Essential oil microcapsules and methods for their preparation

Abstract

The application discloses essential oil microcapsules and a preparation method thereof, and relates to the technical field of essential oil microcapsules. The method comprises the following steps: dispersing essential oil in a soybean protein isolate water phase, adding sodium alginate, adjusting pH, and performing complex coacervation to obtain primary microcapsule slurry; adding calcium lactate to perform ion cross-linking to obtain reinforced microcapsule slurry; adding type A gelatin and whey protein isolate under acidic conditions to change the surface of the microcapsules from negative electricity to positive electricity, and form a protein interface coupling layer; and then adding soluble soybean polysaccharide to deposit the soluble soybean polysaccharide on the outside of the coupling layer to form a hydrated dispersion stable layer with negative electricity, so that the essential oil microcapsules are prepared. The essential oil microcapsules are constructed by multi-step interface assembly to build a multi-layer wall material structure, and the stability and dispersibility of the microcapsules are effectively improved.

Description

Technical Field

[0001] This invention relates to the field of essential oil microcapsule technology, specifically to an essential oil microcapsule and its preparation method. Background Technology

[0002] Essential oil microcapsules typically use proteins, polysaccharides, or their complexes as wall materials, encapsulating the essential oil within the capsule wall to form micron-sized particles. Proteins possess good interfacial adsorption and film-forming abilities, while polysaccharides can bind to proteins through electrostatic interactions, hydrogen bonding, and other mechanisms. Therefore, using proteins and polysaccharides to construct composite capsule walls is a common technical approach in the current preparation of essential oil microcapsules.

[0003] However, existing protein-polysaccharide composite capsule walls primarily rely on electrostatic attraction, hydrogen bonding, and molecular chain entanglement to maintain their structure. The lack of sufficiently stable connection points between the wall material molecules results in capsule walls that are typically quite loose. When microcapsules are subjected to shearing, collision, and compression during stirring, pumping, filtration, conveying, or subsequent compounding processes, the capsule walls are prone to deformation, cracking, or localized damage. Especially under conditions of microcapsule particle collisions or continuous mechanical action, polymer segments within the capsule wall are prone to relative slippage, leading to localized stress concentration and further increasing the likelihood of microcapsule rupture. Therefore, the mechanical strength of existing essential oil microcapsules still falls short of the requirements for some processing and application processes.

[0004] On the other hand, the dispersion performance of essential oil microcapsules in aqueous phase also needs improvement. Microcapsule particles have a large specific surface area. When the surface hydration of the particles is insufficient, the surface charge is low, or the repulsive force between particles is weak, the particles are prone to agglomeration after approaching each other during Brownian motion, stirring, or storage, gradually forming large aggregates, which then lead to flocculation and sedimentation. Agglomerated microcapsules are not only difficult to redisperse uniformly, but also result in inconsistent microcapsule content in different areas of the product, affecting subsequent processing and usage effects.

[0005] Existing technologies typically employ methods such as ionic crosslinking, increasing the amount of wall material, or improving the degree of crosslinking to strengthen the microcapsule wall. However, as the capsule wall structure becomes denser, the distribution of functional groups and the charge state on the microcapsule surface may also change. If the effective charge on the particle surface is insufficient after strengthening treatment, or if there are many interactive active sites on the particle surface, strong mutual attraction may occur between microcapsules, leading to particle aggregation. Furthermore, the presence of crosslinking ions may also shield the surface charge of the particles, weakening the electrostatic repulsion between particles, making it difficult to simultaneously improve mechanical strength and dispersion stability. Summary of the Invention

[0006] The purpose of this invention is to provide an essential oil microcapsule and its preparation method to solve the technical problems mentioned in the background.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing essential oil microcapsules includes the following steps:

[0009] (1) Disperse the essential oil in the aqueous phase of soy protein isolate, add sodium alginate and adjust the pH of the system to cause the soy protein isolate and sodium alginate to undergo coagulation to obtain a primary microcapsule slurry;

[0010] (2) Add calcium lactate to the primary microcapsule slurry to allow calcium ions to undergo ionic cross-linking with alginate in the microcapsule wall to obtain a reinforced microcapsule slurry;

[0011] (3) Under acidic conditions, type A gelatin and whey protein isolate are added sequentially to the enhanced microcapsule slurry to change the surface of the microcapsule from a negatively charged state to a positively charged state, forming a protein interface coupling layer.

[0012] (4) Add soluble soybean polysaccharide to the microcapsule slurry that forms the protein interface coupling layer, so that the soluble soybean polysaccharide is deposited on the outside of the protein interface coupling layer to form a negatively charged hydrated dispersion stabilizing layer, and obtain the essential oil microcapsules.

[0013] Preferably, step (1) includes:

[0014] Soy protein isolate was added to water and hydrated at 20–30°C for 2–3 hours. The pH was then adjusted to 7.0 ± 0.1 to obtain a soy protein isolate dispersion.

[0015] Sodium alginate was added to water and hydrated at 20–30°C for 2–3 hours to obtain a sodium alginate solution.

[0016] The essential oil was added to the soy protein isolate dispersion and homogenized at high speed. Then, the sodium alginate solution was added, and the pH of the system was adjusted to 3.5±0.1. The mixture was stirred for 30-45 minutes to obtain the primary microcapsule slurry.

[0017] Preferably, the mass ratio of soy protein isolate to sodium alginate is 4:(0.5-1.5).

[0018] Preferably, the essential oil is selected from one or more of sweet orange essential oil, lavender essential oil, peppermint essential oil, clove essential oil and tea tree essential oil; the high-speed homogenization speed in step (1) is 8000-12000 r / min, the homogenization time is 3-5 min, and the material temperature during the homogenization process is not higher than 30℃.

[0019] Preferably, step (2) includes:

[0020] The pH of the primary microcapsule slurry was adjusted to 3.8 ± 0.1;

[0021] Prepare a 1.0% (w / w) calcium lactate solution;

[0022] Under stirring conditions of 150-250 r / min, first add 30% of the total mass of the calcium lactate solution, stir for 15 min, then add the remaining 70% of the calcium lactate solution, and then stir for 45-60 min to mature; the material temperature during the addition of calcium lactate and maturation process is 20-30℃.

[0023] Preferably, step (3) includes:

[0024] The pH of the enhanced microcapsule slurry was adjusted to 3.7 ± 0.1;

[0025] Add type A gelatin solution at 25-30℃ and 150-200r / min stirring conditions until the zeta potential of the microcapsules reaches -5-0mV, then stop adding type A gelatin solution and allow to mature for 15-20min.

[0026] Then add whey protein isolate dispersion until the zeta potential of the microcapsules reaches +10 to +15 mV, then stop adding whey protein isolate dispersion and allow to mature for 30 to 45 minutes.

[0027] Preferably, the mass fraction of the type A gelatin solution is 2.0%, and its preparation method includes dissolving type A gelatin in water at 45-50°C, cooling to 28-30°C, and adjusting the pH to 3.7±0.1.

[0028] The whey protein isolate dispersion has a mass fraction of 0.5%, and its preparation method includes hydrating the whey protein isolate at pH=6.5~7.0 and 20~30℃ for 60~90min, and then adjusting the pH to 3.7±0.1.

[0029] Preferably, after the surface charge reversal is completed in step (3), a cross-flow microfiltration membrane is used to wash the microcapsule slurry with a lactic acid aqueous solution of pH=3.7±0.1 as the washing solution to remove unadsorbed type A gelatin and whey protein isolate.

[0030] Preferably, step (4) includes:

[0031] Prepare a 2.0% (w / w) soluble soybean polysaccharide solution and adjust its pH to 4.0 ± 0.1;

[0032] The microcapsule slurry with the protein interface coupling layer formed is adjusted to pH=4.0±0.1, and the soluble soybean polysaccharide solution is added under stirring conditions of 100-150 r / min until the zeta potential of the microcapsules is -20 to -30 mV. Then, the addition of the soluble soybean polysaccharide solution is stopped and the mixture is allowed to mature for 45-60 min.

[0033] After maturation, the microcapsule slurry was concentrated into a solid state using a cross-flow microfiltration membrane under transmembrane pressure differential conditions.

[0034] An essential oil microcapsule was prepared by the method described above.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. The capsule wall of primary essential oil microcapsules mainly relies on the electrostatic complexation between soy protein isolate and sodium alginate to maintain its structure. However, there is still some space between the polymer segments, making them prone to segment slippage and capsule wall deformation under high-speed stirring, pumping, or external extrusion. After calcium lactate treatment, calcium ions form multiple ionic cross-linking regions with the carboxylate groups in the alginate segments, establishing more stable connection points between adjacent segments. When the capsule wall is subjected to external force, these connection points can restrict the large-scale movement of the segments and disperse local stress over a wider area, thereby reducing the possibility of localized cracking. The segmented addition of calcium lactate also mitigates the instantaneous surface hardening caused by excessively high local calcium ion concentrations, resulting in a more uniform distribution of calcium ions within the capsule wall. Therefore, the capsule wall's resistance to deformation, shearing, and rupture is improved.

[0037] 2. After soluble soybean polysaccharides are adsorbed onto the outside of the microcapsules, their branched hydrophilic segments extend into the continuous aqueous phase and bind water molecules, forming a hydration layer of a certain thickness on the particle surface. When two microcapsules approach each other, the hydration segments are compressed, generating steric repulsion, thereby reducing the probability of direct contact between the particle surfaces. Simultaneously, the soluble soybean polysaccharides convert the particle surface to a negative charge, and under conditions where the ionic strength of the system is not too high, electrostatic repulsion also occurs between adjacent particles. The steric hindrance and electrostatic repulsion together reduce the possibility of irreversible aggregates forming after particle collisions, ensuring that the microcapsules maintain a good dispersion state during storage, transportation, and dilution.

[0038] 3. After calcium ion reinforcement, the outer layer of the microcapsule wall still retains a large number of alginate carboxylate groups, resulting in an overall negatively charged particle surface. The soluble soybean polysaccharide used to improve dispersion performance is also negatively charged. If the soluble soybean polysaccharide is added directly, the repulsion between the like charges will lead to low polysaccharide adsorption or incomplete surface coverage. Therefore, this scheme uses type A gelatin in combination with whey protein isolate to construct an interfacial coupling layer. Type A gelatin is positively charged under acidic conditions, has a long molecular chain, and possesses a certain degree of flexibility, enabling it to form multiple adsorption points on the negatively charged capsule wall surface and cover a large area. However, if only type A gelatin is used, increasing the amount of gelatin added is usually necessary to completely convert the particle surface to a positive charge. Excessive gelatin can easily increase the viscosity of the continuous phase and may simultaneously adsorb onto the surfaces of two or more microcapsules, increasing the possibility of particle bridging. The main proteins in whey protein isolate are generally positively charged under acidic conditions, and their relatively compact molecular structure allows them to continue adsorbing onto the negatively charged regions still exposed after gelatin treatment. However, if whey protein isolate is used alone, the resulting interfacial layer is mainly composed of relatively compact protein particles, which may result in insufficient continuity of coverage and charge regulation stability on the capsule wall surface. Based on the different molecular conformations and interfacial adsorption characteristics of the two, type A gelatin is added first, and the addition is stopped when the particle zeta potential reaches -5 to 0 mV, allowing the gelatin to preferentially complete large-scale, multi-point adsorption while retaining some negative potential points. Then, whey protein isolate is added, allowing it to continue occupying the uncovered negatively charged regions, and the particle zeta potential is adjusted to +10 to +15 mV. Compared with using type A gelatin alone, this method can reduce the amount of gelatin used and the risk of particle bridging caused by excessive use; compared with using whey protein isolate alone, the pre-adsorption of gelatin is beneficial for establishing a more continuous initial coating layer. Adding them sequentially can also reduce the competition for the same batch of negative potential points when two positively charged proteins are added at the same time, allowing the particle surface to gradually complete the transition from negative to positive charge, thus providing the necessary conditions for the subsequent electrostatic deposition of soluble soybean polysaccharides and improving the uniformity and controllability of the outer layer deposition. Attached Figure Description

[0039] Figure 1 The image shows the overall morphology of the essential oil microcapsules prepared in Example 3 of this invention under a scanning electron microscope.

[0040] Figure 2 This is a distribution diagram of different components of the essential oil microcapsules prepared in Example 3 of the present invention after being fluorescently labeled under a laser confocal microscope.

[0041] Figure 3 This is a volume fraction particle size distribution diagram of the essential oil microcapsules prepared in Example 3 of the present invention.

[0042] Figure 4 This is a graph showing the change in surface charge of the essential oil microcapsules prepared in Example 3 of the present invention with different treatment stages. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] The soy protein isolate used in this specific embodiment is a food-grade powder with a protein content of 91.8%, a nitrogen solubility index of 85, and a moisture content of 5.6%. The sodium alginate used is food-grade high-guluronic acid sodium alginate with a mannouronic acid to guluronic acid molar ratio of 0.80, and a viscosity of 400 mPa·s for a 1.0% sodium alginate aqueous solution at 20°C. The type A gelatin used is food-grade porcine skin-derived type A gelatin with a Bloom strength of 220 and an isoelectric point of 8.5. The whey protein used... The isolate was a food-grade low-mineral whey protein isolate with a protein content of 92.0% and an ash content of 2.5%. The calcium lactate used was food-grade calcium lactate pentahydrate with a purity of 98.5%. The soluble soybean polysaccharide used was food-grade powder with a dietary fiber content of 75.0%, a galacturonic acid content of 18.0%, and a protein content of 5.0%. The sweet orange essential oil used was cold-pressed sweet orange essential oil with a D-limonene content of 94.0% and a density of 0.842 g / mL at 20°C. All the above raw materials were stored in a sealed, light-proof, and dry environment before use.

[0045] Example 1

[0046] A method for preparing essential oil microcapsules includes the following steps:

[0047] (1) Weigh 8.0g of soy protein isolate and slowly add it to 800.0g of deionized water. Hydrate for 2.5h at 25℃ and 400r / min. After hydration, adjust the pH of the dispersion to 7.0±0.1 using a 1% sodium hydroxide aqueous solution or a 5% lactic acid aqueous solution to obtain a soy protein isolate dispersion. Weigh 2.5g of sodium alginate and slowly sprinkle it into 200.0g of deionized water while stirring at 400r / min to prevent sodium alginate from clumping. Continue stirring and hydrating for 2.5h at 25℃ to obtain a sodium alginate solution. Weigh 8.0g of sweet orange essential oil and slowly add it to the soy protein isolate dispersion. Homogenize at 10000r / min for 4min. Circulating cooling water is installed outside the homogenizing container to keep the material temperature below 30℃ during homogenization to obtain a sweet orange essential oil emulsion. The sweet orange essential oil emulsion was placed in a reaction vessel equipped with a mechanical stirrer. At 25°C and 400 rpm, the sodium alginate solution was slowly added over 20 minutes. After addition, stirring continued for 10 minutes to ensure uniform mixing of the soy protein isolate and sodium alginate. While maintaining stirring at 400 rpm, a 5% (w / w) lactic acid aqueous solution was added dropwise over 35 minutes to slowly adjust the pH of the system to 3.5 ± 0.1. Once the target pH was reached, the stirring speed was reduced to 250 rpm, and stirring continued for 35 minutes to mature, yielding the primary sweet orange essential oil microcapsule slurry.

[0048] (2) Using a 1% sodium hydroxide aqueous solution, the pH of the primary microcapsule slurry obtained in step (1) was slowly adjusted to 3.8 ± 0.1. 0.45 g of calcium lactate pentahydrate was weighed and added to 44.55 g of deionized water. The solution was stirred at 25 °C until it became clear, thus obtaining a calcium lactate solution. The primary microcapsule slurry was kept at 25 °C and stirred at 200 r / min. 13.5 g of calcium lactate solution was slowly added over 10 min. After the addition was completed, stirring was continued for 15 min. Then, the remaining 31.5 g of calcium lactate solution was slowly added over 18 min. After the addition was completed, stirring was continued for 50 min to allow calcium ions to undergo ionic cross-linking with the alginate in the capsule wall, thus obtaining a reinforced microcapsule slurry. After the calcium ion reinforcement was completed, the slurry was washed using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm. The transmembrane pressure difference was controlled at 0.03 MPa. A lactic acid aqueous solution with pH=3.8±0.1 was used as the washing filtrate, and the amount of washing filtrate was 0.5 times the volume of the enhanced microcapsule slurry, in order to remove free calcium lactate that did not participate in the cross-linking of the capsule wall.

[0049] (3) Weigh 0.80g of type A gelatin and add it to 39.20g of deionized water. Stir at 48℃ and 300r / min until completely dissolved to obtain a type A gelatin solution. Cool the type A gelatin solution to 29℃ and adjust its pH to 3.7±0.1 using a 5% (w / w) lactic acid aqueous solution. Weigh 0.30g of whey protein isolate and add it to 59.70g of deionized water. Stir and hydrate at 25℃, 300r / min and pH=6.8±0.1 for 80min to obtain a whey protein isolate dispersion. After hydration, slowly add a 5% (w / w) lactic acid aqueous solution while stirring to adjust the pH of the whey protein isolate dispersion to 3.7±0.1. Adjust the pH of the enhanced microcapsule slurry to 3.7±0.1, control the temperature at 28℃, and control the stirring speed at 180r / min. Slowly add the type A gelatin solution to the enhanced microcapsule slurry in batches. Initially, 2.0 g of type A gelatin solution was added each time, with stirring for 5 minutes after each addition and a sample taken to measure the zeta potential of the microcapsules. When the zeta potential rose above -8 mV, the amount added at one time was reduced to 0.5 g. Addition of type A gelatin solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -5 to 0 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 18 minutes for maturation.

[0050] The whey protein isolate dispersion was slowly added to the microcapsule slurry. Initially, 2.0 g of whey protein isolate dispersion was added each time, with stirring for 5 min after each addition and measurement of the zeta potential. When the zeta potential rose above +8 mV, the single addition amount was reduced to 0.5 g. Addition of the whey protein isolate dispersion was stopped when the average zeta potential measured from two consecutive samples was within the range of +10 to +15 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 35 min to allow maturation and the formation of a protein interface coupling layer. After the protein interface coupling layer was formed, filtration was performed using a 0.45 μm polyethersulfone cross-flow microfiltration membrane. A lactic acid aqueous solution with pH = 3.7 ± 0.1 was used as the washing solution, the transmembrane pressure difference was controlled at 0.03 MPa, and the volume of washing solution was 0.5 times the volume of the microcapsule slurry to remove unadsorbed type A gelatin and whey protein isolate.

[0051] (4) Weigh 1.0 g of soluble soybean polysaccharide and add it to 49.0 g of deionized water. Stir and hydrate for 2.5 h at 25 °C and 300 r / min to obtain a soluble soybean polysaccharide solution. Adjust the pH of the soluble soybean polysaccharide solution to 4.0 ± 0.1 using a 1% sodium hydroxide aqueous solution. Adjust the pH of the microcapsule slurry obtained in step (3) to 4.0 ± 0.1, control the temperature at 25 °C, and control the stirring speed at 120 r / min.

[0052] Soluble soybean polysaccharide solution was slowly added to the microcapsule slurry. Initially, 2.0 g of soluble soybean polysaccharide solution was added each time, with stirring for 5 minutes after each addition and sampling to measure the zeta potential of the microcapsules. When the zeta potential decreased to below -18 mV, the single addition amount was reduced to 0.5 g. Addition of soluble soybean polysaccharide solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -20 to -30 mV, the standard deviation of parallel measurements was no greater than 2 mV, and no visible flocculants were found in the microcapsule slurry. After stopping the addition, stirring was continued at 25℃ and 120 r / min for 55 minutes to allow the soluble soybean polysaccharide to deposit on the outer side of the protein interface coupling layer, forming a negatively charged hydrated dispersion stable layer. The microcapsule slurry was concentrated using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm under a transmembrane pressure difference of 0.03 MPa until the solid content of the microcapsule slurry reached 15%, yielding a concentrated sweet orange essential oil microcapsule solution. The obtained concentrated microcapsule solution was sealed, protected from light, and stored at 2–8 °C.

[0053] Example 2

[0054] A method for preparing essential oil microcapsules includes the following steps:

[0055] (1) Weigh 8.0g of soy protein isolate and slowly add it to 800.0g of deionized water. Hydrate for 2.5h at 25℃ and 400r / min. After hydration, adjust the pH of the dispersion to 7.0±0.1 using a 1% sodium hydroxide aqueous solution or a 5% lactic acid aqueous solution to obtain a soy protein isolate dispersion. Weigh 1.5g of sodium alginate and slowly sprinkle it into 200.0g of deionized water while stirring at 400r / min to prevent sodium alginate from clumping. Continue stirring and hydrating for 2.5h at 25℃ to obtain a sodium alginate solution. Weigh 8.0g of sweet orange essential oil and slowly add it to the soy protein isolate dispersion. Homogenize at 10000r / min for 4min. Circulating cooling water is installed outside the homogenizing container to keep the material temperature below 30℃ during homogenization to obtain a sweet orange essential oil emulsion. The sweet orange essential oil emulsion was placed in a reaction vessel equipped with a mechanical stirrer. The sodium alginate solution was slowly added over 20 minutes at 25°C and 400 rpm. After addition, stirring continued for 10 minutes to ensure uniform mixing of the soy protein isolate and sodium alginate. While maintaining stirring at 400 rpm, a 5% (w / w) lactic acid aqueous solution was added dropwise over 35 minutes to slowly adjust the pH of the system to 3.5 ± 0.1. Once the target pH was reached, the stirring speed was reduced to 250 rpm, and stirring continued for 40 minutes to mature, yielding the primary sweet orange essential oil microcapsule slurry.

[0056] (2) Using a 1% sodium hydroxide aqueous solution, the pH of the primary microcapsule slurry obtained in step (1) was slowly adjusted to 3.8 ± 0.1. 0.45 g of calcium lactate pentahydrate was weighed and added to 44.55 g of deionized water. The solution was stirred at 25 °C until it became clear, thus obtaining a calcium lactate solution. The primary microcapsule slurry was kept at 25 °C and stirred at 200 r / min. 13.5 g of calcium lactate solution was slowly added over 10 min. After the addition was completed, stirring was continued for 15 min. Then, the remaining 31.5 g of calcium lactate solution was slowly added over 18 min. After the addition was completed, stirring was continued for 50 min to allow calcium ions to undergo ionic cross-linking with the alginate in the capsule wall, thus obtaining a reinforced microcapsule slurry. After the calcium ion reinforcement was completed, the slurry was washed using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm. The transmembrane pressure difference was controlled at 0.03 MPa. A lactic acid aqueous solution with pH=3.8±0.1 was used as the washing filtrate, and the amount of washing filtrate was 0.5 times the volume of the enhanced microcapsule slurry, in order to remove free calcium lactate that did not participate in the cross-linking of the capsule wall.

[0057] (3) Weigh 0.80g of type A gelatin and add it to 39.20g of deionized water. Stir at 48℃ and 300r / min until completely dissolved to obtain a type A gelatin solution. Cool the type A gelatin solution to 29℃ and adjust its pH to 3.7±0.1 using a 5% (w / w) lactic acid aqueous solution. Weigh 0.30g of whey protein isolate and add it to 59.70g of deionized water. Stir and hydrate at 25℃, 300r / min and pH=6.8±0.1 for 70min to obtain a whey protein isolate dispersion. After hydration, slowly add a 5% (w / w) lactic acid aqueous solution while stirring to adjust the pH of the whey protein isolate dispersion to 3.7±0.1. Adjust the pH of the enhanced microcapsule slurry to 3.7±0.1, control the temperature at 28℃, and control the stirring speed at 180r / min. Slowly add the type A gelatin solution to the enhanced microcapsule slurry in batches. Initially, 2.0 g of type A gelatin solution was added each time, with stirring for 5 minutes after each addition and a sample taken to measure the zeta potential of the microcapsules. When the zeta potential rose above -8 mV, the amount added at one time was reduced to 0.5 g. Addition of type A gelatin solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -5 to 0 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 18 minutes for maturation.

[0058] The whey protein isolate dispersion was slowly added to the microcapsule slurry. Initially, 2.0 g of whey protein isolate dispersion was added each time, with stirring for 5 min after each addition and measurement of the zeta potential. When the zeta potential rose above +8 mV, the single addition amount was reduced to 0.5 g. Addition of the whey protein isolate dispersion was stopped when the average zeta potential measured from two consecutive samples was within the range of +10 to +15 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 35 min to allow maturation and the formation of a protein interface coupling layer. After the protein interface coupling layer was formed, filtration was performed using a 0.45 μm polyethersulfone cross-flow microfiltration membrane. A lactic acid aqueous solution with pH = 3.7 ± 0.1 was used as the washing solution, the transmembrane pressure difference was controlled at 0.03 MPa, and the volume of washing solution was 0.5 times the volume of the microcapsule slurry to remove unadsorbed type A gelatin and whey protein isolate.

[0059] (4) Weigh 1.0 g of soluble soybean polysaccharide and add it to 49.0 g of deionized water. Stir and hydrate for 2.5 h at 25 °C and 300 r / min to obtain a soluble soybean polysaccharide solution. Adjust the pH of the soluble soybean polysaccharide solution to 4.0 ± 0.1 using a 1% sodium hydroxide aqueous solution. Adjust the pH of the microcapsule slurry obtained in step (3) to 4.0 ± 0.1, control the temperature at 25 °C, and control the stirring speed at 120 r / min.

[0060] Soluble soybean polysaccharide solution was slowly added to the microcapsule slurry. Initially, 2.0 g of soluble soybean polysaccharide solution was added each time, with stirring for 5 min after each addition and sampling to measure the zeta potential of the microcapsules. When the zeta potential decreased to below -18 mV, the single addition amount was reduced to 0.5 g. Addition of soluble soybean polysaccharide solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -20 to -30 mV, the standard deviation of parallel measurements was no greater than 2 mV, and no visible flocculants were found in the microcapsule slurry. After stopping the addition, stirring was continued at 25℃ and 120 r / min for 48 min to allow the soluble soybean polysaccharide to deposit on the outer side of the protein interface coupling layer, forming a negatively charged hydrated dispersion stabilizing layer. The microcapsule slurry was concentrated using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm under a transmembrane pressure difference of 0.03 MPa until the solid content of the microcapsule slurry reached 15%, yielding a concentrated sweet orange essential oil microcapsule solution. The obtained concentrated microcapsule solution was sealed, protected from light, and stored at 2–8 °C.

[0061] Example 3

[0062] A method for preparing essential oil microcapsules includes the following steps:

[0063] (1) Weigh 8.0g of soy protein isolate and slowly add it to 800.0g of deionized water. Hydrate for 2.5h at 25℃ and 400r / min. After hydration, adjust the pH of the dispersion to 7.0±0.1 using a 1% sodium hydroxide aqueous solution or a 5% lactic acid aqueous solution to obtain a soy protein isolate dispersion. Weigh 2g of sodium alginate and slowly sprinkle it into 200.0g of deionized water while stirring at 400r / min to prevent sodium alginate from clumping. Continue stirring and hydrating for 2.5h at 25℃ to obtain a sodium alginate solution. Weigh 8.0g of sweet orange essential oil and slowly add it to the soy protein isolate dispersion. Homogenize at 10000r / min for 4min. Circulating cooling water is installed outside the homogenizing container to keep the material temperature below 30℃ during homogenization to obtain a sweet orange essential oil emulsion. The sweet orange essential oil emulsion was placed in a reaction vessel equipped with a mechanical stirrer. At 25°C and 400 rpm, the sodium alginate solution was slowly added over 20 minutes. After addition, stirring continued for 10 minutes to ensure uniform mixing of the soy protein isolate and sodium alginate. While maintaining stirring at 400 rpm, a 5% (w / w) lactic acid aqueous solution was added dropwise over 35 minutes to slowly adjust the pH of the system to 3.5 ± 0.1. Once the target pH was reached, the stirring speed was reduced to 250 rpm, and stirring continued for 35 minutes to mature, yielding the primary sweet orange essential oil microcapsule slurry.

[0064] (2) Using a 1% sodium hydroxide aqueous solution, the pH of the primary microcapsule slurry obtained in step (1) was slowly adjusted to 3.8 ± 0.1. 0.45 g of calcium lactate pentahydrate was weighed and added to 44.55 g of deionized water. The solution was stirred at 25 °C until it became clear, thus obtaining a calcium lactate solution. The primary microcapsule slurry was kept at 25 °C and stirred at 200 r / min. 13.5 g of calcium lactate solution was slowly added over 10 min. After the addition was completed, stirring was continued for 15 min. Then, the remaining 31.5 g of calcium lactate solution was slowly added over 18 min. After the addition was completed, stirring was continued for 50 min to allow calcium ions to undergo ionic cross-linking with the alginate in the capsule wall, thus obtaining a reinforced microcapsule slurry. After the calcium ion reinforcement was completed, the slurry was washed using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm. The transmembrane pressure difference was controlled at 0.03 MPa. A lactic acid aqueous solution with pH=3.8±0.1 was used as the washing filtrate, and the amount of washing filtrate was 0.5 times the volume of the enhanced microcapsule slurry, in order to remove free calcium lactate that did not participate in the cross-linking of the capsule wall.

[0065] (3) Weigh 0.80g of type A gelatin and add it to 39.20g of deionized water. Stir at 48℃ and 300r / min until completely dissolved to obtain a type A gelatin solution. Cool the type A gelatin solution to 29℃ and adjust its pH to 3.7±0.1 using a 5% (w / w) lactic acid aqueous solution. Weigh 0.30g of whey protein isolate and add it to 59.70g of deionized water. Stir and hydrate at 25℃, 300r / min and pH=6.8±0.1 for 75min to obtain a whey protein isolate dispersion. After hydration, slowly add a 5% (w / w) lactic acid aqueous solution while stirring to adjust the pH of the whey protein isolate dispersion to 3.7±0.1. Adjust the pH of the enhanced microcapsule slurry to 3.7±0.1, control the temperature at 28℃, and control the stirring speed at 180r / min. Slowly add the type A gelatin solution to the enhanced microcapsule slurry in batches. Initially, 2.0 g of type A gelatin solution was added each time, with stirring for 5 minutes after each addition and a sample taken to measure the zeta potential of the microcapsules. When the zeta potential rose above -8 mV, the amount added at one time was reduced to 0.5 g. Addition of type A gelatin solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -5 to 0 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 18 minutes for maturation.

[0066] The whey protein isolate dispersion was slowly added to the microcapsule slurry. Initially, 2.0 g of whey protein isolate dispersion was added each time, with stirring for 5 min after each addition and measurement of the zeta potential. When the zeta potential rose above +8 mV, the single addition amount was reduced to 0.5 g. Addition of the whey protein isolate dispersion was stopped when the average zeta potential measured from two consecutive samples was within the range of +10 to +15 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 35 min to allow maturation and the formation of a protein interface coupling layer. After the protein interface coupling layer was formed, filtration was performed using a 0.45 μm polyethersulfone cross-flow microfiltration membrane. A lactic acid aqueous solution with pH = 3.7 ± 0.1 was used as the washing solution, the transmembrane pressure difference was controlled at 0.03 MPa, and the volume of washing solution was 0.5 times the volume of the microcapsule slurry to remove unadsorbed type A gelatin and whey protein isolate.

[0067] (4) Weigh 1.0 g of soluble soybean polysaccharide and add it to 49.0 g of deionized water. Stir and hydrate for 2.5 h at 25 °C and 300 r / min to obtain a soluble soybean polysaccharide solution. Adjust the pH of the soluble soybean polysaccharide solution to 4.0 ± 0.1 using a 1% sodium hydroxide aqueous solution. Adjust the pH of the microcapsule slurry obtained in step (3) to 4.0 ± 0.1, control the temperature at 25 °C, and control the stirring speed at 120 r / min.

[0068] Soluble soybean polysaccharide solution was slowly added to the microcapsule slurry. Initially, 2.0 g of soluble soybean polysaccharide solution was added each time, with stirring for 5 minutes after each addition and sampling to measure the zeta potential of the microcapsules. When the zeta potential decreased to below -18 mV, the single addition amount was reduced to 0.5 g. Addition of soluble soybean polysaccharide solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -20 to -30 mV, the standard deviation of parallel measurements was no greater than 2 mV, and no visible flocculants were found in the microcapsule slurry. After stopping the addition, stirring was continued for 50 minutes at 25℃ and 120 r / min to allow the soluble soybean polysaccharide to deposit on the outer side of the protein interface coupling layer, forming a negatively charged hydrated dispersion stabilizing layer. The microcapsule slurry was concentrated using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm under a transmembrane pressure difference of 0.03 MPa until the solid content of the microcapsule slurry reached 15%, yielding a concentrated sweet orange essential oil microcapsule solution. The obtained concentrated microcapsule solution was sealed, protected from light, and stored at 2–8 °C.

[0069] Figure 1 The image shows the overall morphology of the essential oil microcapsules prepared in Example 3 of this invention under a scanning electron microscope. The microcapsules are generally nearly spherical with some differences in particle size. The surface has slight wrinkles and irregular textures, reflecting the possible shrinkage morphology of the protein-polysaccharide complex capsule wall under dehydration observation conditions. Figure 2 This is a distribution diagram of different components of the essential oil microcapsules prepared in Example 3 of the present invention under a laser confocal microscope after fluorescent labeling. The orange-red area represents the essential oil core, the green area represents the protein interface coupling layer, and the blue area represents the soluble soybean polysaccharide outer layer. The colors are approximately concentrically distributed to visually demonstrate the encapsulation of essential oil and the deposition of outer layer materials. Figure 3 The volume fraction particle size distribution of the essential oil microcapsules prepared in Example 3 of this invention is shown in the distribution curve, which has a single peak shape and a median particle size D50 of 9.6 μm, representing the particle size corresponding to when the volume fraction reaches 50% in the sample. This is used to evaluate the average size of the microcapsules and the degree of concentration of particle size distribution. Figure 4 The graph shows the changes in surface charge of the essential oil microcapsules prepared in Example 3 of this invention during different treatment stages. The zeta potential of the microcapsules after calcium ion strengthening is approximately -16 mV; it increases to approximately -2 mV after the addition of type A gelatin; it changes to approximately +12 mV after the further addition of whey protein isolate; and finally decreases to approximately -26 mV after the adsorption of soluble soybean polysaccharides. This potential change is used to illustrate the process of sequential adsorption of interfacial materials and the change of surface charge from negative to positive and then from positive to negative.

[0070] Example 4

[0071] A method for preparing essential oil microcapsules includes the following steps:

[0072] (1) Weigh 8.0g of soy protein isolate and slowly add it to 800.0g of deionized water. Hydrate for 3 hours at 30℃ and 400r / min. After hydration, adjust the pH of the dispersion to 7.0±0.1 using a 1% sodium hydroxide aqueous solution or a 5% lactic acid aqueous solution to obtain a soy protein isolate dispersion. Weigh 3g of sodium alginate and slowly sprinkle it into 200.0g of deionized water while stirring at 400r / min to prevent sodium alginate from clumping. Continue stirring and hydrating for 3 hours at 30℃ to obtain a sodium alginate solution. Weigh 8.0g of sweet orange essential oil and slowly add it to the soy protein isolate dispersion. Homogenize at 12000r / min for 5 minutes. Circulating cooling water is installed outside the homogenizing container to keep the material temperature below 30℃ during homogenization to obtain a sweet orange essential oil emulsion. The sweet orange essential oil emulsion was placed in a reaction vessel equipped with a mechanical stirrer. The sodium alginate solution was slowly added over 20 minutes at 25°C and 400 rpm. After addition, stirring continued for 10 minutes to ensure uniform mixing of the soy protein isolate and sodium alginate. While maintaining stirring at 400 rpm, a 5% (w / w) lactic acid aqueous solution was added dropwise over 35 minutes to slowly adjust the pH of the system to 3.5 ± 0.1. Once the target pH was reached, the stirring speed was reduced to 250 rpm, and stirring continued for 45 minutes to mature, yielding the primary sweet orange essential oil microcapsule slurry.

[0073] (2) Using a 1% sodium hydroxide aqueous solution, the pH of the primary microcapsule slurry obtained in step (1) was slowly adjusted to 3.8 ± 0.1. 0.45 g of calcium lactate pentahydrate was weighed and added to 44.55 g of deionized water. The solution was stirred at 25 °C until it became clear, thus obtaining a calcium lactate solution. The primary microcapsule slurry was kept at 30 °C and stirred at 250 r / min. 13.5 g of calcium lactate solution was slowly added over 10 min. After the addition was completed, stirring was continued for 15 min. Then, the remaining 31.5 g of calcium lactate solution was slowly added over 18 min. After the addition was completed, stirring was continued for 60 min to allow calcium ions to undergo ionic cross-linking with the alginate in the capsule wall, thus obtaining a reinforced microcapsule slurry. After the calcium ion reinforcement was completed, the slurry was washed using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm. The transmembrane pressure difference was controlled at 0.03 MPa. A lactic acid aqueous solution with pH=3.8±0.1 was used as the washing filtrate, and the amount of washing filtrate was 0.5 times the volume of the enhanced microcapsule slurry, in order to remove free calcium lactate that did not participate in the cross-linking of the capsule wall.

[0074] (3) Weigh 0.80g of type A gelatin and add it to 39.20g of deionized water. Stir at 50℃ and 300r / min until completely dissolved to obtain a type A gelatin solution. Cool the type A gelatin solution to 30℃ and adjust its pH to 3.7±0.1 using a 5% (w / w) lactic acid aqueous solution. Weigh 0.30g of whey protein isolate and add it to 59.70g of deionized water. Stir and hydrate at 30℃, 300r / min and pH=6.8±0.1 for 90min to obtain a whey protein isolate dispersion. After hydration, slowly add a 5% (w / w) lactic acid aqueous solution while stirring to adjust the pH of the whey protein isolate dispersion to 3.7±0.1. Adjust the pH of the enhanced microcapsule slurry to 3.7±0.1, control the temperature at 30℃, and control the stirring speed at 200r / min. Slowly add the type A gelatin solution to the enhanced microcapsule slurry in batches. In the initial stage, 2.0 g of type A gelatin solution was added each time, with stirring for 5 minutes after each addition and sampling to measure the zeta potential of the microcapsules. When the zeta potential rose above -8 mV, the amount added at one time was reduced to 0.5 g. When the average zeta potential measured from two consecutive samples was within the range of -5 to 0 mV, and the standard deviation of parallel measurements was no greater than 2 mV, the addition of type A gelatin solution was stopped. After stopping the addition, stirring was continued for 20 minutes for maturation.

[0075] The whey protein isolate dispersion was slowly added to the microcapsule slurry. Initially, 2.0 g of whey protein isolate dispersion was added each time, with stirring for 5 min after each addition and measurement of the zeta potential. When the zeta potential rose above +8 mV, the single addition amount was reduced to 0.5 g. Addition of the whey protein isolate dispersion was stopped when the average zeta potential measured from two consecutive samples was within the range of +10 to +15 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 45 min to allow maturation and the formation of a protein interface coupling layer. After the protein interface coupling layer was formed, filtration was performed using a 0.45 μm polyethersulfone cross-flow microfiltration membrane. A lactic acid aqueous solution with pH = 3.7 ± 0.1 was used as the washing solution, the transmembrane pressure difference was controlled at 0.03 MPa, and the volume of washing solution was 0.5 times the volume of the microcapsule slurry to remove unadsorbed type A gelatin and whey protein isolate.

[0076] (4) Weigh 1.0 g of soluble soybean polysaccharide and add it to 49.0 g of deionized water. Stir and hydrate for 2.5 h at 25 °C and 300 r / min to obtain a soluble soybean polysaccharide solution. Adjust the pH of the soluble soybean polysaccharide solution to 4.0 ± 0.1 using a 1% sodium hydroxide aqueous solution. Adjust the pH of the microcapsule slurry obtained in step (3) to 4.0 ± 0.1, control the temperature at 25 °C, and control the stirring speed at 150 r / min.

[0077] Soluble soybean polysaccharide solution was slowly added to the microcapsule slurry. Initially, 2.0 g of soluble soybean polysaccharide solution was added each time, with stirring for 5 minutes after each addition and sampling to measure the zeta potential of the microcapsules. When the zeta potential decreased to below -18 mV, the amount added at one time was reduced to 0.5 g. Addition of soluble soybean polysaccharide solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -20 to -30 mV, the standard deviation of parallel measurements was no greater than 2 mV, and no visible flocculants were found in the microcapsule slurry. After stopping the addition, the mixture was stirred for 60 minutes at 25℃ and 120 r / min to allow the soluble soybean polysaccharide to deposit on the outer side of the protein interface coupling layer, forming a negatively charged hydrated dispersion stabilizing layer. The microcapsule slurry was concentrated using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm under a transmembrane pressure difference of 0.03 MPa until the solid content of the microcapsule slurry reached 15%, yielding a concentrated sweet orange essential oil microcapsule solution. The obtained concentrated microcapsule solution was sealed, protected from light, and stored at 2–8 °C.

[0078] Example 5

[0079] A method for preparing essential oil microcapsules includes the following steps:

[0080] (1) Weigh 8.0g of soy protein isolate and slowly add it to 800.0g of deionized water. Hydrate at 20℃ and 400r / min for 2 hours. After hydration, adjust the pH of the dispersion to 7.0±0.1 using a 1% sodium hydroxide aqueous solution or a 5% lactic acid aqueous solution to obtain a soy protein isolate dispersion. Weigh 1g of sodium alginate and slowly sprinkle it into 200.0g of deionized water while stirring at 400r / min to prevent sodium alginate from clumping. Continue stirring and hydrating at 20℃ for 2 hours to obtain a sodium alginate solution. Weigh 8.0g of sweet orange essential oil and slowly add it to the soy protein isolate dispersion. Homogenize at 8000r / min for 3 minutes. Circulating cooling water is installed outside the homogenizing container to keep the material temperature below 30℃ during homogenization to obtain a sweet orange essential oil emulsion. The sweet orange essential oil emulsion was placed in a reaction vessel equipped with a mechanical stirrer. The sodium alginate solution was slowly added over 20 minutes at 25°C and 400 rpm. After addition, stirring continued for 10 minutes to ensure uniform mixing of the soy protein isolate and sodium alginate. While maintaining stirring at 400 rpm, a 5% (w / w) lactic acid aqueous solution was added dropwise over 35 minutes to slowly adjust the pH of the system to 3.5 ± 0.1. Once the target pH was reached, the stirring speed was reduced to 250 rpm, and stirring continued for 30 minutes to mature the mixture, yielding the primary sweet orange essential oil microcapsule slurry.

[0081] (2) Using a 1% sodium hydroxide aqueous solution, the pH of the primary microcapsule slurry obtained in step (1) was slowly adjusted to 3.8 ± 0.1. 0.45 g of calcium lactate pentahydrate was weighed and added to 44.55 g of deionized water. The solution was stirred at 25 °C until it became clear, thus obtaining a calcium lactate solution. The primary microcapsule slurry was kept at 20 °C and stirred at 150 r / min. 13.5 g of calcium lactate solution was slowly added over 10 min. After the addition was completed, stirring was continued for 15 min. Then, the remaining 31.5 g of calcium lactate solution was slowly added over 18 min. After the addition was completed, stirring was continued for 45 min to allow calcium ions to undergo ionic cross-linking with the alginate in the capsule wall, thus obtaining a reinforced microcapsule slurry. After the calcium ion reinforcement was completed, the slurry was washed using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm. The transmembrane pressure difference was controlled at 0.03 MPa. A lactic acid aqueous solution with pH=3.8±0.1 was used as the washing filtrate, and the amount of washing filtrate was 0.5 times the volume of the enhanced microcapsule slurry, in order to remove free calcium lactate that did not participate in the cross-linking of the capsule wall.

[0082] (3) Weigh 0.80g of type A gelatin and add it to 39.20g of deionized water. Stir at 45℃ and 300r / min until completely dissolved to obtain a type A gelatin solution. Cool the type A gelatin solution to 28℃ and adjust its pH to 3.7±0.1 using a 5% (w / w) lactic acid aqueous solution. Weigh 0.30g of whey protein isolate and add it to 59.70g of deionized water. Stir and hydrate at 20℃, 300r / min and pH=6.8±0.1 for 60min to obtain a whey protein isolate dispersion. After hydration, slowly add a 5% (w / w) lactic acid aqueous solution while stirring to adjust the pH of the whey protein isolate dispersion to 3.7±0.1. Adjust the pH of the enhanced microcapsule slurry to 3.7±0.1, control the temperature at 25℃, and control the stirring speed at 150r / min. Slowly add the type A gelatin solution to the enhanced microcapsule slurry in batches. In the initial stage, 2.0 g of type A gelatin solution was added each time, with stirring for 5 minutes after each addition and sampling to measure the zeta potential of the microcapsules. When the zeta potential rose above -8 mV, the amount added at one time was reduced to 0.5 g. When the average zeta potential measured from two consecutive samples was within the range of -5 to 0 mV, and the standard deviation of parallel measurements was no greater than 2 mV, the addition of type A gelatin solution was stopped. After stopping the addition, stirring was continued for 15 minutes for maturation.

[0083] The whey protein isolate dispersion was slowly added to the microcapsule slurry. Initially, 2.0 g of whey protein isolate dispersion was added each time, with stirring for 5 min after each addition and measurement of the zeta potential. When the zeta potential rose above +8 mV, the single addition amount was reduced to 0.5 g. Addition of the whey protein isolate dispersion was stopped when the average zeta potential measured from two consecutive samples was within the range of +10 to +15 mV, and the standard deviation of parallel measurements was no greater than 2 mV. After stopping the addition, stirring was continued for 30 min to allow maturation and the formation of a protein interface coupling layer. After the protein interface coupling layer was formed, filtration was performed using a 0.45 μm polyethersulfone cross-flow microfiltration membrane. A lactic acid aqueous solution with pH = 3.7 ± 0.1 was used as the washing solution, the transmembrane pressure difference was controlled at 0.03 MPa, and the volume of washing solution was 0.5 times the volume of the microcapsule slurry to remove unadsorbed type A gelatin and whey protein isolate.

[0084] (4) Weigh 1.0 g of soluble soybean polysaccharide and add it to 49.0 g of deionized water. Stir and hydrate for 2.5 h at 25 °C and 300 r / min to obtain a soluble soybean polysaccharide solution. Adjust the pH of the soluble soybean polysaccharide solution to 4.0 ± 0.1 using a 1% sodium hydroxide aqueous solution. Adjust the pH of the microcapsule slurry obtained in step (3) to 4.0 ± 0.1, control the temperature at 25 °C, and control the stirring speed at 100 r / min.

[0085] Soluble soybean polysaccharide solution was slowly added to the microcapsule slurry. Initially, 2.0 g of soluble soybean polysaccharide solution was added each time, with stirring for 5 minutes after each addition and sampling to measure the zeta potential of the microcapsules. When the zeta potential decreased to below -18 mV, the single addition amount was reduced to 0.5 g. Addition of soluble soybean polysaccharide solution was stopped when the average zeta potential measured from two consecutive samples was within the range of -20 to -30 mV, the standard deviation of parallel measurements was no greater than 2 mV, and no visible flocculants were found in the microcapsule slurry. After stopping the addition, stirring was continued at 25℃ and 120 r / min for 45 minutes to allow the soluble soybean polysaccharide to deposit on the outer side of the protein interface coupling layer, forming a negatively charged hydrated dispersion stabilizing layer. The microcapsule slurry was concentrated using a polyethersulfone cross-flow microfiltration membrane with a pore size of 0.45 μm under a transmembrane pressure difference of 0.03 MPa until the solid content of the microcapsule slurry reached 15%, yielding a concentrated sweet orange essential oil microcapsule solution. The obtained concentrated microcapsule solution was sealed, protected from light, and stored at 2–8 °C.

[0086] Comparative Example 1: Compared with Example 5, the calcium lactate strengthening treatment in step (2) was omitted, and the calcium lactate solution was replaced with an aqueous lactic acid solution of equal mass and the same pH. The amount of other raw materials and operating conditions were the same as in Example 5.

[0087] Comparative Example 2: Compared with Example 5, 45g of calcium lactate solution from step (2) was added to the primary microcapsule slurry all at once, without using the 30% and 70% segmented feeding method. The amount of other raw materials and operating conditions were the same as in Example 5.

[0088] Comparative Example 3: Compared with Example 5, the treatment of type A gelatin and whey protein isolate in step (3) was omitted. The calcium-enhanced microcapsule slurry was directly mixed with soluble soybean polysaccharide solution, and the reduced liquid mass was made up with an equal mass of lactic acid aqueous solution with the same pH. All other operating conditions were the same as in Example 5.

[0089] Comparative Example 4: Compared with Example 5, only type A gelatin solution was added in step (3), and the addition continued until the microcapsule ζ potential reached +10 to +15mV. Whey protein isolate dispersion was not added, and lactic acid aqueous solution of equal mass and the same pH was used instead of whey protein isolate dispersion. All other operating conditions were the same as in Example 5.

[0090] Comparative Example 5: Compared with Example 5, in step (3), no type A gelatin solution was added, only whey protein isolate dispersion was added until the microcapsule ζ potential reached +10 to +15 mV, and type A gelatin solution was replaced with an equal mass of lactic acid aqueous solution with the same pH. All other operating conditions were the same as in Example 5.

[0091] Comparative Example 6: Compared with Example 5, the type A gelatin solution and whey protein isolate dispersion actually consumed in Example 5 in step (3) were pre-mixed and added to the enhanced microcapsule slurry at one time. The sequential feeding method of adding type A gelatin first and then whey protein isolate was not adopted. All other operating conditions were the same as in Example 5.

[0092] Comparative Example 7: Compared with Example 5, the soluble soybean polysaccharide treatment in step (4) was omitted, and the soluble soybean polysaccharide solution was replaced with an equal mass of lactic acid aqueous solution with pH 4.0 ± 0.1. The amounts of other raw materials and operating conditions were the same as in Example 5.

[0093] Performance testing

[0094] 1. Essential Oil Encapsulation Rate Test: Accurately weigh 1.00 g of the essential oil microcapsule concentrate from each sample. For surface essential oil determination, add 10 mL of hexane containing n-decane as an internal standard to the sample, shake at 100 r / min for 60 s in a sealed glass bottle, then centrifuge at 3000 × g for 5 min and collect the supernatant. For total essential oil determination, separately weigh 1.00 g of the same sample, add 20 mL of a 1:1 mixture of anhydrous ethanol and n-hexane, sonicate at 25 °C and 35 kHz for 20 min in a sealed glass bottle, then centrifuge at 9000 × g for 10 min and collect the supernatant. The D-limonene content in two extracts was determined by gas chromatography-FID. A DB-5 capillary column (30 m × 0.25 mm × 0.25 μm) was used. The injection port and detector temperatures were both 250 °C, the split ratio was 50:1, and the carrier gas flow rate was 1.0 mL / min. The column temperature was initially set at 60 °C and held for 2 min, then increased to 220 °C at a rate of 10 °C / min and held for 3 min. A calibration curve was established using D-limonene standards, with n-decane as the internal standard. The encapsulation efficiency was calculated as: Encapsulation efficiency = (Total essential oil mass - Surface essential oil mass) ÷ Total essential oil mass × 100%. Three independent batches of each sample were tested, and the results were the arithmetic mean.

[0095] 2. Microcapsule Particle Size and Distribution Test: Each sample was diluted with a lactic acid aqueous solution (pH=4.0, conductivity matching that of the original continuous phase) and gently mixed without ultrasonic treatment. Particle size was determined using a wet laser particle size analyzer. During the test, the shading rate was controlled at 5%–15%, and the refractive index of the dispersion medium was set to 1.333. The particle refractive index should be verified by the particle size results from microscopic images; 1.45 was not used as a fixed value before verification. Each sample was independently sampled and measured three times, and D10, D50, and D90 were recorded simultaneously. The particle size distribution width was calculated according to "Span = (D90-D10) ÷ D50". A smaller D50 indicates a smaller overall particle size, and a smaller Span indicates a more concentrated particle size distribution.

[0096] 3. Zeta Potential Test: Each sample was diluted 20-fold with the continuous phase obtained by filtering the sample through a 0.22 μm filter membrane to maintain consistent pH and ionic strength before and after dilution. The diluted sample was added to a folded capillary electrophoresis cell and equilibrated at 25°C for 120 s. Electrophoretic mobility was measured using electrophoretic light scattering, and the zeta potential was calculated according to the Smoluchowski model based on the viscosity, dielectric constant, and conductivity of the medium. Each sample was taken independently three times, with three consecutive measurement cycles performed each time. If significant particle sedimentation, a continuous measurement deviation exceeding 2 mV, or an instrument quality report was found to be unqualified during the test, video microelectrophoresis was used instead. The final result is expressed as the arithmetic mean of three independent batches.

[0097] 4. Microcapsule rupture stress test: Each sample was diluted with a pH 4.0 lactic acid aqueous solution to a solid content of 0.1%. A small amount of sample was placed in a transparent wet test chamber and tested at 25°C using a microscope and a single-particle micromanipulation compression device. Using a flat-headed probe with a 50 μm end-face diameter, a single microcapsule was compressed at a speed of 2.0 μm / s until the capsule wall ruptured. The peak force F before the sudden drop in the force-displacement curve was recorded. r The actual diameter D of the tested microcapsule before compression was measured using microscopic imaging. According to σ... r =4F r / (πD 2 Calculate the nominal fracture stress, where σ r The unit is MPa. Fifty microcapsules with intact outlines and no adhesion were randomly tested from each batch, and three independently prepared batches were tested for each sample. A higher nominal burst stress indicates a stronger ability of the capsule wall to withstand compressive loads after excluding the influence of particle diameter. Microparticle micromanipulation test method.

[0098] 5. Essential Oil Leakage Rate Test After Shearing: Each sample was diluted with a lactic acid aqueous solution at pH 4.0 to a solids content of 1.0%. 50 mL of each sample was placed in a cylindrical container with an inner diameter of 35 mm and processed using a high-speed shearing device with a rotor diameter of 20 mm and a stator-rotor gap of 0.5 mm. The shearing speed was 8000 r / min, corresponding to a rotor end linear velocity of approximately 8.38 m / s. The processing time was 3 min, and the material temperature was controlled below 30℃ using external cooling. The surface essential oil mass before and after shearing was determined according to the surface essential oil extraction method, and the total essential oil mass before shearing was determined according to the total essential oil extraction method. The leakage rate of essential oil after shearing was calculated as: (Surface essential oil mass after shearing - Surface essential oil mass before shearing) ÷ Total essential oil mass before shearing × 100%. Three independent batches were tested for each sample. A lower leakage rate after shearing indicates better resistance to shear damage of the capsule wall.

[0099] 6. Multiple Light Scattering Stability Test: Each sample was diluted with a pH 4.0 lactic acid aqueous solution to a solids content of 1.0%. 20 mL of sample was added to a cylindrical glass test tube with an inner diameter of 25 mm, avoiding air bubbles, and the liquid level was recorded. A multiple light scattering stability analyzer with a wavelength of 880 nm was used to scan from the bottom to the top of the test tube at 25°C, scanning once every 1 hour for 7 consecutive days. The Global TSI was calculated over the entire liquid level range using the same instrument and software version. The Global TSI on day 7 was used as the evaluation result. Three independent parallel test tubes were set up for each sample. A lower TSI indicates a smaller overall degree of sedimentation, flotation, flocculation, and particle size change during the test period.

[0100] Table 1:

[0101] Example 1 89.4 10.7 1.24 −25.0 1.42 10.9 2.6 Example 2 86.1 9.0 1.18 −24.3 1.26 13.8 2.2 Example 3 90.8 9.6 1.05 −26.0 1.48 9.5 1.8 Example 4 87.9 13.3 1.46 −23.8 1.31 8.4 4.1 Example 5 82.5 8.5 1.29 −23.5 1.08 16.3 3.2 Comparative Example 1 78.1 8.2 1.36 −24.0 0.58 28.7 3.9 Comparative Example 2 80.3 10.4 1.72 −22.9 0.91 24.9 5.6 Comparative Example 3 79.0 12.5 1.91 −15.2 1.03 18.1 9.4 Comparative Example 4 81.4 11.8 1.68 −22.2 1.12 20.6 6.8 Comparative Example 5 80.5 9.9 1.54 −20.6 1.00 17.5 5.9 Comparative Example 6 80.9 10.7 1.63 −21.5 1.06 19.8 6.3 Comparative Example 7 82.0 8.7 1.31 +12.2 1.10 16.9 12.5

[0102] Compared to Example 5, in Comparative Example 1, omitting the calcium lactate reinforcement treatment resulted in a decrease in nominal burst stress from 1.08 MPa to 0.58 MPa, and an increase in essential oil leakage rate after shearing from 16.3% to 28.7%. This indicates that the ionic cross-linking structure formed by calcium ions and alginate can limit the slippage of capsule wall segments and improve the compressive and shear resistance of microcapsules. In Comparative Example 2, after adding calcium lactate all at once, D50, Span, and Global TSI increased to 10.4 μm, 1.72, and 5.6, respectively. This indicates that the segmented addition of calcium lactate is beneficial in reducing the rapid surface cross-linking and particle bridging caused by excessively high local calcium ion concentration. In Comparative Example 3, without using type A gelatin and whey protein isolate to construct the interfacial coupling layer, the final zeta potential was only -15.2 mV, and the Span and Global TSI increased to 1.91 and 9.4, respectively. This indicates that without surface positive charge reversal, soluble soybean polysaccharides are difficult to form a uniform and stable coating layer on the negatively charged capsule wall. Comparative Examples 4 and 5 used type A gelatin and whey protein isolate separately, respectively. Comparative Example 6 added both proteins premixed and then added them all at once. Their Global TSI values ​​were 6.8, 5.9, and 6.3, respectively, all higher than the 3.2 of Example 5. This indicates that adding type A gelatin first, followed by whey protein isolate, is beneficial for gradually adjusting the surface charge and improving the controllability of the interface layer construction. Comparative Example 7 did not add soluble soybean polysaccharide, and its zeta potential remained at +12.2 mV. On day 7, the Global TSI increased to 12.5, indicating that the negatively charged hydrated outer layer formed by soluble soybean polysaccharide can reduce the aggregation tendency of microcapsules through electrostatic repulsion and steric hindrance. In summary, segmental crosslinking of calcium lactate mainly improves the mechanical strength of the microcapsule wall. Sequential treatment with type A gelatin and whey protein isolate provides suitable interfacial conditions for the deposition of soluble soybean polysaccharide, while the soluble soybean polysaccharide outer layer further improves the aqueous dispersion stability of the microcapsules.

[0103] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the essence and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing essential oil microcapsules, characterized in that, Includes the following steps: (1) Disperse the essential oil in the aqueous phase of soy protein isolate, add sodium alginate and adjust the pH of the system to cause the soy protein isolate and sodium alginate to undergo coagulation to obtain a primary microcapsule slurry; (2) Add calcium lactate to the primary microcapsule slurry to allow calcium ions to undergo ionic cross-linking with alginate in the microcapsule wall to obtain a reinforced microcapsule slurry; (3) Under acidic conditions, type A gelatin and whey protein isolate are added sequentially to the enhanced microcapsule slurry to change the surface of the microcapsule from a negatively charged state to a positively charged state, forming a protein interface coupling layer. (4) Add soluble soybean polysaccharide to the microcapsule slurry that forms the protein interface coupling layer, so that the soluble soybean polysaccharide is deposited on the outside of the protein interface coupling layer to form a negatively charged hydrated dispersion stabilizing layer, and obtain the essential oil microcapsules.

2. The method for preparing essential oil microcapsules according to claim 1, characterized in that, Step (1) includes: Soy protein isolate was added to water and hydrated at 20–30°C for 2–3 hours. The pH was then adjusted to 7.0 ± 0.1 to obtain a soy protein isolate dispersion. Sodium alginate was added to water and hydrated at 20–30°C for 2–3 hours to obtain a sodium alginate solution. The essential oil was added to the soy protein isolate dispersion and homogenized at high speed. Then, the sodium alginate solution was added, and the pH of the system was adjusted to 3.5±0.

1. The mixture was stirred for 30-45 minutes to obtain the primary microcapsule slurry.

3. The method for preparing essential oil microcapsules according to claim 2, characterized in that, The mass ratio of soy protein isolate to sodium alginate is 4:(0.5-1.5).

4. A method for preparing essential oil microcapsules according to claim 1 or 2, characterized in that, The essential oil is selected from one or more of sweet orange essential oil, lavender essential oil, peppermint essential oil, clove essential oil and tea tree essential oil; the high-speed homogenization speed in step (1) is 8000-12000 r / min, the homogenization time is 3-5 min, and the material temperature during the homogenization process is not higher than 30℃.

5. The method for preparing essential oil microcapsules according to claim 1, characterized in that, Step (2) includes: The pH of the primary microcapsule slurry was adjusted to 3.8 ± 0.1; Prepare a 1.0% (w / w) calcium lactate solution; Under stirring conditions of 150-250 r / min, first add 30% of the total mass of the calcium lactate solution, stir for 15 min, then add the remaining 70% of the calcium lactate solution, and then stir for 45-60 min to mature; the material temperature during the addition of calcium lactate and maturation process is 20-30℃.

6. The method for preparing essential oil microcapsules according to claim 1, characterized in that, Step (3) includes: The pH of the enhanced microcapsule slurry was adjusted to 3.7 ± 0.1; Add type A gelatin solution at 25-30℃ and 150-200r / min stirring conditions until the zeta potential of the microcapsules reaches -5-0mV, then stop adding type A gelatin solution and allow to mature for 15-20min. Then add whey protein isolate dispersion until the zeta potential of the microcapsules reaches +10 to +15 mV, then stop adding whey protein isolate dispersion and allow to mature for 30 to 45 minutes.

7. The method for preparing essential oil microcapsules according to claim 6, characterized in that, The mass fraction of the type A gelatin solution is 2.0%, and its preparation method includes dissolving type A gelatin in water at 45-50°C, cooling to 28-30°C, and adjusting the pH to 3.7±0.

1. The whey protein isolate dispersion has a mass fraction of 0.5%, and its preparation method includes hydrating the whey protein isolate at pH=6.5~7.0 and 20~30℃ for 60~90min, and then adjusting the pH to 3.7±0.

1.

8. A method for preparing essential oil microcapsules according to claim 6 or 7, characterized in that, After completing the surface charge reversal in step (3), the microcapsule slurry is washed with a cross-flow microfiltration membrane and a lactic acid aqueous solution with pH=3.7±0.1 as the washing solution to remove unadsorbed type A gelatin and whey protein isolate.

9. The method for preparing essential oil microcapsules according to claim 1, characterized in that, Step (4) includes: Prepare a 2.0% (w / w) soluble soybean polysaccharide solution and adjust its pH to 4.0 ± 0.1; The microcapsule slurry with the protein interface coupling layer formed is adjusted to pH=4.0±0.1, and the soluble soybean polysaccharide solution is added under stirring conditions of 100-150 r / min until the zeta potential of the microcapsules is -20 to -30 mV. Then, the addition of the soluble soybean polysaccharide solution is stopped and the mixture is allowed to mature for 45-60 min. After maturation, the microcapsule slurry was concentrated into a solid state using a cross-flow microfiltration membrane under transmembrane pressure differential conditions.

10. An essential oil microcapsule, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

Images