Method for improving interfacial properties of oil-in-water emulsion by using soybean protein isolate-quercetin isomer

Abstract

The invention discloses a method for improving interfacial properties of an oil-in-water emulsion by using a soybean protein isolate-quercetin isomer, and belongs to the technical field of protein modification. The method comprises the following steps: (1) preparing a soybean protein isolate (SPI) stock solution and a quercetin / morin (Q / M) stock solution; (2) preparing a soybean protein isolate-quercetin / morin non-covalent compound (SPI-Q / M); and (3) preparing an SPI-Q / M oil-in-water (O / W) emulsion. The modification method provided by the invention can greatly improve the interface characteristics of the protein-based emulsion, contributes to determining the difference of different types of polyphenol-protein composite emulsifier stable emulsion systems, and provides a theoretical basis for reasonable design and construction of functionalized and steady-state emulsions.

Description

Technical Field

[0001] The present invention mainly relates to a method for improving the interfacial properties of oil-in-water emulsions by using soy protein isolate - quercetin isomers, belonging to the technical field of protein modification. Background Art

[0002] Soy protein isolate (SPI) has a protein content of over 90%, with a total of nearly 20 kinds of amino acids, and is rich in beneficial bioactive peptides, making it a high-quality protein supplement. Due to its amphiphilicity, aggregation properties, and charged characteristics, SPI is commonly used as an emulsifier in food systems such as emulsions. However, the dense globular structure of SPI leads to poor solubility and emulsifying performance, and SPI has the characteristics of weak electrostatics and spatial attraction, usually forming an unstable emulsion system. Therefore, it is very important to seek and study a composite emulsifier that can improve the stability of protein-based emulsions and their applications in the food industry.

[0003] Quercetin (3, 5, 7, 3′, 4′-pentahydroxyflavone) is a plant flavonoid substance with rich nutritional value, widely present in vegetables, fruits, grains, herbs, beverages, tea, and red wine. Morin (3, 5, 7, 2', 4'-pentahydroxyflavone) has the same source and physiological activities as quercetin, and the only difference is that the hydroxyl group is replaced by 2' instead of 3'. Quercetin has various biological activities, such as antioxidant, anti-inflammatory, and anti-allergic effects, which can add nutritional value to food. It can be used as a functional ingredient and added to beverages, cereal products, pasta, processed fruits and juices, and gummies. Currently, quercetin cannot be directly applied to ordinary foods and health foods in China, but its reduced form, dihydroquercetin, was approved as a new food raw material in 2021. Due to its potential health benefits, research on fortifying foods with quercetin has received increasing attention and research from scholars. For example, incorporating quercetin into bread can reduce the digestion rate of starch, inhibit the accumulation of AGEs, thereby reducing its glycemic index, and at the same time provide antioxidant properties. Consuming quercetin-fortified functional foods may improve human health.

[0004] In recent years, dietary polyphenol analogs can bind to functional proteins and cause changes in the nutritional properties of polyphenols and proteins, which has received extensive attention from scholars. Proteins and polyphenols are mostly complexed through non-covalent interactions in food systems. Non-covalent interactions are usually reversible and are mainly caused by hydrogen bonds, hydrophobic interactions, and electrostatic interactions. After the interaction between polyphenols and proteins, the structure of the protein will be changed, optimizing its adsorption behavior at the oil-water interface, thereby improving the stability of the emulsion. This property gives it certain application prospects in dairy products. In addition, polyphenol-protein complexes can also reduce the allergenicity of proteins and improve the bioavailability of polyphenols.

[0005] However, current research by scholars at home and abroad mainly focuses on encapsulating polyphenols in protein-based emulsion systems for delivery to improve their bioactivity. There are few studies on the regulation of emulsion cross-sectional properties by polyphenol-protein complexes to improve emulsion stability. Therefore, in this invention, soy protein isolate (SPI) is used as a raw material, and different concentrations of quercetin / morin (Q / M) are added for modification to prepare non-covalent complexes. Then, using the SPI-Q / M non-covalent complex as an emulsifier, an oil-in-water emulsion is prepared by a two-step homogenization method. This not only provides new insights into the study of the steady-state mechanism of polyphenol-regulated protein-based emulsions, improves the application potential of protein-polyphenol complexes, but also provides a theoretical basis for the rational design and construction of functionalized and stabilized emulsions. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for improving the interfacial properties of oil-in-water emulsions using soy protein isolate-quercetin isomers. To achieve the above object, this invention adopts the following scheme: A method for improving the interfacial properties of oil-in-water emulsions using soy protein isolate-quercetin isomers, the method comprising the following steps: Preparation of soy protein isolate (SPI) and quercetin / morin (Q / M) stock solutions: Dissolve SPI in deionized water, stir at room temperature for 2 h, and then hydrate completely overnight at 4°C to obtain a 1% (w / v) SPI solution; dissolve 0.015122 g of quercetin and morin in 1 mL of absolute ethanol respectively to obtain their 50 mmol / L stock solutions.

[0007] Preparation of soy protein isolate-quercetin / morin non-covalent complex (SPI-Q / M): Add the quercetin / morin stock solutions to the SPI solution respectively, stir in the dark at 25°C for 2 h, and the final concentration of Q / M is 0.2, 0.4, 0.8, 1.6 mmol / L. The soy protein isolate solution without adding quercetin / morin is reacted under the same conditions as a control group.

[0008] Preparation of SPI-Q / M oil-in-water (O / W) emulsion: Using 10% (w / v) soybean oil as the oil phase and 90% (w / v) SPI-Q / M solution (10 mg / mL) as the water phase, initially homogenize at 10000 rpm for 2 min using high-speed shearing, and then homogenize twice at 80 MPa to obtain a stable SPI-Q / M emulsion. The preferred conditions are that the optimal stirring time is 2 h in a 25°C environment; The preferred condition is that the high-pressure homogenization pressure is 80 MPa; The preferred condition is that the soybean oil content is 10%; The preferred condition is that the concentration of quercetin is 0.8 mmol / L.

[0009] The method of the present invention has improved the interfacial properties of the protein-based emulsion to a certain extent. The average particle size of the soy protein isolate-quercetin-stabilized oil-in-water emulsion has decreased by 7.23%; the interfacial protein adsorption rate has increased by 22.87%; and the interfacial protein concentration has increased by 101.44%.

[0010] The protein-based emulsion obtained by the above preparation method has excellent interfacial properties, which improves the application potential of the protein-polyphenol complex and helps to promote the rational design and development of functional and stable emulsions. Description of the Drawings

[0011] Appendix Figure 1 Technical roadmap of the method (using soy protein isolate - quercetin isomers to improve the interfacial properties of oil-in-water emulsions); Appendix Figure 2 Average particle size of the soy protein isolate - quercetin isomer-stabilized emulsion at different concentrations; Appendix Figure 3 Interfacial protein adsorption rate of the soy protein isolate - quercetin isomer-stabilized emulsion at different concentrations; Appendix Figure 4 Interfacial protein concentration of the soy protein isolate - quercetin isomer-stabilized emulsion at different concentrations. Detailed Embodiments

[0012] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0013] A method for improving the interfacial properties of oil-in-water emulsions using soy protein isolate - quercetin isomers, the method comprising the following steps: (1)Preparation of soy protein isolate (SPI), quercetin / morin (Q / M) stock solutions: Dissolve SPI in deionized water, stir at room temperature for 2 h, and then hydrate completely overnight at 4 °C to obtain a 1% (w / v) SPI solution; separately dissolve 0.015122 g of quercetin and morin in 1 mL of absolute ethanol to obtain their 50 mmol / L stock solutions. (2) Preparation of soy protein isolate - quercetin / morin non-covalent complexes (SPI-Q / M): Add the quercetin / morin stock solutions to the SPI solution respectively, stir in the dark at 25 °C for 2 h, and the final concentrations of Q / M are 0.2, 0.4, 0.8, 1.6 mmol / L. The soy protein isolate solution without added quercetin / morin reacts under the same conditions as the control group. (3) Preparation of SPI-Q / M oil-in-water (O / W) emulsions: Using 10% (w / v) soybean oil as the oil phase and 90% (w / v) SPI-Q / M solution (10 mg / mL) as the water phase, initially homogenize at 10000 rpm for 2 min with high-speed shearing, and then homogenize twice at 80 MPa by high-pressure homogenization to obtain stable SPI-Q / M emulsions.

[0014] Dissolve SPI in deionized water, stir at room temperature for 2 h, and then hydrate completely overnight at 4 °C to obtain a 1% (w / v) SPI solution; separately dissolve 0.015122 g of quercetin in 1 mL of absolute ethanol to obtain its 50 mmol / L stock solution. Then add the quercetin stock solution to the SPI solution respectively, stir in the dark at 25 °C for 2 h, and the final concentration of morin is 0.8 mmol / L. The soy protein isolate solution without added quercetin reacts under the same conditions as the control group. Using 10% (w / v) soybean oil as the oil phase and 90% (w / v) SPI-Q solution (10 mg / mL) as the water phase, initially homogenize at 10000 rpm for 2 min with high-speed shearing, and then homogenize twice at 80 MPa by high-pressure homogenization to obtain stable SPI-Q emulsions. The average particle size of the soy protein isolate - quercetin stable oil-in-water emulsion decreased by 7.23%; the interfacial protein adsorption rate increased by 22.87%; the interfacial protein concentration increased by 101.44%.

[0015] Dissolve SPI in deionized water, stir at room temperature for 2 h, and then hydrate completely overnight at 4 °C to obtain a 1% (w / v) SPI solution; then dissolve 0.015122 g of quercetin in 1 mL of absolute ethanol to obtain its 50 mmol / L stock solution. Then add the quercetin stock solution to the SPI solution and stir in the dark at 25 °C for 2 h, and the final concentration of morin is 0.2 mmol / L. The soy protein isolate solution without adding quercetin was reacted under the same conditions as a control group. Using 10% (w / v) soybean oil as the oil phase and 90% (w / v) SPI-Q solution (10 mg / mL) as the aqueous phase, primary homogenization was carried out at 10000 rpm for 2 min with high-speed shearing, and then high-pressure homogenization was carried out twice at 80 MPa to obtain a stable SPI-Q emulsion. The average particle size of the soy protein isolate - quercetin stable oil-in-water emulsion decreased by 1.37%; the interfacial protein adsorption rate increased by 12.65%; the interfacial protein concentration increased by 45.4%.

[0016] Dissolve SPI in deionized water, stir at room temperature for 2 h, and then hydrate completely overnight at 4 °C to obtain a 1% (w / v) SPI solution; then dissolve 0.015122 g of morin in 1 mL of absolute ethanol respectively to obtain its 50 mmol / L stock solution. Then add the morin stock solution to the SPI solution and stir in the dark at 25 °C for 2 h, and the final concentration of morin is 0.8 mmol / L. The soy protein isolate solution without adding morin was reacted under the same conditions as a control group. Using 10% (w / v) soybean oil as the oil phase and 90% (w / v) SPI-M solution (10 mg / mL) as the aqueous phase, primary homogenization was carried out at 10000 rpm for 2 min with high-speed shearing, and then high-pressure homogenization was carried out twice at 80 MPa to obtain a stable SPI-M emulsion. The average particle size of the soy protein isolate - morin stable oil-in-water emulsion decreased by 6.88%; the interfacial protein adsorption rate increased by 17.62%; the interfacial protein concentration increased by 96.70%.

Claims

1. A method for improving the interfacial properties of an oil-in-water emulsion by using soy protein isolate-quercetin isomers, the method comprising the following steps: (1) Preparation of soy protein isolate (SPI) and quercetin / morin (Q / M) stock solutions: SPI was dissolved in deionized water, stirred at room temperature for 2 h, and then completely hydrated at 4°C overnight to obtain a 1% (w / v) SPI solution; 0.015122 g of quercetin and morin were dissolved in 1 mL of anhydrous ethanol to obtain their 50 mmol / L stock solutions; (2) Preparation of soy protein isolate-quercetin / morin non-covalent complex (SPI-Q / M): Quercetin / morin stock solutions were added to SPI solution and stirred at 25°C in the dark for 2 h. The final concentrations of Q / M were 0.2, 0.4, 0.8, and 1.6 mmol / L, and the soy protein isolate solution without quercetin / mulin was reacted under the same conditions as the control group; (3) Preparation of SPI-Q / M oil-in-water (O / W) emulsion: 10% (w / v) soybean oil was used as the oil phase and 90% (w / v) SPI-Q / M solution (10 mg / mL) was used as the aqueous phase. The emulsion was initially homogenized at 10000 rpm for 2 min using high-speed shearing, and then homogenized twice at 80 MPa under high pressure to obtain a stable SPI-Q / M emulsion.

2. The method for improving the interfacial properties of oil-in-water emulsions by utilizing soy protein isolate-quercetin isomers according to claim 1, characterized in that: The high-pressure homogenization pressure is 80 MPa.

3. The method for improving the interfacial properties of oil-in-water emulsions by utilizing soy protein isolate-quercetin isomers according to claim 1, characterized in that: The content of soybean oil is 10%.

4. The method for improving the interfacial properties of oil-in-water emulsions by utilizing soy protein isolate-quercetin isomers according to claim 1, characterized in that: The concentration of quercetin was 0.8 mmol / L.

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