A flaxseed oil microcapsule based on composite coacervation and a preparation method and application thereof

Abstract

This invention discloses a flaxseed oil microcapsule based on composite coagulation, its preparation method, and its application. The invention involves mixing OSA starch dispersion and chitosan dispersion to obtain a mixed dispersion of OSA starch and chitosan; the mass ratio of chitosan to OSA starch in the mixed dispersion is 1:12 to 1:24. Flaxseed oil is added to the mixed dispersion, and the mixture is subjected to high-speed shearing to obtain an emulsion. The pH of the emulsion is adjusted to 6.0 to 6.5, and the mixture is allowed to stand and decanted to obtain a composite coagulant. The composite coagulant is dried, ground, and sieved to obtain flaxseed oil microcapsules. The flaxseed oil microcapsules prepared by this invention achieve an encapsulation efficiency of 95.10% and a payload of 52.52%, exhibiting good antioxidant properties. Furthermore, the process is green and environmentally friendly, making it suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the fields of food, pharmaceutical and chemical technology, and specifically relates to a flaxseed oil microcapsule based on composite coagulation, its preparation method and application. Background Technology

[0002] Flaxseed oil is a dried oil extracted from flaxseeds. It is yellow and transparent with a unique aroma. The total content of unsaturated fatty acids in flaxseed oil is over 90%, with α-linolenic acid (ω-3) accounting for as much as 45%–65%. The ratio of ω-3 to ω-6 fatty acids is approximately (4–6):1, close to the ideal ratio recommended by the Chinese Nutrition Society and the Food and Agriculture Organization of the United Nations. Flaxseed oil has high nutritional value and important physiological functions, including lowering blood lipids and blood pressure, improving cardiovascular and cerebrovascular diseases, and preventing diabetes, rheumatism, rheumatoid arthritis, and tumors.

[0003] Because of its high content of unsaturated fatty acids, flaxseed oil is prone to oxidation during processing and storage, reducing its food safety and commercial value. Microencapsulation is a technique that encapsulates a target substance (core material) with various natural or synthetic macromolecular substances (wall materials). Microencapsulation can increase the solubility of flaxseed oil in water, reduce its odor, and improve its physical and chemical stability against environmental factors such as light, humidity, air, and heat. Currently, the most common method for oil microencapsulation is emulsification-spray drying. However, this method has some drawbacks, such as the need to add surfactants like Tween 20 to ensure the stability of the emulsion, and the high temperatures during high-pressure homogenization and spray drying can easily lead to the oxidation of oils rich in polyunsaturated fatty acids. Composite coagulation microencapsulation technology is an effective encapsulation method that uses two polymers with opposite charges as wall materials and electrostatic interaction as the main driving force to prepare microcapsules. It does not require specialized equipment, has mild process conditions, and causes less damage to the quality of the core material during the process, achieving both high load capacity and high encapsulation efficiency. Currently, the wall materials used in composite microcapsule technology are typically combinations of proteins and polysaccharides. However, due to the requirements of the preparation process for functional properties such as solubility and emulsification, animal proteins such as gelatin or casein are often used as wall materials. But the use of animal proteins limits the addition and application range of the product. Therefore, a combination of two polysaccharides with opposite charges becomes a better choice. Chitosan is a natural linear cationic polysaccharide with good biodegradability, gelling properties, and antibacterial effects, and is commonly used as a film-forming matrix and microcapsule wall material. OSA starch is obtained by esterification of starch with octenyl succinic anhydride, introducing both hydrophilic carboxyl groups and hydrophobic alkenyl chains into the starch chain, giving it a certain emulsifying ability. It has been widely used as a wall material for microcapsules and a Pickering emulsion stabilizer. Under certain conditions, the NH3 carried by chitosan... + Able to react with the COO carried by OSA starch -Electrostatic complexation occurs, leading to a complex coagulation reaction. Studies have successfully used OSA starch-chitosan composite particles to stabilize high-internal-phase Pickering emulsions (Journal of Agricultural and Food Chemistry, 2019, 67(39):10937-10946). However, there are few reports on the preparation of flaxseed oil microcapsules using commercial OSA starch and chitosan as composite coagulation wall materials, and the influence of chitosan self-aggregation at pH ≥ 6.5 on the structure and properties of composite coagulated microcapsules is also rarely reported.

[0004] Furthermore, vacuum freeze-drying technology is a dehydration technique that directly sublimates water from a solid state to a gaseous state under low temperature and low oxygen conditions. This method can maximally preserve the original structure and shape of the material and is suitable for drying heat-sensitive active substances. Therefore, the combination of composite coagulation and freeze-drying technology is a good choice for microencapsulated flaxseed oil. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a flaxseed oil microcapsule based on composite coagulation, its preparation method, and its application.

[0006] The technical problem to be solved by the present invention is to composite and condense two polysaccharide-based wall materials with opposite charges to achieve stable encapsulation of flaxseed oil, thereby preparing a microcapsule. Its advantages are that it is simple to operate, the process is green and environmentally friendly, and it has good encapsulation effect and antioxidant effect.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for preparing flaxseed oil microcapsules based on complex coagulation includes the following steps:

[0009] (1) OSA starch dispersion and chitosan dispersion are mixed to obtain a mixed dispersion of OSA starch and chitosan; the mass ratio of chitosan to OSA starch in the mixed dispersion is 1:12 to 1:24.

[0010] (2) Add flaxseed oil to the mixed dispersion of step (1) and shear at high speed to obtain an emulsion;

[0011] (3) Adjust the pH of the emulsion from step (2) to 6.0-6.5, let it stand and decant to obtain the composite coagulant;

[0012] (4) The composite aggregate from step (3) is dried, ground and sieved to obtain flaxseed oil microcapsules.

[0013] Preferably, in step (1), the OSA starch is PG2000; and the chitosan is low-viscosity chitosan.

[0014] More preferably, the low-viscosity chitosan has a viscosity of <200 mPa·s and a mass-volume concentration of 1%, g / mL.

[0015] Preferably, in step (1), the mass-volume concentration of OSA starch in the mixed dispersion is 5% to 10% (g / mL); and the mass-volume concentration of chitosan in the mixed dispersion is 0.21% to 0.50% (g / mL).

[0016] More preferably, in step (1), the mass-volume concentration of OSA starch in the mixed dispersion is 5% to 7.5% (g / mL); and the mass-volume concentration of chitosan in the mixed dispersion is 0.21% to 0.42% (g / mL).

[0017] Preferably, in step (1), the concentration of the OSA starch dispersion is 10% to 20% (w / v, g / mL); the concentration of the chitosan dispersion is 0.42% to 1.0% (w / v, g / mL); and the volume ratio of the OSA starch dispersion to the chitosan dispersion is 1:1.

[0018] Preferably, in step (2), the ratio of the mass of the flaxseed oil to the total mass of chitosan and OSA starch in the mixed dispersion is 2:1 to 1:2;

[0019] More preferably, in step (2), the ratio of the mass of the flaxseed oil to the combined mass of chitosan and OSA starch in the mixed dispersion is 1:1.

[0020] Preferably, in step (2), the high-speed shearing speed is 8000-16000 rpm and the high-speed shearing time is 2-6 min.

[0021] More preferably, in step (2), the high-speed shearing time is 3 minutes.

[0022] Preferably, in step (3), the pH of the emulsion is adjusted to 6.0 to 6.5, excluding 6.0; after pH adjustment, the emulsion is stirred for 2 to 10 minutes, and the stirring speed is 250 to 500 rpm;

[0023] More preferably, after adjusting the pH of the emulsion, stirring is continued for 10 minutes at a speed of 350 rpm.

[0024] Preferably, in step (3), the temperature for standing is 4 to 25°C and the standing time is 6 to 24 hours.

[0025] Preferably, in step (4), the drying is vacuum freeze drying, and the drying time is 12 to 48 hours;

[0026] Preferably, in step (4), the mesh size of the sieve is ≥50 mesh.

[0027] The flaxseed oil microcapsules prepared by the above method are based on composite coagulation.

[0028] The above-mentioned application of flaxseed oil microcapsules based on complex coagulation in the preparation of flaxseed oil fortified foods.

[0029] Compared with the prior art, the advantages of the present invention are as follows:

[0030] This invention utilizes OSA starch and chitosan as a composite coagulation wall material to encapsulate flaxseed oil. The OSA starch used is PG2000, a commercial OSA starch with a high amylopectin content and a large molecular weight. The raw material is readily available and has good emulsifying ability. No crosslinking agent or surfactant needs to be added during the preparation process. By adjusting the pH, OSA starch and chitosan can be induced to form a thick and dense composite coagulation wall material through electrostatic interaction. The prepared flaxseed oil microcapsules have high encapsulation efficiency (95.10%) and effective loading (52.52%), low moisture content, and can effectively improve the oxidative stability of flaxseed oil. Compared with traditional technologies, the microencapsulation method of this invention can prepare flaxseed oil microcapsules with significantly improved oxidative stability even with low chitosan addition levels via chitosan-OSA starch composite coagulation. Furthermore, the microencapsulation process of this invention is green and simple, requiring only one high-speed dispersion to form an emulsion with good dispersibility and stability. During the pH-induced composite coagulation process, only a period of standing is needed to obtain the lower layer composite coagulated material encapsulating flaxseed oil. It does not involve high-temperature, high-pressure homogenization, ultrasonic emulsification, centrifugal washing, spray drying, or other process steps, thus avoiding oil oxidation during preparation and eliminating the need to add antioxidants to the oil in advance. Furthermore, chitosan has a pKa value of approximately 6.5. When pH ≥ 6.5, the amino groups of chitosan gradually deprotonate, reducing electrostatic repulsion between molecules. Chitosan then undergoes self-aggregation through hydrophobic interactions. Therefore, in conventional techniques, the induction pH for the composite coagulation reaction involving chitosan is typically set below 6.5. However, in this invention, the oxidative stability of the composite coagulated microcapsules at pH 6.5 is higher than that at pH < 6.5. This may be because the chitosan used in this invention is a low-viscosity chitosan, which undergoes a smaller degree of self-aggregation at pH 6.5, increasing its hydrophobicity. OSA starch can still form composite coagulates with the self-aggregated chitosan. The structure and properties of the composite coagulated wall material at pH 6.5 are superior to those at pH < 6.5. Attached Figure Description

[0031] Figure 1 The image shows the appearance of the composite condensation system under the conditions of Comparative Example 5.

[0032] Figure 2CLSM images of the composite aggregates in the initial stage of the composite coagulation reaction under the conditions of Comparative Example 2 and Examples 1-3.

[0033] Figure 3 This is a cryo-scanning electron microscope image of the lower layer of composite aggregates after standing under the conditions of Example 1.

[0034] Figure 4 The diagram shows the mechanism of chitosan / OSA starch composite coagulation for encapsulating flaxseed oil under the conditions of Examples 1-7.

[0035] Figure 5 Optical micrographs of the composite aggregates in the early stage of the composite coagulation reaction under the conditions of Examples 1 and 4-7.

[0036] Figure 6 The images show the appearance of the composite condensation system after standing under the conditions of Examples 1 and 4-7. Detailed Implementation

[0037] To better understand the present invention, the following description is based on embodiments, but the present invention is not limited to the scope described in the embodiments.

[0038] 1. Test method for microcapsule encapsulation effect: (1) Surface oil content determination: Accurately weigh 1.00g of microcapsule powder onto Whatman No.4 filter paper, rinse with 10mL of n-hexane, collect the filtrate through a funnel into a pre-weighed flask, evaporate the collected n-hexane solution at 50℃, then dry the sample in the flask in a 60℃ oven to constant weight, cool to room temperature in a desiccator, and weigh to obtain the surface oil mass. (2) Total oil content determination: Accurately weigh 1.00g of microcapsule powder into a 50mL centrifuge tube, add 10mL of 4mol / L HCl and 20mL of n-hexane, stir magnetically at 400rpm overnight to fully extract the oil into the n-hexane phase. Centrifuge the mixture at 1500g for 15min, and collect the upper organic solution into a pre-weighed flask. Add 20mL of n-hexane to the centrifuge tube again, stir magnetically at 600rpm for 30min, centrifuge to collect the upper organic solution, and repeat twice. The collected n-hexane solution was rotary evaporated at 50°C, and the sample in the bottle was then dried in an oven at 60°C until constant weight. After cooling to room temperature in a desiccator, the total oil mass was obtained by weighing. The effective loading and encapsulation efficiency of the microcapsules were calculated based on the surface oil content, total oil content, and the following formula:

[0039]

[0040]

[0041] 2. Test method for oxidative stability of microcapsules: The oxidative stability of flaxseed oil and its microcapsules was analyzed by differential scanning calorimetry (DSC) according to the method of Feng et al. (CarbohydratePolymers, 2022, 292). (1) Oxidation onset temperature (OOT): 3.5±0.2 mg of microcapsule powder or flaxseed oil was weighed into an uncapped aluminum pan. Using an uncapped empty aluminum pan as a reference, the DSC test procedure was as follows: (a) Under nitrogen atmosphere (30 mL / min), the temperature was heated from 25 °C to 120 °C at a rate of 20 °C / min; (b) Under nitrogen atmosphere (30 mL / min) and 120 °C, the temperature was maintained for 3 min to stabilize the sample temperature and reduce the temperature gradient in the sample; (c) Under oxygen atmosphere (30 mL / min), the temperature was increased from 120 °C to 300 °C at a rate of 20 °C / min. The initial oxidation temperature is the temperature at which the extrapolated baseline intersects the maximum slope of the reaction curve. (2) Oxidation induction time (OIT): Weigh 3.5±0.2 mg of microcapsule powder or linseed oil into an uncapped aluminum pan. Using an uncapped empty aluminum pan as a reference, the DSC test procedure is as follows: (a) Under a nitrogen atmosphere (50 mL / min), the temperature is heated from 25 °C to 130 °C at a rate of 20 °C / min; (b) Maintain the temperature at 130 °C and nitrogen atmosphere (50 mL / min) for 3 min; (c) Keep the temperature constant and replace nitrogen with oxygen (50 mL / min) until the oxidation reaction occurs. OIT is the time at which the extrapolated baseline intersects the maximum slope of the reaction curve.

[0042] The chitosan used in the examples and comparative examples was low-viscosity chitosan (C804728, <200 mPa.s, mass-volume concentration of 1%, g / mL), purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; the OSA starch was PG2000, purchased from American Ingenium Company.

[0043] In the examples and comparative examples, w / v is g / mL.

[0044] In the examples and comparative examples, the solvent for the PG2000 dispersion and the low-viscosity chitosan dispersion was deionized water.

[0045] Comparative Example 1

[0046] A 10% (w / v) PG2000 dispersion was prepared. Flaxseed oil was added to the dispersion at a mass ratio of 1:1 to PG2000. The mixture was sheared at 10,000 rpm for 3 min to obtain a flaxseed oil emulsion. After pre-freezing, the emulsion was freeze-dried under vacuum for 48 h, ground, and sieved (100 mesh) to obtain flaxseed oil microcapsules.

[0047] Comparative Example 2

[0048] A 10% (w / v) PG2000 dispersion and a 0.84% ​​(w / v) low-viscosity chitosan dispersion were prepared and mixed in equal volumes to obtain a chitosan / PG2000 mixed dispersion with a chitosan / PG2000 mass ratio of 1:12. Flaxseed oil was added to the mixed dispersion, with the mass ratio of flaxseed oil to the sum of the mass of chitosan and PG2000 in the mixed dispersion being 1:1. The mixture was sheared at 10,000 rpm for 3 min to obtain a flaxseed oil emulsion. After pre-freezing, the emulsion was freeze-dried under vacuum for 48 h, ground, and sieved (100 mesh) to obtain flaxseed oil microcapsules.

[0049] Comparative Example 3

[0050] A 20% (w / v) PG2000 dispersion was prepared. Flaxseed oil was added to the dispersion at a mass ratio of 1:1 (flaxseed oil to PG2000 dispersion). The mixture was sheared at 10000 rpm for 3 min and homogenized twice under high pressure at 40 MPa to obtain a flaxseed oil emulsion. The spray drying parameters were: inlet air temperature 180℃, outlet air temperature 90℃, and injection rate 300 mL / h to obtain flaxseed oil microcapsules.

[0051] Comparative Example 4

[0052] A 10% (w / v) PG2000 dispersion and a 1.67% (w / v) low-viscosity chitosan dispersion were prepared and mixed in equal volumes to obtain a chitosan / PG2000 mixed dispersion with a chitosan / PG2000 mass ratio of 1:6. Flaxseed oil was added to the mixed dispersion, with a flaxseed oil mass ratio to the sum of chitosan and PG2000 masses in the mixed dispersion of 1:1. The mixture was sheared at 10,000 rpm for 3 minutes to obtain a flaxseed oil emulsion. Due to the high chitosan content, the emulsion had a high viscosity, and the viscosity further increased during the pH=6.5 induced coagulation process, making it impossible to maintain pH uniformity even under high-speed magnetic stirring.

[0053] Comparative Example 5

[0054] A 10% (w / v) PG2000 dispersion and a 0.84% ​​(w / v) low-viscosity chitosan dispersion were prepared and mixed in equal volumes to obtain a chitosan / PG2000 mixed dispersion with a chitosan / PG2000 mass ratio of 1:12. Flaxseed oil was added to the mixed dispersion, with the mass ratio of flaxseed oil to the sum of the mass of chitosan and PG2000 in the mixed dispersion being 1:1. The mixture was sheared at 10,000 rpm for 3 min to obtain a flaxseed oil emulsion. The pH of the resulting flaxseed oil emulsion was adjusted to 7.0. Figure 1 It can be seen that at this time, there are many loosely structured flocculent substances in the system and they float to the surface. This may be because chitosan has a high degree of self-aggregation at pH 7.0 and carries a small amount of positive charge, so it cannot combine with PG2000 to form complex aggregates.

[0055] Comparative Example 6

[0056] A method for preparing composite coagulated flaxseed oil microcapsules includes the following steps:

[0057] A 15% (w / v) PG2000 dispersion and a 0.84% ​​(w / v) low-viscosity chitosan dispersion were prepared and mixed in equal volumes to obtain a chitosan / PG2000 mixed dispersion with a chitosan / PG2000 mass ratio of 1:18. Flaxseed oil was added to the mixed dispersion, with a flaxseed oil mass ratio to the sum of chitosan and PG2000 masses in the mixed dispersion of 1:1. The mixture was sheared at 10,000 rpm for 3 min to obtain a flaxseed oil emulsion. The pH of the obtained flaxseed oil emulsion was adjusted to 6.0, and the mixture was stirred at 350 rpm for 5 min. After standing at 25°C for 12 h, the supernatant was discarded by decanting. The resulting precipitate was pre-frozen and then freeze-dried under vacuum for 30 h. The precipitate was then ground and sieved (100 mesh) to obtain flaxseed oil microcapsules.

[0058] Example 1

[0059] A method for preparing composite coagulated flaxseed oil microcapsules includes the following steps:

[0060] A 10% (w / v) PG2000 dispersion and a 0.84% ​​(w / v) low-viscosity chitosan dispersion were prepared and mixed in equal volumes to obtain a chitosan / PG2000 mixed dispersion with a chitosan / PG2000 mass ratio of 1:12. Flaxseed oil was added to the mixed dispersion, with a flaxseed oil mass ratio to the sum of chitosan and PG2000 masses in the mixed dispersion of 1:1. The mixture was sheared at 10,000 rpm for 3 min to obtain a flaxseed oil emulsion. The pH of the obtained flaxseed oil emulsion was adjusted to 6.5, and the mixture was stirred at 350 rpm for 5 min. After standing at 4℃ for 24 h, the supernatant was discarded by decanting. The resulting precipitate was pre-frozen and then freeze-dried under vacuum for 48 h. The precipitate was then ground and sieved (100 mesh) to obtain flaxseed oil microcapsules.

[0061] Example 2

[0062] A method for preparing composite coagulated flaxseed oil microcapsules includes the following steps:

[0063] A 15% (w / v) PG2000 dispersion and a 0.84% ​​(w / v) low-viscosity chitosan dispersion were prepared and mixed in equal volumes to obtain a chitosan / PG2000 mixed dispersion with a chitosan / PG2000 mass ratio of 1:18. Flaxseed oil was added to the mixed dispersion, with a flaxseed oil mass ratio to the sum of chitosan and PG2000 masses in the mixed dispersion of 1:1. The mixture was sheared at 10,000 rpm for 3 min to obtain a flaxseed oil emulsion. The pH of the obtained flaxseed oil emulsion was adjusted to 6.5, and the mixture was stirred at 350 rpm for 5 min. After standing at 25°C for 12 h, the supernatant was discarded by decanting. The resulting precipitate was pre-frozen and then freeze-dried under vacuum for 30 h. The precipitate was then ground and sieved (100 mesh) to obtain flaxseed oil microcapsules.

[0064] Example 3

[0065] A method for preparing composite coagulated flaxseed oil microcapsules includes the following steps:

[0066] A 10% (w / v) PG2000 dispersion and a 0.42% (w / v) low-viscosity chitosan dispersion were prepared and mixed in equal volumes to obtain a chitosan / PG2000 mixed dispersion with a chitosan / PG2000 mass ratio of 1:24. Flaxseed oil was added to the mixed dispersion, with a flaxseed oil mass ratio to the sum of chitosan and PG2000 masses in the mixed dispersion of 1:1. The mixture was sheared at 10,000 rpm for 3 min to obtain a flaxseed oil emulsion. The pH of the obtained flaxseed oil emulsion was adjusted to 6.5, and the mixture was stirred at 350 rpm for 5 min. After standing at 25°C for 6 h, the supernatant was discarded by decanting. The resulting precipitate was pre-frozen and then freeze-dried under vacuum for 12 h. The precipitate was then ground and sieved (100 mesh) to obtain flaxseed oil microcapsules.

[0067] Example 4

[0068] Flaxseed oil microcapsules based on composite coagulation were prepared according to the steps of Example 1, except that the dispersion speed of the flaxseed oil emulsion was 8000 rpm.

[0069] Example 5

[0070] Flaxseed oil microcapsules based on composite coagulation were prepared according to the steps of Example 1, except that the dispersion speed of the flaxseed oil emulsion was 12,000 rpm.

[0071] Example 6

[0072] Flaxseed oil microcapsules based on composite coagulation were prepared according to the steps of Example 1, except that the dispersion speed of the flaxseed oil emulsion was 14,000 rpm.

[0073] Example 7

[0074] Flaxseed oil microcapsules based on composite coagulation were prepared according to the steps of Example 1, except that the dispersion speed of the flaxseed oil emulsion was 16,000 rpm.

[0075] Data Analysis:

[0076] Figure 2 CLSM images of the composite aggregates in the initial stage of the composite coagulation reaction under the conditions of Comparative Example 2 and Examples 1-3 (PG2000 and chitosan are labeled with Nile Blue A and appear in green, while the oil phase is labeled with Nile Red and appears in red).

[0077] Figure 3 This is a cryo-scanning electron microscope image of the lower layer of composite aggregates after standing under the conditions of Example 1.

[0078] Figure 4 The diagram shows the mechanism of chitosan / OSA starch composite coagulation for encapsulating flaxseed oil under the conditions of Examples 1-7.

[0079] Figure 5 Optical micrographs of the composite aggregates in the early stage of the composite coagulation reaction under the conditions of Examples 1 and 4-7.

[0080] Figure 6 The images show the appearance of the composite condensation system after standing under the conditions of Examples 1 and 4-7.

[0081] The encapsulation effect data of the microcapsules prepared in Examples 1-3 and Comparative Examples 1-3 are shown in Table 1.

[0082] The oxidative stability data of the microcapsules and flaxseed oil prepared in Examples 1-7, Comparative Examples 1-3 and Comparative Example 6 are shown in Table 2.

[0083] Table 1. Encapsulation effect of microcapsules

[0084]

[0085] As shown in Table 1, the microcapsules prepared in Examples 1-3 all exhibited higher encapsulation efficiency and effective loading, which were superior to those in Comparative Examples 1-3. In Examples 1-3, chitosan was added during the emulsion preparation process. Chitosan can increase the viscosity of the continuous phase and the electrostatic repulsion between emulsion droplets, reduce the emulsion particle size, and increase the stability of the emulsion. Figure 2 and Figure 3It can be seen that Examples 1-3 induce a complex coagulation reaction between chitosan and PG2000 by adjusting the pH. The resulting complex coagulated material is adsorbed onto the oil-water interface and aggregates in the continuous phase to form a polysaccharide gel network, creating a thick and dense complex coagulated shell. This is superior to the adsorption layer barrier formed by PG2000 and chitosan at the oil-water interface solely through emulsification in Comparative Example 2, and is less likely to be destroyed during drying and grinding. Therefore, Examples 1-3 exhibit higher encapsulation efficiency. Furthermore, the complex coagulated material in Examples 1-3 settles during the settling process, and the supernatant is discarded, resulting in a reduced drying time and an increased effective load of the microcapsules, higher than that in Comparative Examples 1-3. Compared to Comparative Example 3, the microcapsules prepared in Examples 1-3 can simultaneously exhibit high encapsulation efficiency and effective load at a relatively low wall material concentration.

[0086] Table 2 Oxidative stability of microcapsules

[0087]

[0088] As shown in Table 2, the microcapsules prepared in Examples 1-7 all have high OOT and OIT values, higher than those of unencapsulated flaxseed oil and Comparative Examples 1-3. The OOT and OIT values ​​of the microcapsules prepared in Comparative Example 3 are lower than those of unencapsulated flaxseed oil, possibly due to oil oxidation caused by the high temperatures during high-pressure homogenization and spray drying. Examples 1-7, however, do not use high-pressure homogenization or high temperatures, resulting in a milder preparation process that reduces the impact of the preparation process on the quality of the flaxseed oil. Furthermore, Examples 1-7 formed a thick and dense chitosan-PG2000 composite condensed shell through pH induction, effectively blocking factors that easily cause oil oxidation, such as oxygen and ultraviolet radiation. Therefore, the oxidative stability of the resulting microcapsules is higher than that of Comparative Examples 1-3.

[0089] Chitosan has a pKa value of approximately 6.5. When pH ≥ 6.5, the amino groups of chitosan gradually deprotonate, reducing electrostatic repulsion between molecules. Chitosan then undergoes self-aggregation through hydrophobic interactions. Therefore, in conventional techniques, the inducing pH for composite coagulation reactions involving chitosan is typically set below 6.5. However, the oxidative stability of the composite coagulated microcapsules prepared in Examples 1-7 (pH 6.5) is higher than that of the composite coagulated microcapsules prepared in Comparative Example 6 (pH 6.0). This may be because low-viscosity chitosan undergoes a smaller degree of self-aggregation at pH 6.5, increasing its hydrophobicity. OSA starch can still form composite coagulates with the self-aggregated chitosan, leading to increased hydrophobicity of the composite coagulates and a tighter connection with the core material. Furthermore, the self-aggregated chitosan may also adsorb at the oil-water interface, further increasing the thickness and hydrophobicity of the wall material. Consequently, the structure and properties of the composite coagulated wall material at pH 6.5 are superior to those at pH < 6.5 (see mechanism diagram). Figure 4 ).

[0090] The differences between Examples 1-3 are mainly due to the different emulsion particle sizes. Figure 2 It can be seen that the emulsion particle size gradually decreases with the increase of the chitosan / PG2000 mass ratio, while the oxidative stability of the microcapsules gradually increases with the decrease of the emulsion particle size. Furthermore, comparing Examples 1 and Examples 4-7, it can be found that with the increase of dispersion speed, the OOT and OIT values ​​of the microcapsules show a trend of first increasing and then decreasing. When the dispersion speed is 10000 rpm (Example 1), the OOT and OIT values ​​of the microcapsules are the highest. This may be because PG2000 has a certain foaming property; with the increase of dispersion speed, the droplet size gradually decreases, but at the same time, the bubble content gradually increases. A large number of bubbles will disrupt the continuity of the composite cohesive wall material. Figure 5 This causes the composite aggregate to float after standing. Figure 6 During freeze-drying and grinding, the microcapsule structure is more easily damaged, and the core material is more likely to come into contact with air and oxidize.

[0091] It is evident that the composite condensed microcapsules prepared in this embodiment possess high encapsulation efficiency, effective load, and oxidative stability, and have broad application prospects in the encapsulation, delivery, and stabilization of lipid-soluble bioactive substances.

[0092] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing flaxseed oil microcapsules based on composite coagulation, characterized in that, Includes the following steps: (1) OSA starch dispersion and chitosan dispersion are mixed to obtain a mixed dispersion of OSA starch and chitosan; the mass ratio of chitosan to OSA starch in the mixed dispersion is 1:12 to 1:24; the OSA starch is PG2000; the chitosan is low viscosity chitosan; the viscosity of the low viscosity chitosan is <200 mPa·s; the mass-volume concentration of OSA starch in the mixed dispersion is 5% to 10% (g / mL); the mass-volume concentration of chitosan in the mixed dispersion is 0.21% to 0.50% (g / mL); (2) Add flaxseed oil to the mixed dispersion of step (1) and shear at high speed to obtain an emulsion; (3) Adjust the pH of the emulsion from step (2) to 6.0 ~ 6.5, let it stand and decant to obtain the composite coagulant; (4) The composite aggregate from step (3) is dried, ground and sieved to obtain flaxseed oil microcapsules.

2. The preparation method according to claim 1, characterized in that, The low-viscosity chitosan has a mass-volume concentration of 1%, g / mL.

3. The preparation method according to claim 1, characterized in that, In step (2), the ratio of the mass of the flaxseed oil to the total mass of chitosan and OSA starch in the mixed dispersion is 2:1 to 1:2; In step (2), the rotation speed of the high-speed shearing is 8000 ~ 16000 rpm, and the high-speed shearing time is 2 ~ 6 min.

4. The preparation method according to claim 1, characterized in that, In step (3), the pH of the emulsion is adjusted to 6.0 to 6.5, excluding 6.0; after pH adjustment, the emulsion is stirred for 2 to 10 minutes at a speed of 250 to 500 rpm.

5. The preparation method according to claim 1, characterized in that, In step (3), the temperature for standing is 4 ~ 25℃ and the standing time is 6 ~ 24 h.

6. The preparation method according to claim 1, characterized in that, In step (4), the drying is vacuum freeze drying, and the drying time is 12 to 48 hours. In step (4), the mesh size of the sieve used in the sieving process is ≥ 50 mesh.

7. Flaxseed oil microcapsules based on composite coagulation prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the composite coagulation-based flaxseed oil microcapsules as described in claim 7 in the preparation of flaxseed oil-fortified foods.

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