CN113501973A

CN113501973A - Pickering emulsion stabilized by nano-cellulose hydrogel

Info

Publication number: CN113501973A
Application number: CN202110782874.7A
Authority: CN
Inventors: 范柳萍; 倪洋; 李进伟; 吴晶晶; 姜妍婷; 周宇林
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2021-07-12
Filing date: 2021-07-12
Publication date: 2021-10-15
Anticipated expiration: 2041-07-12
Also published as: CN113501973B

Abstract

The invention discloses a Pickering emulsion stabilized by using a nano-cellulose hydrogel, belonging to the technical field of Pickering emulsions. The invention takes cellulose nanocrystals as raw materials, and adds cations to induce cellulose suspension to form hydrogel. The hydrogel-based gel characteristics stabilize the high internal phase Pickering emulsion, and the stable high internal phase Pickering emulsion can be prepared by only one-step emulsification method. The emulsion disclosed by the invention is simple to prepare, green and safe in raw materials, and can be widely applied to the fields of foods and cosmetics.

Description

Pickering emulsion stabilized by nano-cellulose hydrogel

Technical Field

The invention relates to a Pickering emulsion stabilized by using a nano-cellulose hydrogel, belonging to the technical field of Pickering emulsions.

Background

An emulsion is a dispersion of one or more liquids in the form of droplets dispersed in another liquid immiscible therewith. High Internal Phase Emulsions (HIPEs), also known as super concentrated emulsions, refer to a class of emulsions having a dispersed phase volume fraction of above 74%. High internal phase emulsions find wide application in food and cosmetic products, such as mayonnaise, ice cream, which are frequently consumed; a cream, a hand cream, etc., which are often film-coated. Due to the large volume fraction of the oil phase, conventional HIPEs require large amounts of surfactants (5-50%) to stabilize the emulsion. The use of large amounts of active agents not only increases costs, but also presents a potential health hazard. In recent years, there has been increasing interest in stabilizing Pickering emulsions with solid particles that irreversibly adsorb at the oil-water interface, exhibiting very good emulsion stabilizing capacity.

At present, a lot of researches prove that inorganic particles such as silicon dioxide and titanium dioxide nanoparticles can effectively stabilize Pickering emulsion, but the inorganic particles have certain risks in the aspects of biological safety and environmental compatibility, so that the application of the inorganic particles in the field of food is limited. Therefore, the development of food grade solid particle stabilizers is an important and challenging task.

Cellulose, which is a biopolymer most abundant in natural sources, has the characteristics of good biocompatibility, biodegradability, renewability, low cost and the like, and is widely concerned in the fields of materials, biomedicines and cosmetics. Cellulose Nanocrystals (CNCs), also known as nanocrystalline cellulose or cellulose nanowhiskers, are a type of nanofibrous particle extracted from lignocellulosic biomass that exhibits a wide rod or needle shape with high crystallinity (CrI) and high aspect ratio. In recent years, related studies have reported the preparation of stable high internal phase Pickering emulsions using CNCs. However, these documents and patents presuppose the formation of high internal phase emulsions by appropriate hydrophobic modification of CNCs or by adding a certain amount of protein to increase hydrophobicity, which is not only cumbersome but also costly.

For example, SCI article [ Food Hydrocolloids 75(2018)125-130] similar to the patent of the present invention, the authors adopt Octenyl Succinic Anhydride (OSA) to perform hydrophobic modification on CNCs to improve the emulsification property thereof, and then prepare high internal phase emulsion by using modified cellulose. However, this hydrophobic modification process is relatively cumbersome, requires multiple steps of sample mixing, lyophilization, reaction, and washing, not only increases the cost, but also is not conducive to industrial large-scale processing.

Chinese invention patent similar to the present invention, "a modified bacterial cellulose nanofiber stable high internal phase Pickering emulsion and a preparation method thereof" (CN 111205479A), which mixes a bacterial nanocellulose solution and a soy protein isolate solution, obtains a mixed colloidal solution by shearing, homogenizing and concentrating operations, and then adds grease into the colloidal solution to obtain the high internal phase emulsion by shearing and emulsifying. Although the colloidal solution is obtained as a simple physical mixing process, the subsequent water bath rotary evaporation process (rotary evaporation to 20% of the original mass at 45 ℃) is a very time consuming process relative to the present patent. The preparation time of the CNCs hydrogel is obviously shorter than that of the colloidal solution. Moreover, the dosage of the cellulose in the colloidal solution of the invention is always less than that of the soybean protein (the mass ratio of the bacterial cellulose nano-fiber to the soybean protein isolate is (3-10): (22-28)), which may mean that the protein plays a more important role in stabilizing the high internal phase emulsion.

The invention relates to a Chinese invention patent similar to the invention, in particular to a preparation method of a stable high internal phase Pickering emulsion of cellulose nanocrystals (CN 108530649A), which takes cotton as a raw material, adopts an acid hydrolysis method to prepare the cellulose nanocrystals, takes a dispersed phase of the cellulose nanocrystals with a certain concentration as a water phase, dissolves a certain amount of alkaline polymer in an organic solvent as an oil phase, and prepares the high internal phase Pickering emulsion by a one-step shearing method. The preparation method of the high internal phase emulsion disclosed by the invention is simple and easy to operate. However, the oil phase of the emulsion is an organic solvent and a certain amount of basic polymer, such as poly-N, N-dimethylaminoethyl methacrylate, poly-N, N-diethylaminoethyl methacrylate, must be added to the oil phase, which completely limits the use of such high internal phase Pickering emulsions in food systems.

Disclosure of Invention

[ problem ] to provide a method for producing a semiconductor device

The invention aims to provide a high internal phase Pickering emulsion which can be applied to the fields of food and cosmetics and has a simple preparation method.

[ technical solution ] A

The invention takes cellulose nanocrystals as raw materials, and adds cations to induce cellulose suspension to form hydrogel. The hydrogel-based gel characteristics stabilize the high internal phase Pickering emulsion, and the stable high internal phase Pickering emulsion can be prepared by only one-step emulsification method. The emulsion disclosed by the invention is simple to prepare, green and safe in raw materials, and can be widely applied to the fields of foods and cosmetics. The preparation of the nano-cellulose hydrogel system is based on a physical crosslinking method generated by electrostatic shielding effect caused by cations, and the cellulose hydrogel obtained by the preparation method has good biological safety because other additional chemical reagents are not required to be added. In addition, the emulsions of the present invention are high internal phase emulsions with oil phases up to 85%.

The first purpose of the invention is to provide a method for preparing nano-cellulose hydrogel, which takes cellulose nano-crystals as raw materials and induces cellulose suspension to form the nano-cellulose hydrogel by adding cations.

In one embodiment of the present invention, the preparation method of the cellulose nanocrystal suspension can refer to the preparation methods of nanocellulose disclosed in the prior literature [ int.j.biol.macromol,1992,14, 170-172 ] and the Chinese patent of invention [ CN 110591117B ]. The method comprises the following specific steps: the method comprises the steps of hydrolyzing cotton serving as a raw material for 30-90 min in a water bath environment at 45 ℃ by adopting sulfuric acid with the concentration of 62-64%. After the hydrolysis was completed, the reaction was terminated with 10 times deionized water, followed by centrifugation to remove the supernatant and collecting the precipitate. And dispersing the precipitate in deionized water again, and performing dialysis treatment by using an 8-14 kDa dialysis bag to remove redundant inorganic salt ions to finally obtain a cellulose nanocrystal suspension with the pH value of 5-7 and the concentration of 0.5-10%.

In one embodiment of the present invention, the cellulose nanocrystals have a length of 100 to 300 nm; the cellulose content of the cellulose suspension is 1-4%.

In one embodiment of the invention, the cation comprises Al³⁺，Ca²⁺，Mg²⁺，Zn²⁺，Na⁺And K⁺One or more of (a).

In one embodiment, the cation is added in an amount of 5 to 50 mM.

The second purpose of the invention is to provide the nano-cellulose hydrogel prepared by the method.

The third purpose of the invention is to provide the application of the nano-cellulose hydrogel in the aspects of preparing emulsion, protecting nutrient substances and improving the product quality.

The fourth purpose of the invention is to provide a Pickering emulsion, wherein the Pickering emulsion is formed by mixing the nanocellulose hydrogel serving as a water phase with an oil phase.

In one embodiment of the invention, the water phase of the emulsion consists of nano-cellulose hydrogel and water, wherein the addition amount of the nano-cellulose hydrogel is 20-80% of the mass of the water phase.

In one embodiment of the present invention, the ratio of the emulsion water phase and the oil phase to be mixed is (mass ratio): 1:3 to 7.

In one embodiment of the invention, the oil phase is an oil-soluble substance, including edible oils, nutrients, drugs, food additives, cosmetics; the oil phase can be edible oil such as corn oil, soybean oil, peanut oil, fish oil, etc., or cosmetic raw material such as mineral oil, glycerol, propylene glycol, ethylhexyl palmitate, etc.

In one embodiment of the present invention, preferably, the cation is at least one of the following: ca²⁺，Mg² ⁺，Zn²⁺，Na⁺，K⁺Or their combination, the specific source can be CaCl₂，CaCO₃，MgCl₂，ZnCl₂NaCl, KCl, etc.

The invention provides a high internal phase Pickering emulsion stabilized by nano-cellulose hydrogel and a preparation method thereof, wherein the method comprises the following steps:

(1) preparing the nano-cellulose hydrogel: adding a certain amount of cations into the cellulose nanocrystal suspension with the mass fraction of 1-5%, uniformly stirring, and standing for 2-10 min to form the nanocellulose hydrogel.

(2) Preparation of high internal phase Pickering emulsion: adding deionized water into a certain mass of nano-cellulose hydrogel to form a water phase, mixing the water phase and the oil phase, and forming a high internal phase Pickering emulsion under the action of high-speed dispersion and shearing. According to the mass ratio of 1: 3-7, and shearing for 1-3 min under the high-speed dispersing shearing action of 8000-12000 rpm to prepare the high internal phase Pickering emulsion.

In one embodiment, the cation in step (1) is at least one of: ca²⁺，Mg²⁺，Zn² ⁺，Na⁺，K⁺Or their combination, the specific source can be CaCl₂，CaCO₃，MgCl₂，ZnCl₂NaCl, KCl, etc.

In one embodiment, the cation is added in an amount of 5 to 50mM in the step (1).

In one embodiment, the aqueous phase of the emulsion in the step (2) is composed of nanocellulose hydrogel and water, wherein the addition amount of the nanocellulose hydrogel is 20-80% of the mass of the aqueous phase.

In one embodiment, the mixing ratio of the emulsion water phase and the oil phase in the step (2) is (mass ratio): 1:3 to 7.

In one embodiment, the oil phase in step (2) may be edible oil such as corn oil, soybean oil, peanut oil, fish oil, or mineral oil, glycerin, propylene glycol, ethylhexyl palmitate, or other cosmetic raw materials.

In one embodiment, the emulsion preparation process in step (2) is as follows: and (3) mixing the water phase and the oil phase, and shearing for 1-3 min at a shearing rate of 8000-12000 rpm to obtain the high internal phase Pickering emulsion.

A sixth object of the present invention is to provide a composition comprising the Pickering emulsion described above.

In one embodiment, the composition comprises a food or cosmetic product.

The invention has the beneficial effects that:

the invention stabilizes the high internal phase Pickering emulsion based on the nano-cellulose hydrogel formed by cation induction, the oil phase can reach 85 percent at most, the emulsion process is simple and easy to operate, the stable high internal phase emulsion can be prepared from the hydrogel with the ion concentration of more than 5mM, the nano-cellulose hydrogel dosage is less, and the high internal phase emulsion can be stabilized by the hydrogel dosage of more than 20 percent of the water phase quality. On the other hand, the cellulose nanocrystals used in the invention have good biological safety and environmental compatibility, and the formed high internal phase emulsion can be used as a food structure modification base material, a nutrient delivery carrier and the like in the food field, and can reduce or replace the application of an artificially synthesized surfactant in cosmetics.

Drawings

FIG. 1 is an atomic force microscope picture of the prepared cellulose nanocrystals;

FIG. 2 is a high internal phase emulsion prepared with varying amounts of hydrogel added;

FIG. 3 is a high internal phase emulsion microstructure;

FIG. 4 is a nano-cellulose hydrogel prepared with different amounts of added sodium chloride;

FIG. 5 is a nanocellulose hydrogel dynamic rheological properties;

figure 6 is a high internal phase emulsion prepared from hydrogels of different ionic strengths.

Detailed Description

The following description of the preferred embodiments of the present invention is provided for the purpose of better illustrating the invention and is not intended to limit the invention thereto.

1. Method for testing gel strength

The rheological properties and gel strength of the cellulose hydrogel were tested by reference to the method in [ International Journal of Biological Macromolecules 149(2020) (617-626) ], using a DHR-3 rheometer, with a 40mm plate as the measuring tool, and a measurement gap value of 1mm, under the following specific test conditions: firstly, under the constant frequency of 1Hz, strain scanning is carried out by changing strain (0.01-100 percent), and the linear viscoelastic region of the hydrogel system is determined. On the basis, the dynamic viscoelasticity is measured by adopting a constant strain of 0.5 percent and an angular frequency of 0.1-100 rad/s. The complex viscosity G of the system was calculated according to equation 1:

G*＝G’+iG”

where G 'is the storage modulus and G' is the loss modulus, the values of G 'and G' being taken from measurements at an angular frequency of 1 rad/s.

2. Emulsion storage stability test:

20mL of freshly prepared emulsion was slowly added to the sample bottle, which was then placed in a room temperature environment and observed for changes in the appearance of the emulsion.

3. Centrifugal stability of the emulsion:

3mL of the high internal phase emulsion was added to a 5mL centrifuge tube and then centrifuged at 8000rpm for 5min to observe changes in the appearance of the emulsion.

4. Measurement of particle size before and after storage of emulsion:

referring to the method in [ Food Hydrocolloids 112(2021)106279], the particle size of the high internal phase emulsion was measured by diluting 1mL of the high internal phase emulsion (fresh emulsion and emulsion stored for 6 months) with 5mL of deionized water, mixing uniformly, and measuring the particle size of the emulsion by using a laser particle size analyzer.

Example 1

(1) Preparation of cellulose nanocrystal suspensions: mixing the crushed cotton and a sulfuric acid solution with the mass concentration of 64% according to the ratio of material to liquid of 1:15(w/v), reacting for 60min in a water bath environment at 45 ℃, immediately adding 10 times of deionized water to terminate the reaction after the reaction is finished, and then centrifuging (8000rpm, 15min) to collect precipitates. And (3) dispersing the collected precipitate by deionized water again, then dialyzing by using a dialysis bag with the molecular weight cutoff of 8-14 kDa to remove inorganic salt ions, and collecting the cellulose nanocrystal suspension until the pH value is stable. The final suspension concentration is 5%, and the suspension is diluted or concentrated according to subsequent requirements.

FIG. 1 shows the morphology of CNCs prepared by sulfuric acid hydrolysis, the CNCs are in the form of short needles with a length of 100-300 nm and a diameter of 15-40 nm.

(2) Preparing the nano-cellulose hydrogel: diluting the cellulose nanocrystal suspension in the step (1) to 2%, and weighing 0.165g of CaCl₂Adding the nano-crystalline into 100mL of 2% cellulose nanocrystal suspension, stirring uniformly, and standing for 5min to obtain the nano-cellulose hydrogel.

(3) Preparation of high internal phase Pickering emulsion: according to the ratio of the water phase to the oil phase of 1:3, preparing emulsion with the total mass of 200g, weighing 150g of soybean oil as emulsion oil phase, weighing 30g of nano-cellulose hydrogel and 20g of water as water phase (the hydrogel accounts for 60% of the mass of the water phase), adding the oil phase into the water phase, and shearing for 2min at the rotating speed of 10000rpm to prepare the high internal phase Pickering emulsion. After standing at room temperature for 6 months, the emulsion was not unstable, as shown in FIG. 2. Also, the high internal phase emulsion is in a gel state and can be inverted. The microstructure of the emulsion was examined by confocal laser microscopy (fig. 3), and the cellulose and oil were stained with fluorescent white dye and nile red dye, respectively. As is apparent from fig. 3, the close proximity of the oil droplets and no flocculation between the oil droplets is typical of the oil droplet distribution of high internal phase emulsions. As can be seen from the cellulose distribution, the cellulose fills in between the oil droplets of the emulsion, wrapping the oil droplets, ensuring that the high internal phase emulsion is stable. The microstructure of these emulsions clearly demonstrates that the cellulose hydrogel can effectively prepare a high internal phase Pickering emulsion.

Comparative example 1

The cellulose nanocrystals obtained in example 1 above were diluted to 4% and the ratio of water phase to oil phase was 1:3, preparing emulsion with the total mass of 200g, weighing 150g of soybean oil as emulsion oil phase and 50g of cellulose suspension (4%), mixing the water phase and the oil phase, and shearing for 3min at the rotating speed of 10000rpm to obtain the emulsion. After 6 months at room temperature, the emulsion separated completely from the oil, see fig. 2, meaning that the cellulose suspension alone did not stabilize the high internal phase emulsion.

Example 2 high internal phase emulsions prepared with varying amounts of cellulose hydrogel added

The nanocellulose (2%) hydrogel obtained in example 1 above was taken and mixed in a water phase to oil phase ratio of 1:3, preparing emulsion with the total mass of 200g, weighing 150g of soybean oil as emulsion oil phase, adding the cellulose hydrogel according to the weight proportions of 10%, 20%, 40%, 60%, 80% and 100% of the water phase, namely 5g, 10g, 20g, 30g, 40g and 50g (the water phase concentrations of corresponding cellulose nanocrystals are respectively 0.2%, 0.4%, 0.8%, 1.2%, 1.6% and 2.0%), complementing the rest water phase with deionized water, adding the oil phase into the water phase, and then shearing for 2min at the rotating speed of 10000rpm to prepare the high internal phase Pickering emulsion. As can be seen from FIG. 2, 20% to 80% of the hydrogel can effectively stabilize the high internal phase emulsion, and no instability occurs after the hydrogel is placed at normal temperature for 6 months. Whereas 10% hydrogel failed to stabilize the emulsion, and in addition 100% hydrogel addition failed to stabilize the high internal phase emulsion because the mobility of the hydrogel was poor, and if the aqueous phase was all hydrogel, the shear process failed to effectively disperse the aqueous phase, resulting in failure to form a high internal phase emulsion.

Example 3 cellulose hydrogels prepared with different amounts of cation added and their high internal phase Pickering emulsions

The cellulose nanocrystal suspension obtained in the example 1 is diluted to 3%, 0, 0.029, 0.058, 0.117, 0.175, 0.282 and 0.338g of NaCl are respectively weighed and added into 100mL of 3% cellulose nanocrystal suspension, the ionic strength in the system is respectively 0, 5, 10, 20, 30, 50 and 60mM, and after uniform stirring, the mixture is placed for 10min, so that the nanocellulose hydrogel is obtained. These nanocellulose hydrogel appearance figures are shown in fig. 4, and it can be seen that the flowing suspension gradually gelled and the sample could be completely inverted after the cellulose suspension was added NaCl. The dynamic rheological properties of the hydrogel are shown in FIG. 5, with the solid line representing the elastic modulus (G') of the sample and the dashed line representing the viscous modulus (G ") of the sample. If G ' is greater than G ', it indicates that the sample exhibits gel properties, and if G "is greater than G ', it indicates that the sample exhibits viscous properties. The gel strength of the sample without NaCl (0mM) added was very small and thus not shown in FIG. 5. As can be seen in fig. 5, G' is greater than G "for all samples, meaning that all samples exhibit gel behavior. Further, the larger the amount of NaCl added, the larger the G' of the hydrogel, indicating that the gel strength of the sample is stronger.

According to the ratio of the water phase to the oil phase of 1: 5, preparing emulsion with the total mass of 200g, weighing 166g of soybean oil as emulsion oil phase, weighing 24g of nano-cellulose hydrogel and 10g of water as water phase (the hydrogel accounts for 70 percent of the water phase), adding the oil phase into the water phase, and shearing for 2min at the rotating speed of 10000rpm to prepare the high internal phase Pickering emulsion. Fig. 6 shows high internal phase emulsions prepared from hydrogels with different ionic strengths, and it can be seen that when the ionic strength is 5mM, the formed cellulose hydrogel cannot stabilize the emulsion, probably because the gel strength under the condition is too weak to effectively form a three-dimensional network structure, which plays a role in stabilizing the high oil phase. When the ionic strength is more than 50mM, the emulsion is unstable during storage, and oil-water separation occurs after 6 months. This is probably because too high an ionic strength adversely affects the emulsifying properties of the cellulose. Table 1 shows the effect of different cationic addition amounts on the cellulose hydrogel and the Pickering emulsion, further showing the effect of ionic strength. With the increase of the addition amount of NaCl, the gel strength of the cellulose hydrogel tends to be unchanged after being enhanced. The gel strength has no influence on the particle size of the emulsion, namely, the particle sizes of the emulsions prepared from 5 mM-50 mM of hydrogel are all about 65 μm. The gel strength, however, affects the particle size change and emulsion stability of the emulsion during storage. Wherein the higher the gel strength of the hydrogel, the smaller the change in particle size of the emulsion during storage, and the better the storage stability and the centrifuge stability of the emulsion. This is probably because the high gel strength hydrogel can provide the emulsion with a more robust three-dimensional network structure that "immobilizes" the oil droplets so that the emulsion does not change much in particle size, even during centrifugation, and the oil and water phases cannot be separated. According to the data in the table 1, for a hydrogel system formed by NaCl induction, when the gel strength range of the hydrogel is 65-100 Pa, the emulsion can have good storage stability, and further, when the gel strength range of the hydrogel is 84-100 Pa, the emulsion has good centrifugal stability. However, the addition of NaCl in excess of 50mM may affect the emulsifying properties of CNC due to excessively high salt concentration, and may adversely decrease the emulsion stability.

TABLE 1 Effect of different cationic additions on cellulose hydrogels and Pickering emulsions

Example 4: cellulose hydrogel prepared from different sources of same cations and high internal phase Pickering emulsion thereof

The cellulose nanocrystal suspension obtained in example 1 was diluted to 2% and 0.165g of CaCl was weighed out separately₂0.150g of CaCO₃0.191g of CaSO₄The final ion concentration of the system was adjusted to 15mM, and the mixture was stirred and left for 10 min. However, only CaCl is finally present₂Form a strong hydrogel system, CaCO₃Completely failing to form a hydrogel system, CaSO₄A weak hydrogel system is formed. This is because the three calcium salts have different solubilities in water, CaCl₂Has good water solubility, CaSO₄Only slightly soluble in water, CaCO₃Is substantially insoluble in water.

According to the ratio of the water phase to the oil phase of 1: 5, preparing emulsion with the total mass of 200g, weighing 166g of soybean oil as emulsion oil phase, weighing 24g of nano-cellulose hydrogel and 10g of water as the aqueous phase (70% of the hydrogel) was added to the aqueous phase, followed by shearing at 10000rpm for 2min to prepare a high internal phase emulsion. Finally, only CaCl₂The hydrogel system forms a stable emulsion. This means that the source of the calcium salt has a great influence on the formation of hydrogels and high internal phases.

Example 5: cellulose hydrogel prepared from different cation types and high internal phase Pickering emulsion thereof

The cellulose nanocrystal suspension obtained in example 1 was diluted to 3% and weighed 0.117g NaCl (20mM), 0.149g KCl (20mM), and 0.222g CaCl₂(20mM)，0.190g MgCl₂(20mM), and 0.2668g AlCl₃(20mM) is added into 100mL of cellulose nanocrystal suspension to enable the final ion concentration of the system to reach 20mM, and after the mixture is uniformly stirred, the mixture is placed for 10min to obtain the nano-cellulose hydrogel. The gel strength (complex modulus G) of the cellulose hydrogel obtained above was measured using a DHR-3 rheometer, and the complex modulus (G) characterizes the stiffness of the gel when deformed below the yield stress, and the specific values are given in table 2. G of the hydrogel is: 84.21Pa for NaCl hydrogel, 106.45Pa for KCl hydrogel, and CaCl₂The hydrogel is 337.63Pa, MgCl₂The hydrogel is 254.42Pa, AlCl₃The hydrogel was 456.67. It can be seen that the higher the cation valence, the stronger the strength of the hydrogel formed.

According to the ratio of the water phase to the oil phase of 1:3, preparing an emulsion with the total mass of 200g, weighing 150g of soybean oil as an emulsion oil phase, respectively weighing 30g of the five nanocellulose hydrogels and 20g of water as a water phase (the hydrogel accounts for 60 percent of the water phase), adding the oil phase into the water phase, and then shearing at the rotating speed of 12000rpm for 1min to obtain the high internal phase Pickering emulsion. Wherein, AlCl₃The hydrogel does not stabilize the emulsion. After being placed at room temperature for 6 months, the other four emulsions are not unstable. The four emulsions were further centrifuged to observe the centrifugal stability of the emulsions at 5000rpm for 5 min. The centrifugal results show that the emulsion prepared by univalent cations (NaCl and KCl) has partial water phase separated out at the bottom after centrifugation, and divalent cations (CaCl)₂And MgCl₂) The emulsion prepared was stable after centrifugation with no water and oil separation. This is because the divalent cations induce the cellulose to form a stronger hydrogel, so that the emulsion also exhibits stronger gel strength.

TABLE 2 Effect of different cationic species on cellulose hydrogels and Pickering emulsions

Example 6: improving food quality

Taking the CaCl in the above example 4₂And (3) hydrogel formed by induction, wherein the sunflower seed oil is used as an oil phase, the addition amount of the hydrogel is 70% of that of a water phase, and the weight ratio of the water phase to the oil phase is 1: 4 ratio high internal phase emulsions were prepared (oil phase content could reach 80%). Adding a high internal phase emulsion to an ice cream in place of a portion of butter, the butter ice cream formulation comprising: 70% of skimmed milk, 8.5% of butter, 6.0% of egg yolk and 15.5% of soft sugar; the high internal phase emulsion ice cream was added as follows: 70% skimmed milk, 5% butter, 2.5% high internal phase emulsion, 6.0% egg yolk, 15.5% soft sugar. The preparation process of the ice cream comprises the following steps: heating milk to boil, slowly adding the mixture of beaten yolk and soft sugar, stirring while adding, sieving, pouring into a milk pan, continuously heating with slow fire, stirring to prevent the sample from being burnt, adding butter or the mixture of butter and high internal phase emulsion when the mixture can be thinly coated on a scraper, uniformly stirring, refrigerating and aging the sample in a refrigerator at 4 deg.C, pouring the refrigerated sample into an ice cream mixer, stirring for 1h, placing into a mold, and hardening at-18 deg.C. The method for measuring the solubility of the ice cream comprises the following steps: the ice cream samples hardened for more than 48 hours were taken for study. Firstly, weighing a certain mass of hardened ice cream, putting the weighed hardened ice cream into a Buchner funnel of a 37 ℃ incubator, and placing a clean beaker below the Buchner funnel for receiving the melted ice creamPouring, taking out the beaker after 30min, and weighing, wherein the calculation formula of the melting rate is as follows: the melting rate (weight of ice cream after melting/total weight of ice cream) x 100%.

Experiments have found that the melting rate of butter ice cream reaches 70% and that the melting rate of ice cream after the addition of the high internal phase emulsion drops to 60%, from which it can be seen that the addition of the high internal phase increases the resistance of the ice cream to dissolution.

Example 7: protecting active ingredients in food

A high internal phase emulsion was prepared from the hydrogel induced by 30mM NaCl as described in example 3 above, at a ratio of oil to water of 1: 3. First, β -carotene was dissolved in 150g soybean oil, 40g cellulose hydrogel and 10g deionized water were taken as the aqueous phase, and the oil phase was added to the aqueous phase followed by shearing at 12000rpm for 2min to prepare a high internal phase emulsion. Determination of the degradation rate of beta-carotene: 0.5g of the emulsion was taken, added to a mixture of ethanol and n-hexane in a certain volume (volume ratio of 2:3), shaken up, the n-hexane phase was collected, diluted appropriately with n-hexane, and then the absorbance was measured at 450nm by an ultraviolet-visible spectrometer. The formula of degradation rate: the degradation rate (100%) ═ m₁/m₂×100，m₁Mass of curcumin after standing in emulsion, m₂Is the quality of curcumin before emulsion placement.

Experiments have found that high internal phase emulsions can effectively protect beta-carotene. After 27 days of storage, the retention of beta-carotene in the emulsion compared to that in the pure oil can still reach 90% because the diffusion of free radicals and pro-oxidants is hindered by the presence of cellulose particles.

Comparative example 2:

commercial products of CNCs were used: cotton CNCs (MCNCs) obtained by sulfuric acid hydrolysis have the length of 100-300 nm and the diameter of 15-40 nm; the needle-leaved wood CNCs (denoted ZCNCCs) obtained by enzymatic hydrolysis have the length of 1000nm and the diameter of 50 nm. The concentration of the above CNCs was diluted to 1%, 2%. Then 0.165g of CaCl was weighed₂Respectively adding into 100mL of 1% and 2% cellulose nanocrystal suspension of MCNCs and ZCNCs with ion concentration of 15mM, stirring, standing for 5min to obtain nanocelluloseA hydrogel.

According to the ratio of the water phase to the oil phase of 1: 5, preparing emulsion with the total mass of 200g, weighing 166g of soybean oil as emulsion oil phase, weighing 24g of the nano-cellulose hydrogel and 10g of water as water phase (the hydrogel accounts for 70 percent of the water phase), adding the oil phase into the water phase, and shearing for 3min at the rotation speed of 10000rpm to prepare the high internal phase Pickering emulsion. The complex viscosity G of the emulsion was measured using a DHR-3 rheometer and at an angular frequency of 1rad/s was: 1% MCNCs hydrogel stabilized emulsion 96.77 Pa; 2% MCNCs hydrogel stabilized emulsion 150.21 Pa; 1% ZCNCCs hydrogel stabilized emulsion 146.81 Pa; 2% ZCNCs hydrogel stabilized emulsion 192.47 Pa. From the complex viscosity results, it is seen that long nanocellulose stabilized high internal phase emulsions exhibit higher gel strength, with 1% ZCNCs having a gel strength close to that of 2% MCNCs stabilized emulsions. In addition, by measuring the centrifugal stability of the emulsion (5000rpm, 5min), only 1% MCNCs stabilized emulsion had a small amount of water phase separated out, and the remaining emulsions all exhibited excellent stability. Further, similar stabilization results were obtained with less long nanocellulose than with short nanocellulose.

Although the present invention has been described with reference to the preferred embodiments, it should be understood that various changes and modifications can be made therein by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. The method for preparing the nano-cellulose hydrogel is characterized in that cellulose nanocrystals are used as raw materials, and cation is added to induce a cellulose suspension to form the nano-cellulose hydrogel; the cation comprises Al³⁺，Ca² ⁺，Mg²⁺，Zn²⁺，Na⁺And K⁺One or more of (a).

2. The method according to claim 1, wherein the cellulose nanocrystals have a length of 100 to 300 nm; the cellulose content of the cellulose suspension is 1-4%.

3. The method according to claim 1 or 2, wherein the cation is added in an amount of 5 to 50 mM.

4. A nanocellulose hydrogel prepared by the method of any one of claims 1-3.

5. Use of the nanocellulose hydrogel of claim 4 for the preparation of emulsions, for the protection of nutrients, for the improvement of product quality.

6. A Pickering emulsion, which is characterized in that the Pickering emulsion is formed by mixing the nanocellulose hydrogel of claim 5 as a water phase with an oil phase.

7. The Pickering emulsion of claim 6, wherein the cation comprises CaCl₂，CaCO₃，MgCl₂，ZnCl₂One or more of NaCl and KCl.

8. The Pickering emulsion according to claim 6 or 7, characterized in that the aqueous phase of the emulsion consists of nanocellulose hydrogel and water, wherein the amount of nanocellulose hydrogel added is 20-80% of the mass of the aqueous phase; the mixing ratio of the emulsion water phase and the emulsion oil phase is (mass ratio): 1:3 to 7.

9. Pickering emulsion according to any of claims 6 to 8, characterized in that the oil phase is an oil-soluble substance, including edible oils, nutritional substances, drugs, food additives, cosmetics.

10. A composition comprising the Pickering emulsion of any of claims 6-9.