Cellulose nanocrystal Pickering emulsion gel with stable protein hydrophobic modification as well as preparation method and application of cellulose nanocrystal Pickering emulsion gel

Abstract

The invention discloses cellulose nanocrystal Pickering emulsion gel with stable protein hydrophobic modification and a preparation method of the cellulose nanocrystal Pickering emulsion gel, oil-in-water type emulsion gel is prepared and formed under the shearing action based on cellulose nanocrystals (CNCs) coated with protein or protein sodium salt with an isoelectric point in a range of 4-6, so that a stable gel network structure is formed; by adjusting conditions of different protein coating proportions, particle concentrations and internal phase proportions, the emulsion gel can obtain different processability, and the emulsion gel based on different performance differences has good application flexibility in 3D printing. The main materials are safe in source and have good biocompatibility and biodegradability, the modification method is green and safe, and the prepared emulsion gel can be used as a food 3D printing base material or a nutrient substance loading material.

Description

Technical Field

[0001] The present invention relates to the field of food industry, and in particular to a protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel and a preparation method and application thereof, especially application in food 3D printing. Background Art

[0002] As the application of 3D printing technology in the food industry gradually increases, edible emulsion gels have attracted much attention in the industry due to their hardness, elasticity, water holding capacity and expansion rate that are suitable for application in this technology.

[0003] However, the use of emulsion gels for 3D printing of food also needs to meet the conditions of biocompatibility, biodegradability, good self-support and high temperature resistance. At present, the types of emulsion gels available for food 3D printing on the market are still relatively limited. The preparation of green and safe emulsion gels through mild modification methods provides new ideas for its application in food 3D printing materials.

[0004] The stabilizers of traditional emulsion gels are mostly surfactants. These substances are not only used in large amounts, highly toxic and have obvious side effects during the preparation process, but also have poor stability and cannot be reused, which limits their application in the field of biomedical materials. In recent years, the method of using amphiphilic solid nanoparticles and micron particles to replace surfactants to stabilize emulsions has gradually attracted attention. This emulsion gel with solid particles as stabilizers is called Pickering emulsion gel. Compared with traditional surfactants, the advantages of solid particles as emulsion stabilizers are small dosage, ability to avoid cytotoxicity, and irreversible interfacial particle self-assembly characteristics, high stability and excellent mechanical properties, which are very suitable for stabilizing emulsions and gel systems. However, most of the current particles are inorganic and synthetic materials, which are not suitable for food occasions. There is an urgent need to find food-grade solid particles that can stabilize emulsion gel systems, such as protein particles, polysaccharide particles and other particles.

[0005] Cellulose nanocrystals (CNCs) are nanofibers with a wide range of sources, biocompatibility, and biodegradability; however, the high hydrophilicity of CNCs limits their application as emulsion stabilizers, requiring surface modification. Common modification methods are divided into chemical and physical methods, of which the chemical method involves changes in covalent bonds and is generally not applicable to the food industry; while physical modification is mainly through surfactant adsorption, which is safer.

[0006] Edible protein is a good amphiphilic stabilizing material that can impart stable emulsions or enhance the amphiphilicity of other particles. It is often used as an emulsifier, thickener and emulsion stabilizer to stabilize edible emulsion / gel materials. Therefore, by coating the surface of CNCs with protein to hydrophobically modify them, the amphiphilicity of the protein can be imparted to them and their surface activity can be improved. The emulsion gel system formed in this way not only has the advantages of CNCs, but also provides convenient conditions for the large-scale application of food 3D printing technology. Summary of the invention

[0007] The purpose of the present invention is to provide a protein hydrophobically modified and stable cellulose nanocrystal Pickering emulsion gel, which has good biocompatibility and biodegradability, and the method is green and safe, and can be well used as a printing material in food 3D printing.

[0008] To achieve the above purpose, the present invention is implemented by the following technical means: A method for preparing a protein hydrophobically modified and stable cellulose nanocrystal Pickering emulsion gel, which is prepared by the following steps: Step 1: Fully stir and evenly dissolve 5%-10% mass / volume concentration of cellulose nanocrystal mother liquor in deionized water until the mass / volume concentration of cellulose nanocrystal is 1%-5%, and adjust the pH to 3.0 to prepare a cellulose nanocrystal dispersion; Step 2: Fully stirring an edible protein material having a mass / volume concentration of 1% to 5% to dissolve it in deionized water, allowing it to stand until it is fully hydrated, and then adjusting the pH to 3.0 to obtain a protein solution, wherein the edible protein material is a protein or a sodium salt of a protein having an isoelectric point in the range of 4 to 6; Step 3: using a mass ratio of cellulose nanocrystals to edible protein material of 4-10:1, using deionized water to dilute the protein solution and / or cellulose nanocrystal dispersion, and then mixing and stirring to obtain a protein-cellulose nanocrystal particle dispersion; Step 4: Mix the protein-cellulose nanocrystal particle dispersion with soybean oil in a volume ratio of 1:1-4, and use a high-speed shearing machine for high-speed shearing emulsification to obtain the Pickering emulsion gel.

[0009] Furthermore, in the step three, the mass ratio of the cellulose nanocrystals to the edible protein material is 4.8-5.2:1.

[0010] Furthermore, in the step three, the particle concentration of the protein-CNCs particle dispersion is 2%-3%.

[0011] Furthermore, in step 2, the edible protein material is one or more combinations of bovine serum albumin, sodium caseinate, and soy protein isolate.

[0012] Furthermore, in the step 4, the protein-cellulose nanocrystal particle dispersion is mixed with soybean oil in a volume ratio of 1:3.5-4.

[0013] Furthermore, in the step 4, a high-speed shearing machine is used to perform high-speed shear emulsification at a shearing speed of 10000-20000 rpm for 30-60 seconds.

[0014] The protein hydrophobically modified and stable cellulose nanocrystal Pickering emulsion gel prepared by the above-mentioned preparation methods of the present invention has good biocompatibility and biodegradability, as well as good self-support, high stability and excellent mechanical properties. It can be used as a material for 3D food printing technology and can be effectively absorbed by the consumer, thereby achieving the delivery of the nutrients embedded and loaded therein to the body of the consumer.

[0015] The present invention also discloses a 3D printing method for the protein hydrophobically modified and stable cellulose nanocrystal Pickering emulsion gel, which uses the emulsion gel as a material and performs 3D printing by a food 3D printer with a nozzle diameter of 0.7-0.85 mm, a nozzle temperature of 20-30° C., and an extrusion speed of 18-20 mm / s.

[0016] The present invention has at least the following benefits: The main materials used in the present invention are of safe sources. By selecting appropriate edible proteins or edible protein sodium salts, and matching the coating ratio of the edible proteins or edible protein sodium salts with CNCs particles, particle concentration, water-oil ratio and other conditions, the physical hydrophobic modification of CNCs is achieved through mild electrostatic interaction to form a stable coating modification structure. The prepared Pickering emulsion gel can form a stable gel network structure at the microscopic level, which can effectively slow down or inhibit the stratification of the emulsion, prevent the emulsion droplets from approaching and colliding, and reduce the generation of agglomeration between emulsion droplets. The Pickering emulsion gel of the present invention provides flexible performance adjustment by reasonably changing the isoelectric point of edible protein or edible protein sodium salt, and can be reasonably adjusted according to different 3D printing equipment, processes and model complexity, so that food models of different shapes and sizes can be prepared according to needs and practical applications, thereby realizing customized food 3D printing; The Pickering emulsion gel prepared in the present invention can be used as a green, safe and edible scaffold material for 3D printing, and can also be directly used as an excellent embedding and delivery system in new functional foods. The preparation materials are easy to obtain, the preparation process is simple and easy, and has great application and promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is the measurement result of the viscosity of each Pickering emulsion gel as a function of shear rate in Example 1 of the present invention; Figure 2 are the measurement results of the storage modulus and loss modulus of each Pickering emulsion gel in Example 1 of the present invention as a function of frequency; Figure 3 This is a 3D printed appearance diagram of each Pickering emulsion gel of Example 1 of the present invention; Figure 4 is the measurement result of the viscosity of each Pickering emulsion gel as a function of shear rate in Example 2 of the present invention; Figure 5 are the measurement results of the storage modulus and loss modulus of each Pickering emulsion gel in Example 2 of the present invention as a function of frequency; Figure 6 This is the appearance of each Pickering emulsion gel after 3D printing in Example 2 of the present invention; Figure 7 is the measurement result of the viscosity of each Pickering emulsion gel as a function of shear rate in Example 3 of the present invention; Figure 8 are the measurement results of the storage modulus and loss modulus of each Pickering emulsion gel in Example 3 of the present invention as a function of frequency; Fig. 9 This is the appearance of each Pickering emulsion gel after 3D printing in Example 3 of the present invention; Fig.10 Example 3 is a laser confocal microscopy image of the Pickering emulsion gel with an internal phase ratio of 0.8 (inside is the oil phase); Fig.11 is the measurement result of the viscosity of each Pickering emulsion gel as a function of shear rate in Example 4 of the present invention; Fig.12 are the measurement results of the storage modulus and loss modulus of each Pickering emulsion gel in Example 4 of the present invention as a function of frequency; Fig.13 This is the appearance of each Pickering emulsion gel after 3D printing in Example 4 of the present invention. DETAILED DESCRIPTION

[0018] In order to further explain the technical means and effects adopted by the present invention, the technical solution of the present invention is further described below in conjunction with the preferred embodiments of the present invention, but the present invention is not limited to the scope of the embodiments.

[0019] Example 1 - Investigating the effects of different protein ratios on the properties of emulsion gel printing In this example, bovine serum albumin (BSA, isoelectric point 4.7) with excellent surface activity is used as the hydrophobic modified protein of CNCs to prepare the Pickering emulsion gel. The BSA protein solution is diluted to 0.2%, 0.16%, and 0.1% as a variable for testing. This example includes the following steps: Step 1: Dilute the CNCs mother solution with a mass / volume concentration of 8% with deionized water, and stir with a magnetic stirrer to promote the dissolution of the CNCs mother solution in the deionized water until the mass / volume concentration of CNCs is 1%; then adjust the pH to 3.0 with 1 mol / L HCl and 1 mol / L NaOH to prepare a cellulose nanocrystal dispersion; Step 2: Stirring with a magnetic stirrer, BSA with a mass / volume concentration of 1% was fully stirred and uniformly dissolved in deionized water, and after standing overnight until it was completely hydrated, the pH was adjusted to 3.0 using 1 mol / L HCl and 1 mol / L NaOH to prepare a BSA protein solution; Step 3: Use deionized water to dilute the BSA protein solution to form BSA protein solutions with mass / volume concentrations of 0.2%, 0.16%, and 0.1%, respectively, and then mix them with the above-mentioned cellulose nanocrystal dispersion with a mass / volume concentration of 1% in equal volumes, and stir them thoroughly. Finally, three different ratios of BSA protein-cellulose nanocrystal particle dispersions with a cellulose nanocrystal: edible protein material coating mass ratio of 10:2, 10:1.6, and 10:1 were obtained; Step 4: Three different ratios of BSA protein-cellulose nanocrystal particle dispersions were mixed with soybean oil in a volume ratio of 1:4, and high-speed shear emulsification was performed at a shear speed of 13,000 rpm using a high-speed shear machine for 30 s to obtain three Pickering emulsion gels with cellulose nanocrystal: edible protein material coating mass ratios of 10:2, 10:1.6, and 10:1.

[0020] Viscosity change with shear rate test: like Figure 1As shown, the results of the viscosity change test of three Pickering emulsion gels based on cellulose nanocrystal: edible protein material coating mass ratios of 10:2, 10:1.6, and 10:1 are shown. The results show that the three Pickering emulsion gels all show similar measurement results and have typical shear thinning test results.

[0021] Storage modulus (G') and loss modulus (G") test with frequency: like Figure 2 As shown, it shows the changing relationship between the storage modulus / frequency and the loss modulus / frequency of three Pickering emulsion gels based on the mass ratio of cellulose nanocrystals: edible protein materials coating of 10:2, 10:1.6, and 10:1. In the entire frequency range, the storage modulus of all samples is nearly an order of magnitude higher than the loss modulus, indicating that each sample can form a self-supporting gel network structure and exhibit good solid viscoelastic effect; and in the entire range of 0.1-8Hz, the storage modulus is almost independent of frequency, and the loss modulus increases at 8-10Hz, which shows that the gel-like emulsion maintains the stability of the gel network within a reasonable vibration frequency range, reflecting the characteristics of 3D printing processing.

[0022] Based on the above two test results, it is shown that this formula has the potential application function as a food 3D printing material. The above three Pickering gel samples are actually used in food 3D printing machines to carry out 3D printing performance tests.

[0023] 3D printing performance test: The three Pickering gel samples obtained in step 4 were evenly filled into the syringe of the food 3D printer. The food 3D printer was used with a nozzle diameter of 0.84 mm, a nozzle temperature of 25°C, and an extrusion speed of 20 mm / s to perform 3D molding printing. After being placed at room temperature for 1 hour, the appearance of the three models was observed.

[0024] Figure 3The fishbone-shaped finished models printed by food 3D printers are displayed. From the appearance of each model, it can be found that the model has water seepage to varying degrees; compared with the model prepared by Pickering emulsion gel with a coating mass ratio of 10:2 for cellulose nanocrystals: BSA; the model prepared by Pickering emulsion gel with a coating mass ratio of 10:1.6 has a slight structural adhesion phenomenon in the relatively complex fishbone part; the model prepared by Pickering emulsion gel with a coating mass ratio of 10:1 has a slight water seepage in the edge of the fish head with a larger volume and a more complex structure. However, all three can present a good fishbone-shaped structural state, indicating that the Pickering emulsion gel prepared with BSA as the hydrophobic modified protein of CNCs has relatively good processability. Through formula optimization or related post-drying treatment processes, the prepared products have certain commerciality. This technology has a high potential application value in food 3D printing technology.

[0025] Example 2 - Study on the stability of particle-stabilized emulsion gels prepared at different particle concentrations and their printed models This example is based on Example 1, by changing the particle concentration of CNCs, and testing with a coating mass ratio of cellulose nanocrystals: edible protein material of 5:1, and preparing BSA protein-cellulose nanocrystal particle dispersions with final cellulose nanocrystal particle mass / volume concentrations of 0.5%, 1%, 2%, and 3% for testing. This example includes the following steps: Step 1: dilute the CNCs mother solution with a mass / volume concentration of 8% with deionized water, and stir the CNCs mother solution in the deionized water by a magnetic stirrer to promote the dissolution of the CNCs mother solution to obtain CNCs dilution solutions with a mass / volume concentration of 1%, 2%, 4%, and 6%, respectively; then adjust the CNCs dilution solutions with a mass / volume concentration of 1%, 2%, 4%, and 6% to a pH of 3.0 with 1 mol / L HCl and 1 mol / L NaOH, respectively, to obtain cellulose nanocrystal dispersions with a mass / volume concentration of 1%, 2%, 4%, and 6%; Step 2: Stirring with a magnetic stirrer, thoroughly stir BSA with a mass / volume concentration of 2% until it is dissolved in deionized water, leaving overnight until it is fully hydrated, and then adjusting the pH to 3.0 with 1 mol / L HCl and 1 mol / L NaOH to prepare a BSA protein solution; Step 3: Use deionized water to dilute the BSA protein solution in proportion to form BSA protein solutions with mass / volume concentrations of 0.2%, 0.4%, 0.8%, and 1.2%; then mix them with the above-mentioned cellulose nanocrystal dispersions with mass / volume concentrations of 1%, 2%, 4%, and 6% in equal volumes, and stir them evenly to finally obtain a BSA protein-cellulose nanocrystal particle dispersion with a cellulose nanocrystal: edible protein material coating mass ratio of 5:1. In each group of BSA protein-cellulose nanocrystal particle dispersions, the final mass / volume concentrations of cellulose nanocrystal particles are 0.5%, 1%, 2%, and 3%, respectively;

[0026] Step 4: The BSA protein-cellulose nanocrystal particle dispersions with four different final concentrations of cellulose nanocrystal particles were mixed with soybean oil at a volume ratio of 1:4, and high-speed shear emulsification was performed at a shear speed of 13,000 rpm using a high-speed shear machine for 30 s to obtain four corresponding Pickering emulsion gels.

[0027] Viscosity change with shear rate test: like Figure 4 As shown, it shows the results of the viscosity change test of four Pickering emulsion gels prepared based on four BSA protein-cellulose nanocrystal particle dispersions with a final mass / volume concentration of cellulose nanocrystal particles of 0.5%, 1%, 2%, and 3%, respectively. The results show that the four Pickering emulsion gels all show similar measurement results and have typical shear thinning test results. When the two Pickering emulsion gels with a final concentration of cellulose nanocrystal particles of 2% and 3% are above about 35r / s, their viscosity changes are relatively stable as the shear rate increases, reflecting that the two Pickering emulsion gels can maintain relatively stable processing performance when the extrusion rate of food 3D printing is changed.

[0028] Storage modulus (G') and loss modulus (G") test with frequency: like Figure 5As shown, it shows the relationship between the storage modulus / frequency and loss modulus / frequency of four Pickering emulsion gels prepared based on the final mass / volume concentration of cellulose nanocrystal particles of 0.5%, 1%, 2%, and 3% in the BSA protein-cellulose nanocrystal particle dispersion. In the entire frequency range, the storage modulus of all samples is nearly an order of magnitude higher than the loss modulus, indicating that each sample can form a self-supporting gel network structure and exhibit good solid viscoelastic effect; and in the entire range of 0.1-8Hz, the storage modulus is almost independent of frequency, and the storage modulus increases at 8-10Hz, which shows that the gel-like emulsion maintains the stability of the gel network within a reasonable vibration frequency range, reflecting the characteristics of 3D printing processing; in addition, with the increase of the final concentration of cellulose nanocrystal particles, the storage modulus and loss modulus of each Pickering emulsion gel are increased relative to the previous test concentration.

[0029] Based on the above two test results, it is shown that this formula has the potential application function as a food 3D printing material. The above four Pickering gel samples were actually used in food 3D printing machines to carry out 3D printing performance tests.

[0030] 3D printing performance test: The four Pickering gel samples obtained in step 4 were evenly filled into the syringe of the food 3D printer. The food 3D printer was used with a nozzle diameter of 0.84 mm, a nozzle temperature of 25°C, and an extrusion speed of 20 mm / s to perform 3D molding printing. After being placed at room temperature for 1 hour, the appearance of the four models was observed.

[0031] Test results: Figure 6As shown, it shows the fishbone-shaped finished models printed by food 3D printer using four kinds of Pickering emulsion gels with final mass / volume concentration of cellulose nanocrystal particles of 0.5%, 1%, 2%, and 3%. From the appearance of each model, it can be found that the fishbone-shaped finished models with three kinds of Pickering emulsion gels with final mass / volume concentration of cellulose nanocrystal particles of 0.5%, 1%, and 2% all have model seepage phenomenon to varying degrees, and with the increase of the final concentration of cellulose nanocrystal particles, the seepage phenomenon gradually alleviates; while the Pickering emulsion gel with final mass / volume concentration of cellulose nanocrystal particles of 3% The fishbone-shaped finished model made of emulsion gel has no water seepage phenomenon; however, the fishbone-shaped finished models prepared by using two Pickering emulsion gels with a final concentration of 2% and 3% cellulose nanocrystal particles by mass / volume have slight convexity to varying degrees at the edge of the fish head with a larger volume and a more complex structure, while the Pickering emulsion gel prepared based on a final concentration of 3% cellulose nanocrystal particles by mass / volume has a clearer outline, a more complete shape, and a higher texture clarity (the fine cracks of the fish mouth are obvious and clear), presenting a more complete appearance as a whole, and the model structure is stable, with good storage stability. Taking all factors into consideration, the subsequent examples use a final concentration of 3% cellulose nanocrystal particles by mass / volume as the research condition.

[0032] Example 3 - Study on the stability of particle-stabilized emulsion gels prepared with different internal phase ratios and their printed models This example is based on Examples 1 and 2, and is based on changing the ratio of BSA protein-cellulose nanocrystal particle dispersion to soybean oil to form Pickering emulsion gels with different internal phase ratios. This example includes the following steps: Step 1: Dilute the CNCs mother solution with a mass / volume concentration of 8% with deionized water, and stir the CNCs mother solution in the deionized water by a magnetic stirrer to promote the dissolution of the CNCs mother solution until the mass / volume concentration of CNCs is 3% CNCs dilution solution; then adjust the mass / volume concentration of 3% CNCs dilution solution to pH 3.0 with 1 mol / L HCl and 1 mol / L NaOH to prepare a cellulose nanocrystal dispersion with a mass / volume concentration of 3%; Step 2: Stirring with a magnetic stirrer, thoroughly stir BSA with a mass / volume concentration of 2% until it is dissolved in deionized water, leaving overnight until it is fully hydrated, and then adjusting the pH to 3.0 with 1 mol / L HCl and 1 mol / L NaOH to prepare a BSA protein solution; Step 3: Use deionized water to dilute the BSA protein solution to form a BSA protein solution with a mass / volume concentration of 1.2%; then mix it with the above-mentioned cellulose nanocrystal dispersion with a mass / volume concentration of 6% in equal volumes, and stir it evenly to finally obtain a BSA protein-cellulose nanocrystal particle dispersion with a cellulose nanocrystal: edible protein material coating mass ratio of 5:1;

[0033] Step 4: The BSA protein-cellulose nanocrystal particle dispersion was mixed with soybean oil in volume ratios of 5:5, 4:6, 3:7, and 2:8, respectively, that is, the internal phase ratios were 0.5, 0.6, 0.7, and 0.8, respectively. A high-speed shearing machine was used to perform high-speed shear emulsification at a shear speed of 13,000 rpm for 30 s to obtain four types of Pickering emulsion gels with a cellulose nanocrystal: edible protein material coating mass ratio of 5:1 and internal phase ratios of 0.5, 0.6, 0.7, and 0.8, respectively.

[0034] Viscosity change with shear rate test: like Figure 7 As shown, it shows the results of the viscosity change test of four Pickering emulsion gels based on internal phase ratios of 0.5, 0.6, 0.7, and 0.8 with shear rate. The results show that the four Pickering emulsion gels all show relatively close measurement results in the high shear rate range, and the curves in the high shear rate range all show high stability, and have typical shear thinning test results; and the two Pickering emulsion gels based on internal phase ratios of 0.6 and 0.8 have obvious shear thinning phenomena when their viscosities are below about 10r / s, reflecting the shear thinning effect that can be obtained at low speeds; and as the shear rate increases, their viscosity changes are relatively stable, reflecting that the two Pickering emulsion gels provide changes in the extrusion rate of food 3D printing, while maintaining relatively stable processing performance, so that Pickering emulsion gels can be printed in a low-speed jet processing mode, providing processing possibilities for 3D printing of models with complex shapes.

[0035] Storage modulus (G') and loss modulus (G") test with frequency: like Figure 8As shown, it shows the changing relationship between the storage modulus / frequency and the loss modulus / frequency of four Pickering emulsion gels based on the internal phase ratio of 0.5, 0.6, 0.7, and 0.8. In the entire frequency range, the storage modulus of all samples is nearly one order of magnitude higher than the loss modulus, indicating that each sample can form a self-supporting gel network structure and exhibit good solid viscoelastic effect; and in the entire range of 0.1-8 Hz, the storage modulus is almost independent of the frequency, which shows that the gel-like emulsion maintains the stability of the gel network within a reasonable vibration frequency range, reflecting the characteristics of 3D printing processing; in addition, with the increase of the oil phase ratio, the storage modulus and loss modulus of each Pickering emulsion gel are significantly increased relative to the oil phase ratio of the previous test, indicating that the oil phase ratio plays an important role in the properties of the emulsion gel.

[0036] Based on the above two test results, it is shown that this formula has the potential application function as a food 3D printing material. The above four Pickering gel samples were actually used in food 3D printing machines to carry out 3D printing performance tests.

[0037] 3D printing performance test: The four Pickering gel samples obtained in step 4 were evenly filled into the syringe of the food 3D printer. The food 3D printer was used with a nozzle diameter of 0.84 mm, a nozzle temperature of 25°C, and an extrusion speed of 20 mm / s to perform 3D molding printing. After being placed at room temperature for 1 hour, the appearance of the four models was observed.

[0038] Test results: Fig. 9 As shown, it shows the fishbone-shaped finished product models printed by food 3D printers using four Pickering emulsion gels with internal phase ratios of 0.5, 0.6, 0.7, and 0.8. From the appearance of each model, it can be found that the fishbone-shaped finished product models with four Pickering emulsion gels with internal phase ratios of 0.5, 0.6, 0.7, and 0.8 do not have model water seepage, but the fishbone-shaped finished product models with three Pickering emulsion gels with internal phase ratios of 0.5, 0.6, and 0.7 have larger and more complex fishtails and fish heads, and the appearance has different degrees of demulsification, while the fishbone-shaped finished product model with Pickering emulsion gel with internal phase ratio of 0.8 has a stable appearance structure and a complete appearance. This is because in this embodiment, the oil phase in the emulsion gel with an internal phase ratio of 0.8 is an "active" filler, which can play a synergistic stabilizing role with the external phase, so the higher the oil phase ratio, the stronger the filling effect and the better the gel properties.

[0039] like Fig.10The laser scanning confocal microscope images show that in the Pickering emulsion gel with an internal phase ratio of 0.8, most of the emulsion droplets are regularly distributed and have a regular spherical state, which indicates that during the gelation process, the emulsion droplets have no or very little merging, indicating that the emulsion gel has good stability. The reason is that on the one hand, the Pickering stabilization effect of the particles adsorbed on the oil-water interface during the gelation process effectively inhibits the coalescence of oil droplets, and on the other hand, the three-dimensional network structure formed by the continuous phase effectively slows down or inhibits the stratification of the emulsion.

[0040] Example 4 - Study on the stability of particle-stabilized emulsion gels prepared with different protein types and their printed models This embodiment is based on the embodiment 1-3, and the type of edible protein material is changed for testing, and bovine serum albumin (BSA, isoelectric point 4.7), sodium caseinate (CAS, isoelectric point 4.6), and soy protein isolate (SPI, isoelectric point 4.5) are selected as test materials. This embodiment includes the following steps: Step 1: Dilute the CNCs mother solution with a mass / volume concentration of 8% with deionized water, and stir the CNCs mother solution in the deionized water by a magnetic stirrer to promote the dissolution of the CNCs mother solution until the mass / volume concentration of CNCs is 3% CNCs dilution solution; then adjust the mass / volume concentration of 3% CNCs dilution solution to pH 3.0 with 1 mol / L HCl and 1 mol / L NaOH to prepare a cellulose nanocrystal dispersion with a mass / volume concentration of 3%; Step 2: BSA, CAS, and SPI with a mass / volume concentration of 2% were stirred and uniformly dissolved in deionized water by a magnetic stirrer, and left overnight until fully hydrated, and then the pH was adjusted to 3.0 using 1 mol / L HCl and 1 mol / L NaOH to prepare BSA, CAS, and SPI protein solutions; Step 3: Use deionized water to dilute the BSA, CAS, and SPI protein solutions in proportion to form BSA, CAS, and SPI protein solutions with a mass / volume concentration of 1.2%; then mix them with the above-mentioned cellulose nanocrystal dispersion with a mass / volume concentration of 6% in equal volumes, and stir them evenly to finally obtain BSA protein-cellulose nanocrystal particle dispersion, CAS protein-cellulose nanocrystal particle dispersion, and SPI protein-cellulose nanocrystal particle dispersion with a cellulose nanocrystal: edible protein material coating mass ratio of 5:1;

[0041] Step 4: The BSA protein-cellulose nanocrystal particle dispersion, the CAS protein-cellulose nanocrystal particle dispersion, and the SPI protein-cellulose nanocrystal particle dispersion were mixed with soybean oil at a volume ratio of 2:8, and high-speed shear emulsification was performed at a shear speed of 13,000 rpm using a high-speed shear machine for 30 s to obtain three Pickering emulsion gels with a cellulose nanocrystal: edible protein material coating mass ratio of 5:1 and an internal phase ratio of 0.8.

[0042] Viscosity change with shear rate test: like Fig.11 As shown, it shows the results of viscosity change with shear rate test of three Pickering emulsion gels prepared based on BSA protein-cellulose nanocrystal particle dispersion, CAS protein-cellulose nanocrystal particle dispersion, and SPI protein-cellulose nanocrystal particle dispersion. The results show that the three Pickering emulsion gels all show similar measurement results and have typical shear thinning test results; their viscosity can show obvious shear thinning phenomenon starting from about 20r / s, reflecting the shear thinning effect that can be obtained at low rotation speed; and when the three Pickering emulsion gels are above about 35r / s, their viscosity changes are relatively stable with the increase of shear rate; combined with the test results of BSA protein-cellulose nanocrystal particle dispersion based on isoelectric point 5.8 in Example 3, it shows that the Pickering emulsion gel system prepared by using CNCs as the basic material, with reasonable protein ratio coating, particle concentration, and internal phase ratio, and by reasonably adjusting the isoelectric point of edible protein or protein sodium salt in the isoelectric point range of 4-6, can provide flexible corresponding solutions to meet different processing requirements, especially can provide good low-speed jet processing performance, and can maintain relatively stable processing performance when the extrusion rate of food 3D printing changes.

[0043] Storage modulus (G') and loss modulus (G") test with frequency: like Fig.12As shown, it shows the changing relationship between the storage modulus / frequency and the loss modulus / frequency of three Pickering emulsion gels prepared based on BSA protein-cellulose nanocrystal particle dispersion, CAS protein-cellulose nanocrystal particle dispersion, and SPI protein-cellulose nanocrystal particle dispersion. In the entire frequency range, the storage modulus of all samples is nearly one order of magnitude higher than the loss modulus, indicating that each sample can form a self-supporting gel network structure, showing a good solid viscoelastic effect; and in the entire range of 0.1-8Hz, the storage modulus is almost independent of the frequency, and the storage modulus increases at 8-10Hz, which shows that the gel-like emulsion maintains the stability of the gel network within a reasonable vibration frequency range, reflecting the 3D printable processing characteristics; and combined with the test results of Example 3, it can be found that the four Pickering emulsion gels based on BSA protein-cellulose nanocrystal particle dispersion with an isoelectric point of 5.8, BSA protein-cellulose nanocrystal particle dispersion with an isoelectric point of 4.7, CAS protein-cellulose nanocrystal particle dispersion with an isoelectric point of 4.6, and SPI protein-cellulose nanocrystal particle dispersion with an isoelectric point of 4.5 have similar properties. When a relatively high isoelectric point edible protein is selected, the Pickering emulsion gel presents a thinner texture state.

[0044] Based on the above two test results, it is shown that this formula has the potential application function as a food 3D printing material. The above three Pickering gel samples are actually used in food 3D printing machines to carry out 3D printing performance tests.

[0045] 3D printing performance test: The three Pickering gel samples obtained in step 4 were evenly filled into the syringe of the food 3D printer. The food 3D printer was used with a nozzle diameter of 0.84 mm, a nozzle temperature of 25°C, and an extrusion speed of 20 mm / s to perform 3D molding printing. After being placed at room temperature for 1 hour, the appearance of the three models was observed.

[0046] Test results: Fig.13As shown, it shows the fishbone-shaped finished models printed by food 3D printers using three Pickering emulsion gels prepared based on BSA protein-cellulose nanocrystal particle dispersion, CAS protein-cellulose nanocrystal particle dispersion, and SPI protein-cellulose nanocrystal particle dispersion. From the appearance of each model, it can be found that the fishbone-shaped finished models using the three Pickering emulsion gels as materials do not have the model seepage phenomenon, and the fishbone-shaped finished models prepared using the three Pickering emulsion gels as materials have clearer contours, more complete shapes and higher texture clarity (the fine cracks in the fish mouth are obvious and clear) at the edges of the larger and more complex fish heads. Although the fishbone part of the model printed by the food 3D printer using the Pickering emulsion gel prepared based on the SPI protein-cellulose nanocrystal particle dispersion has slight adhesion, it does not affect the overall appearance. The three models all have good appearance and stable model structure, and have good storage stability. In combination with Example 3, it was verified that there was no significant difference in the Pickering emulsion gel-printed models prepared based on the hydrophobic modified stabilizing system formed by coating CNCs with edible protein or edible protein sodium salt with an isoelectric point in the range of 4-6. It can be considered that this method does not strictly restrict the protein itself within the isoelectric point range of 4-6. This scheme is universal and has the performance of flexible formula adjustment.

[0047] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Anyone familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A method for preparing a protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel, characterized by the following steps: Step 1: Fully stir and evenly dissolve 5%-10% mass / volume concentration of cellulose nanocrystal mother liquor in deionized water until the mass / volume concentration of cellulose nanocrystal is 1%-5%, and adjust the pH to 3.0 to prepare a cellulose nanocrystal dispersion; Step 2: Fully stirring an edible protein material having a mass / volume concentration of 1% to 5% to dissolve it in deionized water, allowing it to stand until it is fully hydrated, and then adjusting the pH to 3.0 to obtain a protein solution, wherein the edible protein material is a protein or a sodium salt of a protein having an isoelectric point in the range of 4 to 6; Step 3: using a mass ratio of cellulose nanocrystals to edible protein material of 4-10:1, using deionized water to dilute the protein solution and / or cellulose nanocrystal dispersion, and then mixing and stirring to obtain a protein-cellulose nanocrystal particle dispersion; Step 4: Mix the protein-cellulose nanocrystal particle dispersion with soybean oil in a volume ratio of 1:1-4, and use a high-speed shearing machine for high-speed shearing emulsification to obtain the Pickering emulsion gel.

2. The method for preparing the protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel according to claim 1, characterized in that: In the step three, the mass ratio of the cellulose nanocrystals to the edible protein material is 4.8-5.2:

1.

3. The method for preparing the protein hydrophobically modified and stable cellulose nanocrystal Pickering emulsion gel according to claim 2, characterized in that: In the step 3, the particle concentration of the protein-CNCs particle dispersion is 2%-3%.

4. The method for preparing the protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel according to claim 3, characterized in that: In the step 2, the edible protein material is one or more combinations of bovine serum albumin, sodium caseinate, and soy protein isolate.

5. The method for preparing the protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel according to claim 1, characterized in that: In the step 4, the protein-cellulose nanocrystal particle dispersion is mixed with soybean oil in a volume ratio of 1:3.5-4.

6. The method for preparing the protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel according to claim 5, characterized in that: In the step 4, a high-speed shearing machine is used to perform high-speed shear emulsification at a shearing speed of 10000-20000 rpm for 30-60 seconds.

7. The protein hydrophobically modified and stable cellulose nanocrystal Pickering emulsion gel prepared by the preparation method as described in any one of claims 1 to 6.

8. Use of the protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel as claimed in claim 7 as a material for 3D food printing technology.

9. Use of the protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel as claimed in claim 7 as a material for embedding, loading or delivering nutrients.

10. The 3D printing method of the protein hydrophobically modified and stabilized cellulose nanocrystal Pickering emulsion gel according to claim 7, characterized in that: The emulsion gel is used as a material, and 3D molding printing is performed by a food 3D printer with a nozzle diameter of 0.7-0.85 mm, a nozzle temperature of 20-30° C., and an extrusion speed of 18-20 mm / s.

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