A functional oil body composite coating, its preparation method and application in food preservation

Abstract

This invention provides a functional oil-based composite coating, its preparation method, and its application in food preservation, belonging to the field of food preservation technology. The invention uses a deep eutectic solvent as a plasticizer and interface modifier, mixed with carboxymethyl chitosan and carrageenan, and then adds a functional oil-based emulsion to obtain a composite coating liquid, which is then dried to obtain the composite coating. Utilizing the natural "shell-core" amphiphilic structure of plant oils, hydrophobic antibacterial active substances are loaded onto the hydrophobic core of the oil body through self-assembly technology, while hydrophilic polyphenolic substances (antioxidant activity) are stabilized and coupled to the interface layer to construct a functional oil-based emulsion. This invention utilizes the characteristics of functional oils to obtain an edible composite coating with both antioxidant and antibacterial activities, which can extend the shelf life of fruits and vegetables such as bananas and cherry tomatoes, maintaining their quality and components without loss.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, and in particular to a functional oil-based composite coating, its preparation method, and its application in food preservation. Background Technology

[0002] Fruits and vegetables continue to exhibit active life processes after harvesting, making them susceptible to microbial contamination, moisture loss, and oxidative spoilage, leading to severe spoilage losses. Current preservation research primarily focuses on three dimensions: physical, chemical, and biological induction. However, these approaches face challenges such as high equipment costs, the risk of chemical residues, and difficulty in meeting diverse preservation needs.

[0003] As people become increasingly health-conscious, their demands and standards for the safety of daily necessities and food are also rising. Compared to traditional materials, the development of biodegradable, green, and safe natural polymer-based materials has become a research hotspot and important development direction in the fields of materials science, food science, traditional Chinese medicine, and biomedicine. Edible coatings, as a green and environmentally friendly preservation solution, are gradually becoming a focus of industry research. Compared to traditional preservation technologies, edible coatings form a semi-permeable barrier on the surface of fruits and vegetables, effectively regulating gas exchange, reducing oxygen absorption, and increasing internal carbon dioxide concentration, thereby inhibiting the respiration rate of fruits and vegetables and slowing down the aging process. Biomaterials constructed from natural plant components are biodegradable and renewable, better meeting the needs of green and environmentally friendly development, while also acting as a barrier against the entry of external substances, thus attracting widespread attention in the food packaging field.

[0004] Carboxymethyl chitosan (CMCS) is a polysaccharide obtained by carboxylation of chitosan. It exhibits better water solubility, biocompatibility, and bioactivity, as well as broad-spectrum antibacterial properties. CMCS shares similar chemical properties with chitosan, but the introduction of carboxymethyl groups disrupts the secondary structure of the chitosan molecule, significantly reducing its crystallinity to almost amorphous. However, due to its superior water solubility and antibacterial activity compared to chitosan, it largely compensates for the shortcomings of chitosan, expanding its bioavailability and making it an ideal candidate material in many fields. Carrageenan (CAR) molecules contain sulfate ester bonds, resulting in a negatively charged solution. CMCS solutions, after protonation, become positively charged. In existing technologies, CAR-CMCS polysaccharide-based coatings are obtained by mixing carrageenan solutions and protonated CMCS solutions in different proportions to form polyionic complexes, followed by solvent evaporation. However, these coatings are brittle, have poor toughness, and exhibit limited and short-lived functional activity. Summary of the Invention

[0005] The purpose of this invention is to provide a functional oil-based composite coating, its preparation method, and its application in food preservation, thereby solving the problems of limited and unsustainable functional activity and poor toughness of existing polysaccharide-based coatings.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a functional oil-based composite coating, comprising the following steps: Carboxymethyl chitosan, carrageenan, and water were mixed and dispersed to obtain a polysaccharide-based coating solution. The polysaccharide-based coating liquid is mixed with a deep eutectic solvent to form a composite coating liquid. The composite coating liquid is mixed with functional oil and water, poured into a petri dish, and dried to form a functional oil composite coating. The method for preparing the functional oil includes the following steps: The plant oil, hydrophilic polyphenol compound, and water were mixed, and the pH was adjusted to 9.0 to carry out the first loading, thus obtaining the oil with loaded hydrophilic groups. The oil body loaded with hydrophilic groups is mixed with a hydrophobic antibacterial compound and water for a second loading to obtain a functional oil body.

[0007] Preferably, the mass ratio of carboxymethyl chitosan to carrageenan is 0.5~2:0.1~1; and the dispersion temperature is 50~70℃.

[0008] Preferably, the deep eutectic solvent is a mixture of choline chloride and glycerol, wherein the molar ratio of choline chloride to glycerol is 1:2 to 2:1; The mass of the deep eutectic solvent is 7.5-15% of the mass of the polysaccharide-based coating liquid; The composite process is carried out at a temperature of 50-80℃ for 1-3 hours.

[0009] Preferably, the plant oil includes soybean oil, linseed oil, perilla oil, safflower oil, or peanut oil; the hydrophilic polyphenolic compound includes ferulic acid, gallic acid, chlorogenic acid, catechin, epicatechin, rosmarinic acid, salvianolic acid A, salvianolic acid B, sesaminol, proanthocyanidin B1, or proanthocyanidin B2; the hydrophobic antibacterial compound includes allicin, carvacrol, cinnamaldehyde, eugenol, quercetin, luteolin, apigenin, linalool, eucalyptol, matrine, berberine, or medium-chain fatty acids.

[0010] Preferably, the mass ratio of the plant oil to the hydrophilic polyphenol compound is 1:0.02~0.1; and the mass ratio of the oil loaded with hydrophilic groups to the hydrophobic antibacterial compound is 1:0.005~0.2.

[0011] Preferably, the conditions for the first load include: a temperature of 4~10 ℃, a time of 8~16 h, and a static reaction. The conditions for the second loading include: the concentration of the hydrophobic antibacterial compound is 2-15 mmol / L; the ultrasonic power is 100-300W; and the time is 2-10 min.

[0012] Preferably, the volume ratio of the composite coating liquid to the mass of the functional oil is 20mL:1mg to 1mL:50mg; and the mixing temperature of the composite coating liquid with the functional oil and water is 38 to 42°C.

[0013] Preferably, the drying temperature is room temperature and the time is 1 to 3 hours.

[0014] The present invention provides a functional oil-based composite coating prepared by the preparation method described in the above technical solution.

[0015] This invention provides the application of the functional oil-based composite coating described above in food preservation.

[0016] This invention provides a method for preparing a functional oil-based composite coating. A deep eutectic solvent is used as a plasticizer and interface modifier, blended and modified with carboxymethyl chitosan and carrageenan. A functional oil emulsion is then added to obtain a composite coating liquid, which is subsequently dried to obtain an edible, preservative-resistant, and antibacterial coating. Utilizing the natural "shell-core" amphiphilic structure of plant oils, hydrophobic antibacterial active substances are loaded onto the hydrophobic core of the oil through self-assembly technology, while hydrophilic polyphenols (antioxidant activity) are stabilized and coupled to the interface layer to construct a functional oil emulsion. This invention leverages the amphiphilic characteristics of functional oils to achieve a coating where the hydrophilic end adheres to fruits and vegetables, while the hydrophobic end blocks external elements, resulting in an edible composite coating with both antioxidant and antibacterial activities. This can extend the shelf life of fruits and vegetables such as bananas and cherry tomatoes, maintaining their quality and preventing the loss of their components.

[0017] The present invention has the following beneficial effects: (1) By introducing the natural "shell-core" amphiphilic structure of soybean oil, the water vapor permeability of the composite coating is significantly reduced, overcoming the defect of high brittleness of traditional polysaccharide-based coatings. When combined with carboxymethyl chitosan and carrageenan, and combined with deep eutectic solvent as plasticizer and interface modifier, the flexibility and film density of the coating are improved.

[0018] (2) By utilizing the amphiphilic characteristics of functional oils, hydrophobic antibacterial compounds are loaded onto the hydrophobic core of the oil, and hydrophilic polyphenols are stabilized and coupled to the interface layer of the oil, thus constructing a "functional oil" with multifunctional synergistic antioxidant and antibacterial activity, which solves the problem of limited and unsustainable functional activity of existing coatings.

[0019] (3) It expands the new application of deep eutectic solvents in food preservation coatings, acting as plasticizers and interface modifiers, and has good compatibility with polysaccharide matrices.

[0020] (4) All raw materials are of natural origin or food-grade ingredients: soybean oil, carboxymethyl chitosan, carrageenan, choline chloride, glycerin, ferulic acid, and allicin. Synthetic emulsifiers or chemical cross-linking agents are avoided, eliminating the risk of chemical residues and meeting the development needs of green, environmentally friendly, and edible packaging. Attached Figure Description

[0021] Figure 1 The images show the appearance of the functional oil-based composite coating in Example 1 and the coatings in Comparative Examples 1 and 2. Figure 2 The tensile strength and mechanical load-bearing capacity of the functional oil-based composite coating in Example 1; Figure 3 The antioxidant properties of the functional oil-based composite coating in Example 1, the polysaccharide-DES coating in Comparative Example 1, and the polysaccharide-based coating in Comparative Example 2 are compared, where A is the ABTS scavenging rate and B is the DPPH scavenging rate. Figure 4 The antibacterial properties of the functional oil-based composite coating in Example 1, the polysaccharide-DES coating in Comparative Example 1, and the polysaccharide-based coating in Comparative Example 2 against Escherichia coli were compared. Figure 5 The antibacterial properties of the functional oil-based composite coating in Example 1, the polysaccharide-DES coating in Comparative Example 1, and the polysaccharide-based coating in Comparative Example 2 against Staphylococcus aureus were compared. Figure 6 The images show the appearance of bananas preserved using the functional oil-based composite coating in Example 1 and the coatings in Comparative Examples 1 and 2. Figure 7 The images show the appearance of the functional oil-based composite coating in Example 1 and the coatings in Comparative Examples 1 and 2, respectively, during the preservation of cherry tomatoes. Figure 8 The figures show the thermal properties of the coatings in Example 1 and Comparative Examples 1-2, where A is the TG curve, B is the DTG curve, and C is the DSC curve. Detailed Implementation

[0022] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0023] This invention provides a method for preparing a functional oil-based composite coating, comprising the following steps: Carboxymethyl chitosan, carrageenan, and water were mixed and dispersed to obtain a polysaccharide-based coating solution. The polysaccharide-based coating liquid is mixed with a deep eutectic solvent to form a composite coating liquid. The composite coating liquid is mixed with functional oil and water, poured into a petri dish, and dried to form a functional oil composite coating. The method for preparing the functional oil includes the following steps: The plant oil, hydrophilic polyphenol compound, and water were mixed, and the pH was adjusted to 9.0 to carry out the first loading, thus obtaining the oil with loaded hydrophilic groups. The oil body loaded with hydrophilic groups is mixed with a hydrophobic antibacterial compound and water for a second loading to obtain a functional oil body.

[0024] This invention involves mixing carboxymethyl chitosan (CMCS), carrageenan (CAR), and water to disperse them, thereby obtaining a polysaccharide-based coating liquid.

[0025] In this invention, the mass ratio of carboxymethyl chitosan to carrageenan is preferably 0.5~2:0.1~1, more preferably 0.5~1:0.4~0.8.

[0026] In this invention, carboxymethyl chitosan (CMCS) and carrageenan (CAR) are preferably dissolved in ultrapure water. The mixture is then continuously stirred at a constant rate under constant temperature water bath conditions to disperse and dissolve the mixture until the initial turbid and heterogeneous state gradually transforms into a clear, homogeneous colloidal solution, thus obtaining a polysaccharide-based coating liquid. This invention does not have a specific limitation on the amount of water used; as long as the materials are mixed evenly, it is acceptable.

[0027] In this invention, the dispersion temperature is preferably 50~70 ℃, more preferably 60~65 ℃, and the temperature is maintained by a constant temperature water bath.

[0028] After obtaining the polysaccharide-based coating liquid, the present invention mixes the polysaccharide-based coating liquid with a deep eutectic solvent to form a composite coating liquid.

[0029] In this invention, the deep eutectic solvent (DES) is preferably a mixture of choline chloride and glycerol, and the molar ratio of choline chloride to glycerol is preferably 1:2 to 2:1, more preferably 1:1. In this invention, choline chloride and glycerol are preferably mixed by continuously heating and stirring at 75°C using a magnetic stirrer, and then allowed to cool naturally at room temperature (25±2°C) for later use.

[0030] In this invention, the mass of the deep eutectic solvent is 7.5-15% of the mass of the polysaccharide-based coating liquid, more preferably 8-13%, and even more preferably 10-12%.

[0031] In this invention, a deep eutectic solvent is added to a polysaccharide-based coating liquid, which is then placed in a constant-temperature water bath and continuously stirred to achieve composite coating liquid.

[0032] In this invention, the temperature of the composite process is preferably 50~80℃, more preferably 60~75℃, and the time is preferably 1~3h, more preferably 2h.

[0033] After obtaining the composite coating liquid, the present invention mixes the composite coating liquid with functional oil and water, pours it into a petri dish, and dries it to form a functional oil composite coating.

[0034] In this invention, the method for preparing the functional oil includes the following steps: The plant oil, hydrophilic polyphenol compound, and water were mixed, and the pH was adjusted to 9.0 to carry out the first loading, thus obtaining the oil with loaded hydrophilic groups. The oil body loaded with hydrophilic groups is mixed with a hydrophobic antibacterial compound and water for a second loading to obtain a functional oil body.

[0035] In this invention, the plant oil preferably includes soybean oil, linseed oil, perilla oil, safflower oil, or peanut oil; the hydrophilic polyphenolic compound preferably includes ferulic acid, gallic acid, chlorogenic acid, catechin, epicatechin, rosmarinic acid, salvianolic acid A, salvianolic acid B, sesaminol, proanthocyanidin B1, or proanthocyanidin B2; the mass ratio of the plant oil to the hydrophilic polyphenolic compound is preferably 1:0.02~0.1, more preferably 1:0.029~0.05.

[0036] The present invention does not impose any particular limitation on the extraction method of the plant oil; the corresponding oil can be obtained by extracting it according to methods well known in the art.

[0037] In an embodiment of the present invention, the preferred method for extracting soybean oil is as follows: soybeans are mixed with ultrapure water, soaked, crushed and stirred, homogenized and filtered, the resulting slurry is added to a sucrose solution, mixed evenly, centrifuged, and the supernatant is collected; the collected supernatant is washed three times repeatedly, and the collected paste-like substance is the soybean oil. Sucrose can both regulate osmotic pressure to promote the release of cell contents and help separate impurities, resulting in a higher purity oil.

[0038] In this invention, the water used to mix the vegetable oil, hydrophilic polyphenol compound and water is preferably sterile water. This invention does not have a special limitation on the amount of water used, as long as the materials are mixed evenly.

[0039] The present invention preferably uses NaOH solution to adjust to the required pH value. The present invention does not have a special limitation on the concentration of the NaOH solution, which can be adjusted according to the requirements.

[0040] In this invention, the vegetable oil and hydrophilic polyphenol compound are preferably dispersed in sterile water, stirred evenly, and the pH value is adjusted to 9.0 using NaOH solution and stirred evenly; the first loading is carried out overnight in a refrigerator.

[0041] In this invention, the preferred conditions for the first loading include: a temperature of 4-10°C, more preferably 6-8°C, a time of 8-16 h, more preferably 12 h, and a static reaction. During the first loading process, the carboxyl groups of the hydrophilic polyphenol compound combine with the hydroxyl groups (-OH) of the plant oil.

[0042] After the first loading is completed, the present invention preferably adjusts the pH of the obtained product to 7.0 with 2 mol / L HCl solution, dialyzes for 8 h to remove salt ions, centrifuges, collects the upper paste-like substance, and obtains an oil body loaded with hydrophilic groups.

[0043] In this invention, the hydrophobic antibacterial compound preferably includes allicin, carvacrol, cinnamaldehyde, eugenol, quercetin, luteolin, apigenin, linalool, eucalyptol, matrine, berberine, or medium-chain fatty acids.

[0044] In this invention, the mass ratio of the oil body loaded with hydrophilic groups to the hydrophobic antibacterial compound is 1:0005~0.2, preferably 1:0.005~0.05, and more preferably 1:0.0097~0.02.

[0045] In this invention, the hydrophilic group-loaded oil body is preferably mixed with water (more preferably ultrapure water), and a hydrophobic antibacterial compound is added to the resulting hydrophilic group-loaded oil body solution, and a second loading is performed under ultrasonic conditions.

[0046] In this invention, the concentration of the oil solution loaded with hydrophilic groups is preferably 100 mg / mL.

[0047] In this invention, the preferred conditions for the second loading include: the concentration of the hydrophobic antibacterial compound is preferably 2-15 mM, more preferably 6 mM; the ultrasonic power is 100-300 W, more preferably 200-250 W; and the time is 2-10 min, more preferably 6-8 min. During the second loading process, the reactive functional groups (such as thiosulfinate groups, aldehyde groups, carboxyl groups, etc.) in the hydrophobic antibacterial compound can undergo covalent reactions with thiol, amino, hydroxyl groups, etc. on the plant oil body protein to form stable chemical bonds (such as disulfide bonds, Schiff base bonds, etc.), significantly improving the loading stability.

[0048] After the second loading is completed, the present invention preferably centrifuges the obtained product at 4°C and 10,000 rpm for 20 min, and takes the upper oil layer to obtain the functional oil.

[0049] In this invention, the temperature at which the composite coating liquid is mixed with the functional oil and water is preferably 30~50°C, more preferably 40°C, and the volume ratio of the composite coating liquid to the mass ratio of the functional oil is preferably 20mL:1mg~1mL:50mg, more preferably 1mL:20mg.

[0050] In this invention, the functional oil is uniformly dispersed in ultrapure water to a concentration of 1 g / mL under constant temperature water bath conditions. The resulting suspension is added to the composite coating liquid to make the final concentration of the functional oil 5~40 mg / mL (more preferably 10~20 mg / mL). The mixture is stirred for 10 min, degassed, poured into a petri dish, and dried at room temperature to form a coating.

[0051] The present invention does not have any particular limitation on the flat dish; any vessel known in the art is acceptable.

[0052] In this invention, the drying temperature is preferably room temperature, and the drying time is preferably 1 to 3 hours, more preferably 2 hours.

[0053] The present invention provides a functional oil-based composite coating prepared by the preparation method described in the above technical solution.

[0054] The present invention provides the application of the functional oil-based composite coating described above in food preservation, and more preferably in fruit and vegetable preservation.

[0055] The present invention preferably uses a dip-coating method to coat the outer periphery of fruits and vegetables with a layer of functional oil-based composite coating liquid, which forms a transparent film with good adhesion on the surface after drying. Through visual observation and testing, the shelf life of bananas is extended from 3 days to more than 9 days, and the shelf life of cherry tomatoes is doubled.

[0056] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0057] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the raw materials used are all commercially available products, and the proportions are all by mass percentage.

[0058] Example 1

[0059] 1) Extraction of soybean oil

[0060] Soybeans were soaked in ultrapure water at a ratio of 9:100 for 18.5 h, stirred for 160 s, and the homogenate was filtered through three layers of nylon cloth to obtain raw soy milk. The raw soy milk was then heated in a 75°C water bath for 30 min and cooled to room temperature. 25% sucrose was added to the raw soy milk and mixed thoroughly. The mixture was then centrifuged at 12,000 rpm for 20 min at 4°C. The supernatant was collected. The mixture was washed for the first time with 5 times its weight of ultrapure water, and then 25% sucrose was added and mixed thoroughly. The mixture was then centrifuged at 12,000 rpm for 20 min at 4°C. The supernatant was collected, and the mixture was washed a second time using the same method as the first washing. The mixture was then centrifuged again under the same conditions, and the supernatant oil was collected to obtain soybean oil (SOB).

[0061] 2) Construction of soybean oil bodies loaded with ferulic acid

[0062] 1 g of soybean oil SOB was uniformly dispersed in 10 mL of deionized water, and 0.029 g of ferulic acid was added. The pH was adjusted to 9.0 with 2 mol / L NaOH. The concentration of soybean oil SOB in the mixture was 10% (w / v), and the concentration of ferulic acid was 15 mmol / L. The mixture was placed in a refrigerator at 4℃ and reacted continuously at pH=9 for 12 h. After the reaction was completed, the pH was adjusted to 7.0 with 2 mol / L HCl solution, and dialyzed for 8 h. After the dialyz was completed, the dialysate was centrifuged (12000 rpm, 4℃), and the upper paste-like substance was collected to obtain ferulic acid-loaded soybean oil SOBF.

[0063] 3) Screening and preparation process of soybean oil bodies loaded with ferulic acid and encapsulated with allicin

[0064] First, the central values ​​of influencing factors are determined through single-factor experiments. Then, response surface experiments are designed based on the single-factor results. The optimal value obtained from the single-factor experiments is used as the center point, and a certain range of parameters is designed before and after. Then, the optimal experimental parameters are determined by combining various factors. Finally, the preparation process parameters are determined by verifying the algorithm and combining it with the feasibility of actual operation.

[0065] ① Single-factor screening of soybean oil bodies loaded with ferulic acid and encapsulated with allicin

[0066] A single-factor parameter optimization experiment was established using allicin concentration, ultrasonic power (100~300 W), and ultrasonic time (2~10 min): S1: Screening of allicin concentration: Ferulic acid-loaded soybean oil was uniformly dispersed in ultrapure water, and allicin was added to achieve a concentration of 2.5–10 mM. The mixture was sonicated at 200 W for 5 min. As the allicin concentration increased from 2.5 mM to 6 mM, the encapsulation efficiency of allicin in the ferulic acid-loaded soybean oil showed a significant upward trend (P<0.05), reaching a maximum at 6 mM (85.23%±2.11%). Single-factor screening determined the allicin concentration to be 6 mM.

[0067] S2: The mixture was ultrasonically treated using an ultrasonic processor (100~300 W): As the ultrasonic power increased from 100 W to 150 W, the oil particle size increased significantly; when the power was further increased to 250 W, the particle size decreased significantly to 789.6 nm ± 17.9 nm; at 300 W, the particle size increased again to 1056.3 nm ± 20.4 nm. The absolute value of the zeta potential showed a trend of first increasing and then decreasing with increasing ultrasonic power: -4.2 mV at 100 W, reaching a minimum of -8.3 mV at 250 W, and rising back to -5.9 mV at 300 W. Single-factor screening determined that the ultrasonic power was 250 W.

[0068] S3: Effects of different ultrasonic times (2–10 min) on the encapsulation efficiency, particle size, and zeta potential of allicin-loaded soybean oil containing ferulic acid: Within the range of 2–6 min, the particle size of SOBFA oil decreased. The encapsulation efficiency peaked at 6 min (87.35% ± 2.03%). However, when the ultrasonic time exceeded 6 min, the encapsulation efficiency decreased accordingly, dropping to 74.21% ± 2.56% at 8 min and 68.19% ± 2.37% at 10 min. A single-factor screening determined the ultrasonic time to be 6 min.

[0069] In summary, based on encapsulation efficiency, particle size, and potential, the optimal parameters for a single factor were determined as follows: allicin concentration 6 mM, ultrasonic power 250 W, and ultrasonic time 6 min.

[0070] ② Response surface optimization of SOB encapsulation process for allicin

[0071] Based on the results of the single-factor screening, a three-factor, three-level experiment was designed (Table 1), which resulted in 12 experimental points. On this basis, 5 additional center points were added to ensure the accuracy of the experimental data and the reliability of the model. Finally, 17 experimental design points were determined.

[0072] Using allicin concentration (A), ultrasonic power (B), and ultrasonic time (C) as independent variables, and encapsulation rate as the response value, the optimal process conditions for SOBFA preparation were determined. The results showed that the encapsulation rate was within the range of 0.562%–0.809%, with the central experimental group (allicin concentration 6 mM, ultrasonic power 250 W, ultrasonic time 6 min) having an average encapsulation rate of 0.8012%, indicating good repeatability. Excessively high or low allicin concentration, ultrasonic power, and ultrasonic time all led to a decrease in encapsulation rate, and there was a significant interaction among the three. The optimal process range for encapsulation rate was preliminarily determined to be an allicin concentration of 5.48 mM, an ultrasonic power of 250.088 W, and an ultrasonic time of 5.969 min, at which the allicin encapsulation rate reached 81.38%.

[0073] Table 1. Factors and levels in response surface methodology experiments

[0074] ③ Artificial Neural Network-Genetic Algorithm Optimization

[0075] A prediction model was established using a three-layer BP neural network, combined with a genetic algorithm (GA) to construct an ANN-GA model. Allicin concentration, ultrasonic power, and ultrasonic time were used as input variables, and the encapsulation efficiency of SOBs containing allicin was used as the output. A complete training sample set was obtained based on response surface methodology. The artificial neural network-genetic algorithm model was then constructed to verify and compare the optimal conditions for SOBFA preparation obtained by the response surface methodology and the artificial neural network. Based on practical operation, the optimal process conditions were determined to be an allicin concentration of 5.5 mM, an ultrasonic power of 250 W, and an ultrasonic time of 6 min.

[0076] 4) Preparation of functional soybean oil bodies (SOBFA)

[0077] Disperse 1 g of the above-mentioned soybean oil SOBF loaded with ferulic acid in 10 mL of ultrapure water.

[0078] After homogenization, add 9.7 mg of allicin to bring the final allicin concentration to 6 mM. Place the mixture in an ultrasonic cell disruptor and sonicate at a constant power of 250 W for 6 min. Then transfer the sample to a 5 mL centrifuge tube and centrifuge at 4℃ and 10000 rpm for 20 min. Collect the supernatant to obtain functional soybean oil body SOBFA.

[0079] 5) Preparation of deep eutectic solvent DES

[0080] Weigh 18.08 g of choline chloride and 11.92 g of glycerol in a molar ratio of 1:1. Transfer them to a 50 mL preheated beaker and heat and stir continuously in a 75°C water bath to disperse the solid choline chloride in the glycerol until the solution gradually changes from an initial turbid suspension to a homogeneous, transparent, viscous liquid, forming a clear, stable DES without visible particles. Allow it to cool naturally at room temperature (25±2°C) to obtain deep eutectic solvent DES.

[0081] 6) Preparation of polysaccharide-DES composite coating liquid

[0082] Dissolve 1 g CMCS and 0.8 g CAR in 100 mL of ultrapure water. Stir continuously at 60 °C until CMCS and CAR are completely dissolved to obtain a polysaccharide-based coating solution. Then add 10% by mass of deep eutectic solvent DES and place in a 75 °C constant temperature water bath. Stir continuously for 2 h to obtain a composite coating solution.

[0083] 7) Preparation of functional oil-based composite coatings

[0084] Under constant temperature water bath conditions of 40°C, 1g of functional oil SOBFA was uniformly dispersed in 1 mL of ultrapure water to prepare a SOBFA suspension with a mass concentration of 1 g / mL. 50 mL of the composite coating solution from step 6) above was taken, and 0.5 mL of the 1 g / mL SOBFA suspension was added to make the final SOBFA concentration 10 mg / mL. The mixture was stirred for 10 min to ensure uniform and stable dispersion of SOBFA in the coating matrix. Then, the mixture was degassed, poured into a petri dish, and dried at room temperature for 2 h to form a polysaccharide-DES-SOBFA composite coating, denoted as CMCS+CAR+DES+SOBFA.

[0085] Comparative Example 1

[0086] 1 g CMCS and 0.8 g CAR were dissolved in 100 mL of ultrapure water. The mixture was stirred continuously at 60 °C until CMCS and CAR were completely dissolved to obtain a polysaccharide-based coating solution. Then, 10% DES (same as in Example 1) was added. The resulting mixture was degassed and poured into a petri dish to obtain a polysaccharide-DES coating, denoted as CMCS+CAR+DES.

[0087] Comparative Example 2

[0088] 1 g CMCS and 0.8 g CAR were dissolved in 100 mL of ultrapure water. The mixture was stirred continuously at 60 °C until CMCS and CAR were completely dissolved to obtain a polysaccharide-based coating solution. After degassing, the solution was poured into a petri dish to obtain a polysaccharide-based coating, denoted as CMCS+CAR.

[0089] Test Example 1

[0090] Light transmittance test of coating

[0091] Figure 1 The images show the appearance of the functional oil-based composite coating in Example 1 and the coatings in Comparative Examples 1 and 2, where CC represents Comparative Example 2, CCD represents Comparative Example 1, and CCDS represents Example 1; Figure 1 It can be seen that the functional oil-based composite coating prepared by the present invention exhibits good optical transparency, and the architectural outline, the number "1948" and the English lettering of the base stamp can be clearly observed through the coating without obvious turbidity or whitening.

[0092] Test Example 2

[0093] Mechanical property testing of coating

[0094] The mechanical properties of functional oil-based composite coatings were determined by tensile strength and load-bearing capacity. Axial tensile tests were performed on the films using a high-precision digital push-pull force gauge, and the dynamic tensile force values ​​of the films during the stress process were monitored and recorded in real time. The results are shown in […]. Figure 2 .

[0095] Figure 2 The tensile strength and mechanical load-bearing properties of the functional oil-based composite coating in Example 1; by Figure 2 It can be seen that the composite coating exhibits the best ductility, with the value before and after stretching increasing from 3.01 mm to 4.57 mm, proving that it has higher strain tolerance.

[0096] Test Example 3

[0097] Antioxidant performance test of coating

[0098] The DPPH and ABTS free radical scavenging rates of the coating were determined. Experimental conditions were set as follows: 0.5 g of the coating sample was accurately weighed and placed in a centrifuge tube containing 10 mL of ultrapure water. The sample was extracted in a 30℃ water bath for 12 h. After extraction, the sample was centrifuged at 7000 r / min for 15 min, and the supernatant was collected for later use. 4.0 mg of DPPH powder was weighed, dissolved in 80% ethanol, and the volume was adjusted to 100 mL. 2 mL of the above sample solution (1 mg / mL) was taken, and 2 mL of DPPH ethanol solution was added. After mixing, the mixture was reacted for 30 min (in the dark). The absorbance of the sample at 517 nm was measured and recorded as A1. The absorbance of 2 mL of each sample solution and 2 mL of 80% ethanol at 517 nm was measured and recorded as A0. The absorbance of 2 mL of DPPH ethanol solution and 2 mL of 80% ethanol at 517 nm was also measured and recorded as A. The DPPH free radical scavenging rate was calculated according to Formula 1. Formula 1.

[0099] Accurately weigh 0.5 g of the coating sample and place it in a centrifuge tube containing 10 mL of ultrapure water. Incubate at 30°C for 12 h. After extraction, centrifuge at 7000 r / min for 15 min and collect the supernatant for later use. Preparation of ABTS solution: Mix equal volumes of 5 mL ABTS solution (7 mmol / L) and 5 mL potassium persulfate solution (2.45 mmol / L), and react for 12–16 h (protected from light). Before the experiment, dilute the ABTS stock solution with phosphate buffer (PBS: 10 mmol / L, pH=7.4) to an absorbance of 0.70 ± 0.02 at 734 nm. Take 100 μL of each sample solution (0.5 mg / mL), add 3.9 mL of ABTS solution, shake to mix, and react in a 37℃ water bath for 10 min. Measure the absorbance at 734 nm and record it as A. Under the same conditions, measure the absorbance of the mixture of 100 μL PBS and 3.9 mL ABTS solution at 734 nm and record it as A0. Calculate the ABTS+ concentration according to Formula 2. Clearance rate.

[0100] Formula 2.

[0101] Figure 3 The antioxidant properties of the functional oil-based composite coating in Example 1, the polysaccharide-DES coating in Comparative Example 1, and the polysaccharide-based coating in Comparative Example 2 are compared, where A represents the ABTS scavenging rate and B represents the DPPH scavenging rate. Figure 3 It can be seen that the antioxidant capacity of the composite coatings shows the order of polysaccharide-DES-SOBFA composite coating (Example 1) > polysaccharide-DES coating (Comparative Example 1) > polysaccharide coating (Comparative Example 2), with the polysaccharide-DES-SOBFA composite coating exhibiting the best antioxidant performance in Example 1. Compared to the polysaccharide coating, the ABTS radical scavenging rate of the functional oil-based composite coating increased from 10% to 30%, and the DPPH radical scavenging rate increased from 38% to 75%.

[0102] Test Example 4

[0103] Antibacterial performance test of coating

[0104] The antibacterial activity of the composite coating was evaluated using a plate count method. First, *Escherichia coli* and *Staphylococcus aureus* bacterial suspensions were prepared. Colonies were inoculated into 5 mL of LB liquid medium and incubated at 37°C with shaking for 12 h. The bacterial suspensions were then diluted to 1×10⁻⁶. 6CFU / mL. The coating was cut into 1 cm long and 1 cm wide squares and sterilized under UV light for 30 min. One coating and 2 mL of sterile water were added to a sterile EP tube as the experimental group, and 2 mL of bacterial suspension was added to the control group. Each group was repeated three times. 500 μL of the coating solution was pipetted into a sterile 2 mL EP tube and 500 μL of the prepared *E. coli* bacterial suspension was added, and the mixture was thoroughly mixed. This was the experimental group; the control group consisted of 500 μL of sterile water and 500 μL of *E. coli* bacterial suspension. Each group was repeated three times. 35 μL of each dilution was evenly spread onto nutrient agar plates and incubated upside down at 37°C for 12 h. Colony growth was observed. Results are shown below. Figures 4-5 .

[0105] Figure 4 The antibacterial properties of the functional oil-based composite coating in Example 1, the polysaccharide-DES coating in Comparative Example 1, and the polysaccharide-based coating in Comparative Example 2 against Escherichia coli were compared. Figure 4 In the table, A represents the E. coli coating in the control group, B represents the CMCS+CAR coating in Comparative Example 2, C represents the CMCS+CAR+DES coating in Comparative Example 1, and D represents the CMCS+CAR+DES+SOBFA composite coating in Example 1. Figure 5 The antibacterial properties of the functional oil-based composite coating in Example 1, the polysaccharide-DES coating in Comparative Example 1, and the polysaccharide-based coating in Comparative Example 2 against Staphylococcus aureus were compared. Figure 5 In the diagram, A represents the Staphylococcus aureus coating in the control group, B represents the CMCS+CAR coating in Comparative Example 2, C represents the CMCS+CAR+DES coating in Comparative Example 1, and D represents the CMCS+CAR+DES+SOBFA composite coating in Example 1. Figures 4-5 It can be seen that the CMCS+CAR+DES+SOBFA composite coating in Example 1 exhibits the best antibacterial performance. The inhibition rate against Escherichia coli is approximately 70%. Figure 4 ), with an inhibition rate of up to 80% against Staphylococcus aureus ( Figure 5 ).

[0106] Test Example 5

[0107] Preservation performance test of functional oil-based composite coating

[0108] Fresh bananas and cherry tomatoes were selected, washed, and dried. The degassed composite coating liquid from step 7) of Example 1 and the degassed coating liquid from Comparative Examples 1 and 2 were then applied to the surface of the bananas / cherry tomatoes, respectively. After the surface solutions dried, they were stored at room temperature, and their appearance was observed. Results are shown below. Figures 6-7 Where Control represents the blank control without any preservative coating, CC represents Comparative Example 2, CCD represents Comparative Example 1, and CCDS represents Example 1.

[0109] Figure 6 Images show the appearance of bananas treated with the functional oil-based composite coating in Example 1 and the coatings in Comparative Examples 1 and 2, respectively, during their preservation process. Figure 6 As shown, the preservation effect was the worst after 9 days of storage at room temperature without any coating. In Comparative Example 2, the polysaccharide-coated group showed that the peel turned completely black and the flesh became soft and rotten on day 9. In Example 1, the functional oil group exhibited excellent preservation performance. Throughout the entire period, the peel remained bright in color, with only slight local spots visible on day 9, and the flesh did not become soft and rotten, thus maximizing the preservation of the fruit's commercial value.

[0110] Figure 7 The images show the appearance of the cherry tomatoes treated with the functional oil-based composite coating in Example 1 and the coatings in Comparative Examples 1 and 2, respectively, during their preservation process. Figure 7 As shown, the aging and deterioration process of cherry tomatoes exhibits significant step-like differences. In the blank control, the cherry tomatoes without coating protection deteriorated the most rapidly, showing severe dehydration, shrinkage, and rotting by day 12, and completely becoming moldy and losing all commercial value by day 24. In contrast, the cherry tomatoes with the functional oil composite coating in Example 1 did not experience large-scale rotting by day 24; the fruits only showed slight local shrinkage, maintained an intact overall shape, and had a bright color, greatly extending the commercial life of the tomatoes.

[0111] Figure 8 The figures show the thermal properties of the coatings in Example 1 and Comparative Examples 1-2, where A is the TG curve, B is the DTG curve, and C is the DSC curve; the inflection point of the TG curve corresponds to the peak value of the weight loss rate, which represents the temperature at which the coating undergoes violent thermal decomposition (i.e., the thermal decomposition temperature).

[0112] like Figure 8 As shown, the highest inflection point temperature of the green curve indicates a high thermal decomposition initiation temperature; the inflection points of the red and blue curves indicate that the material undergoes drastic decomposition at lower temperatures after the addition of DES and SOBFA. Fruit and vegetable preservation coatings need to possess barrier and antibacterial properties at room temperature (or low temperature) while preventing high-temperature decomposition. More importantly, coatings with added functional ingredients (DES, SOBFA) often have greater advantages in antibacterial properties and preservation time. A higher DTG peak temperature indicates a higher thermal decomposition temperature and stronger thermal stability of the material. For example... Figure 8As shown, in Comparative Example 2, the CMCS+CAR coating has a main decomposition peak at 268℃, and in Comparative Example 1, the CMCS+CAR+DES coating also has a main decomposition peak at 268℃, consistent with the black curve. In Example 1, the CMCS+CAR+DES+SOBFA composite coating has a main decomposition peak at 273℃, 5℃ higher than the black curve. The addition of DES did not change the thermal stability. However, the addition of SOBFA increased the thermal decomposition temperature of the coating, enhancing its thermal stability. Fruit and vegetable preservation coatings need to maintain structural stability during processing and storage. Higher thermal stability means better tolerance to temperature changes during processing and storage, and slower physical and chemical degradation rates during storage, thus extending shelf life.

[0113] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a functional oil-based composite coating, characterized in that, Includes the following steps: Carboxymethyl chitosan, carrageenan, and water were mixed and dispersed to obtain a polysaccharide-based coating solution. The polysaccharide-based coating liquid is mixed with a deep eutectic solvent to form a composite coating liquid. The composite coating liquid is mixed with functional oil and water, poured into a petri dish, and dried to form a functional oil composite coating. The method for preparing the functional oil includes the following steps: The plant oil, hydrophilic polyphenol compound, and water were mixed, and the pH was adjusted to 9.0 to carry out the first loading, thus obtaining the oil with loaded hydrophilic groups. The oil body loaded with hydrophilic groups is mixed with a hydrophobic antibacterial compound and water for a second loading to obtain a functional oil body.

2. The preparation method according to claim 1, characterized in that, The mass ratio of carboxymethyl chitosan to carrageenan is 0.5~2:0.1~1; the dispersion temperature is 50~70℃.

3. The preparation method according to claim 1, characterized in that, The deep eutectic solvent is a mixture of choline chloride and glycerol, wherein the molar ratio of choline chloride to glycerol is 1:2 to 2:

1. The mass of the deep eutectic solvent is 7.5-15% of the mass of the polysaccharide-based coating liquid; The composite process is carried out at a temperature of 50-80℃ for 1-3 hours.

4. The preparation method according to claim 1, characterized in that, The plant oils include soybean oil, linseed oil, perilla oil, safflower oil, or peanut oil; the hydrophilic polyphenolic compounds include ferulic acid, gallic acid, chlorogenic acid, catechin, epicatechin, rosmarinic acid, salvianolic acid A, salvianolic acid B, sesaminol, proanthocyanidin B1, or proanthocyanidin B2; the hydrophobic antibacterial compounds include allicin, carvacrol, cinnamaldehyde, eugenol, quercetin, luteolin, apigenin, linalool, eucalyptol, matrine, berberine, or medium-chain fatty acids.

5. The preparation method according to claim 1 or 4, characterized in that, The mass ratio of the plant oil to the hydrophilic polyphenol compound is 1:0.02~0.1; the mass ratio of the oil loaded with hydrophilic groups to the hydrophobic antibacterial compound is 1:0.005~0.

2.

6. The preparation method according to claim 1, characterized in that, The conditions for the first load include: a temperature of 4~10℃, a time of 8~16 h, and a static reaction. The conditions for the second loading include: the concentration of the hydrophobic antibacterial compound is 2-15 mmol / L; the ultrasonic power is 100-300W; and the time is 2-10 min.

7. The preparation method according to claim 1, characterized in that, The volume ratio of the composite coating liquid to the mass of the functional oil is 20mL:1mg to 1mL:50mg; the mixing temperature of the composite coating liquid with the functional oil and water is 38 to 42°C.

8. The preparation method according to claim 1, characterized in that, The drying temperature is room temperature, and the time is 1 to 3 hours.

9. The functional oil-based composite coating prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the functional oil-based composite coating of claim 9 in food preservation.

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