CN111820291B

CN111820291B - Water-in-oil type high internal phase Pickering emulsion and preparation method and application thereof

Info

Publication number: CN111820291B
Application number: CN202010744604.2A
Authority: CN
Inventors: 仇超颖; 刘颖尉; 汪勇; 张震
Original assignee: Jinan University
Current assignee: Jinan University
Priority date: 2020-07-29
Filing date: 2020-07-29
Publication date: 2022-06-10
Anticipated expiration: 2040-07-29
Also published as: CN111820291A

Abstract

The invention discloses a water-in-oil type high internal phase Pickering emulsion and a preparation method and application thereof. The method comprises the following steps: dissolving and dispersing emulsifier polyglycerol ricinoleate and diglyceride in the oil phase; then slowly adding the water phase into the mixed oil phase at a constant speed, premixing by using a stirrer, and then carrying out high-speed shearing emulsification on the crude emulsion; and after homogenizing, quickly cooling to room temperature by using an ice water bath to obtain the water-in-oil type high internal phase Pickering emulsion with the water phase volume percentage of 75-85%, wherein the emulsion has excellent plasticity and stability, low fat content and higher nutritional characteristics. The emulsion in the method does not need large-scale equipment in the preparation process, is environment-friendly and pollution-free, has low cost, does not need complex procedures, is easy to produce, and can be used as a novel health functional ingredient to be applied to various fields such as food, cosmetics and the like.

Description

Water-in-oil type high internal phase Pickering emulsion and preparation method and application thereof

Technical Field

The invention belongs to the field of food, and particularly relates to a water-in-oil (W/O) high internal phase Pickering emulsion based on diglyceride stability, and a preparation method and application thereof. Overcomes the problem that saturated hydrogenated oil, wax or non-food-grade particles are mostly adopted to prepare the water-in-oil type high internal phase emulsion at present.

Background

High internal phase emulsions generally refer to emulsion systems having a dispersed phase volume percentage of greater than 74%, and are widely used in the fields of food, cosmetics, medicine, and the like.

At present, most of special food oil and fat used in margarine, waffle and the like in domestic markets are saturated fat or hydrogenated oil, and the risk of suffering from atherosclerosis and cardiovascular diseases is easily increased by higher content of saturated fat and possibly existing trans-fat. The high internal phase emulsion has similar appearance and mechanical properties to margarine and is expected to be a substitute for traditional plastic fat. The high internal phase W/O emulsion is prepared by replacing part of fat matrix with high-concentration filling water phase, so that the fat content of the product can be effectively reduced, and the product has good plasticity and stability and becomes a new generation of nutritional healthy low-fat food. Meanwhile, the high internal phase W/O emulsion can be used as a delivery system of active substances, more water-soluble active substances can be embedded compared with the common emulsion, the stability and the bioactivity of the active substances are improved, or the slow release purpose is achieved, and the high internal phase W/O emulsion has great development potential in the aspects of health-care food, drug delivery and the like.

Conventional high internal phase W/O emulsions are typically stabilized by a large amount of surfactant. The Pickering high internal phase emulsion prepared based on the solid particles can avoid the use of a large amount of synthetic surfactant and improve the product performance, and the particles which are applied to the stabilization of the Pickering emulsion at present are mostly inorganic or organic synthetic particles, so the application in the industries of food, medicine and the like is limited. Although food grade or biogenic particles have been reported for Pickering emulsion stabilization, they are mostly used for stabilizing high internal phase oil-in-water (O/W) emulsions, and the materials and preparation methods suitable for food grade high internal phase water-in-oil emulsions are limited.

In recent years, fat crystals have shown great potential in stabilizing Pickering emulsions. Diglyceride is a functional oil, belongs to natural components of oil, can be synthesized in large batch by a chemical or enzymatic method, and is safe to eat. Has effects in inhibiting fat deposition in vivo, preventing obesity, and reducing postprandial serum triglyceride and blood glucose. Diglyceride is a structural lipid in which one fatty acid residue in triglyceride is substituted by hydroxyl, and has two isomers, 1, 3-diglyceride and 1, 2-diglyceride. The hydrophilic-lipophilic balance (HLB) value is between 2 and 5. Due to the simultaneous possession of both hydrophilic and lipophilic groups, diglycerides are better able to reduce oil-water interfacial tension compared to triglycerides of the same fatty acid composition. The medium-long chain diglyceride is a structural lipid containing medium-chain fatty acid (C10-C12) and long-chain fatty acid (C14-C24), and has the advantages of the long-chain diglyceride and the unique functions of quickly supplying energy to the medium-chain fatty acid and reducing blood fat. The high melting point and nutritional characteristics of diglyceride provide a strong basis for application of diglyceride in W/O high internal phase emulsion. At present, there is no literature reporting the use of diglycerides to stabilize high internal phase water-in-oil emulsions.

Chinese patent application (CN102838773A) discloses a method for preparing an ultra-low density polymer porous material by freeze drying by using water-in-oil high internal phase emulsion stabilized by styrene, acrylic acid and methyl methacrylate triblock copolymer nanoparticles as a precursor. Although this preparation method avoids the use of large amounts of surfactants, the raw materials used are not those available in natural foods.

Chinese patent application (CN106578335A) discloses a preparation method of stable high-internal-phase gelatinous wheat gliadin Pickering emulsion. The invention can obtain the wheat alcohol soluble protein Pickering emulsion which has high stability and good viscoelasticity and can embed a large amount of grease, and has better prospect in the application aspects of novel nutrient substance conveying carriers and food structure modification base materials. However, this method requires the use of ethanol, an organic solvent, and the preparation process is complicated, and an oil-in-water type high internal phase emulsion is prepared, in which the internal phase is an oil phase.

Chinese invention patent application (CN110946285A) discloses a water-in-oil Pickering emulsion based on phytosterol stabilization, and a preparation method and application thereof. Compared with the traditional preparation method of the water-in-oil particle stabilizer, the method can produce the water-in-oil Pickering emulsion with good stability without adding a surfactant or chemical modification, but the method can only stabilize 70 percent of the internal phase water content at most. Meanwhile, the phytosterol particles used in the invention are prepared by an anti-solvent precipitation method, and an organic reagent ethanol is needed.

For studies on the preparation of food grade high internal phase water-in-oil emulsions, Lee et al in the paper (Lee., Tan., Ravanfar, et al, ultrastable water-in-oil high internal phase emulsions creating internal phase and biological network stabilization [ J ]. ACS Applied Materials & Interfaces,2019,11(29):26433-26441.) reported the preparation of high internal phase water-in-oil emulsions using the emulsifier oleic acid monoglyceride and the gelling agent beeswax, but did not involve the use of functional oil diglycerides in the high internal phase emulsions. Meanwhile, after the high internal phase emulsion is placed for two days, a large amount of water is separated out, the stability is low, and the application is limited. In view of this, we invented a process for the preparation of high stability water-in-oil type Pickering high internal phase emulsions based on diglycerides.

Disclosure of Invention

In order to solve the defects of the prior art and develop a low-fat food which is more nutritional and healthy, the invention mainly aims to provide a preparation method of a water-in-oil type high internal phase Pickering emulsion. The high internal phase emulsion provided by the invention has good stability in the storage and processing processes, the interfacial crystallization and network crystallization characteristics of diglyceride play a role in solidifying the internal phase, and the synergistic effect of the emulsifier can reduce the particle size of liquid drops and increase the stability of the internal phase. The inner phase can also be filled with polysaccharide hydrogel, so that the physical stability of the high inner phase emulsion is further improved, the fat content of the obtained high inner phase emulsion is greatly reduced while the product volume is kept, the high inner phase emulsion is low in saturation and free of trans fat, contains functional structural lipid diglyceride, and is high in nutritional value.

Another object of the present invention is to provide a high internal phase Pickering water-in-oil emulsion of diglycerides prepared by the above method.

The invention further aims to provide application of the diglyceride high internal phase Pickering water-in-oil emulsion. The emulsion obtained by the invention has low total fat content, is rich in unsaturated fat, is semisolid, has good plasticity, spreadability and stability, is suitable for replacing the traditional saturated fat and trans fat to be used as special grease for food, can also be used for loading active substances such as water-soluble polyphenol, vitamins and the like, and endows the corresponding functional property and nutritional property to the product.

The purpose of the invention is realized by the following technical scheme:

a preparation method of a water-in-oil type high internal phase Pickering emulsion comprises the following steps:

(1) preparation of water-in-oil type high internal phase emulsion: adding an emulsifier and diglyceride into vegetable oil, heating and stirring to fully dissolve the emulsifier and the diglyceride to obtain an oil phase; adding the water phase into the oil phase at a constant speed, and premixing by using a stirrer to obtain a coarse emulsion; then shearing and homogenizing the crude emulsion at a high speed to obtain a diglyceride-stable high internal phase water-in-oil emulsion with the water phase volume percentage of not less than 75 percent;

(2) cooling: and after homogenization, cooling to room temperature, and storing at low temperature.

Preferably, the diglyceride contains 10-18 carbon atoms, has a melting point range of 40-70 ℃, has a purity of not less than 50%, contains 10-18 carbon atoms of fatty acid, and is more than one of capric acid, lauric acid, myristic acid, palmitic acid or stearic acid; the emulsifier is polyglycerol ricinoleate (PGPR); the vegetable oil is at least one of soybean oil, corn oil, olive oil, sunflower seed oil, peanut oil, tea seed oil, cottonseed oil, rice bran oil and linseed oil.

Preferably, the diglyceride in the step (1) can be prepared by esterifying or transesterifying monoglyceride of fatty acid having 10 to 18 carbon atoms and fatty acid having 10 to 18 carbon atoms or corresponding triglyceride under the catalysis of lipase, or can be prepared by esterifying glycerol and fatty acid having 10 to 18 carbon atoms; the fatty acid containing 10-18 carbon atoms is more than one of capric acid, lauric acid, myristic acid, palmitic acid or stearic acid. Purifying the crude product by molecular distillation or solvent method to obtain diglyceride with purity not less than 50%.

Preferably, the volume ratio of the oil phase to the water phase in step (1) is 15: 85-25: 75, adding 4-8 wt% of diglyceride and 0.5-1.5 wt% of emulsifier into vegetable oil, wherein the oil phase consists of vegetable oil, diglyceride and emulsifier.

Preferably, in the step (1), a mixed system of the diglyceride and the vegetable oil needs to be stirred for 5-15 min, the temperature of the solution reaches 50-85 ℃, and the diglyceride is guaranteed to be melted and uniformly mixed with the oil phase.

Preferably, in step (1), the water phase is one of water or polysaccharide solution, and the volume ratio of the oil phase to the water phase is 15: 85-25: 75; the polysaccharide is at least one of iota-carrageenan, kappa-carrageenan, agar and gellan gum; the mass concentration of the polysaccharide solution is 0.5-1.5%, more preferably 1%.

Preferably, the water phase in the step (1) needs to be preheated to 50-85 ℃, and is added into the uniformly mixed oil phase within 3-6 min at a constant speed, and simultaneously, a stirrer is used for fully mixing the water phase and the oil phase at a rotating speed of 500-1000 rpm; after the water phase is completely added, continuously mixing for 3-6 min under stirring to obtain a coarse emulsion, wherein the temperature of the emulsion is maintained at 50-85 ℃ in the mixing process;

in the step (1), the crude emulsion is immediately sheared and homogenized at a high speed of 12000-15000 rpm for 3-6 min, and the water bath temperature is kept at about 50-85 ℃ in the homogenization process.

Preferably, in the step (2), the emulsion is placed in an ice-water bath, and is cooled to room temperature by a stirrer at a stirring speed of 500-1000 rpm, and then is stored at 5 ℃.

The high internal phase water-in-oil emulsion uses functional grease diglyceride crystals as a stabilizer, realizes immobilization of a high internal phase content by using the high melting point of diglyceride and the crystallization characteristic of a Pickering interface, realizes adjustment of surface wettability of fat crystals and enhancement of adsorption capacity through the synergistic effect of a small amount of emulsifier, has good spreadability and storage stability, greatly reduces fat content, and has wide application in food or cosmetics. For example, in baked products, in place of margarine based on hydrogenated vegetable oil; it can also be used for preparing low-fat food such as chocolate product, cream product or candy, and the internal phase can reduce the fat consumption of the product while maintaining the volume; in addition, the high internal phase W/O emulsion also has the advantages of packaging and protecting more water-soluble bioactive substances (such as polyphenols, vitamins, minerals and polypeptides), can also be used in cosmetics such as emulsion, skin care oil, cream and other products, and has simple preparation process and easy operation.

Compared with the prior art, the invention has the advantages and beneficial effects that:

(1) the raw materials used in the invention are natural and healthy, have high nutritive value and strong physiological activity, and the diglyceride is used as a functional structural lipid, has excellent biological activity and functionality, and has the effects of reducing blood fat, inhibiting weight gain and the like. Solves the safety problems that the prior high internal phase emulsion mostly adopts non-food grade solid particles or relates to the use of organic solvents, and the like.

(2) The vegetable oil added with the diglyceride and the emulsifier and the water phase are simply mixed, sheared and homogenized to form the viscoelastic emulsion, 75-85% of high internal phase water phase or polysaccharide solution can be wrapped, the particle size of the emulsion is small, and the emulsion has good storage stability and a soft plastic structure. The system is rich in unsaturated fatty acid, has no trans-fatty acid, greatly reduces the fat content of the system under the condition of same volume, and can replace margarine products for smearing which take hydrogenated vegetable oil containing more saturated fat as a main component or be used for producing low-calorie health-care food.

(3) The diglyceride has excellent surface activity and Pickering interface crystallization characteristics, can effectively improve the stability of the emulsion in a stable mode of interface crystallization and network crystallization, and endows the emulsion with good mechanical properties and plasticity. The diglyceride fat crystals adsorbed on the interface are solidified on the surfaces of the water drops to endow the surface with an anti-coagulation characteristic, the fat crystals in the continuous phase can reduce the collision among the water drops to the maximum extent and prevent the product instability caused by flocculation and coalescence of the water drops, and the addition of the emulsifier PGPR ensures that the emulsion has a lower particle size and the system stability is increased. The preparation process can be further optimized, the hydrogel formed by adding the polysaccharide promotes the structuring of the internal phase, delays the movement of emulsion droplets, improves the stability of two phases and reduces the dosage of the emulsifier in the emulsion.

(4) The raw materials used in the preparation process of the emulsion are food-grade raw materials, large-scale equipment is not needed, the emulsion is environment-friendly and pollution-free, the cost is low, complex procedures are not needed, and the emulsion is easy to produce; the product has high nutritional characteristics, can be used as a nutritional food product, can also be used as a carrier of a water-soluble active substance, and is widely applied to development of low-fat foods, functional foods or cosmetics and the like.

Drawings

FIG. 1 is a schematic flow diagram of the present invention.

FIG. 2 is an optical microscope photograph and the appearance of the water-in-oil type high internal phase emulsion prepared in example 1.

FIG. 3 is an optical microscope photograph and the appearance of the water-in-oil type high internal phase emulsion prepared in example 2.

FIG. 4 is a graph of the amplitude-scanning viscoelastic properties of the water-in-oil high internal phase Pickering emulsions prepared in examples 1 and 2.

FIG. 5 is an appearance diagram of the water-in-oil high internal phase Pickering emulsion containing the aqueous solution of polysaccharide agar as the internal phase prepared in example 3.

FIG. 6 is an appearance diagram of the water-in-oil high internal phase Pickering emulsion prepared in example 4.

FIG. 7 is an appearance diagram of the water-in-oil high internal phase Pickering emulsion prepared in example 5.

FIG. 8 is a graph showing the appearance of water-in-oil Pickering emulsions prepared in comparative example 1 with different water phase volume ratios: the volume ratio of the water phase from left to right is 10%, 20%, 30%, 40%, 50% and 60%, the upper graph is fresh emulsion, and the lower graph is emulsion after standing for 30 days.

FIG. 9 is an appearance diagram of the water-in-oil high internal phase emulsion prepared in comparative example 2.

FIG. 10 is an appearance diagram of a water-in-oil high internal phase emulsion prepared in comparative example 3.

Detailed Description

The present invention will be described in further detail with reference to the following examples and drawings, but the embodiments and the scope of the present invention are not limited thereto.

The diglycerides in the examples of the present invention can be prepared by the prior art methods, and in the examples, the diglycerides can be prepared according to the methods reported in the prior art, and can be prepared by the transesterification method (Wang, Xiongdong, Zhang. A method for preparing diglycerides by transesterifying monoglycerides with medium-chain triglycerides, patent application No. 201810320537.4, application No. 2018.04.11) or the esterification method (Enzymatic preparation and fat purification of medium-chain, and medium-and long-chain fatty acids diacylglycerol [ J ]. LWT-Food Science and Technology,2018,92, 227-.

Example 1

(1) Taking long-chain diglyceride containing stearic acid and palmitic acid and having the purity of about 60%, and a certain amount of emulsifier polyglycerol ricinoleate (PGPR) and rapeseed oil, placing the long-chain diglyceride and the emulsifier polyglycerol ricinoleate (PGPR) in the same beaker, wherein the long-chain diglyceride accounts for 4% of the total mass of the oil phase, the PGPR accounts for 1% of the mass of the water phase, and the volume ratio of the oil phase to the water phase is 25: and 75, magnetically stirring to enable the temperature of the oil phase to reach 85 ℃, slowly dripping water preheated to 85 ℃ into the uniformly mixed oil phase, and fully mixing the water phase and the oil phase for 5min at 700rpm to obtain a crude emulsion with the water phase volume percentage of 75%.

(2) Shearing and homogenizing the coarse emulsion obtained in the step (1) for 5min at the rotating speed of 15000rpm by using a high-speed dispersion machine, and simultaneously maintaining the temperature of a water bath at about 85 ℃ in the emulsification process. Finally, cooling and crystallizing the sheared emulsion by using a magnetic stirrer at the stirring speed of 700rpm to obtain stable high internal phase Pickering emulsion, and storing at 5 ℃.

The emulsion prepared in example 1 was a water-in-oil emulsion, which was observed by a dyeing test and an optical microscope. The plastic appearance and microstructure of the high internal phase emulsion is shown in fig. 2, and the addition of 1% emulsifier PGPR and 4% long chain diglycerides stabilizes the 75% aqueous phase, indicating that the emulsifier and diglycerides synergistically enhance the stability of the high internal phase emulsion.

The analysis of the rheological properties of the emulsions in the examples is as follows: the test was carried out using a TA DHR-2 rheometer, with a parallel plate diameter of 20mm, a test temperature of 25 ℃ and a gap between the sample and the parallel plate of 0.5 mm. The conditions for the amplitude sweep were: the change of the viscoelastic modulus with strain was recorded under the conditions of frequency control at 1Hz and strain range of 0.01-100%. The conditions for the amplitude sweep were: the amplitude variation range is 0.01-1000 Pa.

In the embodiment, the microstructure of the emulsion is observed by an optical microscope, the particle size distribution is analyzed by Image-Pro Plus software, the average particle size of the emulsion is about 7 mu m, the standing property of the emulsion is good, the appearance property and the mechanical property are similar to those of margarine or salad dressing, and the appearance and the particle size of the emulsion are not obviously changed after the emulsion is placed at 5 ℃ for 3 months, so that the coverage rate of a droplet interface is increased by the fat crystal particles and the emulsifier together, and the stability of the high internal phase emulsion is enhanced. The emulsion droplets are observed by adopting an Olymbus polarizing microscope, and interface Pickering crystals are adsorbed around the droplets, so that the diglyceride has good interface activity, a compact adsorption interface layer is formed around the droplets, the interface strength and the interface viscoelasticity are increased, and the emulsion stability is favorably improved. The elastic modulus G' of the prepared emulsion in a linear viscoelastic region is larger than the viscous modulus G (figure 4) through amplitude scanning measurement, and the emulsion shows viscoelastic solid characteristics and has better plasticity.

Example 2

(1) Referring to the procedure and conditions of example 1, except that the diglyceride in the step (1) is a medium-long-chain diglyceride containing medium-chain lauric acid and long-chain stearic acid, the diglyceride purity is about 70%; in the step (2), the weight ratio of the emulsifier polyglycerol ricinoleate (PGPR) to the water phase is 0.5%, the oil phase is stirred by magnetic force to reach 70 ℃, then water preheated to 70 ℃ is slowly dripped into the uniformly mixed oil phase, and the water phase and the oil phase are fully mixed for 5min at 700rpm to obtain a coarse emulsion with the water phase volume percentage of 75%.

The temperature of the water bath is maintained at about 70 ℃ during the emulsification process. A high internal phase water-in-oil emulsion with 75% by volume of aqueous phase was prepared.

The plastic appearance and microstructure of the water-in-oil Pickering emulsion prepared in example 2 are shown in fig. 3, when the addition amount of the emulsifier PGPR is 0.5%, the medium-long chain diglyceride can also stabilize 75% of the water phase, the average particle size of the emulsion is 35 μm, the standing property of the emulsion is good, the appearance property and the mechanical property are very similar to those of margarine, and the appearance and the particle size of the emulsion are not obviously changed after being placed at 5 ℃ for 3 months. The elastic modulus G 'of the prepared emulsion is larger than the viscous modulus G' in a linear viscoelastic region (figure 4), and the prepared emulsion shows viscoelastic solid characteristics and has better plasticity and gel strength.

Example 3

(1) With reference to the procedure and conditions of example 1, except that in step (2), the diacylglycerol accounts for 8% by mass of the total mass of the oil phase, the aqueous phase is an agar aqueous solution dissolved by heating, and the vegetable oil is soybean oil, a crude emulsion having an aqueous polysaccharide solution as the inner phase was prepared.

(2) And (2) rapidly shearing and homogenizing the crude emulsion obtained in the step (1) for 6min at the rotating speed of 12000rpm by using a high-speed dispersion machine, and maintaining the temperature of the water bath at about 80 ℃ in the emulsification process. Finally, cooling and crystallizing the sheared emulsion by using a magnetic stirrer at the stirring speed of 1000rpm to obtain stable emulsion, and storing the stable emulsion at 5 ℃.

Unlike example 1, the mass ratio of agar to the aqueous phase in the agar aqueous solution in example 3 was 1%. This example produced a high internal phase emulsion with an internal phase of 75% aqueous phase and the resulting water-in-oil Pickering emulsion had an appearance as shown in fig. 5, which was good in standability and good in plasticity. The diglyceride is crystallized in the cooling process, meanwhile, the polysaccharide forms gel, and the fat crystal structure and the macromolecular network structure in the interface and the continuous phase are favorable for fixing the inner phase in the emulsion, so that the precipitation of water drops is avoided, and the emulsion has better viscoelastic property and stability.

Example 4

(1) Referring to the steps and conditions of example 1, except that in step (1), the fatty acid composition of the diglycerides is stearic acid, the purity is about 55%, the total mass ratio of the diglycerides to the oil phase is 8%, and the volume ratio of the oil phase to the water phase is 15: 85, the aqueous phase and the oil phase were thoroughly mixed at 1000rpm for 8min to give a crude emulsion with an aqueous phase volume percentage of 85%. And (3) preparing a high internal phase Pickering emulsion according to the step (2).

The appearance of the water-in-oil high internal phase Pickering emulsion prepared in example 4 is shown in fig. 6. The stable emulsion with 85% of water phase volume percentage prepared in the embodiment has good standing property, similar appearance property and mechanical property to margarine, and has no obvious change of appearance after being placed for 3 months.

Example 5

(1) Referring to the steps and conditions of example 1, except that the diglyceride in step (1) is medium-chain diglyceride laurate, the ratio of the diglyceride laurate to the total mass of the oil phase in step (2) is 8%, and the temperature of the water bath is maintained at about 60 ℃ during the emulsification process. Slowly dripping water preheated to 60 ℃ into the uniformly mixed oil phase, and fully mixing the water phase and the oil phase for 5min at 1000rpm to obtain a coarse emulsion with the water phase volume percentage of 75%.

(2) Shearing and homogenizing the coarse emulsion obtained in the step (1) for 4min at the rotating speed of 15000rpm by using a high-speed dispersion machine, and maintaining the temperature of the water bath at about 60 ℃ in the emulsification process. Finally, cooling and crystallizing the sheared emulsion by using a magnetic stirrer at the stirring speed of 1000rpm to obtain stable high internal phase Pickering emulsion, and storing at 5 ℃.

This example produced an emulsion having 75% by volume of aqueous phase and the appearance is shown in figure 7. The emulsion has a certain plasticity. The appearance and mechanical properties of the emulsion were similar to margarine or salad dressing, and the appearance of the emulsion did not change significantly after 3 months of storage.

Comparative example 1

(1) Accurately weighing a certain amount of long-chain diglyceride containing palmitic acid and stearic acid and rapeseed oil in a beaker, wherein the mass ratio of the long-chain diglyceride to the oil phase is 4%, magnetically stirring to enable the temperature of the oil phase to reach 85 ℃, slowly dripping preheated deionized water into the uniformly mixed oil phase, and fully mixing the water phase and the oil phase for 5min at 700rpm to obtain crude emulsions with the water phase volume percentages of 10%, 20%, 30%, 40%, 50% and 60%.

(2) And (2) rapidly shearing and homogenizing the crude emulsion obtained in the step (1) for 5min at the rotating speed of 15000rpm by using a high-speed dispersion machine, and maintaining the temperature of a water bath at 85 ℃ in the emulsification process.

(3) And cooling and crystallizing the sheared emulsion by using a magnetic stirrer at the stirring speed of 700rpm, and storing the obtained emulsion at the temperature of 5 ℃.

Figure 8 is a 10%, 20%, 30%, 40%, 50%, 60% water-in-oil emulsion with no emulsifier PGPR addition, respectively, water phase volume percentage stabilized by long chain diglycerides only. It can be seen from the figure that when the volume ratio of the water phase in the emulsion is less than 10%, the emulsion is layered after being left at 5 ℃ for 30 days, while when the volume ratio of the water phase in the emulsion is 60%, partial water drops are separated out. It was shown that the use of long chain diglycerides alone did not produce stable high internal phase emulsions (> 74% internal phase) and only stabilized the aqueous phase below 60%.

Comparative example 2

(1) Accurately weighing an emulsifier PGPR accounting for 1% of the mass ratio of the water phase into the rapeseed oil, stirring by magnetic force to completely dissolve the emulsifier, slowly dripping deionized water into the uniformly mixed oil phase, and fully mixing the water phase and the oil phase for 5min at 700rpm to obtain a coarse emulsion with the water phase volume percentage of 75%.

(2) And (2) rapidly shearing and homogenizing the crude emulsion obtained in the step (1) for 5min at the rotating speed of 15000rpm by using a high-speed dispersion machine, and storing the prepared emulsion at 5 ℃.

Appearance of the water-in-oil type high internal phase emulsion containing only PGPR prepared in comparative example 2 is shown in FIG. 9, and the obtained emulsion sample is a water-in-oil type emulsion, but compared with the example, the emulsion liquid formed in comparative example 2 is fluid, indicating that the high internal phase emulsion prepared only from the emulsifier PGPR cannot form a gelatinous plastic structure without diglyceride addition, and cannot effectively replace the conventional plastic fat such as hydrogenated oil and the like to prepare a margarine product. The emulsion showed a clear oil phase floating after 1 week of storage, which further illustrates that the structural support of diglycerides on high internal phase emulsions, in conjunction with PGPR, is only able to form stable, gelatinous high internal phase emulsions.

Comparative example 3

(1) Reference is made to the procedure and conditions of comparative example 2, except that the emulsifier PGPR in step (1) is 0.5% by mass of the aqueous phase.

(2) And (2) rapidly shearing and homogenizing the crude emulsion obtained in the step (1) at room temperature for 3min at the rotating speed of 15000rpm by using a high-speed dispersion machine. Finally, the sheared emulsion is cooled and crystallized by a magnetic stirrer at the stirring speed of 700rpm, and the prepared emulsion is stored at 5 ℃.

As shown in fig. 10, in the emulsion obtained in comparative example 3, when the mass concentration of the emulsifier PGPR was 0.5%, oil-water separation occurred one day after the end of shearing of the emulsion, and a stable emulsion could not be formed, indicating that when no diglyceride was added, the emulsifier PGPR at a low concentration (0.5%) failed to form a good emulsified aqueous phase and failed to form a stable high internal phase emulsion.

Comparative example 4

(1) Reference is made to the procedure and conditions of comparative example 2, except that 4% Hydrogenated Palm Oil (HPO) is added to the oil phase in step (2). And (3) magnetically stirring to enable the temperature of the oil phase to reach 85 ℃, slowly dripping water preheated to 85 ℃ into the uniformly mixed oil phase, and fully mixing the water phase and the oil phase for 5min at 700rpm to obtain a crude emulsion with the water phase volume percentage of 75%.

(2) And (2) rapidly shearing and homogenizing the crude emulsion obtained in the step (1) at room temperature for 3min at the rotating speed of 15000rpm by using a high-speed dispersion machine. Finally, cooling and crystallizing the sheared emulsion by using a magnetic stirrer at the stirring speed of 700rpm, and storing the prepared emulsion at 5 ℃.

The hydrogenated oil of solid fat used in comparative example 4 contains more saturated fat and even a small amount of trans fat which is not good for human health, the prepared emulsion cannot stand well, obvious water drops are separated out after the emulsion is stored for 1 month, and the hydrogenated oil has no surface activity, cannot form an interface adsorption crystal structure, and can only crystallize through a network to stabilize the emulsion, so that the stability of the high internal phase emulsion is limited.

Comparative example 5

(1) Reference is made to the procedure and conditions of comparative example 2 except that in step (2) 10% beeswax is added to the oil phase and the aqueous phase is a 1% iota carrageenan solution. Magnetic stirring is carried out to enable the temperature of the oil phase to reach 85 ℃, then carrageenan solution preheated to 85 ℃ is slowly dripped into the oil phase which is uniformly mixed, and the water phase and the oil phase are fully mixed for 5min at 700rpm to obtain crude emulsion with 75% of water phase volume percentage.

The emulsion prepared in the comparative example 5 has certain viscoelasticity, the elastic modulus is greater than the viscous modulus, but after the emulsion is stored for 2 days, obvious water drops are separated out, more water is separated out after the emulsion is stored for 1 month, the emulsion is obviously instable, and the stability of the high internal phase emulsion is lower because the interface activity of the solid fat beeswax is lower, and a better interface adsorption structure cannot be formed.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such modifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a water-in-oil type high internal phase Pickering emulsion is characterized by comprising the following steps:

(1) preparation of water-in-oil type high internal phase emulsion: adding an emulsifier and diglyceride into vegetable oil, heating and stirring to fully dissolve the emulsifier and the diglyceride to obtain an oil phase; preheating the water phase to 50-85 ℃, adding the water phase into the uniformly mixed oil phase within 3-6 min at a constant speed, and simultaneously fully mixing the water phase and the oil phase by using a stirrer at a rotating speed of 500-1000 rpm; after the water phase is completely added, continuously mixing for 3-6 min under stirring to obtain a coarse emulsion, wherein the temperature of the emulsion is maintained at 50-85 ℃ in the mixing process; immediately shearing and homogenizing the crude emulsion at 12000-15000 rpm for 3-6 min, and keeping the water bath temperature at 50-85 ℃ in the homogenizing process to obtain a diglyceride-based high-stability high internal phase water-in-oil emulsion with the water phase volume percentage not less than 75%;

(2) cooling: after homogenizing, cooling to room temperature, and storing at low temperature;

the purity of the diglyceride in the step (1) is more than 50%, the carbon number of fatty acid contained in the diglyceride is 10-18, and the fatty acid is more than one of capric acid, lauric acid, myristic acid, palmitic acid or stearic acid; the emulsifier is polyglycerol ricinoleate; the vegetable oil is at least one of soybean oil, corn oil, olive oil, sunflower seed oil, peanut oil, tea seed oil, cottonseed oil, rice bran oil and linseed oil.

2. The preparation method of the water-in-oil type high internal phase Pickering emulsion as claimed in claim 1, wherein the weight ratio of the added diglyceride to the oil phase in step (1) is 4-8%, the weight ratio of the added emulsifier to the water phase is 0.5-1.5%, and the volume ratio of the water phase to the total volume is 75-85%.

3. The preparation method of the water-in-oil type high internal phase Pickering emulsion as claimed in claim 1, wherein the mixing system of the diglyceride and the vegetable oil in the step (1) needs to be stirred for 5-15 min, the solution temperature reaches 50-85 ℃, and the diglyceride is completely melted and uniformly mixed with the oil phase;

the water phase in the step (1) is one of water or polysaccharide solution; the mass concentration of the polysaccharide solution is 0.5-1.5%; the polysaccharide is at least one of iota-carrageenan, kappa-carrageenan, agar and gellan gum.

4. The method for preparing a water-in-oil type high internal phase Pickering emulsion according to claim 1, wherein in the step (2), the emulsion is placed in an ice water bath, stirred by a stirrer at a stirring speed of 500-1000 rpm and cooled to room temperature, and then stored at 5 ℃.

5. A water-in-oil high internal phase Pickering emulsion prepared by the process of any one of claims 1 to 4.

6. Use of a water-in-oil high internal phase Pickering emulsion according to claim 5 in the food and cosmetic field.