Process for producing microemulsion system of nano essential oil

Abstract

The invention relates to the process for producing an microemulsion system of nano essential oil, the process comprising the following steps: (i) preparing a dispersed phase of essential oil; (ii) preparing of a carrier formed from a mixture of diethylene glycol monoethyl ether and lecithin; (iii) adding the carrier to the dispersed phase while keeping the dispersed phase temperature between 60 and 100° C. after addition of the carrier, while simultaneously stirring under vacuum; then pass the entire solution mixture through the system of high-pressure homogeneous machine integrated dispersion nozzle; (iv) adding the solution mixture obtained in step (iii) to Capryol 90 while keeping the mixture temperature between 60 and 100° C., and stirring at a rate ranging from 400 up to 800 rpm under vacuum; (v) cooling the mixture, homogenizing the mixture by ultrasonication to achieve a droplet size smaller than 100 nm.

Claims

1. A process for producing a microemulsion system of nano essential oil comprising the steps of: (i) preparing a dispersed phase by heating an essential oil to a temperature between 60 and 100° C., the essential oil selected from a group consisting of: Basil; Rose; Amber; Bergamot; Rosemary; Black tea; Black pepper; Tea tree; Tabac; Cedarwood; Thyme; Fig leaf; Clove; Ylang Ylang; Ambroxan; Frankincense; Grapefruit; Daisy; Geranium; Vetiver; Saffron; Lavender; Sandalwood; Oud; Nutmeg; Musk; Whisky wine; Palmarosa; Jasmine; Rum; Patchouli; Magnolia flower; and Cinnamon; (ii) preparing a carrier by heating a mixture of diethylene glycol monoethyl ether and lecithin at a weight ratio of between 5:1.5 and 6:1 to a temperature ranging from 60° C. to 100° C. under vacuum by using a rotary vacuum evaporator system, followed by cooling the mixture to 30° C., then ultrasonicating the mixture for 30 minutes, followed by magnetic stirring, and then heating the mixture at a temperature from 60° C. to 100° C., within 30 minutes, collecting the mixture and introducing into the rotary vacuum evaporator system, and continuing to stir at 100° C.; (iii) adding the carrier to the dispersed phase obtained in step (i) at a weight ratio of between 2:1.5 and 2:1 while keeping a dispersed phase temperature between 60° C. and 100° C. after addition the carrier, while simultaneously stirring at a rate ranging from 400 to 800 rpm under vacuum; then passing the mixture through a system of a high-pressure homogeneous machine integrated with a dispersion nozzle; (iv) adding the mixture obtained in step (iii) to Capryol 90 (propylene glycol monocaprylate) at a weight ratio of between 4:1.5 and 4.5:1 while keeping the mixture temperature between 60° C. and 100° C. after the addition of Capryol 90, then stirring at a rate ranging from 400 to 800 rpm under vacuum; and (v) preparing a microemulsion system of nano essential oil by cooling the mixture obtained in step (iv) to 25° C., homogenizing the mixture by ultrasonication using an ultrasonic homogenizer over a period from 30 to 60 minutes to achieve a droplet size smaller than 100 nm, controlling a quality of a resultant product by dissolution in water and performing emulsifying on the mixture in an emulsifying device at a stirring rate ranging from 400 to 800 rpm to obtain a microemulsion system of nano essential oil.

2. The process according to claim 1, in which in step (ii), the weight ratio of diethylene glycol monoethyl ether and lecithin is 5:1.

3. The process according to claim 1, in which in step (iii), the weight ratio of the carrier and the dispersed phase is 2:1.

4. The process according to claim 1, in which in step (iv), the weight ratio of the solution mixture obtained in step (iii) and Capryol 90 (propylene glycol monocaprylate) is 4:1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an image to compare the dispersibility in water of between (A) essential oil and (B) nano essential oil obtained by the process according to the invention; and

(2) FIG. 2 represents a TEM spectrum of essential oil nanodroplets with size smaller than 100 nm obtained by the process according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) A process for producing a microemulsion system of nano essential oil according to the invention is performed as follows: (i) Preparing a dispersed phase by heating an essential oil to a temperature between 60 and 100° C. The heating enables the dispersed phase to be better combined with a carrier. (ii) Preparing the carrier by heating a mixture of diethylene glycol monoethyl ether and lecithin at the weight ratio of between 5:1.5 and 6:1, preferably 5:1, to a temperature between 60 and 100° C. under vacuum by using a rotary vacuum evaporator system over a period ranging from 30 to 60 minutes, followed by cooling the mixture to 30° C., then respectively ultrasonicating for 30 minutes, magnetic stirring, and heating at a temperature between 60 and 100° C. for 30 minutes, collecting the solution and introducing into the rotary vacuum evaporator system, and continuing to stir at 100° C. over a period ranging from 30 to 60 minutes.

(4) When used, the essential oils can be denatured by light, and temperature, and are often destroyed in the digestive tract. Therefore, there is a demand for a process for producing essential oil microdroplets of small size with capsule, having a stable structure, a non-binding property, and a high solubility. Because the microemulsion system according to the invention is used in food and pharmaceutical industries, the carriers selected for use must be highly safe, and non-toxic with few side effects. Diethylene glycol monoethyl ether is a mixture of propylene glycol monoester and fatty acid dieter composed mainly of caprylic acid. The contents of monoester and diester vary for the two types (Type I and Type II) of propylene glycol monocaprylate with acknowledged safety.

(5) With properties as a specific soluble carrier for injections, solutions (in pharmacy and veterinary), and agents for adjustment and stabilization of viscosity, and for formation of microemulsion liquids, diethylene glycol monoethyl ether helps to emulsify and form good microemulsion systems with increased absorption. However, since the carrier if used on the skin in high dosages will cause irritation, the maximum level of essential oil-based carrier must not exceed 10%. Lecithin is a very popular food additive and is acknowledged as safe to human health by the Europe.

(6) Lecithin is essentially a type of phospholipid which is found in every cell of the human body. The chemical formula of lecithin shows that lecithin is a fat, but a structural component of the lecithin molecule can dissolve in water. This allows lecithin to emulsify essential oils, and advocate their dispersion in water. However, lecithin itself is only capable of loading up to 5-10% of the active ingredient and for effective loading, it is required for a certain level of purity, and complicated separation processes.

(7) In addition, the lecithin price is very high, with the cosmetic production processes using only lecithin still containing impurities, being not refined, and having low delivery efficiency. Therefore, in order to form a stable and safe microemulsion system for users that the product can be used both on the skin and orally, the combination of diethylene glycol monoethyl ether and lecithin at the weight ratio of 5:1.5 to 6:1, preferably 5:1, to form an optimal delivery efficiency for the essential oil of up to 30%, while ensuring formation of nanodroplets with a size smaller than 100 nm that are completely dispersed in water to form a homogeneous transparent solution system. This is a complete difference that has produced advantageous delivery efficiency when compared to existing processes.

(8) If the ratio of diethylene glycol monoethyl ether and lecithin is less than 5:1.5, it is possible that the resulting carrier may not carry the whole amount of oil, resulting in the droplet sizes being inconsistent, and the resultant system being unstable and likely to have layer separation. If the above ratio is higher than 6:1, the lecithin amount will remain in the system, which goes wasted and makes the system less stable.

(9) In the carrier preparing, the invention uses diethylene glycol monoethyl ether and lecithin with a studied ratio, that is different from the known solutions, particularly from the solution described in CN105640846 A (Wang Lu) for producing peppermint essential oil emulsion preparation. The preparation when directly applied on the skin inducing a whitening effect is in oil emulsion form, used for direct application and no applicable to other products. This process only involves the use of lecithin herein for stabilization of the system, but not for retention of the droplet stability in a long term, and the resultant emulsion system is insoluble in water, which is completely different from when using diethylene glycol monoethyl ether and lecithin at the same ratio according to the invention. According to the invention, the studied ratio by the inventors under said conditions helps to reduce the impact on the lecithin structure, and the diethylene glycol monoethyl ether helps to increase the delivery capacity of the active substance, and the combination of the two substances at said ratio allow the loading capacity to increase as many times as using lecithin alone.

(10) (iii) Adding the carrier to the dispersed phase at the weight ratio of between 2:1.5 and 2:1, preferably 2:1, while keeping the temperature of the dispersed phase from 60 to 100° C. after addition of the carrier, while simultaneously stirring at a rate ranging from 400 to 800 rpm under vacuum over a period ranging from 30 to 60 minutes; then introducing the whole solution mixture into a high-pressure homogenizer integrated with a dispersion nozzle.

(11) At the weight ratio of the carrier to the dispersed phase ranging from 2:1.5 to 2:1, preferably 2:1, the reaction yield is the most optimal that ensures that all substances in the dispersed phase are fully delivered by the carrier, and there is no excess carrier in the system.

(12) The combination of the carrier as a mixture of diethylene glycol monoethyl ether and lecithin, and specialized processing steps helps to achieve the most optimal interaction with and encapsulation of the dispersed phase. The use of the high-pressure homogenizer integrated with a dispersion nozzle increases the encapsulation efficiency while improving the durability of biofilm, allowing the oleophilic heads to fully interact and form optimal bonds. The inventors have produced a dispersion nozzle for integration with the homogenizer to not only utilize high-pressure homogenization to form droplets, but also help to disperse the droplets right after their formation in avoidance of droplet aggregation before addition of other substances in the subsequent step. This plays a very important role in increasing the stability of the nano system, which helps increase the yield and stable duration of the system.

(13) (iv) Adding the solution mixture obtained in step (iii) to Capryol 90 (propylene glycol monocaprylate) at the weight ratio of between 4:1.5 and 4.5:1, preferably 4:1 while keeping the mixture temperature between 60 and 100° C. after the addition of Capryol 90, then stirring at a rate ranging from 400 to 800 rpm under vacuum over a period ranging from 30 to 60 minutes.

(14) From theoretical and empirical studies, the inventors found that in order to prepare a nano essential oil which dissolves well in water, the emulsion system needs to be in the form of an oil-in-water emulsion. The selection of an emulsifier to increase the stability of the microemulsion system is based on the properties of the microemulsion system (e.g., oil-in-water microemulsion, water-in-oil microemulsion, etc.). Therefore, the inventors select the emulsifier Capryol 90 (propylene glycol monocaprylate) because Capryol 90 (propylene glycol monocaprylate) is a non-ionic water-insoluble surfactant used as a surfactant in oil-based emulsion and microemulsion formulations with no toxicity and great safety. The addition of the solution mixture obtained in step (iii) to Capryol 90 (propylene glycol monocaprylate) at the weight ratio of between 4:1.5 and 4.5:1, preferably 4:1, makes sure that the HLB index of the system is suitable to make it possible for dispersion in the aqueous phase, wherein if the ratio is lower, the system will be oil-based and difficult to disperse well in water, and if the ratio is greater, the system will be water-based but less stable.

(15) (v) Preparing a microemulsion system of nano essential oil by cooling the mixture to 25° C., homogenizing the mixture by ultrasonication using an ultrasonic homogenizer over a period ranging from 30 to 60 minutes to achieve a droplet size smaller than 100 nm, controlling the quality of the resultant product by dissolution in water and measurement of the transparency, in which if the required transparency is not met, continue heating and measure the transparency every 30 minutes until the required transparency is met, stopping the reaction, and performing emulsifying on the solution mixture in a emulsifying device at a stirring rate ranging from 400 to 800 rpm at the room temperature to obtain the microemulsion system of nano essential oil.

(16) Nanodroplets tend to aggregate; therefore it is required to provide sufficient energy to overcome the binding forces. The use of ultrasonic homogenizer is an effective means of nanodroplet dispersion and reduction of nanodroplet size, which forms droplets with smaller and more uniform size. The dispersion and the aggreagation disruption of nanodroplets result from gas penetration by ultrasound. As the ultrasound is propagated in the solvent, alternating cycles between the high and low pressures are formed, which makes an impact on the binding forces of the nanodroplets. At the same time, when a series of bubbles burst, it forms a very high pressure on the nanodroplet beams so that they separate easily from each other. From the experiments, the inventors identify the ultrasonication timepoints to help form the droplet structure of product interest.

(17) From theoretical and empirical studies, the inventors found that to produce nano essential oil with good solubility in water, the microemulsion system needs to be in the form of an oil-in-water emulsion. Selection of an emulsifier to increase the stability of the microemulsion system is based on the properties of the microemulsion system (e.g., oil-in-water microemulsion, water-in-oil microemulsion, etc.).

(18) The microemulsion system obtained by a process according to the invention has a pH ranging from 7 to 7.4. With this pH value, the microdroplets are stable because in this neutral environment, the bonds between the essential oil and the carrier are retained in the dispersion process, while if the microemulsion system has a pH<7, the bonds are weakened, leading to destruction of the essential oil nanodroplets in the digestive tract.

(19) The nano essential oil microemulsion system obtained by a process according to the invention has a hydrophilic-lipophilic balance (HLB) index ranging from 13 to 18, therefore it is a water-based microemulsion system. This microemulsion system has microdroplets containing water-based, and non-aggregated essential oil, wherein the size of the droplets is uniform and stable, so it can increase the solubility in water, thereby increasing its applicability to many various types of products.

EXAMPLES

Example: Production of 225 g of the Microemulsion System of Nano Essential Oil

(20) Preparation of a dispersed phase: 60 g of essential oil was stirred at 400 rpm, being heating at 60° C. until uniformity was achieved with a magnetic hotplate stirrer (IKA C-MAG HS 7; power: 1000 W).

(21) Preparation of a carrier: A mixture of 100 g of Transcutol P diethylene glycol monoethyl ether and 20 g of lecithin was subjected to heating to 60° C. for 40 minutes by a rotary vacuum evaporator system (RV 10 Digital V-C IKA; power of 1400 W). Then, the mixture is left to cool to 30° C., respectively followed by ultrasonication by an ultrasonic atomizer nozzle for 30 minutes, magnetic stirring, and heating by magnetic hotplate stirrer (IKA C-MAG HS 7; power: 1000 W) at 60° C. for 30 minutes. The solution was collected and introduced into a rotary vacuum evaporator system (RV 10 Digital VC IKA; power: 1400 W), and continued with stirring at 100° C.

(22) 120 g of the carrier was added to 60 g of the dispersed phase prepared above. The dispersed phase with the added carrier was further heated to 60° C. and stirred at 600 rpm under vacuum for 40 minutes by using a magnetic hotplate stirrer (IKA C-MAG HS 7; power: 1000 W). Then the whole solution mixture was introduced into a high pressure homogenizer (maximum pressure: 60 Mpa) integrated with a dispersion nozzle.

(23) Capryol 90 was added to the mixture obtained in step (iii) at the weight ratio of 1:4, corresponding to 45 g of Capryol 90 to 180 g of the mixture, while keeping the mixture temperature between 60 and 100° C. after the addition of Capryol 90. The resultant was stirred at 600 rpm under vacuum for 40 minutes by using magnetic hotplate stirrer (IKA C-MAG HS 7; power: 1000 W) to yield 225 g of mixture.

(24) The obtained mixture was left to cool to 25° C. and homonized using an ultrasonic homogenizer (200-400 W). Since the time period of ultrasonication would make an impact on the droplet size, it is necessary to ultrasonicate from 10 to 20 minutes in order to achieve droplets size of between 100 and 500 nm; it is necessary to ultrasonicate from 30 to 60 minutes in order to achieve a droplets size smaller than 100 nm.

(25) The quality of the resultant product was controlled by dissolving the product in water and measuring the transparency, in which if the required transparency was not met, heating was continued and the transparency was measured every 30 minutes until the required transparency was met. The reaction was stopped, and the temperature was slowly lowered to 50° C. At 50° C., emulsification was performed on the solution mixture at a rate of 500 rpm for 30 minutes.

(26) Before filling, 225 g of the microemulsion system of nano essential oil with good water dispersibility was collected.

(27) By a UV-vis spectroscopic method, the inventors have found that the positions of the peaks of the essential oil material and peaks of the microemulsion system of nano essential oil were completely overlapped. This shows that the microemulsion system obtained by the process according to the invention still retained its structure and essential oil activity during nanoization. The UV-Vis spectroscopic method was used to quantify the content of the essential oil in the microemulsion system. The results showed that the concentration of the essential oil in the microemulsion system of nano essential oil fell in the range of 25-30%.

(28) Size measurement of the essential oil nanodroplets by a scanning transmission electron microscope is shown in FIG. 2, which shows the droplet size ranging from 10 nm to 50 nm that accounts for the substantially maximum percentage of 100% in the solution.

(29) The droplet size was measured by Dynamic Light Scattering (DLS): The suspended droplets in a liquid constantly underwent random movements, and the droplet size directly affects their velocity. Smaller droplets move faster than larger droplets. In DLS, light passes through a sample, and the scattered light is detected and recorded at a certain angle.

(30) Zeta potential or dynamic potential: the potential between the dispersed phase and the dispersion medium.

(31) The following table shows the measurement data by the Dynamic Light Scattering (DLS) method:

(32) TABLE-US-00002 Nano essential oil with experiments to achieve droplet sizes smaller Diameter Density Width than 100 nm (nm) % (nm) Average droplet size Spectral 15.90 100 2.516 (diameter: nm): 15.90 peak 1 Pdl: 0.136 Spectral 0.00 0.00 0.00 peak 2 Probability: 0.939 Spectral 0.00 0.00 0.00 peak 3 Evaluation result: good

(33) Analysis: data from this table reflected an average droplet size of 15.90 nm, accounting for a density of 100% in the system.

(34) TABLE-US-00003 Size (nm, Size (nm, Zeta according according potential Stability Solubility in to TEM) to DLS) (mV) (month) water 10-50 10-50 −40 >12 good solubility in water, after dissolution in water, the system is stable for >7 days

(35) Above results show that, by using of diethylene glycol monoethyl ether and lecithin in combination with Capryol 90, it is possible to obtain a microemulsion system containing microdroplets of small size, ranging from 10 nm to 50 nm, and high stability (>12 months), and good solubility in water, and after being dissolved in water the system is stable for >7 days. Large of value Zeta potential indicates that the droplets are highly charged and that the system tends to be stable.

(36) According to FIG. 1, which is a picture comparing the dispersibility in water between a known essential oil and the nano essential oil obtained by the process according to the invention, vial A contained the known essential oil dispersed in water, and vial B contained the nano essential oil obtained by the process according to the invention; both of the essential oils were dispersed in water. The nano essential oil obtained by the process according to the invention was completely dispersed in water to form a transparent and homogeneous solution, while the known essential oil was insoluble in water and floated on the surface.

(37) According to FIG. 2, which represents a TEM spectrum of essential oil nanodroplets obtained by the process according to the invention, it is shown that the average droplet size fell in the range of 10-50 nm.

ADVANTAGEOUS EFFECTS OF THE INVENTION

(38) The process for producing a microemulsion system of nano essential oil according to the invention has been successful in the production of the microemulsion system that contains essential oil microdroplets with a size ranging from 10 to 50 nm, and of great uniformity and good solubility in water while retaining the structure and activity of an essential oil during nanoization.

(39) The substances used in the process for producing nano essential oil with good water dispersibility are highly safe, non-toxic and have few side effects; therefore the microemulsion system of nano essential oil obtained by the process according to the invention is highly safe when used.

(40) The process according to the invention is simple, easy to implement, and suitable for the current practice in Vietnam.