Preparation method of pickering emulsion with good stability loaded with epsilon-polylysine

Abstract

The application discloses a preparation method of a Pickering emulsion loaded with epsilon-polylysine with good stability, and comprises the following steps: (1) preparing nano-chitin fibers; (2) preparing a Pickering emulsion; and (3) loading epsilon-polylysine. The carboxyl content of the chitin fibers is improved by using a TEMPO-NaBr-NaClO catalytic oxidation system to perform oxidation modification on the chitin fibers, and the efficient stabilization of the Pickering emulsion is realized by accurately controlling the carboxyl content. The epsilon-polylysine solution is added into the Pickering emulsion, the epsilon-polylysine is uniformly dispersed in the emulsion, the Pickering emulsion loaded with epsilon-polylysine is formed, the loading and slow-release functions of the epsilon-polylysine are realized, and an efficient and environment-friendly solution is provided for the development of food preservation, drug delivery and antibacterial materials.

Description

Technical Field

[0001] This invention relates to the field of Pickering emulsion preparation technology, and in particular to a method for preparing a stable ε-polylysine-loaded Pickering emulsion. Background Technology

[0002] Pickering emulsions are a type of emulsion stabilized by solid particles. Due to their excellent stability and environmental friendliness, they are widely used in the food industry, drug delivery, and materials science. Compared to traditional emulsifiers, picking emulsions form a stable physical barrier through interfacial adsorption of solid particles, avoiding interfacial tension imbalance and oil droplet aggregation, resulting in higher stability and environmental friendliness. Chitin, as an abundant and renewable natural biopolymer, has potential for development in picking emulsions due to its good biocompatibility, non-toxicity, and antibacterial properties. However, traditional chitin fibers, due to strong hydrogen bonding and high crystallinity, exhibit poor dispersibility at aqueous and oil-water interfaces, making it difficult to form a stable emulsion interface structure, thus limiting their application in picking emulsions. Although some studies have attempted to use nano-chitin fibers for the stabilization of picking emulsions, systematic research on the specific effects of different carboxyl group contents on emulsion stability is still lacking. Especially in food industry applications, there is no clear solution for optimizing the chemical modification of chitin to achieve efficient emulsion stabilization.

[0003] Furthermore, recent studies have found that, based on stable emulsions, Pickering emulsions not only possess structural stability but can also serve as functional carriers for loading and delivering active ingredients. By adding functional ingredients to the Pickering emulsion system, its interfacial adsorption capacity and nanofiber network structure can be fully utilized, significantly improving the stability, sustained-release performance, and target application effects of the functional ingredients. ε-Polylysine, a natural polypeptide with broad-spectrum antibacterial properties, has important applications in food preservation, antibacterial coatings, and biomedicine. However, its traditional aqueous solution form cannot achieve long-term antibacterial effects due to the excessively rapid release rate of the active ingredient. If ε-Polylysine can be introduced into a stable Pickering emulsion system, its loading and sustained-release functions can be achieved, thus providing an efficient and environmentally friendly solution for food preservation, drug delivery, and the development of antibacterial materials. Summary of the Invention

[0004] This invention addresses the issues of poor stability and ε-polylysine in existing chitosan fiber Pickering emulsions by providing a method for preparing a stable ε-polylysine-loaded Pickering emulsion. This method improves the stability of the Pickering emulsion while achieving both loading and sustained-release functions of ε-polylysine.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing a stable ε-polylysine-loaded Pickering emulsion, comprising the following steps:

[0006] (1) Preparation of nano-chitosan fibers

[0007] Chitosan fibers were dispersed in water, and then TEMPO and NaBr were added to obtain a mixed system. Sodium hypochlorite solution was added to the mixed system, and the reaction was carried out under stirring conditions, maintaining the pH of the reaction system at 10±0.5 during the reaction. After the reaction was completed, the reaction product was thoroughly washed with deionized water to obtain oxidized chitosan fibers with a carboxyl content of 1000 μmol / g. The oxidized chitosan fibers were subjected to high-pressure homogenization until the particle size of the oxidized chitosan fibers was less than 500 nm to obtain nano-chitosan fibers. This invention utilizes a TEMPO-NaBr-NaClO catalytic oxidation system to oxidize and modify chitin fibers, thereby increasing the carboxyl content of the chitin fibers. The inventors discovered in experiments that only oxidized chitin fibers with a carboxyl content of 1000 μmol / g yielded ε-polylysine-loaded Pickering emulsions with the best stability. The mechanism may be that only moderate carboxylation can balance electrostatic effects and the mechanical strength of the fiber network, thus significantly improving the long-term stability of the emulsion. A 75% (w / w) sodium hypochlorite solution is preferred, and the amount added and reaction time are determined to obtain oxidized chitin fibers with a carboxyl content of 1000 μmol / g. Real-time monitoring of the pH value ensures the selectivity of oxidation; the pH can be adjusted by adding sodium hydroxide solution or other conventional methods. High-pressure homogenization reduces the particle size of the oxidized chitin fibers to below 500 nm, forming uniformly carboxylated nano-chitin fibers (ChNFs). The physical structure of the fibers is optimized, exhibiting stronger interfacial adsorption capacity and lower desorption energy.

[0008] (2) Preparation of Pickering emulsion

[0009] Under ice-water bath conditions, nano-chitosan fibers were dispersed in an oil-water system to obtain Pickering emulsion.

[0010] (3) Loading ε-polylysine

[0011] An ε-polylysine solution was added to a Pickering emulsion and homogenized under ice-water bath conditions to obtain an ε-polylysine-loaded Pickering emulsion.

[0012] Preferably, in step (1), the mass ratio of chitin fiber, TEMPO, NaBr and water in the mixed system is 5:0.08:0.8:500.

[0013] As a preferred option, in step (1), the homogenization conditions are: pressure 1000-1600 bar, and 2-5 cycles.

[0014] Preferably, in step (2), the oil-water system is prepared by mixing sunflower seed oil and water at a mass ratio of 1:(4-5) and then homogenizing.

[0015] Preferably, in step (2), the mass percentage of nano-chitosan fibers in the Pickering emulsion is 0.8% to 1%. The amount of nano-chitosan fibers added to the emulsion is controlled at 0.8% to 1% of the total mass of the emulsion to ensure that it can form a stable adsorption network at the interface.

[0016] Preferably, the droplet size in the Pickering emulsion is 2–5 μm.

[0017] Preferably, in step (3), an ε-polylysine solution is added according to the final concentration of 0.5 mg / mL ε-polylysine in the loaded ε-polylysine Pickering emulsion.

[0018] Therefore, the present invention has the following beneficial effects:

[0019] (1) Chitin fibers were oxidized and modified using the TEMPO-NaBr-NaClO catalytic oxidation system to increase the carboxyl content of chitin fibers, and the Pickering emulsion was stabilized efficiently by precisely controlling the carboxyl content.

[0020] (2) Adding ε-polylysine solution to Pickering emulsion allows ε-polylysine to be uniformly dispersed in the emulsion, forming a Pickering emulsion loaded with ε-polylysine. This achieves the loading and sustained-release function of ε-polylysine, providing an efficient and environmentally friendly solution for food preservation, drug delivery and the development of antibacterial materials. Attached Figure Description

[0021] Figure 1 This is a SEM microstructure image of the nano-chitosan fibers in the embodiment.

[0022] Figure 2 This is a TEM microstructure diagram of the nano-chitosan fibers in the embodiment.

[0023] Figure 3 This is a graph showing the sustained-release performance of the ε-polylysine-loaded Pickering emulsion prepared in the examples.

[0024] Figure 4 These are experimental photographs of the inhibition zones (fluorescent Pseudomonas) of the ε-polylysine-loaded Pickering emulsion prepared in the examples.

[0025] Figure 5 This is an experimental photograph of the antibacterial zone (Bacillus subtilis) of the ε-polylysine-loaded Pickering emulsion prepared in the example.

[0026] Figure 6 These are photographs showing the appearance of the Pickering emulsions prepared in the examples and comparative examples after 30 days of storage.

[0027] Figure 7 These are microstructure images of the Pickering emulsions prepared in the examples and comparative examples after 30 days of storage. Detailed Implementation

[0028] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0029] In this invention, chitin fibers are prepared according to the preparation method in ("Role of chitin nanocrystals and nanofiberson physical, mechanical and functional properties in thermoplastic starchfilms", "Food Hydrocolloids", AM Salaberria). Other raw materials can be purchased from the market or are commonly used in this industry. Unless otherwise specified, the methods in the following examples are conventional methods in the art.

[0030] Example

[0031] (1) Preparation of nano-chitosan fibers

[0032] Chitosan fibers were dispersed in water, and then TEMPO and NaBr were added to obtain a mixed system. The mass ratio of chitosan fibers, TEMPO, NaBr, and water in the mixed system was 5:0.08:0.8:500. Sodium hypochlorite solution was added to the mixed system, and the reaction was carried out under stirring conditions, maintaining the pH of the reaction system at 10±0.5 during the reaction. After the reaction was completed, the reaction product was thoroughly washed with deionized water to obtain oxidized chitosan fibers with a carboxyl content of 1000 μmol / g. The oxidized chitosan fibers were then subjected to high-pressure homogenization until the particle size of the oxidized chitosan fibers was less than 500 nm to obtain nano-chitosan fibers. The homogenization pressure was 1600 bar, and the treatment was repeated 3 times. The SEM microstructure of the nano-chitosan fibers is shown below. Figure 1 As shown in the TEM microstructure image of the nano-chitosan fibers, Figure 2 As shown.

[0033] (2) Preparation of Pickering emulsion

[0034] Under ice-water bath conditions, nano-chitosan fibers were dispersed in an oil-water system to obtain a Pickering emulsion. The oil-water system was prepared by mixing sunflower seed oil and water at a mass ratio of 1:5 and then homogenizing. The mass percentage of nano-chitosan fibers in the Pickering emulsion was 1%.

[0035] (3) Loading ε-polylysine

[0036] ε-polylysine solution was added to the Pickering emulsion and homogenized under ice-water bath conditions to obtain an ε-polylysine-loaded Pickering emulsion. ε-polylysine solution was added to achieve a final concentration of 0.5 mg / mL ε-polylysine in the loaded ε-polylysine Pickering emulsion. Performance characterization revealed: Encapsulation efficiency: Measured by UV-Vis spectroscopy, the encapsulation efficiency of the loaded emulsion was 97.2%; Sustained-release performance: Monitoring the release rate by dialysis showed that the sustained-release time of the loaded emulsion was extended to 206 hours (e.g., ...). Figure 3 (As shown), it exhibits excellent sustained-release properties. Antibacterial properties: The minimum inhibitory concentrations (MICs) against *Pseudomonas fluorescens* and *Bacillus subtilis* are 125 μg / mL and 100 μg / mL, respectively; inhibition zone experiments show that the diameter of the inhibition zone of the loaded emulsion is 14 mm (for *Pseudomonas fluorescens*, such as...). Figure 4 ) and 15mm (Bacillus subtilis, such as Figure 5 (As shown).

[0037] Comparative Example 1

[0038] The difference between Comparative Example 1 and Example 1 is that in step (1), the chitin fiber was not oxidized using the TEMPO-NaBr-NaClO catalytic oxidation system, but otherwise it was exactly the same as Example 1.

[0039] Comparative Example 2

[0040] The difference between Comparative Example 2 and Example 1 is that the carboxyl content of the oxidized chitin fiber is 580 μmol / g.

[0041] Comparative Example 3

[0042] The difference between Comparative Example 3 and Example 1 is that the carboxyl content of the oxidized chitin fiber is 1305 μmol / g.

[0043] Stability tests were conducted on the emulsions obtained in Examples 1-3: the emulsions were stored in a refrigerator at 4°C, and observations were made at regular intervals (droplet distribution of the emulsion was observed using an optical microscope and a laser particle size analyzer). The results are as follows. Figure 6 , Figure 7 As shown in the figure, the emulsion of Comparative Example 1 showed obvious stratification after 30 days; the oil droplet size of the emulsions of Comparative Examples 2 and 3 increased significantly after 30 days; while the oil droplet size of the emulsion of the Example remained uniformly distributed.

[0044] The nano-chitosan fibers and Pickering emulsions prepared by this invention can be widely used in the food industry, drug delivery, and biomaterials fields. For example, in the food industry, they can be used for the stabilization of vegetable oil-based emulsions and functional beverages, extending shelf life; in the drug delivery field, they can be used as carrier materials to improve drug bioavailability; and in the biomaterials field, they can be used to prepare biodegradable multifunctional emulsion materials.

[0045] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for preparing a stable ε-polylysine-loaded Pickering emulsion, characterized in that, Includes the following steps: (1) Preparation of nano-chitosan fibers Chitosan fibers were dispersed in water, and then TEMPO and NaBr were added to obtain a mixed system. The mass ratio of chitosan fibers, TEMPO, NaBr, and water in the mixed system was 5:0.08:0.8:

500. Sodium hypochlorite solution was added to the mixed system, and the reaction was carried out under stirring conditions, maintaining the pH of the reaction system at 10±0.5 during the reaction. After the reaction was completed, the reaction product was thoroughly washed with deionized water to obtain oxidized chitosan fibers with a carboxyl content of 1000 μmol / g. The oxidized chitosan fibers were subjected to high-pressure homogenization until the particle size of the oxidized chitosan fibers was less than 500 nm to obtain nano-chitosan fibers. (2) Preparation of Pickering emulsion Under ice-water bath conditions, nano-chitosan fibers were dispersed in an oil-water system to obtain a Pickering emulsion. The oil-water system was prepared by mixing sunflower seed oil and water at a mass ratio of 1:(4~5) and then homogenizing. The mass percentage of nano-chitosan fibers in the Pickering emulsion was 0.8~1%. (3) Loaded with ε-polylysine The ε-polylysine solution was added to the Pickering emulsion to achieve a final concentration of 0.5 mg / mL ε-polylysine in the loaded ε-polylysine Pickering emulsion, and homogenized under ice-water bath conditions to obtain the loaded ε-polylysine Pickering emulsion.

2. The method for preparing a stable ε-polylysine-loaded Pickering emulsion according to claim 1, characterized in that, In step (1), the homogenization conditions are: pressure 1000~1600 bar, and 2~5 cycles.

3. The method for preparing a stable ε-polylysine-loaded Pickering emulsion according to claim 1, characterized in that, The droplet size in the Pickering emulsion is 2~5μm.

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