A method for preparing a fat substitute with controllable rheological properties and applications thereof

Abstract

The application belongs to the technical field of food processing, and discloses a preparation method and application of a fat substitute with controllable rheological properties.The application provides a preparation method of a fat substitute with controllable rheological properties, in which long-chain alkanoic acid and a chitosan solution are reacted to obtain hydrophobically modified chitosan; then the hydrophobically modified chitosan microgel is prepared by using a sodium alginate solution; and finally, the lipid is added, and homogenization is performed to obtain an oil-in-water emulsion fat substitute. The oil-in-water emulsion fat substitute has good stability, can be applied to food processing as a fat substitute, and has good fat replacement effect.

Description

Technical Field

[0001] This invention belongs to the field of food processing technology, specifically relating to a method for preparing and applying a fat substitute with controllable rheological properties. Background Technology

[0002] Meat products, as an important food ingredient, not only provide the human body with high-quality protein, fat, vitamins, and minerals, but also, through processing, solid fats provide consumers with ideal taste, texture, flavor, and nutrition. However, these solid fats contain large amounts of saturated fatty acids and trans fatty acids, and long-term excessive intake can pose significant threats to consumers' health, such as coronary heart disease, cardiovascular disease, atherosclerosis, type II diabetes, and obesity.

[0003] To replace fat in meat products, many researchers have used proteins, polysaccharides, and other materials to create hydrogels and other fat substitutes. However, these hydrogels, lacking oil, significantly impact food quality during application. Furthermore, most emulsions are liquids with limited fluidity, exhibiting poor rheological properties and failing to effectively simulate solid fats. Therefore, this invention aims to construct a semi-solid fat with controllable rheological properties. Summary of the Invention

[0004] [Technical Issues] The present invention aims to solve the problem that current emulsions have a certain degree of fluidity and cannot effectively simulate solid fats.

[0005] [Technical Solution] To address the aforementioned problems, this invention provides a method for preparing a fat substitute with controllable rheological properties. The constructed oil-in-water emulsion exhibits good stability and can be used as a fat substitute in food processing, demonstrating a good fat substitution effect. The method specifically includes the following steps: (1) Preparation of hydrophobic modified chitosan: Chitosan (CS) and glacial acetic acid are dissolved in water and magnetically stirred to completely dissolve the chitosan to obtain a chitosan solution; long-chain alkyl acid, N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) are dissolved in ethanol and magnetically stirred in an ice bath for 1-2 h to activate the long-chain alkyl acid; the activated long-chain alkyl acid is then added to the chitosan solution during the stirring process and reacted for 12-36 h. After the reaction is completed, the pH is adjusted to 8-10 with NaOH solution and then stored at 4℃ for 18-27 h. Then, the precipitate is collected by centrifugation, washed, dried, and the dried sample is ground into powder to obtain hydrophobic modified chitosan powder. (2) Preparation of hydrophobic modified chitosan microgel: Dissolve the hydrophobic modified chitosan powder from step (1) in an aqueous solution of acetic acid with a concentration of 0.5% and stir to obtain a hydrophobic modified chitosan solution; at the same time, dissolve sodium alginate in water; add the prepared sodium alginate solution to the above hydrophobic modified chitosan solution to prepare hydrophobic modified chitosan microgel; (3) Preparation of oil-in-water emulsion fat substitute: lipids were added to hydrophobically modified chitosan microgel and homogenized to obtain oil-in-water emulsion fat substitute.

[0006] In one embodiment of the present invention, the amount of glacial acetic acid added in step (1) is 0.2-1% of the water volume, preferably 0.3-0.8%; the concentration of chitosan aqueous solution (m / v) is 8-20 g / L, preferably 10-15 g / L.

[0007] In one embodiment of the present invention, the long-chain alkyl acid mentioned in step (1) is 12-18C alkyl acid; the molar ratio of chitosan to long-chain alkyl acid is 1:0.2 – 1:1; and the molar ratio of NHS, EDC and long-chain alkyl acid is 1:1:1.

[0008] In one embodiment of the present invention, the centrifugation mentioned in step (1) refers to a centrifugal force of 4000-7000g and a centrifugation time of 15-25min.

[0009] In one embodiment of the present invention, the drying in step (1) is carried out in a vacuum drying oven.

[0010] In one embodiment of the present invention, the concentration of the hydrophobic modified chitosan solution in step (2) is 4-6 g / L.

[0011] In one embodiment of the present invention, the concentration of sodium alginate solution in step (2) is the same as the concentration of hydrophobic modified chitosan solution, which is 4-6 g / L.

[0012] In one embodiment of the present invention, the stirring speed in step (2) is 4000-6000 rpm; wherein the volume ratio of the hydrophobic modified chitosan solution to the sodium alginate solution is 1:0 - 1:2, preferably 1:0.2 - 1:1.

[0013] In one embodiment of the present invention, in step (3), the lipids include, but are not limited to, one or more of soybean oil, peanut oil, flaxseed oil, and fish oil; the lipid mass fraction is 30-80%, preferably 60-80%; the homogenization speed is preferably 10000-15000 rpm; and the homogenization time is preferably 2-5 min.

[0014] The application of the oil-in-water fat substitute of this invention in the food industry.

[0015] Beneficial effects: (1) The present invention uses vegetable oil instead of animal fat, which can enrich the fatty acid composition of the product and avoid excessive intake of saturated fatty acids; (2) By constructing hydrophobically modified chitosan microgel, the present invention improves the emulsifying properties and viscosity, so that the prepared emulsion can form a stable solid-like emulsion with an oil content of 60-80% and has different rheological properties, and can be used as a fat substitute in different scenarios. (3) The present invention utilizes chitosan modified with long-chain alkyl acids to improve the hydrophobicity of chitosan, thereby enhancing the emulsifying properties of the emulsion and playing an important role in the formation of chitosan-based oil-in-water emulsions. (4) In this invention, chitosan is hydrophobically modified and crosslinked with sodium alginate through ionic interactions to form a supramolecular micelle structure, which facilitates the subsequent preparation of a stable emulsion. The fat substitute obtained after adding 60-80% oil and homogenizing has good storage stability. Attached Figure Description

[0016] Figure 1 A) Physical images, optical microscope images, and cold field scanning electron microscope images of oil-in-water emulsions using hydrophobically modified chitosan microgel as emulsifier in Examples 1-2; B) Optical microscope images of oil-in-water emulsions with different oil loadings using CS-LA (1:0.5) directly as emulsifier in Comparative Example 5; C) Optical microscope images of oil-in-water emulsions with different oil loadings using hydrophobically modified chitosan microgel as emulsifier in Examples 1-2; D) Cold field scanning electron microscope images of oil-in-water emulsions with different oil loadings using hydrophobically modified chitosan microgel as emulsifier in Examples 1-2. Figure 2 Applications of the fat substitutes prepared in Examples 1-2 in different scenarios: A, Application of 60% oil-loaded fat substitute with commercial salad dressing; B, Shaping ability of 70% oil-loaded fat substitute after replacing butter, with R50 and R60 replacing 50% and 60% of commercial butter, respectively; C, Application of 80% oil-loaded fat substitute replacing pork back fat in fish cake, with R0, R25, R50, R75, and R100 replacing 0%, 25%, 50%, 75%, and 100% of pork back fat in the emulsion, respectively. Figure 3 Rheological properties of hydrophobically modified chitosan emulsion fat substitutes with different oil loadings in Examples 1-2: A, viscosity; B, storage modulus and loss modulus at different frequencies; Figure 4 Examples 1-2: Physical images of oil-in-water emulsions with different oil loadings stored at room temperature for 2 months; Figure 5Example 1, Comparative Examples 3-4: Interfacial tension and viscosity test diagrams of chitosan microgel solutions; A, Interfacial tension diagram of chitosan microgel solutions; B, Viscosity test diagram of chitosan microgel solutions. Detailed Implementation

[0017] Contact angle determination: The contact angles of chitosan and hydrophobically modified powder samples were measured using a contact angle meter (DSA25, Kruss, Germany) via the droplet method. CS and h-CS powder samples were prepared into thin films using a tablet press. 10 μL of deionized water was dropped onto the thin film, the image was recorded, and the angle between the tangent and the cross-section was calculated as the contact angle of the sample.

[0018] Interfacial tension was measured at the oil-water interface using a surface tension meter (K100, Kruss, Germany) to determine the interfacial tension between chitosan and a 5 g / L hydrophobically modified chitosan microgel solution. First, a platinum plate was immersed in a test tube containing 10 mL of sample to a depth of 2 mm. Then, 30 g of linseed oil was gradually added along the inner wall of the test tube to form an oil-water interface. The interfacial tension was continuously recorded at 25°C for 1 h.

[0019] Rheological properties: The apparent viscosity of the hydrophobically modified chitosan microgels and emulsions was characterized using a rheometer (Rheometics Discovery HR-2, TA, New Castle, USA). The experimental setup employed a plate-to-plate structure, utilizing a gap between plates with a diameter of 40 mm and a diameter of 500 μm. The shear rate range during viscosity testing was 0.01–100 s⁻¹. -1 The storage modulus (G') and loss modulus (G”) of the emulsion were determined by oscillation mode with a scanning frequency range of 0.1 ~ 100 rad / s.

[0020] Microstructure: Fresh emulsion was dropped onto a glass slide and capped. The sample was observed under a 400x microscope (BX51, Olympus Corporation, Tokyo, Japan), and images were captured for documentation. The microstructure of the emulsion was observed using a cryo-scanning electron microscope (cryo-SEM: cryo-transfer system PP3010T, Quorum, UK) paired with a high-resolution field emission scanning electron microscope (FE-SEM) (Regulus 8100, Hitachi, Tokyo, Japan). In short, 2.0 μL of the emulsion was frozen in liquid nitrogen, transferred to a cryostat, a cross-section was cut, and then sublimated at -80°C for 20 min. The sample was sputtered at 10 mA for 60 s and then observed at 3 kV.

[0021] Texture characteristics of fish cake: Freshly steamed fish cake was cut into 2 × 2 × 2 cm cubes and analyzed using a texture analyzer (TA-XT Plus, Godalming, UK). The microstructure of the fish cake was observed using cryo-scanning electron microscopy.

[0022] The present invention will be further explained and described below with reference to specific embodiments.

[0023] Example 1 (1) Preparation of hydrophobically modified chitosan 2.4 g of chitosan (CS) and 1 mL of glacial acetic acid were placed in 200 mL of water and magnetically stirred for 2 h, followed by sonication for 10 min. Lauric acid (LA), N-hydroxysuccinimide (NHS) and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were added to ethanol and magnetically stirred in an ice bath for 2 h. The mixture was then gradually added to the chitosan solution under magnetic stirring and reacted for 24 h (the molar ratio of CS, LA, NHS, and EDC was 2:1:1:1). The pH of the solution was adjusted to 9 using NaOH solution (2 mol / L), and the final solution was stored at 4 °C for 24 h. After this step, the solution was centrifuged at 5000 g for 20 min. The precipitate was washed three times with distilled water to remove NaOH, and then washed three times with ethanol to remove unreacted alkyl acids, EDC, and NHS. Subsequently, the precipitate was dried in a vacuum drying oven to obtain hydrophobically modified chitosan. The dried sample was then ground into powder using a ball mill for subsequent use. (2) Preparation of hydrophobically modified chitosan microgels The dried hydrophobic modified chitosan powder was dissolved in 0.5% acetic acid water to obtain a hydrophobic modified chitosan solution (CS-LA) with a concentration of 5 g / L; a sodium alginate solution (Alg) with a concentration of 5 g / L was prepared; the sodium alginate solution was added to the hydrophobic modified chitosan solution stirred at 5000 rpm (the ratio of hydrophobic modified chitosan solution to sodium alginate solution was 2:1 (v / v)) to obtain hydrophobic modified chitosan microgels; (3) Preparation of oil-in-water emulsion fat substitutes Add 60% flaxseed oil to the hydrophobically modified chitosan microgel and homogenize at 12,000 rpm for 3 min using an IKA T25 homogenizer to obtain an oil-in-water emulsion fat substitute with an oil loading of 60%.

[0024] Example 2 The preparation method of Example 1 is the same, except that 60% flaxseed oil is replaced with 30%, 40%, 50%, 70%, or 80% flaxseed oil by mass.

[0025] Figure 1Images A, C, and D in the figures are photographs, optical microscope images, and cold field scanning electron microscope images of the oil-in-water emulsion fat substitutes with different oil loadings prepared in Examples 1 and 2, respectively. Figure 1 The prepared oil-in-water emulsion fat substitute exhibits semi-solid properties when the lipid content is greater than or equal to 60%, allowing it to be inverted in a bottle and mimicking the appearance of fat. Microscopic and cold field electron microscopy images show that the emulsion particle size is 3-8 micrometers.

[0026] like Figure 2 A. The oil-in-water emulsion fat substitute with a 60% oil loading prepared in Example 1 was placed on a slice of bread, and its spreadability was evaluated. The figure shows that the spreadability of the 60% oil-in-water emulsion prepared in this invention as a fat substitute is not significantly different from that of commercial salad dressings.

[0027] The oil-in-water emulsion with a 70% oil loading from Example 2 was used to replace butter in a pre-formed cylindrical mold and extruded to evaluate its plasticity. R50 and R60 represent the emulsion replacing 50% and 60% of commercial butter, respectively. Figure 2 As shown in Figure B, the oil-in-water emulsion fat substitute of the present invention, with a 70% oil content, replaces 50% of the heavy cream. When placed in a cylindrical mold, it exhibits good shape retention and remains unchanged for 3 days. However, when replacing 60% of the cream, the cylinder shows significant collapse. Therefore, the 70% oil-in-water emulsion fat substitute prepared in this invention can replace 50% of the cream while maintaining its shape retention.

[0028] Rheological properties of oil-in-water emulsion fat substitutes with different oil loadings in Examples 1-2 were analyzed, and the results are as follows: Figure 3 As shown in the figure, where A is the change of emulsion viscosity with shear rate, it can be seen that oil-in-water emulsions with different oil loadings all have shear-thinning properties, and the viscosity of the emulsion increases with the increase of oil loading. Figure 3 B is the modulus versus frequency graph. It can be seen that when the oil load is 30%-50%, the storage modulus of the emulsion is consistently less than the loss modulus. Therefore, superficially... Figure 1 As shown, emulsions with 30%-50% oil loading are flowable liquids. However, emulsions with 60-80% oil loading consistently exhibit a storage modulus greater than their loss modulus, and appear to be semi-solid. This indicates that the hydrophobically modified chitosan microgels used in this invention can construct emulsions with 60-80% oil loading as fat substitutes. Furthermore, the controllability of their rheological properties allows for application in various scenarios.

[0029] The fat substitutes constructed in Examples 1-2 of this invention were left at room temperature for 2 months, and their morphology was observed. Figure 4 As shown: Compared to fresh emulsion ( Figure 1(A) The oil-in-water emulsion fat substitute with an oil loading of 60-80% showed no significant change. The fat substitute of this invention exhibits good storage stability.

[0030] Fish cake was prepared using fish paste (60%), pork back fat (20%), water (10%), corn starch (9%), and salt (1%). The pork back fat was replaced with an 80% oil-in-water emulsion prepared in Example 2. After thorough mixing, the mixture was placed in a mold and steamed for 20 minutes. R0, R25, R50, R75, and R100 represent the 80% oil-in-water emulsion replacing 0%, 25%, 50%, 75%, and 100% of the pork back fat, respectively. Figure 2 The results in section C show that there was no significant difference in the surface and cross-section of fish cakes made with emulsion fat substitutes for pork back fat. Cold field electron microscopy images show that the void structure significantly increased after substitution rates of 75% and 100%. The fish cakes were evaluated using a texture analyzer, and the test results are shown in Table 1. Table 1. Texture properties of fish cakes prepared using an 80% oil-loading emulsion as a fat substitute for different proportions of pork back fat.

[0031] Table 1 shows that when the oil-in-water emulsion with an 80% oil loading was used as a fat substitute in fish cake, the texture of the fish cake did not change significantly when the substitution rate was 25% and 50%. However, when the substitution rate was 75% and 100%, the hardness, adhesiveness, and chewiness of the fish cake decreased slightly. Therefore, the oil-in-water emulsion with an 80% oil loading prepared in this invention can be used as a fat substitute in fish cake products.

[0032] Comparative Example 1 Compared with Example 1, the only difference is that different chain lengths of long-chain alkyl acids were grafted, and myristic acid (tetradecanoic acid, MA), palmitic acid (hexadecanoic acid, PA), and stearic acid (octadecanoic acid, SA) were used instead of lauric acid.

[0033] (1) Preparation of hydrophobically modified chitosan 2.4 g of chitosan (CS) and 1 mL of glacial acetic acid were placed in 200 mL of water and magnetically stirred for 2 h, followed by sonication for 10 min. Myristic acid (tetradecanoic acid, MA), palmitic acid (hexadecanoic acid, PA), stearic acid (octadecanoic acid, SA), N-hydroxysuccinimide (NHS), and 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) were added to ethanol and magnetically stirred in an ice bath for 2 h. These were then gradually added to the chitosan solution under magnetic stirring, and the reaction was allowed to proceed for 24 h (where the molar ratios of CS:LA, CS:MA, CS:PA, ​​and CS:SA were all 1:2). The pH of the solution was adjusted to 9 using NaOH solution (2 mol / L), and the final solution was stored at 4 °C for 24 h. After this step, the solution was centrifuged at 5000 g for 20 seconds. The precipitate was washed three times with distilled water to remove NaOH, and then washed three times with ethanol to remove unreacted alkyl acids, EDC and NHS. Subsequently, the precipitate was dried in a vacuum drying oven to obtain hydrophobically modified chitosan. The dried sample was ground into powder using a ball mill for subsequent use. (2) Preparation of hydrophobically modified chitosan microgels The dried hydrophobic modified chitosan powder was dissolved in 0.5% acetic acid water to obtain a hydrophobic modified chitosan solution (CS-LA) with a concentration of 5 g / L; a sodium alginate solution (Alg) with a concentration of 5 g / L was prepared; the sodium alginate solution was added to the hydrophobic modified chitosan solution stirred at 5000 rpm (the ratio of hydrophobic modified chitosan solution to sodium alginate solution was 1:0.5 (v / v)) to obtain hydrophobic modified chitosan microgels; (3) Preparation of oil-in-water emulsion fat substitutes 60% flaxseed oil was added to the hydrophobically modified chitosan microgel, and homogenized at 12,000 rpm for 3 min using an IKA T25 homogenizer to obtain an oil-in-water emulsion fat substitute with an oil loading of 60%. The contact angle of chitosan was tested, and the results are shown in Table 2 below.

[0034] Comparative Example 2 Compared to Example 1, the only difference was the adjustment of the molar ratio of chitosan and lauric acid. The contact angle of chitosan was tested, and the results are shown in Table 2 below: Table 2 Effect of hydrophobic modification on the contact angle of chitosan

[0035] As shown in Table 2, chitosan itself has poor hydrophobicity, with a contact angle of 72.85°, which significantly affects its emulsifying activity and is not conducive to the subsequent preparation of fat substitutes. Comparative Example 1 modified chitosan with alkyl acids of different carbon chain lengths, finding that grafting lauric acid resulted in the highest hydrophobicity (95.55°). Furthermore, in Example 1, the largest contact angle (105.31°) was observed when chitosan and lauric acid were grafted at a molar ratio of 1:0.5. Therefore, the optimal modification method under these conditions was determined to be a 1:0.5 grafting ratio of chitosan and lauric acid.

[0036] Comparative Example 3 Compared with Example 1, the difference is that the emulsion was prepared directly using hydrophobically modified chitosan, without constructing a microgel with sodium alginate.

[0037] (1) Preparation of hydrophobically modified chitosan 2.4 g of chitosan and 1 mL of glacial acetic acid were placed in 200 mL of water and magnetically stirred for 2 h, followed by sonication for 10 min. Lauric acid, NHS, and EDC were added to ethanol and magnetically stirred in an ice bath for 2 h. The mixture was then gradually added to the chitosan solution under magnetic stirring and reacted for 24 h (the molar ratio of CS, LA, NHS, and EDC was 2:1:1:1). The pH of the solution was adjusted to 9 using NaOH solution (2 mol / L). The final solution was stored at 4 °C for 24 h. After this step, the solution was centrifuged at 5000 g for 20 min. The precipitate was washed three times with distilled water to remove NaOH, and then washed three times with ethanol to remove unreacted alkyl acids, EDC, and NHS. Subsequently, the precipitate was dried in a vacuum drying oven to obtain hydrophobically modified chitosan. The dried sample was then ground into powder using a ball mill for subsequent use.

[0038] (2) Preparation of oil-in-water emulsion fat substitutes Hydrophobically modified chitosan powder was dissolved in a 0.5% aqueous acetic acid solution, and then 60% flaxseed oil was added. The mixture was homogenized at 12,000 rpm for 3 minutes using an IKA T25 homogenizer to obtain an emulsion with an oil loading of 60%.

[0039] Comparative Example 4 Compared with Example 1, the difference lies in changing the volume ratio of hydrophobically modified chitosan solution (CS-LA) and sodium alginate solution (Alg) in step (2), which are 1:0.2, 1:1, and 1:2, respectively.

[0040] Interfacial tension and viscosity were tested on the chitosan microgel solutions of Example 1 and Comparative Example 4. For emulsifiers, lower oil-water interfacial tension generally results in better emulsion stability. Furthermore, viscosity is a crucial indicator in this invention for constructing fatty acid substitutes with a semi-solid structure. Figure 5As shown, compared to Comparative Example 3 without sodium alginate, the addition of sodium alginate significantly reduced the interfacial tension between oil and water while increasing the solution viscosity. Furthermore, when the ratio of hydrophobically modified chitosan solution to sodium alginate solution was 1:0.5, it exhibited relatively low interfacial tension while maintaining high viscosity (viscosity of 2.41 Pa·s at a shear rate of 0.01 1 / s). Therefore, the CS-LA to Alg ratio of 1:0.5 used in this invention exhibits both low surface tension and high viscosity.

[0041] Comparative Example 5 Compared with Comparative Example 3, the only difference was that 60% flaxseed oil was replaced with 30%, 40%, 50%, 70%, and 80% flaxseed oil by mass.

[0042] (1) Preparation of hydrophobically modified chitosan 2.4 g of chitosan and 1 mL of glacial acetic acid were placed in 200 mL of water and magnetically stirred for 2 h, followed by sonication for 10 min. Lauric acid, NHS, and EDC were added to ethanol and magnetically stirred in an ice bath for 2 h. The mixture was then gradually added to the chitosan solution under magnetic stirring and reacted for 24 h (the molar ratio of CS, LA, NHS, and EDC was 2:1:1:1). The pH of the solution was adjusted to 9 using NaOH solution (2 mol / L), and the final solution was stored at 4 °C for 24 h. After this step, the solution was centrifuged at 5000 g for 20 min. The precipitate was washed three times with distilled water to remove NaOH, and then washed three times with ethanol to remove unreacted alkyl acids, EDC, and NHS. Subsequently, the precipitate was dried in a vacuum drying oven to obtain hydrophobically modified chitosan. The dried sample was then ground into powder using a ball mill for subsequent use.

[0043] (2) Preparation of oil-in-water emulsion fat substitutes Hydrophobically modified chitosan powder was dissolved in a 0.5% aqueous acetic acid solution, and then 30%, 40%, 50%, 70%, and 80% flaxseed oil by mass fraction were added respectively. The mixture was homogenized at 12,000 rpm for 3 minutes using an IKA T25 homogenizer to obtain oil-in-water emulsion fat substitutes with an oil loading of 30%-80%.

[0044] Figure 1 B is a micrograph of the oil-in-water emulsion fat substitutes with different oil loadings constructed in Comparative Example 5 using CS-LA (1:0.5) as the emulsifier. As can be seen from the figure, compared to Examples 1 and 2 (…),… Figure 1 C), the emulsion prepared in Comparative Example 5 had a larger particle size, and could not construct a stable semi-solid fat substitute when the oil loading was 70% and 80%.

[0045] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing an oil-in-water fat substitute, characterized in that, The steps include the following: (1) Preparation of hydrophobic modified chitosan: Chitosan and glacial acetic acid are dissolved in water and magnetically stirred to completely dissolve the chitosan to obtain a chitosan solution; long-chain alkyl acid, N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide are dissolved in ethanol and magnetically stirred in an ice bath for 1-2 h. After stirring, the mixture is added to the above chitosan solution and reacted for 12-36 h. After the reaction, the pH is adjusted to 8-10 with NaOH solution and then stored at 4℃ for 18-27 h. The precipitate is then centrifuged, collected, washed and dried to obtain hydrophobic modified chitosan, which is then ground into powder; the long-chain alkyl acid is 12-18C alkyl acid; the molar ratio of chitosan to long-chain alkyl acid is 1:0.5-1:1; (2) Preparation of hydrophobic modified chitosan microgel: Dissolve the hydrophobic modified chitosan powder from step (1) in a 0.5% aqueous acetic acid solution and stir to obtain a hydrophobic modified chitosan solution; at the same time, dissolve sodium alginate in water to obtain a sodium alginate solution; add the prepared sodium alginate solution to the above hydrophobic modified chitosan solution to prepare hydrophobic modified chitosan microgel; the volume ratio of hydrophobic modified chitosan solution to sodium alginate solution is 1:0.2 - 1:2; (3) Preparation of oil-in-water emulsion fat substitute: lipids were added to hydrophobically modified chitosan microgels and homogenized to obtain oil-in-water emulsion fat substitute; the lipid mass fraction was 60-80%.

2. The method for preparing an oil-in-water fat substitute according to claim 1, characterized in that, In step (1), the amount of glacial acetic acid added is 0.2-1% of the water volume; the concentration of chitosan aqueous solution is 8-20 g / L.

3. The method for preparing an oil-in-water fat substitute according to claim 1, characterized in that, In step (1), the amount of glacial acetic acid added is 0.3-0.8% of the water volume; the concentration of chitosan aqueous solution is 10-15 g / L.

4. The method for preparing an oil-in-water fat substitute according to claim 1, characterized in that, In step (1), the molar ratio of N-hydroxysuccinimide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and long-chain alkyl acid is 1:1:1; the centrifugation refers to a centrifugal force of 4000-7000g and a centrifugation time of 15-25min; the drying is carried out in a vacuum drying oven.

5. The method for preparing an oil-in-water fat substitute according to claim 1, characterized in that, In step (2), the concentration of hydrophobically modified chitosan is 4-6 g / L.

6. The method for preparing an oil-in-water fat substitute according to claim 1, characterized in that, In step (2), the concentration of sodium alginate solution is the same as that of hydrophobic modified chitosan solution.

7. The method for preparing an oil-in-water fat substitute according to claim 1, characterized in that, In step (2), the stirring speed is 4000-6000 rpm.

8. The method for preparing an oil-in-water fat substitute according to claim 1, characterized in that, In step (3), the lipids include one or more of soybean oil, peanut oil, flaxseed oil, and fish oil; the homogenization speed is 10,000-15,000 rpm; and the homogenization time is 2-5 min.

9. The oil-in-water fat substitute prepared by any one of claims 1-8.

10. The application of the oil-in-water fat substitute of claim 9 in the food industry.

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