Spirulina emulsion gel prepared by starch pre-emulsification process and preparation method thereof

Abstract

This invention discloses a spirulina emulsion gel prepared by a starch pre-emulsification process and its preparation method, belonging to the field of emulsion gel preparation technology. The raw materials for the spirulina emulsion gel include fresh spirulina (freeze-dried spirulina powder), starch, protein, edible oil, and water. The preparation process is as follows: first, the protein is mixed evenly with a portion of water and then hydrated under cold conditions to obtain a protein solution; then, the starch is mixed with the remaining water and homogenized at high speed with edible oil to obtain a starch-oil pre-emulsion; subsequently, the protein solution is mixed with spirulina to form a protein-spirulina mixture; finally, the starch-oil pre-emulsion and the protein-spirulina mixture are homogenized again at high speed, and then heat-induced and cold-cured to obtain the spirulina emulsion gel. This invention constructs a dense, rigid starch adsorption layer at the oil-water interface through the starch pre-emulsification process, greatly enhancing the interfacial stability and network cross-linking degree of the emulsion gel.

Description

Technical Field

[0001] This invention belongs to the field of emulsion gel preparation technology, specifically relating to a spirulina emulsion gel prepared by starch pre-emulsification process and its preparation method. Technical Background

[0002] Spirulina, a recognized high-quality microalgae resource, is rich in high-quality protein (60-70%), essential fatty acids, phycocyanin, and various active polysaccharides, and has broad application prospects in functional foods and nutrient delivery. Emulsion gels, as a semi-solid system combining the characteristics of a solid gel network and a liquid oil phase, can effectively encapsulate, protect, and deliver fat-soluble bioactive substances, and are currently a hot topic in food colloid science research.

[0003] Currently, most existing technologies for preparing spirulina emulsion gels employ the following process pathways: First, a protein pre-emulsification process, which utilizes the emulsifying activity of proteins to mix the oil and water phases to form an emulsion, and then introduces other components such as starch for gelation. However, the flexible adsorption film formed by a single protein at the oil-water interface is relatively thin, and during thermally induced gelation, it is prone to interfacial rupture or rearrangement, resulting in a brittle gel network with weak deformation recovery and insufficient protective barrier for oil droplets. Second, a co-homogenization process, which directly mixes all components such as spirulina, protein, starch, oil, and water together and emulsifies them through high-speed shear homogenization. While this process is simplified, the lack of a priority order for interfacial adsorption leads to disordered competitive adsorption between starch particles, protein molecules, and oil droplets, preventing the formation of an effective and continuous interfacial layer. Oil droplets are prone to aggregation or coalescence, resulting in low cross-linking density within the system and a loose gel structure. Third, a dual-gel mixing process, which involves preparing protein gel and starch gel separately, and then mechanically mixing them under thermal melting conditions. While this process can combine the properties of two colloids, the two pre-formed gel networks have different rheological and thermal properties, making macroscopic phase separation highly likely during mixing. This results in numerous interface defects, extremely poor cohesion, and the resulting gel often exhibits obvious continuous aqueous phase channels. This not only significantly reduces the mechanical strength of the gel but also exposes oil droplets to the aqueous environment. The aforementioned existing technologies generally suffer from numerous technical bottlenecks.

[0004] Furthermore, existing technologies for processing spirulina raw materials typically fail to adequately differentiate between fresh and freeze-dried spirulina powder in terms of the retention of active ingredients, and also lack comparative studies on the impact of different microalgal cell wall structures on gel network construction. The abundant natural active polysaccharides and intact proteins in fresh spirulina should provide more physical cross-linking sites for the gel network, but traditional processes often impair their activity due to harsh processing, failing to fully realize their structural enhancement effects.

[0005] In view of this, the present invention aims to propose a method that uses fresh spirulina (freeze-dried spirulina powder) and starch as the main raw materials. Through a starch pre-emulsification process, starch particles preferentially form a dense rigid adsorption layer at the oil-water interface, and then undergo deep cross-linking with a protein-spirulina mixture system that has been activated by low-temperature hydration. This results in the construction of a continuous, uniform, and dense three-dimensional network structure without macroscopic phase separation, simultaneously achieving a significant improvement in gel mechanical properties, an effective improvement in interfacial hydrophobicity, and a comprehensive enhancement in lipid oxidation stability. Summary of the Invention

[0006] The present invention aims to overcome the problems of easy loss of active ingredients and loose gel network structure and poor texture properties in the existing spirulina processing, and provides a spirulina emulsion gel with high retention of active ingredients, dense and stable gel network and excellent interfacial hydrophobic properties and its preparation method.

[0007] This invention is achieved through the following technical solution:

[0008] An emulsion gel, wherein the raw materials comprise, by weight percentage, any one of the following:

[0009] (1) Spirulina mud (moisture content 80-90%) 8-16%, starch 10-20%, protein 8-12%, edible oil 27-42%, water 21-32%.

[0010] (2) Freeze-dried spirulina powder 1-6%, starch 10-20%, protein 8-12%, edible oil 35-46%, water 27-35%.

[0011] The method for preparing the spirulina emulsion gel via starch pre-emulsification includes the following steps:

[0012] (1) Protein hydration: Mix the protein with some deionized water to prepare a protein solution with a mass concentration of 30-40%. Stir at 150-300 rpm at 25°C for 1-3 hours. After stirring, transfer to 4°C and refrigerate for 12-16 hours to allow the hydration to complete.

[0013] (2) Starch-oil pre-emulsion: Mix starch with the remaining deionized water and stir at 150 rpm - 300 rpm for 20 - 40 min at 25℃ to obtain a starch solution. Mix the starch solution with oil and homogenize at 12000 - 16000 rpm for 2 - 6 min to obtain a starch-oil pre-emulsion.

[0014] (3) Protein-spirulina mixture: Mix the protein solution from step (1) with spirulina and stir at 150 rpm - 300 rpm for 20 - 40 min to obtain a protein-spirulina mixture;

[0015] (4) Emulsion homogenization: Mix the starch-oil pre-emulsion from step (2) with the protein-spirulina mixture from step (3) and homogenize at 12000-16000 rpm for 2-6 min to obtain an emulsion;

[0016] (5) Gel formation: The emulsion obtained in step (4) is heated at 70-80℃ for 10-20 min, and then refrigerated at 4℃ for 1-3 h to form spirulina emulsion gel.

[0017] The protein is selected from at least one of pea protein isolate, soy protein isolate, and whey protein;

[0018] The starch is selected from at least one of pea starch, potato starch, corn starch, and wheat starch;

[0019] The oil phase is selected from at least one of soybean oil, sunflower oil, coconut oil, and peanut oil;

[0020] The beneficial effects of this invention include:

[0021] (1) Excellent nutrient retention and delivery performance: Fresh spirulina and freeze-dried spirulina powder are used as raw materials. The protein is pre-hydrated before being added to the spirulina for mixing, which avoids the damage to phycocyanin, β-carotene and active polysaccharides in fresh spirulina caused by drastic processing. Moreover, the dense starch-protein complex interface constructed by the starch pre-emulsification process effectively avoids the premature disintegration and loss of active ingredients during the digestion stage, exhibiting excellent delivery performance.

[0022] (2) Good gel properties and structural uniformity: Starch preferentially adsorbs the oil-water interface during the pre-emulsification stage, forming a thick rigid starch adsorption layer, and undergoes deep physical cross-linking with the subsequently introduced protein-spirulina system, ultimately constructing a continuous, uniform, and macroscopically crack-free three-dimensional gel network.

[0023] (3) The process is simple and has advantages: the whole process is completed in conventional gelatinization, homogenization and cooling equipment, and the starch pre-emulsification process changes the limitations of traditional disordered competitive adsorption or pre-gelation processes. Attached Figure Description

[0024] To make the technical solutions of the embodiments of the present invention clearer, the accompanying drawings involved in each embodiment are now briefly described. It should be understood that the drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope of the present invention. For those skilled in the art, other related drawings can still be obtained based on these drawings without creative effort.

[0025] Figure 1 Photograph of a composite emulsion gel.

[0026] Figure 2 Photograph of the water contact angle of the composite emulsion gel.

[0027] Figure 3 This is a CLSM image of a composite emulsion gel. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The present invention will be further described in detail with reference to the following embodiments and comparative examples, but the scope of protection of the present invention is not limited thereto.

[0029] Example 1

[0030] A method for preparing fresh spirulina emulsion gel via starch pre-emulsification includes the following steps:

[0031] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 19mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0032] (2) Starch-oil pre-emulsion: Weigh 16g of pea starch and mix it with 11mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution. Mix the pea starch solution with 38mL of soybean oil and homogenize at 15000rpm for 5min to obtain pea starch-soybean oil pre-emulsion.

[0033] (3) Protein-spirulina mixture: Mix the pea protein isolate solution from step (1) with 10g of fresh spirulina paste and stir at 200rpm for 30min to obtain pea protein isolate-fresh spirulina mixture.

[0034] (4) Emulsion homogenization: The pea starch-soybean oil pre-emulsion from step (2) is mixed with the pea protein isolate-fresh spirulina mixture from step (3) and homogenized at 15000 rpm for 5 min to obtain fresh spirulina emulsion.

[0035] (5) Gel formation: The fresh spirulina emulsion obtained in step (4) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a fresh spirulina emulsion gel.

[0036] Example 2

[0037] A method for preparing spirulina powder emulsion gel via starch pre-emulsification includes the following steps:

[0038] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 21mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0039] (2) Starch-oil pre-emulsion: Weigh 16g of pea starch and mix it with 12mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution. Mix the pea starch solution with 43mL of soybean oil and homogenize at 15000rpm for 5min to obtain pea starch-soybean oil pre-emulsion.

[0040] (3) Protein-spirulina mixture: Mix the pea protein isolate solution from step (1) with 2g of freeze-dried spirulina powder and stir at 200rpm for 30min to obtain pea protein isolate-spirulina powder mixture.

[0041] (4) Emulsion homogenization: The pea starch-soybean oil pre-emulsion from step (2) is mixed with the pea protein isolate-spirulina powder mixture from step (3) and homogenized at 15000 rpm for 5 min to obtain a spirulina powder emulsion.

[0042] (5) Gel formation: The spirulina powder emulsion obtained in step (4) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a spirulina powder emulsion gel.

[0043] Example 3

[0044] A method for preparing fresh spirulina emulsion gel via starch pre-emulsification includes the following steps:

[0045] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 17mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0046] (2) Starch-oil pre-emulsion: Weigh 16g of pea starch and mix it with 10mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution. Mix the pea starch solution with 36mL of soybean oil and homogenize at 15000rpm for 5min to obtain pea starch-soybean oil pre-emulsion.

[0047] (3) Protein-spirulina mixture: Mix the pea protein isolate solution from step (1) with 15g of fresh spirulina paste and stir at 200rpm for 30min to obtain pea protein isolate-fresh spirulina mixture.

[0048] (4) Emulsion homogenization: The pea starch-soybean oil pre-emulsion from step (2) is mixed with the pea protein isolate-fresh spirulina mixture from step (3) and homogenized at 15000 rpm for 5 min to obtain fresh spirulina emulsion.

[0049] (5) Gel formation: The fresh spirulina emulsion obtained in step (4) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a fresh spirulina emulsion gel.

[0050] Example 4

[0051] A method for preparing spirulina powder emulsion gel via starch pre-emulsification includes the following steps:

[0052] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 20mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is hydrated, transfer it to 4℃ and refrigerate for 14 hours until hydration is complete.

[0053] (2) Starch-oil pre-emulsion: Weigh 16g of pea starch and mix it with 12mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution. Mix the pea starch solution with 42mL of soybean oil and homogenize at 15000rpm for 5min to obtain pea starch-soybean oil pre-emulsion.

[0054] (3) Protein-spirulina mixture: Mix the pea protein isolate solution from step (1) with 4g of freeze-dried spirulina powder and stir at 200rpm for 30min to obtain pea protein isolate-spirulina powder mixture.

[0055] (4) Emulsion homogenization: The pea starch-soybean oil pre-emulsion from step (2) is mixed with the pea protein isolate-spirulina powder mixture from step (3) and homogenized at 15000 rpm for 5 min to obtain a spirulina powder emulsion.

[0056] (5) Gel formation: The spirulina powder emulsion obtained in step (4) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a spirulina powder emulsion gel.

[0057] Comparative Example 1

[0058] A method for preparing fresh spirulina emulsion gel using a dual-gel mixing method includes the following steps:

[0059] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 19mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0060] (2) Preparation of starch emulsion gel: Weigh 16g of pea starch and mix with 11mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution. Mix pea starch solution with 38mL of soybean oil and homogenize at 15000rpm for 5min. Then heat at 75℃ for 15min to obtain pea starch emulsion gel.

[0061] (3) Protein-spirulina mixture: Mix the pea protein isolate solution from step (1) with 10g of fresh spirulina mud and stir at 200rpm for 30min, then heat at 75℃ for 15min to obtain fresh spirulina protein gel.

[0062] (4) Emulsion gel formation: The pea starch emulsion gel from step (2) and the fresh spirulina protein gel from step (3) are mixed while hot and homogenized at 15000 rpm for 5 min, heated at 75℃ for 15 min, and immediately transferred to 4℃ for refrigeration for 2 h to form a fresh spirulina emulsion gel.

[0063] Comparative Example 2

[0064] A method for preparing a spirulina powder emulsion gel using a dual-gel mixing method includes the following steps:

[0065] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 21mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0066] (2) Preparation of starch emulsion gel: Weigh 16g of pea starch and mix with 12mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution. Mix pea starch solution with 43mL of soybean oil and homogenize at 15000rpm for 5min. Then heat at 75℃ for 15min to obtain pea starch emulsion gel.

[0067] (3) Protein-spirulina mixture: Mix the pea protein isolate solution from step (1) with 2g of freeze-dried spirulina powder and stir at 200rpm for 30min, then heat at 75℃ for 15min to obtain spirulina powder protein gel.

[0068] (4) Emulsion gel formation: The pea starch emulsion gel from step (2) and the spirulina powder protein gel from step (3) are mixed while hot and homogenized at 15000 rpm for 5 min, heated at 75℃ for 15 min, and immediately transferred to 4℃ for refrigeration for 2 h to form spirulina powder emulsion gel.

[0069] Comparative Example 3

[0070] A method for preparing fresh spirulina emulsion gel via a protein pre-emulsification process includes the following steps:

[0071] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 19mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0072] (2) Protein-spirulina-oil pre-emulsion: Mix the pea protein isolate solution from step (1) with 10g of fresh spirulina mud and stir at 200rpm for 30min to obtain pea protein isolate-fresh spirulina mixture. Then add 38mL of soybean oil and homogenize at 15000rpm for 5min to obtain pea protein isolate-fresh spirulina pre-emulsion.

[0073] (3) Preparation of starch solution: Weigh 16g of pea starch and mix it with 11mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution.

[0074] (4) Emulsion homogenization: The pea protein isolate-fresh spirulina pre-emulsion from step (2) was mixed with the pea starch solution from step (3) and homogenized at 15000 rpm for 5 min to obtain fresh spirulina emulsion.

[0075] (5) Gel formation: The fresh spirulina emulsion obtained in step (4) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a fresh spirulina emulsion gel.

[0076] Comparative Example 4

[0077] A method for preparing spirulina powder emulsion gel via a protein pre-emulsification process includes the following steps:

[0078] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 21mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0079] (2) Protein-spirulina-oil pre-emulsion: The pea protein isolate solution from step (1) was mixed with 2g of freeze-dried spirulina powder and stirred at 200rpm for 30min to obtain a pea protein isolate-spirulina powder mixture. Then, 43mL of soybean oil was added and homogenized at 15000rpm for 5min to obtain a pea protein isolate-spirulina powder pre-emulsion.

[0080] (3) Preparation of starch solution: Weigh 16g of pea starch and mix it with 12mL of deionized water. Stir at 200rpm for 30min at 25℃ to obtain pea starch solution.

[0081] (4) Emulsion homogenization: The pea protein isolate-spirulina powder pre-emulsion from step (2) was mixed with the pea starch solution from step (3) and homogenized at 15000 rpm for 5 min to obtain a spirulina powder emulsion.

[0082] (5) Gel formation: The spirulina powder emulsion obtained in step (4) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a spirulina powder emulsion gel.

[0083] Comparative Example 5

[0084] A method for preparing a fresh spirulina emulsion gel using a common homogenization process includes the following steps:

[0085] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 30mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0086] (2) Mixing of protein-spirulina-starch: Weigh 16g of pea starch and 10g of fresh spirulina paste and add them to the protein solution in step (1). Stir at 200rpm for 30min to mix evenly and obtain a mixed solution.

[0087] (3) Emulsion homogenization: The mixed solution from step (2) was mixed with 38 mL of soybean oil and homogenized at 15000 rpm for 5 min to obtain a fresh spirulina emulsion;

[0088] (4) Gel formation: The fresh spirulina emulsion obtained in step (3) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a fresh spirulina emulsion gel.

[0089] Comparative Example 6

[0090] A method for preparing a spirulina powder emulsion gel via a common homogenization process includes the following steps:

[0091] (1) Protein hydration: Weigh 6g of pea protein isolate and mix with 33mL of deionized water. Stir at 200rpm for 2 hours at 25℃. After the mixture is finished, transfer it to 4℃ and refrigerate for 14 hours to allow it to fully hydrate.

[0092] (2) Protein-spirulina-starch mixture: Weigh 16g of pea starch and 2g of freeze-dried spirulina powder and add them to the protein solution in step (1). Stir at 200 rpm for 30 minutes to mix evenly and obtain a mixed solution.

[0093] (3) Emulsion homogenization: The mixed solution from step (2) was mixed with 43 mL of soybean oil and homogenized at 15000 rpm for 5 min to obtain spirulina powder emulsion;

[0094] (4) Gel formation: The spirulina powder emulsion obtained in step (3) is heated at 75°C for 15 min and then refrigerated at 4°C for 2 h to form a spirulina powder emulsion gel.

[0095] Comparative Example 7

[0096] A method for preparing fresh Chlorella emulsion gel via starch pre-emulsification includes the following steps:

[0097] The steps are the same as in Example 1, except that the fresh spirulina mud is replaced with an equal amount of fresh chlorella mud.

[0098] Comparative Example 8

[0099] A method for preparing Chlorella powder emulsion gel via starch pre-emulsification includes the following steps:

[0100] The steps are the same as in Example 2, except that the freeze-dried spirulina powder is replaced with an equal amount of freeze-dried chlorella powder.

[0101] Properties of composite emulsion gels

[0102] (1) Texture properties of composite emulsion gel

[0103] Table 1. Hardness and elasticity of composite emulsion gels

[0104] Example 1 188.54 0.95 Example 2 198.78 0.91 Example 3 200.49 0.93 Example 4 205.28 0.89 Comparative Example 1 150.47 0.68 Comparative Example 2 144.85 0.65 Comparative Example 3 176.16 0.75 Comparative Example 4 170.54 0.72 Comparative Example 5 206.21 0.85 Comparative Example 6 207.41 0.82 Comparative Example 7 183.89 0.80 Comparative Example 8 181.27 0.78

[0105] The hardness and elasticity of the gel are macroscopic reflections of the interaction between the internal continuous and dispersed phases. Data are shown in Table 1. Examples 1-4 demonstrate that the starch pre-emulsified group is the optimal group for balancing hardness and elasticity. The starch pre-emulsification process first forms a dense starch adsorption layer at the oil-water interface through high-speed homogenization. Its rigid granular layer acts as a base point for cross-linking with the subsequently added protein-spirulina mixture, constructing a uniform and highly resilient three-dimensional network, endowing the gel with extremely strong deformation recovery ability. Moreover, in the starch pre-emulsified group, Examples 1 and 3 showed significantly higher elasticity than Examples 2 and 4. This is because fresh spirulina is rich in natural active polysaccharides and intact proteins, and its surface has more active groups that can form denser hydrogen bonds and hydrophobic interactions with pea protein isolate, enhancing the physical cross-linking points of the gel network; while the freeze-drying process may cause protein denaturation or aggregation, weakening its interfacial binding ability with the matrix. Comparative Examples 5 and 6 showed moderate hardness and elasticity, indicating that the co-homogenization method, which mixes all components in one step, cannot form an ordered interfacial adsorption layer, resulting in a lower cross-linking density. Protein pre-emulsification has a certain interfacial stabilizing effect. Although the elasticity of Comparative Examples 3 and 4 is relatively high, it is still relatively low, indicating that although the protein film formed by this process is relatively flexible, the network as a whole is relatively brittle. The other double-gel method, due to the pre-formation of protein gel and starch gel, disrupts the continuity of their independent systems during subsequent mixing, resulting in the most interfacial defects and the weakest cohesion. Therefore, Comparative Examples 1 and 2 have the lowest hardness and elasticity. Comparing Examples 1 and 2 with Comparative Examples 7 and 8, it was found that under the same process conditions, the Spirulina group was superior to the Chlorella group. This is mainly attributed to the unique phycocyanin and polysaccharide composition in the Spirulina cell wall, which more readily participates in the construction of a stable three-dimensional network framework during heat-induced gelation.

[0106] (2) Surface hydrophobicity of composite emulsion gel

[0107] Table 2 BPB binding amount of composite emulsion gel

[0108] Example 1 142.09 Example 2 131.66 Example 3 135.72 Example 4 128.36 Comparative Example 1 83.47 Comparative Example 2 78.11 Comparative Example 3 98.52 Comparative Example 4 95.04 Comparative Example 5 122.38 Comparative Example 6 119.34 Comparative Example 7 114.90 Comparative Example 8 110.18

[0109] The surface hydrophobicity of emulsion gels directly reflects the stability of the oil-water interface and the density of oil droplet encapsulation. Table 2 shows that Examples 1-4, representing the starch pre-emulsification group, exhibited the highest surface hydrophobicity, with BPB binding amounts ranging from 128.36 to 142.09 μg. This is because starch particles preferentially adsorbed and tightly covered the oil droplet surface during the pre-emulsification stage, forming a thick and rigid interface. During subsequent heating and gelation, these exposed starch hydrophobic groups effectively migrated to the gel surface, significantly enhancing surface hydrophobicity. In contrast, Comparative Examples 3 and 4 relied solely on flexible protein adsorption, resulting in a thinner interface layer and limited exposure of hydrophobic groups. Comparative Examples 5 and 6 lacked a preferential adsorption sequence, leading to a free mixed state of oil droplets and starch, making it difficult for hydrophobic groups to align. Comparative Examples 1 and 2 had the worst surface hydrophobicity because the oil droplets were pre-fixed inside the starch and protein gels and could not migrate to the outer surface of the gel, with BPB binding amounts only between 78.11 and 83.47 μg. In all examples and comparative examples, the groups with added fresh spirulina exhibited stronger hydrophobicity, which is attributed to the greater amount of natural amphiphilic substances (such as phycocyanin) retained in fresh spirulina, resulting in stronger synergistic adsorption at the interface.

[0110] (3) Water contact angle of composite emulsion gel

[0111] Table 3. Left and right angles of the water contact angle of the composite emulsion gel.

[0112] Example 1 103.4 102.5 Example 2 94.4 94.7 Example 3 100.8 101.3 Example 4 91.9 91.8 Comparative Example 1 57.7 57.5 Comparative Example 2 51.3 49.3 Comparative Example 3 75.3 73.2 Comparative Example 4 69.0 71.5 Comparative Example 5 89.0 89.1 Comparative Example 6 85.5 86.8 Comparative Example 7 82.8 83.0 Comparative Example 8 79.5 78.6

[0113] Figure 2 The morphology of water droplets on the gel surface under different preparation processes is visually demonstrated, and their macroscopic wetting behavior strictly confirms the left and right θ data in Table 3. The water droplets in Examples 1-4 exhibit a high-domed spherical shape with contact angles generally above 90º, and the left θ of Example 1 reaches as high as 103.4º. From Comparative Examples 5 and 6 to Comparative Examples 3 and 4, the droplets spread further, and the angle gradually decreases. In contrast, the droplets in Comparative Examples 1 and 2 are almost flat on the surface, with contact angles only between 50º and 58º. The reason for the highest water contact angle θ in Examples 1-4 is that in the starch pre-emulsification process, the starch particles are strongly adsorbed at the oil-water interface during the emulsification stage. This rigid particle layer preferentially aligns to the surface during subsequent gelation, exposing a large number of hydrophobic groups, resulting in a larger θ. The two processes in Comparative Examples 3-6 result in limited exposure of hydrophobic groups, leading to a smaller θ. Because the oil droplets are pre-encapsulated within the internal gel network, the continuous aqueous phase occupies the surface, thus Comparative Examples 1 and 2 exhibit extremely strong hydrophilicity. In addition, the θ of Example 1 was significantly higher than that of Comparative Example 7. This is because the active polysaccharides and phycocyanin on the surface of fresh Spirulina cells have better interfacial alignment ability, while Chlorella cell walls contain more hydrophilic cellulose, which is not conducive to the hydrophobic modification of the gel surface.

[0114] (4) CLSM of composite emulsion gel

[0115] Figure 3 In the CLSM images, the starch-protein continuous phase is labeled with green fluorescence, and the oil phase is labeled with red fluorescence. In the images of Examples 1-4, the green and red channels show a highly overlapping, densely packed structure. The oil droplets are tightly coated by the starch-protein complex, forming uniform and clearly defined spherical droplets. This structure, after heating and gelling, constructs a continuous, dense, and non-porous three-dimensional network, directly endowing the gel with extremely high elasticity and resistance to lipid oxidation. Compared with Example 2, the green network in Example 1 is denser and more uniform, indicating that the active substances of fresh algae participate in and promote cross-linking. In Comparative Examples 3 and 4, although the oil droplets are coated with the green phase, the interface layer is thin and there are discontinuous regions. The flexible protein membrane is easily deformed when subjected to external shear, causing some oil droplets to aggregate. Next, in Comparative Examples 5 and 6, the images show that the green and red phases are loosely interlocked. The oil droplets lack continuous and dense interface protection, and some oil droplets exhibit a connected or large aggregated state. This disordered stacking microstructure confirms the defect that common homogeneity cannot effectively construct a good interface. Comparative Examples 1 and 2 exhibited the worst structural stability because large red oil aggregates were visible in the images, and the green starch and protein networks were unevenly distributed, showing obvious fractures. This phase separation resulted in numerous continuous aqueous channels in the gel network, directly causing extremely weak surface hydrophobicity. Finally, comparing the CLSM images of Example 1 and Comparative Example 7, the interpenetrating network at the protein-starch interface in the Spirulina group was more coherent and uniform; while the Chlorella group, due to its thicker cell wall, formed a certain degree of barrier at the interface, resulting in more black cavities near the red oil droplets, indicating that its network cross-linking degree was lower than that of the Spirulina system.

[0116] (5) Oil oxidation properties of composite emulsion gels

[0117] The degree of oil oxidation is fundamental to evaluating the antioxidant capacity of interfacial barriers. Tables 4 and 5 below show that Examples 1-4 exhibited the lowest degree of oil oxidation during 14 days of storage at room temperature. This is because the dense interfacial layer constructed by starch pre-emulsification possesses both strong steric hindrance and physical isolation, effectively preventing the diffusion of dissolved oxygen and pro-oxidizing metal ions (such as Fe²⁺) from the aqueous phase to the oil droplet core, thus fundamentally breaking the initiation chain of oil oxidation. Comparative Examples 3 and 4, due to their interfacial layers relying solely on flexible protein molecules for adsorption, have thinner films with micropores, resulting in limited barrier effects. In the co-homogenization process of Comparative Examples 5 and 6, oil droplets, starch, and protein exhibit disordered competitive adsorption, failing to form a continuous and complete coating layer, leading to partial exposure of the oil droplets to the aqueous phase and significantly intensified oxidation. Comparative Examples 1 and 2, with their numerous continuous water channels and macroscopic network cracks, have the largest contact area between the oil and the aqueous phase, resulting in the most intense pro-oxidation reaction. Comparing Examples 1 and 2, it was found that the endogenous antioxidant active substances (such as phycocyanin and β-carotene) in fresh spirulina were not completely inactivated during the thermogelation process. These active substances, together with the dense physical interface barrier, exerted a significant synergistic antioxidant effect, effectively quenching free radicals generated in the system and further reducing the oxidation rate of lipids. However, the freeze-drying process resulted in the partial loss of some heat-sensitive antioxidant components, relatively weakening the synergistic defense capability. Simultaneously, comparing Comparative Examples 1 and 2 and Comparative Examples 7 and 8, it was found that Chlorella, compared to spirulina, lacks potent phycocyanin and similar potent antioxidant peptides, and its endogenous antioxidant system is limited. Therefore, its ability to inhibit lipid oxidation during long-term storage is significantly weaker.

[0118] Table 4. POV values ​​of composite emulsion gels (after 14 days of storage)

[0119] Example 1 1.21 2.36 3.52 Example 2 1.47 2.78 4.02 Example 3 1.33 2.57 3.85 Example 4 1.56 2.94 4.39 Comparative Example 1 2.84 5.41 7.68 Comparative Example 2 3.12 6.06 8.35 Comparative Example 3 3.55 6.82 9.17 Comparative Example 4 3.98 7.57 10.28 Comparative Example 5 1.89 3.63 5.18 Comparative Example 6 2.06 4.10 5.64 Comparative Example 7 2.28 4.53 6.21 Comparative Example 8 2.59 4.99 6.94

[0120] Table 5. TBARS values ​​of composite emulsion gels (after 14 days of storage)

[0121] Example 1 5.20 11.54 18.03 Example 2 6.03 13.21 21.02 Example 3 5.62 12.33 19.54 Example 4 6.54 14.15 22.84 Comparative Example 1 17.12 40.25 62.33 Comparative Example 2 19.58 46.38 70.49 Comparative Example 3 13.05 31.14 48.21 Comparative Example 4 14.87 35.09 54.18 Comparative Example 5 8.07 19.04 30.12 Comparative Example 6 9.11 21.53 34.17 Comparative Example 7 10.24 24.08 38.55 Comparative Example 8 11.53 27.06 43.06

[0122] (5) In vitro digestion properties of composite emulsion gel

[0123] Tables 6 and 7 show in vitro simulated digestion data, revealing that the gel's ability to protect and target the release of core nutrients is closely related to its structural density. During gastric digestion, Examples 1-4 exhibited extremely low degrees of hydrolysis, indicating that the dense starch-protein complex interface constructed by the starch pre-emulsification process formed the strongest physical barrier, effectively resisting the erosion of gastric acid and pepsin, thus providing the most adequate protection for oil droplets and active ingredients in the stomach and preventing premature disintegration. Conversely, Comparative Examples 1 and 2 had the loosest structure, and the active ingredients rapidly disintegrated in gastric juice. Upon entering the intestinal tract, Examples 1-4 showed the highest final degree of hydrolysis, reaching 77.53-82.54%, with the least residue, only 48.25-64.52 mg. This is attributed to its excellent protection in the stomach, enabling the safe and efficient delivery of large amounts of oil and active ingredients to the intestines. In the intestinal environment, amylase and protease work synergistically, causing the dense interface to disintegrate in an orderly manner, allowing for the full release of the core components. Conversely, Comparative Examples 1 and 2, due to premature release in the stomach, had significantly reduced substrate available for hydrolysis by the time they entered the intestines, resulting in the lowest intestinal hydrolysis rate (only 49.54-52.31%) and the highest digestive residue. Under the same process pathway, the intestinal release rate and residue amount of the fresh spirulina group were superior to those of the corresponding freeze-dried spirulina powder group. For example, the DH of Example 1 was 82.54% compared to 79.25% of Example 2. This demonstrates the positive contribution of the fully preserved natural active polysaccharides and proteins in fresh algae to the cross-linking degree of the gel network, making the barrier more robust. A horizontal comparison of algal species was also conducted. For example, Example 1 had an intestinal DH of 82.54% and a residue of 48.25 mg; while Comparative Example 7 had only 65.52% and a residue as high as 102.58 mg. Combining these results with CLSM images reveals that Chlorella, due to the presence of a large amount of tough cellulose in its cell walls, creates a certain degree of barrier and defect at the gel network interface, resulting in a weak gastric protective layer and incomplete intestinal release. In contrast, Spirulina's unique phycocyanin and polysaccharide components are more likely to undergo deep cross-linking with the starch-protein network, thereby ensuring efficient intestinal-directed release and extremely high bioavailability.

[0124] Table 6. Degree of hydrolysis of the composite emulsion gel at different digestion stages.

[0125] Example 1 2.82 15.23 82.54 Example 2 3.12 17.15 79.25 Example 3 3.01 16.04 80.83 Example 4 3.34 18.32 77.53 Comparative Example 1 4.83 31.09 52.31 Comparative Example 2 5.05 33.28 49.54 Comparative Example 3 4.32 27.28 59.05 Comparative Example 4 4.54 28.94 55.83 Comparative Example 5 3.53 20.54 71.06 Comparative Example 6 3.72 22.13 68.34 Comparative Example 7 3.94 23.85 65.52 Comparative Example 8 4.13 25.47 62.76

[0126] Table 7. Residual weight after digestion of the composite emulsion gel.

[0127] Example 1 48.25 Example 2 58.36 Example 3 52.14 Example 4 64.52 Comparative Example 1 169.45 Comparative Example 2 192.72 Comparative Example 3 130.24 Comparative Example 4 148.36 Comparative Example 5 82.17 Comparative Example 6 91.43 Comparative Example 7 102.58 Comparative Example 8 114.69

Claims

1. A spirulina emulsion gel prepared by a starch pre-emulsification process, characterized in that, The raw materials of the emulsion gel include any of the following options by weight percentage: (1) Spirulina algae mud (moisture content 80-90%) 8-16%, starch 10-20%, protein 8-12%, edible oil 27-42%, water 21-32%; (2) Freeze-dried spirulina powder 1-6%, starch 10-20%, protein 8-12%, edible oil 35-46%, water 27-35%.

2. The spirulina emulsion gel according to claim 1, characterized in that, Includes the following steps: (1) Protein hydration: Mix the protein with some deionized water to prepare a protein solution with a mass concentration of 30-40%. Stir at 150-300 rpm at 25°C for 1-3 hours. After stirring, transfer to 4°C and refrigerate for 12-16 hours to allow the hydration to complete. (2) Starch-oil pre-emulsion: Mix starch with the remaining deionized water and stir at 150 rpm - 300 rpm for 20 - 40 min at 25℃ to obtain a starch solution. Mix the starch solution with oil and homogenize at 12000 - 16000 rpm for 2 - 6 min to obtain a starch-oil pre-emulsion. (3) Protein-spirulina mixture: Mix the protein solution from step (1) with spirulina and stir at 150 rpm - 300 rpm for 20 - 40 min to obtain a protein-spirulina mixture; (4) Emulsion homogenization: Mix the starch-oil pre-emulsion from step (2) with the protein-spirulina mixture from step (3) and homogenize at 12000-16000 rpm for 2-6 min to obtain an emulsion; (5) Gel formation: The emulsion obtained in step (4) is heated at 70-80℃ for 10-20 min, and then refrigerated at 4℃ for 1-3 h to form spirulina emulsion gel.

Images