fruit were observed on day 0, day 3, and day 5. The results are as follows. Figure 15 As shown.

[0263] See Figure 15Group A showed no growth of *Aspergillus charcoalis* and no disease. Group C grapes wrapped with a film without peppermint oil emulsion showed similar disease incidence to Group B grapes without the composite film. In Groups D and F, the severity of disease gradually decreased with increasing peppermint oil emulsion concentration. On day 3, Group D grapes had begun to rot and developed lesions, while Group E only showed *Aspergillus charcoalis* mycelium growth at the inoculation holes without lesions. Group F showed no mycelial growth. On day 5, Groups B and E all showed varying degrees of rot, Groups BD grapes were completely rotten and showed lesions, Group E only showed lesions on half of the grapes, and Group F still showed no lesions or mycelial growth, achieving a good antibacterial effect. Research indicates that the diffusion of antibacterial substances in food is affected by steric hindrance within the food, often requiring higher concentrations of antibacterial agents to achieve the same effect as in vitro antibacterial experiments. Therefore, the peppermint oil emulsion concentration in Group F was approximately 1.5 times that in Group E to investigate the antibacterial ability of the composite film on grapes. Meanwhile, no disease spots were observed in the Kyoho grapes treated with the liquid film during the five-day storage period. The weight loss rate of the grapes wrapped in the composite film was significantly lower than that of the control group, and the firmness was well maintained. The Kyoho grapes treated with the high-concentration peppermint oil emulsion showed the smallest decrease in firmness and the lowest weight loss rate. In addition, the pH, soluble solids, titratable acid, and reducing sugar of the wrapped Kyoho grapes changed less significantly compared with the control group, and the fruit quality remained stable. The composite film has a good preservation effect on grapes. In conclusion, the sodium alginate / citrus pectin / peppermint oil emulsion film can effectively reduce the economic losses caused by fruit diseases and has become a new material for preserving fruits and vegetables.

Claims

1. A method for preparing an edible preservative film based on emulsion encapsulation, characterized by comprising the following steps: 1) Preparation of essential oil emulsions 1.1) A protein, a polysaccharide stabilizer, and water are mixed to obtain an aqueous solution, wherein the mass ratio of the protein to the polysaccharide stabilizer is 1~5:1; and the mass fraction of the protein in the aqueous solution is 1.5%. 1.2) Add essential oil to the aqueous solution of step 1.1), and shear to obtain an essential oil emulsion; the essential oil accounts for 40% to 60% of the volume of the essential oil emulsion; 2) Preparation of sodium alginate-based essential oil emulsion film Take the essential oil emulsion from step 1), add plasticizer and film-forming material, mix and stir for 10 min to 60 min to obtain an emulsion-like plastic wrap; The protein is soy protein isolate, whey protein isolate, zein, gelatin, or wheat protein isolate; The polysaccharide stabilizer is chitosan quaternary ammonium salt, gum arabic, konjac glucomannan, chitosan, or sodium carboxymethyl cellulose; The film-forming material is sodium alginate.

2. The method for preparing an edible preservative film based on emulsion encapsulation according to claim 1, characterized in that, In step 1.2), the shearing speed is 7000 r / min to 23000 r / min, and the shearing time is 1 min to 5 min.

3. The method for preparing an edible preservative film based on emulsion encapsulation according to claim 2, characterized in that, The essential oils mentioned are peppermint oil, tea tree oil, lavender oil, thyme oil, oregano oil, ginger oil, or sweet orange oil.

4. The method for preparing an edible preservative film based on emulsion encapsulation according to any one of claims 1-3, characterized in that, In step 2), the ratio of essential oil emulsion, plasticizer and film-forming material is 0.1g~25g:0.1g~25g:0.1ml~50mL.

5. The method for preparing an edible preservative film based on emulsion encapsulation according to claim 4, characterized in that, The plasticizer is glycerol, sorbitol, mannitol, monosaccharide, disaccharide, or oligosaccharide.

6. A cling film prepared by the method for preparing an edible cling film based on emulsion encapsulation as described in claim 1.

7. The application of the plastic wrap as described in claim 6 in improving the antibacterial rate of Aspergillus niger, Aspergillus ochraceus and Penicillium esculentum.

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