A method for preparing porous rs3 microspheres

Abstract

The application discloses a preparation method of porous RS3 microspheres, and belongs to the technical field of microcapsule carrier materials. The method uses resistant starch with a melting temperature (peak temperature measured by DSC method) of greater than or equal to 120 DEG C as the only structural base material, and the porous spherical particles with micron-sized cavities are prepared through a forming and poring process. The specific steps include: mixing the resistant starch with a liquid medium to form a precursor mixture; performing forming treatment on the mixture to form micron-sized individual units; removing the liquid medium during or after the forming process, and forming a plurality of micron-sized cavities in situ by removing pre-existing occupying materials in the individual units, thereby obtaining the porous RS3 microspheres. The resistant starch can resist 100 DEG C cooking, keep structural stability in simulated gastric juice, is not hydrolyzed by digestive enzymes in the small intestine, and can be fermented by probiotics in the large intestine. The application does not need a chemical crosslinking agent in the whole process, and the obtained microspheres have excellent heat resistance, gastric acid resistance, digestion resistance and biocompatibility. The application also protects the porous RS3 microsphere product prepared by the method, and the porous microspheres defined by the characteristics of the product itself.

Description

Technical Field

[0001] This invention belongs to the field of microcapsule carrier material technology, specifically relating to a method for preparing porous spherical particles with multiple micron-sized cavities inside, using high-melting-point resistant starch as the substrate prepared by a purely physical method, as well as the porous microsphere products obtained by this method and their applications. Background Technology Microencapsulation technology is widely used in the food, pharmaceutical, daily chemical, and agricultural industries to protect active substances, mask unpleasant odors, improve processing stability, or achieve controlled-release delivery. Commonly used microcapsule wall materials include gelatin, gum arabic, maltodextrin, cyclodextrin, and various chemically modified starches. However, existing wall materials generally suffer from at least one of the following technical bottlenecks: (1) Insufficient heat resistance. Most natural polymer wall materials swell significantly or disintegrate at temperatures above 80°C, failing to meet the needs of food processing scenarios such as steaming, baking, and high-temperature sterilization. (2) Insufficient digestibility. Conventional starch-based wall materials are hydrolyzed by α-amylase in the small intestine, failing to protect the active substances intact for targeted release in the large intestine. (3) Poor gastric acid stability. Most wall materials swell or dissolve in the low pH environment of gastric juice, leading to premature leakage of active substances. (4) Risk of chemical residues. Some wall materials require the use of chemical cross-linking agents such as glutaraldehyde and sodium trimetaphosphate for curing, introducing potential food safety or biocompatibility risks. Therefore, there is an urgent need in this field for a porous microsphere carrier material and its preparation method that simultaneously meets multiple core requirements such as high temperature resistance, gastric acid resistance, small intestinal digestion resistance, and pure physical preparation. Summary of the Invention This invention provides a method for preparing porous RS3 microspheres. The prepared microspheres use resistant starch prepared by a purely physical method as the sole structural substrate, with a melting temperature ≥120℃, can withstand boiling water at 100℃, maintain structural stability in simulated gastric juice, are not hydrolyzed by digestive enzymes in the small intestine, and have multiple micron-sized cavities inside, making them suitable for the encapsulation and controlled release of various active substances. In this specification, the resistant starch refers to a known, commercially available resistant starch manufactured using purely physical methods. The resistant starch has a melting point ≥120°C as determined by DSC and has been confirmed in in vitro simulated digestion experiments not to be hydrolyzed by small intestinal digestive enzymes. Its resistance to gastric acid is due to: the formation of a dense, ordered starch double-helix microcrystalline structure through purely physical annealing and regeneration; dense cross-linking of intermolecular hydrogen bonds; high crystal density; and the difficulty for gastric juice water molecules and hydrogen ions to penetrate the crystal lattice. Gastric juice contains only pepsin and no amylase capable of breaking starch glycosidic bonds. Furthermore, its melting temperature ≥120°C is far higher than the human digestive tract's working temperature of 37°C, preventing hydration and gelatinization. The soluble short-chain components of starch are encapsulated within the microcrystalline framework and cannot dissolve in acidic gastric juice. Therefore, it maintains an intact granular structure throughout its digestive process. It is manufactured using purely physical methods and contains no chemical cross-linking agents or residual biological enzymes. The resistant starch is used directly as a known raw material in subsequent embodiments. The method for preparing porous RS3 microspheres provided by the present invention includes the following steps: (a) providing a resistant starch prepared by a purely physical method with a melting temperature (peak temperature determined by DSC) ≥120℃, mixing it with a liquid medium to obtain a precursor mixture; (b) molding the precursor mixture to form micron-sized individual units; (c) removing the liquid medium during or after molding, and forming multiple micron-sized cavities inside the individual units to obtain porous RS3 microspheres. In step (a), the liquid medium is used to adjust the flowability and formability of the precursor mixture. The liquid medium is selected from water or a mixture of water and ethanol, wherein the volume percentage of water is not less than 50%. The solid content of the precursor mixture is controlled within the range of 15%-45%, which ensures that the mixture has a viscosity suitable for subsequent molding processes. When the solid content is below 15%, the resulting microspheres have insufficient support for their cavity structure and are prone to collapse after drying; when the solid content is above 45%, the viscosity of the mixture is too high, which is not conducive to the formation of micron-sized individual units during the molding process. In step (a), the precursor mixture may optionally include an auxiliary film-forming material. The auxiliary film-forming material may be one or more of hydroxypropyl methylcellulose (HPMC), sodium alginate, pectin, or pullulan. The addition of the auxiliary film-forming material can improve the mechanical strength and surface film-forming properties of the microspheres, but its amount shall not exceed 20% of the mass of the resistant starch. In step (b), the purpose of the molding process is to segment and shape the precursor mixture into micron-sized individual units. Applicable molding methods include, but are not limited to: spray drying, emulsification-solvent evaporation, cryo-spray granulation, microfluidic droplet generation, template impregnation, or electrostatic spraying. Those skilled in the art can select a suitable molding method based on the target microsphere size, production volume, and equipment conditions. In step (c), the formation of micron-sized cavities within individual units is achieved in situ by removing pre-existing occupying material within the micron-sized individual units. In a preferred embodiment, the occupying material is a porogen, and a porogen-occupying-removal method is employed. Specifically, a porogen is introduced into the precursor mixture, occupying a certain space within the formed individual units. Subsequently, the porogen is removed through methods such as heating decomposition, water washing dissolution, freeze-drying sublimation, or depressurization vaporization, transforming the original occupying space into a micron-sized cavity. Suitable porogens include, but are not limited to: ammonium bicarbonate, ammonium carbonate, sodium bicarbonate (thermally decomposable), sodium chloride, sucrose (water-soluble), ice crystals (sublimation type), and supercritical carbon dioxide (depressurization vaporization type). In another preferred embodiment, a freeze-drying method using ice crystals as a pore-forming agent is used: the formed micron-sized individual units are placed in a low-temperature environment, causing the liquid medium contained therein to freeze and form ice crystals, and then freeze-drying is carried out under vacuum conditions. The ice crystals directly sublimate and escape, leaving a honeycomb porous structure inside the microspheres. After step (c) is completed, the obtained porous RS3 microspheres can be selectively subjected to annealing stabilization treatment (step d): place the microspheres in an environment of 40℃-90℃ and relative humidity of 50%-95% for 5 minutes to 2 hours. This treatment can promote the fusion and stress release between particles inside the RS3 microspheres, further improving the structural integrity and heat resistance of the microspheres. The porous RS3 microspheres prepared by the method of this invention have an average particle size between 1 μm and 2000 μm, a specific surface area between 5 and 200 m² / g, and an average pore size of 0.1 μm to 100 μm. These parameters can be controlled by adjusting the molding method, solid content, type and amount of pore-forming agent, etc. Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: (1) Significant high temperature resistance. Based on the characteristic that the melting temperature of the resistant starch is ≥120℃, the obtained porous microspheres can withstand boiling water at 100℃ for more than 30 minutes without structural disintegration. (2) Excellent gastric acid resistance. After the microspheres are incubated in simulated gastric juice at pH=1.2 at 37℃ for 4 hours, the solid mass retention rate is ≥90%, and the intact structure can be maintained throughout the stomach. (3) Resistance to small intestinal digestion. The microspheres maintain structural integrity during the small intestinal digestion stage, and can protect the encapsulated active substances to the large intestine before release. (4) Pure physical preparation throughout the process. No chemical cross-linking agent or biological enzyme is required, the product has no chemical residue, and no characteristic peaks of chemical cross-linking agents are detected in the infrared spectrum, making it suitable for food, medicine and other fields with strict safety requirements. (5) Controllable cavity structure. By adjusting the type, amount and molding method of the pore-forming agent, the pore size and porosity can be precisely controlled to meet the loading requirements of different active substances. Detailed Implementation The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto. In the following embodiments, the resistant starch is a commercially available product with a peak melting point ≥120℃ as determined by DSC method and a mass loss rate of less than 5% in in vitro simulated small intestinal digestion. Example 1 – Spray Drying Method: 100g of resistant starch was weighed and added to 400mL of deionized water, stirring to form a uniform slurry with a solid content of approximately 20%. 15g of ammonium bicarbonate was added to the slurry as a pore-forming agent and stirred thoroughly to dissolve. The resulting precursor mixture was processed using a spray dryer with an inlet air temperature of 180℃, an outlet air temperature of 90℃, and a feed rate of 10mL / min. During the spray drying process, ammonium bicarbonate decomposed upon heating into ammonia and carbon dioxide gases, leaving numerous cavities inside the formed microspheres. The product was collected, yielding porous RS3 microspheres. Measurements showed an average particle size of approximately 45μm, a specific surface area of ​​approximately 28m² / g, and internal cavity pore sizes ranging from 0.5μm to 15μm. Infrared spectroscopy revealed no characteristic peaks of chemical cross-linking agents. Example 2 – Freeze-drying method: 80g of resistant starch was weighed and added to 320mL of deionized water, stirring to form a homogeneous slurry with a solid content of approximately 20%. The slurry was dripped into liquid nitrogen using a microfluidic device to form frozen microspheres with a diameter of approximately 200μm. The frozen microspheres were transferred to a freeze dryer and dried at -40℃ and a vacuum of 10Pa for 24 hours. After the ice crystals sublimated, a porous structure remained. The obtained porous RS3 microspheres had an average particle size of approximately 180μm and a specific surface area of ​​approximately 45m² / g. Example 3 – Emulsification-Solvent Evaporation Method: Weigh 50g of resistant starch and add 200mL of deionized water, stirring to form a slurry. Add 10g of sodium chloride as a pore-forming agent and stir to dissolve. Slowly drop this aqueous slurry into edible-grade vegetable oil containing a surfactant, stirring at high speed to form a W / O emulsion. Heat the emulsion to 60℃ and continue stirring to allow the water to gradually evaporate. Filter and collect the obtained microspheres, wash with ethanol to remove the residual oil phase, then soak in deionized water to wash away the sodium chloride pore-forming agent. After drying, porous RS3 microspheres are obtained. The average particle size is approximately 120μm, and the internal cavity pore size is 1μm-30μm. Comparative Example 1 – Ordinary corn starch porous microspheres were prepared using the same process as in Example 1, except that the resistant starch was replaced with ordinary edible corn starch (gelatinization temperature 72°C). Comparative Example 2 – Chemically Cross-linked Starch Porous Microspheres: The same process as in Example 1 was used, with ordinary corn starch as raw material. In step (a), sodium tripolyphosphate was added as a chemical cross-linking agent (the amount added was 3% of the starch mass) to obtain chemically cross-linked starch porous microspheres. Performance tests were conducted on the microspheres obtained in Example 1, Comparative Example 1 and Comparative Example 2, and the following performance tests were performed: (1) Structural integrity rate after cooking at 100℃: The samples were placed in boiling water at 100℃ and cooked for 30 minutes. The particle size distribution before and after cooking was measured by a laser particle size analyzer. The structural integrity rate was calculated by the ratio of D50 after cooking to D50 before cooking. (2) Retention rate of simulated gastric juice: The samples were incubated in simulated gastric juice at pH=1.2 at 37℃ for 4 hours. After centrifugation, the solid mass retention rate was measured. (3) Retention rate of in vitro small intestinal digestion: The samples were incubated in simulated small intestinal digestion fluid (pH6.8, 37℃) containing α-amylase for 2 hours. The mass retention rate was measured. (4) Residue of chemical crosslinking agent: The residue of sodium trimetaphosphate was detected according to GB 9685 standard. At the same time, the characteristic peak of chemical crosslinking agent was detected by infrared spectroscopy. The test results are as follows: Test Item Example 1 Comparative Example 1 Comparative Example 2 After cooking at 100℃ for 30 minutes, the structural integrity rate was 93.5%; 0% (complete gelatinization and disintegration) was 82.1%. At pH 1.2, the retention rates of simulated gastric juice after 4 hours were 92.3%, 8.7%, and 65.4%, respectively. The 2-hour retention rates after in vitro small intestinal digestion were 89.2%, 10.3%, and 68.3%, respectively. No chemical cross-linking agent residue was found (sodium tripolyphosphate was detected). Infrared spectroscopy crosslinking agent characteristic peaks not detected. As shown in the table above, the porous RS3 microspheres obtained in Example 1 of this invention are significantly superior to the ordinary starch microspheres of Comparative Example 1 and the chemically cross-linked starch microspheres of Comparative Example 2 in terms of the three core indicators of high temperature cooking resistance, gastric acid resistance, and small intestinal digestion resistance. Moreover, no characteristic peaks of chemical cross-linking agents were detected in the infrared spectrum, indicating better safety.

Claims

1. A method for preparing porous RS3 microspheres, characterized in that, Includes the following steps: (a) A resistant starch with a melting temperature (peak temperature determined by DSC) ≥120°C prepared by a purely physical method is provided and mixed with a liquid medium to obtain a precursor mixture; (b) The precursor mixture is subjected to molding treatment to form micron-sized individual units; (c) During or after molding, the liquid medium is removed and multiple micron-sized cavities are formed inside the individual units to obtain porous RS3 microspheres.

2. The method according to claim 1, characterized in that, The liquid medium in step (a) is selected from water or a mixture of water and ethanol, wherein the volume percentage of water is not less than 50%; the solid content of resistant starch in the precursor mixture is 15%-45%, preferably 25%-40%, and more preferably 30%-38%.

3. The method according to claim 1, characterized in that, The precursor mixture in step (a) further comprises an auxiliary film-forming material selected from at least one of hydroxypropyl methylcellulose, sodium alginate, pectin, and pullulan.

4. The method according to claim 1, characterized in that, The molding process described in step (b) is selected from at least one of spray drying, emulsification-solvent evaporation, cryo-spray granulation, microfluidic droplet generation, template impregnation, and electrostatic spraying.

5. The method according to claim 1, characterized in that, The multiple micron-sized cavities mentioned in step (c) are formed in situ by removing pre-existing occupying material inside the micron-sized individual units.

6. The method according to claim 5, characterized in that, The occupying material is a pore-forming agent, which is selected from at least one of ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium chloride, sucrose, ice crystals, and supercritical carbon dioxide; the removal method of the pore-forming agent is selected from at least one of heating decomposition, water washing and dissolution, freeze drying and sublimation, or depressurization and vaporization.

7. The method according to claim 1, characterized in that, The multiple micron-sized cavities mentioned in step (c) are formed by freeze-drying, that is, using ice crystals as pore-forming agents, freezing the individual units after molding to form ice crystals in the liquid medium, and then sublimating the ice crystals by freeze-drying, thereby leaving micron-sized cavities inside the microspheres.

8. The method according to claim 1, characterized in that, The method also includes step (d): annealing and stabilizing the obtained porous RS3 microspheres at 40℃-90℃ and relative humidity of 50%-95% for a duration of 5 minutes to 2 hours.

9. The method according to any one of claims 1 to 8, characterized in that, The resistant starch was incubated in simulated small intestinal digestive fluid (containing α-amylase, pH 6.8, 37°C) for 2 hours, and its mass loss rate was less than 5%.

10. The method according to any one of claims 1 to 8, characterized in that, The porous RS3 microspheres have an average particle size of 1μm-2000μm, a specific surface area of ​​5-200m² / g, and an average pore size of 0.1μm-100μm in their internal cavities.

11. A porous RS3 microsphere, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 10.

12. The porous RS3 microspheres according to claim 11, characterized in that, The porous RS3 microspheres retained ≥90% of their solid mass after incubation at 37°C for 4 hours in simulated gastric fluid at pH 1.2; and ≥85% of their solid mass after incubation for 2 hours in a simulated small intestinal digestive environment.

13. The porous RS3 microspheres according to claim 11, characterized in that, The porous RS3 microspheres are loaded with active substances within their cavities. These active substances are selected from at least one of flavoring substances, probiotics, vitamins, drugs, enzyme preparations, and essential oils.

14. The application of the porous RS3 microspheres according to any one of claims 11 to 13 as a carrier of active substances in the fields of food, medicine, daily chemicals, and agriculture.

15. A porous microsphere, composed of a starch substrate, having multiple micron-sized cavities inside, characterized in that, The starch substrate simultaneously meets the following conditions: (a) melting temperature (peak temperature determined by DSC) ≥ 120℃; (b) mass loss rate is less than 5% after incubation in simulated small intestinal digestive fluid (containing α-amylase, pH 6.8, 37℃) for 2 hours; and (c) no characteristic peaks of chemical crosslinking agents are detected in the infrared spectrum.