Dha algal oil microcapsule based on pickering emulsion and preparation method thereof

Abstract

The application provides a DHA algal oil microcapsule based on a Pickering emulsion and a preparation method thereof, and belongs to the technical field of functional oil microencapsulation. The preparation method of the DHA algal oil microcapsule based on the Pickering emulsion comprises the following steps: mixing a protein solution and a sodium alginate solution to obtain a protein-sodium alginate dispersion; mixing the protein-sodium alginate dispersion and a filler to obtain a wall material solution; mixing the wall material solution and DHA algal oil to obtain a Pickering emulsion; and drying the Pickering emulsion to obtain the DHA algal oil microcapsule. The DHA algal oil microcapsule powder prepared by the application is regular spherical, smooth and compact in surface, has excellent fluidity and solubility, is high in whiteness value, low in moisture content and water activity, and is excellent in product quality. The microcapsule powder can be directly applied to the fields of food and health care products, is suitable for various terminal product forms, and has high practicability.

Description

Technical Field

[0001] This invention relates to the field of functional oil microencapsulation technology, and in particular to a DHA algal oil microcapsule based on Pickering emulsion and its preparation method. Background Technology

[0002] Docosahexaenoic acid (DHA) is an essential omega-3 long-chain polyunsaturated fatty acid for the human body. It can lower serum triglyceride levels and blood viscosity, thus playing a role in preventing cardiovascular diseases. It also possesses bioactivity in preventing inflammation, rheumatoid arthritis, diabetes, kidney dysfunction, osteoporosis, and Alzheimer's disease. Furthermore, it plays an important role in the brain and visual development of infants. Algal oil DHA, due to its advantages such as being free of fishy odor, lacking marine pollutant residues, and being sustainably produced, has become one of the main sources of DHA in functional foods. DHA is a long-chain polyene highly unsaturated fatty acid. Due to its highly unsaturated state and unique molecular structure, it is highly susceptible to oxidation under light, heat, and oxygen conditions. This not only reduces its nutritional value but also produces off-flavor substances such as aldehydes and ketones, severely limiting its application in food systems.

[0003] Microencapsulation technology is one of the effective means to protect DHA algal oil and improve its stability. By physically encapsulating the core material with a wall material, oxygen and light can be effectively isolated. Commonly used microcapsule preparation methods include interfacial polymerization, composite coagulation, freeze-drying, spray drying, and air suspension. Among these, spray drying is widely used for encapsulating oils rich in unsaturated fatty acids due to its low cost, high flexibility, and continuous production capability. Traditional microcapsule wall materials often use single proteins (such as gelatin, whey protein isolate, soy protein isolate, pea protein isolate, casein, zein, etc.) or single polysaccharides (such as konjac glucomannan, xanthan gum, xylan, pectin, gum arabic, etc.). However, these methods still have drawbacks such as insufficient mechanical strength of the wall material, low encapsulation efficiency, or the need to use organic solvents.

[0004] In recent years, Pickering emulsion technology has provided a new approach for microencapsulation. Pickering emulsions utilize solid particles adsorbed at the oil-water interface to form a stable interfacial film. Compared to emulsions stabilized by traditional surfactants, they offer advantages such as lower toxicity, better biocompatibility, and a more robust interfacial film. Food-grade bioparticles (such as proteins and polysaccharides) have attracted significant attention due to their natural origin, biodegradability, and high nutritional value. Proteins, with their inherent amphiphilicity and excellent emulsifying ability, are ideal raw materials for preparing food-grade Pickering emulsion particles. However, single protein particles are sensitive to environmental conditions (such as pH and ionic strength), easily aggregate near their isoelectric point, and the interfacial film formed by a single component has limited stability, making it difficult to meet the requirements for long-term stabilization of DHA algal oil. Combining proteins and polysaccharides through electrostatic attraction is an effective improvement strategy. Sodium alginate (SA), a natural anionic polysaccharide extracted from brown algae, possesses good biocompatibility and thickening properties. The carboxyl groups on its molecular chain can interact electrostatically or through hydrogen bonding with protein molecules. The protein-sodium alginate complex can synergistically regulate the surface charge, wettability, and interfacial rheological properties of particles, thereby significantly enhancing the stability of emulsions. Existing studies have preliminarily confirmed the potential of protein-polysaccharide complexes in Pickering emulsions, but systematic research and comparisons are still lacking regarding how different protein sources (such as animal-derived whey protein isolate / casein and plant-derived soy protein isolate / pea protein isolate) synergistically stabilize DHA algal oil Pickering emulsions with the sodium alginate complex, and how this complex ultimately affects the oil loading, encapsulation efficiency, and storage stability of spray-dried microcapsule products.

[0005] There are existing reports on the preparation of algal oil microcapsules. For example, CN 112754016 A discloses a method for preparing highly stable algal oil DHA microcapsules: octenyl succinate starch, calcium chloride, maltodextrin, and water are mixed in a specific ratio and stirred in a 50°C water bath for 10 min; then DHA algal oil is added, and stirring continues in a 50°C water bath for 5 min; the resulting water-oil mixture is pre-emulsified and then homogenized in multiple steps under a pressure of 20-40 MPa to obtain a final emulsion; finally, microcapsule powder is obtained by spray drying. The surface oil content of the microcapsules obtained by this method can be controlled below 0.39%, the leaching rate is less than 0.48%, and the encapsulation efficiency reaches 98.07%. However, despite the high encapsulation efficiency, the amount of DHA algal oil added in this method is extremely low, making it impossible to prepare microcapsules with high DHA algal oil content. For example, CN 113768156 A discloses a DHA microcapsule and its preparation method: maltodextrin and a lecithin-protein solution are mixed at a mass ratio to obtain a first mixed solution; high-DHA fish oil is then added to obtain a second mixed solution; the second mixed solution is sheared to obtain a primary emulsion, which is then homogenized and spray-dried to obtain DHA microcapsules. The microcapsules obtained by this method can effectively reduce the peroxide value during storage, but their encapsulation rate is only 60%, indicating low encapsulation efficiency.

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a DHA algal oil Pickering emulsion microcapsule based on the synergistic stabilization of animal and plant protein-sodium alginate composite particles, aiming to solve the problems of low oil loading, low encapsulation rate, poor oxidative stability, and poor product flowability of existing DHA algal oil microcapsules. Summary of the Invention

[0007] The purpose of this invention is to provide a DHA algal oil microcapsule based on Pickering emulsion and its preparation method.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing DHA algal oil microcapsules based on Pickering emulsion, comprising the following steps: (1) Mix plant protein or animal protein with water to obtain a protein solution; (2) Mix sodium alginate with water to obtain a sodium alginate solution; (3) The protein solution is mixed with the sodium alginate solution to obtain a protein-sodium alginate dispersion; (4) The protein-sodium alginate dispersion is mixed with a filler to obtain a wall material solution; (5) The wall material solution and DHA algal oil are mixed to obtain Pickering emulsion; (6) The Pickering emulsion is dried to obtain DHA algal oil microcapsules.

[0009] Preferably, in step (1), the plant protein is soy protein isolate or pea protein isolate; the animal protein is whey protein isolate or casein; the mass-to-volume ratio of protein to water is 1.5~2.5 g: 80~120 mL; the mixing rate is 400~800 rpm and the time is 1~3 h.

[0010] Preferably, in step (2), the mass-to-volume ratio of sodium alginate to water is 0.8~1.2 g: 80~120 mL.

[0011] Preferably, the obtained protein solution and sodium alginate solution are stored at 3-5°C for 8-24 hours.

[0012] Preferably, in step (3), the volume ratio of the protein solution to the sodium alginate solution is 1~3:1~3; the mixing temperature is 23~27℃, the mixing speed is 400~800 rpm, and the mixing time is 30~90 min.

[0013] Preferably, in step (4), the filler is any one of inulin, β-cyclodextrin, and maltodextrin; and the mass fraction of solids in the wall material solution is 20-30%.

[0014] Preferably, in step (5), the mass of the DHA algal oil accounts for 25-50% of the total mass of the Pickering emulsion; the mixing rate is 8000-16000 rpm and the time is 1-5 min.

[0015] Preferably, in step (6), the drying is spray drying, the inlet air temperature is 160~180℃, the outlet air temperature is 80~90℃, the feed rate is 400~800 mL / h, and the atomization pressure is 0.8~1.2 MPa.

[0016] This invention provides a DHA algal oil microcapsule prepared by the method described above.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention forms a dual physical barrier through a combination of "protein-sodium alginate composite particle-stabilized Pickering emulsion + spray-dried wall material". Leveraging the synergistic advantages of protein and polysaccharides, combined with the filling and supporting effect of fillers, a dense and stable microcapsule structure is formed, effectively solving the problems of easy oxidation, poor water solubility, and low bioavailability of DHA algal oil. The solid particles of the Pickering emulsion form a physical barrier for DHA algal oil at the interface, and combined with the wall material formed by spray drying, it provides dual protection for the core material, while simultaneously delaying the release of the core material and improving its storage stability.

[0018] 2. The composite particles formed by the electrostatic interaction between animal protein (whey protein isolate, casein) and sodium alginate have significantly better interfacial activity than plant protein composite systems and single protein systems. They can form a denser and more viscoelastic interfacial film at the oil-water interface, thus giving Pickering emulsion excellent anti-agglomeration ability.

[0019] 3. Thanks to the robust interfacial film formed by the composite particles, the method of the present invention can stabilize a high proportion of DHA algal oil (accounting for 30-40% of the total mass of the emulsion). Among them, Example 7 (whey protein isolate + sodium alginate, 40% oil loading) has an encapsulation rate as high as 84.54% and a surface oil content as low as 8.28%, achieving a good balance between high oil loading and high encapsulation.

[0020] 4. The DHA algal oil microcapsules prepared by the present invention using protein and sodium alginate as wall materials have strong antioxidant capacity, good stability and are not easily oxidized and deteriorated, thereby improving the oxidative stability of DHA algal oil.

[0021] 5. The DHA algal oil microcapsule powder prepared by this invention is in the form of regular spheres with a smooth and dense surface, exhibiting excellent flowability and solubility, high whiteness, low moisture content and water activity, and superior product quality. The microcapsule powder can be directly applied in the food and health product fields, is adaptable to various end-product forms, and has strong practicality.

[0022] 6. The raw materials used in this invention are safe and environmentally friendly. The core raw materials are animal and plant proteins, sodium alginate, fillers, and DHA algal oil, all of which are food-grade, highly safe, and have no harmful residues, conforming to the modern food industry's trend towards clean labeling. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0024] Figure 1 The results of the core material retention rate determination for different DHA algal oil microcapsules in Experiment Example 4; Figure 2 A visual representation of different DHA algal oil microcapsule powders in Experiment Example 5; Figure 3 The image shows SEM images of different DHA algal oil microcapsule powders in Experiment Example 5. Detailed Implementation

[0025] This invention provides a method for preparing DHA algal oil microcapsules based on Pickering emulsion, comprising the following steps: (1) Mix plant protein or animal protein with water to obtain a protein solution; (2) Mix sodium alginate with water to obtain a sodium alginate solution; (3) The protein solution is mixed with the sodium alginate solution to obtain a protein-sodium alginate dispersion; (4) The protein-sodium alginate dispersion is mixed with a filler to obtain a wall material solution; (5) The wall material solution and DHA algal oil are mixed to obtain Pickering emulsion; (6) The Pickering emulsion is dried to obtain DHA algal oil microcapsules.

[0026] In this invention, in step (1), the plant protein is soy protein isolate or pea protein isolate; the animal protein is whey protein isolate or casein; the mass-to-volume ratio of protein to water is 1.5~2.5 g: 80~120 mL, preferably 1.8~2.2 g: 90~110 mL, more preferably 2 g: 100 mL; the mixing rate is 400~800 rpm, preferably 500~700 rpm, more preferably 600 rpm, and the time is 1~3 h, preferably 1.5~2.5 h, more preferably 2 h.

[0027] In this invention, in step (2), the mass-to-volume ratio of sodium alginate to water is 0.8~1.2 g: 80~120 mL, preferably 0.9~1.1 g: 90~110 mL, and more preferably 1 g: 100 mL.

[0028] In this invention, the obtained protein solution and sodium alginate solution are stored at 3-5°C for 8-24 hours, preferably at 4°C for 12 hours.

[0029] In this invention, in step (3), the volume ratio of the protein solution to the sodium alginate solution is 1~3:1~3, preferably 1~2:1~2, and more preferably 1:1; the mixing temperature is 23~27℃, preferably 25℃, the mixing speed is 400~800 rpm, preferably 500~700 rpm, and more preferably 600 rpm, and the mixing time is 30~90 min, preferably 45~75 min, and more preferably 60 min.

[0030] In this invention, in step (4), the filler is any one of inulin, β-cyclodextrin, and maltodextrin; the mass fraction of solids in the wall material solution is 20-30%, preferably 22-28%, more preferably 24-26%, and even more preferably 25%.

[0031] In this invention, in step (5), the mass of the DHA algal oil accounts for 25-50% of the total mass of the Pickering emulsion, preferably 30-40%, and more preferably 35%; the mixing rate is 8000-16000 rpm, preferably 10000-14000 rpm, and more preferably 12000 rpm, and the time is 1-5 min, preferably 2-4 min, and more preferably 3 min.

[0032] In this invention, in step (6), the drying is spray drying, the inlet air temperature of the spray drying is 160~180℃, preferably 165~175℃, more preferably 170℃, the outlet air temperature is 80~90℃, preferably 85℃, the feed rate is 400~800 mL / h, preferably 500~700 mL / h, more preferably 700 mL / h, and the atomization pressure is 0.8~1.2 MPa, preferably 0.9~1.1 MPa, more preferably 1.0 MPa.

[0033] This invention provides a DHA algal oil microcapsule prepared by the method described above.

[0034] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention. The soy protein isolate, pea protein isolate, whey protein isolate, casein, sodium alginate, maltodextrin, and DHA algal oil used in the following embodiments are all commercially available and are food-grade.

[0035] Example 1

[0036] A method for preparing DHA algal oil microcapsules based on Pickering emulsion, comprising the following steps: (1) Dissolve 2.0 g of soy protein isolate in 100 mL of deionized water and stir magnetically at 600 rpm for 2 h to obtain a 2% soy protein isolate solution; dissolve 1.0 g of sodium alginate in 100 mL of deionized water and stir until completely dissolved to obtain a 1% sodium alginate solution. Soy protein isolate solution and sodium alginate solution were stored at 4°C for 12 h to achieve complete hydration.

[0037] (2) The obtained sodium alginate solution was added dropwise to the soy protein isolate solution and stirred at 600 rpm for 1 h at room temperature (25℃) to obtain a protein-sodium alginate dispersion.

[0038] (3) Add maltodextrin as a filler to the protein-sodium alginate dispersion so that the mass fraction of solids (protein, polysaccharide and maltodextrin) in the whole system is 25% (m / v) and fully dissolved to obtain the wall material solution.

[0039] (4) Add DHA algal oil to the wall material solution and shear at 12,000 rpm for 3 min using a high-speed homogenizer to prepare Pickering emulsion; wherein the amount of DHA algal oil added is 30% of the total mass of Pickering emulsion.

[0040] (5) Set the relevant parameters for spray drying, and immediately spray dry the prepared Pickering emulsion. The inlet air temperature of the spray drying is controlled at 170℃, the outlet air temperature is 85℃, the feed rate is 600 mL / h, and the atomization pressure is 1.0 MPa. Finally, the DHA algal oil microcapsule powder product is obtained.

[0041] Example 2

[0042] The only difference between this embodiment and Embodiment 1 is that the soy protein isolate is replaced with an equal amount of pea protein isolate; the other raw materials and steps are the same as in Embodiment 1.

[0043] Example 3

[0044] The only difference between this embodiment and Embodiment 1 is that the soy protein isolate is replaced with an equal amount of whey protein isolate; the other raw materials and steps are the same as in Embodiment 1.

[0045] Example 4

[0046] The only difference between this embodiment and Embodiment 1 is that the soy protein isolate is replaced with an equal amount of casein; the other raw materials and steps are the same as in Embodiment 1.

[0047] Example 5

[0048] The only difference between this embodiment and embodiment 1 is that the amount of DHA algal oil added in step (4) is 40% of the total mass of Pickering emulsion, while the other raw materials and steps are the same as in embodiment 1.

[0049] Example 6

[0050] The only difference between this embodiment and Embodiment 5 is that the soy protein isolate is replaced with an equal amount of pea protein isolate; the other raw materials and steps are the same as in Embodiment 5.

[0051] Example 7

[0052] The only difference between this embodiment and embodiment 5 is that the soy protein isolate is replaced with an equal amount of whey protein isolate; the other raw materials and steps are the same as in embodiment 5.

[0053] Example 8

[0054] The only difference between this embodiment and embodiment 5 is that the soy protein isolate is replaced with an equal amount of casein; the other raw materials and steps are the same as in embodiment 5.

[0055] Comparative Example 1

[0056] The difference between this comparative example and Example 1 is that an equal amount of soy protein isolate is used to replace sodium alginate, while the other raw materials and steps are the same as in Example 1.

[0057] Comparative Example 2

[0058] The difference between this comparative example and Example 2 is that an equal amount of pea protein isolate is used to replace sodium alginate, while the other raw materials and steps are the same as in Example 2.

[0059] Comparative Example 3

[0060] The difference between this comparative example and Example 3 is that an equal amount of whey protein isolate is used to replace sodium alginate, while the other raw materials and steps are the same as in Example 3.

[0061] Comparative Example 4

[0062] The difference between this comparative example and Example 4 is that an equal amount of casein is used to replace sodium alginate, while the other raw materials and steps are the same as in Example 4.

[0063] Comparative Example 5

[0064] The difference between this comparative example and Example 3 is that an equal amount of sodium alginate is used to replace whey protein isolate, while the other raw materials and steps are the same as in Example 3.

[0065] Comparative Example 6

[0066] The difference between this comparative example and Example 3 is that maltodextrin is replaced with an equal amount of β-cyclodextrin, while the other raw materials and steps are the same as in Example 3.

[0067] Experiment Example 1: Sensory Evaluation

[0068] Twenty people were selected as evaluators to conduct sensory evaluations of the DHA algal oil microcapsules of Examples 1-8 and Comparative Examples 1-6 according to the microcapsule sensory scoring criteria shown in Table 1. The average results are shown in Table 2.

[0069] Table 1 Sensory evaluation criteria for microcapsules

[0070] Table 2 Sensory evaluation results of DHA algal oil microcapsules

[0071] As shown in Table 2, the Pickering emulsion system stabilized by the protein-sodium alginate composite particles of this invention has significantly better sensory quality than the control group (Comparative Examples 1-5) using single wall materials. Among them, Example 7 (whey protein isolate + sodium alginate, 40% DHA algal oil loading, maltodextrin filler) had the highest sensory score, reaching 93.7 points.

[0072] The sensory scores of the animal protein (whey protein isolate, casein) and sodium alginate complex system were generally higher than those of the plant protein complex system. This is due to the higher interfacial activity of animal protein, which can form a denser adsorption layer at the oil / water interface, effectively masking the inherent fishy smell of DHA algal oil.

[0073] Comparing the sensory effects of composite wall materials (Examples 1-8) and single wall materials (Comparative Examples 1-5), it can be seen that the sensory scores of protein and sodium alginate composites are significantly improved. This proves that the composite particles formed by the electrostatic interaction between protein and sodium alginate can build a dense interfacial film at the oil-water interface, thereby more effectively masking the fishy smell of DHA algal oil and improving the overall sensory quality of microcapsules.

[0074] Regarding the selection of fillers, maltodextrin (Example 3) scored 2.1 points higher in sensory evaluation than β-cyclodextrin (Comparative Example 6), indicating that maltodextrin has better compatibility with composite wall materials, stronger filling and supporting effect, and helps to form microcapsule powder with uniform particles and good solubility.

[0075] Regarding oil loading adaptability, the sensory score of the animal protein composite system increased rather than decreased under a high oil loading condition of 40%, breaking through the technical bottleneck of traditional microcapsules where high oil loading and sensory properties are difficult to balance. This is attributed to the stronger interfacial stability of the Pickering emulsion system and the efficient encapsulation capability of the composite wall material. In contrast, the sensory score of the plant protein composite system decreased under high oil loading conditions, reflecting the relatively limited interfacial stability of plant proteins under high oil content.

[0076] Experimental Example 2: Determination of Surface Oil, Total Oil, and Embedding Rate

[0077] 1. Determination of surface oil content

[0078] Dry the beaker in an oven at 105℃ for 1 h, then remove and cool in a desiccator for 30 min. Weigh m1 for later use. Add 20 mL of petroleum ether to 1 g (m) of microcapsule powder and shake for 50 s to ensure complete immersion. Filter and collect the filtrate in a pre-weighed beaker. Rinse the remaining powder after filtration with 5 mL of petroleum ether and add it to the beaker. Evaporate the petroleum ether in the filtrate under a 60℃ water bath. Finally, dry in an oven at 105℃ for 1 h, cool in a desiccator for 30 min, and weigh m2. Calculate the surface oil content using the following formula.

[0079]

[0080] In the formula, m2 is the weight of the beaker and residual oil after drying, m1 is the weight of the beaker, and m is the weight of the microcapsule powder.

[0081] 2. Determination of total oil content

[0082] Dry the beaker in an oven at 105℃ for 1 h, then remove and cool in a desiccator for 30 min. Weigh M1 for later use. Add 1 mL of ammonia and 7.5 mL of methanol to 1 g of (M) microcapsule powder and vortex for 2 min. Then add 17 mL of anhydrous diethyl ether and vortex for 2 min. Finally, add 17 mL of petroleum ether and vortex for 2 min. Filter and collect the filtrate in a pre-weighed beaker. Rinse the remaining powder after filtration with 5 mL of petroleum ether. Evaporate the organic reagents in the filtrate under a 60℃ water bath. Finally, dry in an oven at 105℃ for 1 h, cool in a desiccator for 30 min, and weigh M2. Calculate the total oil content according to the following formula.

[0083]

[0084] In the formula, M2 is the weight of the dried beaker and residual oil, M1 is the weight of the beaker, and M is the weight of the microcapsule powder.

[0085] 3. Determination of embedding rate

[0086] The encapsulation efficiency is calculated based on the total oil and surface oil content of the microcapsule powder, using the following formula:

[0087] The measurement results are shown in Table 3. From the encapsulation rate data, Example 7 showed the highest encapsulation rate at 84.54%, while having the lowest surface oil content at 8.28% and a total oil content of 53.57%, achieving a good balance between high oil loading and high encapsulation. Examples 8 and 3 showed encapsulation rates of 83.52% and 82.38%, respectively, also demonstrating excellent core material encapsulation capabilities.

[0088] Comparison of composite wall material systems from different protein sources reveals that the encapsulation efficiency of animal protein (whey protein isolate, casein) combined with sodium alginate is generally higher than that of plant protein (soy protein isolate, pea protein isolate) composite systems. Under a 30% oil loading condition, the encapsulation efficiencies of the whey protein and casein composite systems are 82.38% and 82.40%, respectively, while those of the soy protein and pea protein composite systems are 81.12% and 79.12%, respectively. Under a 40% oil loading condition, the encapsulation efficiency of the animal protein composite system further increases to 84.54% and 83.52%, while that of the plant protein composite system decreases slightly. This difference is mainly attributed to the higher interfacial activity and amphiphilic structure of animal proteins, which enable them to rapidly form a dense adsorption layer at the oil-water interface, effectively reducing leakage of the core material during emulsification and spray drying.

[0089] Further comparison of the encapsulation effects of composite wall materials and single wall materials revealed a significant improvement in encapsulation efficiency after combining protein with sodium alginate. The encapsulation rates of Examples 1-4 were 0.75-2.77 percentage points higher than those of the corresponding single protein wall materials (Comparative Examples 1-4), confirming the positive impact of the synergistic effect of protein-polysaccharide electrostatic composite on enhancing interfacial membrane density and improving encapsulation efficiency. In contrast, the encapsulation rate of the single sodium alginate wall material (Comparative Example 5) was only 76.01%, lower than all protein-sodium alginate composite systems, indicating that the interfacial membrane strength of the single polysaccharide wall material was insufficient, making it difficult to effectively encapsulate high-content DHA algal oil.

[0090] From the perspective of the effect of oil loading on encapsulation efficiency, the encapsulation efficiency of the animal protein complex system increased rather than decreased under a high oil loading condition of 40%, while that of the plant protein complex system decreased slightly, indicating that animal protein has better tolerance to high oil content. This feature overcomes the technical limitation of traditional microcapsules in achieving both high oil loading and high encapsulation efficiency, providing a feasible technical path for the microencapsulation of high-DHA algal oil.

[0091] In summary, microcapsules prepared by spray drying Pickering emulsion using a combination of animal protein and sodium alginate and maltodextrin as a filler can effectively reduce surface oil content and improve encapsulation efficiency. Among them, Example 7 has the best overall performance, providing a reliable technical solution for the industrial production of DHA algal oil microcapsules.

[0092] Table 3. Results of surface oil, total oil, and encapsulation efficiency of DHA algal oil microcapsules.

[0093] Experimental Example 3: Determination of whiteness, moisture content and water activity of microcapsules

[0094] 1. Determination of whiteness of microcapsules

[0095] Three samples were selected from each group as test samples, and L was measured using a colorimeter CR 400. a b Each test was performed 6 times, and the average result was taken. Whiteness (W) was calculated using the following formula:

[0096] 2. Determination of moisture content

[0097] The moisture content of the microcapsules was determined using a rapid moisture analyzer.

[0098] 3. Determination of water activity

[0099] The water activity was measured using a water activity meter. 1g of microcapsule sample was accurately weighed and placed on the sample test stage. After equilibration for 10 minutes, the measurement was performed, and the data was recorded after the instrument stabilized.

[0100] The results are shown in Table 4. Overall, Example 7 has the highest whiteness value, reaching 87.53, while its moisture content (2.45%) and water activity (0.16) are the lowest, demonstrating excellent physicochemical quality. Example 8 is second best, with a whiteness value of 87.01, a moisture content of 2.56%, and a water activity of 0.18, also showing good performance.

[0101] Comparing composite wall material systems from different protein sources reveals that the overall whiteness value of animal protein (whey protein isolate, casein) composites with sodium alginate is higher than that of plant protein (soy protein isolate, pea protein isolate) composite systems, while the moisture content and water activity are generally lower. Under a 30% oil loading condition, the whiteness values ​​of the whey protein composite system and the casein composite system are 85.26 and 85.52, respectively, with moisture contents of 2.58% and 2.69%, and water activities of 0.20 and 0.22, respectively. In contrast, the whiteness values ​​of the soybean protein composite system and the pea protein composite system are 84.16 and 84.81, respectively, with moisture contents of 2.77% and 2.81%, and water activities of 0.24 and 0.25, respectively. Under a 40% oil loading condition, the whiteness values ​​of the animal protein composite system further increased to 87.53 and 87.01, while the moisture content further decreased to 2.45% and 2.56%, and the water activity decreased to 0.16 and 0.18, respectively. In contrast, the whiteness values ​​of the plant protein composite system decreased to 83.31 and 82.21, while the moisture content increased to 2.87% and 2.93%, and the water activity increased to 0.26 and 0.28. This difference is mainly attributed to the more dense and uniform particle structure of the composite particles formed by animal protein and sodium alginate. Animal protein has higher interfacial activity, enabling it to form a tight adsorption layer at the oil-water interface. After spray drying, it forms smooth, dense microcapsule particles, thus exhibiting higher whiteness values ​​and lower moisture content and water activity. In contrast, the interfacial film of the plant protein composite system is relatively loose, resulting in more residual moisture during drying and lower particle surface gloss, leading to lower whiteness values.

[0102] Further comparison of the physicochemical properties of composite wall materials and single wall materials reveals that the whiteness value of the composite material with sodium alginate is improved, while the moisture content and water activity are reduced. This may be because the introduction of sodium alginate helps to form a denser microcapsule structure, reducing moisture residue and improving the product's appearance.

[0103] From the perspective of the impact of oil loading on physicochemical properties, the whiteness value of the animal protein complex system under a high oil loading of 40% was actually higher than that under a high oil loading of 30% (whey protein: 85.26→87.53; casein: 85.52→87.01), while the water content and water activity further decreased, indicating that animal proteins can still form dense microcapsule structures under high oil loading conditions. In contrast, the whiteness value of the plant protein complex system decreased significantly under high oil loading conditions, while the water content and water activity increased significantly, reflecting that the interfacial stability and film-forming ability of plant proteins are relatively limited under high oil loading conditions.

[0104] Table 4. Results of whiteness, moisture content, and water activity determination of DHA algal oil microcapsules

[0105] Experimental Example 4 Core Material Retention Rate

[0106] After storing the encapsulated algal oil samples in a 45℃ constant temperature drying oven in a sealed, light-protected environment for 30 days, each sample was taken, and the surface oil content and total oil content of the algal oil microcapsules were determined according to the method in Experimental Example 2. The core material retention rate was calculated according to the following formula:

[0107] In the formula, m0 is the total oil mass of the original microcapsules; m1 is the surface oil mass of the original microcapsules; and m2 is the surface oil mass of the microcapsules after storage.

[0108] The results are as follows Figure 1 As shown, core material retention rate is a key indicator for measuring the ability of microcapsules to protect the core material from oxidation during processing. Figure 1 Data shows that Example 7 had the highest core material retention rate at 65.80%, followed by Example 8 at 64.97%, and Examples 3 and 4 at 64.27% and 63.44% respectively, all significantly higher than the 54.09% retention rate of the unencapsulated algal oil control group. This result indicates that microencapsulation can effectively slow down the oxidative degradation of DHA algal oil during high-temperature spray drying.

[0109] From the perspective of oxidative protection mechanisms, the Pickering emulsion system formed by the combination of animal protein and sodium alginate plays a crucial role in the antioxidant protection of DHA algal oil through its interfacial structure. Whey protein isolate and casein molecules contain abundant sulfur-containing amino acids (such as cysteine ​​and methionine) and hydrophobic groups. These structural units endow protein molecules with strong free radical scavenging and interfacial anchoring capabilities. During emulsification, animal protein can rapidly adsorb at the oil-water interface, with its hydrophobic regions embedding into the oil phase to form physical proximity with DHA molecules. The sulfur-containing amino acid residues can act as endogenous antioxidants, capturing free radicals and interrupting the lipid peroxidation chain reaction. The introduction of sodium alginate further strengthens this protective mechanism. The composite interfacial layer formed by sodium alginate and protein through electrostatic interactions increases the thickness and density of the interfacial film, reducing the diffusion rate of oxygen from the aqueous phase to the oil phase. Furthermore, the carboxyl groups on the sodium alginate molecular chain can form a hydrogen bond network with protein molecules, limiting the thermal denaturation and aggregation of protein molecules during drying, thereby maintaining the integrity of the interfacial film. This dual protection mechanism of "chemical antioxidant + physical barrier" enables the animal protein composite system to maintain a high core material retention rate (65.80%) even under 40% high oil loading conditions. However, due to the low content of sulfur amino acids and insufficient interfacial membrane flexibility, the plant protein has a relatively weaker interfacial protection ability under high oil loading conditions, resulting in a decrease in core material retention rate.

[0110] From the perspective of the impact of spray drying process on core material retention, the film-forming behavior of the protein-sodium alginate composite system during the drying process directly determines the protective effect of the core material. During spray drying, droplets undergo rapid water evaporation and temperature rise, making the film-forming rate and membrane structure integrity of the wall material crucial. The electrostatic complex formed by animal protein and sodium alginate can rapidly form a continuous gel film on the droplet surface in the early stage of drying. This film has a high glass transition temperature, which can resist structural collapse caused by high temperature, thus continuously playing an oxygen barrier role in the later stage of drying. In contrast, the film-forming rate of single protein wall material is slower, and surface cracking is prone to occur during the drying process, causing some DHA algal oil to be directly exposed to the high-temperature airflow and undergo oxidation; single sodium alginate wall material lacks interfacial activity and cannot form effective adsorption at the oil-water interface. Most of the DHA algal oil separates from the wall material before drying, resulting in the most severe oxidation loss, with a core material retention rate of only 57.38%.

[0111] Experiment Example 5: Structural Observation of DHA Algal Oil Microcapsule Powder

[0112] The structures of the DHA algal oil microcapsule powders prepared in Examples 5-8 were observed, and their visual representations are shown below. Figure 2 As shown, the scanning electron microscope (SEM) image is as follows: Figure 3As shown, SPI-SA, PPI-SA, WPI-SA, and CN-SA represent the DHA algal oil microcapsule powders prepared in Examples 5-8, respectively.

[0113] Depend on Figure 2 As can be seen, the WPI-SA (Example 7) and CN-SA (Example 8) microcapsule powders are uniform in color, light milky white, and have a fine and fluffy texture. In contrast, the SPI-SA (Example 5) and PPI-SA (Example 6) microcapsule powders are slightly darker in color, have a relatively rough texture, and show slight particle agglomeration in some areas. This difference indicates that the animal protein complex system can form more uniform and better dispersed microcapsule powders during spray drying, which is highly consistent with the higher scores obtained by the animal protein complex system in sensory evaluation (WPI-SA 93.7 points, CN-SA 92.2 points, SPI-SA 86.3 points, PPI-SA 85.8 points).

[0114] Depend on Figure 3 As can be seen, the WPI-SA and CN-SA microcapsule particles exhibit a regular spherical or near-spherical morphology, with uniform particle size distribution, smooth and dense surfaces, and no obvious cracks, depressions, or pores. This complete spherical structure is the result of rapid film formation and uniform shrinkage of the wall material during spray drying, indicating that the electrostatic complex formed by whey protein isolate and casein with sodium alginate has good film-forming properties and structural stability. The smooth and dense surface means that the wall material forms a complete physical encapsulation of the core material, effectively blocking oxidation-inducing factors such as oxygen and light. This is highly consistent with the physicochemical properties of WPI-SA and CN-SA, which have lower surface oil content (8.28% and 8.82%, respectively), higher encapsulation rates (84.54% and 83.52%, respectively), and higher core material retention rates (65.80% and 64.97%, respectively). In contrast, the SPI-SA and PPI-SA microcapsule particles have irregular morphologies, rougher surfaces, and some particles show obvious depressions, wrinkles, and even cracks. The surface of SPI-SA microcapsule particles shows irregular depressions and a wide particle size distribution; PPI-SA microcapsule particles, on the other hand, exhibit more obvious surface roughness and interparticle adhesion, with some particles having tiny pores on their surface.

[0115] comprehensive Figure 2 and Figure 3Morphological analysis reveals that microcapsules formed by animal proteins (whey protein isolate, casein) and sodium alginate exhibit significantly superior macroscopic appearance and microstructure compared to plant protein (soy protein isolate, pea protein isolate) composite systems. WPI-SA and CN-SA microcapsules display ideal morphologies with regular spherical shapes, smooth and dense surfaces, and uniform particle dispersion, providing a reliable physical protective barrier for DHA algal oil. In contrast, SPI-SA and PPI-SA microcapsules suffer from structural defects such as rough surfaces, pitted cracks, and particle adhesion, resulting in relatively limited interfacial protection capabilities. This morphological difference reveals, from a microstructural perspective, the intrinsic reason why animal protein composite systems outperform plant proteins in terms of encapsulation rate, core material retention rate, and sensory quality, providing a clear technical basis for the selection of wall materials for high-content DHA algal oil microcapsules.

[0116] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing DHA algal oil microcapsules based on Pickering emulsion, characterized in that, Includes the following steps: (1) Mix plant protein or animal protein with water to obtain a protein solution; (2) Mix sodium alginate with water to obtain a sodium alginate solution; (3) The protein solution is mixed with the sodium alginate solution to obtain a protein-sodium alginate dispersion; (4) The protein-sodium alginate dispersion is mixed with a filler to obtain a wall material solution; (5) The wall material solution and DHA algal oil are mixed to obtain Pickering emulsion; (6) The Pickering emulsion is dried to obtain DHA algal oil microcapsules.

2. The preparation method according to claim 1, characterized in that, In step (1), the plant protein is soy protein isolate or pea protein isolate; the animal protein is whey protein isolate or casein; the mass-to-volume ratio of protein to water is 1.5~2.5 g: 80~120 mL; the mixing rate is 400~800 rpm and the time is 1~3 h.

3. The preparation method according to claim 1, characterized in that, In step (2), the mass-to-volume ratio of sodium alginate to water is 0.8~1.2 g: 80~120 mL.

4. The preparation method according to claim 1, characterized in that, The obtained protein solution and sodium alginate solution were then stored at 3-5℃ for 8-24 hours.

5. The preparation method according to claim 1, characterized in that, In step (3), the volume ratio of the protein solution to the sodium alginate solution is 1~3:1~3; the mixing temperature is 23~27℃, the mixing speed is 400~800 rpm, and the mixing time is 30~90 min.

6. The preparation method according to claim 1, characterized in that, In step (4), the filler is any one of inulin, β-cyclodextrin, and maltodextrin; the mass fraction of solids in the wall material solution is 20-30%.

7. The preparation method according to claim 1, characterized in that, In step (5), the mass of the DHA algal oil accounts for 25-50% of the total mass of the Pickering emulsion; the mixing rate is 8000-16000 rpm and the time is 1-5 min.

8. The preparation method according to claim 1, characterized in that, In step (6), the drying is spray drying, the inlet air temperature is 160~180℃, the outlet air temperature is 80~90℃, the feed rate is 400~800 mL / h, and the atomization pressure is 0.8~1.2 MPa.

9. A DHA algal oil microcapsule obtained by the preparation method according to any one of claims 1 to 8.

Images