A bacteriostatic antioxidant edible coating and method of making same

Abstract

This invention belongs to the field of food preservation technology, specifically relating to an antibacterial and antioxidant edible coating and its preparation method. The antibacterial and antioxidant edible coating comprises the following components in parts by weight: 0.5-0.8 parts nanocellulose, 0.3-0.5 parts chitosan, 0.3-0.5 parts composite antioxidant, 0.5-0.8 parts cephalosporin antimicrobial peptide, 0.3-0.5 parts plasticizer, and 90-95 parts water; the composite antioxidant is a liposome encapsulated with natural antioxidants, formed from modified soybean lecithin and cholesterol. This invention significantly improves the encapsulation efficiency of natural antioxidants by modifying soybean lecithin, thus endowing the coating with antioxidant properties; furthermore, by improving the structure of the plasticizer, the barrier properties of the coating are enhanced, synergistically with the natural antibacterial agent, giving the coating excellent antibacterial, antioxidant, and barrier properties, resulting in a significant preservation effect.

Description

Technical Field

[0001] This invention belongs to the field of food preservation technology, specifically relating to an antibacterial and antioxidant edible coating and its preparation method. Background Technology

[0002] Fresh agricultural products such as fruits and vegetables are prone to quality decline and severe spoilage during post-harvest distribution due to factors such as water loss, respiration, microbial contamination, and oxidative deterioration. To extend shelf life, edible preservation coating technology has attracted widespread attention because it can form a selective barrier on the food surface (regulating gas and inhibiting moisture loss) and is safe for consumption.

[0003] Currently, edible coatings often use polysaccharides (such as nanocellulose and chitosan) and lipids as the main matrix. However, while commonly used hydrophilic plasticizers such as glycerol can improve the flexibility of coatings, their strong hydrophilicity significantly increases the water vapor permeability of the coating in high humidity environments, weakening its moisture-blocking performance. Furthermore, they suffer from problems such as easy migration and limited functionality, restricting their application in long-term preservation or high-humidity environments. On the other hand, natural phospholipids such as soybean lecithin are often used to construct liposomes to encapsulate functional components due to their amphiphilicity. However, their inherently low HLB value (hydrophilic-lipophilic balance value) leads to poor dispersibility and insufficient oxidative stability in aqueous systems, thus affecting the encapsulation efficiency and stability of the prepared liposomes, ultimately weakening the long-term antioxidant function of the coating.

[0004] Furthermore, a single coating component often fails to simultaneously meet multiple requirements such as long-lasting antibacterial properties, antioxidant properties, high barrier properties, and mechanical properties. Therefore, developing a novel multifunctional edible composite coating that can simultaneously optimize the hydrophilicity-hydrophobicity balance of plasticizers to improve barrier properties and enhance the water dispersibility and load stability of phospholipids through directional modification is of great significance for improving the preservation quality of fresh agricultural products. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide an antibacterial and antioxidant edible coating and its preparation method.

[0006] The objective of this invention is achieved through the following technical solution: The first aspect of this invention provides an antibacterial and antioxidant edible coating comprising the following components in parts by weight: 0.5-0.8 parts of nanocellulose, 0.3-0.5 parts of chitosan, 0.3-0.5 parts of composite antioxidant, 0.5-0.8 parts of cephalosporin antimicrobial peptide, 0.3-0.5 parts of plasticizer, and 90-95 parts of water; The compound antioxidant is a liposome encapsulated with natural antioxidants, formed from modified soybean lecithin and cholesterol.

[0007] Furthermore, the preparation process of the modified soybean lecithin is as follows: (1) Dissolve soybean lecithin in a solvent, then add a chlorine-containing oxidant to carry out a chlorination reaction to obtain chlorinated lecithin; (2) The chlorinated lecithin and citric acid were reacted under the action of an alkaline catalyst to obtain the modified soybean lecithin.

[0008] Further, the chlorine-containing oxidant in step (1) is sodium hypochlorite; the chlorination reaction is carried out for 1-3 h under pH 4-5 conditions; the solvent is n-hexane; the mass ratio of soybean lecithin to chlorine-containing oxidant is 1:(0.1-0.2); this step introduces active chlorine atoms into the double bonds of the unsaturated fatty acid chain of lecithin through an electrophilic addition reaction.

[0009] Further, in step (2), the alkaline catalyst is sodium carbonate; the solvent for the reaction is chloroform, the temperature is 40-50℃, and the time is 3-5 h; the mass ratio of chlorinated lecithin, citric acid, and alkaline catalyst is 1:(0.3-0.5):(0.2-0.3). In this step, the phenolic hydroxyl group of citric acid undergoes a nucleophilic substitution reaction with the chlorine atom in chlorinated lecithin to form a stable ether bond, thereby covalently grafting the citric acid structural unit onto the lecithin molecule.

[0010] Further, the mass ratio of the modified soybean lecithin, cholesterol, and natural antioxidant is 1:(0.15-0.25):(0.05-0.1); the natural antioxidant is bamboo leaf flavonoids or eugenol. This step utilizes the liposome structure formed by the modified soybean lecithin and cholesterol to encapsulate the hydrophobic natural antioxidant.

[0011] Furthermore, the preparation process of the plasticizer is as follows: (a) In the presence of p-toluenesulfonic acid, p-hydroxycinnamic acid and glycerol are esterified to obtain intermediate 1; the structural formula of intermediate 1 is as follows: (b) Under acidic conditions, intermediate 1 is subjected to a formylation reaction with hexamethylenetetramine to obtain intermediate 2; the structural formula of intermediate 2 is as follows: (c) Under the action of an organic catalyst, intermediate 2 is reacted with 2-aminocyclohexanol to form a 4,5-dihydrooxazole ring structure to obtain the plasticizer; the structural formula of the plasticizer is as follows: .

[0012] Further, in step (a), the molar ratio of p-hydroxycinnamic acid, glycerol and p-toluenesulfonic acid is 1:(3-4):(0.0125-0.025); the esterification reaction is carried out at a temperature of 90-110°C for 8-16 h.

[0013] Further, the formylation reaction process described in step (b) is as follows: first react in acetic acid at 90-100℃ for 2-3 hours, then add hydrochloric acid and continue reacting at 90-100℃ for 1-1.5 hours; the molar ratio of intermediate 1 to hexamethylenetetramine is 1:(1.5-2).

[0014] Further, the organic catalyst in step (c) is N,N,N',N'-tetrabromobenzene-1,3-disulfonamide; the molar ratio of the organic catalyst, intermediate 2, and 2-aminocyclohexanol is (0.027-0.035):1:(1.5-2); and the reaction time is 3-5 h.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned antibacterial and antioxidant edible coating, comprising the following steps: Nanocellulose, plasticizer, and chitosan are added to water and stirred. Then, a composite antioxidant and cephalosporin antimicrobial peptide are added and stirred evenly. After emulsification and vacuum degassing, a slurry is obtained. The slurry is coated and then dried to obtain the final product.

[0016] The present invention has the following advantages over the prior art: 1. This invention significantly improves the encapsulation efficiency of liposomes for natural antioxidants by modifying soybean lecithin, thus endowing the coating with antioxidant properties. In addition, by improving the structure of the plasticizer, the barrier properties of the coating are enhanced, and in conjunction with natural antibacterial agents, the coating has excellent antibacterial, antioxidant and barrier properties, resulting in a significant preservation effect.

[0017] 2. This invention significantly improves the hydrophilic-lipophilic balance and membrane rigidity of soybean lecithin through chlorination and graft modification with thymol. Thymol, with its linear hydrophobic structure, can stably embed itself into the hydrophobic regions of the phospholipid bilayer, effectively regulating membrane fluidity: during the hydration stage of liposome preparation, it promotes full swelling of the lipid membrane, providing ample space for encapsulating natural antioxidants; during storage, it maintains membrane rigidity by enhancing intermolecular interactions, reducing the risk of drug leakage. Thymol synergistically works with cholesterol to construct a "rigid-flexible" balanced microdomain structure within the liposome membrane, significantly enhancing drug loading capacity.

[0018] 3. The plasticizer synthesized in this invention contains a 4,5-dihydrooxazole heterocycle and a benzene ring hydrophobic structure, and its hydrophilicity is significantly lower than that of glycerol. Therefore, it can significantly reduce water vapor permeability and improve the barrier properties of the coating. In addition, the 2,3-dihydroxypropyl and phenolic hydroxyl groups can form a multiple hydrogen bond network with nanocellulose, and the aromatic ring can generate π-π stacking and hydrophobic interaction with nanocellulose. The interfacial compatibility is better than that of glycerol, which effectively inhibits plasticizer migration. Attached Figure Description

[0019] Figure 1 The image shows the FT-IR spectrum of soybean lecithin in Example 1. Figure 2 FT-IR spectrum of chlorinated soybean lecithin in Example 1; Figure 3 The image shows the FT-IR spectrum of the modified soybean lecithin in Example 1. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to specific embodiments. However, those skilled in the art should understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are all conventional products obtained through commercial channels.

[0021] Preparation Example 1 A composite antioxidant is prepared as follows: (1) Soybean lecithin, sodium hypochlorite, and n-hexane were dissolved in n-hexane at a mass ratio of 1:0.15:5. Sodium hypochlorite was added in portions while stirring at 35°C. Acetic acid was then added to adjust the pH of the reaction system to 4.5, and the reaction was carried out for 2 h. After the reaction was completed, the mixture was washed with water, extracted, and the organic phase was separated and concentrated to obtain chlorinated lecithin.

[0022] (2) According to the mass ratio of chlorinated lecithin, citronellol, sodium carbonate and chloroform 1:0.4:0.2:100, the chlorinated lecithin and citronellol obtained in step (1) were added to chloroform, stirred evenly and then sodium carbonate was added. The mixture was stirred at 45°C for 4 h. After the reaction was completed, the crude product was obtained by washing with water, extraction and concentration. The crude product was first dissolved, filtered and concentrated using a mixed solvent of chloroform-acetonitrile with a volume ratio of 3:1. Then the same operation was performed using a mixed solvent of acetone-methanol with a volume ratio of 5:1. Finally, the filtrate was concentrated to obtain modified soybean lecithin.

[0023] (3) According to the mass ratio of modified soybean lecithin, cholesterol, bamboo leaf flavonoids and mixed solvent of 1:0.2:0.08:5, the modified soybean lecithin, cholesterol and bamboo leaf flavonoids were weighed and dissolved in chloroform-methanol (2:1, v / v) mixed solvent. The organic solvent was removed by vacuum evaporation on a rotary evaporator in a 40℃ water bath to form a uniform lipid film. The lipid film was added to 10 mL of phosphate buffer (PBS, 0.01M, pH 7.4) and hydrated by shaking in a 60℃ water bath for 60 min. Then, it was subjected to ice bath probe ultrasonic treatment (power 300 W, working for 5 s / interval for 5 s, total duration 10 min). After freeze drying, the composite antioxidant was obtained.

[0024] Preparation Example 2 A composite antioxidant is prepared as follows: (1) Soybean lecithin, sodium hypochlorite and n-hexane were dissolved in n-hexane at a mass ratio of 1:0.1:5. Sodium hypochlorite was added in portions while stirring at 30°C. Acetic acid was then added to adjust the pH of the reaction system to 4, and the reaction was carried out for 3 hours. After the reaction was completed, the mixture was washed with water, extracted, and the organic phase was separated and concentrated to obtain chlorinated lecithin.

[0025] (2) According to the mass ratio of chlorinated lecithin, citronellol, sodium carbonate and chloroform 1:0.3:0.2:100, the chlorinated lecithin and citronellol obtained in step (1) were added to chloroform, stirred evenly and then sodium carbonate was added. The mixture was stirred at 40°C for 5 h. After the reaction was completed, the crude product was obtained by washing with water, extraction and concentration. The crude product was first dissolved, filtered and concentrated using a mixed solvent of chloroform-acetonitrile with a volume ratio of 3:1. Then the same operation was performed using a mixed solvent of acetone-methanol with a volume ratio of 5:1. Finally, the filtrate was concentrated to obtain modified soybean lecithin.

[0026] (3) According to the mass ratio of modified soybean lecithin, cholesterol, bamboo leaf flavonoids and mixed solvent of 1:0.15:0.05:5, the modified soybean lecithin, cholesterol and bamboo leaf flavonoids were weighed and dissolved in chloroform-methanol (2:1, v / v) mixed solvent. The organic solvent was removed by vacuum evaporation in a rotary evaporator in a water bath at 40℃ to form a uniform lipid film. The lipid film was added to 10 mL of phosphate buffer (PBS, 0.01M, pH 7.4) and hydrated by shaking in a water bath at 60℃ for 60 min. Then, it was subjected to ultrasonic treatment with an ice bath probe (power 300 W, working for 5 s / interval for 5 s, total duration 10 min). After freeze drying, the composite antioxidant was obtained.

[0027] Preparation Example 3 A composite antioxidant is prepared as follows: (1) Soybean lecithin, sodium hypochlorite and n-hexane were dissolved in n-hexane at a mass ratio of 1:0.2:5. Sodium hypochlorite was added in portions while stirring at 40°C. Acetic acid was then added to adjust the pH of the reaction system to 5 and the reaction was carried out for 1 hour. After the reaction was completed, the mixture was washed with water, extracted, and the organic phase was separated and concentrated to obtain chlorinated lecithin.

[0028] (2) According to the mass ratio of chlorinated lecithin, citronellol, sodium carbonate and chloroform 1:0.5:0.3:100, the chlorinated lecithin and citronellol obtained in step (1) were added to chloroform, stirred evenly and then sodium carbonate was added. The mixture was stirred at 50°C for 3 h. After the reaction was completed, the crude product was obtained by washing with water, extraction and concentration. The crude product was first dissolved, filtered and concentrated using a mixed solvent of chloroform-acetonitrile with a volume ratio of 3:1. Then the same operation was performed using a mixed solvent of acetone-methanol with a volume ratio of 5:1. Finally, the filtrate was concentrated to obtain modified soybean lecithin.

[0029] (3) According to the mass ratio of modified soybean lecithin, cholesterol, bamboo leaf flavonoids and mixed solvent of 1:0.25:0.1:5, the modified soybean lecithin, cholesterol and bamboo leaf flavonoids were weighed and dissolved in chloroform-methanol (2:1, v / v) mixed solvent. The organic solvent was removed by vacuum evaporation in a rotary evaporator in a water bath at 40℃ to form a uniform lipid film. The lipid film was added to 10 mL of phosphate buffer (PBS, 0.01M, pH 7.4) and hydrated by shaking in a water bath at 60℃ for 60 min. Then, it was subjected to ultrasonic treatment with an ice bath probe (power 300 W, working for 5 s / interval for 5 s, total duration 10 min). After freeze drying, the composite antioxidant was obtained.

[0030] Preparation Example 4 Preparation Example 4 is basically the same as Preparation Example 1, except that steps (1) and (2) are omitted and the modified soybean lecithin in step (3) is replaced with soybean lecithin.

[0031] Preparation Example 5 A plasticizer, the preparation process of which is as follows: (a) p-hydroxycinnamic acid (20 mmol), glycerol (70 mmol), and p-toluenesulfonic acid (0.3 mmol) were added to 40 mL of toluene and reacted at 100 °C for 12 h. The reaction solution was cooled to room temperature, diluted with ethyl acetate, and the organic phase was washed with saturated sodium carbonate aqueous solution. The organic phase was separated, the aqueous phase was extracted with ethyl acetate, and the organic phases were combined. The organic phase was dried with sodium sulfate and concentrated to obtain intermediate 1. 1 H NMR (C 12 H 14O5, 400 MHz, DMSO): δ 9.64 (s, 1H), 7.48 (d, 1H), 7.45(d, 2H), 6.59 (d, 2H), 6.31 (d, 1H), 5.74 (s, 1H), 4.43-4.41 (m, 1H), 4.19-4.16 (m, 2H), 3.94 (s, 1H), 3.59-3.52 (m, 2H); HRMS(ESI + ): [M+H] + The calculation yields 239.08, and the value is found to be 239.08.

[0032] (b) Hexamethylenetetramine (18 mmol) and intermediate 1 (10 mmol) were added to acetic acid (90 mL) and reacted at 95 °C for 2.5 h. Subsequently, dilute hydrochloric acid (40 mL 3 mol / L) was added to the reaction solution and the reaction was continued at 95 °C for 1 h. After cooling to room temperature, the solution was filtered through diatomaceous earth, extracted with dichloromethane, dried with magnesium sulfate, filtered, and the solution was rotary evaporated to obtain intermediate 2. 1 H NMR (C 13 H 14 O6, 400 MHz, DMSO): δ 15.38 (s, 1H), 10.20 (s, 1H), 7.73 (d,1H), 7.48 (d, 1H), 7.01 (s, 1H), 6.95 (d, 1H), 6.31 (d, 1H), 5.74 (s, 1H),4.43-4.41 (m, 1H), 4.19-4.16 (m, 2H), 3.94 (s, 1H), 3.59-3.52 (m, 2H); HRMS(ESI + ): [M+H] + The calculation yields 267.08, and the value is found to be 267.08.

[0033] (c) Intermediate 2 (10 mmol) and 2-aminocyclohexanol (18 mmol) were added to a mixture of acetonitrile (20 mL) and water (10 mL), and then N,N,N',N'-tetrabromobenzene-1,3-disulfonamide (TBBDS, CAS: 848408-54-8, 0.3 mmol) was added. The mixture was reacted at room temperature for 4 h. After the reaction was completed, the acetonitrile was removed by concentration, and the mixture was extracted with dichloromethane to separate the organic phase. The organic phase was dried with anhydrous sodium sulfate, and the solvent was removed by vacuum evaporation to obtain the plasticizer. 1 H NMR (C 19 H 23NO6, 400 MHz, DMSO): δ 10.27 (s, 1H), 7.50 (d, 1H), 7.48 (d, 1H), 7.35 (d, 1H), 6.87 (d,1H), 6.31 (d, 1H), 5.74 (s, 1H), 4.43-4.41 (m, 1H), 4.19-4.16 (m, 2H), 3.94(s, 1H), 3.59-3.50 (m, 3H), 3.08 (q, 1H), 2.19-1.94 (m, 2H), 1.72-1.43 (m,6H); + ): [M+H] + The calculation yields 362.15. 362.15 is found.

[0034] Preparation Example 6 A plasticizer, the preparation process of which is as follows: (a) p-hydroxycinnamic acid (20 mmol), glycerol (60 mmol), and p-toluenesulfonic acid (0.25 mmol) were added to 40 mL of toluene and reacted at 90 °C for 16 h. The reaction solution was cooled to room temperature, diluted with ethyl acetate, and the organic phase was washed with saturated sodium carbonate aqueous solution. The organic phase was separated, the aqueous phase was extracted with ethyl acetate, and the organic phases were combined. The organic phase was dried with sodium sulfate and concentrated to obtain intermediate 1. (b) Hexamethylenetetramine (15 mmol) and intermediate 1 (10 mmol) were added to acetic acid (90 mL) and reacted at 90 °C for 3 h; then, dilute hydrochloric acid (30 mL, 3 mol / L) was added to the reaction solution and the reaction was continued at 90 °C for 1.5 h; after cooling to room temperature, the solution was filtered through diatomaceous earth, extracted with dichloromethane, dried with magnesium sulfate, filtered, and the solution was rotary evaporated to obtain intermediate 2; (c) Intermediate 2 (10 mmol) and 2-aminocyclohexanol (15 mmol) were added to a mixture of acetonitrile (20 mL) and water (10 mL), and then TBBDS (0.27 mmol) were added. The mixture was reacted at room temperature for 3 h. After the reaction was completed, the acetonitrile was removed by concentration, and the mixture was extracted with dichloromethane to separate the organic phase. The organic phase was dried with anhydrous sodium sulfate and the solvent was removed by vacuum evaporation to obtain the plasticizer.

[0035] Preparation Example 7 A plasticizer, the preparation process of which is as follows: (a) p-hydroxycinnamic acid (20 mmol), glycerol (80 mmol), and p-toluenesulfonic acid (0.5 mmol) were added to 40 mL of toluene and reacted at 110 °C for 8 h. The reaction solution was cooled to room temperature, diluted with ethyl acetate, and the organic phase was washed with saturated sodium carbonate aqueous solution. The organic phase was separated, the aqueous phase was extracted with ethyl acetate, and the organic phases were combined. The organic phase was dried with sodium sulfate and concentrated to obtain intermediate 1. (b) Hexamethylenetetramine (20 mmol) and intermediate 1 (10 mmol) were added to acetic acid (90 mL) and reacted at 100 °C for 2 h. Subsequently, dilute hydrochloric acid (50 mL, 3 mol / L) was added to the reaction solution and the reaction was continued at 100 °C for 1 h. After cooling to room temperature, the solution was filtered through diatomaceous earth, extracted with dichloromethane, dried over magnesium sulfate, filtered, and the solution was rotary evaporated to obtain intermediate 2. (c) Intermediate 2 (10 mmol) and 2-aminocyclohexanol (20 mmol) were added to a mixture of acetonitrile (20 mL) and water (10 mL), and then TBBDS (0.35 mmol) were added. The mixture was reacted at room temperature for 5 h. After the reaction was completed, the acetonitrile was removed by concentration, and the mixture was extracted with dichloromethane to separate the organic phase. The organic phase was dried with anhydrous sodium sulfate and the solvent was removed by vacuum evaporation to obtain the plasticizer.

[0036] Example 1 An antibacterial and antioxidant edible coating comprises the following components in parts by weight: 0.6 parts nanocellulose, 0.4 parts chitosan, 0.4 parts composite antioxidant of Preparation Example 1, 0.6 parts cephalosporin antimicrobial peptide, 0.4 parts plasticizer of Preparation Example 5, and 92 parts water.

[0037] This embodiment also provides a method for preparing the above-mentioned antibacterial and antioxidant edible coating, the steps of which are as follows: Nanocellulose, plasticizer, and chitosan were added to water and stirred at 70°C for 1.5 h. Then, a composite antioxidant and cephalosporin antimicrobial peptide were added and stirred for 15 min. Emulsification (5 min) and vacuum degassing (8 min) were then performed sequentially to obtain a coating liquid. Food samples were immersed in the coating liquid for 8 s, and after drying, the antibacterial and antioxidant edible coating was obtained.

[0038] Example 2 An antibacterial and antioxidant edible coating comprises the following components in parts by weight: 0.5 parts nanocellulose, 0.3 parts chitosan, 0.3 parts composite antioxidant of Preparation Example 2, 0.5 parts cephalosporin antimicrobial peptide, 0.3 parts plasticizer of Preparation Example 6, and 95 parts water.

[0039] This embodiment also provides a method for preparing the above-mentioned antibacterial and antioxidant edible coating, the steps of which are as follows: Nanocellulose, plasticizer, and chitosan were added to water and stirred at 75°C for 1 h. Then, a composite antioxidant and cephalosporin antimicrobial peptide were added and stirred for 10 min. Emulsification (5 min) and vacuum degassing (5 min) were then performed sequentially to obtain a coating liquid. Food samples were immersed in the coating liquid for 5 s and then removed to obtain the antibacterial and antioxidant edible coating.

[0040] Example 3 An antibacterial and antioxidant edible coating comprises the following components in parts by weight: 0.8 parts nanocellulose, 0.5 parts chitosan, 0.5 parts composite antioxidant of Preparation Example 3, 0.8 parts cephalosporin antimicrobial peptide, 0.5 parts plasticizer of Preparation Example 7, and 90 parts water.

[0041] This embodiment also provides a method for preparing the above-mentioned antibacterial and antioxidant edible coating, the steps of which are as follows: Nanocellulose, plasticizer, and chitosan were added to water and stirred at 75°C for 2 h. Then, a composite antioxidant and cephalosporin antimicrobial peptide were added and stirred for 20 min. Emulsification (5 min) and vacuum degassing (10 min) were then performed sequentially to obtain a coating liquid. Food samples were immersed in the coating liquid for 10 s, removed, and dried to obtain the antibacterial and antioxidant edible coating.

[0042] Comparative Example 1 The content of Comparative Example 1 is basically the same as that of Example 1, except that the plasticizer of Example 1 is replaced with an equal amount of glycerin.

[0043] Comparative Example 2 The content of Comparative Example 2 is basically the same as that of Example 1, except that the composite antioxidant in Example 1 is replaced with the composite antioxidant in Preparation Example 4.

[0044] Structural characterization FT-IR tests were performed on the soybean lecithin, chlorinated soybean lecithin, and modified soybean lecithin in Example 1, and the results are as follows: Figure 1-3 As shown.

[0045] Figure 1 The image shows the FT-IR spectrum of soybean lecithin. Figure 2 The image shows the FT-IR spectrum of chlorinated soybean lecithin. Figure 3 The image shows the FT-IR spectrum of modified soybean lecithin. Figure 1-3 A comparison shows that, compared to soybean lecithin, chlorinated lecithin has a lower concentration at 3100 cm⁻¹. -1 and 1620cm -1 The characteristic absorption peak of the unsaturated double bond in the vicinity was significantly weakened, while at 762 cm⁻¹... -1A new absorption peak appears at 2925 cm⁻¹, which can be attributed to the stretching vibration of the C-Cl bond formed after the double bond is chlorinated with hypochlorous acid; compared with chlorinated lecithin, modified soybean lecithin shows a higher absorption peak at 2925 cm⁻¹. -1 and 2854 cm -1 The absorption peak at 1120 cm⁻¹ was significantly enhanced, which is attributed to the increased alkyl chain content after the introduction of thymol; -1 A characteristic absorption peak appears at 1621 cm⁻¹, corresponding to the stretching vibration of the COC ether bond; -1 The increased peak intensity is related to the aromatic ring structure in the notopterygium molecule; 762 cm⁻¹ -1 The absorption peak intensity is basically consistent with that of soybean lecithin, indicating that the chlorine atoms introduced into chlorinated lecithin have been consumed. These results demonstrate that the present invention successfully prepared modified soybean lecithin.

[0046] Experimental Example 1 The encapsulation efficiency of the composite antioxidants obtained in Preparation Examples 1-4 was determined using the following method: Weigh 10 mg of the compound antioxidants from Preparation Examples 1-4, reconstitute them with 1.0 mL of PBS, and centrifuge at 15000 rpm for 30 min at 4℃. Dilute the supernatant appropriately and measure the absorbance at 350 nm using ultraviolet spectrophotometry. Calculate the free drug content by substituting the absorbance into the bamboo leaf flavonoid standard curve. Separately weigh 10 mg of the same batch of sample, dissolve it thoroughly in anhydrous ethanol, and determine the total drug content using the same method. The encapsulation efficiency was calculated using the formula: Encapsulation efficiency = [(Total drug content - Free drug content) / Total drug content] × 100%. The results are shown in Table 1.

[0047] Table 1 As can be seen from Table 1, the encapsulation efficiency of the composite antioxidant in Preparation Example 1 reached 89.3%, which was significantly higher than that of Preparation Example 4 (54.6%), indicating that the modified soybean lecithin of the present invention can significantly improve the encapsulation capacity of liposomes for bamboo leaf flavonoids.

[0048] Experimental Example 2 The barrier and antibacterial properties of the coatings obtained in Examples 1-3 and Comparative Examples 1-2 were determined using the following methods: (1) Barrier performance: The water vapor barrier performance was tested according to GB1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets by Cup Weight Gain and Weight Loss Method"; the oxygen barrier performance was tested using an oxygen permeameter. The specific method was as follows: one side of the coated film was filled with pure oxygen, and the other side was evacuated. Due to the osmotic pressure difference between the two sides of the film, oxygen permeated through the pure oxygen into the vacuum side. The oxygen barrier performance of the preservation coating could be obtained by monitoring the pressure change on the vacuum side; the results are shown in Table 2.

[0049] (2) Antibacterial properties: The coating liquids prepared in Examples 1-3 and Comparative Examples 1-2 were poured into polytetrafluoroethylene templates and dried at room temperature for 48 h. The films were then peeled off and circular films with a diameter of 6 mm were made using a punch for later use.

[0050] According to the WS / T 650-2019 testing standard, *E. coli* was inoculated onto nutrient agar medium for culture. Then, four of the aforementioned membranes were affixed to the surface of contaminated plates, with 6.0 mm diameter sterile blank filter paper discs serving as negative controls. After incubation at 37 ℃ for 18 h, the diameter of the inhibition zone was measured. The test results are shown in Table 2.

[0051] Table 2 The results in Table 2 show that the coating films of Examples 1-3 of the present invention have excellent water vapor and oxygen barrier properties, and the diameter of the inhibition zone against Escherichia coli reaches 8.79–9.26 mm, which is significantly higher than that of the negative control group (6.05 mm). The antibacterial performance of Comparative Example 1 is comparable to that of the Examples, but the barrier performance is significantly reduced due to the enhanced hydrophilicity of the plasticizer. The barrier and antibacterial performance of Comparative Example 2 are comparable to those of the Examples. This indicates that the plasticizer and composite antioxidant of the present invention do not affect the inherent antibacterial activity of the coating while improving the barrier and antioxidant properties.

[0052] Experimental Example 3 Testing the effect of coating on strawberry preservation Fresh strawberries free from pests, diseases, and mechanical damage were selected. The strawberries were immersed in the coating solutions of Examples 1-3 or Comparative Examples 1-2 for 10 seconds, then removed and quickly dried in a fume hood before being placed at room temperature. Uncoated strawberries were selected as blank controls, and the changes were detected after storage at 25°C and 50% relative humidity for 15 days.

[0053] (1) Rot rate: The rot rate is calculated according to the formula: rot rate = (A1 / A2) × 100%, where A1 is the number of rotten strawberries and A2 is the total number of strawberries; the results are shown in Table 3.

[0054] (2) Weight loss rate: The strawberries were weighed and recorded on day 0 of storage. The weight was recorded again after 15 days. n The weight loss rate w (%) is calculated using the following formula: w = [(m0 - m n [(m0)×100%, 5 strawberries per group, average value of each group, see Table 3 for results.]

[0055] (3) Hardness: A physical property tester was used with a P / 2 probe at a test speed of 0.5 mm / s. The test was performed by piercing the equatorial part of the strawberry and recording the maximum peak force (N). The results are shown in Table 3.

[0056] (4) The VC content of strawberries was determined by titration method of 2,6-dichlorophenolindophenol in GB 5009.86-2016 "National Food Safety Standard for Determination of Ascorbic Acid in Food". The VC retention rate (%) was calculated according to the formula = VC content after storage / initial VC content × 100%. The results are shown in Table 3.

[0057] Table 3 The results in Table 3 show that the coatings in Examples 1-3 of the present invention can significantly reduce the rot rate and weight loss of strawberries during storage, maintain fruit firmness and VC content, and have a significantly better preservation effect than comparative examples 1-2 and the blank control group.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. An antibacterial, antioxidant, and edible coating, characterized in that, It includes the following components in parts by weight: 0.5-0.8 parts nanocellulose, 0.3-0.5 parts chitosan, 0.3-0.5 parts compound antioxidant, 0.5-0.8 parts cephalosporin antimicrobial peptide, 0.3-0.5 parts plasticizer, and 90-95 parts water; The compound antioxidant is a liposome encapsulated with natural antioxidants, formed from modified soybean lecithin and cholesterol.

2. The antibacterial, antioxidant, and edible coating according to claim 1, characterized in that, The preparation process of the modified soybean lecithin is as follows: (1) Dissolve soybean lecithin in a solvent, then add a chlorine-containing oxidant to carry out a chlorination reaction to obtain chlorinated lecithin; (2) The chlorinated lecithin and citric acid were reacted under the action of an alkaline catalyst to obtain the modified soybean lecithin.

3. The antibacterial, antioxidant, and edible coating according to claim 2, characterized in that, The chlorine-containing oxidant in step (1) is sodium hypochlorite; the chlorination reaction is carried out for 1-3 h under pH 4-5 conditions; the solvent is n-hexane; the mass ratio of soybean lecithin to chlorine-containing oxidant is 1:(0.1-0.2).

4. The antibacterial, antioxidant, and edible coating according to claim 2, characterized in that, The alkaline catalyst in step (2) is sodium carbonate; the solvent for the reaction is chloroform, the temperature is 40-50℃, and the time is 3-5 h; the mass ratio of chlorinated lecithin, citric acid and alkaline catalyst is 1:(0.3-0.5):(0.2-0.3).

5. The antibacterial, antioxidant, and edible coating according to claim 1, characterized in that, The mass ratio of the modified soybean lecithin, cholesterol, and natural antioxidant is 1:(0.15-0.25):(0.05-0.1); the natural antioxidant is at least one of bamboo leaf flavonoids, pine bark extract, ginkgo leaf extract, or phytosterols.

6. The antibacterial, antioxidant, and edible coating according to claim 1, characterized in that, The preparation process of the plasticizer is as follows: (a) In the presence of p-toluenesulfonic acid, p-hydroxycinnamic acid and glycerol are esterified to obtain intermediate 1; the structural formula of intermediate 1 is as follows: (b) Under acidic conditions, intermediate 1 is subjected to a formylation reaction with hexamethylenetetramine to obtain intermediate 2; the structural formula of intermediate 2 is as follows: (c) Under the action of an organic catalyst, intermediate 2 is reacted with 2-aminocyclohexanol to form a 4,5-dihydrooxazole ring structure to obtain the plasticizer; the structural formula of the plasticizer is as follows: 。 7. The antibacterial, antioxidant, and edible coating according to claim 1, characterized in that, The molar ratio of p-hydroxycinnamic acid, glycerol and p-toluenesulfonic acid in step (a) is 1:(3-4):(0.0125-0.025); the esterification reaction is carried out at a temperature of 90-110℃ for 8-16 h.

8. The antibacterial, antioxidant, and edible coating according to claim 1, characterized in that, The formylation reaction process described in step (b) is as follows: first react in acetic acid at 90-100℃ for 2-3 h, then add hydrochloric acid and continue to react at 90-100℃ for 1-1.5 h; the molar ratio of intermediate 1 to hexamethylenetetramine is 1:(1.5-2).

9. The antibacterial, antioxidant, and edible coating according to claim 1, characterized in that, The organic catalyst in step (c) is N,N,N',N'-tetrabromobenzene-1,3-disulfonamide; the molar ratio of the organic catalyst, intermediate 2 and 2-aminocyclohexanol is (0.027-0.035):1:(1.5-2); the reaction time is 3-5 h.

10. A method for preparing an antibacterial and antioxidant edible coating according to any one of claims 1-9, characterized in that, Includes the following steps: Nanocellulose, plasticizer, and chitosan are added to water and stirred. Then, a composite antioxidant and cephalosporin antimicrobial peptide are added and stirred evenly. After emulsification and vacuum degassing, a coating liquid is obtained. The coating liquid is then applied and dried to obtain the final product.

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