Method for improving functional characteristics of soybean protein isolate and anthocyanin compound by combining ultrasound with weak base

Abstract

The invention relates to a method for improving functional characteristics of a soybean protein isolate and anthocyanin compound by combining ultrasound with weak base, which belongs to the technical field of protein modification and comprises the following steps: (1) preparing a soybean protein isolate (SPI) solution; (2) carrying out pH-migration treatment on the SPI solution; (3) carrying out ultrasonic treatment on the SPI protein after pH-migration treatment; (4) preparing an SPI-BANs solution; and (5) preparing the SPI-BANs single-layer emulsion. The modification method provided by the invention can greatly improve the functional characteristics of the soybean protein isolate and anthocyanin compound, and is of great significance in expanding the application of the soybean protein isolate to functional and nutritional components in a food delivery system.

Description

Technical Field

[0001] The present invention adopts a technical method for modifying protein by combining ultrasonic means with pH-shift technology, and the method has a significant effect on optimizing the functional properties of soy protein isolate. Background Art

[0002] Soy protein isolate (SPI) is mainly composed of two globular proteins, 7S (β-conglobulin) and 11S (globulin), and has excellent biocompatibility and processing properties. However, unmodified soy protein isolate forms a compact globular structure due to the action of hydrogen bonds and disulfide bonds, has low molecular flexibility and poor emulsification ability, and its application in emulsification, gelation and other processing properties is limited. Proteins can obtain better functional properties after modification, which is of great significance for the innovation of functional and nutritional ingredients in food delivery systems. In view of this, it is imperative to modify soy protein isolate to make it have better functional properties.

[0003] Anthocyanin is a flavonoid polyphenol substance. Due to the rich phenolic hydroxyl groups in its molecular structure, it has excellent antioxidant properties. In addition, it has multiple biological activities such as scavenging free radicals, regulating blood lipids, anti-inflammatory and anti-cancer. However, anthocyanin is unstable in the aqueous phase and is easily affected by stresses such as temperature, pH, light and metal ions. It is attacked by nucleophilic water molecules, resulting in hydroxylation of 2-benzopyran cations and degradation. Therefore, the structure of anthocyanin should be modified to improve its stability.

[0004] The principle of pH-shift treatment is to use electrostatic repulsion to unfold the structure of the molecule. Under weak alkaline conditions, the hydrophobic properties of soy protein isolate will be affected to a certain extent. This is mainly attributed to the fact that the alkaline environment will cause the disulfide bonds of the protein to break, the subunits to dissociate, and the hydrophobic groups embedded in the molecules are exposed on the molecular surface, thereby improving the hydrophilicity of the material. Weak alkali denatures soy protein isolate, exposing the hydrophobic groups and improving the hydrophilicity of the interface, thereby improving the interfacial bonding strength and interfacial layer density, and improving the emulsification performance of SPI.

[0005] As an efficient and economical modification method, ultrasonic treatment can effectively change the molecular structure of proteins and promote intramolecular bonding of proteins. Its working principle is based on the mechanical effect and cavitation effect. In the emulsion system, the cavitation bubble will cause extreme phenomena such as high temperature, high pressure and local micro-injection at the moment of breaking. These extreme phenomena will then exert shear force on the dispersed phase macromolecules and release energy, thereby promoting the emulsification process.

[0006] At present, although it has been confirmed that anthocyanins can interact with proteins and polysaccharides in the surrounding environment through non-covalent bonds (such as hydrogen bonds and hydrophobic interactions) to improve their own stability, there are still few studies on the effects of pH-shift combined with ultrasonic treatment on the interaction and emulsification function of soy protein isolate and anthocyanin complexes, which restricts the application of anthocyanins in the field of functional foods. The present invention utilizes pH-shift and ultrasonic treatment technology to denature soy protein isolate and optimizes the combination parameters. This will hopefully obtain a soy protein isolate and anthocyanin complex with better functional properties, and broaden the application of SPI protein in food delivery systems. Summary of the invention

[0007] The present invention provides a method for improving the functional properties of a soy protein isolate and anthocyanin complex by utilizing ultrasound combined with weak alkali, aiming to further improve the functional properties of the soy protein isolate and broaden its application in the food industry.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for improving the functional properties of a complex of soy protein isolate and anthocyanin by using ultrasound combined with weak alkali, the method comprising the following steps:

[0010] (1) Preparation of soy protein isolate (SPI) solution: soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4°C, 9000×g, 20 min), and the supernatant was collected and precipitated with 2 mol / L sodium hydroxide. The pH was initially adjusted to 5.0 with 1 / L hydrochloric acid, magnetically stirred for 30 min, centrifuged (4°C, 3000×g, 15 min), and the precipitate was collected. The pH of the supernatant was adjusted to 4.5, magnetically stirred for 20 min, centrifuged (4°C, 4000×g, 15 min), and the precipitate was collected. Three times the volume of deionized water was added to the precipitate for dispersion, and the precipitate was collected after centrifugation (4°C, 8000×g, 10 min). A certain proportion of deionized water was added, and the pH was adjusted to 7.0 with 2 mol / L sodium hydroxide to obtain the SPI solution.

[0011] (2) pH-shift treatment of SPI solution: At room temperature, the pH value of the SPI solution was adjusted to 2.0 or 12.0 using 2 mol / L hydrochloric acid or 2 mol / L sodium hydroxide. After stirring at room temperature for 1 hour, the pH value was adjusted to 7.0 and stirred for 1 hour to obtain a pH-shifted soy protein isolate solution.

[0012] (3) Ultrasonic treatment of the SPI protein after pH-shift treatment: the SPI solution prepared in step (2) was placed under an ultrasonic power of 400 W and ultrasonicated for 10 min to obtain the SPI protein treated with a pH-shift combined with ultrasonic treatment;

[0013] (4) Preparation of SPI-BANs solution: The SPI protein prepared in step (3) was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer to make the final SPI protein solution have a mass concentration of 1.0 mg / mL, heated at 80°C for 10 min, cooled to room temperature for use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, and the mixture was thoroughly stirred. The SPI protein and BANs were mixed at a mass ratio of 1:1, and stirred in the dark at room temperature for 12 h to obtain a SPI-BANs solution;

[0014] (5) Preparation of SPI-BANs monolayer emulsion: The SPI-BANs solution prepared in step (4) was added with corn oil at an oil-water ratio of 1:9 (volume ratio), and the mixture was homogenized at 10,000 rpm for 3 min. The high-pressure homogenizer was cycled for 3 times at 80 MPa to obtain a SPI-BANs oil-in-water emulsion.

[0015] The preferred condition is that the protein concentration is 10 mg / mL;

[0016] The preferred condition is that the stirring time is 1h;

[0017] The preferred condition is that the mass ratio of soy protein isolate and anthocyanin after weak base combined with ultrasonic treatment is 1:1;

[0018] The preferred condition is 400W ultrasound for 10 min at pH 12.0.

[0019] The functional properties of the soy protein isolate and anthocyanin complex prepared by the method of the present invention are improved, and preferably the emulsification activity of the complex combined with ultrasound treatment at pH 12.0 is increased by 39.91%, the emulsification stability is increased to 1.24 times the original, the foaming ability is increased by 50.91%, and the foam stability is 1.26 times that of the initial state.

[0020] The above preparation method can obtain a soy protein isolate and anthocyanin complex with good functional properties, which is of great significance to the innovation of the delivery system of functional and nutritional ingredients in food. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Attached Figure 1 Flow chart of this method;

[0022] Attached Figure 2Emulsifying activity and emulsifying stability of soy protein isolate and anthocyanin complex after pH-shift combined with ultrasound treatment;

[0023] Attached Figure 3 Foaming ability and foam stability of soy protein isolate and anthocyanin complex after pH-shift combined with ultrasound treatment. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0025] A method for improving the functional properties of a soy protein isolate and anthocyanin complex by using ultrasound combined with weak alkali, the method comprising the following steps: (1) preparing a soy protein isolate (SPI) solution: grinding soybeans with a grinder for 1 minute and passing through an 80-mesh sieve, mixing with ether at a ratio of 1:4 (g / mL) and stirring for 1 hour; collecting a precipitate after standing and stratifying, repeating twice, air-drying the precipitate naturally, dispersing it in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension, adjusting the pH of the suspension to 9.5 with 2 mol / L sodium hydroxide, magnetically stirring for 1 hour, centrifuging (4°C, 9000×g, 20 minutes), collecting the supernatant, initially adjusting the pH to 5.0 with 2 mol / L hydrochloric acid, magnetically stirring for 30 minutes, centrifuging (4°C, 3000×g, 15 minutes), collecting the precipitate, adjusting the pH of the supernatant to 4.5, magnetically stirring for 20 minutes, centrifuging (4°C, 4000×g, 15 minutes), collecting the precipitate; (1) precipitate, add 3 times the volume of deionized water to the precipitate to disperse it, collect the precipitate after centrifugation (4°C, 8000×g, 10 min), add a certain proportion of deionized water, and adjust the pH to 7.0 with 2 mol / L sodium hydroxide to obtain SPI solution; (2) pH-shift treatment of SPI solution: at room temperature, use 2 mol / L hydrochloric acid or 2 mol / L sodium hydroxide to adjust the pH value of the SPI solution to 2.0 or 12.0, stir at room temperature for 1 hour, then adjust the pH value to 7.0 and stir for 1 hour to obtain the soy protein isolate solution treated with pH-shift; (3) ultrasonic treatment of SPI protein after pH-shift treatment: place the SPI solution prepared in step (2) under ultrasonic power of 400 W and ultrasonicate for 10 min to obtain SPI protein treated with dual synergistic treatment of pH-shift and ultrasonication; (4) preparation of SPI-BANs solution: take the SPI protein prepared in step (3) and dissolve it in 0.1 mol / L, pH 6.0 citric acid buffer solution to make the final SPI protein solution mass concentration of 1.0 mg / mL, heat at 80°C for 10 min, cool to room temperature for use, dissolve BANs in 0.1 mol / L, pH 4.0 citric acid buffer solution, add 0.05% ascorbic acid, stir well, mix SPI protein and BANs at a mass ratio of 1:1, stir in the dark at room temperature for 12 h to obtain SPI-BANs solution; (5) Preparation of SPI-BANs monolayer emulsion: add corn oil at an oil-water ratio of 1:9 (volume ratio) to the SPI-BANs solution obtained in step (4), coarsely homogenize at 10000 rpm for 3 min, and cycle the high-pressure homogenizer at 80 MPa for 3 times to obtain SPI-BANs water-in-oil emulsion.

[0026] Implementation Case 1

[0027] 20 g of soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4 ° C, 9000 × g, 20 min), the supernatant was collected, and the pH was adjusted to 9.5 with 2 mol / L hydrochloric acid. Initially adjust to 5.0, magnetically stir for 30 minutes, centrifuge (4°C, 3000×g, 15 minutes), collect the precipitate, adjust the pH of the supernatant to 4.5, magnetically stir for 20 minutes, centrifuge (4°C, 4000×g, 15 minutes), collect the precipitate, add 3 times the volume of deionized water to the precipitate to disperse, centrifuge (4°C, 8000×g, 10 minutes), collect the precipitate, add a certain proportion of deionized water, adjust the pH to 7.0 with 2 mol / L sodium hydroxide to obtain the SPI solution. The SPI protein was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer to make the final SPI protein solution mass concentration of 1.0 mg / mL, heated at 80 ° C for 10 min, cooled to room temperature for use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, and the mixture was fully stirred. The SPI protein and BANs were mixed at a mass ratio of 1:1, and stirred at room temperature in the dark for 12 hours to obtain a SPI-BANs solution. The SPI-BANs solution was added with corn oil at an oil-water ratio of 1:9 (volume ratio), coarsely homogenized at 10000 rpm for 3 min, and the high-pressure homogenizer was cycled 3 times at 80 MPa to obtain a SPI-BANs water-in-oil emulsion as a control group. The emulsifying activity of the soy protein isolate and anthocyanin complex obtained at this time was 42.93 m 2 / g, the emulsification stability is 60.53%, the foaming property is 41.25%, and the foam stability is 67.25%.

[0028] Implementation Case 2

[0029] 20 g of soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4 ° C, 9000 × g, 20 min), the supernatant was collected, and the pH was adjusted to 9.5 with 2 mol / L hydrochloric acid. Initially adjusted to 5.0, magnetically stirred for 30 minutes, centrifuged (4°C, 3000×g, 15 minutes), collected the precipitate, adjusted the pH of the supernatant to 4.5, magnetically stirred for 20 minutes, centrifuged (4°C, 4000×g, 15 minutes), collected the precipitate, added 3 times the volume of deionized water to the precipitate for dispersion, centrifuged (4°C, 8000×g, 10 minutes), collected the precipitate, added a certain proportion of deionized water, and adjusted the pH to 7.0 with 2 mol / L sodium hydroxide to obtain the SPI solution. The SPI solution was placed under an ultrasonic power of 400W and ultrasonicated for 10 minutes to obtain the ultrasonically treated SPI protein. The prepared SPI protein was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer, so that the final SPI protein solution had a mass concentration of 1.0 mg / mL, heated at 80 ° C for 10 min, cooled to room temperature for use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, fully stirred, SPI protein and BANs were mixed at a mass ratio of 1:1, stirred at room temperature in the dark for 12 hours, and SPI-BANs solution was obtained. The SPI-BANs solution was added to corn oil according to an oil-water ratio of 1:9 (volume ratio), coarsely homogenized at 10000 rpm for 3 minutes, and the high-pressure homogenizer was cycled 3 times at 80 MPa to obtain a SPI-BANs oil-in-water emulsion. At this time, the emulsification activity of the soy protein isolate and anthocyanin complex obtained by the treatment increased by 8.46%, the emulsification stability increased by 1.04 times, the foaming increased by 9.70%, and the foam stability increased by 1.09 times.

[0030] Implementation Case 3

[0031] 20 g of soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4 ° C, 9000 × g, 20 min), the supernatant was collected, and the pH was adjusted to 9.5 with 2 mol / L hydrochloric acid. Initially adjusted to 5.0, magnetically stirred for 30 minutes, centrifuged (4°C, 3000×g, 15 minutes), collected the precipitate, adjusted the pH of the supernatant to 4.5, magnetically stirred for 20 minutes, centrifuged (4°C, 4000×g, 15 minutes), collected the precipitate, added 3 times the volume of deionized water to the precipitate for dispersion, centrifuged (4°C, 8000×g, 10 minutes), collected the precipitate, added a certain proportion of deionized water, and adjusted the pH to 7.0 with 2mol / L sodium hydroxide to obtain the SPI solution. At room temperature, use 2mol / L hydrochloric acid to adjust the solution pH to 2.0, stir at room temperature for 1 hour, adjust the pH to 7.0, and stir for 1 hour to obtain the soy protein isolate solution treated with pH-shift. The prepared SPI protein was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer, so that the final SPI protein solution had a mass concentration of 1.0 mg / mL, heated at 80 ° C for 10 min, cooled to room temperature for use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, fully stirred, SPI protein and BANs were mixed at a mass ratio of 1:1, stirred at room temperature in the dark for 12 hours, and SPI-BANs solution was obtained. The SPI-BANs solution was added to corn oil according to an oil-water ratio of 1:9 (volume ratio), coarsely homogenized at 10000 rpm for 3 minutes, and the high-pressure homogenizer was cycled 3 times at 80 MPa to obtain a SPI-BANs water-in-oil emulsion. At this time, the emulsification activity of the soy protein isolate and anthocyanin complex obtained by the treatment increased by 13.43%, the emulsification stability increased by 1.09 times, the foaming increased by 18.18%, and the foam stability increased by 1.12 times.

[0032] Implementation Case 4

[0033] 20 g of soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4 ° C, 9000 × g, 20 min), the supernatant was collected, and the pH was adjusted to 9.5 with 2 mol / L hydrochloric acid. Initially adjusted to 5.0, magnetically stirred for 30 minutes, centrifuged (4°C, 3000×g, 15 minutes), collected the precipitate, adjusted the pH of the supernatant to 4.5, magnetically stirred for 20 minutes, centrifuged (4°C, 4000×g, 15 minutes), collected the precipitate, added 3 times the volume of deionized water to the precipitate for dispersion, centrifuged (4°C, 8000×g, 10 minutes), collected the precipitate, added a certain proportion of deionized water, and adjusted the pH to 7.0 with 2mol / L sodium hydroxide to obtain the SPI solution. At room temperature, the solution pH was adjusted to 12.0 with 2mol / L sodium hydroxide, stirred at room temperature for 1 hour, and then the pH was adjusted to 7.0 and stirred for 1 hour to obtain the soy protein isolate solution treated with pH-shift. The prepared SPI protein was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer, so that the final SPI protein solution had a mass concentration of 1.0 mg / mL, heated at 80 ° C for 10 min, cooled to room temperature for use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, and the mixture was fully stirred. The SPI protein and BANs were mixed at a mass ratio of 1:1, and stirred at room temperature in the dark for 12 hours to obtain a SPI-BANs solution. The SPI-BANs solution was added to corn oil according to an oil-water ratio of 1:9 (volume ratio), coarsely homogenized at 10000 rpm for 3 min, and the high-pressure homogenizer was cycled 3 times at 80 MPa to obtain a SPI-BANs oil-in-water emulsion. At this time, the emulsification activity of the soy protein isolate and anthocyanin complex obtained by the treatment increased by 21.43%, the emulsification stability increased by 1.16 times, the foaming property increased by 32.73%, and the foam stability increased by 1.17 times.

[0034] Implementation Case 5

[0035] 20 g of soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4 ° C, 9000 × g, 20 min), the supernatant was collected, and the pH was adjusted to 9.5 with 2 mol / L hydrochloric acid. Initially adjusted to 5.0, magnetically stirred for 30 minutes, centrifuged (4°C, 3000×g, 15 minutes), collected the precipitate, adjusted the pH of the supernatant to 4.5, magnetically stirred for 20 minutes, centrifuged (4°C, 4000×g, 15 minutes), collected the precipitate, added 3 times the volume of deionized water to the precipitate for dispersion, centrifuged (4°C, 8000×g, 10 minutes), collected the precipitate, added a certain proportion of deionized water, and adjusted the pH to 7.0 with 2mol / L sodium hydroxide to obtain the SPI solution. At room temperature, the pH value of the solution was adjusted to 2.0 with 2mol / L hydrochloric acid, stirred at room temperature for 1 hour, and then the pH value was adjusted to 7.0 and stirred for 1 hour, which was the soy protein isolate solution treated with pH-shift. The SPI solution was placed under ultrasonic power of 400W and ultrasonicated for 10 minutes to obtain the SPI protein treated with pH-shift combined with ultrasonic dual synergistic treatment. The prepared SPI protein was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer, so that the final SPI protein solution had a mass concentration of 1.0 mg / mL, heated at 80 ° C for 10 min, cooled to room temperature for use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, and the mixture was fully stirred. The SPI protein and BANs were mixed at a mass ratio of 1:1, and stirred at room temperature in the dark for 12 h to obtain a SPI-BANs solution. The SPI-BANs solution was added to corn oil at an oil-water ratio of 1:9 (volume ratio), coarsely homogenized at 10000 rpm for 3 min, and the high-pressure homogenizer was cycled 3 times at 80 MPa to obtain a SPI-BANs oil-in-water emulsion. At this time, the emulsification activity of the soy protein isolate and anthocyanin complex obtained by the treatment was increased by 31.52%, the emulsification stability was increased to 1.20 times the original, the foaming property increased by 38.79%, and the foam stability was enhanced to 1.21 times.

[0036] Implementation Case 6

[0037] 20 g of soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4 ° C, 9000 × g, 20 min), the supernatant was collected, and the pH was adjusted to 9.5 with 2 mol / L hydrochloric acid. Initially adjusted to 5.0, magnetically stirred for 30 minutes, centrifuged (4°C, 3000×g, 15 minutes), collected the precipitate, adjusted the pH of the supernatant to 4.5, magnetically stirred for 20 minutes, centrifuged (4°C, 4000×g, 15 minutes), collected the precipitate, added 3 times the volume of deionized water to the precipitate for dispersion, centrifuged (4°C, 8000×g, 10 minutes), collected the precipitate, added a certain proportion of deionized water, and adjusted the pH to 7.0 with 2mol / L sodium hydroxide to obtain the SPI solution. At room temperature, the pH value of the solution was adjusted to 12.0 with 2mol / L sodium hydroxide, stirred at room temperature for 1 hour, and then the pH value was adjusted to 7.0 and stirred for 1 hour, which was the soy protein isolate solution treated with pH-shift. The SPI solution was placed under ultrasonic power of 400W and ultrasonicated for 10 minutes to obtain the SPI protein treated with double synergistic treatment of pH-shift and ultrasound. The prepared SPI protein was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer, so that the final SPI protein solution had a mass concentration of 1.0 mg / mL, heated at 80 ° C for 10 min, cooled to room temperature for standby use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, fully stirred, SPI protein and BANs were mixed at a mass ratio of 1:1, stirred at room temperature in the dark for 12 hours, and SPI-BANs solution was obtained. The SPI-BANs solution was added with corn oil according to an oil-water ratio of 1:9 (volume ratio), coarsely homogenized at 10000 rpm for 3 min, and the high-pressure homogenizer was cycled 3 times at 80 MPa to obtain a SPI-BANs oil-in-water emulsion. At this time, the emulsification activity of the soy protein isolate and anthocyanin complex obtained by the treatment was increased by 39.91%, the emulsification stability was increased to 1.24 times the original, the foaming property increased by 50.10%, and the foam stability was enhanced to 1.26 times.

Claims

1. A method for improving the functional properties of a complex of soy protein isolate and anthocyanin by using ultrasound combined with weak alkali, the method comprising the following steps: (1) Preparation of soy protein isolate (SPI) solution: soybeans were crushed with a grinder for 1 min and passed through an 80-mesh sieve, mixed with ether at a ratio of 1:4 (g / mL) and stirred for 1 h; after standing and stratification, the precipitate was collected and repeated twice. The precipitate was naturally air-dried and dispersed in deionized water at a volume ratio of 1:15 (g / mL) to form a uniform suspension. The pH of the suspension was adjusted to 9.5 with 2 mol / L sodium hydroxide, magnetically stirred for 1 h, centrifuged (4°C, 9000×g, 20 min), and the supernatant was collected and precipitated with 2 mol / L sodium hydroxide. The pH was initially adjusted to 5.0 with 1 / L hydrochloric acid, magnetically stirred for 30 min, centrifuged (4°C, 3000×g, 15 min), and the precipitate was collected. The pH of the supernatant was adjusted to 4.5, magnetically stirred for 20 min, centrifuged (4°C, 4000×g, 15 min), and the precipitate was collected. Three times the volume of deionized water was added to the precipitate for dispersion, and the precipitate was collected after centrifugation (4°C, 8000×g, 10 min). A certain proportion of deionized water was added, and the pH was adjusted to 7.0 with 2 mol / L sodium hydroxide to obtain the SPI solution. (2) pH-shift treatment of SPI solution: At room temperature, the pH value of the SPI solution was adjusted to 2.0 or 12.0 using 2 mol / L hydrochloric acid or 2 mol / L sodium hydroxide. After stirring at room temperature for 1 hour, the pH value was adjusted to 7.0 and stirred for 1 hour to obtain a pH-shifted soy protein isolate solution. (3) Ultrasonic treatment of the SPI protein after pH-shift treatment: the SPI solution prepared in step (2) was placed under an ultrasonic power of 400 W and ultrasonicated for 10 min to obtain the SPI protein treated with a pH-shift combined with ultrasonic treatment; (4) Preparation of SPI-BANs solution: The SPI protein prepared in step (3) was dissolved in 0.1 mol / L, pH 6.0 citric acid buffer to make the final SPI protein solution have a mass concentration of 1.0 mg / mL, heated at 80°C for 10 min, cooled to room temperature for use, BANs were dissolved in 0.1 mol / L, pH 4.0 citric acid buffer, 0.05% ascorbic acid was added, and the mixture was thoroughly stirred. The SPI protein and BANs were mixed at a mass ratio of 1:1, and stirred in the dark at room temperature for 12 h to obtain a SPI-BANs solution; (5) Preparation of SPI-BANs monolayer emulsion: The SPI-BANs solution prepared in step (4) was added with corn oil at an oil-water ratio of 1:9 (volume ratio), and the mixture was homogenized at 10,000 rpm for 3 min. The high-pressure homogenizer was cycled for 3 times at 80 MPa to obtain a SPI-BANs oil-in-water emulsion.

2. The method of claim 1, wherein the method comprises: Soy protein isolate was dissolved in deionized water to obtain a protein solution with a concentration of 10 mg / mL.

3. The method of claim 1, wherein the method comprises: The optimal stirring time is 1h.

4. The method of claim 1, wherein the method comprises: The mass ratio of SPI and BANs after pH-shift combined with ultrasonic treatment was 1:

1.

5. The method of claim 1, wherein the method comprises: The optimal condition for the functional properties of the SPI-BANs complex obtained by pH-shift combined with ultrasonic treatment of SPI is 400W ultrasound for 10 min at pH 12.0.

Images