An egg white protein-based antioxidant composite coating, and a preparation method and application thereof

Abstract

The application provides an egg white protein-based antioxidant composite coating as well as a preparation method and application thereof, and belongs to the technical field of food active packaging. The preparation method comprises the following steps: preparing an egg white protein solution, encapsulating resveratrol Res by a pH driving method, preparing a composite coating liquid, and preparing an antioxidant composite coating. The application adopts a composite coating form in which egg white protein is compounded with pullulan to improve the mechanical performance of the coating, and combines the pH driving method to efficiently deliver resveratrol to improve the antioxidant performance of the coating, so as to ensure the green edible property and the antioxidant property of the coating. The obtained composite coating has an encapsulation rate of Res of greater than or equal to 66%, and a DPPH free radical scavenging rate of greater than or equal to 50%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food active packaging, in particular to an egg white protein-based antioxidant composite coating and a preparation method and application thereof. BACKGROUND

[0002] Nuts are a classification of closed fruits, with hard pericarp and one or more seeds inside. Nuts are diverse, such as hazelnuts, chestnuts, almonds, pistachios, pine nuts, walnuts, and peanuts. Nuts are the essence of plants and are generally rich in nutrients, such as protein, oil, minerals, and vitamins. In addition, nuts contain monounsaturated fatty acids and polyunsaturated fatty acids, including linolenic acid and linoleic acid, and many other essential unsaturated fatty acids for the human body, which have excellent effects on human growth and development, physical fitness, and disease prevention. Nuts are dried fruits, although most nuts have shells, and the shelled nuts can be well preserved at room temperature. However, many factors can cause oxidation and spoilage of oil in nuts during storage, reducing the nutritional value and commercial value of nuts.

[0003] Edible coating refers to a packaging material that is directly formed and applied to the surface of a food component. Its formation can be divided into using coating solution or pre-melted liquid coating material for coating treatment. It can be applied to the target packaging food by brushing, spraying, or dipping. Edible coating can effectively block water loss, block some gas damage, and inhibit microbial growth to a certain extent to achieve food preservation. However, the coating itself often does not have antioxidant properties, so the preservation effect on food is limited. To improve the antioxidant effect of edible coating, antioxidants such as clove oil and thyme oil can be added to give the coating stronger antioxidant capacity. However, there are certain limitations in the current antioxidant edible coating and antioxidant soybean coating, such as weak antioxidant properties and complex operation. Therefore, it is urgent to develop new edible coatings with good film-forming effect and good antioxidant effect. SUMMARY

[0004] Therefore, the present application aims to provide an egg white protein-based antioxidant composite coating and a preparation method and application thereof. The composite coating provided by the present application has good film-forming effect, good antioxidant effect, and is edible.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A preparation method of an egg white protein-based antioxidant composite coating, comprising the following steps:

[0007] S1, preparing an egg white protein solution: dissolving glycerol in deionized water, adding egg white protein powder, stirring uniformly, adjusting the pH value to 12, and obtaining an egg white protein solution;

[0008] S2, pH-driven method for encapsulating resveratrol Res: prepare a Res solution, pour it into the egg white protein solution obtained in S1 after uniform stirring in the dark, mix evenly, stir in a water bath in the dark, adjust the pH value to 7 after taking it out, and obtain an egg white protein-Res solution;

[0009] S3, prepare a composite coating solution: add pullulan to the egg white protein-Res solution obtained in S2, stir and then remove bubbles by ultrasonic, and obtain a composite coating solution;

[0010] S4, prepare an antioxidant composite coating: immerse the object to be coated in the composite coating solution obtained in S3, soak and coat, and take it out and dry it in a cool and ventilated place.

[0011] Preferably, the concentration of the egg white protein solution in S1 is 0.04 g / mL-0.08 g / mL.

[0012] Preferably, the g:mL of glycerol to deionized water in S1 is (0.03-0.04):1.

[0013] Preferably, the concentration of the Res solution in S2 is 0.8 mg / mL.

[0014] Preferably, the volume ratio of the Res solution to the egg white protein solution in S2 is 1:1.

[0015] Preferably, the final concentration of pullulan in S3 is 0.02 g / mL-0.04 g / mL.

[0016] Preferably, the coating amount in S4 relative to the weight of the object to be coated is 0.3 mL / g-0.6 mL / g.

[0017] The application also provides an egg white protein-based antioxidant composite coating prepared by the preparation method described in the above technical solution.

[0018] The application also provides an application of the egg white protein-based antioxidant composite coating described in the above technical solution in food active packaging.

[0019] The application also provides an application of the egg white protein-based antioxidant composite coating described in the above technical solution in nut storage.

[0020] Beneficial technical effects: The application provides a preparation method of an egg white protein-based antioxidant composite coating, comprising the following steps: preparing an egg white protein solution, encapsulating resveratrol Res by a pH-driven method, preparing a composite coating liquid, and preparing an antioxidant composite coating. BRIEF DESCRIPTION OF DRAWINGS

[0021] Fig. 1 A scanning electron microscope image of the composite coating obtained in Example 1;

[0022] Fig. 2 A scanning electron microscope image of the composite coating obtained in Example 2;

[0023] Fig. 3 A scanning electron microscope image of the composite coating obtained in Example 3;

[0024] Fig. 4 A scanning electron microscope image of the coating obtained in Comparative Example 1;

[0025] Fig. 5 A scanning electron microscope image of the coating obtained in Comparative Example 2;

[0026] Fig. 6 A scanning electron microscope image of the coating obtained in Comparative Example 3. DETAILED DESCRIPTION

[0027] The application provides a preparation method of an egg white protein-based antioxidant composite coating, comprising the following steps:

[0028] S1, preparing an egg white protein solution: glycerol is dissolved in deionized water, egg white protein powder is added, stirring is uniformly performed, the pH value is adjusted to 12, and the egg white protein solution is obtained;

[0029] S2, encapsulating resveratrol Res by a pH-driven method: a Res solution is prepared, is uniformly stirred in the dark, is then poured into the egg white protein solution obtained in S1, is uniformly mixed, is stirred in a water bath in the dark, the pH value is adjusted to 7 after being taken out, and the egg white protein-Res solution is obtained;

[0030] S3, preparing a composite coating liquid: pultrusion is added to the egg white protein-Res solution obtained in S2, is stirred, and is deaerated by ultrasonic, and the composite coating liquid is obtained;

[0031] S4, preparing an antioxidant composite coating: the object to be coated is immersed in the composite coating liquid obtained in S3, is soaked and coated, and is taken out and is placed in a cool and ventilated place to dry.

[0032] The egg white protein solution is prepared by dissolving glycerol in deionized water, adding egg white protein powder, stirring uniformly, and adjusting the pH value to 12.

[0033] In the present application, the concentration of the egg white protein solution is preferably 0.04 g / mL to 0.08 g / mL, more preferably 0.06 g / mL to 0.08 g / mL; the g:mL of glycerol to deionized water is preferably (0.03 to 0.04):1, more preferably 0.036:1. The egg white protein (EWP) in the present application is a high-nutrition protein, and its digestion rate and absorption rate in the human body can reach 98%. And because the egg white protein itself contains rich disulfide bonds and sulfhydryl groups, it has excellent film-forming performance. However, when single egg white protein is used as a matrix, the coating is brittle, the mechanical properties are poor, and the cost is high, which limits its development and promotion in actual production in many aspects. The composite coating prepared by the interaction of egg white protein and polysaccharide can effectively improve the brittleness and poor mechanical properties of single protein coating. At the same time, by adding a certain proportion of glycerol, the mechanical properties of the coating can also be assisted to be enhanced.

[0034] In the present application, the adjustment of the pH value is preferably using a sodium hydroxide solution or a hydrochloric acid solution with a concentration of 1 mol / L to adjust the required pH value.

[0035] The present application adopts a pH driving method to encapsulate resveratrol Res: prepare a Res solution, stir uniformly in the dark, then pour it into the egg white protein solution obtained in the above technical solution, mix uniformly, stir in the dark in a water bath, adjust the pH value to 7 after taking it out, and obtain an egg white protein-Res solution.

[0036] In the present application, the Res solution is preferably prepared by adjusting the pH value of deionized water to 12, and then dissolving Res in it, and the concentration of the Res solution is preferably 0.8 mg / mL; the uniform stirring in the dark is preferably uniform stirring at 600 rpm to 900 rpm in the dark for 3 min to 8 min, more preferably uniform stirring at 800 rpm in the dark for 5 min; the volume ratio of the Res solution to the egg white protein solution is preferably 1:1, and the uniform stirring in the dark in a water bath is preferably uniform stirring at 800 rpm in a 45°C to 55°C water bath for 5 min to 10 min, more preferably uniform stirring at 800 rpm in a 50°C water bath for 5 min.

[0037] The pH-driven method is based on the pH-dependent solubility of the delivered substance to deliver the substance into the carrier. When the delivered substance is dissolved in an alkaline solution, the hydroxyl group ionizes, and the molecule is converted into a negatively charged state, and the water solubility is enhanced. After the solution changes to neutral, the molecule becomes a hydrophobic state. Because of the sudden change in water solubility, the delivered substance spontaneously forms nanocrystals. At the same time, the nanocrystals enter the particle solution with a hydrophobic structure driven by hydrophobic force, so that the delivered substance is encapsulated. The molecular state of the egg white protein selected in the present application is more obviously affected by the change of pH. When the pH value is greater than the isoelectric point of the egg white protein, the charge on the egg white protein molecule will induce the extension of its functional chain, so that the molecule produces an unfolded state. Therefore, when the egg white protein molecule is in an unfolded state, resveratrol is mixed with it, and after uniform mixing, the egg white protein molecule is changed by changing the pH value of the solution, and the resveratrol is wrapped.

[0038] Resveratrol (Res) is a natural polyphenolic compound isolated from various plants, which can eliminate free radicals and significantly increase the antioxidant activity of lipoproteins. However, due to its hydrophobic nature, it is currently mostly dissolved in organic solvents, but these organic solvents are mostly dangerous and flammable, and cannot be added to food, which limits the application of Res in the food industry. The present application encapsulates resveratrol with egg white protein by pH-driven method, which is not only safe and green, but also realizes high-efficiency and stable antioxidant effect.

[0039] The present application prepares a composite coating liquid: adding pullulan to the egg white protein-Res solution obtained in the above technical solution, stirring, and then ultrasonic degassing to obtain a composite coating liquid.

[0040] In the present application, the final concentration of the pullulan is preferably 0.02 g / mL to 0.04 g / mL. Pullulan is a linear polysaccharide polymerized by α-1, 6 glycosidic bond from maltotriose repeating units connected by α-1, 4 glycosidic bond, which is non-toxic and harmless, biodegradable, has excellent film-forming ability, super oxygen barrier performance and oil resistance. In the present application, the amino group of egg white protein is combined with the carbonyl group of pullulan, which not only improves the stability of the composite material and the mechanical properties of the coating, but also improves the compactness of the coating and effectively blocks oxygen.

[0041] In the present application, the stirring is preferably 600 rpm to 900 rpm for 50 min to 70 min, and more preferably 800 rpm for 60 min; the ultrasonic is preferably 730 W for 5 min to 10 min, and more preferably 730 W for 8 min.

[0042] The antioxidative composite coating is prepared by immersing the object to be coated into the composite coating solution obtained in the technical solution, soaking and coating, and then placing the object to be coated in a cool and ventilated place for air-drying.

[0043] In the present application, the coating amount of the soaking coating with respect to the weight of the object to be coated is preferably 0.3 mL / g to 0.6 mL / g, and more preferably 0.4 mL / g to 0.5 mL / g.

[0044] In the present application, the object to be coated includes but is not limited to walnut, almond, peanut, hazelnut, chestnut, apricot kernel, pistachio and pine nut.

[0045] The present application also provides an egg white protein-based antioxidative composite coating prepared by the preparation method.

[0046] In the present application, the encapsulation rate of Res in the composite coating is preferably greater than or equal to 66%, and the scavenging rate of DPPH free radicals is preferably greater than or equal to 50%. The present application uses egg white protein to encapsulate Res, improves the antioxidative property of the composite coating, and improves the mechanical property of the composite coating by adding pullulan, thereby obtaining a composite coating with good film-forming effect, good antioxidative effect and edibility.

[0047] The present application also provides an application of the egg white protein-based antioxidative composite coating in food active packaging.

[0048] In the present application, the composite coating can be used in the storage and packaging of oxidizable food.

[0049] The present application also provides an application of the egg white protein-based antioxidative composite coating in nut storage.

[0050] In the present application, the composite coating can be used in the storage and packaging of various nuts.

[0051] In order to better understand the present application, the content of the present application is further illustrated below in combination with examples, but the content of the present application is not limited to the following examples. The materials, reagents and the like used in the examples and test examples of the present application can be obtained from commercial channels unless otherwise specified. The methods used in the examples and test examples of the present application are conventional methods unless otherwise specified.

[0052] Example 1

[0053] (1) Preparation of egg white protein solution: 1.08 g of glycerol (3.6% (w / v)) was dissolved in 30 mL of deionized water, 2.4 g of egg white protein powder was added, and the mixture was stirred uniformly. The pH value was adjusted to 12 by using 1 mol / L sodium hydroxide, and the egg white protein solution was obtained.

[0054] (2) pH-driven method for encapsulating resveratrol Res: 30 mL of deionized water was first adjusted to pH 12, 24 mg of Res was dissolved therein, and stirred at 800 rpm for 5 min in the dark. The egg white protein solution obtained in (1) was poured into the solution, mixed uniformly, and placed in a 50 °C water bath. The solution was stirred at 800 rpm in the dark for 10 min. After being taken out, the pH value was adjusted to 7 to obtain an egg white protein-Res solution;

[0055] (3) Preparation of a composite coating solution: 0.02 g / mL of pullulan was added to the egg white protein-Res solution obtained in (2) and stirred for 60 min. The solution was ultrasonically treated for 5 min to obtain a composite coating solution;

[0056] (4) Preparation of an antioxidant composite coating: the almond was immersed in the composite coating solution obtained in (3) for coating. The coating amount was 0.5 mL / g, and the coated almond was placed in a cool and ventilated place to dry.

[0057] Example 2

[0058] (1) Preparation of an egg white protein solution: 0.9 g of glycerol (3.0% (w / v)) was dissolved in 30 mL of deionized water, 1.8 g of egg white protein powder was added, and stirred uniformly. The pH value was adjusted to 12 using 1 mol / L sodium hydroxide to obtain an egg white protein solution;

[0059] (2) pH-driven method for encapsulating resveratrol Res: 30 mL of deionized water was first adjusted to pH 12, 24 mg of Res was dissolved therein, and stirred at 800 rpm for 5 min in the dark. The egg white protein solution obtained in (1) was poured into the solution, mixed uniformly, and placed in a 50 °C water bath. The solution was stirred at 800 rpm in the dark for 10 min. After being taken out, the pH value was adjusted to 7 to obtain an egg white protein-Res solution;

[0060] (3) Preparation of a composite coating solution: 0.02 g / mL of pullulan was added to the egg white protein-Res solution obtained in (2) and stirred for 60 min. The solution was ultrasonically treated for 5 min to obtain a composite coating solution;

[0061] (4) Preparation of an antioxidant composite coating: the almond was immersed in the composite coating solution obtained in (3) for coating. The coating amount was 0.5 mL / g, and the coated almond was placed in a cool and ventilated place to dry.

[0062] Example 3

[0063] (1) Preparation of an egg white protein solution: 1.2 g of glycerol (4.0% (w / v)) was dissolved in 30 mL of deionized water, 1.2 g of egg white protein powder was added, and stirred uniformly. The pH value was adjusted to 12 using 1 mol / L sodium hydroxide to obtain an egg white protein solution;

[0064] (2) pH-driven method for encapsulating Res: 30 mL of deionized water was adjusted to pH 12, 24 mg of Res was dissolved therein, and the solution was stirred at 900 rpm for 3 min in the dark. The solution was poured into the egg white protein solution obtained in (1), and the mixture was stirred at 800 rpm for 8 min in the dark in a 55°C water bath. The pH of the solution was adjusted to 7, and an egg white protein-Res solution was obtained;

[0065] (3) Preparation of a composite coating solution: 0.04 g / mL of pullulan was added to the egg white protein-Res solution obtained in (2), and the mixture was stirred for 70 min and ultrasonically treated for 6 min to obtain a composite coating solution;

[0066] (4) Preparation of an antioxidant composite coating: almond was immersed in the composite coating solution obtained in (3), and the coating amount was 0.3 mL / g. The almond was taken out and dried in a cool and ventilated place.

[0067] Comparative Example 1

[0068] Comparative Example 1 was different from Example 1 in that Res was not encapsulated, and pullulan was directly added to the egg white protein solution. The other operations and parameters were the same as in Example 1.

[0069] Comparative Example 2

[0070] Comparative Example 2 was different from Example 1 in that pullulan was not added. The other operations and parameters were the same as in Example 1.

[0071] Comparative Example 3

[0072] 1.08 g of glycerol (3.6% (w / v)) was dissolved in 60 mL of deionized water, and 3.6 g of egg white protein was added and stirred until uniform. The solution was ultrasonically treated for 5 min to remove bubbles, and was ready for use. The almond was coated using the dipping method in Example 1 (4).

[0073] Test Example 1

[0074] The antioxidant performance of the coating solutions obtained in Examples 1 to 3 and Comparative Examples 1 to 3 was determined, and the encapsulation rate of Res in Examples 1 to 3 and Comparative Example 2 was determined. The encapsulation rate and antioxidant performance were determined as follows:

[0075] (1) Encapsulation rate determination: free resveratrol was separated by high-speed centrifugation (8000 rpm, 10 min), the supernatant was diluted 10 times with anhydrous ethanol, vortexed, and the absorbance at 307 nm was measured, and the standard curve of Res at 307 nm was drawn, and the concentration of encapsulated resveratrol was calculated by regression curve. The encapsulation rate of Res was calculated as follows:

[0076] EE (%) = encapsulated Res concentration in protein / total added Res concentration x 100;

[0077] (2) Antioxidant performance determination: the antioxidant performance of the coating solution was determined by DPPH (2,2-diphenyl-1-pyrindyl hydrazine) radical scavenging method. A DPPH solution with a concentration of 1.2 mmol / L was prepared using ethanol, 1 mL of sample solution was added to 2 mL of DPPH-ethanol solution, mixed and placed in the dark, and the absorbance at 517 nm was measured after reaction at room temperature for 30 min. The DPPH radical scavenging rate was calculated as follows:

[0078] DPPH radical scavenging rate (%) = A 空白 -A 样品 / A 空白 x 100;

[0079] The results of encapsulation rate and antioxidant performance detection are shown in Table 1. As can be seen from Table 1, the encapsulation rate (%) of Res using the pH-driven method for encapsulating resveratrol Res according to the present application can reach 79.27 ± 0.20; the DPPH radical scavenging rate (%) of Examples 1-3 is also greatly improved compared with Comparative Examples 1-3.

[0080] Table 1: Detection results of encapsulation rate and antioxidant performance

[0081]

[0082] Note: In the same row of data, if several data have the same letter after them, it means that there is no significant difference between the several data, and if the letters after the several data are different, it means that there is a significant difference between the several data.

[0083] Test Example 2

[0084] The coating of Examples 1-3 and Comparative Examples 1-3 was fixed on the conductive glue of the sample disc, and the surface was gold sprayed, and then observed by SU 8010 field emission scanning electron microscope at an acceleration voltage of 5.0 KV. The observation results are shown in Figs. 1-6 As can be seen from Figs. 1-6 , the surface of the coating without adding pullulan is often cracked, and the tightness is low. The coating prepared in Examples 1-3 of the present application has high molecular tightness and excellent mechanical properties.

[0085] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing an egg white protein-based antioxidant composite coating, characterized by, It comprises the following steps: S1, preparing egg white protein solution: glycerol is dissolved in deionized water, egg white protein powder is added, stirred uniformly, and pH value is adjusted to 12 to obtain egg white protein solution; the concentration of the egg white protein solution in S1 is 0.04 g / mL-0.08 g / mL; the g:mL of glycerol and deionized water in S1 is (0.03-0.04):1; S2, pH-driven method for encapsulating resveratrol Res: preparing Res solution, stirring uniformly in the dark, then pouring into the egg white protein solution obtained in S1, mixing uniformly, stirring in the dark in water bath, adjusting the pH value to 7 after taking out, obtaining egg white protein-Res solution; the concentration of the Res solution in S2 is 0.8 mg / mL; the volume ratio of the Res solution and the egg white protein solution in S2 is 1:1; S3, preparing composite coating solution: adding pullulan to the egg white protein-Res solution obtained in S2, stirring and then ultrasonic degassing to obtain composite coating solution; the final concentration of pullulan in S3 is 0.02 g / mL-0.04 g / mL; S4, preparing antioxidant composite coating: immersing the object to be coated into the composite coating solution obtained in S3, soaking and coating, taking out and placing in a cool and ventilated place to dry; the coating amount in S4 relative to the weight of the object to be coated is 0.3 mL / g-0.6 mL / g.

2. An egg white protein-based antioxidant composite coating prepared by the preparation method of claim 1.

3. The application of the egg white protein-based antioxidant composite coating of claim 2 in food active packaging.

4. The application of the egg white protein-based antioxidant composite coating of claim 2 in nut storage.

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