A composite emulsion gel loaded with alpha-linolenic acid and a preparation method and application thereof

Abstract

The application discloses a kind of composite emulsion gel loaded alpha-linolenic acid and its preparation method and application, it is related to the field of polymer compound composition.The application first adds alpha-linolenic acid to soybean protein isolate-tannic acid complex solution, is prepared into emulsion by high-speed shearing, then adds carrageenan to form emulsion gel, and the emulsion gel is soaked in salt solution, to obtain the composite emulsion gel loaded alpha-linolenic acid.Experiments prove that salt solution can change the structure of emulsion gel, and has positive effect on improving the loading rate of gel to active substance alpha-linolenic acid, thermal stability, mechanical strength and antioxidant property, etc., is suitable for making food with high elasticity and relatively hard texture, and the emulsion gel can better protect active substance in gastric environment, so that it has wide application prospect in food industry and biological medicine and other fields, further promotes the high-quality development of protein-based food and biological dressing industry.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high molecular compound compositions, in particular to a composite emulsion gel loaded with α-linolenic acid and a preparation method and application thereof. BACKGROUND

[0002] Soybean protein isolate (SPI) is a high-quality plant protein with extremely high nutritional value, containing essential amino acids for the human body. It has good emulsifying properties and can effectively reduce the oil-water interfacial tension to form stable emulsions. This property makes SPI have wide application prospects in food and biological dressing fields, and its emulsion can protect, embed and deliver lipophilic bioactive substances, improve their dispersibility and stability in water, thereby enhancing their bioavailability and providing new possibilities for the development of functional foods and dressing materials.

[0003] Tannic acid (TA) is a natural plant polyphenol with functional properties such as antioxidant, antibacterial and anti-inflammatory. It has strong binding capacity with amphiphilic biopolymers such as proteins and polysaccharides. The complex of TA and protein can improve the functional properties of protein in food, such as improving the ability of protein to form and stabilize emulsions under certain conditions. In addition, TA can effectively inhibit lipid oxidation and microbial growth in emulsions. These properties make TA have important potential in the development of functional foods, especially in inhibiting the oxidation of polyunsaturated lipids.

[0004] Alpha-linolenic acid (ALA) is an essential omega-3 fatty acid with important physiological functions such as improving cardiovascular health, anti-inflammatory and promoting brain development, but the daily intake is generally insufficient. Moreover, ALA is chemically unstable, easily oxidized and degraded, and has poor water solubility, which limits its bioavailability. Embedding or loading ALA in delivery systems such as emulsions, microcapsules and nanolipid carriers can improve the stability, solubility and absorption efficiency of ALA, making it more bioavailable in functional foods.

[0005] Kappa-carrageenan (KC) is an anionic polysaccharide widely used in the food industry, with functional properties such as thickening, gelling and stabilizing. When complexed with protein, KC can significantly improve the performance of protein emulsion gels, such as enhancing the cohesion of the gel network, forming a more compact three-dimensional structure, and improving the texture properties (such as viscosity, water holding capacity and hardness), thereby directly affecting the processing performance and sensory quality of the final product.

[0006] The present application is to add α-linolenic acid to a soybean protein isolate-tannic acid complex solution, prepare an emulsion by high-speed shearing, and then add kappa-carrageenan to form an emulsion gel. The emulsion gel is soaked in a salt solution to enhance the gel performance and improve the stability of α-linolenic acid, with a view to further promoting the high-quality development of protein-based food and biological dressing industries. SUMMARY

[0007] The application aims to provide a composite emulsion gel loaded with alpha-linolenic acid and a preparation method and application thereof.

[0008] To achieve the above-mentioned purpose, the technical scheme of the application is as follows:

[0009] In the first aspect, the composite emulsion gel loaded with alpha-linolenic acid is prepared by mixing a soybean protein isolate-tannic acid composite solution loaded with alpha-linolenic acid into an emulsion through high-speed shearing, adding polysaccharides to prepare an emulsion gel, and further modifying the emulsion gel through the ionic effect of a salt solution; the soybean protein isolate-tannic acid composite solution is prepared by mixing a soybean protein isolate solution with a mass concentration of 20 mg / mL and a tannic acid solution with a mass concentration of 3.4 mg / mL in equal volumes; the volume ratio of alpha-linolenic acid to the soybean protein isolate-tannic acid composite solution is 1:5-1:20; the polysaccharides are carrageenan with a mass concentration of 0.5%-2%; and the salt solution is a KSCN solution or a KCl solution with a mass concentration of 50 mg / mL-150 mg / mL.

[0010] Preferably, the mass concentration of the carrageenan is 1%.

[0011] Preferably, the salt solution is a KSCN solution or a KCl solution with a mass concentration of 100 mg / mL.

[0012] Preferably, the volume ratio of alpha-linolenic acid to the soybean protein isolate-tannic acid composite solution is 1:15.

[0013] Preferably, the preparation method of the composite emulsion gel loaded with alpha-linolenic acid comprises the following steps:

[0014] S1, soybean protein isolate powder is weighed and dissolved in distilled water to have a mass concentration of 20 mg / mL and is magnetically stirred for 2 h; tannic acid powder is weighed and dissolved in distilled water to have a mass concentration of 3.4 mg / mL and is magnetically stirred for 1 h; the soybean protein isolate solution and the tannic acid solution are mixed in equal volumes to obtain a soybean protein isolate-tannic acid composite solution;

[0015] S2, based on the prepared soybean protein isolate-tannic acid composite solution, alpha-linolenic acid is added thereto according to a volume ratio of alpha-linolenic acid to the soybean protein isolate-tannic acid composite solution of 1:15, and a high-speed shearing homogenizer is used to process under the condition of 12000 r for 90 s to obtain a composite emulsion loaded with alpha-linolenic acid;

[0016] S3, under magnetic stirring at 60 DEG C, add carrageenan powder to the compound emulsion to make its mass concentration 1%, after stirring evenly, stand to obtain emulsion gel;

[0017] S4, weigh KCl powder and dissolve in distilled water to make its mass concentration 100 mg / mL, after completely dissolving, immerse the prepared emulsion gel in the salt solution, stand at 4 DEG C overnight to obtain the compound emulsion gel loaded with alpha-linolenic acid.

[0018] Preferably, the preparation method of the compound emulsion gel loaded with alpha-linolenic acid above comprises the following steps:

[0019] S1, weigh soybean protein isolate powder and dissolve in distilled water to make its mass concentration 20 mg / mL, magnetically stir for 2h; weigh tannic acid powder and dissolve in distilled water to make its mass concentration 3.4 mg / mL, magnetically stir for 1h; mix the soybean protein isolate solution and the tannic acid solution in equal volume to obtain a soybean protein isolate-tannic acid compound solution;

[0020] S2, on the basis of the prepared soybean protein isolate-tannic acid compound solution, add alpha-linolenic acid according to the volume ratio of alpha-linolenic acid to soybean protein isolate-tannic acid compound solution 1:15, use high-speed shearing dispersion homogenizer to process under the condition of 12000 r for 90 s to obtain a compound emulsion loaded with alpha-linolenic acid;

[0021] S3, under magnetic stirring at 60 DEG C, add carrageenan powder to the compound emulsion to make its mass concentration 1%, after stirring evenly, stand to obtain emulsion gel;

[0022] S4, weigh KSCN powder and dissolve in distilled water to make its mass concentration 100 mg / mL, after completely dissolving, immerse the prepared emulsion gel in the salt solution, stand at 4 DEG C overnight to obtain the compound emulsion gel loaded with alpha-linolenic acid.

[0023] Secondly, the application provides a compound emulsion gel loaded with alpha-linolenic acid, which is prepared by the method described in any one of the above.

[0024] Thirdly, the application provides the application of the compound emulsion gel loaded with alpha-linolenic acid described above in the preparation of protein-based medical dressings or functional foods.

[0025] Compared with the prior art, the technical effects of the application are:

[0026] The method provided by the application first adds alpha-linolenic acid into a soybean protein isolate-tannic acid complex solution, prepares an emulsion through high-speed shearing, then adds carrageenan to form an emulsion gel, and soaks the emulsion gel in a salt solution to obtain a complex emulsion gel loaded with alpha-linolenic acid. Experiments prove that the salt solution can change the structure of the emulsion gel, promote the release of alpha-linolenic acid molecules in the emulsion to the binding sites in the gel matrix, present a solid-like gel network, and have a positive effect on improving the loading rate, thermal stability, mechanical strength and antioxidant property of the gel to active substances alpha-linolenic acid, and is suitable for making foods with high elasticity and hard texture. The emulsion gel can better protect active substances in the stomach environment, and has a wide application prospect in the fields of food industry and biological medicine, and further promotes the high-quality development of protein-based foods and biological dressings industry. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The emulsion gel thermal stability graph provided by the different carrageenan addition amounts of the embodiment of the application.

[0028] Figure 2 The emulsion gel particle size and PDI graph provided by the different carrageenan addition amounts of the embodiment of the application.

[0029] Figure 3 The emulsion gel water holding capacity graph provided by the different carrageenan addition amounts of the embodiment of the application.

[0030] Figure 4 The real object graph of the complex emulsion gel loaded with alpha-linolenic acid provided by the embodiment of the application.

[0031] Figure 5 The alpha-linolenic acid loading rate graph of the complex emulsion gel loaded with alpha-linolenic acid provided by the embodiment of the application.

[0032] Figure 6 The rheological graph of the complex emulsion gel loaded with alpha-linolenic acid provided by the embodiment of the application.

[0033] Figure 7 The thermal weight loss rate graph of the complex emulsion gel loaded with alpha-linolenic acid provided by the embodiment of the application.

[0034] Figure 8 The DPPH free radical scavenging capacity graph of the complex emulsion gel loaded with alpha-linolenic acid provided by the embodiment of the application.

[0035] Figure 9 The ABTS free radical scavenging capacity graph of the complex emulsion gel loaded with alpha-linolenic acid provided by the embodiment of the application.

[0036] Figure 10The simulated in-vitro digestion chart of the alpha-linolenic acid-loaded composite emulsion gel provided by the embodiment of the present application. Figure 10 A is the release rate of alpha-linolenic acid in the stomach, and B is the release rate of alpha-linolenic acid in the intestine. DETAILED DESCRIPTION

[0037] In order for those skilled in the art to better understand the technical solutions of the present application, the present application will be further described in detail below in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0038] The experimental methods in the following embodiments are all conventional methods unless otherwise specified.

[0039] The experimental materials used in the following embodiments are all purchased from conventional biochemical reagent stores unless otherwise specified. Soybean protein isolate is purchased from Shanghai Yuan Ye Biotechnology Co., Ltd. Tannic acid is purchased from Shanghai Yuan Ye Biotechnology Co., Ltd. Alpha-linolenic acid is purchased from Shanghai Aladdin Biochem Technology Co., Ltd. Carrageenan is purchased from Shanghai Yuan Ye Biotechnology Co., Ltd. Potassium chloride (KCl) is purchased from Shanghai Aladdin Biochem Technology Co., Ltd. Potassium thiocyanate (KSCN) is purchased from Shanghai Yuan Ye Biotechnology Co., Ltd.

[0040] Example 1 Preparation of soybean protein isolate-tannic acid composite solution

[0041] A certain amount of soybean protein isolate powder was dissolved in distilled water to have a mass concentration of 10 mg / mL, 15 mg / mL, 20 mg / mL, and 25 mg / mL, respectively, and was magnetically stirred for 2 h. A certain amount of tannic acid powder was dissolved in distilled water to have a mass concentration of 1.7 mg / mL, 3.4 mg / mL, and 6.8 mg / mL, respectively, and was magnetically stirred for 1 h. To ensure the consistency of the molar ratio of soybean protein isolate to tannic acid, the two were mixed in equal volumes to obtain a soybean protein isolate-tannic acid composite solution. According to the pre-experiment, the soybean protein isolate concentration of 20 mg / mL and the tannic acid concentration of 3.4 mg / mL are the best. Under this concentration and ratio, the product has good emulsification properties and gel properties, and is suitable for preparing high-elasticity and hard-texture products while reducing the amount of colloid.

[0042] Example 2 Preparation of alpha-linolenic acid-loaded composite emulsion

[0043] A certain amount of soybean protein isolate powder was dissolved in distilled water to make its mass concentration 20 mg / mL, and magnetically stirred for 2 h. A certain amount of tannic acid powder was dissolved in distilled water to make its mass concentration 3.4 mg / mL, and magnetically stirred for 1 h. The two were mixed in equal volume to obtain a soybean protein isolate-tannic acid complex solution.

[0044] On the basis of the soybean protein isolate-tannic acid complex solution, α-linolenic acid was added to make the volume ratio of α-linolenic acid to soybean protein isolate-tannic acid complex solution 1:5, 1:10, 1:15, and 1:20, respectively. A high-speed shear dispersion homogenizer was used to process for 90 s at 12000 r to obtain a complex emulsion loaded with α-linolenic acid. Through pre-experiment, it was found that when the volume ratio was 1:15, the complex emulsion had smaller particle size and higher stability, and could also avoid the problem of too high viscosity caused by high oil phase.

[0045] Example 3 Preparation of complex emulsion gel

[0046] A certain amount of soybean protein isolate powder was dissolved in distilled water to make its mass concentration 20 mg / mL, and magnetically stirred for 2 h. A certain amount of tannic acid powder was dissolved in distilled water to make its mass concentration 3.4 mg / mL, and magnetically stirred for 1 h. The two were mixed in equal volume to obtain a soybean protein isolate-tannic acid complex solution.

[0047] On the basis of the soybean protein isolate-tannic acid complex solution, α-linolenic acid was added to make the volume ratio of α-linolenic acid to soybean protein isolate-tannic acid complex solution 1:15, and a high-speed shear dispersion homogenizer was used to process for 90 s at 12000 r to obtain a complex emulsion loaded with α-linolenic acid (denoted as SPI-TA-0%KC).

[0048] Under magnetic stirring at 60°C, carrageenan powder was added to the complex emulsion uniformly and slowly to make its mass concentration 0.5%, 1%, 1.5%, and 2%, respectively, to obtain emulsion gels, denoted as SPI-TA-0.5%KC, SPI-TA-1%KC, SPI-TA-1.5%KC, and SPI-TA-2.0%KC, respectively. Through experiment, it was found that 1% was the best concentration. Under this concentration, the emulsion gel had good thermal stability, particle size, and gel water retention, and the comprehensive performance was the best.

[0049] The thermal stability of emulsion gels with different carrageenan concentrations was tested as follows: 3-5 mg of the freeze-dried powder of the composite gel was placed in an aluminum crucible, and the crucible with the sample was placed in the instrument after pressing the lid. The empty crucible was placed in the instrument as a control and was removed after the measurement was completed. The test conditions were as follows: the initial temperature was 20°C, the temperature rise rate was 10°C / min, the reaction termination temperature was 200°C, and the nitrogen flow rate was 50 mL / min. After the test, the thermal characteristics of the sample were analyzed using analysis software matched with the instrument.

[0050] Figure 1 The thermal stability of emulsion gels with different carrageenan concentrations is shown in the figure. After the addition of KC, the peak values of the thermal denaturation curves of the emulsion gels were significantly increased, indicating that the synergistic effect of carrageenan and the polymer chains of the emulsion gel improved the thermal stability of the emulsion gel, and the overall trend was an initial increase followed by a decrease.

[0051] The particle size and PDI of emulsion gels with different carrageenan concentrations were tested as follows: the freeze-dried sample powder was dissolved in ultrapure water to prepare a 1 mg / mL solution, and the particle size, polydispersity coefficient (PDI), and Zeta potential of the sample were measured by dynamic light scattering (DLS) using a nanoparticle size potential analyzer.

[0052] Figure 2 The particle size of emulsion gels with different carrageenan concentrations is shown in the figure. The particle size of the emulsion gel increased significantly after the addition of KC, which was due to the fact that soybean protein isolate is a charged amphiphilic molecule, while KC usually carries a negative charge due to the presence of sulfate groups. When they are combined, strong electrostatic attraction occurs, forming larger composite particles. In addition, there are hydrophobic and hydrogen bonding forces between proteins and polysaccharides, which can further combine soybean protein isolate and KC molecules to form larger complexes. When the concentration of carrageenan is 1% and 2%, the particle size of the emulsion gel is relatively small, and the PDI value is smaller when the concentration is 1%, indicating that the system is more uniform.

[0053] The water holding capacity of emulsion gels with different carrageenan concentrations was tested as follows: the same mass of emulsion gel samples was placed in a centrifuge tube. The sample was centrifuged at 10,000 rpm for 20 min using a high-speed centrifuge, the centrifuge tube was removed, and the water in the tube was removed with filter paper. The total mass of the centrifuge tube and the emulsion gel was tested. The water holding capacity was calculated as shown in the formula:

[0054]

[0055] In the formula, m1 is the total mass of water contained in the emulsion gel sample, and m2 is the total mass of water separated by centrifugation, both in grams.

[0056] Figure 3 The water retention of emulsion gels with different carrageenan addition amounts is shown in the figure. The water retention of emulsion gels after KC addition has a large increase, because the KC molecular structure contains a large number of sulfate groups and hydroxyl groups, which have strong hydrophilicity and can combine with water molecules through hydrogen bonds, thereby adsorbing a large amount of water. In addition, the addition of KC is embedded into the network structure of the emulsion gel through hydrogen bonds and electrostatic interactions, promoting the crosslinking and stability of the gel network and improving its water retention capacity. Among them, the water retention is the highest when the KC addition amount is 1%, and with further increase of the KC concentration, the water retention decreases, because at this addition amount, the KC molecules can be more uniformly dispersed in the emulsion gel system. At a higher concentration, the viscosity of the solution increases, affecting the fluidity and interaction between molecules in the system, hindering the full compounding of different components, resulting in a non-uniform network structure of the gel, and the local density is too high to capture more free water.

[0057] Example 4 Preparation of modified composite emulsion gel

[0058] A certain amount of soybean protein isolate powder was dissolved in distilled water to make its mass concentration 20 mg / mL, and magnetically stirred for 2 h. A certain amount of tannic acid powder was dissolved in distilled water to make its mass concentration 3.4 mg / mL, and magnetically stirred for 1 h. The two were mixed in equal volumes to obtain a soybean protein isolate-tannic acid composite solution.

[0059] On the basis of the soybean protein isolate-tannic acid composite solution, α-linolenic acid was added to it according to a volume ratio of α-linolenic acid to soybean protein isolate-tannic acid composite solution of 1:15, and a high-speed shear dispersion homogenizer was used to treat it under the condition of 12000 r for 90 s to obtain a composite emulsion loaded with α-linolenic acid.

[0060] Under magnetic stirring at 60°C, carrageenan powder was added to the composite emulsion uniformly and slowly to make its mass concentration 1%, and after uniform stirring, an emulsion gel was obtained by standing, which was recorded as STK-ALA.

[0061] 5 g, 10 g, and 15 g of KCl and KSCN powder were weighed respectively and dissolved in 100 mL of distilled water. The prepared emulsion gel was soaked in the salt solution. The selection of the salt solution is based on the fact that Cl - and SCN - can induce SPI to form different aggregate states, respectively. Through pre-experiments, it is found that the optimal concentration of KCl or KSCN salt solution is 100 mg / mL. The emulsion gel obtained by modification treatment under this ion concentration is recorded as KCl-ALA and KSCN-ALA, respectively. Under this concentration condition, the formed gels all present ideal texture properties, with moderate hardness and elasticity (as shown in Figure 4 ).

[0062] Example 5 STK-ALA, KCl-ALA and KSCN-ALA α-linolenic acid loading rate determination

[0063] Respectively, 0.5 g of gel sample STK-ALA, KCl-ALA and KSCN-ALA were weighed, 10 mL of n-hexane was added to each, and ultrasonic treatment was performed for 30 min, centrifugation was performed at 4000 rpm for 10 min, the supernatant was taken, and the remaining precipitate was added with 10 mL of n-hexane, and the ultrasonic treatment and centrifugation operation were repeated twice, and all the supernatants were combined, n-hexane was rotary evaporated until the solvent was completely evaporated, and linolenic acid extract was obtained, which was redissolved with anhydrous ethanol, and the volume was made to 10 mL for standby. 10 mg of linolenic acid standard was dissolved in anhydrous ethanol to prepare a 1 mg / mL linolenic acid stock solution, and standard solutions of different concentrations (such as 10 μg / mL, 20 μg / mL, 50 μg / mL, 100 μg / mL and 200 μg / mL, etc.) were prepared for drawing a standard curve, 1 mL of each standard solution was taken in a centrifuge tube, 1 mL of lipase solution (1 mg / mL, dissolved in PBS buffer) was added, and incubation was performed at 37°C water bath for 30 min, 1 mL of DTNB solution (0.005 M) was added, mixed, and color development was performed in a 37°C water bath for 15 min, and the absorbance at 412 nm was determined by ultraviolet-visible spectrophotometer, and the concentration of the standard solution was taken as the abscissa, and the absorbance (A value) was taken as the ordinate, and a standard curve was drawn. 1 mL of the extract from the previous step was taken in a centrifuge tube, 1 mL of lipase solution (1 mg / mL, dissolved in PBS buffer) was added, and incubation was performed in a 37°C water bath for 30 min, 1 mL of DTNB solution (0.005 M) was added, mixed, and color development was performed at 37°C water bath for 15 min, and the absorbance at 412 nm was determined by enzyme marker, and the concentration of linolenic acid was calculated according to the standard curve. The calculation was performed according to the following formula:

[0064]

[0065] Figure 5 The loading rate of the emulsion gel on α-linolenic acid is shown. The loading rates of KCl-ALA and KSCN-ALA are higher than that of STK-ALA. This is because the addition of carrageenan can limit the binding sites of α-linolenic acid with proteins and tannic acid. K + , SCN - can effectively interfere with the structure of the emulsion gel, promote the release of linolenic acid molecules in the emulsion to the binding sites in the gel matrix, and SCN -is a weakly coordinating anion, which can produce specific interactions with active sites in protein or tannin molecules, resulting in an increase in the loading rate of α-linolenic acid in the gel. The effect of KCl is relatively weak, and the effect of SCN - The charge neutralization of the surface of the emulsion gel and the rearrangement of the gel structure are better than those of Cl - This makes the treatment effect of the KSCN solution better.

[0066] Example 6 Determination of the rheological properties of STK-ALA, KCl-ALA and KSCN-ALA

[0067] The prepared STK-ALA, KCl-ALA and KSCN-ALA composite emulsion gel samples were respectively taken to a thin slice matching the shape of the mold, placed in the center of the cone plate, the plate was spaced 1 mm, the excess sample was scraped off with a spatula, and the dynamic viscoelasticity of the sample was determined at 25°C using a PP25 probe, the strain force was set to 0.1%, and the shear frequency range was 0.1-10 Hz.

[0068] Figure 6 The storage modulus and loss modulus of the emulsion gel loaded with α-linolenic acid are shown. The results show that the storage modulus (G') and loss modulus (G'') of KCl-ALA and KSCN-ALA are significantly higher than those of STK-ALA, indicating that both salt solutions improve the viscoelastic properties of the emulsion gel. The storage modulus is significantly higher than the loss modulus at the same frequency, which reflects the typical curve of the elastic behavior and modulus change of the hydrogel. The tangent value of the loss angle tan δ is less than 1, indicating that the elastic behavior of the system dominates, and the gel stores more energy than it loses. At this time, under the action of external force, it will show strong elasticity, the system becomes rigid, and presents a gel network similar to a solid, with high mechanical strength and shape retention ability. Among them, the storage modulus of KCl-ALA is significantly higher than that of KSCN-ALA. This indicates that KCl-ALA is more suitable for making food with high elasticity and hard texture, such as frozen food, meat gel, etc., and for making tissue engineering materials such as biological scaffolds or artificial cartilage that require strong support in the medical field.

[0069] Example 7 Determination of the thermal weight loss rate of STK-ALA, KCl-ALA and KSCN-ALA

[0070] The prepared STK-ALA, KCl-ALA and KSCN-ALA emulsion gels were respectively heated in a water bath at 30°C, 40°C, 50°C and 60°C for 30 min, then taken out and allowed to stand, and cooled to room temperature. The weight of the emulsion gel after heat treatment was accurately weighed. The following formula was used for calculation:

[0071]

[0072] In the formula: m1 is the mass of the initial measurement of the gel sample, unit g; m2 is the mass of the gel sample after heating in a water bath, unit g.

[0073] Figure 7 The thermal weight loss rate of the emulsion gel loaded with a-linolenic acid is shown. The results show that the thermal weight loss rate of STK-ALA increases significantly with the increase of temperature, indicating that its structure is less stable at high temperature and is prone to water loss. The thermal weight loss rates of KCl-ALA and KSCN-ALA are significantly lower than that of STK-ALA, and the increase with temperature is smaller. Within the entire temperature range, the thermal weight loss rate of KSCN-ALA is slightly higher than that of KCl-ALA. This is because K + and Cl - The stability of the gel network is enhanced by electrostatic interaction and ion shielding effect, reducing the structural collapse and water loss of the gel at high temperature. Compared with KCl, SCN - in KSCN can form stronger interactions with water molecules, so that part of the water in the gel network exists in the form of free water, which is more likely to escape when the temperature rises, resulting in a higher thermal weight loss rate of KSCN-ALA.

[0074] Example 8 Determination of DPPH free radical scavenging capacity of STK-ALA, KCl-ALA and KSCN-ALA

[0075] According to the instructions of the DPPH free radical scavenging kit, the sample solution was prepared. The extract was mixed with reagent I at a volume ratio of 1:19 to prepare a blank group, and the sample and reagent I were mixed at a volume ratio of 1:19 to prepare a sample group. After the solution was fully mixed, it was reacted at room temperature for 20 min in the dark. 200 μL of each was taken to the enzyme-labeled plate, and the absorbance of the blank and sample groups was tested at 515 nm using an enzyme-labeled instrument and calculated. The enzyme-labeled instrument was preheated for 30 min after starting. The DPPH free radical scavenging rate was calculated according to the following formula:

[0076]

[0077] In the formula: A 空白 is the absorbance of the blank group, and A 测定 is the absorbance of the sample group.

[0078] Figure 8DPPH radical scavenging capacity of the emulsion gels loaded with a-linolenic acid is shown. The results show that the DPPH radical scavenging capacity of KCl-ALA and KSCN-ALA increases to varying degrees compared with STK-ALA. This is because the DPPH radical scavenging capacity of the emulsion gel mainly comes from the soybean protein isolate-tannic acid complex and a-linolenic acid in the system. In STK-ALA, its internal structure is relatively dense, which limits the release of antioxidant components and the efficiency of the reaction with DPPH radicals. The ions in the salt solution change the network structure of the emulsion gel, making the gel more loose, promoting the release of antioxidant components, and the structure of the protein complex is partially rearranged under the action of salt ions, improving the antioxidant performance. Compared with KCl, SCN-in KSCN solution has stronger protein deconstruction effect, which can significantly affect the microstructure of the emulsion gel, making the active substances more easily released, so the DPPH radical scavenging capacity of KSCN-ALA is the highest.

[0079] Example 9 Determination of ABTS radical scavenging capacity of STK-ALA, KCl-ALA and KSCN-ALA

[0080] According to the instructions of the ABTS radical scavenging kit, the sample solution was prepared, the extract and the working solution were mixed according to the volume ratio of 1:19 to prepare the blank group, and the sample and the working solution were mixed according to the volume ratio of 1:19 to prepare the sample group. After the solution was fully mixed, it was left for 6 min. The absorbance of the blank group and the sample group was tested at 734 nm using a microplate reader, and the calculation was performed. The microplate reader was preheated for 30 min after starting. The ABTS radical scavenging rate was calculated according to the following formula:

[0081]

[0082] In the formula: A 空白 is the absorbance of the blank group, A 测定 is the absorbance of the sample group.

[0083] Figure 9 ABTS radical scavenging capacity of the emulsion gels loaded with a-linolenic acid is shown. The results show that the ABTS radical scavenging capacity of KCl-ALA and KSCN-ALA increases compared with STK-ALA. This is because salt ions can affect the hydrogen bonds and van der Waals forces between soybean protein isolate and tannic acid, and other non-covalent interactions, thereby changing the structure and functional properties of the complex, as well as the network structure and stability of the gel, causing the ABTS radical scavenging capacity to increase. And some salt ions may directly react with free radicals, enhancing the overall antioxidant capacity. In summary, salt solution can effectively enhance the antioxidant activity of the gel.

[0084] Example 10 Determination of in vitro digestion release rate

[0085] (1) Artificial saliva was prepared by mixing 15.1 mL of a 0.5 mol / L potassium chloride solution, 3.7 mL of a 0.5 mol / L potassium dihydrogen phosphate solution, 6.8 mL of a 1 mol / L sodium chloride solution, 0.5 mL of a 0.15 mol / L magnesium chloride hexahydrate solution, 0.06 mL of a 0.5 mol / L ammonium carbonate solution, 0.09 mL of a 6 mol / L hydrochloric acid solution, and 0.025 mL of a 0.3 mol / L calcium chloride dihydrate solution, and adjusting the pH to 7.0.

[0086] (2) Artificial gastric juice was prepared by mixing 6.9 mL of a 0.5 mol / L potassium chloride solution, 0.9 mL of a 0.5 mol / L potassium dihydrogen phosphate solution, 12.5 mL of a 1 mol / L sodium chloride solution, 11.8 mL of a 2 mol / L sodium chloride solution, 0.4 mL of a 0.15 mol / L magnesium chloride hexahydrate solution, 0.5 mL of a 0.5 mol / L ammonium carbonate solution, 1.3 mL of a 6 mol / L hydrochloric acid solution, and 0.005 mL of a 0.3 mol / L calcium chloride dihydrate solution.

[0087] (3) Artificial intestinal juice was prepared by mixing 6.8 mL of a 0.5 mol / L potassium chloride solution, 0.8 mL of a 0.5 mol / L potassium dihydrogen phosphate solution, 42.5 mL of a 1 mol / L sodium chloride solution, 9.6 mL of a 2 mol / L sodium chloride solution, 1.1 mL of a 0.15 mol / L magnesium chloride hexahydrate solution, 0.09 mL of a 6 mol / L hydrochloric acid solution, and 0.04 mL of a 0.3 mol / L calcium chloride dihydrate solution.

[0088] (4) Determination of release rate: 8 mL of the above artificial saliva was taken, 0.1 g of the gel sample STK-ALA, KCl-ALA and KSCN-ALA was added respectively, 0.025 mL of calcium chloride dihydrate solution with a molar concentration of 0.3 mol / L was added, and distilled water was added to 10 mL, and reacted for 2 min under 37°C water bath. After the oral part digestion was completed, 8 mL of the above prepared artificial gastric juice was added to the digestate, 0.005 mL of calcium chloride dihydrate solution with a molar concentration of 0.3 mol / L was added, and distilled water was added to 20 mL. The pH was adjusted to 3.0, 13.3 mg of pepsin was added, and fully reacted for 2 h in a 37°C water bath shaker. During the reaction process, 2 mL of sample was taken at 30, 60, 90 and 120 min respectively. The sample was immediately frozen and inactivated after the reaction was completed, and the sample taken at each time during the digestion process was also frozen and inactivated. After the gastric digestion was completed, 8 mL of the above prepared artificial intestinal juice was added to the remaining 10 mL of the gastric digestate, 0.02 mL of calcium chloride dihydrate solution with a molar concentration of 0.3 mol / L and 150 mg of cholic acid were added, distilled water was added to 20 mL, the pH was adjusted to 7.0, 0.1 mL of 2000 U / mL pancrelipase solution and 8 mg of trypsin were added, and fully reacted for 2 h in a 37°C water bath shaker. During the reaction process, 2 mL of sample was taken at 30, 60, 90 and 120 min respectively. The sample was immediately frozen and inactivated after the reaction was completed, and the sample taken at each time during the digestion process was also frozen and inactivated. After the above sample was restored to room temperature (25°C), an equal volume of 15% trichloroacetic acid was added, and centrifuged at 10000 rpm for 10 min, and the linolenic acid content of the supernatant was determined. The in vitro release rate was calculated according to the following formula:

[0089]

[0090] Figure 10 The release rate curve of α-linolenic acid in the emulsion gel in the gastrointestinal tract is shown. The combination of proteins and small molecule organic matters can affect the microstructure of proteins, and salt solution can also affect the network structure and internal forces of the gel, thereby affecting the digestion rate of linolenic acid. The results show that compared with STK-ALA, the release rate of KCl-ALA and KSCN-ALA in the stomach is lower, which indicates that KCl-ALA and KSCN-ALA can more effectively protect α-linolenic acid, avoid its decomposition under the influence of the stomach environment, and promote the release of linolenic acid in the intestine.

[0091] Based on the above experimental results, the following conclusions are drawn:

[0092] Through the test results of the loading rate, it is shown that the salt solution KCl and KSCN can change the structure of the emulsion gel, promote the release of the alpha-linolenic acid molecules in the emulsion to the binding sites in the gel matrix, and improve the loading rate of the alpha-linolenic acid.

[0093] Through the rheological results, it is shown that the emulsion gel will exhibit strong elasticity under external force, present a solid-like gel network, have high mechanical strength and shape retention capacity, and be suitable for making food with high elasticity and hard texture.

[0094] Through the test results of the thermal weight loss rate, it is shown that the thermal stability of the emulsion gel modified by the salt solution is significantly increased, and the structure collapse and water loss of the gel at high temperature are reduced.

[0095] Through the test results of the antioxidant property, it is shown that the ions in the salt solution can promote the release of the alpha-linolenic acid in the emulsion gel and improve the antioxidant property.

[0096] Through the test results of the in-vitro digestion simulation, it is shown that the emulsion gel can better protect the alpha-linolenic acid in the stomach environment, so that the alpha-linolenic acid can reach the intestine for release.

[0097] The above only describes certain exemplary embodiments of the present application in a descriptive manner, and it is needless to say that the described embodiments can be modified in various ways without departing from the spirit and scope of the present application for those skilled in the art. Therefore, the above figures and description are illustrative in nature and should not be understood as limiting the scope of protection of the claims of the present application.

Claims

1. A method for preparing a composite emulsion gel loaded with α-linolenic acid, characterized in that: The following steps are involved: S1. Weigh soy protein isolate powder and dissolve it in distilled water to a mass concentration of 20 mg / mL, and stir magnetically for 2 hours; weigh tannic acid powder and dissolve it in distilled water to a mass concentration of 3.4 mg / mL, and stir magnetically for 1 hour; mix equal volumes of the soy protein isolate solution and the tannic acid solution to obtain a soy protein isolate-tannic acid composite solution; S2. Adding α-linolenic acid to the prepared soy protein isolate-tannic acid composite solution at a volume ratio of α-linolenic acid to the soy protein isolate-tannic acid composite solution of 1:15, and treating the mixture with a high-speed shearing homogenizer at 12,000 rpm for 90 seconds to obtain a composite emulsion loaded with α-linolenic acid; S3. Add carrageenan powder to the composite emulsion under magnetic stirring at 60° C. to a mass concentration of 1%, stir evenly, and allow to stand to obtain an emulsion gel; S4. Weigh KSCN powder and dissolve it in distilled water to a mass concentration of 100 mg / mL. After it is completely dissolved, soak the prepared emulsion gel in a KSCN salt solution and let it stand overnight at 4°C to obtain a composite emulsion gel loaded with α-linolenic acid.

2. A composite emulsion gel loaded with α-linolenic acid, characterized in that: The method according to claim 1 is used to make the 3. Use of the composite emulsion gel loaded with α-linolenic acid according to claim 2 in the preparation of protein-based medical dressings or functional foods.

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