Lavender essential oil nano-emulsion with antibacterial activity and preparation method thereof

Abstract

The invention relates to the technical field of emulsion preparation, and discloses a lavender essential oil nano-emulsion with antibacterial activity and a preparation method thereof. The lavender essential oil nano-emulsion provided by the invention takes lavender essential oil and medium chain triglyceride as oil phases and sodium caseinate and tea polyphenol as compound emulsifiers, and the preparation method comprises the following steps: (1) dissolving the sodium caseinate and the tea polyphenol in water according to a mass ratio of (1-4): 2 to prepare a compound emulsifier water phase; (2) mixing lavender essential oil with medium chain triglyceride to prepare an oil phase; (3) mixing the water phase and the oil phase, and performing high-speed shearing to form a coarse emulsion; and (4) carrying out high-pressure homogenization treatment on the crude emulsion, and preparing the nano-emulsion under the condition that the homogenization pressure is 30 to 100 MPa. Through measurement, the average particle size of the prepared nano-emulsion is smaller than 200 nm, the polydispersity index is smaller than 0.2, the encapsulation efficiency is larger than 95%, and the nano-emulsion has high stability and can achieve long-acting slow release of the lavender essential oil.

Description

Technical Field

[0001] This invention relates to the field of emulsion preparation technology, and in particular to a lavender essential oil nanoemulsion with antibacterial activity and its preparation method. Background Technology

[0002] Plant essential oils, especially lavender essential oil (LEO), have shown great potential for application in food preservation, cosmetics, and pharmaceuticals due to their broad-spectrum antibacterial activity, natural origin, and good consumer acceptance. The main active components of lavender essential oil, such as linalool and linalyl acetate, have significant inhibitory effects on foodborne pathogens (such as Escherichia coli and Staphylococcus aureus). However, lavender essential oil itself has inherent drawbacks such as high volatility, poor water solubility, and chemical instability (easily oxidized and sensitive to light and heat). These inherent drawbacks lead to the easy loss of active ingredients during processing, storage, and use, resulting in low bioavailability and severely limiting its direct application.

[0003] To overcome the aforementioned drawbacks, microencapsulation and emulsification technologies are often used to encapsulate and protect essential oils. Nanoemulsion technology, as an effective strategy, can disperse essential oils into nanoscale droplets (typically <500 nm), significantly improving their specific surface area, stability, and bioavailability.

[0004] Existing technologies have made some attempts at nanoemulsion encapsulation and protection of lavender essential oil. For example, Chinese patent application CN114010541A discloses a method for preparing lavender essential oil emulsion. This method involves adding deionized water, gelatin, glycerin, and an emulsifier to xanthan gum to obtain a continuous phase; using lavender essential oil as the dispersed phase; and using an essential oil emulsion membrane as the emulsification medium. Pressure is provided by a compressed air tank, and under the transmembrane pressure difference, the dispersed phase is forced into the membrane tubes of the essential oil emulsion membrane to form a jet. Under the shear force of the continuous phase, the dispersed phase leaves the surface of the membrane tubes and enters the continuous phase, forming the lavender essential oil oil-in-water emulsion. This patented method achieves the emulsification of lavender essential oil by strictly controlling the conditions of the essential oil emulsion membrane formation process. However, the emulsification effect of this method is still not ideal. The average particle size of the emulsion droplets is 800 nm. The larger droplets are prone to flocculation and aggregation, resulting in poor stability of the lavender essential oil emulsion. At the same time, excessively large particle size or uneven distribution may lead to a rough and not delicate texture of the emulsion.

[0005] In addition, the emulsifier system used in the method of this patent is a single emulsifier. In complex food environments (such as different pH, ionic strength, and temperature fluctuations), the interfacial film of such emulsions is often not dense enough, and droplet aggregation, Ostwald ripening, or stratification are likely to occur, which will cause the encapsulated active ingredients to leak out prematurely, thus failing to achieve long-term sustained release. Summary of the Invention

[0006] To address the aforementioned technical problems of large droplet size and poor emulsion stability in lavender essential oil emulsions, this invention provides a lavender essential oil nanoemulsion with antibacterial activity and its preparation method.

[0007] The specific technical solution of this invention is as follows:

[0008] In a first aspect, the present invention provides a lavender essential oil nanoemulsion with antibacterial activity, comprising an oil phase, an aqueous phase, and a composite emulsifier, wherein:

[0009] The aqueous phase is used as a continuous phase;

[0010] The oil phase serves as the dispersed phase and contains lavender essential oil and medium-chain triglycerides (MCT).

[0011] The composite emulsifier is composed of sodium caseinate (NaCas) and tea polyphenols (TP).

[0012] This invention aims to address the problems of high volatility, low water solubility, poor thermal stability, easy oxidation and degradation, and low bioavailability of lavender essential oil during application, while overcoming the shortcomings of traditional emulsions such as large droplet size, poor stability in complex food systems, and easy leakage of active ingredients. The invention provides the aforementioned lavender essential oil nanoemulsion.

[0013] The lavender essential oil nanoemulsion provided by this invention uses lavender essential oil and medium-chain triglycerides as the oil phase and sodium caseinate and tea polyphenols as a composite emulsifier. Through the action of the composite emulsifier, the oil phase is stably dispersed in the aqueous phase in the form of tiny droplets. Specifically, sodium caseinate forms a stable protective film on the surface of the oil droplets, and the composite structure formed by tea polyphenols rich in phenolic hydroxyl groups and sodium caseinate through hydrogen bonding and electrostatic interactions enhances the density and stability of the interfacial film, thereby giving the oil phase a better emulsification effect. The synergistic effect of these two components effectively inhibits essential oil oxidation and droplet aggregation, significantly improving the physicochemical stability of the system. Measurements show that the average particle size of the prepared nanoemulsion is less than 200 nm, the polydispersity index is less than 0.2, and the encapsulation efficiency is greater than 95%. Furthermore, this nanoemulsion exhibits high stability and can achieve long-term sustained release of lavender essential oil.

[0014] As a preferred option, the mass ratio of sodium caseinate to tea polyphenols is (1~4):2.

[0015] Sodium caseinate and tea polyphenols work synergistically to effectively inhibit essential oil oxidation and oil droplet aggregation, significantly improving the physicochemical stability of the system. Sodium caseinate acts as an interfacial membrane, forming a physical barrier between the oil and aqueous phases, while tea polyphenols strengthen this physical barrier.

[0016] When the sodium caseinate content is too low, the interfacial coverage is poor and the membrane strength is weak. Tea polyphenols need to adhere to sodium caseinate to exert their reinforcing effect. Without sufficient sodium caseinate as a "membrane skeleton," tea polyphenols cannot effectively strengthen the interfacial membrane. In this case, the interfacial membrane is very fragile and incomplete. Therefore, when the sodium caseinate content is too low, the droplets of the prepared emulsion are very prone to agglomeration upon collision after formation, leading to a rapid increase in emulsion particle size, a wider distribution (increased PDI value), and even rapid phase separation.

[0017] When the sodium caseinate content is excessive, the excess sodium caseinate molecules will adsorb at the interface, but may not form the most compact aggregate. This results in a thick interfacial film, but with a relatively loose structure and insufficient mechanical strength. Under the stress of high-pressure homogenization or long-term storage, this film is easily damaged, and droplets are more likely to coalesce. At the same time, when the sodium caseinate content is excessive, there are free sodium caseinate molecules in the solution that have not been adsorbed to the interface. These molecules may simultaneously adsorb to the interface of two or more oil droplets, connecting the droplets like "bridges," leading to bridging flocculation problems and a sharp decrease in emulsion stability.

[0018] Further optimization yields a mass ratio of sodium caseinate to tea polyphenols of 2:1.

[0019] Experiments have verified that the lavender essential oil nanoemulsion prepared with a mass ratio of sodium caseinate to tea polyphenols of 2:1 exhibits the best performance, with an average particle size of 142.8 nm, uniform distribution (PDI=0.089), and a Zeta potential of -30.89 mV, demonstrating excellent physical stability. Its encapsulation efficiency for lavender essential oil is as high as 98.61%, and the cumulative release rate within 15 days is less than 7.5%, following zero-order release kinetics, thus achieving long-term and controllable release of the active ingredients of the essential oil.

[0020] Preferably, the volume ratio of lavender essential oil to medium-chain triglycerides is 1:(0.8~1.2).

[0021] This invention uses medium-chain triglycerides as the oil phase filler, which is mixed with lavender essential oil to form the oil phase of the emulsion system. Pure lavender essential oil has low viscosity and is highly volatile; excessively high essential oil concentrations may put excessive pressure on the emulsion film or emulsifier interface. Mixing lavender essential oil with medium-chain triglycerides, using the medium-chain triglycerides as the matrix, helps reduce the risk of rapid emulsion separation due to excessive density differences between the oil and water phases, thus improving the physical stability of the emulsion. Furthermore, during emulsification, the molecular structure of medium-chain triglycerides helps emulsifier molecules to arrange themselves more tightly at the oil-water interface. Working together with the components of lavender essential oil, this strengthens the "protective layer" surrounding each essential oil droplet, significantly inhibiting droplet aggregation, coalescence (agglomeration), and buoyancy (emulsification), ensuring the long-term stability of the nanoemulsion.

[0022] Preferably, the aqueous phase is water. For example, deionized water is used as a continuous aqueous phase.

[0023] Secondly, the present invention provides a method for preparing lavender essential oil nanoemulsion, characterized by comprising the following steps:

[0024] Step S1: Dissolve sodium caseinate and tea polyphenols in water to obtain an aqueous solution;

[0025] Step S2: Mix lavender essential oil with medium-chain triglycerides to obtain an oil phase solution;

[0026] Step S3: Mix the oil phase and the aqueous phase, and shear at high speed to obtain a crude emulsion;

[0027] Step S4: Take the crude emulsion and perform high-pressure homogenization to obtain a lavender essential oil nanoemulsion.

[0028] In the lavender essential oil nanoemulsion of this invention, lavender essential oil and medium-chain triglycerides are used as the oil phase, and sodium caseinate and tea polyphenols are used as composite emulsifiers. This invention uses high-pressure homogenization to form a homogeneous system, so that the oil phase is stably dispersed in the aqueous phase in the form of nano-sized droplets.

[0029] Preferably, in step S4, the pressure of the high-pressure homogenization process is 30 MPa to 100 MPa.

[0030] Further optimization can be achieved by using a homogenization period of 1 to 10 cycles.

[0031] Preferably, in step S3, the high-speed shearing speed is 10000~15000 rpm.

[0032] Further optimization involves a high-speed shearing rate of 1 to 10 minutes.

[0033] Thirdly, the present invention provides the application of lavender essential oil nanoemulsion or emulsion prepared by the preparation method according to any one of claims 6 to 8 in the preparation of antibacterial agents.

[0034] Preferably, the antibacterial agent is used in the preparation of food, cosmetics or pharmaceutical products.

[0035] Compared with the prior art, the present invention has the following technical effects:

[0036] (1) The lavender essential oil nanoemulsion provided by the present invention is formed with lavender essential oil and medium-chain triglycerides as the oil phase and sodium caseinate and tea polyphenols as composite emulsifiers. Through the action of the composite emulsifiers, the oil phase is stably dispersed in the aqueous phase in the form of tiny droplets. Among them, sodium caseinate forms a stable protective film on the surface of the oil droplets, and tea polyphenols rich in phenolic hydroxyl groups form a composite structure with sodium caseinate through hydrogen bonding and electrostatic interaction, which enhances the density and stability of the interfacial film, thereby making the oil phase have a better emulsification effect. Based on this, the present invention provides an optimal mass ratio of (1~4):2 between the two to form a synergistic effect, thereby effectively inhibiting the oxidation of essential oil and the aggregation of oil droplets, and significantly improving the physicochemical stability of the system. It has been determined that the average particle size of the prepared nanoemulsion is less than 200 nm, the polydispersity index is less than 0.2, the encapsulation rate is greater than 95%, and the nanoemulsion has high stability and can achieve long-term sustained release of lavender essential oil.

[0037] (2) This invention provides a method for preparing a lavender essential oil nanoemulsion, comprising: (1) dissolving sodium caseinate and tea polyphenols in water at a mass ratio of (1~4):2 to prepare a composite emulsifier aqueous phase; (2) mixing lavender essential oil with medium-chain triglycerides to prepare an oil phase; (3) mixing the aqueous phase and the oil phase and then shearing at high speed to form a crude emulsion; (4) subjecting the crude emulsion to high-pressure homogenization treatment, and obtaining the nanoemulsion under a homogenization pressure of 30 MPa~100 MPa. This invention achieves efficient encapsulation and effective dispersion of lavender essential oil through high-pressure homogenization technology. Attached Figure Description

[0038] Figure 1 The results of CLSM measurement of tea polyphenols in the nanoemulsion prepared in Example 1 are shown below.

[0039] Figure 2 The results of CLSM measurements of free LEO in the nanoemulsion prepared in Example 1 are shown.

[0040] Figure 3 The cumulative LEO release percentage of the nanoemulsion prepared in Example 1 was measured.

[0041] Figure 4 The results are the antibacterial properties test results of the nanoemulsions prepared in Examples 1, 4 and 7. Detailed Implementation

[0042] The present invention will be further described below with reference to embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0043] In the following examples, the medium-chain triglycerides were purchased from Shanghai Yuanye Biotechnology Co., Ltd., model S25953.

[0044] Example 1

[0045] A lavender essential oil nanoemulsion is provided, and the preparation steps are as follows:

[0046] (1) Preparation of the aqueous phase of the composite emulsifier:

[0047] Sodium caseinate and tea polyphenols were accurately weighed at a mass ratio of 2:1 and added to deionized water to prepare a composite emulsifier solution with a total concentration of 2% (w / v). The solution was stirred with a magnetic stirrer at room temperature for 2 hours until it was completely dissolved, forming a clear and transparent aqueous solution for later use.

[0048] (2) Preparation of the oil phase:

[0049] Mix lavender essential oil and medium-chain triglycerides (MCT) at a volume ratio of 1:1, and stir overnight at a constant temperature of 25°C to ensure that the two oil phases are fully miscible and form a stable oil phase system for later use.

[0050] (3) Initial formation of crude emulsion:

[0051] The aqueous phase and oil phase were mixed at a volume ratio of 95:5 and sheared for 2 minutes at 12,000 rpm using a high-speed shearing machine to form a preliminary coarse emulsion, ensuring that the oil phase was uniformly dispersed in the aqueous phase.

[0052] (4) Refining treatment of nanoemulsions:

[0053] The crude emulsion was transferred to a high-pressure homogenizer and immediately refined using the homogenizer. The homogenization pressure was set to 70 MPa, and the cycle time was set to 5 cycles. After the high-pressure homogenization process was completed, a lavender essential oil nanoemulsion with uniform particle size and stable dispersion was obtained.

[0054] Example 2

[0055] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the homogenization pressure in step (4) is set to 30 MPa. The other steps are the same as in Example 1.

[0056] Example 3

[0057] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the homogenization pressure in step (4) is set to 100 MPa. The other steps are the same as in Example 1.

[0058] Example 4

[0059] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 1:2. The other steps are the same as in Example 1.

[0060] Example 5

[0061] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, the only difference is that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 1:2, and the homogenization pressure in step (4) is set to 30 MPa. The other steps are the same as in Example 1.

[0062] Example 6

[0063] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, the only difference is that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 1:2, and the homogenization pressure in step (4) is set to 50 MPa. The other steps are the same as in Example 1.

[0064] Example 7

[0065] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 1:1. The other steps are the same as in Example 1.

[0066] Example 8

[0067] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, the only difference is that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 1:1, and the homogenization pressure in step (4) is set to 30 MPa. The other steps are the same as in Example 1.

[0068] Example 9

[0069] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, the only difference is that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 1:1, and the homogenization pressure in step (4) is set to 50 MPa. The other steps are the same as in Example 1.

[0070] Example 10

[0071] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the volume ratio of lavender essential oil to medium-chain triglycerides in step (3) is 1:0.8. The other steps are the same as in Example 1.

[0072] Example 11

[0073] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the volume ratio of lavender essential oil to medium-chain triglycerides in step (3) is 1:1.2. The other steps are the same as in Example 1.

[0074] Comparative Example 1

[0075] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 0:1, that is, sodium caseinate is not added. The other steps are the same as in Example 1.

[0076] Comparative Example 2

[0077] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 3:1. The other steps are the same as in Example 1.

[0078] Comparative Example 3

[0079] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that the mass ratio of sodium caseinate to tea polyphenols in step (1) is 1:0, that is, no tea polyphenols are added. The other steps are the same as in Example 1.

[0080] Comparative Example 4

[0081] A lavender essential oil nanoemulsion is provided. The preparation method is the same as that in Example 1, except that medium-chain triglycerides are not added in step (3). The other steps are the same as in Example 1.

[0082] Performance Characterization

[0083] 1. The particle size, PDI (polydispersity index), and Zeta potential of the lavender essential oil nanoemulsions obtained in Examples 1 to 11 and Comparative Examples 1 to 3 were determined. The test conditions were 25°C, and the samples were diluted 1000 times before measurement. Each group of samples was repeated three times, and the average value was taken as the final result. The results are shown in Table 1.

[0084] Table 1 Average particle size (nm) PDI Zeta potential (mV) Example 1 142.8±0.5 0.089 -30.89 Example 2 156.3±1.2 0.105 -28.45 Example 3 138.7±0.8 0.095 -31.22 Example 4 185.6±2.1 0.165 -22.17 Example 5 198.4±2.8 0.178 -20.56 Example 6 189.2±2.3 0.171 -21.34 Example 7 165.4±1.5 0.128 -25.67 Example 8 178.9±1.9 0.142 -24.13 Example 9 171.3±1.7 0.135 -24.85 Example 10 148.2±1.1 0.098 -29.78 Example 11 145.6±0.9 0.092 -30.15 Comparative Example 1 559.4±15.2 0.335 -36.65 Comparative Example 2 287.3±8.5 0.256 -18.47 Comparative Example 3 326.7±9.8 0.298 -15.23 Comparative Example 4 412.5±11.4 0.312 -12.45 .

[0085] The test results show that the lavender essential oil nanoemulsions obtained in Examples 1 to 11 of this invention have particle sizes in the nanoscale range (<200 nm) and PDI below 0.2, indicating that the emulsion droplets prepared by the method of this invention have highly uniform droplet sizes. The absolute value of the Zeta potential is higher than 20 mV, indicating that there is sufficient electrostatic repulsion between droplets, and the system has good dispersion stability. This is due to the effect of the composite emulsifier of this invention forming a dense interfacial film through hydrogen bonding and hydrophobic interaction, effectively inhibiting droplet aggregation.

[0086] Furthermore, in Example 1, compared with other examples and comparative examples, the emulsifier ratios (i.e., homogenization parameters) were different. Specifically, when the mass ratio of sodium caseinate to tea polyphenols was 2:1 and the homogenization pressure was 70 MPa, the resulting emulsion had an average particle size of 142.8 ± 0.5 nm, a PDI of 0.0899, and a Zeta potential of −30.89 mV, exhibiting optimal emulsion characterization data. Therefore, it is evident that optimizing the emulsifier ratio and homogenization parameters plays a crucial role in controlling the particle size and improving the stability of the emulsion.

[0087] 2. The lavender essential oil nanoemulsions obtained in Examples 1 to 11 and Comparative Examples 1 to 3 were subjected to storage stability tests. The test method was as follows: the nanoemulsions were placed in a sealed container and stored at room temperature (25±1℃) in the dark for 28 days. The changes in particle size, PDI, and Zeta potential were measured periodically (0 days, 7 days, 14 days, 21 days, and 28 days). The particle size change rate, PDI value, and Zeta potential value of each emulsion on the 28th day of storage were recorded in Table 2.

[0088] Table 2 Average particle size change rate (%) PDI Zeta potential (mV) Example 1 4.55 0.095 -31.45 Example 2 7.94 0.118 -27.89 Example 3 5.41 0.102 -30.56 Example 4 17.67 0.203 -19.34 Example 5 23.89 0.235 -16.78 Example 6 20.77 0.218 -18.92 Example 7 12.64 0.152 -24.11 Example 8 14.98 0.171 -22.45 Example 9 13.60 0.163 -23.18 Example 10 5.80 0.106 -28.92 Example 11 5.22 0.101 -29.34 Comparative Example 1 56.08 0.478 +12.47 Comparative Example 2 43.57 0.389 -8.56 Comparative Example 3 48.73 0.425 -6.78 Comparative Example 4 53.87 0.445 -4.23 .

[0089] The results showed that the lavender essential oil nanoemulsions obtained in Examples 1 to 11 of this invention exhibited excellent storage stability during a 28-day storage period. The emulsions were uniform and transparent in appearance, without any stratification or separation. The nanoemulsion prepared by the sodium caseinate-tea polyphenol (2:1) composite emulsifier had an initial particle size of 142.8 nm, a PDI of 0.089, and a Zeta potential of -30.89 mV. After 28 days of storage, the particle size change rate was less than 10%, the PDI remained below 0.2, and the absolute value of the Zeta potential was still above 30 mV, indicating that it has high electrostatic stability. This confirms that the composite emulsifier forms a dense interfacial film through hydrogen bonding and hydrophobic interactions, effectively inhibiting changes such as oil droplet aggregation, and achieving long-term stable encapsulation of lavender essential oil.

[0090] Compared to the composite emulsifier (sodium caseinate-tea polyphenols) system, the sodium caseinate-only emulsifier system in Comparative Example 1 exhibited poor stability. The sodium caseinate-only emulsifier system showed significant instability after 14 days of storage, with the particle size fluctuating from an initial 559.4 nm to 472.7 nm, the PDI changing dramatically between 0.335 and 0.478, and the absolute value of the Zeta potential reversing from 36.65 mV to 44.5 mV, indicating a significant decrease in stability. Meanwhile, Comparative Example 2, using a sodium caseinate to tea polyphenol mass ratio of 3:1 as the emulsification system, also showed poor stability. This demonstrates the synergistic effect between sodium caseinate and tea polyphenols; their synergy effectively inhibits essential oil oxidation and oil droplet aggregation, significantly improving the physicochemical stability of the system. When the sodium caseinate content is too low, the interfacial coverage is low, the membrane strength is poor, and the interfacial membrane is very fragile and incomplete. When the sodium caseinate content is too high, excess sodium caseinate molecules will be adsorbed at the interface, but may not be able to form the densest packing. Neither too much nor too little sodium caseinate content can form a dense interfacial membrane, resulting in poor emulsion stability.

[0091] Compared to the composite emulsifier (sodium caseinate-tea polyphenols) system, the system using only tea polyphenols as the emulsifier in Comparative Example 3 exhibited extremely poor stability. While sodium caseinate alone could form an adsorption layer at the interface, it lacked the hydrophobic effect and antioxidant enhancement of tea polyphenols. The interfacial film structure was simple and insufficiently dense, making it susceptible to oxidative stress and molecular rearrangement during long-term storage. Data showed that its initial particle size was as high as 326.7 nm, further increasing to 485.9 nm by day 28, with a particle size change rate of 48.73%. The PDI value reached 0.425, indicating extremely uneven droplet distribution. The absolute value of the Zeta potential decreased to 6.78 mV, resulting in insufficient electrostatic repulsion and ultimately obvious stratification. This confirms that tea polyphenols do not merely play an auxiliary role, but rather significantly enhance the rigidity and chemical stability of the interfacial film through synergistic effects of hydrogen bonding and hydrophobicity. The absence of this component prevented the emulsion from inhibiting essential oil oxidation and droplet aggregation, leading to a sharp decline in physicochemical stability.

[0092] Compared to the lavender essential oil and medium-chain triglyceride composite oil phase in Example 1, Comparative Example 4, which did not include medium-chain triglycerides, exhibited poor emulsion stability. Lacking the synergistic effect of MCT, the oil phase viscosity was excessively high and its crystallization behavior was unstable, making it difficult to break down to the nanoscale during high-pressure homogenization. Simultaneously, the pure essential oil lacked the flexible molecular filling effect provided by MCT, making it difficult for the emulsifier to form a tightly packed "protective layer" at the interface. The initial particle size of this system was as high as 412.5 nm. During storage, due to aging and oil droplet aggregation, the particle size surged to 634.7 nm on day 28, an increase of 53.87%, with a PDI of 0.445 and a Zeta potential of only 4.23 mV. The electrostatic barrier almost completely failed, resulting in severe stratification. This fully demonstrates that MCT is not only an oil phase diluent but also plays a decisive role in achieving stable nanoscale dispersion by adjusting the polarity of the oil phase, inhibiting essential oil crystallization, and enhancing the molecular packing density of the interfacial film.

[0093] 3. Fluorescent labeling of the emulsion was observed using a laser confocal scanning microscope (CLSM). The method was as follows: Nile red was used to label lavender essential oil (green fluorescence), and fluorescein isothiocyanate (FITC) was used to label tea polyphenols (red fluorescence). 10 μL of the stained sample was placed on a glass slide, covered with a coverslip, and observed under CLSM. The excitation wavelengths were set to 433 nm (Nile red) and 688 nm (FITC), respectively. Images were acquired and overlaid for analysis. The CLSM measurement results of tea polyphenols in the emulsion in Example 1 are shown below. Figure 1 The CLSM measurement chart of free LEO in this emulsion is shown below. Figure 2 .

[0094] The image results show that the emulsion droplets in Example 1 are regular spherical with uniform particle size distribution. The core of the oil droplets exhibits green fluorescence, and the surface is uniformly coated with red fluorescence, indicating that tea polyphenols and sodium caseinate together form a stable interfacial film, successfully encapsulating lavender essential oil inside.

[0095] 4. Determine the encapsulation efficiency and release performance of the lavender essential oil nanoemulsion prepared in Example 1. The method was as follows: the content of free lavender essential oil in the emulsion was determined by ultraviolet spectrophotometry, and the encapsulation efficiency (EE) was calculated; the release behavior of the emulsion at 4°C was monitored. The cumulative LEO release percentage of the nanoemulsion is shown in [the table below]. Figure 3 .

[0096] The results showed that the emulsion obtained in Example 1 had an encapsulation efficiency of up to 98.61% for lavender essential oil, and the free essential oil content was only 34.64 μg / mL.

[0097] The results also showed that the cumulative LEO release rate of the emulsion obtained in Example 1 was less than 7.5% within 15 days, and the release process conformed to the zero-order kinetic model (R0). 2= 0.97), exhibiting good sustained-release performance. This is mainly attributed to the "network barrier" structure formed by sodium caseinate and tea polyphenols, which effectively inhibits the diffusion and volatilization of essential oil molecules. The cumulative LEO release percentage results of the nanoemulsions in Examples 1 to 9 also show that the release process conforms to the zero-order kinetic model (R0.97). 2 = 0.97).

[0098] 5. The antibacterial properties of the lavender essential oil nanoemulsions obtained in Examples 1, 4, and 7 were evaluated using the inhibition zone method and the minimum inhibitory concentration (MIC) method. The test bacteria were *Escherichia coli* and *Staphylococcus aureus*, with a bacterial concentration of 10⁻⁶. 7 CFU / mL. Results are shown below. Figure 4 In this context, “SC:TP=2:1” represents the emulsion of Example 1, “SC:TP=1:1” represents the emulsion of Example 7, and “SC:TP=1:2” represents the emulsion of Example 4.

[0099] The results showed that the lavender essential oil nanoemulsions of Examples 1, 4, and 7 all exhibited significant antibacterial activity against both types of bacteria, with clear inhibition zones and a MIC value of 62.5 μg / mL. The inhibition zone diameter against Staphylococcus aureus was larger than that against Escherichia coli, possibly due to differences in their cell wall structures: Staphylococcus aureus is a Gram-positive bacterium with a thick peptidoglycan layer, allowing hydrophobic essential oil components to penetrate more easily; Escherichia coli is a Gram-negative bacterium with a stronger outer membrane barrier, resulting in a slower essential oil penetration rate. Furthermore, the results also showed that the emulsion prepared in Example 1 had the largest inhibition zone, followed by Example 7, while Example 4 had the smallest.

[0100] Under the condition of maintaining a consistent total addition amount, the differences in the antibacterial zone observed in the experimental results are essentially determined by the different SC:TP ratios. These different SC:TP ratios directly determine the effective release concentration of lavender essential oil from the nanoemulsion in the agar diffusion system. This indicates that the nanoemulsion prepared in Example 1, when the sodium caseinate to tea polyphenol ratio is 2:1, forms a dense interfacial film structure (achieving a minimum particle size of 142.8 nm and a maximum encapsulation rate of 98.61%, as shown in Table 1). This not only enhances the stability of the essential oil but, more importantly, avoids the sudden depletion of active ingredients by slowing down the release rate. Consequently, the number of free essential oil molecules continuously diffusing into the agar during the 24-hour experimental period is significantly higher than in other ratio groups, resulting in a higher dynamic equilibrium concentration within the antibacterial zone. Conversely, when SC:TP = 1:2, the excessively low sodium caseinate content leads to a loose interfacial film, causing the essential oil to be rapidly released and degraded in the early stages of the experiment, significantly reducing the effective concentration.

[0101] Therefore, it is evident that improving the utilization efficiency of essential oils through synergistic optimization with emulsifiers can achieve a more significant antibacterial effect, providing crucial technical support for this invention. Furthermore, compared to unencapsulated pure essential oils, the nanoemulsion exhibits a stronger antibacterial effect at the same essential oil concentration, indicating that nano-encapsulation not only protects the activity of the essential oils but also enhances their interaction with bacterial cells, thereby improving antibacterial efficiency. These results demonstrate that the nanoemulsion system constructed in this invention possesses excellent antibacterial application potential and is suitable for fields such as food preservation and antibacterial packaging.

[0102] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A lavender essential oil nanoemulsion with antibacterial activity, characterized in that: Includes oil phase, aqueous phase, and complex emulsifiers, among which: The aqueous phase is a continuous phase; The oil phase serves as the dispersed phase and comprises lavender essential oil and medium-chain triglycerides; The composite emulsifier is composed of sodium caseinate and tea polyphenols.

2. The lavender essential oil nanoemulsion as described in claim 1, characterized in that: The mass ratio of sodium caseinate to tea polyphenols is (1~4):

2.

3. The lavender essential oil nanoemulsion as described in claim 1 or 2, characterized in that: The mass ratio of sodium caseinate to tea polyphenols is 2:

1.

4. The lavender essential oil nanoemulsion as described in claim 1, characterized in that: The volume ratio of lavender essential oil to medium-chain triglycerides is 1:(0.8~1.2).

5. The lavender essential oil nanoemulsion as described in claim 1, characterized in that: The aqueous phase is water.

6. A method for preparing a lavender essential oil nanoemulsion as described in any one of claims 1 to 5, characterized in that: Includes the following steps: Step S1: Dissolve sodium caseinate and tea polyphenols in water to obtain an aqueous solution; Step S2: Mix lavender essential oil with medium-chain triglycerides to obtain an oil phase solution; Step S3: Mix the oil phase and the aqueous phase, and shear at high speed to obtain a crude emulsion; Step S4: Take the crude emulsion and perform high-pressure homogenization to obtain a lavender essential oil nanoemulsion.

7. The preparation method according to claim 6, characterized in that: In step S4, the pressure of the high-pressure homogenization process is 30 MPa to 100 MPa.

8. The preparation method according to claim 6, characterized in that: In step S3, the high-speed shearing speed is 10000~15000 rpm.

9. The use of the lavender essential oil nanoemulsion as described in any one of claims 1 to 5 or the emulsion prepared by the preparation method as described in any one of claims 6 to 8 in the preparation of antibacterial agents.

10. The application as described in claim 9, characterized in that: The antibacterial agent is used in the preparation of food, cosmetics or pharmaceutical products.

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