Long-acting antibacterial / antioxidant biomass-based essential oil microcapsule and preparation method thereof

Abstract

The invention provides a long-acting antibacterial / antioxidant biomass-based essential oil microcapsule and a preparation method thereof. The preparation method comprises the following steps: firstly, uniformly stirring and mixing a chitosan stock solution and a casein stock solution, adjusting the pH value of a mixed system, and promoting the formation of nanoparticles through reverse charge neutralization of casein and chitosan; centrifuging the mixed solution, collecting a supernatant, slowly dripping essential oil into the supernatant, stirring and emulsifying, and ultrasonically preparing an emulsion; and finally, adding a natural cross-linking agent for cross-linking, and filtering and drying after reaction to obtain the long-acting antibacterial / antioxidant biomass-based essential oil capsule. The method does not need an additional emulsifier, is simple in process and low in cost, and is suitable for the fields of drug delivery, cosmetics and food preservation. The prepared microcapsule has the advantages of better stability, high coating rate, good slow release performance, long-acting antibacterial / antioxidant property and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of microcapsules, and in particular relates to a long-acting antibacterial / antioxidant biomass-based essential oil microcapsule with casein and chitosan as a substrate and a preparation method thereof. Background Art

[0002] With the recent rise in people's preference for natural and green foods, the application of natural active ingredients has become increasingly widespread. Many essential oils extracted from plants possess antioxidant and antimicrobial properties and are expected to become key ingredients in natural preservatives. However, essential oils are unstable, volatile, water-insoluble, and heat-sensitive, which limit their application. Essential oil microencapsulation can prolong the release time of essential oils and is an effective method to protect their functional components, improve their release, enhance their stability, and expand their application range. Therefore, they show promising applications in personal care products, drug delivery, cosmetics, and food preservation.

[0003] Microencapsulation technology is widely used to encapsulate essential oils, effectively protecting them during transportation and storage. Common microcapsule wall materials fall into three main categories: natural, semi-synthetic, and fully synthetic polymers, such as chitosan, alginate, gelatin, casein, ethyl cellulose, and polyvinyl alcohol. Given the increasingly severe global environmental challenges and growing public awareness of environmental protection, natural biodegradable polymers offer the greatest potential for future development in microcapsule wall materials, particularly due to their non-toxicity, abundant availability, low cost, and improved biocompatibility compared to semi-synthetic and fully synthetic polymers.

[0004] Natural biodegradable polymers are macromolecular organic compounds widely found in animals, plants, and microorganisms. Many types possess the functional properties required for microencapsulation wall materials, such as mechanical strength, solubility, flowability, emulsification, and stability. Currently, natural biodegradable polymers used as microencapsulation wall materials are primarily classified into polysaccharides, proteins, and lipids. Casein (CA), the primary protein component in milk, accounts for up to 80%. Its low cost, high nutritional value, strong emulsification ability, excellent surface activity, and good biocompatibility make it an ideal wall material for microcapsules. Furthermore, chitosan (CS), known for its environmental friendliness, non-toxicity, hydrophilicity, and biodegradability, is a promising raw material for the food, textile, and pharmaceutical industries. Chitosan forms positively charged cationic groups when dissolved in dilute acid. Functional groups such as C3-OH, C2-NH2, and C6-OH in CS can form intramolecular and intermolecular hydrogen bonds. Theoretically, they can form stable composite wall materials with casein through non-covalent interactions (primarily electrostatic interactions). Therefore, casein and chitosan can be used to prepare microcapsules through electrostatic adsorption interactions between opposite charges without the need for additional surfactants.

[0005] However, casein and chitosan bind primarily through electrostatic interactions between anions and cations, making polymer microcapsules highly unstable under certain conditions. Studies have shown that crosslinkers significantly affect microcapsule morphology, with their curing effect leading to a denser internal structure. Crosslinking can effectively enhance the stability of the microcapsule core. Chemical crosslinkers, such as formaldehyde or glutaraldehyde, react with hydroxyl residues on polysaccharides and free amino groups on proteins to improve microcapsule stability. However, chemical crosslinkers like glutaraldehyde are highly toxic and can pose health risks such as genotoxicity, posing potential hazards to the environment and human health. In contrast, natural crosslinkers have attracted extensive research due to their lower toxicity. Natural crosslinkers are substances derived from nature that can be used to crosslink polymers, proteins, or other macromolecules, thereby enhancing the physical and chemical properties of the materials. Leveraging the crosslinking effect of natural crosslinkers with casein and chitosan can enhance microcapsule stability and exhibit controlled release, while also offering environmental advantages and meeting current requirements for green chemistry and sustainable development.

[0006] The Pickering emulsion template method is an emerging microencapsulation technology that has garnered widespread attention and application in the microencapsulation field in recent years. This method utilizes the self-assembly of solid particles at the oil-water interface to form a stable emulsion, which is then immobilized through physical or chemical methods to produce microcapsules. Compared with traditional emulsions, Pickering emulsions offer greater stability and require lower surfactant dosages, effectively avoiding potential environmental and human health hazards of surfactants. Currently, the Pickering emulsion template method has been successfully applied to the preparation of a variety of microcapsules, such as the encapsulation and sustained release of drugs, food additives, and flavors. For example, studies have used the Pickering emulsion template method to prepare drug-loaded microcapsules. By adjusting the emulsion composition and preparation conditions, efficient drug encapsulation and sustained release were achieved. Furthermore, the Pickering emulsion template method can be combined with other techniques, such as polymerization and physical gelation, to further enhance the performance and application range of microcapsules. However, this method still faces challenges in practical application, such as the relatively stringent emulsion preparation conditions and the recovery and reuse of solid particles, which require further research and optimization. Summary of the Invention

[0007] In view of the problems existing in the above-mentioned prior art, the present invention adopts the Pickering emulsion template method and combines the cross-linking effect of a natural cross-linking agent to prepare a long-lasting antibacterial / antioxidant biomass-based essential oil microcapsule emulsion.

[0008] The specific technical solutions of the present invention are as follows.

[0009] A method for preparing long-lasting antibacterial / antioxidant biomass-based essential oil microcapsules comprises the following steps: (1) Prepare casein stock solution: dissolve casein in alkaline solution, heat and stir; (2) Preparation of chitosan stock solution: dissolve chitosan in acetic acid aqueous solution; (3) Mixing casein stock solution and chitosan stock solution and adjusting the pH to form nanocomposite particles through reverse charge neutralization; (4) emulsifying the essential oil in the nanocomposite particle solution and ultrasonically treating the solution to form a Pickering emulsion; (5) Add a natural cross-linking agent to carry out a cross-linking reaction, and then dry to obtain microcapsules.

[0010] The alkaline solution is one of sodium hydroxide, sodium bicarbonate, sodium acetate, triethanolamine, sodium silicate and sodium carbonate.

[0011] The natural cross-linking agent is one of transglutaminase, horseradish peroxidase, laccase, genipin, tannic acid and phytic acid.

[0012] The essential oil is one of oregano essential oil, thyme essential oil, lemon essential oil, rosemary essential oil, orange essential oil, peppermint essential oil, tea tree essential oil and lavender essential oil.

[0013] The specific steps include: Step 1: Preparation of nanocomposite particles 0.4 parts by mass of casein and 50.0 parts by mass of an alkaline solution are mixed, added to a three-necked flask, and stirred continuously for 1-2 hours under heating conditions in a water bath at 45-65°C with a stirrer to obtain a casein stock solution; 0.04-0.4 parts by mass of chitosan are weighed and added to 50.0 parts by mass of a 0.5% acetic acid aqueous solution, and stirred at room temperature overnight to ensure complete dissolution to obtain a chitosan stock solution; the casein stock solution and the chitosan stock solution are mixed, the system is adjusted to a weak acidic state, and stirring is continued on a stirrer for 0.5-2 hours, and then the mixed solution is centrifuged and the supernatant is collected to obtain a casein / chitosan nanocomposite particle emulsion; Step 2: Preparation of essential oil-encapsulated casein / chitosan-based Pickering microcapsule emulsion At room temperature, 0.06-1.8 parts by weight of essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 1-2 minutes, and then stirred on a stirrer for 0.5-1 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil; Step 3: Preparation of cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil 0.01-0.16 parts by mass of a natural cross-linking agent is added to the mixed emulsion, and the mixture is stirred for 1-3 hours to carry out a cross-linking reaction. The mixed solution is filtered and dried to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0014] After the casein stock solution and the chitosan stock solution are mixed, the pH of the system is adjusted to 4.5-6.5 using 5 mol / L NaOH and 3 mol / L HCl.

[0015] The specific centrifugation condition of the mixed solution is centrifugation at 5000 rpm for 15 minutes.

[0016] A long-acting antibacterial / antioxidant biomass-based essential oil microcapsule prepared by any of the above preparation methods.

[0017] The particle size of the microcapsules is 100-500 nm.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the Pickering emulsion template method, combined with the crosslinking effect of a natural crosslinker, to prepare a long-lasting antibacterial / antioxidant biomass-based essential oil microcapsule emulsion. The reaction conditions are mild, the experimental equipment is simple, and the method is straightforward, without the need for the addition of surfactants. Furthermore, both casein and chitosan are natural polymers, offering advantages such as safety, nontoxicity, good biocompatibility, and biodegradability.

[0019] The present invention uses widely available natural casein and chitosan as raw materials to prepare long-lasting antibacterial / antioxidant biomass-based essential oil capsules with good structural stability and controllable sustained release. The existing microcapsule coverage rate is only 60% to 75%, while the microcapsules prepared by the present invention have a higher coverage rate, effectively improving the encapsulation efficiency and stability of essential oils. This research provides valuable information for the preparation of essential oil microcapsules, which can protect bioactive substances by encapsulating them in microcapsules. The present invention combines natural crosslinkers with the Pickering emulsion template method for the first time. Casein / chitosan crosslinked with natural crosslinkers can be prepared using food-grade materials, so it has great application potential in the food and pharmaceutical industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the cumulative release curve of the microcapsules in Example 5; Figure 2 The total antioxidant capacity of the microcapsules in Example 5 is compared with the free radical scavenging rates of the samples before and after cross-linking and the pure essential oil; Figure 3 The antibacterial ability of the microcapsules of Example 5 (after one month of storage) is compared before and after cross-linking. DETAILED DESCRIPTION

[0021] The present invention will be described in further detail below with reference to specific examples, but the embodiments of the present invention include but are not limited to the scope represented by the following examples.

[0022] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0023] The present invention utilizes the good emulsifying properties of casein and the advantages of chitosan, such as its wide availability and low price, to use casein as a substrate to coat essential oils with antibacterial / antioxidant properties to prepare biomass-based essential oil microcapsules with long-lasting antibacterial / antioxidant properties.

[0024] The present invention relates to a long-acting antibacterial / antioxidant biomass-based essential oil capsule and a preparation method thereof, comprising the following steps: Step 1: Take 0.4 parts by mass of casein and 50.0 parts by mass of alkaline solution, mix them, add them to a three-necked flask, and stir them continuously with a stirrer for 1-2 hours under heating conditions in a water bath at 45-65°C to obtain a casein stock solution. Weigh 0.04-0.4 parts by mass of chitosan and add it to 50.0 parts by mass of 0.5% acetic acid aqueous solution, stir overnight at room temperature to ensure complete dissolution to obtain a chitosan stock solution. Mix the casein stock solution with the chitosan stock solution, adjust the pH of the system to 4.5-6.5 with 5mol / LNaOH and 3mol / LHCl, continue stirring on the stirrer for 0.5-2 hours, then centrifuge the mixture at 5000rpm for 15 minutes, collect the supernatant, and obtain a casein / chitosan nanocomposite particle emulsion.

[0025] Step 2: At room temperature, 0.06-1.8 parts by mass of essential oil is slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 1-2 minutes, and then stirred on a stirrer for 0.5-1 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0026] Step 3: adding 0.01-0.16 parts by weight of a natural cross-linking agent to the mixed emulsion, continuing stirring for 1-3 hours to carry out a cross-linking reaction, filtering and drying the mixed solution to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0027] In step 1, the alkaline solution is one of sodium hydroxide, sodium bicarbonate, sodium acetate, triethanolamine, sodium silicate and sodium carbonate.

[0028] In step 2, the essential oil is one of oregano essential oil, thyme essential oil, lemon essential oil, rosemary essential oil, orange essential oil, peppermint essential oil, tea tree essential oil, and lavender essential oil.

[0029] In step 3, the natural cross-linking agent is one of transglutaminase, horseradish peroxidase, laccase, genipin, tannic acid, and phytic acid.

[0030] Example 1 Step 1: Take 0.4 parts by mass of casein and 50.0 parts by mass of sodium hydroxide solution, mix them, add them to a three-necked flask, and stir them continuously for 1 hour under heating conditions in a water bath at 45°C with a stirrer to obtain a casein stock solution. Weigh 0.04 parts by mass of chitosan and add it to 50.0 parts by mass of 0.5% acetic acid aqueous solution, stir overnight at room temperature to ensure complete dissolution to obtain a chitosan stock solution. Mix the casein stock solution with the chitosan stock solution, adjust the pH of the system to 4.5 with 5mol / LNaOH and 3mol / LHCl, continue stirring on the stirrer for 0.5h, then centrifuge the mixture at 5000rpm for 15min, collect the supernatant, and obtain a casein / chitosan nanocomposite particle emulsion.

[0031] Step 2: At room temperature, 0.06 parts by mass of thyme essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 1 minute, and then stirred on a stirrer for 0.5 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0032] Step 3: adding 0.01 parts by mass of transglutaminase to the mixed emulsion, continuing stirring for 1 hour to carry out a cross-linking reaction, filtering and drying the mixed solution to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0033] Example 2 Step 1: Take 0.4 parts by mass of casein and 50.0 parts by mass of sodium bicarbonate solution, mix them, add them to a three-necked flask, and stir them continuously for 1 hour under heating conditions in a water bath at 45°C with a stirrer to obtain a casein stock solution. Weigh 0.1 parts by mass of chitosan and add it to 50.0 parts by mass of 0.5% acetic acid aqueous solution, stir overnight at room temperature to ensure complete dissolution to obtain a chitosan stock solution. Mix the casein stock solution with the chitosan stock solution, adjust the pH of the system to 5 with 5mol / LNaOH and 3mol / LHCl, continue stirring on the stirrer for 0.5h, then centrifuge the mixture at 5000rpm for 15min, collect the supernatant, and obtain a casein / chitosan nanocomposite particle emulsion.

[0034] Step 2: At room temperature, 0.12 parts by mass of lemon essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 1 minute. The solution was further stirred on a stirrer for 0.5 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0035] Step 3: adding 0.03 parts by mass of horseradish peroxidase to the mixed emulsion, continuing stirring for 1 hour to carry out a cross-linking reaction, filtering and drying the mixed solution to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0036] Example 3 Step 1: Take 0.4 parts by mass of casein and 50.0 parts by mass of sodium acetate solution, mix them, add them to a three-necked flask, and stir them continuously for 1 hour under heating conditions in a 55°C water bath with a stirrer to obtain a casein stock solution. Weigh 0.16 parts by mass of chitosan and add it to 50.0 parts by mass of 0.5% acetic acid aqueous solution. Stir overnight at room temperature to ensure complete dissolution to obtain a chitosan stock solution. Mix the casein stock solution with the chitosan stock solution, adjust the pH of the system to 5 with 5mol / LNaOH and 3mol / LHCl, continue stirring on the stirrer for 1 hour, then centrifuge the mixture at 5000rpm for 15min, collect the supernatant, and obtain a casein / chitosan nanocomposite particle emulsion.

[0037] Step 2: At room temperature, 0.3 parts by mass of rosemary essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 1 minute, and then stirred on a stirrer for 0.5 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0038] Step 3: adding 0.06 parts by mass of laccase to the mixed emulsion, continuing stirring for 2 hours to carry out a cross-linking reaction, filtering and drying the mixed solution to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0039] Example 4 Step 1: Take 0.4 parts by mass of casein and 50.0 parts by mass of triethanolamine solution, mix them, add them to a three-necked flask, and stir them continuously for 2 hours under heating conditions in a 55°C water bath with a stirrer to obtain a casein stock solution. Weigh 0.22 parts by mass of chitosan and add it to 50.0 parts by mass of 0.5% acetic acid aqueous solution, stir overnight at room temperature to ensure complete dissolution to obtain a chitosan stock solution. Mix the casein stock solution with the chitosan stock solution, adjust the pH of the system to 5.5 with 5mol / LNaOH and 3mol / LHCl, continue stirring on the stirrer for 1.5 hours, then centrifuge the mixture at 5000rpm for 15 minutes, collect the supernatant, and obtain a casein / chitosan nanocomposite particle emulsion.

[0040] Step 2: At room temperature, 0.6 parts by mass of orange essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 2 minutes, and then stirred on a stirrer for 1 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0041] Step 3: Add 0.09 parts by mass of genipin to the mixed emulsion, continue stirring for 2 hours to perform a cross-linking reaction, and filter and dry the mixed solution to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0042] Example 5 Step 1: Take 0.4 parts by mass of casein and 50.0 parts by mass of sodium carbonate solution, mix them, add them to a three-necked flask, and stir them continuously for 2 hours under the condition of heating in a water bath at 65°C with a stirrer to obtain a casein stock solution. Weigh 0.34 parts by mass of chitosan and add it to 50.0 parts by mass of 0.5% acetic acid aqueous solution, stir overnight at room temperature to ensure complete dissolution to obtain a chitosan stock solution. Mix the casein stock solution with the chitosan stock solution, adjust the pH of the system to 6 with 5mol / LNaOH and 3mol / LHCl, continue stirring on the stirrer for 1.5 hours, then centrifuge the mixture at 5000rpm for 15 minutes, collect the supernatant, and obtain a casein / chitosan nanocomposite particle emulsion.

[0043] Step 2: At room temperature, 1.2 parts by mass of oregano essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 2 minutes, and then stirred on a stirrer for 1 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0044] Step 3: adding 0.12 parts by mass of tannic acid to the mixed emulsion, continuing stirring for 3 hours to carry out a cross-linking reaction, filtering and drying the mixed solution to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0045] Example 6 Step 1: Take 0.4 parts by mass of casein and 50.0 parts by mass of sodium silicate solution, mix them, add them to a three-necked flask, and stir them continuously for 2 hours under heating conditions at 65°C in a water bath with a stirrer to obtain a casein stock solution. Weigh 0.4 parts by mass of chitosan and add it to 50.0 parts by mass of 0.5% acetic acid aqueous solution, stir overnight at room temperature to ensure complete dissolution to obtain a chitosan stock solution. Mix the casein stock solution with the chitosan stock solution, adjust the pH of the system to 6.5 with 5mol / LNaOH and 3mol / LHCl, continue stirring on the stirrer for 2 hours, then centrifuge the mixture at 5000rpm for 15 minutes, collect the supernatant, and obtain a casein / chitosan nanocomposite particle emulsion.

[0046] Step 2: At room temperature, 1.8 parts by mass of peppermint essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 2 minutes, and then stirred on a stirrer for 1 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

[0047] Step 3: adding 0.16 parts by mass of phytic acid to the mixed emulsion, continuing stirring for 3 hours to carry out a cross-linking reaction, filtering and drying the mixed solution to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil. category CACS / OEO CACS / OEO / TA Coverage rate (%) 75.28±0.52 92.35±0.48

[0048] Table 1: Comparison of coverage of microcapsules in Example 5 before and after cross-linking Table 1 shows the comparison of the coverage rate of the microcapsules in Example 5 before and after cross-linking. The comparison shows that the coverage rate of the cross-linked essential oil microcapsules is significantly better than that of the uncross-linked microcapsules, reaching 92.35% ± 0.48%.

[0049] Figure 1 The cumulative release curve of the microcapsules from Example 5 is shown below. Observation shows that when the composite microcapsules are placed in 50% v / v ethanol, the encapsulated substance exhibits a cumulative release rate of 58% over a 50-hour period, demonstrating excellent controlled release.

[0050] Figure 2 The total antioxidant capacity of the microcapsules in Example 5 is compared with the free radical scavenging rates of the uncrosslinked sample and pure essential oil. Observation shows that the free radical scavenging rate of the microcapsules without tannic acid is weaker than that of the pure essential oil because some of the essential oil is encapsulated within the microcapsules. However, the free radical scavenging rate of the composite microcapsules crosslinked with tannic acid far exceeds that of the pure essential oil, due to the potent antioxidant activity of tannic acid. The two exhibit a synergistic antioxidant effect.

[0051] Figure 3 The antibacterial properties of the microcapsules in Example 5 (after one month of storage) are compared before and after crosslinking. Observation shows that the crosslinked essential oil microcapsules exhibit significantly better antibacterial properties than the uncrosslinked ones. This is because the polymer wall material becomes denser after crosslinking, improving sustained-release and stability. The microcapsules maintain good antibacterial properties even after one month of storage, demonstrating the effectiveness of this method.

[0052] The method for preparing an essential oil microcapsule emulsion proposed by the present invention comprises the following steps: first, dissolving chitosan in an acetic acid aqueous solution and stirring overnight to ensure full dissolution to prepare a chitosan stock solution. Casein is then dissolved in an alkaline solution in a water bath and stirred overnight to prepare a casein stock solution. First, the chitosan stock solution and the casein stock solution are stirred and mixed uniformly, and the pH of the mixed system is adjusted to promote the formation of nanoparticles by neutralizing the opposite charges of casein and chitosan. The mixed solution is then centrifuged to collect the supernatant, and the essential oil is slowly dripped into the supernatant, stirred and emulsified, and ultrasonic treatment is performed to prepare an emulsion. Finally, a natural crosslinking agent is added for crosslinking, and after the reaction, the solution is filtered and dried to obtain a long-lasting antibacterial / antioxidant biomass-based essential oil capsule.

[0053] The present invention adopts the Pickering emulsion template method in combination with the cross-linking effect of a natural cross-linking agent to prepare a long-lasting antibacterial / antioxidant biomass-based essential oil microcapsule emulsion. The method has the advantages of mild reaction conditions, simple experimental equipment, simple operation and no need to add additional surfactants. The casein and chitosan used are both natural polymer materials with the characteristics of safety, non-toxicity, good biocompatibility and biodegradability. The prepared microcapsules have good structural stability and controllable sustained release, and the coverage rate is higher than that of the existing microcapsule preparation process, which effectively improves the encapsulation efficiency and stability of the essential oil. The present invention combines a natural cross-linking agent with the Pickering emulsion template method for the first time, providing a new idea and method for the preparation of essential oil microcapsules, and because food-grade materials are used, it has broad application prospects in the food and pharmaceutical industries.

Claims

1. A method for preparing long-lasting antibacterial / antioxidant biomass-based essential oil microcapsules, characterized in that: The following steps are involved: (1) Prepare casein stock solution: dissolve casein in alkaline solution, heat and stir; (2) Preparation of chitosan stock solution: dissolve chitosan in acetic acid aqueous solution; (3) Mixing casein stock solution and chitosan stock solution and adjusting the pH to form nanocomposite particles through reverse charge neutralization; (4) emulsifying the essential oil in the nanocomposite particle solution and ultrasonically treating the solution to form a Pickering emulsion; (5) Add a natural cross-linking agent to carry out a cross-linking reaction, and then dry to obtain microcapsules.

2. The preparation method according to claim 1, characterized in that The alkaline solution is one of sodium hydroxide, sodium bicarbonate, sodium acetate, triethanolamine, sodium silicate and sodium carbonate.

3. The preparation method according to claim 1, characterized in that The natural cross-linking agent is one of transglutaminase, horseradish peroxidase, laccase, genipin, tannic acid and phytic acid.

4. The preparation method according to claim 1, characterized in that The essential oil is one of oregano essential oil, thyme essential oil, lemon essential oil, rosemary essential oil, orange essential oil, peppermint essential oil, tea tree essential oil and lavender essential oil.

5. The preparation method according to claim 1, characterized in that The specific steps include: Step 1: Preparation of nanocomposite particles 0.4 parts by mass of casein and 50.0 parts by mass of an alkaline solution are mixed, added to a three-necked flask, and stirred continuously for 1-2 hours under heating conditions in a water bath at 45-65°C with a stirrer to obtain a casein stock solution; 0.04-0.4 parts by mass of chitosan are weighed and added to 50.0 parts by mass of a 0.5% acetic acid aqueous solution, and stirred at room temperature overnight to ensure complete dissolution to obtain a chitosan stock solution; the casein stock solution and the chitosan stock solution are mixed, the system is adjusted to a weak acidic state, and stirring is continued on a stirrer for 0.5-2 hours, and then the mixed solution is centrifuged and the supernatant is collected to obtain a casein / chitosan nanocomposite particle emulsion; Step 2: Preparation of essential oil-encapsulated casein / chitosan-based Pickering microcapsule emulsion At room temperature, 0.06-1.8 parts by weight of essential oil was slowly dripped into the continuously stirred casein / chitosan nanocomposite particle solution and ultrasonicated for 1-2 minutes, and then stirred on a stirrer for 0.5-1 hour to obtain a casein / chitosan-based Pickering microcapsule emulsion coated with essential oil; Step 3: Preparation of cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil 0.01-0.16 parts by mass of a natural cross-linking agent is added to the mixed emulsion, and the mixture is stirred for 1-3 hours to carry out a cross-linking reaction. The mixed solution is filtered and dried to obtain a cross-linked casein / chitosan-based Pickering microcapsule emulsion coated with essential oil.

6. The preparation method according to claim 5, characterized in that After the casein stock solution and the chitosan stock solution are mixed, the pH of the system is adjusted to 4.5-6.5 using 5 mol / L NaOH and 3 mol / L HCl.

7. The preparation method according to claim 5, characterized in that The specific centrifugation condition of the mixed solution is centrifugation at 5000 rpm for 15 minutes.

8. A long-acting antibacterial / antioxidant biomass-based essential oil microcapsule prepared by the method according to any one of claims 1 to 7.

9. The long-acting antibacterial / antioxidant biomass-based essential oil microcapsules according to claim 8, characterized in that: The particle size of the microcapsules is 100-500 nm.

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