Fruit and vegetable fresh-keeping composite film coating liquid and preparation method thereof

Abstract

The invention provides a fruit and vegetable fresh-keeping composite coating liquid and a preparation method thereof, and relates to the technical field of fruit and vegetable fresh-keeping. The preparation method of the fruit and vegetable fresh-keeping composite coating liquid comprises the following steps: preparing a composite emulsifier according to a mass ratio of mono-and diglycerol fatty acid ester to sucrose fatty acid ester of 2: 3, dissolving 1% by mass of the composite emulsifier in deionized water at 75 DEG C to prepare a water phase, cooling the water phase to 25 DEG C, adding 0.5% and 1% of Chinese prickly ash essential oil, carrying out magnetic stirring (2500r / min, 10min), and carrying out high-speed dispersion homogenization for 3min to obtain the fruit and vegetable fresh-keeping composite coating liquid. The preparation method comprises the following steps: preparing 0.5% and 1% oil-in-water type zanthoxylum bungeanum essential oil nano emulsion (NE) through high-pressure homogenization under the condition of 50 MPa, weighing 2% and 4% citrus pectin (CP) powder, adding deionized water, and dissolving at 70 DEG C to prepare 2% and 4% citrus pectin solutions; the preparation method comprises the following steps: mixing 1% of NE and 4% of CP in a ratio of 1: 1, adding 0.75% of glycerol as a plasticizer, magnetically stirring (2500r / min, 10min), dispersing and homogenizing at a high speed for 3min, and homogenizing at high pressure under the condition of 50MPa to obtain the fruit and vegetable fresh-keeping composite coating liquid (NE-CP). The invention is beneficial to delaying the weight loss during the storage period of fruits and vegetables, slowing down the decline speed of the appearance quality of fruits and vegetables, and delaying the senescence process.

Description

Technical Field

[0001] The invention relates to the technical field of fruit and vegetable preservation, and in particular to a fruit and vegetable preservation composite coating liquid and a preparation method thereof. Background Art

[0002] Edible coatings are made of natural edible macromolecules, with edible plasticizers, cross-linking agents, etc. added. Through intermolecular interactions, dense films are formed. They are then applied to the surface of food by dipping, spraying, and other methods to block the penetration of water vapor, oxygen, or various solutes. Studies have shown that using edible coatings on fruits and vegetables can extend their shelf life during storage. In terms of fresh-keeping effects, similar to controlled atmosphere preservation, semipermeable coating materials slow down the gas exchange between fruits and vegetables and the environment by changing the content of O2, CO2, and water on the surface of fruits and vegetables, improving the internal atmosphere of fruits and vegetables, and slowing down their respiration, reducing water loss, and maintaining their hardness and color. In addition, edible coatings can also be used as a carrier to add various food additives, such as nutrients, antioxidants, and antibacterial agents, thereby extending the shelf life of food and reducing the risk of pathogens multiplying on the surface of food. Zanthoxylum bungeanum essential oil has antibacterial properties against a variety of bacteria and fungi, and can inhibit the growth and reproduction of microorganisms such as Escherichia coli, Staphylococcus aureus, Candida albicans, and Pseudomonas aeruginosa. Its antibacterial mechanism may be that the active substances it contains can destroy the cell wall structure of bacteria and fungi, thereby causing the chemical permeability of the cell wall to decrease or even lose, and the cell membrane then lyses, causing the microorganism to lose its original morphological structure; the organelles of bacteria and fungi swell and necrotize, and DNA, RNA, protein, alkaline phosphatase (AKP), K + Mg 2+ However, the poor stability and poor hydrophilicity of Zanthoxylum bungeanum essential oil limit its practical application. Therefore, how to improve the shortcomings of Zanthoxylum bungeanum essential oil, enhance its uniform distribution effect in a hydrophilic environment, and broaden its application scenarios are the current focus of Zanthoxylum bungeanum essential oil application research. Nanoemulsion encapsulation technology can provide a transport carrier for functional substances and protect the structural functions of functional substances from being affected by the external environment. Nanoemulsion has the following advantages as a carrier system for functional factors: (1) The particle size of nanoemulsion is small, the system is uniform and stable, and the phenomenon of emulsion stratification and aggregation caused by gravity can be prevented. (2) The nanoemulsion system can use green and safe biomacromolecule emulsifiers such as polysaccharides and proteins, and can produce a uniform and stable emulsion system at a lower emulsifier dosage, which is more in line with people's requirements for food safety. (3) Nanoemulsion particles are evenly distributed and have good appearance. They are easy to add to food and beverage systems. Nanoemulsions have little effect on the texture structure and sensory properties of food, which is conducive to the application of functional substances in the food industry. Summary of the invention

[0003] Technical problem to be solved: In view of the above technical problems, the purpose of the present invention is to provide a method for preparing a composite coating liquid for fruit and vegetable preservation and its application in the preservation of cucumbers and tomatoes. By preparing the composite coating liquid for fruit and vegetable preservation, the cucumbers and tomatoes are soaked in the coating liquid and then dried, so as to effectively delay the aging process of cucumbers and tomatoes after harvest, delay the loss of weight and nutrients of cucumbers and tomatoes during storage, and improve the post-harvest preservation effect of cucumbers and tomatoes.

[0004] Technical solution: A method for preparing a composite coating liquid for preserving fruits and vegetables, comprising the following steps: S1. Prepare 1% composite emulsifier by taking mono- and di-glycerol fatty acid esters and sucrose fatty acid esters, dissolve in deionized water at 75 ° C to obtain an aqueous phase, wait for the aqueous phase to be cooled to 25 ° C, add 0.5%, 1% prickly ash essential oil, and prepare 0.5%, 1% water-in-oil type prickly ash essential oil nanoemulsion by high-speed dispersion and homogenization after magnetic stirring; S2. Weigh citrus pectin powder, add deionized water, and dissolve at 70°C to obtain 2% and 4% citrus pectin solutions; S3. Mix 1% Zanthoxylum bungeanum oil-in-water nanoemulsion with 4% citrus pectin solution, add 0.75% glycerol as a plasticizer, and prepare a fruit and vegetable fresh-keeping composite coating liquid by magnetic stirring and high-speed dispersion and homogenization. Furthermore, in step S1, the mass ratio of mono- and di-glycerol fatty acid esters to sucrose fatty acid esters is 2:3. Furthermore, in step S1, the rotation speed of the magnetic stirring is 2500 r / min, and the time is 10 min. Furthermore, in step S1, the high-pressure homogenization pressure is 50 MPa and the time is 3 minutes. Furthermore, in step S3, the volume ratio of the 1% oil-in-water type prickly ash essential oil nanoemulsion to the 4% citrus pectin solution is 1: 1. Furthermore, in step S3, the speed of the magnetic stirring is 2500 r / min, and the time is 10 min. Furthermore, in step S3, the high-pressure homogenization pressure is 50 MPa and the time is 3 minutes. Application of the fruit and vegetable fresh-keeping composite coating liquid prepared by any of the preparation methods described above in fruit and vegetable fresh-keeping. Furthermore, the fruits and vegetables include tomatoes and cucumbers. Beneficial effects: 1. The NE coating liquid prepared by the present invention can be used in tomato preservation to effectively delay the aging process of tomatoes, delay the weight loss during storage, maintain the appearance quality of tomatoes, and improve the preservation effect of tomatoes. 2. The NE-CP composite coating liquid prepared by the present invention can be used for preserving cucumbers and can effectively delay the aging process of cucumbers, delay the weight loss during storage, maintain the appearance quality of cucumbers, and improve the preservation effect of cucumbers. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 This is a graph showing the changes in appearance quality of tomatoes after they are preserved in different ways during storage; Figure 2 This is a graph showing the changes in weight loss rate of tomatoes after they are preserved in different ways during storage; Figure 3 This is a graph showing the changes in the hardness of tomatoes after they are preserved in different ways during storage; Figure 4 This is a graph showing the changes in color difference of tomatoes after they are preserved in different ways during storage; Figure 5 This is a graph showing the changes in soluble solid content of tomatoes after they are preserved in different ways during storage; Figure 6 This is a graph showing the changes in ascorbic acid content in tomatoes after they were preserved in different ways during storage; Figure 7 This is a diagram showing the changes in appearance quality of cucumbers after they are preserved in different ways during storage; Figure 8 This is a graph showing the weight loss rate of cucumbers after they are preserved in different ways during storage; Fig. 9 This is a graph showing the changes in the hardness of cucumbers after they are preserved in different ways during storage; Fig.10 This is a diagram showing the changes in color difference of cucumbers after they are preserved in different ways during storage; Fig.11 This is a graph showing the changes in soluble solid content of cucumbers after they were preserved in different ways during storage; Fig.12 This is a graph showing the changes in ascorbic acid content in cucumbers after they are preserved in different ways during storage. DETAILED DESCRIPTION The present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments: Example 1 A method for preparing a composite coating liquid for preserving fruits and vegetables comprises the following steps: S1. Take mono- and di-glycerol fatty acid esters and sucrose fatty acid esters in a mass ratio of 2:3 to prepare a composite emulsifier, take 1% of the composite emulsifier, dissolve it in 75°C deionized water to prepare an aqueous phase, wait for the aqueous phase to cool to 25°C, add 0.5% and 1% prickly ash essential oil, and stir magnetically (2500r / min, 10min). During the magnetic stirring process, the beaker mouth is covered with multiple layers of plastic wrap to keep the volume of the membrane liquid consistent with that at the beginning of the preparation; high-speed dispersion homogenization for 3min, high-pressure homogenization under 50MPa conditions to obtain 0.5% and 1% water-in-oil type prickly ash essential oil nanoemulsions (NE); S2. Weigh 2 g and 4 g of citrus pectin powder, add 98 mL of deionized water, and dissolve at 70 ° C to obtain 2% and 4% citrus pectin solutions; S3. Mix 1% pepper oil-in-water nanoemulsion and 4% citrus pectin solution in a volume ratio of 1:1, add 0.75% glycerol as a plasticizer, and stir magnetically (2500r / min, 10min). During the magnetic stirring process, cover the beaker mouth with multiple layers of plastic wrap to keep the volume of the coating liquid consistent with that at the beginning of preparation, and obtain NE-CP composite coating liquid after high-speed dispersion and homogenization (50MPa, 3min). Application of the NE coating liquid of the present invention in tomato preservation: The tomato preservation test was carried out using the 0.5% NE coating liquid prepared in Example 1: Tomatoes were washed and dried, soaked in 0.5% NE coating solution for 1 min, dried at room temperature, put into PET fresh-keeping box and wrapped with PE plastic wrap (3 parallel samples in each box), stored at 4±1℃ for 12 days, taken out every 4 days, and various indicators were measured. The parallel measurements were repeated 3 times and the average value was taken. The blank control group (CK group) did not receive any treatment The tomatoes were washed and dried, put into PET fresh-keeping boxes and wrapped with PE plastic wrap (3 parallel samples in each box), stored at 4±1℃ for 12 days, taken out every 4 days, and various indicators were measured. The parallel measurements were performed 3 times and the average value was taken. Control group 1 (CP group) used 2% CP coating solution Tomatoes were washed and dried, soaked in 2% CP coating solution for 1 min, dried at room temperature, placed in PET fresh-keeping boxes and wrapped with PE plastic wrap (3 parallel samples per box), stored at 4±1℃ for 12 days, taken out every 4 days, and various indicators were measured. The parallel measurements were repeated 3 times and the average value was taken. Control group 2 (NE-CP group) used NE-CP coating solution The tomatoes were washed and dried, soaked in NE-CP coating solution for 1 min, dried at room temperature, placed in PET fresh-keeping boxes and wrapped with PE plastic wrap (3 parallel samples per group), stored at 4±1℃ for 12 days, taken out every 4 days, and various indicators were measured. The parallel measurements were repeated 3 times and the average value was taken. Performance Test: (1) Sensory quality Tomatoes were photographed before storage and during storage sampling, and the changes in fruit appearance and color before and after storage were compared. Figure 1 The figure shows the effect of different coating treatments on the appearance quality of tomatoes during storage. As can be seen from the figure, the coating treatment groups can enhance the gloss of the tomato surface to a certain extent. On the 12th day of storage, the blank control group and the NE-CP treatment group showed slight microbial contamination, and the NE treatment group maintained a good appearance quality, indicating that the coating liquid has a certain positive effect on the maintenance of tomato appearance quality. (2) Determination of weight loss rate The weight loss rate of tomatoes during storage was determined by weighing method. Figure 2 The figure shows the changes in weight loss rate of tomatoes during storage. Due to the respiration and surface transpiration of tomatoes during storage, their water loss weight loss rate shows an upward trend. In the early stage of storage, the weight loss rates of the blank control group and each treatment group (NE, CP, and NE-CP groups) showed a slow growth trend. On the eighth day of storage, there were significant differences between the groups, and the weight loss rate of the 0.5% NE treatment group was lower than that of the blank control group. At the end of storage, the weight loss rate of the NE coating treatment group was 0.77%, which was significantly lower than that of the blank control group (1.17%). This shows that the NE coating solution can effectively delay weight loss during storage. (3) Hardness measurement The hardness of randomly selected tomatoes was measured using a texture analyzer with the following instrument parameters: 2 mm P2 probe, pre-test speed 5.00 mm / s, test speed 2.00 mm / s, post-test speed 10.00 mm / s, and test distance: 5 mm. Hardness is an important indicator for measuring the maturity and commercial value of tomato fruit. As the maturity of tomatoes increases, the pectin and cellulose content decreases, and the hardness of tomatoes gradually decreases. The effects of different coating materials on the hardness of tomato fruits during storage are as follows: Figure 3 During the entire storage process, the hardness of tomatoes in the NE and NE-CP treatment groups was always higher than that in the blank control group. On the 12th day of storage, the hardness of tomatoes in the NE and NE-CP treatment groups were 10.19N and 10.18N, respectively, which were significantly higher than those in the control group (8.84N). (4) Color difference measurement The tomato lightness, red-green, and yellow-blue values ​​were measured using a colorimeter, and the color difference ΔE was calculated using the blank control group of tomatoes as the control. Figure 4 It can be found that with the extension of storage time, the color difference value of tomatoes showed an overall upward trend. Among them, the CP treatment group had the largest color difference change value, followed by the blank control group. The NE treatment group was able to effectively maintain the color changes of tomatoes during storage. When stored for 12 days, the color difference value of the NE treatment group was significantly lower than that of the blank control group. (5) Determination of soluble solids content Randomly weigh 2g of sample, grind and determine the soluble solid content of tomatoes. Depend on Figure 4 It can be seen that the soluble solid content of tomatoes during storage showed a downward trend, and the NE and NE-CP treatment groups were able to effectively delay the decline in soluble solid content of tomatoes during storage. On the 12th day of storage, the soluble solid content of tomatoes in the NE-CP treatment group was significantly higher than that in the blank control group, indicating that NE-CP coating treatment has a positive effect on maintaining the soluble solid content of tomatoes. (6) Determination of ascorbic acid content The ascorbic acid content was determined by ultraviolet spectrophotometry. Weigh 1 g of sample, add 2 mL of 5% TCA solution, centrifuge and take 1 mL of supernatant, add 1 mL of 5% TCA solution and mix, add 1 mL of anhydrous ethanol, 0.5 mL of 85% phosphoric acid-ethanol solution, 1 mL of bathophenanthroline-ethanol solution, 0.5 mL of FeCl3 solution, and measure the absorbance at a wavelength of 543 nm. Ascorbic acid is one of the important nutrients in fruits and vegetables and has multiple biological functions. Due to the ripening effect of tomatoes, the ascorbic acid content of tomatoes increases first and then decreases during storage ( Figure 5 ). On the 4th day of storage, the ascorbic acid content of the CP and NE coating treatment groups reached its peak, and the ascorbic acid content of the other test groups reached its peak on the 8th day of storage. In the later stage of storage, the fruit entered the senescence stage, and the oxidized ascorbic acid content decreased accordingly. The ascorbic acid content of the blank control group dropped to 5.04 mg / 100g at the end of storage, the VC content of the NE treatment group was 19.46 mg / 100g, and the VC content of the NE-CP treatment group was 21.92 mg / 100g, which were 3.86 and 4.34 times that of the blank control group, respectively. Therefore, it can be preliminarily determined that the coating treatment is more effective in maintaining the ascorbic acid content in tomatoes. Application of the NE-CP composite coating liquid of the present invention in preserving cucumbers: The NE-CP composite coating liquid prepared in Example 1 was used to carry out a cucumber preservation test: Wash and dry the cucumbers, soak them in the NE-CP composite coating solution for 1 min and then dry them, put them in a PET fresh-keeping box and wrap them with PE fresh-keeping film (3 parallel samples in each box), store them at 15±1℃ for 15 days, take them out every 3 days to measure various indicators, measure them in parallel 3 times, and take the average value. The blank control group (CK group) did not receive any treatment The cucumbers were washed and dried, and then wrapped in PE plastic wrap in PET boxes (3 parallel samples in each box). They were stored at 15±1℃ for 15 days. The samples were taken out every 3 days to measure various indicators. The parameters were measured 3 times in parallel and the average values ​​were taken. Control group 1 (CP group) used 2% CP coating solution The cucumbers were washed and dried, soaked in 2% CP coating solution for 1 min and then dried, placed in a PET fresh-keeping box, wrapped with PE plastic wrap (3 parallel samples per box), stored at 15±1°C for 15 days, taken out every 3 days, and various indicators were measured. The parallel measurements were repeated 3 times and the average value was taken. Control group 2 (NE group) used 0.5% NE coating solution The cucumbers were washed and dried, soaked in 0.5% NE coating solution for 1 min and then dried, placed in a PET fresh-keeping box and wrapped with PE fresh-keeping film (3 parallel samples per box), stored at 15±1℃ for 15 days, taken out every 3 days, and various indicators were measured. The parallel measurements were repeated 3 times and the average value was taken. Performance Test: (1) Sensory quality The cucumbers were photographed before storage and during storage sampling, and the changes in appearance and color of the cucumbers before and after storage were compared. Appearance quality is one of the key factors in evaluating the quality of fruit and vegetable products. Its quality is closely related to the value of fruit and vegetable products. A decline in appearance quality will usually lead to a significant decrease in the value of the product. Figure 6 The figure shows the changes in the appearance of cucumbers during storage. It can be seen from the figure that on the 6th day of storage, nodules appeared on the surface of cucumbers in each treatment group. The cucumbers in the blank control group and the NE treatment group showed slight yellowing, while the cucumbers treated with CP and NE-CP coating did not show this phenomenon. On the 15th day of storage, the yellowing phenomenon of the blank control group and the NE treatment group was significantly aggravated, and the handles of the cucumbers in the blank control group showed obvious shrinkage, which significantly affected their commercial quality, while the color of the cucumbers treated with CP and NE-CP coatings remained better. It can be seen that CP and NE-CP coating materials have a certain positive effect on the preservation of cucumbers, and can slow down the decline in the appearance quality of cucumbers to a certain extent and maintain their commercial value. (2) Determination of weight loss rate The weight loss rate of cucumber during storage was determined by weighing method. The moisture content of fruits and vegetables is a key indicator for evaluating their freshness and plays an important role in the quality assessment of fruits and vegetables. Studies have shown that when the water loss rate of cucumbers exceeds 5%, their commercial value will be significantly reduced. Figure 7 The effect of each treatment on the weight loss rate of cucumbers during different storage periods. As can be seen from the figure, under the storage condition of 15°C, the weight loss rate of cucumbers in each treatment group showed a gradual upward trend. On the 15th day of storage, the weight loss rate of cucumbers in the blank control group reached 5.09%. The weight loss rates of cucumbers treated with CP and NE were relatively low, at 4.16% and 4.02% respectively. This shows that the semipermeable membrane formed by the two coating materials on the surface of cucumbers has a significant effect on delaying the transpiration of the cucumber surface and its own respiration, thereby effectively reducing the water loss of cucumbers during storage and delaying the weight loss of cucumbers during storage. (3) Hardness measurement The hardness of randomly selected cucumbers was measured using a texture analyzer with the following instrument parameters: 2 mm P2 probe, pre-test speed 5.00 mm / s, test speed 2.00 mm / s, post-test speed 10.00 mm / s, and test distance: 5 mm. Hardness is one of the important indicators for evaluating the storage and preservation of fruits and vegetables. Figure 8 As shown in the figure, the hardness of cucumbers showed a downward trend during storage. On the third day of storage, the hardness of cucumbers in each treatment group had changed significantly, and the hardness of cucumbers in the blank control group decreased significantly. Different coating treatments can delay the decline in cucumber hardness to a certain extent. On the 15th day of storage, the hardness of the blank control group was 40.88N. The hardness of cucumbers in the NE-CP and CP coating treatment groups was well maintained, and the hardness was 49.55 and 45.11N respectively on the 15th day of storage. (4) Color difference measurement The colorimeter was used to measure the lightness, red-green, and yellow-blue values ​​of the cucumbers, and the color difference ΔE was calculated using the untreated cucumbers as the control. The color of the cucumbers can reflect their freshness and maturity. When the cucumbers are fully mature, their appearance will change from green to yellow. Fig. 9 It can be seen that with the extension of storage time, the color of cucumbers in the control group changed the fastest, and the color difference value was significantly higher than that of other treatment groups on the 6th day of storage. On the 15th day of storage, the color difference value of cucumbers in the CP and NE-CP treatment groups was significantly lower than that of the blank control group, indicating that the two coating materials have a positive effect on maintaining the color of cucumbers. (5) Determination of soluble solids content The soluble solid content of cucumber was determined by randomly weighing 2 g of sample and grinding it. Depend on Fig.10 It can be seen that the soluble solid content of cucumbers during storage showed a trend of first increasing and then decreasing. Cucumbers undergo a ripening stage at the beginning of storage, and the polysaccharides in the fruit are gradually decomposed into monosaccharides through respiration, causing the soluble solid content to gradually increase and reach a peak. At the end of storage, the soluble solid content of cucumbers treated with NE-CP coating was 3.68°Brix, which was significantly higher than that of the blank control group (3.05°Brix), indicating that the coating treatment maintained the soluble solid content in cucumbers better. (6) Determination of ascorbic acid content The ascorbic acid content was determined by ultraviolet spectrophotometry. Weigh 1 g of sample, add 2 mL of 5% TCA solution, centrifuge and take 1 mL of supernatant, add 1 mL of 5% TCA solution and mix, add 1 mL of anhydrous ethanol, 0.5 mL of 85% phosphoric acid-ethanol solution, 1 mL of bathophenanthroline-ethanol solution, 0.5 mL of FeCl3 solution, and measure the absorbance at a wavelength of 543 nm. Ascorbic acid has multiple biological functions and is one of the important nutrients in fruits and vegetables, but it is prone to oxidation loss during the storage of fruits and vegetables. Fig.11 It can be seen that the ascorbic acid content of each group of cucumbers showed a trend of first increasing and then decreasing with the extension of storage time. On the third day of storage, the cucumbers gradually reached maturity, and the ascorbic acid content also reached a peak at this time. On the 15th day of storage, the ascorbic acid content of cucumbers in the blank control group was lower than that in each coating treatment group. Among the coating treatment groups, the ascorbic acid content of cucumbers treated with CP coating was higher than that of NE and NE-CP coating treatment groups. The ascorbic acid content of blank control group, NE, CP, and NE-CP cucumbers decreased by 81.63%, 68.13%, 65.62%, and 62.74% respectively compared with the ascorbic acid peak on the third day, indicating that the NE-CP coating treatment can better maintain the ascorbic acid content of cucumbers. The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A composite coating liquid for preserving fruits and vegetables and a preparation method thereof, characterized in that: The preparation method is as follows: S1. Prepare 1% composite emulsifier by taking mono- and di-glycerol fatty acid esters and sucrose fatty acid esters, dissolve in deionized water at 75 ° C to obtain an aqueous phase, wait for the aqueous phase to be cooled to 25 ° C, add 0.5%, 1% prickly ash essential oil, and prepare 0.5%, 1% water-in-oil type prickly ash essential oil nanoemulsion by high-speed dispersion and homogenization after magnetic stirring; S2. Weigh 2% and 4% citrus pectin powder, add deionized water, and dissolve at 70°C to obtain 2% and 4% citrus pectin solutions; S3. Mix 1% Zanthoxylum bungeanum oil-in-water nanoemulsion with 4% citrus pectin solution, add 0.75% glycerol as a plasticizer, and prepare a fruit and vegetable preservative composite coating liquid after magnetic stirring, high-speed dispersion and high-pressure homogenization.

2. The composite coating liquid for preserving fruits and vegetables and its preparation method according to claim 1, characterized in that: In the step S1, the mass ratio of mono- and di-glycerol fatty acid esters to sucrose fatty acid esters is 2:

3.

3. The composite coating liquid for preserving fruits and vegetables and its preparation method according to claim 1, characterized in that: The rotation speed of the magnetic stirring in step S1 is 2500 r / min and the time is 10 min.

4. The composite coating liquid for preserving fruits and vegetables and the preparation method thereof according to claim 1, characterized in that: In step S1, the high-pressure homogenization pressure is 50 MPa and the time is 3 minutes.

5. The composite coating liquid for preserving fruits and vegetables and the preparation method thereof according to claim 1, characterized in that: In step S3, the volume ratio of the 1% Zanthoxylum bungeanum oil-in-water nanoemulsion to the 2% citrus pectin solution is 1:

1.

6. The composite coating liquid for preserving fruits and vegetables and the preparation method thereof according to claim 1, characterized in that: The rotation speed of the magnetic stirring in step S3 is 2500 r / min and the time is 10 min.

7. The composite coating liquid for preserving fruits and vegetables and its preparation method according to claim 1, characterized in that: The high-pressure homogenization pressure in step S3 is 50 MPa and the time is 3 minutes.

8. Use of the composite coating liquid for preserving fruits and vegetables prepared by the preparation method according to any one of claims 1 to 7 in preserving fruits and vegetables.

9. The use according to claim 8, characterized in that: The fruits and vegetables include tomatoes and cucumbers.

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