Preparation method of walnut oil body oil gel

Abstract

The invention provides oil gel and a preparation method thereof, and belongs to the technical field of food processing. Comprising the following steps: S1, obtaining a walnut oil body; s2, preparing a walnut oil body emulsion; s3, preparing a chitosan solution; s4, preparing a vanillin solution; s5, preparing a walnut oil body emulsion coated with chitosan; s6, preparing a cross-linked walnut oil body emulsion; and S7, preparing the walnut oil body oil gel. The walnut oil body used in the invention contains a large amount of unsaturated fatty acid beneficial to a human body, the chitosan and the vanillin can protect the unsaturated fatty acid from being oxidized, and the unsaturated fatty acid and the chitosan jointly form a stable gel structure in the oil gel; unsaturated fatty acid can influence the release rate of vanillin in oil gel and control the durability and strength of flavor in food; the prepared oleogel is high in oil holdup and good in thermal stability, mechanical strength and structural stability, meanwhile, the lipid oxidation process of the oleogel can be effectively slowed down, and the application of the oleogel in functional food is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and particularly relates to a method for preparing walnut oil body oil gel. Background Art

[0002] Solid fats can be used in food processing to give foods special flavors, textures, and other functional properties. It is commonly used in the production and processing of baked goods, chocolate, candy, sauces, ice cream, and other foods. Currently, solid fats mainly come from animal fats, fractionated vegetable palm oils, or hydrogenated vegetable oils containing high levels of saturated or trans fatty acids. These fatty acids can lead to various chronic diseases. Therefore, the field of food processing technology urgently needs to explore an innovative way to create healthier food ingredients by reducing or replacing saturated fats with vegetable oils. Recently, more and more studies have shown that oil gelation is a viable strategy. Chitosan has become a potential choice for formulating more beneficial oil gels due to its biodegradable, biocompatible, bioadhesive, non-toxic, and hydrophilic properties. However, the low oil solubility of chitosan limits its application in the preparation of oil gels. Therefore, in order to promote the formation of an appropriate three-dimensional network suitable for oil retention, an auxiliary cross-linking agent needs to be added to overcome this shortcoming. Vanillin contains aldehyde groups and is widely found in vanilla pods and beets, so it can act as a bio-based cross-linking agent. Walnut (Juglans regia L.) is the most widely grown nut in my country, accounting for more than half of the world's total walnut production. Walnuts have high nutritional value and are rich in protein, bioactive compounds and a large number of lipids that are beneficial to health. The lipid content is 60-70%, mainly composed of unsaturated fatty acids. In walnut kernels, lipids accumulate in oil bodies in the form of triglycerides. Oil bodies have a stable structure with a core of triacylglycerols and a surface composed of oil body-associated proteins (oleosin, caleosin, steroleosin and exogenous proteins) and a monolayer phospholipid membrane. The surface layer composed of phospholipids and proteins in the oil body protects the lipid core from severe environmental stresses, including temperature fluctuations, humidity changes and the presence of oxidants. To date, walnut oil bodies have become a hot topic of research due to their higher unsaturated fatty acid content and their wide application in food, edible films, cosmetics and pharmaceuticals. Therefore, in view of the current phenomenon that solid fats contain a large amount of unhealthy lipids, modifying walnut oil bodies using chitosan and vanillin may be an effective way to change their functions and promote their health properties. Summary of the invention

[0003] Technical problems to be solved: In view of the above technical problems, the purpose of the present invention is to provide a method for preparing walnut oil body oil gel, and the chitosan-coated walnut oil body emulsion and vanillin are cross-linked to prepare the walnut oil body oil gel. Vanillin is coated in the chitosan-coated walnut oil body emulsion. On the one hand, the release rate of vanillin can be controlled to achieve a sustained release effect. On the other hand, the vanillin molecule contains hydroxyl groups, which can form hydrogen bonds with the amino and hydroxyl groups in the chitosan molecules. This interaction helps to fix the vanillin in the chitosan-coated walnut oil body emulsion. The present invention converts the oil body in the emulsion state into an oil gel in a solid state, while keeping the oil body structure intact, and the obtained oil gel has a high oil retention rate and stable physical and chemical properties, so as to improve the application of the walnut oil body oil gel in functional foods.

[0004] Technical solution: A method for preparing walnut oil body oil gel, comprising the following steps: S1. Obtaining oil bodies: Walnut kernels were slurried in a blender, distilled water was added to the walnut slurry, and the slurry was ground with a colloid mill, filtered with degreased gauze, and then centrifuged to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: Take walnut oil body, add it into phosphate buffer, and stir for 30 to 40 minutes; S3. Preparation of chitosan solution: Take chitosan powder, dissolve it in acetic acid solution, and stir at 40-50°C for 100-120min; S4. Preparation of vanillin solution: taking vanillin crystals and dissolving them in anhydrous ethanol to obtain a vanillin solution; S5. Preparation of chitosan-coated walnut oil body emulsion: adding chitosan solution dropwise to the walnut oil body emulsion, stirring for 20 to 30 minutes after the addition, and adjusting the pH of the emulsion to 6.0 to 7.0 using NaOH or HCl; S6. Preparation of cross-linked walnut oil body emulsion: adding the vanillin solution dropwise to the chitosan-coated walnut oil body emulsion, stirring for 100 to 120 minutes after the addition is completed; S7. Preparation of oil gel: freeze-dry the cross-linked walnut oil body emulsion, and then high-speed shear to obtain walnut oil body oil gel. Further, in step S1, the walnut kernel should be free of endocarp, the solid-liquid ratio of walnut kernel to distilled water is 1:(5-7), and the centrifugal conditions are: temperature 20-25°C, centrifugal force 1000-1200g, and time 20-30min. Furthermore, in step S2, the pH of the phosphate buffer is 6.0-7.0, and the concentration of the oil emulsion is 0.6-0.9 g / mL. Furthermore, in step S3, the deacetylation degree of chitosan is 95%-100%, and the concentration of chitosan is 0.02-0.05 g / mL. Furthermore, in step S4, the concentration of the vanillin solution is 0.3-0.6 g / mL. Furthermore, in step S5, the mass of the chitosan solution added to the oil emulsion is 1.5-2 wt%. Furthermore, in step S6, the mass of the vanillin solution added to the oil emulsion is 1.5-2 wt%. Furthermore, in step S7, the oil body emulsion is freeze-dried at -55 to -45°C and a vacuum pressure of 0.1 to 1 mBar for 48 to 55 hours, and the freeze-dried product is sheared at 1000 rpm for 2 to 5 minutes. Walnut oil body oil gel prepared by any of the preparation methods described above. Application of the walnut oil body oil gel prepared by any of the preparation methods described above in functional foods. Beneficial effects: 1. In the present invention, chitosan can delay the oxidation process of walnut oil, reduce interfacial tension at the oil-water interface, and increase the stability of the emulsion. On the other hand, chitosan molecules contain a large number of hydroxyl groups and amino groups that can be combined with fatty acid molecules in walnut oil bodies through hydrogen bonds. The amino groups of chitosan and the carboxyl groups of walnut oil bodies can form a complex through amide bonds, thereby improving the stability of the walnut oil body oil gel. Walnut oil bodies contain a variety of unsaturated fatty acids and bioactive ingredients, which can be combined with chitosan to give the complex new biological activity; 2. In the present invention, on the one hand, the vanillin has a certain lipophilicity and can be dissolved in walnut oil. This solubility enables the vanillin to be evenly distributed in the walnut oil, thereby improving the stability of the vanillin. On the other hand, the walnut oil itself has a certain nutty aroma, and the vanillin has a strong vanilla aroma. Adding the vanillin to the walnut oil body can produce a complex aroma, thereby enhancing the sensory appeal of the product. The walnut oil body contains unsaturated fatty acids, which are easily oxidized. The vanillin has a certain antioxidant property, and the addition of the vanillin helps to delay the oxidation process of the walnut oil body. 3. In the present invention, vanillin is coated in the chitosan-coated walnut oil body emulsion. On the one hand, the release rate of vanillin can be controlled to achieve a sustained release effect. On the other hand, the aldehyde group in the vanillin reacts with the amino group in the chitosan to generate an imine bond, thereby forming a stable cross-linked structure. In addition, the hydroxyl group of the vanillin can also form additional hydrogen bonds with the hydroxyl group or amino group in the chitosan chain to further promote the cross-linking effect. This cross-linking mechanism helps to fix the vanillin in the chitosan-coated walnut oil body emulsion, enhances the mechanical strength and thermal stability of the walnut oil body oil gel, and gives the walnut oil body oil gel good water barrier and antioxidant properties. 4. The walnut oil body in the present invention has a large amount of unsaturated fatty acids that are beneficial to the human body and can replace the unhealthy oil source in traditional solid fats; the chitosan and vanillin used are low in price, derived from animals and plants, and have natural and harmless characteristics; the preparation process is simple, the process is controllable, safe and environmentally friendly, the prepared oil gel has a high oil retention rate, and has good thermal stability, mechanical strength and structural stability; it provides a new perspective for the high-value application of walnut oil bodies in the production of functional foods. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The effects of Examples 1-4 and Comparative Examples 1-2 on the oil gel potential and particle size of walnut oil bodies, wherein Figure A shows the effects of Examples 1-4 and Comparative Examples 1-2 on the oil gel potential of walnut oil bodies, and Figure B shows the effects of Examples 1-4 and Comparative Examples 1-2 on the particle size of walnut oil body oil gel; Figure 2 The effects of Examples 1-4 and Comparative Examples 1-2 on the spectrum of walnut oil body oil gel, wherein Figure A shows the effects of Examples 1-4 and Comparative Examples 1-2 on the UV-visible spectrum of walnut oil body oil gel, and Figure B shows the effects of Examples 1-4 and Comparative Examples 1-2 on the fluorescence spectrum of walnut oil body oil gel; Figure 3 The effects of Examples 1-4 and Comparative Examples 1-2 on the thermal stability of walnut oil body oil gel; Figure 4 The effects of Examples 1-4 and Comparative Examples 1-2 on the visual appearance and microstructure of walnut oil body gel, wherein Figures A and B show the effects of Examples 1-4 and Comparative Examples 1-2 on the visual appearance of walnut oil body gel, and Figure C shows the effects of Examples 1-4 and Comparative Examples 1-2 on the microstructure of walnut oil body gel; Figure 5 The effects of Examples 1-4 and Comparative Examples 1-2 on the oil holding rate of walnut oil body oil gel; Figure 6 The effects of Examples 1-4 and Comparative Examples 1-2 on the texture of walnut oil body gel, wherein Figure A shows the effects of Examples 1-4 and Comparative Examples 1-2 on the hardness of walnut oil body gel, Figure B shows the effects of Examples 1-4 and Comparative Examples 1-2 on the elasticity of walnut oil body gel, Figure C shows the effects of Examples 1-4 and Comparative Examples 1-2 on the cohesiveness of walnut oil body gel, Figure D shows the effects of Examples 1-4 and Comparative Examples 1-2 on the adhesion of walnut oil body gel, Figure E shows the effects of Examples 1-4 and Comparative Examples 1-2 on the chewiness of walnut oil body gel, and Figure F shows the effects of Examples 1-4 and Comparative Examples 1-2 on the resilience of walnut oil body gel; Figure 7The effects of Examples 1-4 and Comparative Examples 1-2 on the rheological properties of walnut oil body gels, wherein Figure A is a graph showing the apparent viscosity of walnut oil body gels of Examples 1-4 and Comparative Examples 1-2 as a function of shear rate, Figure B is a graph showing the viscosity of walnut oil body gel fluids of Examples 1-4 and Comparative Examples 1-2 as a function of temperature, Figure C is a graph showing the apparent viscosity of walnut oil body gel fluids of Examples 1-4 and Comparative Examples 1-2 as a function of shear time, and Figure D is a graph showing the storage modulus and loss modulus of walnut oil body gels of Examples 1-4 and Comparative Examples 1-2 as a function of frequency; Figure 8 The effects of Examples 1-4 and Comparative Examples 1-2 on the antioxidant properties of walnut oil body gel, wherein Figure A shows the effects of Examples 1-4 and Comparative Examples 1-2 on lipid hydroperoxides of walnut oil body gel, and Figure B shows the effects of Examples 1-4 and Comparative Examples 1-2 on thiobarbituric acid reactants of walnut oil body gel; Fig. 9 Figure 1 shows the effects of Examples 1-4 and Comparative Examples 1-2 on the digestion characteristics of walnut oil body oleogel, wherein Figure A is a laser confocal image of the oleogel without gastrointestinal digestion, Figure B is a laser confocal image of the oleogel at the end of in vitro simulated gastric digestion, Figure C is a laser confocal image of the oleogel at the end of in vitro simulated intestinal digestion, Figure D shows the effects of Examples 1-4 and Comparative Examples 1-2 on the free fatty acid release rate of walnut oil body oleogel, and Figure E is a first-order kinetic model of the release of free fatty acids over time. DETAILED DESCRIPTION The present invention proposes a method for preparing a walnut oil body oleogel. To make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention will be further described in detail with reference to the following examples. It should be understood that the specific examples described herein are only used to explain the present invention and are not intended to limit the present invention. Example 1 A method for preparing walnut oil body oil gel comprises the following steps: S1. Obtaining oil bodies: taking 200 g of walnut kernels with the endocarp removed, and then using a blender to make the walnut kernels into walnut pulp, adding 1000 mL of distilled water thereto, and then adding a colloid mill to grind to obtain a mixed liquid, filtering the mixed liquid through three layers of degreased gauze to obtain a filtrate, and centrifuging the filtrate at 1200 g for 30 min at 20° C. After centrifugation, carefully collecting the upper cream layer to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: The cream rich in walnut oil body was mixed in a phosphate buffer solution with a pH of 6.0 and stirred for 30 min to obtain a 0.6 g / mL walnut oil body emulsion; S3. Preparation of chitosan solution: Dissolve chitosan powder in acetic acid solution and stir at 50°C for 120 min until completely dissolved to prepare a 0.02 g / mL chitosan solution; S4. Preparation of vanillin solution: Dissolve vanillin in anhydrous ethanol to prepare a 0.3 g / mL vanillin solution; S5. Preparation of chitosan-coated walnut oil body emulsion: chitosan solution was added to the walnut oil body emulsion, stirred for 30 min, and finally the concentration of chitosan added to the emulsion was 1.5 wt %, and the pH value of the emulsion was adjusted to 6 using NaOH or HCl; S6. Preparation of cross-linked walnut oil body emulsion: The vanillin solution was added dropwise as a cross-linking agent to the coated walnut oil body emulsion, stirred for 120 min, and the final concentration of vanillin added to the emulsion was 1.5 wt%; S7. Preparation of oil gel: The cross-linked walnut oil body emulsion was freeze-dried at -55°C and a vacuum pressure of 0.101 mBar for 48 hours, and the freeze-dried product was sheared at a rotation speed of 1000 rpm for 2 minutes to obtain the oil gel. Example 2 A method for preparing walnut oil body oil gel comprises the following steps: S1. Obtaining oil bodies: taking 200 g of walnut kernels with the endocarp removed, and then using a blender to make the walnut kernels into walnut pulp, adding 1000 mL of distilled water thereto, and then adding a colloid mill to grind to obtain a mixed liquid, filtering the mixed liquid through three layers of degreased gauze to obtain a filtrate, and centrifuging the filtrate at 1200 g for 30 min at 20° C. After centrifugation, carefully collecting the upper cream layer to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: The cream rich in walnut oil body was mixed in a phosphate buffer solution with a pH of 6.0 and stirred for 30 min to obtain a 0.6 g / mL walnut oil body emulsion; S3. Preparation of chitosan solution: Dissolve chitosan powder in acetic acid solution and stir at 50°C for 120 min until completely dissolved to prepare a 0.02 g / mL chitosan solution; S4. Preparation of vanillin solution: Dissolve vanillin in anhydrous ethanol to prepare a 0.3 g / mL vanillin solution; S5. Preparation of chitosan-coated walnut oil body emulsion: chitosan solution was added to the walnut oil body emulsion, stirred for 30 min, and finally the concentration of chitosan added to the emulsion was 1.5 wt %, and the pH value of the emulsion was adjusted to 6 using NaOH or HCl; S6. Preparation of cross-linked walnut oil body emulsion: The vanillin solution was added dropwise as a cross-linking agent to the coated walnut oil body emulsion, stirred for 120 min, and the final concentration of vanillin added to the emulsion was 2 wt%; S7. Preparation of oil gel: The cross-linked walnut oil body emulsion was freeze-dried at -55°C and a vacuum pressure of 0.101 mBar for 48 hours, and the freeze-dried product was sheared at a rotation speed of 1000 rpm for 2 minutes to obtain the oil gel. Example 3 A method for preparing walnut oil body oil gel comprises the following steps: S1. Obtaining oil bodies: taking 200 g of walnut kernels with the endocarp removed, and then using a blender to make the walnut kernels into walnut pulp, adding 1000 mL of distilled water thereto, and then adding a colloid mill to grind to obtain a mixed liquid, filtering the mixed liquid through three layers of degreased gauze to obtain a filtrate, and centrifuging the filtrate at 1200 g for 30 min at 20° C. After centrifugation, carefully collecting the upper cream layer to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: The cream rich in walnut oil body was mixed in a phosphate buffer solution with a pH of 6.0 and stirred for 30 min to obtain a 0.6 g / mL walnut oil body emulsion; S3. Preparation of chitosan solution: Dissolve chitosan powder in acetic acid solution and stir at 50°C for 120 min until completely dissolved to prepare a 0.02 g / mL chitosan solution; S4. Preparation of vanillin solution: Dissolve vanillin in anhydrous ethanol to prepare a 0.3 g / mL vanillin solution; S5. Preparation of chitosan-coated walnut oil body emulsion: chitosan solution was added to the walnut oil body emulsion, stirred for 30 min, and finally the concentration of chitosan added to the emulsion was 2 wt %, and the pH value of the emulsion was adjusted to 6 using NaOH or HCl; S6. Preparation of cross-linked walnut oil body emulsion: The vanillin solution was added dropwise as a cross-linking agent to the coated walnut oil body emulsion, stirred for 120 min, and the final concentration of vanillin added to the emulsion was 1.5 wt%; S7. Preparation of oil gel: The cross-linked walnut oil body emulsion was freeze-dried at -55°C and a vacuum pressure of 0.101 mBar for 48 hours, and the freeze-dried product was sheared at a rotation speed of 1000 rpm for 2 minutes to obtain the oil gel. Example 4 A method for preparing walnut oil body oil gel comprises the following steps: S1. Obtaining oil bodies: taking 200 g of walnut kernels with the endocarp removed, and then using a blender to make the walnut kernels into walnut pulp, adding 1000 mL of distilled water thereto, and then adding a colloid mill to grind to obtain a mixed liquid, filtering the mixed liquid through three layers of degreased gauze to obtain a filtrate, and centrifuging the filtrate at 1200 g for 30 min at 20° C. After centrifugation, carefully collecting the upper cream layer to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: The cream rich in walnut oil body was mixed in a phosphate buffer solution with a pH of 6.0 and stirred for 30 min to obtain a 0.6 g / mL walnut oil body emulsion; S3. Preparation of chitosan solution: Dissolve chitosan powder in acetic acid solution and stir at 50°C for 120 min until completely dissolved to prepare a 0.02 g / mL chitosan solution; S4. Preparation of vanillin solution: Dissolve vanillin in anhydrous ethanol to prepare a 0.3 g / mL vanillin solution; S5. Preparation of chitosan-coated walnut oil body emulsion: chitosan solution was added to the walnut oil body emulsion, stirred for 30 min, and finally the concentration of chitosan added to the emulsion was 2 wt %, and the pH value of the emulsion was adjusted to 6 using NaOH or HCl; S6. Preparation of cross-linked walnut oil body emulsion: The vanillin solution was added dropwise as a cross-linking agent to the coated walnut oil body emulsion, stirred for 120 min, and the final concentration of vanillin added to the emulsion was 2 wt%; S7. Preparation of oil gel: The cross-linked walnut oil body emulsion was freeze-dried at -55°C and a vacuum pressure of 0.101 mBar for 48 hours, and the freeze-dried product was sheared at a rotation speed of 1000 rpm for 2 minutes to obtain the oil gel. Comparative Example 1 The difference between this comparative example and Example 1 is that there is no chitosan and vanillin, and pure walnut oil body oil gel is prepared. A method for preparing walnut oil body oil gel comprises the following steps: S1. Obtaining oil bodies: taking 200 g of walnut kernels with the endocarp removed, and then using a blender to make the walnut kernels into walnut pulp, adding 1000 mL of distilled water thereto, and then adding a colloid mill to grind to obtain a mixed liquid, filtering the mixed liquid through three layers of degreased gauze to obtain a filtrate, and centrifuging the filtrate at 1200 g for 30 min at 20° C. After centrifugation, carefully collecting the upper cream layer to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: The cream rich in walnut oil body was mixed in a phosphate buffer solution with a pH of 6.0 and stirred for 30 min to obtain a 0.6 g / mL walnut oil body emulsion; S3. Preparation of oil gel: The walnut oil body emulsion was freeze-dried at -55°C and a vacuum pressure of 0.101 mBar for 48 hours, and the freeze-dried product was sheared at a rotation speed of 1000 rpm for 2 minutes to obtain the oil gel. Comparative Example 2 The difference between this comparative example and Example 1 is that vanillin is not added, as follows: A method for preparing walnut oil body oil gel comprises the following steps: S1. Obtaining oil bodies: taking 200 g of walnut kernels with the endocarp removed, and then using a blender to make the walnut kernels into walnut pulp, adding 1000 mL of distilled water thereto, and then adding a colloid mill to grind to obtain a mixed liquid, filtering the mixed liquid through three layers of degreased gauze to obtain a filtrate, and centrifuging the filtrate at 1200 g for 30 min at 20° C. After centrifugation, carefully collecting the upper cream layer to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: The cream rich in walnut oil body was mixed in a phosphate buffer solution with a pH of 6.0 and stirred for 30 min to obtain a 0.6 g / mL walnut oil body emulsion; S3. Preparation of chitosan solution: Dissolve chitosan powder in acetic acid solution and stir at 50°C for 120 min until completely dissolved to prepare a 0.02 g / mL chitosan solution; S5. Preparation of chitosan-coated walnut oil body emulsion: chitosan solution was added to the walnut oil body emulsion, stirred for 30 min, and finally the concentration of chitosan added to the emulsion was 1.5 wt %, and the pH value of the emulsion was adjusted to 6 using NaOH or HCl; S6. Preparation of oil gel: The chitosan-coated walnut oil body emulsion was freeze-dried at -55°C and a vacuum pressure of 0.101 mBar for 48 hours, and the freeze-dried product was sheared at a rotation speed of 1000 rpm for 2 minutes to obtain the oil gel. Performance Testing 1. Potential and Particle Size Determination First, 0.01 g of the oil gel was dispersed in 100 mL of phosphate buffer solution (pH 6.0), and then stirred at 500 rpm for one hour to obtain a reconstituted emulsion. The reconstituted emulsion was subjected to potential and particle size measurements. In the particle size measurement, the refractive indices of the dispersed phase and the continuous phase were 1.47 and 1.33, respectively. from Figure 1 It can be seen that after adding chitosan, positive zeta potential appears in Comparative Example 2 and Examples 1-4. The reversal of potential from negative to positive indicates that chitosan has been successfully adsorbed to the walnut oil body interface through electrostatic deposition. In addition, when vanillin is added, the potential of the chitosan-coated walnut oil body emulsion will increase, which may be because vanillin and chitosan form a Schiff base structure. Under acidic conditions, the Schiff base can accept protons and carry a positive charge. The change in potential value shows that the coating of walnut oil bodies with chitosan and vanillin is successful. In the particle size measurement, compared with Comparative Example 1, the particle size distribution of Comparative Example 2 and Examples 1-4 is significantly shifted to the right, and the particle size becomes larger. The changes in particle size and potential indicate that chitosan and vanillin have been successfully cross-linked and adsorbed to the surface of walnut oil bodies. 2. Fourier transform infrared spectroscopy First, 100 mg of potassium bromide was mixed with 1 mg of sample powder and pressed into a tablet. Fourier infrared setting conditions: scanning range 4000 to 500 cm-1 , the number of scans is 64 times, the resolution is 4cm -1 The spectral background was removed before scanning each sample, and the results are shown in Figure 2 As shown in Figure A. The characteristic peaks of chitosan and vanillin appear near different absorption bands. The characteristic peak of chitosan-vanillin cross-linked solution basically retains the peak shape characteristics of the chitosan spectrum. With the introduction of vanillin, the chitosan-vanillin spectrum at 1637cm -1 A clear peak appeared at 3425 cm-1, indicating that a Schiff base bond (C--N) structure was formed between chitosan and vanillin. When chitosan was added to comparative example 1, the amide A band of comparative example 2 changed significantly from 3425 cm-1 to 3425 cm-1. -1 Move to 3439cm -1 After adding vanillin, the peak position of the spectrum of the oil gel in Example 1-4 changed. The Schiff base reaction of Example 1-4 was at 1633-1637 cm -1 The peak of the amide A band shifted from 3439 to 3449 cm -1 , and showed a broader band, further proving the cross-linking between vanillin and chitosan-coated walnut oil bodies. 3. Fluorescence spectroscopy 10 mg of oleogel was diluted with 100 mL of phosphate buffer (pH 6.0) to obtain a 0.1 mg / mL mixed solution. Subsequently, oleosin was excited at 295 nm and the emission spectrum from 250 to 350 nm was recorded. The widths of the emission and excitation slits were adjusted to 5 nm and 10 nm, respectively. The results are shown in Figure 2. Figure 2 B. Comparative Example 1 has the highest fluorescence intensity, indicating that the tryptophan residues of the walnut oil body are partially exposed on the surface. After chitosan was added to Comparative Example 1, the fluorescence intensity of Comparative Example 2 decreased by 25.86%. This decrease may be attributed to the fact that chitosan forms a protective layer around the walnut oil body, thereby inhibiting the exposure of tryptophan and tyrosine residues to the adjacent solvent. After different concentrations of vanillin were added to Comparative Example 2, the fluorescence intensity of Examples 1-4 was further reduced. In particular, the fluorescence intensity of Example 4 was significantly reduced by 54.72%. This observation indicates that the chitosan molecules and the walnut oil body proteins bind to each other, resulting in fluorescence quenching. 4. Thermal performance analysis 5 mg of sample was placed in a sealed aluminum pan and then heated at 50 mL / min N 2 The aluminum pan was heated from 30°C to 160°C at a flow rate of 10°C / min and a heating rate of 10°C / min. The thermogram of this process was recorded. Figure 3As shown. The denaturation temperature of Comparative Example 1 was about 115.01°C. After adding chitosan, the denaturation temperature of Comparative Example 2 moved from 115.01°C to 118.02°C. The melting onset temperature increased from 97.86°C to 101.68°C. These findings indicate that chitosan effectively interacts electrostatically with walnut oil bodies, thereby increasing the energy requirement for changing the molecular structure of walnut oil body proteins. After adding vanillin to Comparative Example 2, the denaturation temperature moved to a higher temperature (121.02°C), indicating that both vanillin and chitosan play a role in enhancing the stability and damage resistance of protein structure. 5. Visual Observation of Oil Gel during Preparation The entire oil gel preparation process was photographed, saved and compared. Figure 4 AB. During the preparation process, the colors of Comparative Examples 1-2 to Examples 1-4 gradually changed from white to light yellow, which may be due to electrostatic interaction and the formation of Schiff base bonds. After freeze drying and shearing, Comparative Example 1 could not establish a solid gel structure, and there was a sign of oil release due to the rupture of droplets. Comparative Example 2 and Examples 1-4 can remain in a solid state. 6. Laser Confocal Observation Fluorescence micrographs of the oil gel were captured using laser confocal microscopy. The protein and lipid components in the oil gel were stained with FITC and Nile red, respectively. After staining, the microstructure of the oil gel was observed at 561 nm and 488 nm. The results are shown in Figure 2. Figure 4 C. Proteins are dyed green and lipids are dyed red. The microstructure of Comparative Example 1 shows the most severe signs of oil body damage. This indicates that the stability of walnut oil bodies is easily compromised during freeze drying and shearing, resulting in an irregular oil gel structure. In contrast, in Comparative Example 2, the droplets are spherical and retain the complete walnut oil body membrane structure. In Examples 1-4, the addition of vanillin causes the droplets to be tightly packed in a continuous 3D network structure. The cross-linking reaction initiated by vanillin enhances the intermolecular interactions between walnut oil bodies, thereby forming a continuous oil gel network structure. In addition, with the increase in the concentration of chitosan or vanillin, the oil gel network structure becomes more interconnected, dense and uniform. 7. Determination of oil holding capacity 2 g of oleogel was added to a centrifuge tube and then centrifuged at 10,000 × g for 15 min at 20 °C. After centrifugation, the excess oil was separated and the mass of the centrifuge tube with the remaining oleogel was measured. The oil holding capacity was calculated by the following formula: m and m 1 are the mass of the empty centrifuge tube and the mass of the centrifuge tube containing the remaining oil gel, respectively. M is the original mass of the oil gel added to the centrifuge tube (2 g). Figure 5 As shown. Comparative Example 1 exhibited the lowest oil holding capacity (49.56%). This indicates that the deformation of the walnut oil body structure caused the oil to flow to the surface, resulting in severe oil leakage. In contrast, the oil holding capacity of Comparative Example 2 was significantly enhanced (p<0.05), indicating that the electrostatic deposition of chitosan on the walnut oil bodies promoted the stabilization of its structure. The polymer matrix is ​​tightly packed with the walnut oil bodies, which may help to obtain strong mechanical properties to resist rupture during processing. Compared with Example 1, the oil holding capacity of Example 3 was significantly improved (p<0.05); similarly, the oil holding capacity of Examples 2 and 4 also changed significantly (p<0.05). This shows that the effect of vanillin on the oil holding capacity characteristics of walnut oil body oil gel depends on the chitosan concentration, and excessive vanillin has no effect on the oil gel structure. 8. Texture determination The oil gel was placed in a glass bottle, and a cylindrical probe (model: P / 6) was carefully inserted into the oil gel to a depth of 10 mm. The speed during the test was maintained at 1.0 mm / s, while the speed before and after the test was set to 2.0 mm / s. The data during this process was recorded, and the results are as follows: Figure 6 Compared with Comparative Example 2, the hardness, elasticity, cohesiveness, stickiness, chewiness and resilience of Examples 1-4 were significantly improved. 9. Rheological determination Take an appropriate amount of oil gel and place it on the temperature-controlled base of the rheometer. The test temperature is 25°C, the gap is set to 1mm, and the fixture is a 40mm flat plate. First, the apparent viscosity is measured at a shear rate (γ) of 1 to 100s -1 The apparent viscosity of the oil gel was measured at Figure 7 As shown in A. As the shear rate increases, the apparent viscosity of Comparative Examples 1-2 and Examples 1-4 gradually decreases, showing typical shear thinning behavior. Then, a temperature scan is performed between 10 and 80°C, with a heating rate of 5°C / min, while ensuring a constant shear rate of 50s -1 , the results are as follows Figure 7 B. When the temperature rises from 10°C to 80°C, it is observed that the apparent viscosity of Comparative Examples 1-2 and Examples 1-4 shows a decreasing trend. As the concentrations of chitosan and vanillin increase, the effect of temperature on Examples 1-4 decreases. Next, the structural recovery performance of the oil gel is determined. First, the viscosity of the oil gel is 2s -1 The oil gel was sheared at a rate of 90 s and then at a rate of 100 s -1 Shearing rate for 90s, and finally at 2s -1 The rate of shearing was then continued for 90 seconds. The results were as follows Figure 7 C. In 2s -1When the oil gel is sheared at a rate of 100 s, the viscosity of Comparative Examples 1-2 and Examples 1-4 gradually decreases over time. -1 ), Comparative Examples 1-2 and Examples 1-4 exhibit shear thinning behavior, but when the shear rate drops to 2s -1 Finally, a dynamic vibration evaluation at 1 to 100 Hz was performed at 25°C and 2% strain (determined linear viscoelastic region). Figure 7 D. In the entire scanning frequency range, the storage modulus (G′) of Comparative Examples 1-2 and Examples 1-4 is significantly greater than the loss modulus (G″), and both G′ and G″ increase with increasing angular frequency. In the entire frequency range, G′ is greater than G″. Although G′ increases slightly with increasing frequency, G′ presents a minimum value, which is consistent with the expectation that physically stable polymer gels present entangled networks. 10. Determination of Antioxidant Capacity 10.1 Primary oxidation products 1 g of oil gel was mixed with 20 mL of chloroform-acetic acid mixture (1:3, v / v) and vortexed for 20 s. After centrifugation at 2500 × g for 12 min, the supernatant (0.3 mL) was collected and mixed with 15 μL of 0.072 M Fe 2+ , 15 μL 4M potassium thiocyanate and 3 mL butanol / methanol solution (1:2, v / v) were mixed. The mixture was incubated for 20 min at room temperature in the dark, and the absorbance at 510 nm was recorded. The blank control was butanol / methanol solution, and the lipid hydroperoxide concentration was calculated using the standard calibration curve. The results are shown in Figure 8 As shown in A. 10.2 Secondary Oxidation Products 1% thiobarbituric acid solution (w / v) and 10% trichloroacetic acid solution (w / v) were prepared before analysis. After dissolving 1 g of oil gel in 5 mL of deionized water, 0.4 mL of this mixture was added to 2 mL of 1% thiobarbituric acid solution and 5 mL of 10% trichloroacetic acid solution and boiled for 20 min. The resulting mixture was then mixed with chloroform and centrifuged at 4500 × g for 10 min, and the absorbance of the supernatant was recorded at 532 nm. The TBARS concentration was calculated using a standard calibration curve of 1,1,3,3-tetraethoxypropane. The results are shown in Figure 2. Figure 8 As shown in B. from Figure 8A and 8B show that after 21 days of storage, the lipid hydroperoxide content in Comparative Example 1 increased sharply from 1.53 μmol / kg to 29.68 mmol / kg, and the TBARS content increased sharply from 4.11 μmol / kg to 43.89 μmol / kg. This is caused by the loosening of the structure between the walnut oil bodies in Comparative Example 1 and the exposure of lipids to oxidants. After adding chitosan, the concentrations of lipid hydroperoxides and TBARS decreased significantly. The adsorption of chitosan molecules on walnut oil bodies may hinder the formation of lipid oxidation products in the oil bodies. In addition, chitosan has an antioxidant effect, which may be the fundamental reason for the significant improvement in the antioxidant capacity of oil gel. After adding vanillin, the antioxidant capacity of Comparative Example 2 and Examples 1-4 is further enhanced. This may be because the oil droplets are closely connected in the gel network, limiting the diffusion and movement of free radicals or oxidants. Therefore, oil gelation is an effective method to reduce the oxidation of vegetable oils. 11. In vitro gastrointestinal digestion analysis 11.1 Observation of digesta microstructure Simulated gastric fluid (SGF) with a pH of 2.5 was prepared, containing 3.2 mg / mL pepsin, 0.7% (v / v) HCl, and 2 mg / mL NaCl. Next, 2 g of oleogel was diluted with 20 mL SGF in a glass tube at 37 °C and stirred at 100 rpm for 1 hour. Afterwards, the gastric digesta were collected for further analysis. A 1.6 mg / mL pancreatin, 150 mM NaCl, 10 mM CaCl 2 The gastric digesta were mixed with SIF (1:3 v / v) and then intestinal digestion was performed for 2 h at 100 rpm while maintaining the pH at 7 by adding 0.1 M NaOH. The digestion products obtained in this process were observed by laser confocal microscopy. Fig. 9AC. Red fluorescence represents the oil in the droplets of Comparative Examples 1-2 and Examples 1-4, and green fluorescence represents the protein in Comparative Examples 1-2 and Examples 1-4. Before gastric digestion, it can be seen that the droplets in Comparative Example 1 are completely spherical and evenly dispersed in the emulsion system. After adding chitosan, the droplets in Comparative Example 2 are cross-linked to form a larger sphere. Subsequently, the addition of vanillin increased this phenomenon. After incubation in the in vitro gastric environment for a period of time, pepsin easily hydrolyzes the droplets in Comparative Example 1, causing it to rapidly disintegrate and release free fatty acids. After coating with chitosan, the integrity of the droplets in Comparative Example 2 is maintained in the gastric environment, which may be due to the established interaction between walnut oil body protein and chitosan leading to biopolymerization. In addition, Comparative Example 2 shows minimal aggregation after gastric digestion. When vanillin is added, chitosan and vanillin produce a composite effect. During gastric digestion, this composite effect enhances the aggregation of Examples 1-4, which reduces the mobile space of pepsin, thereby inhibiting the disintegration of walnut oil bodies. In the intestinal stage, it was found that the number of lipid droplets in Comparative Examples 1-2 and Examples 1-4 decreased. Proteolytic and lipolysis byproducts encapsulated Comparative Examples 2 and Examples 1-4, resulting in an increase in lipid droplet size. At the end of intestinal digestion, large and sparse aggregates were visible. This indicates that the complex intestinal environment and increased ionic strength lead to changes in droplet structure. 11.2. FFA Release Kinetics The extent of free fatty acid (FFA) release during in vitro gastrointestinal digestion was calculated using the following formula: Where V NaOH 、M NaOH , W Lipid and M Lipid are the volume of NaOH used (mL), the molar concentration of NaOH (M), the total mass of the oil (g), and the molecular weight of walnut oil (g / mol). The kinetics of the initial FFA generated can be calculated using the following formula: Among them, k 1 , and The reaction rate constants (s -1 ), FFA release at time t and maximum FFA release. The results are as follows Fig. 9DE is shown. The free fatty acid release in Comparative Examples 1-2 and Examples 1-4 increases with the extension of intestinal digestion time. Comparative Examples 1-2 and Examples 1-4 show rapid free fatty acid release in the first 30 minutes, followed by gradual release. Compared with Comparative Example 1 (40.06%), the total free fatty acid release curve of Comparative Example 2 significantly decreases to 32.27%. Unlike Comparative Example 2, the release of free fatty acids in Examples 1-4 is relatively low, and the shape of the kinetic curve shifts to the right. At the end of intestinal digestion, the release of free fatty acids in Examples 1-4 is 30.06%, 27.33%, 25.43% and 23.86%, respectively. It can be found that the concentration of chitosan has a greater effect on the release rate of free fatty acids. The characteristics of lipid digestion can be explained by its interfacial properties. The chitosan coating significantly affects the interfacial properties of the oil gel, thereby hindering the diffusion and adsorption process of bile salts and pancreatic enzymes. The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A method for preparing a walnut oil body oil gel, characterized in that: The following steps are involved: S1. Obtaining oil bodies: Walnut kernels were slurried in a blender, distilled water was added to the walnut slurry, and the slurry was ground with a colloid mill, filtered with degreased gauze, and then centrifuged to obtain purified walnut oil bodies; S2. Preparation of walnut oil body emulsion: Take walnut oil body, add it into phosphate buffer, and stir for 30 to 40 minutes; S3. Preparation of chitosan solution: Take chitosan powder, dissolve it in acetic acid solution, and stir at 40-50°C for 100-120min; S4. Preparation of vanillin solution: taking vanillin crystals and dissolving them in anhydrous ethanol to obtain a vanillin solution; S5. Preparation of chitosan-coated walnut oil body emulsion: adding chitosan solution dropwise to the walnut oil body emulsion, stirring for 20 to 30 minutes after the addition, and adjusting the pH of the emulsion to 6.0 to 7.0 using NaOH or HCl; S6. Preparation of cross-linked walnut oil body emulsion: adding the vanillin solution dropwise to the chitosan-coated walnut oil body emulsion, stirring for 100 to 120 minutes after the addition is completed; S7. Oil gel preparation: The cross-linked walnut oil body emulsion is freeze-dried and then sheared at high speed to obtain the walnut oil body oil gel.

2. The method for preparing a walnut oil body oil gel according to claim 1, characterized in that: In step S1, the walnut kernel should be free of endocarp, the material-liquid ratio of walnut kernel to distilled water is 1:(5-7), and the centrifugal conditions are: temperature 20-25° C., centrifugal force 1000-1200 g, and time 20-30 min.

3. The method for preparing a walnut oil body oil gel according to claim 1, characterized in that: The pH of the phosphate buffer in step S2 is 6.0-7.0, and the concentration of the oil emulsion is 0.6-0.9 g / mL.

4. The method for preparing a walnut oil body oil gel according to claim 1, characterized in that: In step S3, the deacetylation degree of chitosan is 95% to 100%, and the concentration of chitosan is 0.02 to 0.05 g / mL.

5. The method for preparing a walnut oil body oleogel according to claim 1, characterized in that: The concentration of the vanillin solution in step S4 is 0.3-0.6 g / mL.

6. The method for preparing a walnut oil body oil gel according to claim 1, characterized in that: The mass of chitosan solution added to the oil emulsion in step S5 is 1.5-2 wt %.

7. The method for preparing a walnut oil body oil gel according to claim 1, characterized in that: The mass of the vanillin solution added to the oil emulsion in step S6 is 1.5-2 wt %.

8. The method for preparing a walnut oil body oil gel according to claim 1, characterized in that: In step S7, the oil body emulsion is freeze-dried at -55 to -45°C and a vacuum pressure of 0.1 to 1 mBar for 48 to 55 hours, and the freeze-dried product is sheared at 1000 rpm for 2 to 5 minutes.

9. Walnut oil body oil gel prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the walnut oil body oil gel according to claim 9 in functional foods.

Images