Preparation method of double-shell grapefruit essential oil microcapsule with antibacterial property and slow release property

Abstract

The invention discloses a preparation method of a double-shell grapefruit essential oil microcapsule with antibacterial property and slow release property, a sodium alginate shell microcapsule is prepared by an electrostatic spraying method, and the embedding amount of essential oil in the microcapsule can be increased by changing the ratio of the essential oil to a sodium alginate solution. The embedding amount of the essential oil can be greatly increased, and the particle size of the microcapsule can be adjusted by changing the pore size and voltage of the nozzle of the electrostatic spraying device, so that the particle size is controllable, and the preparation flexibility of the microcapsule is improved; and forming a nano-silver shell of the microcapsule by adopting in-situ polymerization. A layer of polydopamine is modified on the surface of the sodium alginate shell microcapsule, and the polydopamine prepared by the method has active groups such as catechol, amino and the like, and can be subjected to coordination reaction with metal Ag ions, so that the material is further subjected to functional modification. According to the preparation method disclosed by the invention, Ag is crosslinked and polymerized on the surface of the microcapsule to form the silver-sodium alginate shell microcapsule with a double-layer shell structure, and the antibacterial effect is remarkable.

Description

Technical Field

[0001] The invention relates to a method for preparing essence microcapsules, and in particular to a method for preparing grapefruit essential oil microcapsules. Background Art

[0002] Essential oils are volatile, aromatic compounds extracted from various plant parts, including roots, stems, leaves, flowers, and fruits, using a variety of extraction methods. These natural substances have diverse properties and are extremely diverse, resulting in their widespread application in many fields.

[0003] For example, grapefruit essential oil, extracted from the peel of grapefruit, has a viscous, watery texture and a unique, refreshing aroma. It promotes fluid circulation, acts as a diuretic, and soothes the body and mind. Lavender essential oil can clear heat and detoxify, cleanse the skin, control oil content, remove freckles and whiten the skin, reduce wrinkles and rejuvenate the skin, and eliminate eye bags and dark circles. It also promotes the regeneration and recovery of damaged tissue, among other skin care benefits. Tea tree essential oil, due to its powerful antibacterial and anti-inflammatory properties, is commonly used in the pharmaceutical and medical industries to treat skin inflammation, oral ulcers, and other conditions. It can also serve as an adjunct treatment to relieve anxiety and improve sleep quality. Rose essential oil can be added to fabric finishing agents to impart a charming rose scent to clothing, enhancing the product's added value.

[0004] However, the high volatility and reactivity of essential oils greatly limit their application. To overcome this limitation, microencapsulation technology has emerged as one of the preferred strategies for retaining and precisely controlling the release of these compounds.

[0005] Microencapsulation technology utilizes natural or synthetic polymers as wall materials to encapsulate a core material, such as essential oils, within a tiny polymer shell. The encapsulated substance is the core material, primarily consisting of essential oils, lipids, and other water-insoluble components. The encapsulating material, known as the wall or shell material, is typically composed of various organic compounds such as proteins and polysaccharides. It exhibits excellent biocompatibility, film-forming properties, and resistance to reaction with the core material. Its principles are primarily based on physical, chemical, or physicochemical methods. Microencapsulation of essential oils not only effectively slows the volatilization rate of the essential oils and enhances their stability, but also enables controlled release and prolongs their duration of action.

[0006] Common methods for encapsulating fragrance microcapsules include in-situ polymerization, interfacial polymerization, and emulsion polymerization. The principle of in-situ polymerization is that in a dispersed system containing fragrance, monomers undergo polymerization under the action of an initiator, forming a polymer wall material on the surface of the fragrance particles to encapsulate them. Interfacial polymerization involves dissolving two monomers that can undergo polymerization in two immiscible phases. Polymerization occurs at the interface between the two phases to form a wall material, thereby encapsulating the essential oil. Emulsion polymerization involves forming an emulsion of monomers under the action of an emulsifier, which then undergoes polymerization under the action of an initiator. The resulting polymer encapsulates the fragrance into microcapsules.

[0007] In recent years, microencapsulation technology has become the most common method to expand the application of essential oils and their volatile compounds in food, medical and industrial fields, control their volatility and thus extend the shelf life of their products.

[0008] Shi Zedong, Li Fujun and others from the School of Agricultural Engineering and Food Science of Shandong University of Technology used oregano essential oil as the core material and gelatin and gum arabic as the wall materials. They used the complex coagulation method to prepare oregano essential oil microcapsules through process optimization, and characterized their physicochemical characteristics and sustained-release properties. Finally, they evaluated the antibacterial effect and preservation mechanism of oregano essential oil microcapsules in the preservation process of apricots, in order to provide a material basis for the application of plant essential oils in the antibacterial preservation of fruits and vegetables, and provide a mechanism reference for the development of green and environmentally friendly plant essential oil microcapsule preservatives and bactericides (K. Wang, Y. Wang, X. Xi, J. Lu, Y. Wang, P. Zhao, M. Cheng, X. Wang, J. Wang, Preparation and characterization of oregano essential oil microcapsules by gelatin / polysaccharide composite coagulation method, Food and Bioproducts Processing 147(000)(2024)12.).

[0009] Li Shugang's team at Hefei University of Technology applied the natural substances and physical properties of eggshell powder (EP) to the development of microcapsules. They used EP, whey protein (WPI), xanthan gum (XG) and maltodextrin (MD) as composite wall materials and lavender essential oil (LEO) as embedding material. By controlling the addition ratio of EP and LEO and using Ca 2+By studying the cross-linking reaction between EP, protein and polysaccharide, sustained-release microcapsules of lavender essential oil wrapped in eggshell powder were successfully prepared. The physicochemical properties, structural characteristics, sustained-release effect and reasons for the controlled release of lavender essential oil microcapsules were studied. Analyzing the functional application of EP in microcapsule sustained-release materials will help to enhance the economic value of eggshells and provide theoretical support for the high-value comprehensive utilization of eggshells (Z. Zhang, Y. Liu, Y. Gao, J. Huo, S. Dong, L. Liu, S. Li, Sustained-release effect of eggshell powder microcapsules on lavender essential oil, Journal of Food Engineering 387(2025).).

[0010] Wang Guiying and Liao Guozhou's team from the College of Food Science and Technology of Yunnan Agricultural University used Litsea cubeba essential oil as the object and prepared Litsea cubeba essential oil microcapsules by vacuum freeze drying. They used the microcapsule embedding efficiency as an indicator and optimized the microencapsulation process of Litsea cubeba essential oil based on single factor and orthogonal test. At the same time, they analyzed the physicochemical properties, microstructure, volatility and peroxide value of Litsea cubeba essential oil microcapsules during storage. The purpose was to change the shortcomings of Litsea cubeba essential oil, such as its volatility and easy oxidation and deterioration, and improve its stability, so as to provide certain theoretical support for the expansion of the application prospects of Litsea cubeba essential oil (K. Simon-Brown, KM Solval, A. Chotiko, L. Alfaro, V. Reyes, C. Liu, B. Dzandu, E. Kyereh, A. G. Barnaby, I. Thompson, Microencapsulation of ginger (Zingiber officinale) extract by spray drying technology, LWT-Food Science and Technology Technology (2016) 119-125.).

[0011] However, a single encapsulation technology and functionality can no longer meet the growing demand for multifunctional products. The preparation method of ordinary essential oil microcapsules cannot simultaneously achieve controllable particle size, sustained release function and antibacterial effect. Summary of the Invention

[0012] The present invention provides a method for preparing bivalve grapefruit essential oil microcapsules with both antibacterial and sustained-release properties. This method utilizes an electrostatic spray method to prepare sodium alginate shell microcapsules, significantly increasing the amount of essential oil encapsulated and the controllability of microcapsule particle size, thus enhancing preparation flexibility. To address the single-function issue of existing essential oil microcapsules, the present invention employs an in-situ polymerization method to perform secondary encapsulation of the microcapsules, achieving both the slow release of grapefruit essential oil fragrance and antibacterial efficacy.

[0013] The purpose of the present invention is achieved through the following technical solutions:

[0014] A method for preparing double-shell grapefruit essential oil microcapsules with antibacterial and sustained-release properties comprises the following steps:

[0015] Step 1: Prepare grapefruit essential oil microcapsules with sodium alginate shells (SA@GEO) by electrostatic spraying:

[0016] Step 1-1, dissolving sodium alginate (SA) in deionized water to obtain a SA solution with a concentration of 1.0 to 2.0 wt.%;

[0017] Step 1-2, adding grapefruit essential oil (GEO) and an appropriate amount of sodium lauryl sulfate to the SA solution under stirring to obtain a GEO emulsion, controlling the mass ratio of GEO to SA solution to be 1:1-5, and the amount of sodium lauryl sulfate added to the SA solution to be 0.5-1.0 wt.%;

[0018] Step 1-3, dissolving calcium chloride in deionized water to prepare a calcium chloride solution with a concentration of 2.0 to 8.0 wt.%;

[0019] Step 1-4: using an electrostatic spray method to drop the emulsion in step 1-2 into a calcium chloride solution, and through an ion exchange reaction between SA and calcium chloride, SA@GEO microcapsules with a cross-linked SA shell are obtained;

[0020] Step 2: The microcapsules form an outer nanosilver shell through in-situ polymerization:

[0021] Step 2-1, dissolve TRIS (tris(hydroxymethyl)aminomethane)) in deionized water to prepare 100 mL of a TRIS buffer solution with a concentration of 5-15 mM;

[0022] Step 2-2, add 4-6 g of SA@GEO microcapsules into TRIS buffer solution and stir until uniformly dispersed;

[0023] Step 2-3, adding 0.1-0.2 wt% dopamine hydrochloride to the solution of step 2-2, and adjusting the pH value of the solution to 6.8-7.2 with hydrochloric acid solution;

[0024] Step 2-4: Place the mixture in step 2-3 into a beaker, heat to 30-50° C. in a water bath, and then stir for 4-6 hours;

[0025] Step 2-5: Filter the mixture and dry it at room temperature to successfully modify a layer of polydopamine on the surface of the SA@GEO microcapsules;

[0026] Step 2-6, dispersing silver nitrate in water to prepare a 0.5-1.5 wt.% silver nitrate aqueous solution;

[0027] Step 2-7, adding aqueous ammonia to the silver nitrate aqueous solution under stirring until the solution becomes transparent to form ammonia silver nitrate;

[0028] Step 2-8, adding the SA@GEO microcapsules obtained in step 2-5 to the silver ammonium nitrate solution, stirring for 10 to 15 minutes, and then adding glucose solution as a reducing agent for the silver ammonium nitrate, wherein the amount of glucose solution added is 4 to 6 wt.% of the silver ammonium nitrate solution;

[0029] Step 2-9: After the reduction reaction for 20 to 40 minutes, a nanosilver shell is formed on the surface of the SA@GEO microcapsule to obtain Ag / SA@GEO microcapsule;

[0030] Step 2-10: vacuum filter the Ag-coated microcapsules and wash them with deionized water, and then freeze-dry them for 5 to 8 hours.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1. The sodium alginate shell microcapsules (SA@GEO microcapsules) prepared by the electrostatic spray method of the present invention can increase the embedding amount of essential oil in the microcapsules by changing the ratio of essential oil to sodium alginate solution, which can significantly increase the embedding amount of essential oil. In addition, the particle size of the microcapsules can be adjusted by changing the aperture size and voltage of the electrostatic spray device nozzle, achieving controllable particle size and improving the flexibility of its preparation.

[0033] 2. The present invention uses in-situ polymerization to form the nanosilver shell of the microcapsules. A layer of polydopamine is modified on the surface of the sodium alginate shell microcapsules. The polydopamine prepared by this method has active groups such as catechol and amino groups, which can react with metal Ag ions to further modify the material's functionality. The present invention cross-links Ag onto the microcapsule surface to form a double-shell structure of silver-sodium alginate shell microcapsules (Ag / SA@GEO), which have significant antibacterial effects.

[0034] 3. The present invention adopts a method combining electrostatic spraying and in-situ polymerization, combining physical and mechanical methods with chemical methods, so that the grapefruit essential oil microcapsules have controllable particle size and sustained release performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a diagram of an electrostatic spray device. A high-voltage electrostatic field is established between the nozzle and the receiving device. The receiving device is a CaCl2 solution. Sodium alginate and calcium ions will quickly exchange to form microcapsules.

[0036] Figure 2 The preparation process of Ag / SA@GEO double-shell microcapsules: A layer of polydopamine is modified on the surface of SA@GEO microcapsules. The active groups on the surface can react with metal Ag ions, thereby modifying a layer of nanosilver particles on the surface of the microcapsules, so that the microcapsules form a double-shell structure.

[0037] Figure 3 The controlled release curves of the weight loss test and the UV-Vis method are shown;

[0038] Figure 4 This is the antibacterial test result of Ag / SA@GEO microcapsules;

[0039] Figure 5 The morphology of SA@GEO microcapsules and single microspheres of Ag / SA@GEO microcapsules;

[0040] Figure 6 This is the morphology of Ag / SA@GEO microcapsules with multiple microspheres;

[0041] Figure 7 EDS morphology of Ag / SA@GEO microcapsules;

[0042] Figure 8 This is the fluorescence scanning image of Ag / SA@GEO microcapsules;

[0043] Figure 9 is the infrared spectrum of Ag / SA@GEO microcapsules;

[0044] Figure 10 is the particle size analysis diagram of Ag / SA@GEO microcapsules;

[0045] Figure 11 TGA, DTA and DSC analysis diagrams of Ag / SA@GEO microcapsules;

[0046] Figure 12 This is the XPS analysis diagram of Ag / SA@GEO microcapsules. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below with reference to the accompanying drawings, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0048] The present invention provides a method for preparing a double-shell grapefruit essential oil microcapsule with antibacterial and sustained-release properties, such as Figure 1 and Figure 2 As shown, the method includes the following steps:

[0049] Step 1: Preparation of SA@GEO microcapsules by electrostatic spraying:

[0050] Step 1-1: dissolve sodium alginate (SA) in deionized water to obtain a SA solution with a concentration of 1.0 to 2.0 wt.%.

[0051] Step 1-2: Under stirring, add grapefruit essential oil (GEO) and an appropriate amount of sodium lauryl sulfate to the SA solution to obtain a GEO emulsion, control the mass ratio of GEO to SA solution to be 1:1-5, and add an amount of sodium lauryl sulfate to the SA solution to be 0.5-1.0 wt.%.

[0052] Step 1-3: dissolving calcium chloride in deionized water to prepare a calcium chloride solution with a concentration of 2.0 to 8.0 wt.%.

[0053] Step 1-4: The emulsion in step 1-2 is dropped into a calcium chloride solution by an electrostatic spray method, and SA@GEO microcapsules with a cross-linked SA shell are obtained through an ion exchange reaction between SA and calcium chloride.

[0054] Step 2: The microcapsules form an outer nanosilver shell through in-situ polymerization:

[0055] Step 2-1: Dissolve TRIS in deionized water to prepare 100 mL of a TRIS buffer solution with a concentration of 5 to 15 mM.

[0056] Step 2-2: Add 4-6 g of SA@GEO microcapsules into TRIS buffer solution and gently stir until evenly dispersed.

[0057] Step 2-3: Add 0.1-0.2 wt% of dopamine hydrochloride to the solution in step 2-2, and adjust the pH value of the solution to 6.8-7.2 with a hydrochloric acid solution.

[0058] Step 2-4: Place the mixture in step 2-3 into a beaker, heat to 30-50° C. in a water bath, and then gently stir for 4-6 hours.

[0059] Step 2-5: Filter the mixture and dry it at room temperature, and modify the surface of the SA@GEO microcapsules with a layer of polydopamine; the dopamine molecule has a nitrogen-to-carbon ratio of 0.125:1 and contains active groups (i.e., amino groups and phenolic hydroxyl groups). Under specific conditions, it can be adsorbed on the substrate surface to form PDA. With the help of TRIS buffer, a layer of PDA is added to the surface by dropwise addition of dopamine hydrochloride solution to modify the SA@GEO microcapsules. The PDA layer prepared by this method has active groups such as catechol and amino groups, which can coordinate with metal ions, thereby further functionally modifying the material.

[0060] Step 2-6: Disperse silver nitrate in 100 mL of water to prepare a silver nitrate aqueous solution with a concentration of 0.5 to 1.5 wt.%.

[0061] Step 2-7: Adding aqueous ammonia to the silver nitrate solution under stirring, the solution gradually becomes transparent, indicating the formation of silver ammonia nitrate.

[0062] Step 2-8: Add the SA@GEO microcapsules obtained in step 2-5 to the silver ammonium nitrate solution, gently stir for 10 to 15 minutes, and then add 4 to 6 wt.% glucose solution as a reducing agent for the silver ammonium nitrate.

[0063] Step 2-9: After a reduction reaction of 20 to 40 minutes, a nanosilver shell forms on the surface of the SA@GEO microcapsules, yielding the target product, Ag / SA@GEO microcapsules. PDA is known to coordinate with silver ammonia. Simultaneously, the weak reducing property of PDA reduces the adsorbed silver ammonia ions to silver, which is then fixed to the microsphere surface as catalytic active sites. Then, in the presence of the reducing agent glucose, the silver ammonia ions in the solution are further reduced, and the Ag active sites grow into nanoparticles, forming a dense and continuous Ag layer, thus obtaining double-shell microcapsules.

[0064] Step 2-10: vacuum filter the Ag-coated microcapsules and wash them with deionized water, and then freeze-dry them for 5 to 8 hours (-50 to -20°C).

[0065] Example 1:

[0066] (1) 0.5 g of sodium alginate (SA) was dissolved in 50 mL of deionized water, and 50 mL of grapefruit essential oil (GEO) and 0.5 g of sodium lauryl sulfate were added. After uniform emulsification, 6 g of calcium chloride was dissolved in 300 g of deionized water to prepare a calcium chloride solution. The emulsion was dropped into the calcium chloride solution by electrostatic spraying to obtain grapefruit essential oil microcapsules with sodium alginate shells (SA@GEO microcapsules).

[0067] (2) 1.21 g of TRIS was dissolved in 100 mL of deionized water to prepare a 10 mM TRIS buffer solution (pH = 8.5). Then, 5 g of the single-shell microcapsules were added to the TRIS buffer solution and stirred. Subsequently, 0.2 g of dopamine hydrochloride was added to the above solution, and the pH was adjusted to 7 with hydrochloric acid solution. The mixture was placed in a 250 mL beaker, heated to 30°C in a water bath, and then gently stirred for 6 hours. After that, it was filtered and dried at room temperature.

[0068] (3) Disperse 1.0 g of silver nitrate in 100 mL of water to prepare a silver nitrate aqueous solution. Add a few drops of ammonia water to the silver nitrate aqueous solution while stirring until the solution gradually becomes transparent. Continue stirring for 10 minutes, add the above-mentioned single-shell microcapsules to the silver ammonium nitrate solution, gently stir for 15 minutes, and then add 5 wt% glucose solution as a reducing agent for the silver ammonium nitrate. After 30 minutes of reduction reaction, a nanosilver shell is formed on the surface of the microcapsule to obtain the target product, Ag / SA double-shell grapefruit essential oil microcapsules (Ag / SA@GEO microcapsules). Finally, vacuum filter and wash with deionized water, and then freeze-dry for 6 hours.

[0069] Example 2:

[0070] (1) 0.4 g of sodium alginate (SA) was dissolved in 40 mL of deionized water, and 20 mL of grapefruit essential oil (GEO) and 0.3 g of sodium lauryl sulfate were added. After uniform emulsification, 6 g of calcium chloride was dissolved in 300 g of deionized water to prepare a calcium chloride solution. The emulsion was dropped into the calcium chloride solution by electrostatic spraying to obtain grapefruit essential oil microcapsules with sodium alginate shells (SA@GEO microcapsules).

[0071] (2) 1.21 g of TRIS was dissolved in 100 mL of deionized water to prepare a 10 mM TRIS buffer solution (pH = 8.5). Then, 5 g of the single-shell microcapsules were added to the TRIS buffer solution and stirred. Subsequently, 0.2 g of dopamine hydrochloride was added to the above solution, and the pH was adjusted to 7 with hydrochloric acid solution. The mixture was placed in a 250 mL beaker, heated to 30°C in a water bath, and then gently stirred for 6 hours. After that, it was filtered and dried at room temperature.

[0072] (3) Disperse 1.0 g of silver nitrate in 100 mL of water to prepare a silver nitrate aqueous solution. Add a few drops of ammonia water to the silver nitrate aqueous solution while stirring until the solution gradually becomes transparent. Continue stirring for 10 minutes, add the above-mentioned single-shell microcapsules to the silver ammonium nitrate solution, gently stir for 15 minutes, and then add 5 wt% glucose solution as a reducing agent for the silver ammonium nitrate. After 30 minutes of reduction reaction, a nanosilver shell is formed on the surface of the microcapsule to obtain the target product, Ag / SA double-shell grapefruit essential oil microcapsules (Ag / SA@GEO microcapsules). Finally, vacuum filter and wash with deionized water, and then freeze-dry for 6 hours.

[0073] Example 3:

[0074] (1) 0.3 g of sodium alginate (SA) was dissolved in 30 mL of deionized water, and 10 mL of grapefruit essential oil (GEO) and 0.2 g of sodium lauryl sulfate were added. After uniform emulsification, 6 g of calcium chloride was dissolved in 300 g of deionized water to prepare a calcium chloride solution. The emulsion was dropped into the calcium chloride solution by electrostatic spraying to obtain grapefruit essential oil microcapsules with sodium alginate shells (SA@GEO microcapsules).

[0075] (2) 1.21 g of TRIS was dissolved in 100 mL of deionized water to prepare a 10 mM TRIS buffer solution (pH = 8.5). 5 g of single-shell microcapsules were then added to the TRIS solution and stirred. 0.2 g of dopamine hydrochloride was then added to the solution, and the pH was adjusted to 7 using hydrochloric acid. The mixture was placed in a 250 mL beaker, heated to 30°C in a water bath, and gently stirred for 6 hours before being filtered and dried at room temperature.

[0076] (3) Disperse 1.0 g of silver nitrate in 100 mL of water to prepare a silver nitrate aqueous solution. Add a few drops of ammonia water to the silver nitrate aqueous solution while stirring until the solution gradually becomes transparent. Continue stirring for 10 minutes, add the above-mentioned single-shell microcapsules to the silver ammonium nitrate solution, gently stir for 15 minutes, and then add 5 wt% glucose solution as a reducing agent for the silver ammonium nitrate. After 30 minutes of reduction reaction, a nanosilver shell is formed on the surface of the microcapsule to obtain the target product, Ag / SA double-shell grapefruit essential oil microcapsules (Ag / SA@GEO microcapsules). Finally, vacuum filter and wash with deionized water, and then freeze-dry for 6 hours.

[0077] Example 4:

[0078] (1) 0.4 g of sodium alginate (SA) was dissolved in 40 mL of deionized water, and 10 mL of grapefruit essential oil (GEO) and 0.5 g of sodium lauryl sulfate were added. After uniform emulsification, 6 g of calcium chloride was dissolved in 300 g of deionized water to prepare a calcium chloride solution. The emulsion was dropped into the calcium chloride solution by electrostatic spraying to obtain grapefruit essential oil microcapsules with sodium alginate shells (SA@GEO microcapsules).

[0079] (2) 1.21 g of TRIS was dissolved in 100 mL of deionized water to prepare a 10 mM TRIS buffer solution (pH = 8.5). 5 g of single-shell microcapsules were then added to the TRIS solution and stirred. 0.2 g of dopamine hydrochloride was then added to the solution, and the pH was adjusted to 7 using hydrochloric acid. The mixture was placed in a 250 mL beaker, heated to 30°C in a water bath, and gently stirred for 6 hours before being filtered and dried at room temperature.

[0080] (3) Disperse 1.0 g of silver nitrate in 100 mL of water to prepare a silver nitrate aqueous solution. Add a few drops of ammonia water to the silver nitrate aqueous solution while stirring until the solution gradually becomes transparent. Continue stirring for 10 minutes, add the above-mentioned single-shell microcapsules to the silver ammonium nitrate solution, gently stir for 15 minutes, and then add 5 wt% glucose solution as a reducing agent for the silver ammonium nitrate. After 30 minutes of reduction reaction, a nanosilver shell is formed on the surface of the microcapsule to obtain the target product, Ag / SA double-shell grapefruit essential oil microcapsules (Ag / SA@GEO microcapsules). Finally, vacuum filter and wash with deionized water, and then freeze-dry for 6 hours.

[0081] Example 5:

[0082] (1) 0.3 g of sodium alginate (SA) was dissolved in 30 mL of deionized water, and 10 mL of grapefruit essential oil (GEO) and 0.8 g of sodium lauryl sulfate were added. After uniform emulsification, 6 g of calcium chloride was dissolved in 300 g of deionized water to prepare a calcium chloride solution. The emulsion was dropped into the calcium chloride solution by electrostatic spraying to obtain grapefruit essential oil microcapsules with sodium alginate shells (SA@GEO microcapsules).

[0083] (2) 1.21 g of TRIS was dissolved in 100 mL of deionized water to prepare a 10 mM TRIS buffer solution (pH = 8.5). 5 g of single-shell microcapsules were then added to the TRIS solution and stirred. 0.2 g of dopamine hydrochloride was then added to the solution, and the pH was adjusted to 7 using hydrochloric acid. The mixture was placed in a 250 mL beaker, heated to 30°C in a water bath, and gently stirred for 6 hours before being filtered and dried at room temperature.

[0084] (3) Disperse 1.0 g of silver nitrate in 100 mL of water to prepare a silver nitrate aqueous solution. Add a few drops of ammonia water to the silver nitrate aqueous solution while stirring until the solution gradually becomes transparent. Continue stirring for 10 minutes, add the above-mentioned single-shell microcapsules to the silver ammonium nitrate solution, gently stir for 15 minutes, and then add 5 wt% glucose solution as a reducing agent for the silver ammonium nitrate. After 30 minutes of reduction reaction, a nanosilver shell is formed on the surface of the microcapsule to obtain the target product, Ag / SA double-shell grapefruit essential oil microcapsules (Ag / SA@GEO microcapsules). Finally, vacuum filter and wash with deionized water, and then freeze-dry for 6 hours.

[0085] Example 6:

[0086] In this example, the performance of the Ag / SA double-shell grapefruit essential oil microcapsules (Ag / SA@GEOmicrocapsule) prepared in Example 5 was tested, and the test results are as follows:

[0087] 1. Weightlessness test and UV-Vis method

[0088] The sustained-release performance of the microcapsules was tested by weight loss test and ultraviolet-visible light (UV-Vis) method, and the controlled-release curve was drawn, such as Figure 3 As shown in the figure. In the weightlessness test, the mass loss of grapefruit essential oil leveled off after 100 hours, reaching a mass loss rate of approximately 22%, while the mass loss of the encapsulated microcapsules was less than 10%. Furthermore, in UV-Vis testing, the release rate of grapefruit essential oil reached a high of 61% after 1 hour and exceeded 95% after 24 hours, while the microcapsules did not reach a similar release rate until 240 hours. Clearly, encapsulation of grapefruit essential oil in microcapsules has a significant sustained-release effect.

[0089] 2. Antibacterial test

[0090] Staphylococcus aureus (ATCC 29213, Gram-positive) and Escherichia coli (ATCC 25922, Gram-negative) are two very common bacterial models and are also one of the most commonly used indicators for testing the antibacterial properties of Ag. The antibacterial test of the encapsulated microcapsules was carried out using the plate coating counting method. From the experimental results, it can be seen that the antibacterial rate of grapefruit essential oil against Staphylococcus aureus is 23.53%, and the antibacterial rate against Escherichia coli is 0.00%. However, at the minimum dilution factor (10 5 ), the antibacterial rate of the encapsulated double-shell microcapsules against Staphylococcus aureus and Escherichia coli was 100%, and the antibacterial effect was significant. The results are shown in Table 1 and Figure 4As shown, a3 and d3 are blank controls of Staphylococcus aureus and Escherichia coli; b3 and e3 are the antibacterial rates of grapefruit essential oil against Staphylococcus aureus and Escherichia coli; c3 and f3 are the antibacterial rates of encapsulated double-shell microcapsules against Staphylococcus aureus and Escherichia coli.

[0091] Table 1

[0092] serial number Colony count Dilution multiple Bacterial concentration (CFU / mL) Antibacterial rate a3 153 <![CDATA[10 6 ]]> <![CDATA[1.53×10 9 ]]> / b3 117 <![CDATA[10 6 ]]> <![CDATA[1.17×10 9 ]]> 23.53％ c3 0 <![CDATA[10 4 ]]> <![CDATA[1.0×10 5 ]]> 100％ d3 103 <![CDATA[10 6 ]]> <![CDATA[1.03×10 9 ]]> / e3 106 <![CDATA[10 6 ]]> <![CDATA[1.06×10 9 ]]> 0.00％ f3 0 <![CDATA[10 4 ]]> <![CDATA[1.0×10 5 ]]> 100％

[0093] 3. Field Emission Scanning Electron Microscopy (FE-SEM)

[0094] pass Figure 5 and Figure 6 SEM images of SA@GEO and Ag / SA@GEO microcapsules reveal a multi-core structure. Through the silver mirror reaction, a uniform layer of silver nanoparticles is applied to the microcapsule surface. After encapsulation, the fragile multi-core structure on the microcapsule surface is significantly reduced, becoming smoother. These silver nanoparticles enhance the microcapsule's sealing properties.

[0095] 4. Energy dispersive spectrometer (EDS) and confocal laser microscopy

[0096] Energy dispersive spectrometer was used to scan and analyze the nanosilver particles on the surface of the microcapsules. Figure 7 It can be seen that Ag is evenly distributed on the surface of the microcapsules. At the same time, a mixture of rare earth fluorescent compounds was added to the essential oil, and fluorescence scanning analysis was performed using a confocal laser microscope. Figure 8 It can be seen that the microcapsules have a multi-core structure.

[0097] 5. Fourier transform infrared (FTIR) and particle size analysis test

[0098] By using FTIR spectroscopy, we tested the changes in the chemical structure of the microcapsules during preparation. Figure 9 It was confirmed that the microcapsules were successfully synthesized as expected, and the average particle size of the microcapsules was measured by a particle size analyzer to be around 271 μm. Figure 10 shown.

[0099] 6. Thermogravimetric analysis (TGA), differential thermal analysis (DTA) and differential scanning calorimetry (DSC)

[0100] pass Figure 11 The TGA, DTG and DSC tests show that the encapsulated microcapsules exhibit good thermal stability, indicating that the microcapsules have a stable core-shell structure. The research method of the present invention has greatly improved the stability and volatility of grapefruit essential oil.

[0101] 7. X-ray Photoelectron Spectroscopy (XPS)

[0102] pass Figure 12 The XPS test of the chemical composition of the surface of the prepared microcapsules and the chemical state of the elements contained therein further proves the successful progress of the reaction.

Claims

1. A method for preparing a double-shell grapefruit essential oil microcapsule with antibacterial and sustained-release properties, characterized in that The method comprises the following steps: Step 1: Prepare grapefruit essential oil microcapsules SA@GEO with sodium alginate shells by electrostatic spraying: Step 1-1, dissolving SA in deionized water to obtain a SA solution with a concentration of 1.0 to 2.0 wt.%; Step 1-2, adding GEO and sodium lauryl sulfate to the SA solution under stirring to obtain a GEO emulsion, controlling the mass ratio of GEO to SA solution to be 1:1-5, and the amount of sodium lauryl sulfate added to the SA solution to be 0.5-1.0 wt.%; Step 1-3, dissolving calcium chloride in deionized water to prepare a calcium chloride solution with a concentration of 2.0 to 8.0 wt.%; Step 1-4: using an electrostatic spray method to drop the emulsion in step 1-2 into a calcium chloride solution, and through an ion exchange reaction between SA and calcium chloride, SA@GEO microcapsules with a cross-linked SA shell are obtained; Step 2: The microcapsules form an outer nanosilver shell through in-situ polymerization: Step 2-1, dissolve TRIS in deionized water to prepare 100 mL of a TRIS buffer solution with a concentration of 5-15 mM; Step 2-2, add 4-6 g of SA@GEO microcapsules into TRIS buffer solution and stir until uniformly dispersed; Step 2-3, adding 0.1-0.2 wt% dopamine hydrochloride to the solution of step 2-2, and adjusting the pH value of the solution to 6.8-7.2 with hydrochloric acid solution; Step 2-4: Place the mixture in step 2-3 into a beaker, heat in a water bath, and stir; Step 2-5: Filter the mixture and dry it at room temperature to successfully modify a layer of polydopamine on the surface of the SA@GEO microcapsules; Step 2-6, dispersing silver nitrate in water to prepare a 0.5-1.5 wt.% silver nitrate aqueous solution; Step 2-7, adding aqueous ammonia to the silver nitrate aqueous solution under stirring until the solution becomes transparent to form ammonia silver nitrate; Step 2-8, adding the SA@GEO microcapsules obtained in step 2-5 to the silver ammonium nitrate solution, stirring, and then adding glucose solution as a reducing agent for the silver ammonium nitrate, wherein the amount of glucose solution added is 4 to 6 wt.% of the silver ammonium nitrate solution; Step 2-9: After the reduction reaction for 20 to 40 minutes, a nanosilver shell is formed on the surface of the SA@GEO microcapsule to obtain Ag / SA@GEO microcapsule; Step 2-10: vacuum filter the Ag-coated microcapsules, wash them with deionized water, and then freeze-dry them.

2. The method for preparing the double-shell grapefruit essential oil microcapsules with antibacterial and sustained-release properties according to claim 1, characterized in that In the steps 2-4, the heating temperature is 30-50° C., and the stirring time is 4-6 hours.

3. The method for preparing the double-shell grapefruit essential oil microcapsules with antibacterial and sustained-release properties according to claim 1, characterized in that In the steps 2-8, the stirring time is 10 to 15 minutes.

4. The method for preparing the double-shell grapefruit essential oil microcapsules with antibacterial and sustained-release properties according to claim 1, characterized in that In the step 2-10, the freeze-drying time is 5 to 8 hours and the temperature is -50 to -20°C.

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