WPI / SPI-based Pickering emulsion gel and preparation method thereof

Abstract

The invention discloses WPI / SPI-based Pickering emulsion gel and a preparation method thereof, and belongs to the field of emulsion gel substitutes. The invention aims to solve the problems that Pickering emulsion gel prepared from soybean protein is relatively weak in gel structure, has relatively large pores and is relatively easy to extrude during centrifugation, and the loose gel structure is not beneficial to moisture retention. The composition is prepared from the following components in percentage by mass: 0.36%-1.8% of whey protein isolate (WPI), 0.36%-1.8% of soybean protein isolate (SPI), 10%-50% of soybean oil and the balance of ultrapure water. The gel network generates larger resistance to external stress in the centrifugal process, and water molecules can be more tightly kept through capillary acting force.

Description

Technical Field

[0001] This invention belongs to the field of emulsion gel substitutes, specifically, it relates to a WPI / SPI-based Pickering emulsion gel and its preparation method. Background Technology

[0002] Dairy products offer numerous health benefits, including maintaining a balanced diet, providing essential micronutrients and bioactive components. With economic development, consumer attitudes are shifting, and consumers are increasingly focused on the nutritional content and additives in dairy products. Many dairy products suffer from deficiencies in texture and taste, and are prone to separation during storage and transportation. Therefore, gums are often added to enhance stability, improve texture and taste, and extend shelf life. However, commonly used gums have limitations. For example, some gums are not easily absorbed by the body, causing discomfort for those with gastrointestinal allergies; they interfere with the absorption of other nutrients, affect the absorption of certain medications, and may even trigger allergies. Some gums exhibit poor stability under specific conditions, failing to fully meet the storage and transportation requirements of dairy products in different environments, and are less effective in improving texture and taste, thus failing to meet consumers' expectations for high-quality dairy products. Therefore, effectively improving the stability of dairy products while ensuring they are healthier, greener, and cleaner has become a pressing issue. In recent years, developing healthy, green, and clean gum substitutes to improve the nutritional quality of food has become a research hotspot in the food industry.

[0003] Pickering emulsion gel is a novel soft material developed based on Pickering emulsion technology. It stabilizes emulsion droplets through solid particles and integrates a three-dimensional gel network to form a semi-solid system. In recent years, Pickering emulsion gel has received increasing attention in the food industry due to its excellent thixotropic and shear-thinning properties, making it suitable as a food gel substitute for various food products. Furthermore, Pickering emulsion gel possesses the ability to load and release active substances, thus attracting widespread attention from scholars both domestically and internationally, with its innovative applications in functional gelled foods being particularly noteworthy.

[0004] Whey protein is a typical high-nutritional-value animal protein, often referred to as the "king of proteins." Its essential amino acid composition is more balanced and complete than that of plant proteins. Soy protein, as one of the most popular plant proteins, boasts low cost and unique emulsifying, foaming, and gelling abilities. Both are ideal materials for producing Pickering emulsion gels. Combining them leverages the advantages of both plant and animal proteins, offering unique advantages in preparing Pickering emulsion gel substitutes. However, the optimal ratio for combining them to prepare stable Pickering emulsion gels and form stable Pickering emulsion gel substitutes remains unclear, representing a major technical challenge. Summary of the Invention

[0005] This invention addresses the problem that Pickering emulsion gels prepared from soybean protein have a weak gel structure with large pores, making them easier to squeeze during centrifugation. This loose gel structure is not conducive to moisture retention. The invention provides a WPI / SPI-based Pickering emulsion gel and its preparation method.

[0006] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a WPI / SPI-based Pickering emulsion gel, which, by mass percentage, consists of the following components: 0.36%-1.8% whey protein isolate (WPI), 0.36%-1.8% soy protein isolate (SPI), 10%-50% soybean oil, and the remainder being ultrapure water. Further specified, the ratio of whey protein isolate to soy protein isolate is 3:2, 1:1, or 2:3.

[0007] Another object of the present invention is to provide a method for preparing the above-mentioned WPI / SPI-based Pickering emulsion gel, comprising the following steps: Step 1: Dissolve whey protein isolate (WPI) powder and soy protein isolate (SPI) powder in ultrapure water, respectively, and stir magnetically until completely dissolved to obtain WPI solution and SPI solution, and hydrate overnight; Step 2: Mix the hydrated WPI solution and SPI solution, adjust the pH to 12, stir magnetically, and adjust to pH 7 to obtain the dual protein complex solution; Step 3: Mix the dual protein complex liquid and soybean oil, disperse at high speed and then homogenize under high pressure to obtain the Pickering emulsion gel.

[0008] Further specifying, in step 1, the concentration of the WPI solution is 1% to 5% (w / v), and the concentration of the SPI solution is 1% to 5% (w / v).

[0009] To further specify, in step 1, hydration is performed at 4°C.

[0010] Further specifying, in step 2, the pH is adjusted to 12 using 1 mol / L sodium hydroxide.

[0011] Further specifying, in step 2, the pH is adjusted to 7 using 1 mol / L hydrochloric acid.

[0012] Further specifying, in step 3, the dispersion is carried out at a high speed of 13000 r / min.

[0013] Further specifying, in step 3, homogenization is performed under a pressure of 20 MPa.

[0014] The present invention has a highly interconnected and compact network structure, and the gel network is more uniform and denser. Therefore, the gel network has greater resistance to external stress during centrifugation and can retain water molecules more tightly through capillary forces.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The method for preparing WPI / SPI-based Pickering emulsion gel substitutes provided by this invention is simple and easy to implement. No organic solvents are required during the preparation process, the raw materials are inexpensive and readily available, and the overall feasibility is high.

[0016] This invention uses whey protein and soy protein as raw materials, combining the advantages of plant and animal proteins. It improves protein utilization through amino acid complementarity, enhances nutritional balance, and reduces the risk of chronic diseases.

[0017] The Pickering emulsion gel prepared by this invention exhibits significant advantages in several textural parameters, specifically higher hardness, viscosity, adhesiveness, and chewiness. Furthermore, when the whey protein to soy protein ratio is 3:2 (WPI to SPI mass ratio), all four textural parameters of the resulting emulsion gel reach their maximum values; the two proteins produce a significant synergistic enhancement effect during gelation. This is mainly due to the synergistic formation of hydrophobic interactions, disulfide bonds, and hydrogen bonds between protein molecules, thereby increasing the cross-linking density of the emulsion gel network structure and forming a more dense and robust three-dimensional gel structure.

[0018] Pickering emulsion gel substitutes were prepared using whey protein isolate and soy protein. These substitutes not only replace gels but also have the potential to deliver nutrients, thereby increasing the nutritional value of food. They are a healthy, green, and clean food ingredient with certain health benefits and have a promising market prospect.

[0019] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0020] Figure 1 The particle size and potential of Pickering emulsion gels stabilized with different proportions of whey protein isolate and soy protein isolate; Figure 2 The water-holding capacity of Pickering emulsion gels stabilized by different proportions of whey protein isolate and soy protein isolate; Figure 3 This is a curve showing the change in the apparent viscosity of the emulsion gel obtained through shear scanning. Figure 4 It is the change in storage modulus (G') of different samples obtained through frequency scanning curves; Figure 5 This refers to the variation of the loss modulus (G) of different samples obtained through frequency scanning curves. Detailed Implementation

[0021] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0022] Example 1: In this example, the WPI / SPI-based Pickering emulsion gel was composed of the following components by mass percentage: whey protein 1.08%, soy protein 0.72%, soybean oil 40%, and the remainder being solvent (ultrapure water); it was prepared according to the following steps: Step 1: Weigh whey protein isolate (WPI) powder and soy protein isolate (SPI) powder separately and dissolve them in ultrapure water. Stir magnetically at 500 rpm until completely dissolved to prepare a 3% (w / v) WPI solution and a 3% (w / v) SPI solution. Place them in a refrigerator at 4°C overnight for hydration. Step 2: After overnight hydration, the WPI solution and SPI solution are mixed evenly, and the pH is adjusted to 12 with 1 mol / L sodium hydroxide. After stirring magnetically at 500 rpm for 2 h, the pH is adjusted to 7 with 1 mol / L hydrochloric acid to obtain the dual protein complex solution. Step 3: Mix the dual protein complex liquid and soybean oil, and use a high-speed disperser to run at 13000 r / min for 5 minutes to form a crude emulsion. Homogenize the emulsion using a high-pressure homogenizer under 20 MPa pressure to obtain Pickering emulsion gel.

[0023] The following experiments were used to verify the effectiveness of the invention. WPI / SPI-based Pickering emulsion gels were prepared using different ratios of whey protein isolate and soy protein isolate, the optimal dual protein concentration (optimal dual protein concentration is 3%, of which whey protein is 1.8% and soy protein is 1.2%), and the optimal oil-water ratio (optimal is 40%). The results are as follows: The mass ratio of whey protein isolate to soy protein isolate is 5:0, 3:2, 1:1, 2:3, and 0:5.

[0024] (1) Particle size and potential of Pickering emulsion gels stabilized with different proportions of whey protein isolate and soy protein isolate As shown in the figure, the Pickering emulsion gel stabilized by the whey protein and soy protein complex has a smaller particle size and a higher absolute potential value compared with the Pickering emulsion gel stabilized by a single protein, indicating that the Pickering emulsion gel stabilized by the whey protein and soy protein complex is more stable.

[0025] (2) Water-holding capacity of Pickering emulsion gels stabilized with different proportions of whey protein isolate and soy protein isolate The water-holding capacity of a gel refers to its ability to prevent the release or expulsion of water from its network under compression or centrifugation. It reflects the stability of Pickering emulsion gels and plays a crucial role in their functional properties. The water-holding capacity of Pickering emulsion gels prepared with different ratios of whey protein and soy protein is shown in the figure. Generally, the water-holding capacity of Pickering emulsion gels prepared with different ratios of whey protein and soy protein is above 60%, and increases significantly with increasing whey protein content (p<0.05). The Pickering emulsion gel prepared with a high ratio of whey protein and a low ratio of soy protein exhibits the best water-holding capacity. It has a highly interconnected and compact network structure; the gel network is more uniform and denser, thus exhibiting greater resistance to external stress during centrifugation and retaining water molecules more tightly through capillary forces. In contrast, the Pickering emulsion gel prepared solely from soy protein has a weaker gel structure with larger pores, making it more easily compressed during centrifugation. This loose gel structure is not conducive to water retention.

[0026] (3) Rheological properties of Pickering emulsion gels stabilized with different proportions of whey protein isolate and soy protein isolate The apparent viscosity variation curves of the emulsion gels obtained by shear scanning are shown in Figure Viscosity. With increasing shear rate, the apparent viscosity of all Pickering emulsion gels gradually decreased, exhibiting typical shear-thinning behavior. This may be because the increased shear rate leads to partial disruption of the aggregated Pickering emulsion gel network structure, reducing flow resistance and thus lowering viscosity. Furthermore, the Pickering emulsion gel prepared with a high proportion of whey protein and a low proportion of soy protein exhibited the highest viscosity and more pronounced shear-thinning characteristics. However, with increasing soy protein content, the viscosity of the Pickering emulsion gel decreased significantly. One possible reason is that the Pickering emulsion gel prepared with a high proportion of whey protein and a low proportion of soy protein has a more compact and uniform gel network, resulting in stronger hydrophobic interactions and hydrogen bonding between droplets, ultimately leading to a higher apparent viscosity. Another reason may be that Pickering emulsion gels prepared with a high proportion of whey protein and a low proportion of soy protein have smaller droplets. Smaller droplets result in a larger number of droplets per unit volume / area, which increases the contact between droplets and further leads to an increase in apparent viscosity.

[0027] The changes in storage modulus (G') and loss modulus (G') of different samples obtained through frequency scanning curves are shown in the figure. Throughout the frequency range, the elastic modulus G' of all samples is greater than the corresponding viscous modulus G'. This phenomenon indicates that all five protein blends with different proportions formed elastic gels, exhibiting a solid-like state with a denser internal structure and greater resistance to strain deformation. Furthermore, it can be seen that the G' of the Pickering emulsion gel prepared from single whey protein is significantly higher than that prepared from single soy protein. Adding whey protein to soy protein improves the elasticity of the Pickering emulsion gel; when the proportion of whey protein is higher, the Pickering emulsion gel has the largest G' value, significantly higher than the Pickering emulsion gel stabilized by single whey protein or soy protein. G' typically represents the formation and strength of the gel structure. The increase in G' indicates that the addition of whey protein improves the network and mechanical properties of the soy protein emulsion gel. When the proportion of whey protein is higher, the Pickering emulsion gel prepared from the protein blend exhibits synergistic strength. The variation in viscoelastic modulus between samples may be attributed to differences in the interactions between oil droplets in the system, such as disulfide bonds, hydrogen bonds, hydrophobic interactions, electrostatic repulsion, and van der Waals forces.

[0028] (3) Texture properties of Pickering emulsion gels stabilized by different proportions of whey protein isolate and soy protein isolate Table 1

[0029] Pickering emulsion gels prepared from single whey protein exhibit significantly higher hardness, viscosity, adhesiveness, and chewiness than those prepared from single soy protein. Furthermore, increasing the proportion of whey protein in the whey / soy protein mixture further enhances these properties. The 3:2 whey-to-soy protein ratio results in the highest levels of hardness, viscosity, adhesiveness, and chewiness in the Pickering emulsion gel. This suggests a synergistic gelation strength between the whey and soy proteins at this ratio. Protein interactions, including hydrophobic interactions, disulfide bonds, and hydrogen bonds, are likely the reasons for this synergistic enhancement of gelation, leading to increased cross-linking density in the Pickering emulsion gel structure and the formation of a denser, more robust emulsion gel.

[0030] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A WPI / SPI-based Pickering emulsion gel, characterized in that, By weight percentage, it consists of the following components: 0.36%-1.8% whey protein isolate (WPI), 0.36%-1.8% soy protein isolate (SPI), 10%-50% soybean oil, and the remainder is ultrapure water.

2. The gel according to claim 1, characterized in that... By weight percentage, it consists of the following components: 1.08% whey protein isolate (WPI), 0.72% soy protein isolate (SPI), 40% soybean oil, and the remainder is ultrapure water.

3. The gel according to claim 1, characterized in that, The ratio of whey protein isolate to soy protein isolate was 3:2, 1:1, and 2:

3.

4. The method for preparing the gel according to claim 1, 2, or 3, characterized in that, Includes the following steps: Step 1: Dissolve whey protein isolate (WPI) powder and soy protein isolate (SPI) powder in ultrapure water, respectively, and stir magnetically until completely dissolved to obtain WPI solution and SPI solution, and hydrate overnight; Step 2: Mix the hydrated WPI solution and SPI solution, adjust the pH to 12, stir magnetically, and adjust to pH 7 to obtain the dual protein complex solution; Step 3: Mix the dual protein complex liquid and soybean oil, disperse at high speed and then homogenize under high pressure to obtain the Pickering emulsion gel.

5. The method according to claim 4, characterized in that, The concentration of WPI solution is 1%–5% (w / v), and the concentration of SPI solution is 1%–5% (w / v).

6. The method according to claim 4, characterized in that, Hydrate at 4°C.

7. The method according to claim 4, characterized in that, Adjust the pH to 12 using 1 mol / L sodium hydroxide.

8. The method according to claim 4, characterized in that, Adjust the pH to 7 using 1 mol / L hydrochloric acid.

9. The method according to claim 4, characterized in that, Disperse at a high speed of 13000 r / min.

10. The method according to claim 4, characterized in that, Homogenize under 20 MPa pressure.

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