Bio-based composite film coating liquid for egg preservation as well as preparation method, use method and application of bio-based composite film coating liquid

Abstract

The invention provides a bio-based composite film coating liquid for egg preservation, and a preparation method, a use method and application thereof. The bio-based composite film coating liquid comprises a nanocellulose solution, coconut oil, cinnamyl aldehyde, sophorolipid and glycerol. The preparation method comprises the following steps: mixing and stirring a nanocellulose solution and coconut oil under a water bath heating condition to obtain an intermediate solution; adding cinnamyl aldehyde, sophorolipid and glycerol into the intermediate solution, and stirring at a high speed to obtain the bio-based composite coating liquid. The bio-based composite coating liquid for prolonging the shelf life of eggs stored at normal temperature is prepared from the nano cellulose solution, the coconut oil, the cinnamyl aldehyde, the sophorolipid and the glycerol as raw materials, and a film layer formed after the bio-based composite coating liquid is sprayed on the surfaces of the eggs to form a film has excellent barrier property and antibacterial property; after the bio-based composite coating liquid provided by the invention is sprayed on eggs, the eggs can be kept at the quality of grade A or above for at least four weeks.

Description

Technical Field

[0001] The invention belongs to the technical field of egg preservation and relates to a bio-based composite coating liquid for egg preservation, a preparation method, a use method and application thereof. Background Art

[0002] Eggs have become an important part of people's daily diet due to their rich nutritional value. However, the preservation of eggs has always been a challenging problem. Due to the tiny pores on the surface of eggs, bacteria and moisture in the air can enter the eggs through these pores, causing them to deteriorate. In addition, eggs are easily mechanically damaged during production and transportation, which further increases the difficulty of preservation.

[0003] Traditional methods of preserving eggs mainly include refrigeration and coating. The refrigeration method inhibits the growth and reproduction of microorganisms by low temperature, thereby extending the shelf life of eggs. However, the refrigeration method requires a lot of energy and equipment investment, is costly, and is difficult to implement in areas without electricity or with insufficient electricity. The coating method is to prevent the invasion of external bacteria and moisture by coating a layer of protective film on the surface of the eggs. Commonly used coating materials include chitosan, soy protein isolate, propolis, etc. Although these materials have a certain preservation effect, they often have problems such as uneven coating and short shelf life.

[0004] In recent years, as people pay more and more attention to food safety and preservation technology, new egg preservation technologies continue to emerge. For example, the method of using plant essential oils to preserve eggs has attracted widespread attention due to its natural and non-toxic properties. Plant essential oils have a broad-spectrum antibacterial effect and can effectively inhibit the growth of microorganisms on the surface of eggs. In addition, some new coating materials, such as modified polyvinyl alcohol and calcium preparations, also show good preservation effects. These materials can not only form a uniform protective film, but also adjust the gas environment inside the egg, thereby achieving a better preservation effect.

[0005] However, the existing egg preservation technology still has some shortcomings. For example, some coating materials are easy to decompose under high temperature environment, affecting the preservation effect; some preservation methods are complicated to operate and costly. Therefore, developing an egg preservation technology with low cost, simple operation and excellent preservation effect is still a technical problem that needs to be solved urgently. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a bio-based composite coating liquid for preserving eggs, a preparation method, a use method and purposes thereof. The present invention uses nanocellulose solution, coconut oil, cinnamaldehyde, sophorolipids and glycerol as raw materials to prepare a bio-based composite coating liquid for extending the shelf life of eggs when stored at room temperature. The film layer formed after spraying on the surface of the eggs has excellent barrier properties and antibacterial properties. After spraying the eggs with the bio-based composite coating liquid provided by the present invention, the eggs can be kept at a quality of above Grade A for at least four weeks.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a bio-based composite coating liquid for preserving eggs, wherein the bio-based composite coating liquid comprises a nanocellulose solution, coconut oil, cinnamaldehyde, sophorolipids and glycerol.

[0009] The present invention uses nanocellulose solution, coconut oil, cinnamaldehyde, sophorolipids and glycerol as raw materials to prepare a bio-based composite coating liquid for extending the shelf life of eggs when stored at room temperature. The film layer formed after spraying on the surface of the eggs has excellent barrier properties and antibacterial properties. After the eggs are sprayed with the bio-based composite coating liquid provided by the present invention, the quality of the eggs can be maintained at or above Grade A for at least four weeks.

[0010] The present invention adds an appropriate amount of nanocellulose to the bio-based composite coating liquid, which is beneficial to improving the mechanical properties and barrier properties of the film layer. Nanocellulose is a fiber filament structure with a high aspect ratio. The filamentous nanocellulose forms a three-dimensional network structure through physical cross-entanglement, which can extend the diffusion path of the gas in the film layer, thereby improving the barrier properties of the film layer and reducing the weight loss rate of eggs during storage. In addition, nanocellulose is a lightweight and high-strength material. After adding it to the bio-based composite coating liquid, the mechanical strength of the coating can be significantly enhanced, effectively preventing the film layer from being damaged due to collision during the transportation and storage of eggs after preservation treatment.

[0011] The present invention adds an appropriate amount of glycerol to the bio-based composite coating liquid. The glycerol can penetrate into the nanocellulose matrix as a plasticizer, so that the interaction force between the nanocellulose molecular chains is reduced, the nanocellulose molecular chains are activated and easy to slide, and the fluidity of the nanocellulose molecular chains is increased, so that the toughness and elasticity of the film layer are improved.

[0012] The present invention can significantly improve the barrier property and antibacterial property of the film layer after adding cinnamaldehyde to the bio-based composite coating liquid. This is because, on the one hand, cinnamaldehyde has good antibacterial activity, and adding an appropriate amount of cinnamaldehyde to the bio-based composite coating liquid can improve the antibacterial property of the film layer; on the other hand, cinnamaldehyde also has certain hydrophobic properties, and an appropriate amount of cinnamaldehyde dispersed in a three-dimensional network structure formed by nanocellulose can effectively hinder the passage of water molecules; on the other hand, cinnamaldehyde has good biocompatibility and can enhance the cross-linking degree of the membrane matrix, improve the membrane structure, and improve the density of the membrane layer. By adding cinnamaldehyde, the antibacterial property and barrier property of the membrane layer can be greatly improved.

[0013] Sophorolipids, a secondary metabolite of microorganisms, are a type of glycolipid biosurfactant obtained by yeast fermentation using glucose and vegetable oil. On the one hand, sophorolipids have physical and chemical properties such as reducing surface tension, emulsification, dispersion, solubilization, and moisturizing. On the other hand, sophorolipids have biological activities such as antibacterial and bactericidal activities. The present invention adds sophorolipids to the bio-based composite coating liquid, and after spraying it on the surface of the egg, the film layer can be evenly and tightly attached to the surface of the eggshell, thereby greatly extending the shelf life of the eggs.

[0014] The present invention simultaneously adds cinnamaldehyde and sophorolipids to the bio-based composite coating liquid, and the two can produce a synergistic effect, significantly improving the antibacterial and antibacterial ability of the film layer. This is because, on the one hand, the sophorolipid molecules can self-assemble to form micelles with a double-layer structure, and the cinnamaldehyde that is insoluble in water can be loaded into its interlayer structure. The sophorolipid micelles with a double-layer structure can cross the bacterial cell membrane with a similar structure, and deliver the cinnamaldehyde molecules to the inside of the bacterial cells. The addition of sophorolipids makes it possible to exert a significant antibacterial effect when a small amount of cinnamaldehyde is added. By using a low dose of cinnamaldehyde, the antibacterial concentration required inside the bacterial cells can be achieved. On the other hand, sophorolipids, as biosurfactants, can change their hydrophobicity after adsorption on the surface of eggs, affecting the adsorption process of bacteria on the surface of eggs, thereby inhibiting the growth of pathogens and destroying the integrity of bacterial biofilms. Since sophorolipids themselves have certain antibacterial ability, when cinnamaldehyde and sophorolipids are used in combination, bacteria need to simultaneously resist two antibacterial drugs with different antibacterial mechanisms. Therefore, the combination of the two can greatly reduce the possibility of bacterial survival and the formation of bacterial resistance.

[0015] As a preferred technical solution of the present invention, the solid content of the nanocellulose solution is 0.3-0.8wt%, for example, it can be 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt%, 0.5wt%, 0.55wt%, 0.6wt%, 0.65wt%, 0.7wt%, 0.75wt% or 0.8wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] As a preferred technical solution of the present invention, the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to the coconut oil is 1:(0.5-2), for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9 or 1:2.0, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] The present invention particularly limits the mass ratio of the dry weight of nanocellulose to coconut oil in the nanocellulose solution to 1: (0.5-2), and as the amount of coconut oil added increases, the moisture barrier capacity of the film layer shows a trend of first increasing and then decreasing. When the amount of coconut oil added is lower than the lower limit of the range defined by the present invention, the moisture barrier performance of the film layer formed after spraying and film formation will be too poor; when the amount of coconut oil added exceeds the upper limit of the range defined by the present invention, the nanocellulose will not be able to wrap the coconut oil droplets well, resulting in a decrease in the stability of the bio-based composite coating solution, and at the same time, the coconut oil will aggregate during film formation, resulting in a decrease in the moisture barrier capacity of the film layer formed after spraying and film formation.

[0018] As a preferred technical solution of the present invention, the added amount of the cinnamaldehyde is 0.025-0.05wt% of the mass of the nanocellulose solution, for example, it can be 0.025wt%, 0.03wt%, 0.032wt%, 0.034wt%, 0.036wt%, 0.038wt%, 0.04wt%, 0.042wt%, 0.044wt%, 0.046wt%, 0.048wt% or 0.05wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] The present invention specifically limits the addition amount of cinnamaldehyde to 0.025-0.05wt% of the mass of the nanocellulose solution. As the addition amount of cinnamaldehyde increases, the moisture barrier capacity of the film layer shows a trend of first increasing and then decreasing. This is because cinnamaldehyde has hydrophobic properties, and an appropriate amount of cinnamaldehyde dispersed in a three-dimensional network structure formed by nanocellulose can effectively hinder the passage of water molecules. When the addition amount of cinnamaldehyde is within the range defined by the present invention, as the addition amount of cinnamaldehyde increases, the water vapor permeability coefficient of the film layer gradually decreases. When the addition amount of cinnamaldehyde exceeds the upper limit of the range defined by the present invention, too much cinnamaldehyde will weaken the polymerization force between the large components, and the excessive cinnamaldehyde will aggregate with coconut oil, resulting in uneven distribution of hydrophobic components in the film layer, thereby reducing the compactness of the film layer, resulting in the water vapor permeability coefficient of the film layer not decreasing but increasing.

[0020] As a preferred technical solution of the present invention, the amount of the sophorolipid added is 0.1-0.5wt% of the mass of the nanocellulose solution, for example, it can be 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.35wt%, 0.4wt%, 0.45wt% or 0.5wt%, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] The present invention specifically limits the addition amount of sophorolipids to 0.1-0.5wt% of the mass of the nanocellulose solution. When the addition amount of sophorolipids is lower than the lower limit of the range defined by the present invention, the surface tension of the bio-based composite coating liquid will be greater than the critical surface energy of the eggshell, so that the bio-based composite coating liquid cannot be evenly attached to the surface of the eggshell, and the thickness of the formed film layer is uneven; when the addition amount of sophorolipids exceeds the upper limit of the range defined by the present invention, the production cost of the bio-based composite coating liquid will increase, and there may be certain health risks.

[0022] As a preferred technical solution of the present invention, the added amount of the glycerol is 25-35wt% of the total mass of the dry weight of the nanocellulose in the nanocellulose solution and the coconut oil, for example, it can be 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, 31wt%, 32wt%, 33wt%, 34wt% or 35wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In a second aspect, the present invention provides a method for preparing the bio-based composite coating liquid for egg preservation according to the first aspect, the preparation method comprising:

[0024] The nanocellulose solution and coconut oil are mixed and stirred under a water bath heating condition to obtain an intermediate solution; cinnamaldehyde, sophorolipids and glycerol are added to the intermediate solution, and the bio-based composite coating solution is obtained after high-speed stirring.

[0025] As a preferred technical solution of the present invention, the temperature of the water bath heating is 30-40°C, for example, it can be 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C or 40°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional examples, the mixing and stirring rotation speed is 300-400 rpm, for example, it can be 300 rpm, 310 rpm, 320 rpm, 330 rpm, 340 rpm, 350 rpm, 360 rpm, 370 rpm, 380 rpm, 390 rpm or 400 rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In some optional examples, the mixing and stirring time is 30 to 40 minutes, for example, it can be 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes or 40 minutes, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] In some optional examples, the rotation speed of the high-speed stirring is 15000-20000 rpm, for example, it can be 15000 rpm, 15500 rpm, 16000 rpm, 16500 rpm, 17000 rpm, 17500 rpm, 18000 rpm, 18500 rpm, 19000 rpm, 19500 rpm or 20000 rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0029] In some optional examples, the high-speed stirring time is 3 to 5 minutes, for example, it can be 3.0 minutes, 3.2 minutes, 3.4 minutes, 3.6 minutes, 3.8 minutes, 4.0 minutes, 4.2 minutes, 4.4 minutes, 4.6 minutes, 4.8 minutes or 5.0 minutes, but it is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0030] In a third aspect, the present invention provides a method for using the bio-based composite coating liquid for egg preservation according to the first aspect, the method comprising:

[0031] Fresh eggs without cracks on the surface are selected, washed and air-dried, and the bio-based composite coating liquid prepared in this embodiment is sprayed on the surface of the eggs at least once, and then air-dried and stored at room temperature.

[0032] In a fourth aspect, the present invention provides a use of the bio-based composite coating liquid for preserving eggs as described in the first aspect, wherein the bio-based composite coating liquid is used to extend the shelf life of eggs when stored at room temperature.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention uses nanocellulose solution, coconut oil, cinnamaldehyde, sophorolipids and glycerol as raw materials to prepare a bio-based composite coating liquid for extending the shelf life of eggs when stored at room temperature. The film layer formed after spraying on the surface of the eggs has excellent barrier properties and antibacterial properties. After the eggs are sprayed with the bio-based composite coating liquid provided by the present invention, the quality of the eggs can be maintained at or above Grade A for at least four weeks.

[0035] The present invention adds an appropriate amount of nanocellulose to the bio-based composite coating liquid, which is beneficial to improving the mechanical properties and barrier properties of the film layer. Nanocellulose is a fiber filament structure with a high aspect ratio. The filamentous nanocellulose forms a three-dimensional network structure through physical cross-entanglement, which can extend the diffusion path of the gas in the film layer, thereby improving the barrier properties of the film layer and reducing the weight loss rate of eggs during storage. In addition, nanocellulose is a lightweight and high-strength material. After adding it to the bio-based composite coating liquid, the mechanical strength of the coating can be significantly enhanced, effectively preventing the film layer from being damaged due to collision during the transportation and storage of eggs after preservation treatment.

[0036] The present invention adds an appropriate amount of glycerol to the bio-based composite coating liquid. The glycerol can penetrate into the nanocellulose matrix as a plasticizer, so that the interaction force between the nanocellulose molecular chains is reduced, the nanocellulose molecular chains are activated and easy to slide, and the fluidity of the nanocellulose molecular chains is increased, so that the toughness and elasticity of the film layer are improved.

[0037] The present invention can significantly improve the barrier property and antibacterial property of the film layer after adding cinnamaldehyde to the bio-based composite coating liquid. This is because, on the one hand, cinnamaldehyde has good antibacterial activity, and adding an appropriate amount of cinnamaldehyde to the bio-based composite coating liquid can improve the antibacterial property of the film layer; on the other hand, cinnamaldehyde also has certain hydrophobic properties, and an appropriate amount of cinnamaldehyde dispersed in a three-dimensional network structure formed by nanocellulose can effectively hinder the passage of water molecules; on the other hand, cinnamaldehyde has good biocompatibility and can enhance the cross-linking degree of the membrane matrix, improve the membrane structure, and improve the density of the membrane layer. By adding cinnamaldehyde, the antibacterial property and barrier property of the membrane layer can be greatly improved.

[0038] Sophorolipids, a secondary metabolite of microorganisms, are a type of glycolipid biosurfactant obtained by yeast fermentation using glucose and vegetable oil. On the one hand, sophorolipids have physical and chemical properties such as reducing surface tension, emulsification, dispersion, solubilization, and moisturizing. On the other hand, sophorolipids have biological activities such as antibacterial and bactericidal activities. The present invention adds sophorolipids to the bio-based composite coating liquid, and after spraying it on the surface of the egg, the film layer can be evenly and tightly attached to the surface of the eggshell, thereby greatly extending the shelf life of the eggs.

[0039] The present invention simultaneously adds cinnamaldehyde and sophorolipids to the bio-based composite coating liquid, and the two can produce a synergistic effect, significantly improving the antibacterial and antibacterial ability of the film layer. This is because, on the one hand, the sophorolipid molecules can self-assemble to form micelles with a double-layer structure, and the cinnamaldehyde that is insoluble in water can be loaded into its interlayer structure. The sophorolipid micelles with a double-layer structure can cross the bacterial cell membrane with a similar structure, and deliver the cinnamaldehyde molecules to the inside of the bacterial cells. The addition of sophorolipids makes it possible to exert a significant antibacterial effect when a small amount of cinnamaldehyde is added. By using a low dose of cinnamaldehyde, the antibacterial concentration required inside the bacterial cells can be achieved. On the other hand, sophorolipids, as biosurfactants, can change their hydrophobicity after adsorption on the surface of eggs, affecting the adsorption process of bacteria on the surface of eggs, thereby inhibiting the growth of pathogens and destroying the integrity of bacterial biofilms. Since sophorolipids themselves have certain antibacterial ability, when cinnamaldehyde and sophorolipids are used in combination, bacteria need to simultaneously resist two antibacterial drugs with different antibacterial mechanisms. Therefore, the combination of the two can greatly reduce the possibility of bacterial survival and the formation of bacterial resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A process flow chart for preparing a bio-based composite coating solution provided in Examples 1-11 of the present invention;

[0041] Figure 2 A bar graph showing changes in egg weight loss rates of eggs provided in Example 1, the comparative example and the blank example of the present invention, obtained by testing on the 7th, 14th, 21st and 35th days of storage;

[0042] Figure 3 A bar graph showing changes in the Haugh units of eggs obtained by testing the eggs provided in Example 1, the comparative example and the blank example on the 7th, 14th, 21st and 35th days of storage;

[0043] Figure 4 A bar graph showing changes in the egg yolk index of eggs provided in Example 1, the comparative example and the blank example of the present invention, obtained by testing on the 7th, 14th, 21st and 35th days of storage;

[0044] Figure 5 These are the colony culture pictures of the blank group and the experimental group after the antibacterial performance test. DETAILED DESCRIPTION

[0045] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments recorded herein.

[0046] Example 1

[0047] This embodiment provides a method for preparing a bio-based composite coating liquid for egg preservation, such as Figure 1 As shown, the preparation method comprises the following steps:

[0048] (1) mixing a nanocellulose solution with a solid content of 0.3 wt% and coconut oil in a water bath at 30° C. and stirring at a speed of 400 rpm for 30 min, wherein the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to the coconut oil is 1:0.5, and mixing them evenly to obtain an intermediate solution;

[0049] (2) Add cinnamaldehyde, sophorolipids and glycerol to the intermediate solution, wherein the amount of cinnamaldehyde added is 0.025wt% of the mass of the nanocellulose solution, the amount of sophorolipids added is 0.1wt% of the mass of the nanocellulose solution, and the amount of glycerol added is 25wt% of the total mass of the dry weight of nanocellulose and coconut oil in the nanocellulose solution, and stir at a high speed of 15000 rpm for 5 minutes to obtain the bio-based composite coating solution.

[0050] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0051] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0052] Example 2

[0053] This embodiment provides a method for preparing a bio-based composite coating liquid for egg preservation, such as Figure 1 As shown, the preparation method comprises the following steps:

[0054] (1) mixing a nanocellulose solution with a solid content of 0.4 wt% and coconut oil in a water bath at 32° C. at a speed of 380 rpm for 32 min, wherein the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to the coconut oil is 1:0.8, and mixing them uniformly to obtain an intermediate solution;

[0055] (2) Add cinnamaldehyde, sophorolipids and glycerol to the intermediate solution, wherein the amount of cinnamaldehyde added is 0.03wt% of the mass of the nanocellulose solution, the amount of sophorolipids added is 0.2wt% of the mass of the nanocellulose solution, and the amount of glycerol added is 28wt% of the total mass of the dry weight of nanocellulose and coconut oil in the nanocellulose solution, and stir at a high speed of 16000 rpm for 4.5 minutes to obtain the bio-based composite coating solution.

[0056] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0057] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0058] Example 3

[0059] This embodiment provides a method for preparing a bio-based composite coating liquid for egg preservation, such as Figure 1 As shown, the preparation method comprises the following steps:

[0060] (1) mixing a nanocellulose solution with a solid content of 0.5 wt% and coconut oil in a water bath at 35° C. and stirring at a speed of 355 rpm for 35 min, wherein the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to the coconut oil is 1:1, and mixing them uniformly to obtain an intermediate solution;

[0061] (2) Add cinnamaldehyde, sophorolipids and glycerol to the intermediate solution, wherein the amount of cinnamaldehyde added is 0.04wt% of the mass of the nanocellulose solution, the amount of sophorolipids added is 0.3wt% of the mass of the nanocellulose solution, and the amount of glycerol added is 30wt% of the total mass of the dry weight of nanocellulose and coconut oil in the nanocellulose solution, and stir at a high speed of 17000 rpm for 4 minutes to obtain the bio-based composite coating solution.

[0062] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0063] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs twice, air-dried at 37° C., and stored at room temperature.

[0064] Example 4

[0065] This embodiment provides a method for preparing a bio-based composite coating liquid for egg preservation, such as Figure 1 As shown, the preparation method comprises the following steps:

[0066] (1) mixing a nanocellulose solution with a solid content of 0.6 wt% and coconut oil in a water bath at 38° C. at a speed of 320 rpm for 38 min, wherein the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to the coconut oil is 1:1.5, and mixing them uniformly to obtain an intermediate solution;

[0067] (2) Add cinnamaldehyde, sophorolipids and glycerol to the intermediate solution, wherein the amount of cinnamaldehyde added is 0.05wt% of the mass of the nanocellulose solution, the amount of sophorolipids added is 0.4wt% of the mass of the nanocellulose solution, and the amount of glycerol added is 32wt% of the total mass of the dry weight of nanocellulose and coconut oil in the nanocellulose solution, and stir at a high speed of 180000 rpm for 3.5 minutes to obtain the bio-based composite coating solution.

[0068] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0069] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs twice, air-dried at 37° C., and stored at room temperature.

[0070] Example 5

[0071] This embodiment provides a method for preparing a bio-based composite coating liquid for egg preservation, such as Figure 1 As shown, the preparation method comprises the following steps:

[0072] (1) mixing a nanocellulose solution with a solid content of 0.8 wt% and coconut oil in a water bath at 40° C. at a speed of 300 rpm for 40 min, wherein the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to the coconut oil is 1:2, and mixing them uniformly to obtain an intermediate solution;

[0073] (2) Add cinnamaldehyde, sophorolipids and glycerol to the intermediate solution, wherein the amount of cinnamaldehyde added is 0.05wt% of the mass of the nanocellulose solution, the amount of sophorolipids added is 0.5wt% of the mass of the nanocellulose solution, and the amount of glycerol added is 35wt% of the total mass of the dry weight of nanocellulose and coconut oil in the nanocellulose solution, and stir at a high speed of 20000 rpm for 3 minutes to obtain the bio-based composite coating solution.

[0074] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0075] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs once, air-dried at 37° C., and stored at room temperature.

[0076] Example 6

[0077] This embodiment provides a method for preparing a bio-based composite coating liquid for preserving eggs. The difference from the preparation method provided in Example 1 is that in step (1), the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to coconut oil is adjusted to 1:0.2, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0078] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0079] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0080] Example 7

[0081] This embodiment provides a method for preparing a bio-based composite coating liquid for preserving eggs. The difference from the preparation method provided in Example 1 is that in step (1), the mass ratio of the dry weight of nanocellulose in the nanocellulose solution to coconut oil is adjusted to 1:2.5, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0082] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0083] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0084] Example 8

[0085] This embodiment provides a method for preparing a bio-based composite coating liquid for preserving eggs. The difference from the preparation method provided in Example 1 is that in step (2), the amount of cinnamaldehyde added is 0.01wt% of the mass of the nanocellulose solution, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0086] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0087] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0088] Example 9

[0089] This embodiment provides a method for preparing a bio-based composite coating liquid for preserving eggs. The difference from Embodiment 1 is that in step (2), the amount of cinnamaldehyde added is 0.06 wt % of the mass of the nanocellulose solution, and the other process parameters and operating steps are exactly the same as those in Embodiment 1.

[0090] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0091] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0092] Example 10

[0093] This embodiment provides a method for preparing a bio-based composite coating liquid for egg preservation, which differs from Example 1 in that, in step (2), the amount of sophorolipid added is 0.05wt% of the mass of the nanocellulose solution, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0094] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0095] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0096] Embodiment 11

[0097] This embodiment provides a method for preparing a bio-based composite coating liquid for egg preservation, which differs from Example 1 in that, in step (2), the amount of sophorolipid added is 0.7wt% of the mass of the nanocellulose solution, and the other process parameters and operating steps are exactly the same as those in Example 1.

[0098] This embodiment also provides a method for preserving eggs, which specifically includes the following steps:

[0099] Fresh eggs without cracks on the surface were selected, washed and air-dried, and the bio-based composite coating liquid prepared in this example was sprayed on the surface of the eggs for three times. The eggs were air-dried at 37° C. and stored at room temperature.

[0100] Comparative Example

[0101] This comparative example provides a method for preserving eggs, which specifically comprises the following steps:

[0102] Select fresh eggs without cracks on the surface, wash them and air-dry them, spray white oil on the surface of the eggs, spray three times, air-dry them at 37℃ and store them at room temperature.

[0103] The water vapor permeability and antibacterial rate of the film layer formed by the bio-based composite coating liquid provided in Examples 1-11 were tested, and the specific test steps were as follows:

[0104] (1) Water vapor transmission rate

[0105] The water vapor barrier coefficient of the film layer is measured by the cup weight gain method of GB / T 1037-2021. Cut the film into a circle of appropriate size and measure the film thickness at points around the center of the circle. Before the test, dry the silica gel at 150°C for 1 hour, cool it to room temperature and move it into the moisture permeability cup test chamber. Place the film carefully on the moisture permeability cup, cover it with a gasket, apply vaseline around it to enhance the seal, and tighten the cup lid. Place the moisture permeability cup in a constant temperature and humidity chamber at 25°C and 60% RH for 12 hours, weigh it every 2 hours, and calculate the water vapor permeability coefficient.

[0106] (2) Antibacterial rate

[0107] The antibacterial property of the membrane layer was tested by co-culturing the membrane with E. coli. First, the E. coli culture was activated, and the absorbance of the culture medium at 600nm was taken as the benchmark. The absorbance of the activated culture was tested and diluted to 1 with PBS buffer. At this time, the number of colonies was about 10 5 CFU / mL.

[0108] A blank group and an experimental group were set up. The blank group was 2 mL of bacterial solution, and the experimental group was 2 mL of bacterial solution added with 0.2 g of the bio-based composite coating solution prepared in Example 1 and mixed thoroughly, and then co-cultured in a 37°C water bath shaker for four hours. The bacterial solution after co-culture was diluted 1000 times, and 100 μL was spread on a nutrient agar plate, and then placed in a 37°C microbial box for culture for 24 hours, and the number of colonies was calculated, and then the number of colonies in the bacterial solution after co-culture was calculated, and the antibacterial rate was calculated.

[0109] in, Figure 5 It is a colony culture diagram of the blank group and the experimental group during the antibacterial performance test. It can be seen from the figure that no obvious colonies are formed on the culture dishes of the experimental group, and obvious colonies are formed on the culture dishes of the blank group, which indicates that the bio-based composite coating liquid provided by the present invention has excellent antibacterial properties.

[0110] The test data of water vapor permeability and antibacterial rate of the film layer formed by the bio-based composite coating liquid provided in Examples 1-11 are shown in Table 1.

[0111] Blank example

[0112] The blank samples were fresh eggs without any cracks on the surface and not sprayed with any coating liquid.

[0113] The eggs after preservation treatment in Example 1 and the comparative example and the eggs provided in the blank example were tested, and the specific test steps are as follows:

[0114] (1) Weight loss rate

[0115] The present invention stores the eggs of Example 1, the comparative example and the blank example for 35 days at a temperature of 37°C, and tests the weight loss rate of the eggs on the 7th, 14th, 21st and 35th days. The bar graph of the change of the weight loss rate of the eggs is shown in FIG. Figure 2 As shown by Figure 2 It can be seen that as the storage time increases, the water inside the egg is released outward through the pores on the eggshell surface due to respiration, and gas exchange is carried out inside and outside. The weight loss rates of the eggs provided by Example 1, the comparative example and the blank example all show an upward trend. However, under the same storage period, the weight loss rate of the eggs provided by Example 1 is less than the weight loss rate of the eggs provided by the comparative example and less than the weight loss rate of the eggs provided by the blank example. In addition, as the storage time increases, the weight loss rate of the eggs provided by Example 1 increases the slowest.

[0116] (2) Haugh unit

[0117] The Haugh unit is an indicator for testing and expressing the freshness of eggs as specified in the egg standards of the U.S. Department of Agriculture. Eggs with a Haugh unit of >72 are fresh eggs (AA grade) and are suitable for use. Eggs with a Haugh unit of 60 to 72 are A grade and are edible. Eggs with a Haugh unit of 30 to 60 are B grade and are not recommended for consumption. Eggs with a Haugh unit of less than 30 are C grade and are not edible. The present invention stores the eggs of Example 1, the comparative example and the blank example for 35 days at a temperature of 37°C. The Haugh unit of the eggs is tested on the 7th, 14th, 21st and 35th days. The histogram of the change of the Haugh unit of the eggs is shown in FIG. Figure 3 As shown by Figure 3 It can be seen that as the storage time increases, the Haugh units of the eggs provided by Example 1, the comparative example and the blank example all show a downward trend, but under the same storage period, the Haugh units of the eggs provided by Example 1> the Haugh units of the eggs provided by the comparative example> the Haugh units of the eggs provided by the blank example. In addition, as the storage time increases, the rate of decrease of the Haugh units of the eggs provided by Example 1 is the slowest.

[0118] (3) Yolk Index

[0119] The fresher the egg, the higher the height of the yolk, the smaller the diameter, and the greater the yolk index. The size of the yolk index of the egg can well reflect the freshness of the egg. However, as the storage time increases, the yolk gradually changes from a nearly spherical shape to a flat shape, and the yolk index gradually decreases. The present invention stores the eggs of Example 1, the comparative example and the blank example for 35 days at a temperature of 37°C, and tests the yolk index of the eggs on the 7th, 14th, 21st and 35th days. The change bar graph of the yolk index is as follows: Figure 4 As shown by Figure 4 It can be seen that as the storage time increases, the yolk index of the eggs provided by Example 1, the comparative example and the blank example all show a downward trend, but under the same storage period, the yolk index of the eggs provided by Example 1> the yolk index of the eggs provided by the comparative example> the yolk index of the eggs provided by the blank example. In addition, as the storage time increases, the rate of decrease of the yolk index of the eggs provided by Example 1 is the slowest.

[0120] The weight loss rate, Haugh unit and yolk index of the eggs provided in Examples 1-11, Comparative Examples and Application Examples on the 35th day are shown in Table 1.

[0121] Table 1

[0122]

[0123] It can be seen from the test data provided in Table 1 that after the eggs are preserved using the bio-based composite coating liquid prepared in Examples 1-5 of the present invention, the weight loss rate of the eggs after storage for 30 days is lower than that of the eggs in Examples 6-11, the comparative examples and the blank examples, and the Haugh unit and yolk index of the eggs after storage for 30 days are higher than those of the eggs in Examples 6-11, the comparative examples and the blank examples. This indicates that the bio-based composite coating liquid provided by the present invention can effectively prevent the invasion of microorganisms and form a film layer with gas barrier properties on the surface of the eggs, thereby greatly extending the shelf life of the eggs.

[0124] It can be seen from the test results of Example 1, Example 6 and Example 7 that the various indicators of the eggs after preservation treatment in Example 6 and Example 7 are inferior to those in Example 1. This is because the amount of coconut oil added in Example 6 is too little and the amount of nanocellulose added is too much, and the amount of coconut oil added in Example 7 is too much and the amount of nanocellulose added is too little, which affects the preservation effect on the eggs.

[0125] It can be seen from the test results of Example 1, Example 8 and Example 9 that the various indicators of the eggs after the preservation treatment in Example 8 and Example 9 are inferior to those in Example 1. This is because the amount of cinnamaldehyde added in Example 8 is too small, and the amount of cinnamaldehyde added in Example 9 is too large, which affects the preservation effect on the eggs.

[0126] It can be seen from the test results of Example 1, Example 10 and Example 11 that the various indicators of the eggs after the preservation treatment in Example 10 and Example 11 are inferior to those in Example 1. This is because the amount of sophorolipid added in Example 10 is too small, and the amount of sophorolipid added in Example 11 is too large, which affects the preservation effect of the eggs.

[0127] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A bio-based composite coating liquid for egg preservation, characterized in that: The bio-based composite coating liquid comprises nanocellulose solution, coconut oil, cinnamaldehyde, sophorolipids and glycerol.

2. The bio-based composite coating liquid for egg preservation according to claim 1, characterized in that: The solid content of the nanocellulose solution is 0.3-0.8 wt %.

3. The bio-based composite coating liquid for egg preservation according to claim 1, characterized in that: The mass ratio of the dry weight of the nanocellulose in the nanocellulose solution to the coconut oil is 1:(0.5-2).

4. The bio-based composite coating liquid for egg preservation according to claim 1, characterized in that: The added amount of the cinnamaldehyde is 0.025-0.05 wt % of the mass of the nanocellulose solution.

5. The bio-based composite coating liquid for egg preservation according to claim 1, characterized in that: The addition amount of the sophorolipid is 0.1-0.5wt% of the mass of the nanocellulose solution.

6. The bio-based composite coating liquid for egg preservation according to claim 1, characterized in that: The amount of glycerol added is 25-35wt% of the total weight of the dry weight of the nanocellulose in the nanocellulose solution and the coconut oil.

7. A method for preparing the bio-based composite coating liquid for egg preservation according to any one of claims 1 to 6, characterized in that: The preparation method comprises: The nanocellulose solution and coconut oil are mixed and stirred under a water bath heating condition to obtain an intermediate solution; cinnamaldehyde, sophorolipids and glycerol are added to the intermediate solution, and the bio-based composite coating solution is obtained after high-speed stirring.

8. The preparation method according to claim 7, characterized in that: The water bath heating temperature is 30-40°C; The mixing and stirring speed is 300-400 rpm; The mixing time is 30 to 40 minutes; The rotation speed of the high-speed stirring is 15000-20000 rpm; The high-speed stirring time is 3 to 5 minutes.

9. A method for using the bio-based composite coating liquid for egg preservation according to any one of claims 1 to 6, characterized in that: The method of use includes: Fresh eggs without cracks on the surface are selected, washed and air-dried, and the bio-based composite coating liquid prepared in this embodiment is sprayed on the surface of the eggs at least once, and then air-dried and stored at room temperature.

10. Use of the bio-based composite coating liquid for preserving eggs as claimed in any one of claims 1 to 6, wherein the bio-based composite coating liquid is used to extend the shelf life of eggs when stored at room temperature.

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