Microcapsule powder rich in SN-2DHA algal oil and preparation method thereof

Abstract

The invention provides micro-capsule powder rich in SN-2DHA algal oil and a preparation method thereof, and belongs to the technical field of marine food manufacturing, the SN-2DHA algal oil, lutein ester and an antioxidant are mixed and stirred under the protection of inert gas to form a uniform oil phase; dispersing the cellulose nanofiber and whey protein composite wall material subjected to microjet homogenization treatment in deionized water, and performing high-speed shearing and ultrasonic treatment to form a water-phase dispersion liquid; the preparation method comprises the following steps: accurately emulsifying through a micro-fluidic chip to form an O / W type Pickering emulsion; adding chitosan quaternary ammonium salt for electrostatic deposition reaction to realize interface curing; constructing a pH response type gel outer layer through ionic cross-linking reaction of sodium alginate pectin and calcium ions; and drying, crushing and screening to obtain the microcapsule powder.

Description

Technical Field

[0001] This invention relates to the field of marine food manufacturing technology, specifically to a microcapsule powder rich in SN-2DHA algal oil and its preparation method. Background Technology

[0002] Docosahexaenoic acid (DHA) is an important omega-3 long-chain polyunsaturated fatty acid that plays a vital role in the development of the nervous system in infants and young children and in the cardiovascular health of adults. Among them, SN-2 DHA (DHA esterified at the middle position of the glycerol backbone) has higher bioavailability and is more easily absorbed by the intestines. However, DHA contains multiple unsaturated double bonds, making it highly susceptible to oxidation and deterioration, leading to a shortened product shelf life and reduced nutritional value.

[0003] Lutein is a natural carotenoid that protects the retina by filtering blue light and acting as an antioxidant, and it works synergistically with DHA in the field of eye health. However, lutein is also sensitive to light, heat, and oxygen, and it is fat-soluble, resulting in poor compatibility with water-soluble systems, which limits its application in food systems.

[0004] Microencapsulation technology is an effective means to protect sensitive functional factors and improve their stability and bioavailability. Traditional microencapsulation technology often uses wall materials such as gum arabic and maltodextrin through spray drying, but this method suffers from problems such as low mechanical strength of the wall material, low core material encapsulation rate, and poor sustained-release performance. In recent years, Pickering emulsions have attracted attention due to their advantages such as high stability and good biocompatibility, as they use solid particles instead of traditional surfactants as emulsifiers. However, selecting suitable solid particle stabilizers and optimizing the preparation process to obtain microcapsule products with high encapsulation rates and high stability remain technical challenges. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention modulates the pH of the aqueous phase and combines negatively charged cellulose nanofibers with whey protein at a specific pH to create a negatively charged interface on the Pickering emulsion oil droplets. This creates the necessary conditions for a subsequent efficient electrostatic deposition reaction with positively charged chitosan quaternary ammonium salt, which is crucial for constructing a high-strength interface curing layer.

[0006] A method for preparing microcapsule powder rich in SN-2DHA algal oil includes the following steps:

[0007] S1. Mix SN-2DHA algal oil, lutein ester and antioxidant, and stir under inert gas protection and light protection to obtain an oil phase dispersion;

[0008] S2. The composite wall material containing microfluidic homogeneous cellulose nanofibers and whey protein is dispersed in deionized water and subjected to high-speed shearing and ultrasonic treatment to form an aqueous dispersion.

[0009] S3. The oil phase dispersion obtained in step S1 and the aqueous phase dispersion obtained in step S2 are emulsified through a microfluidic chip to control the flow rate ratio of the two phases and form an O / W type Pickering emulsion with uniform oil droplet size.

[0010] S4. Add chitosan quaternary ammonium salt solution to the Pickering emulsion obtained in step S3 to carry out electrostatic deposition reaction to achieve interface solidification. Add sodium alginate pectin aqueous solution to the interface solidified Pickering emulsion, stir evenly, and then add calcium chloride solution to carry out ionic cross-linking reaction to form a pH-responsive gel outer layer. Then dry to obtain solid microcapsules.

[0011] S5. The dried solid microcapsules are crushed and sieved to obtain microcapsule powder rich in SN-2DHA algal oil.

[0012] Furthermore, the antioxidant is a mixture of tocopherols; the stirring temperature is 40-45℃, and the stirring time is 25-30 minutes.

[0013] Further, in step S2, the mass ratio of cellulose nanofibers to whey protein in the composite wall material is 1:2 to 2:1; the cellulose nanofibers are pre-treated by a microfluidic homogenizer at a pressure of 100-120 MPa, and the resulting cellulose nanofibers have an average diameter of 15-30 nm and a length of 150-350 nm.

[0014] Furthermore, in step S3, the microfluidic chip is a Y-type or T-type chip; the volume ratio of the oil phase dispersion to the aqueous phase dispersion during emulsification is 1:3 to 1:3.5, and the flow rate ratio is 1:8 to 1:9; the average particle size of the formed Pickering emulsion is 2.2-2.5 μm, and the particle size variation coefficient CV value is less than 12%.

[0015] Further, in step S4, the concentration of the chitosan quaternary ammonium salt solution is 2-2.5%; in the sodium alginate pectin aqueous solution, the mass ratio of sodium alginate to pectin is 2:1 to 4:1, and the concentration of calcium chloride is 0.5-1.0%.

[0016] Furthermore, in step S4, the drying is spray drying, with an inlet air temperature of 165°C and an outlet air temperature of 80°C.

[0017] Furthermore, the pectin is a high-methoxyl pectin with a methoxylation degree of 60%-75% and a molecular weight of 30-100 kDa.

[0018] This invention also proposes a microcapsule powder rich in SN-2DHA algal oil prepared by the above preparation method, comprising the following raw materials by weight:

[0019] SN-2DHA algal oil: 20-40 parts; lutein ester: 5-15 parts; composite wall material based on microfluidic homogeneous cellulose nanofibers and whey protein: 40-60 parts; chitosan quaternary ammonium salt: 3-8 parts; mixed tocopherols: 0.5-2 parts; sodium alginate: 2-5 parts; pectin: 1-2.5 parts; calcium chloride: 0.3-0.8 parts;

[0020] In composite wall materials based on microfluidic homogeneous cellulose nanofibers and whey protein, the mass ratio of cellulose nanofibers to whey protein is 1:2 to 2:1.

[0021] Furthermore, the microcapsule powder has a four-layer structure, with the core being SN-2DHA algal oil and lutein ester, the inner layer being a composite wall material of cellulose nanofibers and whey protein, the middle layer being a chitosan quaternary ammonium salt polyelectrolyte composite layer, and the outer layer being a sodium alginate-pectin calcium pH-responsive gel layer.

[0022] Furthermore, the chitosan quaternary ammonium salt is N-(2-hydroxypropyl)trimethylammonium chloride chitosan or N,N,N-trimethyl chitosan, with a degree of substitution of 60%-90% and a molecular weight of 50-200 kDa.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention constructs a four-layer synergistic protection system. The core consists of SN-2DHA algal oil and lutein esters, the inner layer is a cellulose nanofiber stabilizing layer, the middle layer is a chitosan quaternary ammonium salt interface curing layer, and the outer layer is a sodium alginate pectin calcium pH-responsive gel layer. The four layers complement each other, achieving complete protection from preparation, storage to digestion and absorption.

[0025] Microfluidic precision emulsification ensures uniform emulsion particle size, while electrostatic deposition and interface solidification reduce surface oil content to 0.8-1.2%, achieving a total encapsulation rate of ≥95%. Supercritical CO2 low-temperature drying extends oxidation stability to 52 days, nearly three times longer than traditional processes.

[0026] pH-responsive intelligent release enables targeted release into the gastrointestinal tract. The release rate is ≤15% in gastric juice environment (pH 2.0) after 2 hours and ≥85% in intestinal juice environment (pH 7.0) after 1 hour. The targeted release index is 7.2, which is 3 times higher than that of traditional microcapsule powder. Attached Figure Description

[0027] Figure 1 This is a flowchart of the preparation method of the microcapsule powder rich in SN-2DHA algal oil according to the present invention;

[0028] Figure 2 The particle size distribution curve for the emulsion is shown.

[0029] Figure 3 This is a SEM image of the finished microencapsulated powder product. Detailed Implementation

[0030] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0031] Example 1

[0032] The raw materials are weighed according to the following parts by weight: 30 parts of SN-2DHA algal oil, 10 parts of lutein ester, 5 parts of chitosan quaternary ammonium salt, 1 part of mixed tocopherols, 2 parts of sodium alginate, 1.2 parts of pectin, 0.8 parts of calcium chloride, and 50 parts of composite wall material. The composite wall material contains 20 parts of cellulose nanofibers and 30 parts of whey protein, with a mass ratio of 2:3.

[0033] like Figure 1 As shown, the preparation method includes the following steps:

[0034] S1. Oil Phase Preparation

[0035] 30 parts SN-2DHA algal oil, 10 parts lutein ester, and 1 part mixed tocopherols were placed in a brown glass container and stirred at 400 rpm for 25 minutes in a 45°C water bath under nitrogen protection to ensure complete dissolution of the lutein ester. After thorough mixing of all components, a homogeneous and transparent oil phase was obtained. The entire process was carried out under light-protected conditions to prevent photo-oxidation of the lutein ester and DHA.

[0036] It should be noted that the DHA content in SN-2DHA algal oil is ≥40%, and the source is enzymatically modified algal oil or specific extracts of *Schizochytrium* / *Cryptodinium*; the lutein ester is a lutein diester with a purity ≥90%, and the source is a marigold oil resin transesterification product.

[0037] S2. Aqueous Phase Preparation

[0038] Fifty parts of a composite wall material based on microfluidic homogenized cellulose nanofibers and whey protein were dispersed in 750 parts of deionized water at a solid-liquid mass ratio of 1:15. The mixture was sheared at 10,000 rpm for 12 minutes using a high-speed shear mill to ensure thorough hydration and dispersion. Subsequently, it was ultrasonically treated at 300 W for 8 minutes to further break up agglomerated particles and form a homogeneous and stable aqueous dispersion. The pH of this aqueous dispersion was then adjusted to 3.5-4.0 using 0.1 M hydrochloric acid or citric acid solution and maintained within this pH range in subsequent steps. The cellulose nanofibers were pre-treated using a microfluidic homogenizer at a pressure of 100 MPa for 4 cycles, resulting in cellulose nanofibers with an average diameter of 20-30 nm and a length of 200-300 nm.

[0039] S3. Pickering emulsion formation

[0040] A Y-shaped microfluidic chip with a channel size of 100 μm and a channel depth of 50 μm was used. The oil phase obtained in step S1 and the aqueous phase obtained in step S2 were respectively delivered into the microfluidic chip via precision injection pumps for precise emulsification. The oil-to-water volume ratio was controlled at 1:3, and the flow rate ratio was controlled at 1:8, i.e., the oil phase flow rate was 0.1 mL / min, the aqueous phase flow rate was 0.8 mL / min, and the total flow rate was 0.9 mL / min. Within the Y-shaped confluence channel of the microfluidic chip, the two fluid phases met under laminar flow conditions, forming an O / W type Pickering emulsion through shear force and interfacial tension. In the resulting emulsion, the composite wall material particles spontaneously adsorbed and aggregated at the oil-water interface, forming a physical barrier to stabilize the oil droplets. The emulsion particle size was measured using a laser particle size analyzer, and the result was 2.4 ± 0.4 μm. The particle size distribution was concentrated, and the coefficient of variation (CV) was less than 12%, indicating that the emulsion has good monodispersity.

[0041] S4. Interface curing and drying

[0042] Five parts of a 2% (w / v) aqueous solution of chitosan quaternary ammonium salt were slowly added dropwise to the Pickering emulsion obtained in step S3. Here, (w / v) is an abbreviation for weight / volume percentage, representing mass-volume concentration. The dropping rate was controlled at 0.8 mL / min to avoid excessive local concentration leading to flocculation. Simultaneously, the mixture was continuously stirred at 400 rpm for 45 minutes. During this process, the system was maintained at pH 3.5-4.0. Whey protein has an isoelectric point of approximately pH 4.5-5.2, under which it carries a net positive charge. However, the cellulose nanofibers, after microfluidic homogenization, have a large number of carboxyl groups exposed on their surface. Although partially protonated at this pH, they still retain a considerable negative charge density. When the two are combined and adsorbed at the oil-water interface, the high specific surface area and strong negative charge characteristics of the cellulose nanofibers result in a stable oil droplet interface in the composite wall material exhibiting an overall net negative charge. At this point, a chitosan quaternary ammonium salt solution with a strong positive charge is added, and a strong electrostatic attraction is generated between the two. The chitosan quaternary ammonium salt is rapidly adsorbed and enriched at the oil droplet interface through electrostatic deposition, and forms a dense polyelectrolyte composite layer with the composite wall material through electrostatic interaction and intermolecular forces, thus achieving interface curing.

[0043] Add sodium alginate pectin aqueous solution dropwise to the Pickering emulsion after interface curing. Stir evenly at a stirring speed of 300-400 rpm, a reaction temperature of 35-40℃, and a reaction time of 20-30 minutes. Then add calcium chloride solution to carry out ionic cross-linking reaction to form a pH-responsive gel outer layer. In the sodium alginate pectin aqueous solution, the mass ratio of sodium alginate to pectin is 2:1 to 4:1, the total concentration is 1.5-2.5% (w / v), and the calcium chloride concentration is 0.5-1.0% (w / v).

[0044] Preferably, the composition is: sodium alginate: 2 parts, pectin: 1.2 parts, calcium chloride: 0.8 parts; the pectin is high methoxyl pectin with a methoxylation degree of 60%-75% and a molecular weight of 30-100kDa.

[0045] Subsequently, spray drying technology was used for dehydration and solidification. The spray drying process parameters were: inlet air temperature 165℃, outlet air temperature 80℃, feed rate 8mL / min, and atomization pressure 0.3MPa. Under these conditions, the emulsion droplets rapidly dehydrated to form solid microcapsules, and because the outlet air temperature was controlled below 80℃, the thermal oxidative degradation of DHA and lutein esters was effectively avoided.

[0046] S5. Collection and Screening

[0047] The powder obtained from spray drying in step S4 was collected and lightly pulverized using an air jet mill at a pressure of 0.7 MPa and a classifying speed of 4000 rpm to disperse any soft agglomerates that may have formed during the drying process. It was then passed through a 100-mesh sieve with a pore size of 150 μm to obtain the powder as shown below. Figure 3 The SEM image shown is of the finished microcapsule powder with uniform particle size distribution, sealed in a nitrogen-filled aluminum foil bag and stored in a cool, dry place.

[0048] Example 2

[0049] The raw materials are weighed according to the following parts by weight: 25 parts SN-2DHA algal oil, 8 parts lutein ester, 6 parts chitosan quaternary ammonium salt, 1.5 parts mixed tocopherols, 2.5 parts sodium alginate, 1.2 parts pectin, 0.8 parts calcium chloride, and 55 parts composite wall material. The composite wall material contains 22 parts cellulose nanofibers and 33 parts whey protein, with a mass ratio of 2:3.

[0050] S1. Oil Phase Preparation

[0051] 25 parts SN-2DHA algal oil, 8 parts lutein ester, and 1.5 parts mixed tocopherols were placed in a brown glass container. Nitrogen gas was continuously introduced to replace the air inside the container, creating an inert protective environment. The container was placed in a 40°C constant temperature water bath and stirred at 350 rpm for 30 minutes to ensure that the lutein ester was fully dissolved and formed a homogeneous and stable oil phase system with the DHA algal oil and mixed tocopherols. A nitrogen atmosphere was maintained during stirring to prevent oil oxidation. The resulting oil phase was an orange-yellow transparent liquid without suspended particles.

[0052] S2. Aqueous Phase Preparation

[0053] Fifty-five parts of a composite wall material based on microfluidic homogenized cellulose nanofibers and whey protein were dispersed in 900 parts of deionized water at a solid-liquid mass ratio of 1:16.4. The mixture was sheared at 11,000 rpm for 13 minutes using a high-speed shearing machine to ensure sufficient hydration and dispersion of the cellulose nanofibers and whey protein, and to initially form hydrogen bonds. Subsequently, ultrasonic treatment was performed at a power of 350 W for 6 minutes to further break up the aggregates of the wall material particles using ultrasonic cavitation, promoting the composite effect of cellulose nanofibers and whey protein. The final product was a milky-white aqueous dispersion with good flowability and stability. The cellulose nanofibers were pre-treated with a microfluidic homogenizer at a pressure of 120 MPa for four cycles. The resulting cellulose nanofibers had an average diameter of 15-25 nm and a length of 150-350 nm, exhibiting a high aspect ratio, which is beneficial for forming a stable mechanical barrier at the oil-water interface.

[0054] S3. Pickering emulsion formation

[0055] A T-shaped microfluidic chip with a channel size of 80 μm and a channel depth of 40 μm was used. Its T-shaped structure allows the continuous phase (aqueous phase) and dispersed phase (oil phase) to meet at a precise flow rate ratio at their perpendicular intersection, generating a controllable shear force field. The oil phase prepared in step S1 and the aqueous phase prepared in step S2 were separately delivered to the microfluidic chip using high-precision syringe pumps, controlling the oil-water volume ratio at 1:3.5 and the two-phase flow rate ratio at 1:9, i.e., an oil phase flow rate of 0.08 mL / min, an aqueous phase flow rate of 0.72 mL / min, and a total flow rate of 0.8 mL / min. Within the precise flow channels of the microfluidic chip, the oil phase is broken into tiny droplets under the shearing action of the aqueous phase. Simultaneously, the composite wall material particles (cellulose nanofibers-whey protein complex) are rapidly adsorbed onto the newly formed oil-water interface. The oil droplets are stabilized through irreversible adsorption of solid particles and steric hindrance, forming an O / W type Pickering emulsion. Figure 2 As shown, the emulsion particle size was measured using a laser particle size analyzer. The horizontal axis represents particle size / μm, and the vertical axis represents intensity / %, indicating the percentage of light scattering intensity corresponding to that particle size. The coefficient of variation (CV) is approximately 10%, which is significantly better than the traditional high-shear emulsification process, demonstrating that microfluidic technology can achieve precise control of emulsion particle size.

[0056] S4. Interface curing and drying

[0057] Six parts of a 2.5% (w / v) aqueous solution of chitosan quaternary ammonium salt were slowly added dropwise to the Pickering emulsion obtained in step S3. The dropping rate was precisely controlled at 0.6 mL / min using a peristaltic pump to ensure uniform distribution of the chitosan quaternary ammonium salt in the emulsion and to avoid flocculation or aggregation of oil droplets due to excessively high local concentrations. Simultaneously, the mixture was continuously stirred at 500 rpm for 50 minutes to allow the positively charged chitosan quaternary ammonium salt molecules to fully contact the negatively charged composite wall material. Through electrostatic interaction, a second polyelectrolyte composite layer was formed at the oil-water interface, achieving interface solidification. This polyelectrolyte composite layer, together with the inner composite wall material particle layer, forms a dense double-barrier structure, significantly improving the mechanical strength, barrier properties, and permeation resistance of the microcapsule wall material.

[0058] A sodium alginate pectin aqueous solution was added dropwise to the interface-cured Pickering emulsion. After stirring evenly, calcium chloride solution was added to initiate an ionic cross-linking reaction, forming a pH-responsive gel outer layer. Subsequently, supercritical CO2-assisted low-temperature drying technology was used for dehydration and curing. Specific process parameters were: drying temperature 40℃, operating pressure 10MPa, CO2 flow rate 15L / h, and drying time 3 hours. Under these conditions, supercritical CO2 fluid exhibits a gas-like diffusion rate and a liquid-like dissolving capacity, enabling it to efficiently penetrate the emulsion system and carry away moisture. Furthermore, the operating temperature of only 40℃ is far lower than the inlet air temperature of traditional spray drying (150-180℃), and the entire process is conducted in a closed, oxygen-free environment, minimizing the thermal oxidation, photo-oxidation, and enzymatic oxidation of DHA and lutein esters, effectively preserving the bioactivity of the functional components. During the drying process, the polyelectrolyte composite layer gradually solidifies and sets, forming a dense and stable microcapsule wall structure.

[0059] S5. Collection and Screening

[0060] The powder product obtained from supercritical drying in step S4 is collected and transferred to an air jet mill for light pulverization at a pressure of 0.7 MPa and a classifying speed of 4000 rpm to disperse any soft agglomerates that may form during drying, while avoiding over-pulverization that could damage the microcapsule structure. It is then passed through a 100-mesh sieve (150 μm pore size) to remove a small amount of large particles or insufficiently dispersed agglomerates, resulting in a microcapsule powder product with uniform particle size distribution and good flowability. The finished product is sealed in nitrogen-filled aluminum foil bags and stored in a cool, dry place protected from light at a temperature ≤25℃ and a relative humidity ≤60%.

[0061] Comparative Example 1

[0062] This comparative example uses a traditional spray drying process, without pickering emulsion and interface curing.

[0063] Weigh the raw materials according to the following proportions by weight: 30 parts SN-2DHA algal oil, 10 parts lutein ester, 45 parts maltodextrin (DE value 15), 5 parts gum arabic, and 1 part mixed tocopherols.

[0064] S1. Aqueous Phase Preparation

[0065] Dissolve 45 parts of maltodextrin (DE value 15) and 5 parts of gum arabic in 600 parts of deionized water at a solid-liquid mass ratio of 1:12. Place the solution in a 60°C water bath and stir at 400 rpm for 30 minutes until the wall material is completely dissolved, forming a viscous aqueous solution. Cool to room temperature for later use.

[0066] S2. Oil Phase Preparation

[0067] 30 parts SN-2DHA algal oil, 10 parts lutein ester, and 1 part mixed tocopherols were placed in a brown glass container and stirred at 300 rpm for 15 minutes at room temperature to ensure uniform dispersion of the lutein ester, thus obtaining the oil phase. Since no heating was performed, the lutein ester only partially dissolved, resulting in the presence of fine suspended particles.

[0068] S3. Traditional high-shear emulsification

[0069] The oil phase prepared in step S2 was added to the aqueous phase prepared in step S1, and emulsification was performed by shearing at 10,000 rpm for 15 minutes using a high-speed shear mill. This process relies on the mechanical energy generated by the high shear rate to break the oil phase into tiny droplets. However, due to the lack of solid particle stabilizers, the emulsification process mainly depends on the emulsifying effect of gum arabic, resulting in poor emulsion stability and easy droplet aggregation. During the emulsification process, a large amount of heat is generated due to the high-speed shear, with local temperatures reaching above 70°C, leading to the oxidative degradation of some DHA and lutein esters.

[0070] S4. Does not form a pH-responsive gel outer layer; direct spray drying.

[0071] The emulsion obtained in step S3 was directly spray-dried with the following process parameters: inlet air temperature 180℃ (higher than 165℃ in Example 1), outlet air temperature 85℃ (higher than 80℃ in Example 1), feed rate 10mL / min (higher than 8mL / min in Example 1), and atomization pressure 0.25MPa. The higher inlet and outlet air temperatures exacerbated the thermal oxidation loss of the core material. Simultaneously, the maltodextrin-gum arabic wall material rapidly dehydrated at high temperatures to form a glassy structure, but this structure lacked density and contained numerous internal pores.

[0072] S5. Collection and Screening

[0073] The powder collected from the bottom of the spray drying tower and the cyclone separator was passed through an 80-mesh sieve with a sieve aperture of 180 μm to obtain a control sample.

[0074] Comparative Example 1 uses traditional carbohydrate wall materials, namely maltodextrin or gum arabic, combined with high-shear emulsification and spray drying processes. Its main difference from Examples 1 and 2 of this invention is:

[0075] Traditional wall materials are soluble macromolecules that rely on high viscosity to achieve physical encapsulation. They lack the rigid support of solid particles and cannot form a stable structure like a Pickering emulsion. As a result, the mechanical strength and density of these wall materials are far lower than those of the cellulose nanofiber-whey protein composite wall material of this invention.

[0076] High-shear emulsification is energy-intensive, has a large temperature rise, and a wide droplet size distribution, making it impossible to precisely control emulsion quality. Microfluidic technology, on the other hand, can achieve gentle, precise, and low-energy emulsification.

[0077] Without the electrostatic deposition step of chitosan quaternary ammonium salt, a polyelectrolyte composite layer cannot be formed, resulting in a significant decrease in the barrier properties of the wall material.

[0078] Higher inlet and outlet air temperatures exacerbate the loss and oxidation of heat-sensitive components, while the supercritical CO2 drying in Example 2 is carried out under low-temperature and oxygen-free conditions, which maximizes the preservation of active components.

[0079] It should be noted that the encapsulation efficiency was verified using an organic solvent extraction method combined with differential scanning calorimetry (DSC). The microcapsule powder surface was first washed three times with petroleum ether, and the washing liquid was collected to determine the surface oil content. The remaining powder was then hydrolyzed with hydrochloric acid, and the total oil was extracted using a mixed solvent of diethyl ether and petroleum ether. The DHA content was then determined by gas chromatography. Encapsulation efficiency = (total oil content - surface oil content) / total oil content × 100%.

[0080] In summary, the product of Comparative Example 1 is significantly inferior to that of Example 1 and Example 2 in key indicators such as encapsulation rate, stability, particle size control and flowability, which fully demonstrates the advanced nature and necessity of the technical solution of the present invention.

[0081] Comparative Example 2

[0082] This comparative example uses a single wall material and does not involve chitosan quaternary ammonium salt interface curing.

[0083] Weigh the raw materials by weight as follows: 30 parts SN-2DHA algal oil, 10 parts lutein ester, 50 parts microfluidic homogeneous cellulose nanofibers (without whey protein), 0 parts chitosan quaternary ammonium salt, and 1 part mixed tocopherols.

[0084] S1. Oil Phase Preparation

[0085] Same as in Example 1. 30 parts of SN-2DHA algal oil, 10 parts of lutein ester and 1 part of mixed tocopherols were placed in a brown glass container and stirred at 400 rpm for 25 minutes in a water bath at 45°C under nitrogen protection to obtain a homogeneous oil phase.

[0086] S2. Aqueous Phase Preparation

[0087] Fifty parts of single microfluidically homogenized cellulose nanofibers were pre-treated with a microfluidic homogenizer under the same conditions as in Example 1: pressure 100 MPa, 4 cycles, dispersed in 750 parts of deionized water at a solid-liquid ratio of 1:15, sheared at 10,000 rpm for 12 minutes using a high-speed shearing machine, and then ultrasonically treated at 300 W for 8 minutes to form an aqueous dispersion. Due to the lack of synergistic effect of whey protein, the dispersion stability of the cellulose nanofibers was poor, and slight sedimentation occurred after 30 minutes. In contrast, the composite wall material dispersions of Examples 1 and 2 could remain stable for more than 24 hours under the same conditions.

[0088] S3. Pickering emulsion formation

[0089] Similar to Example 1, a Y-type microfluidic chip was used with a channel size of 100 μm, an oil-to-water volume ratio of 1:3, a flow rate ratio of 1:8, an oil phase flow rate of 0.1 mL / min, an aqueous phase flow rate of 0.8 mL / min, and a total flow rate of 0.9 mL / min. Although cellulose nanofibers can adsorb at the oil-water interface to some extent to form a Pickering emulsion, the stability of the emulsion is worse than that of Example 1 due to the lack of whey protein's auxiliary emulsification and steric stabilization effect, and the droplets are prone to Ostwald ripening. The measured emulsion particle size was 3.2 ± 0.8 μm, with an average particle size larger than that of Example 1 (2.4 ± 0.4 μm), and a wider particle size distribution. The CV value was approximately 22%, higher than the 12% of Example 1.

[0090] S4. No interface curing, no pH-responsive gel outer layer formed, direct spray drying.

[0091] The Pickering emulsion obtained in step S3 was directly spray-dried without undergoing interfacial curing treatment with chitosan quaternary ammonium salt. The process parameters were the same as in Example 1: inlet air temperature 165℃, outlet air temperature 80℃, feed rate 8mL / min, and atomization pressure 0.3MPa. Due to the lack of an interfacial curing step, the emulsion already exhibited a certain degree of droplet aggregation before entering the spray drying tower. Furthermore, the interfacial film formed by the cellulose nanofibers during the drying process was prone to rupture under the impact of high-temperature airflow due to the lack of reinforcement from the polyelectrolyte composite layer, leading to core material leakage.

[0092] S5. Collection and Screening

[0093] Same as in Example 1. The dried powder was collected, pulverized by airflow at a pressure of 0.7 MPa and a classifying speed of 4000 rpm, and then sieved through a 100-mesh sieve to obtain a control sample.

[0094] Comparative Example 2 uses single cellulose nanofibers as the wall material, which can form a Pickering emulsion, but its main difference from Examples 1 and 2 of this invention is:

[0095] Without the synergistic effect of whey protein, the emulsifying ability and dispersion stability of cellulose nanofibers are insufficient, resulting in large emulsion droplet size and easy aggregation, which directly affects the particle size and encapsulation efficiency of the final product. As an amphiphilic biomacromolecule, whey protein can both form hydrogen bonds and hydrophobic interactions with cellulose nanofibers to enhance the strength of the wall material, and reduce interfacial tension and promote the formation of small droplets through its own surface activity. This synergistic effect is lost in a single wall material system.

[0096] Electrostatic deposition of chitosan quaternary ammonium salt is one of the core technologies of this invention. The positively charged chitosan quaternary ammonium salt forms a polyelectrolyte composite layer with the negatively charged composite wall material, which not only enhances the mechanical strength of the interfacial film but also improves its density and barrier properties. Comparative Example 2 lacks this step, resulting in inherent defects in the wall material, making it prone to cracking during drying and causing severe core material leakage.

[0097] The interfacial film formed by single cellulose nanofibers has poor flexibility and is more prone to breakage during the high-temperature airflow impact and rapid dehydration process of spray drying; while the composite wall material of Example 1 has better flexibility and film-forming properties due to the presence of whey protein, and the supercritical drying of Example 2 fundamentally avoids high-temperature impact.

[0098] In summary, the product performance of Comparative Example 2 falls between that of Comparative Example 1 and the Example 2, demonstrating the advantages of Pickering emulsion technology and highlighting the indispensable synergistic effect of composite wall materials and interface curing steps. Example 1 and Example 2, through a complete technical solution involving composite wall materials, microfluidic emulsification, interface curing, and optimized drying, achieved comprehensive improvements in performance such as encapsulation rate, stability, and particle size control.

[0099] As shown in Table 1, the systematic comparison between Comparative Examples 1 and 2 and Examples 1 and 2 fully demonstrates the synergistic effect of the complete technical solution adopted in this invention, which includes composite wall material, microfluidic precise emulsification, chitosan quaternary ammonium salt interface curing, and optimized drying process. Each technical feature works in tandem and is indispensable, collectively achieving high encapsulation rate (≥95%), high oxidation stability (3-fold extension of oxidation period at 60℃), excellent particle size control (10-50 μm, CV < 15%), and good processing performance for DHA and lutein esters, significantly superior to traditional microencapsulation processes and some improved processes.

[0100] It should be noted that the accelerated oxidation stability test conditions are as follows: Schaal oven method, 50g of sample is spread evenly in a 250mL open petri dish, placed in a 60℃ constant temperature oven, without aeration, for natural oxidation. The judgment criteria are: oxidation endpoint is defined as a peroxide value (POV) ≥ 5mmol / kg or an acid value ≥ 3mg / g, or the appearance of a distinct rancid odor. POV is measured periodically, and the time to reach the oxidation endpoint is recorded.

[0101] Table 1

[0102] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Wall material type Cellulose nanofibers, whey protein Cellulose nanofibers, whey protein Maltodextrin, gum arabic Single cellulose nanofibers Emulsification microfluidics microfluidics High shear microfluidics Interface curing and pH-responsive gel outer layer have have none none Drying method spray drying <![CDATA[Supercritical CO2 drying]]> spray drying spray drying Total embedment rate 98.8% 97.2% 80.6% 87.0% Surface oil content 1.2% 0.8% 8.5% 5.3% Accelerate oxidation stability 45 days 52 days 18 days 28 days Average particle size 28μm 22μm 45μm 35μm Particle size uniformity Excellent (CV < 15%) Excellent (CV < 15%) Poor (CV>30%) medium

[0103] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A method for preparing microcapsule powder rich in SN-2DHA algal oil, characterized in that, Includes the following steps: S1. Mix SN-2DHA algal oil, lutein ester and antioxidant, and stir under inert gas protection and light protection to obtain an oil phase dispersion; S2. The composite wall material containing microfluidic homogeneous cellulose nanofibers and whey protein is dispersed in deionized water and subjected to high-speed shearing and ultrasonic treatment to form an aqueous dispersion. S3. The oil phase dispersion obtained in step S1 and the aqueous phase dispersion obtained in step S2 are emulsified through a microfluidic chip to control the flow rate ratio of the two phases and form an O / W type Pickering emulsion with uniform oil droplet size. S4. Add chitosan quaternary ammonium salt solution to the Pickering emulsion obtained in step S3 to carry out electrostatic deposition reaction to achieve interface solidification. Add sodium alginate pectin aqueous solution to the interface solidified Pickering emulsion, stir evenly, and then add calcium chloride solution to carry out ionic cross-linking reaction to form a pH-responsive gel outer layer. Then dry to obtain solid microcapsules. S5. The dried solid microcapsules are crushed and sieved to obtain microcapsule powder rich in SN-2DHA algal oil.

2. The preparation method according to claim 1, characterized in that, In step S1, the antioxidant is a mixture of tocopherols; the stirring temperature is 40-45℃, and the stirring time is 25-30 minutes.

3. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of cellulose nanofibers to whey protein in the composite wall material is 1:2 to 2:1; the cellulose nanofibers are pre-treated by a microfluidic homogenizer at a pressure of 100-120 MPa, and the resulting cellulose nanofibers have an average diameter of 15-30 nm and a length of 150-350 nm.

4. The preparation method according to claim 1, characterized in that, In step S3, the microfluidic chip is a Y-type or T-type chip; during emulsification, the volume ratio of the oil phase dispersion to the aqueous phase dispersion is 1:3 to 1:3.5, and the flow rate ratio is 1:8 to 1:9; the average particle size of the formed Pickering emulsion is 2.2-2.5 μm, and the particle size variation coefficient CV value is less than 12%.

5. The preparation method according to claim 1, characterized in that, In step S4, the concentration of the chitosan quaternary ammonium salt solution is 2-2.5%; in the sodium alginate pectin aqueous solution, the mass ratio of sodium alginate to pectin is 2:1 to 4:1, and the concentration of calcium chloride is 0.5-1.0%.

6. The preparation method according to claim 1, characterized in that, In step S4, the drying is spray drying, with an inlet air temperature of 165°C and an outlet air temperature of 80°C.

7. The preparation method according to claim 5, characterized in that, The pectin is a high-methoxyl pectin with a methoxylation degree of 60%-75% and a molecular weight of 30-100kDa.

8. A microcapsule powder rich in SN-2DHA algal oil prepared by the preparation method according to any one of claims 1-7, characterized in that, By weight, the following raw materials are included: SN-2DHA algal oil: 20-40 parts; lutein ester: 5-15 parts; composite wall material based on microfluidic homogeneous cellulose nanofibers and whey protein: 40-60 parts; chitosan quaternary ammonium salt: 3-8 parts; mixed tocopherols: 0.5-2 parts; Sodium alginate: 2-5 parts; Pectin: 1-2.5 parts; Calcium chloride: 0.3-0.8 parts; In composite wall materials based on microfluidic homogeneous cellulose nanofibers and whey protein, the mass ratio of cellulose nanofibers to whey protein is 1:2 to 2:

1.

9. The microencapsulated powder according to claim 8, characterized in that, The microcapsule powder has a four-layer structure: the core is SN-2DHA algal oil and lutein ester, the inner layer is a composite wall material of cellulose nanofibers and whey protein, the middle layer is a chitosan quaternary ammonium salt polyelectrolyte composite layer, and the outer layer is a sodium alginate-pectin calcium pH-responsive gel layer.

10. The microencapsulated powder according to claim 8, characterized in that, The chitosan quaternary ammonium salt is N-(2-hydroxypropyl)trimethylammonium chloride chitosan or N,N,N-trimethyl chitosan, with a degree of substitution of 60%-90% and a molecular weight of 50-200 kDa.

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