阅读说明：本技术 一种超持水大豆分离蛋白凝胶及其制备方法 (Super water-holding soybean protein isolate gel and preparation method thereof ) 是由 张�浩 史乾坤 刘景圣 王心雅 甄诺 闵伟红 金晓春 安琪 赵城彬 吴玉柱 许秀 于 2021-01-27 设计创作，主要内容包括：一种超持水大豆分离蛋白凝胶及其制备方法,属于食品蛋白质深加工领域。该超持水大豆分离蛋白凝胶的制备方法为：在室温下,将大豆分离蛋白粉进行高压力场预处理,得到修饰预处理的大豆分离蛋白溶液,进行冻干,得到冻干SPI；将冻干SPI加入蒸馏水,得到冻干SPI溶液；再加入酶溶液,搅拌均匀,将均匀混合物置于35～45℃反应0.5～3h,然后置于90～110℃进行灭活10～15min,然后于4～5℃放置24h以上,得到超持水大豆分离蛋白凝胶。该方法通过高压力场预处理后,进行冻干然后配合酶交联,得到超持水大豆分离蛋白凝胶,该超持水大豆分离蛋白凝胶持水能力增加,自由水减少,凝胶的质构特性得到良好的改善。(A super water-holding soy protein isolate gel and a preparation method thereof belong to the field of food protein deep processing. The preparation method of the super water-holding soybean protein isolate gel comprises the following steps: performing high-pressure field pretreatment on the isolated soybean protein powder at room temperature to obtain a modified and pretreated isolated soybean protein solution, and performing freeze-drying to obtain freeze-dried SPI; adding distilled water into the freeze-dried SPI to obtain a freeze-dried SPI solution; and adding an enzyme solution, stirring uniformly, placing the uniform mixture at 35-45 ℃ for reaction for 0.5-3 h, then placing at 90-110 ℃ for inactivation for 10-15 min, and then placing at 4-5 ℃ for more than 24h to obtain the super water-holding soybean protein isolate gel. The method is characterized in that after pretreatment through a high-pressure field, freeze-drying is carried out, and then enzyme crosslinking is carried out, so as to obtain the super water-holding soybean protein isolate gel, wherein the water holding capacity of the super water-holding soybean protein isolate gel is increased, free water is reduced, and the texture characteristics of the gel are well improved.)

1. A preparation method of super water-holding soybean protein isolate gel is characterized by comprising the following steps:

step 1: pretreatment of

Performing high-pressure field pretreatment on the soybean protein isolate powder at room temperature to obtain a modified and pretreated soybean protein isolate solution;

the high pressure field pretreatment mode is as follows: one or more of screw extrusion, dynamic high-pressure microjet homogenization, heat-synergetic high-pressure microjet homogenization, acid-synergetic high-pressure microjet homogenization and ultrahigh-pressure field treatment;

step 2: freeze-drying

Freeze-drying the modified and pretreated soybean protein isolate solution at-50 to-60 ℃ to obtain freeze-dried SPI;

and step 3: preparation of super water-holding soy protein isolate gel

Adding the lyophilized SPI into distilled water, and stirring uniformly to obtain the SPI with the mass concentration of 9 multiplied by 10^-5～1×10^-4g/mL of lyophilized SPI solution;

adding an enzyme solution according to a ratio, stirring at a speed of 700-900 r/min for 8-15 s to obtain a mixture; in the mixture, the mass concentration of the enzyme is 0.3-30U/g; the concentration of the enzyme solution is 10-30U/mL;

and (3) placing the mixture at 35-45 ℃ for reaction for 0.5-3 h, then placing at 90-110 ℃ for inactivation for 10-15 min, and then placing at 4-5 ℃ for more than 24h to obtain the super water-holding soybean protein isolate gel.

2. The method for preparing a super water-retaining soy protein isolate gel as claimed in claim 1, wherein in step 1, the process parameters of the screw extrusion are:

(1) placing the soybean protein isolate powder in an automatic feeder, wherein the rotation speed of a screw is 160-300 r/min, the temperature is 130-150 ℃, the water content is 15-50%, and the head pressure is 5-25 MPa, so as to obtain modified and pretreated soybean protein isolate;

(2) placing the modified and pretreated soybean protein isolate into a hot air drying system for drying treatment; and then crushing and sieving the soybean protein isolate by a 100-mesh sieve to obtain a soybean protein isolate pretreatment sample, and preparing a modified pretreatment soybean protein isolate solution with the mass concentration of 5-10%.

3. The method for preparing a super water-retaining soy protein isolate gel as claimed in claim 1, wherein the dynamic high pressure microjet homogenization process parameters in step 1 are:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) and (3) placing the solution under the pressure of 10-150 MPa, and homogenizing for 10-30 min.

4. The method of claim 1, wherein in step 1, the heat-assisted high pressure microfluidization is performed to:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) firstly, the solution is placed at the constant temperature of 40-100 ℃ for 0.5-3 h, and then the solution is placed at the pressure of 10-150 MPa and the homogenization time is 10-30 min at room temperature.

5. The method of claim 1, wherein in step 1, the acid-assisted high pressure microfluidization is performed to:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) adding a hydrochloric acid aqueous solution with the pH value of 1-6 into the solution to dissolve the soybean protein isolate for 0.5-3 h, washing the solution for the second time until the pH value is 7.0-7.4, and then placing the solution at the room temperature under the pressure of 10-150 MPa for homogenizing for 10-30 min.

6. The method for preparing a super water-retaining soy protein isolate gel as claimed in claim 1, wherein in step 1, the process parameters of the super high pressure field are:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) putting the isolated soy protein solution into a vacuum bag, discharging air bubbles, and carrying out vacuum packaging and sealing; obtaining a sealed solution;

(3) and (3) placing the sealed solution under the pressure of 100-500 MPa at room temperature, and maintaining the pressure for 5-15 min.

7. The method for preparing a super water-holding soy protein isolate gel as claimed in claim 1, wherein in step 1, the modified pre-treated soy protein isolate solution has a free mercapto content of 3.43-4.01 μmol/mL, a fluorescence intensity of 689.9-782.9 a.u., and a enthalpy of 236.94-275.37J/g.

8. The method for preparing a super water-retaining soy protein isolate gel as claimed in claim 1, wherein in step 3, the enzyme is one or more of transglutaminase, peroxidase, and polyphenol oxidase.

9. The method for preparing a super water-holding soy protein isolate gel as claimed in claim 8, wherein the peroxidase is one or more of catalase, horseradish peroxidase and glutathione peroxidase;

the polyphenol oxidase is one or more of tyrosinase, catechol oxidase and laccase.

10. The super water-holding soybean protein isolate gel is characterized by being prepared by the preparation method of any one of claims 1 to 9, and the prepared super water-holding soybean protein isolate gel has the water holding capacity WHC of 85 to 93 percent, the free water content of 94.48 to 96.46 percent, the gel hardness of 55 to 730g, the viscosity of 110 to 555 Ps, the cohesion of 0.45 to 0.75, the chewiness of 25 to 232 and the elasticity value of 0.1 to 0.54.

Technical Field

The invention relates to the technical field of food protein deep processing, in particular to a super water-holding soybean protein isolate gel and a preparation method thereof.

Background

The Soybean Protein Isolate (SPI) is a complete protein food additive produced by using low-temperature desolventized Soybean meal as a raw material, the protein content of the food additive reaches over 90 percent, the amino acids are various, the main amino acid types are beta-glycine (7S) and glycine (11S), the food additive has higher nutritional value, functional characteristics and related health effects, and the Soybean protein isolate is widely applied to the manufacture of foods such as infant formula milk powder, bean curd, meat, dairy products and the like. However, SPI has poor emulsifying properties and its extended use in food and non-food applications is somewhat limited. It is more common practice to improve its emulsibility through enzyme to SPI crosslinking, and the SPI gel that obtains, although emulsibility and emulsion stability have the improvement, but, in the crosslinking process, the SPI gel forms, and the embedding has a large amount of free water, and its SPI gel intensity is low, to SPI gel, all has higher requirement in transportation, quality guarantee. Therefore, it is important to improve the emulsifying property of SPI gel and to improve the water holding capacity and gel strength.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a super water-holding soy protein isolate gel and a preparation method thereof. After pretreatment by a high pressure field, freeze-drying and then cross-linking by matching with enzyme to obtain the super water-holding soybean protein isolate gel, wherein the water holding capacity of the super water-holding soybean protein isolate gel is increased, free water is reduced, and the texture characteristics of the gel are well improved.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention relates to a preparation method of super water-holding soybean protein isolate gel, which comprises the following steps:

step 1: pretreatment of

Performing high-pressure field pretreatment on the soybean protein isolate powder at room temperature to obtain a modified and pretreated soybean protein isolate solution;

the high pressure field pretreatment mode is as follows: one or more of screw extrusion, dynamic high-pressure microjet homogenization, heat-synergetic high-pressure microjet homogenization, acid-synergetic high-pressure microjet homogenization and ultrahigh-pressure field treatment;

step 2: freeze-drying

Freeze-drying the modified and pretreated soybean protein isolate solution at-50 to-60 ℃ to obtain freeze-dried SPI;

and step 3: preparation of super water-holding soy protein isolate gel

Adding the lyophilized SPI into distilled water, and stirring uniformly to obtain the SPI with the mass concentration of 9 multiplied by 10^-5～1×10^-4g/mL of lyophilized SPI solution;

adding an enzyme solution according to a ratio, stirring at a speed of 700-900 r/min for 8-15 s to obtain a mixture; in the mixture, the mass concentration of the enzyme is 0.3-30U/g; the concentration of the enzyme solution is 10-30U/mL;

and (3) placing the mixture at 35-45 ℃ for reaction for 0.5-3 h, then placing at 90-110 ℃ for inactivation for 10-15 min, and then placing at 4-5 ℃ for more than 24h to obtain the super water-holding soybean protein isolate gel.

In the step 1, the screw extrusion process parameters are as follows:

(1) placing the soybean protein isolate powder in an automatic feeder, wherein the rotation speed of a screw is 160-300 r/min, the temperature is 130-150 ℃, the water content is 15-50%, and the head pressure is 5-25 MPa; more preferably, the screw rotation speed is 200-300 r/min, the temperature is 140-150 ℃, and the water content is 15-25%; obtaining modified and pretreated soybean protein isolate;

(2) placing the modified and pretreated soybean protein isolate into a hot air drying system for drying treatment; and then crushing and sieving the soybean protein isolate by a 100-mesh sieve to obtain a soybean protein isolate pretreatment sample, and preparing a modified pretreatment soybean protein isolate solution with the mass concentration of 5-10%.

In the step 1, the technological parameters of the dynamic high-pressure microjet homogenization are as follows:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) and (3) placing the solution under the pressure of 10-150 MPa, preferably 80-150 MPa, and homogenizing for 10-30 min.

In the step 1, the heat-synergetic high-pressure micro-jet homogenization is as follows:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) firstly, the solution is placed at the constant temperature of 40-100 ℃ for 0.5-3 h, and then the solution is placed at the pressure of 10-150 MPa and the homogenization time is 10-30 min at room temperature.

In the step 1, the acid is homogenized into the following components by cooperating with the high-pressure microjet:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) adding a hydrochloric acid aqueous solution with the pH value of 1-6 into the solution to dissolve the soybean protein isolate for 0.5-3 h, washing the solution for the second time until the pH value is 7.0-7.4, and then placing the solution at the room temperature under the pressure of 10-150 MPa for homogenizing for 10-30 min.

In the step 1, the technological parameters of the ultrahigh-pressure field are as follows:

(1) dissolving the soybean protein isolate powder in distilled water according to the proportion to prepare a soybean protein isolate solution with the mass fraction of 5-10%;

(2) putting the isolated soy protein solution into a vacuum bag, discharging air bubbles, and carrying out vacuum packaging and sealing; obtaining a sealed solution;

furthermore, the vacuum bag is made of a high-temperature and high-pressure resistant flexible plastic bag, preferably a polyethylene plastic bag.

(3) And (3) placing the sealed solution under the pressure of 100-500 MPa, more preferably 200-400 MPa, and keeping the pressure for 5-15 min at room temperature.

In the step 1, in the modified and pretreated soybean protein isolate solution, the free mercapto content of the modified and pretreated soybean protein isolate is 3.43-4.01 mu mol/mL, the fluorescence intensity is 689.9-782.9 a.u., and the enthalpy value is 236.94-275.37J/g.

In the step 3, the time for uniformly stirring is preferably 1-2 h.

In the step 3, the enzyme is preferably one or more of transglutaminase, peroxidase and polyphenol oxidase.

The peroxidase is one or more of catalase, horseradish peroxidase and glutathione peroxidase.

The polyphenol oxidase is preferably one or more of tyrosinase, catechol oxidase and laccase.

The super water-holding soybean protein isolate gel disclosed by the invention has the water holding capacity WHC of 85-93%, the free water content of 94.48-96.46%, the gel hardness of 55-730 g, the viscosity of 110-555 Ps, the cohesiveness of 0.45-0.75, the chewiness of 25-232 and the elasticity value of 0.1-0.54.

Compared with the prior art, the super water-holding soybean protein isolate gel and the preparation method thereof have the beneficial effects that:

1. through high-pressure field pretreatment, enzyme-induced SPI gelation can be enhanced, because the pressure field can change the properties of the soybean protein isolate, so that different stretching and folding structures of the soybean protein isolate are formed, the particle size of the soybean protein isolate is changed, free SH of reactive functional groups on the surface of the soybean protein isolate is increased, and the subsequent enzyme crosslinking effect is improved; and the subsequent enzyme crosslinking promotes the formation of hydrophobic interaction and disulfide bonds, thereby enhancing the gel strength and water holding capacity of the soybean protein isolate and obtaining a more uniform three-dimensional network gel structure.

2. The super water-holding soybean protein isolate gel prepared by the invention can provide practical functions in the application of food protein processing systems such as bean curd, cheese, meat protein, protein beverage and the like.

3. The high pressure field pretreatment is combined with enzyme treatment, so that the secondary structure of the soybean protein isolate is changed, the beta-folding content and the random coil content are increased, and the alpha-helix and the beta-turn are reduced. The prepared super water-holding soy protein isolate gel has the advantages of enhanced water holding capacity, reduced free water, and good improvement of gel texture characteristics, and provides good guarantee for the subsequent application of the soy protein isolate gel.

4. The invention adopts the high pressure field for pretreatment, and then carries out the freeze-drying process, which not only can convert ice in the modified and pretreated soybean protein isolate solution into steam under higher vacuum and has smaller change to the structure of the protein, but also has better protection function to active groups in the soybean protein isolate and can not change samples processed by the high pressure field, the obtained freeze-dried soybean protein isolate sample can be compounded into other required concentrations for further processing, and after the high pressure field is processed, the particle size of the soybean protein isolate is reduced, the dispersibility is enhanced, the phase change mode of water is changed, fine and uniform ice crystals are formed in the subsequent freezing process and are in a complete freezing state, the water holding capacity is improved, and simultaneously, the free water content is reduced to a certain extent, the gel stability period is improved, and the SPI after freeze-drying can be stably stored in a dry environment for a long time according to the production progress without influencing the subsequent enzyme crosslinking process.

Drawings

FIG. 1 is a graph showing a comparison of the free thiol content of modified pretreated soybean protein isolates prepared according to the present invention under different pressure field pressures in comparative example 1 and examples 1-5.

FIG. 2 is a graph showing a comparison of particle sizes of modified pretreated soybean protein isolates prepared in comparative example 1 and examples 1 to 5 of the present invention under different pressure field pressures.

FIG. 3 is a graph showing a comparison of fluorescence intensities in modified pretreated soybean protein isolates prepared in comparative example 1 and examples 1 to 5 of the present invention under different pressure field pressures.

FIG. 4 is a graph showing a comparison of water holding capacities of the super water-holding soybean protein isolate gel prepared in comparative example 1 and examples 1 to 5 of the present invention under different pressure field pressures.

FIG. 5 is a graph showing a comparison of the free water content of the gel of the super water-holding soybean protein isolate according to the present invention prepared in comparative example 1 and examples 1 to 5 under different pressure field pressures.

FIG. 6 is a scanning electron microscope photograph of the super water-retained soy protein isolate gel prepared in example 1 of the present invention.

FIG. 7 is a scanning electron microscope photograph of the super water-retained soy protein isolate gel prepared in example 2 of the present invention.

FIG. 8 is a scanning electron microscope photograph of the super water-retained soy protein isolate gel prepared in example 3 of the present invention.

FIG. 9 is a scanning electron microscope photograph of the super water-retained soy protein isolate gel prepared in example 4 of the present invention.

FIG. 10 is a scanning electron microscope photograph of the super water-retained soy protein isolate gel prepared in example 5 of the present invention.

FIG. 11 is a scanning electron microscope photograph of a soybean protein isolate gel prepared in comparative example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and embodiments. The examples herein are merely illustrative of the present invention and are not intended to be limiting. In addition, the technical features mentioned in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

In the following examples, the starting materials used were all commercially available and the purity of the starting materials was all analytically pure unless otherwise specified.

In the following examples, the equipment used is commercially available unless otherwise specified, and the equipment mainly includes a high-speed centrifuge; alpha1-4LDplus freeze dryer; phenom desktop scanning electron microscope; VERTEX 70 Fourier Infrared Spectroscopy; q2000 differential scanning calorimeter; DZ400/2SB vacuum packaging machine; HPP600MPa/30L ultrahigh pressure food processing equipment; DF-101S heat collection type constant temperature heating magnetic stirrer.

In the following examples, the thiol content was determined by the following method:

diluting the modified and pretreated soybean protein isolate solution until the mass concentration of the modified and pretreated soybean protein isolate is 1mg/mL to obtain a diluted sample; 1mL of the diluted sample was taken, 2.0mL of Tris-glycine buffer (pH 8.0, containing 10.4g Tris, 6.9g glycine, 1.2g EDTA/L) and 0.02mL of Ellman's reagent (prepared to contain 4mg DTNB/mL, prepared with pH8.0 Tris-glycine buffer) at a mass concentration of 4g/L were added, the mixture was kept at 25 ℃ for 20min, and the absorbance was measured at 412nm using a spectrophotometer. The experiment was blanked without the addition of egg white solution and with the addition of Ellman reagent. the-SH content was calculated according to the following formula:

-SH(μmol/mL)＝(73.53×A₄₁₂×D)/C

in the formula: a. the₄₁₂Subtracting the light absorption value of the protein liquid without DTNB from the light absorption value of the protein liquid with DTNB; d is the dilution multiple of the protein solution; c is the concentration of the protein solution (mg/mL).

Particle size analysis in the following examples, particle size distribution and mean particle size were measured using a Malvern Mastersizer 2000. The pretreated and untreated soy protein isolate solutions were diluted with phosphate buffer (0.01M, pH 7.0) to a soy protein isolate mass concentration of 1mg/mL, and 1mL was taken for particle size analysis.

In the following examples, the fluorescence spectroscopy method was: the modified pretreated soy protein isolate solution was diluted to a modified pretreated soy protein isolate mass concentration of 0.5mg/mL by adding phosphate buffer. And (3) carrying out fluorescence spectrum scanning at a scanning speed of 600nm/min, wherein the excitation wavelength is 280nm, the emission wavelength is 300-550 nm, and the slit width is 15.0 nm.

In the following examples, gel strength was measured using a TA-XT2 texture analyzer. The super water-holding soybean protein isolate gel is placed on a measuring table, a probe with the ratio of P/0.5 is adopted for measurement, a TPA mode is selected, the speeds before, during and after compression are respectively 3.0, 2.0 and 3.0mm/s, the gel compression ratio is 35 percent, the interval of two times of pressing is 5s, and the trigger force is 5 g. The measured texture parameters and the gel strength are expressed as the maximum induction force during the pressing of the probe.

In the following examples, the Water Holding Capacity (WHC) was determined as follows: weighing 5g of the soybean protein isolate gel with water retention capacity, placing the soybean protein isolate gel with water retention capacity in a 50mL centrifuge tube, centrifuging for 15min at 4 ℃ and 5000rpm, removing the centrifuged water, and measuring the mass of the soybean protein isolate gel with water retention capacity in the centrifuge tube before and after centrifugation. Three replicates of each sample were run. The water binding capacity is calculated according to the formula:

in the formula: m is₀The mass (g) of the centrifuge tube; m is₁The mass (g) of the centrifuge tube before centrifugation and the super water-holding soybean protein isolate gel; m is₂The gel mass (g) of the centrifuged centrifugal tube and the ultra-water-holding soybean protein isolate is shown.

In the following examples, the microstructure morphology of a sample was observed by a scanning electron microscope, dried super water-holding soybean protein isolate gel was fixed on a sample stage with a double-sided conductive adhesive, the surface of the sample was lightly blown with an ear-washing ball to lay the sample on the surface of the sample in a single layer, and then metal was sputtered by ion sputtering and placed on the observation stage of the scanning electron microscope to observe the microstructure. The acceleration voltage was set at 5 kV.

Example 1

A method for preparing super water-holding soy protein isolate gel comprises the following steps:

weighing soybean protein isolate powder, dissolving in distilled water to prepare a soybean protein isolate solution with the mass fraction of 5%, placing the soybean protein isolate solution in a five-layer polyethylene plastic bag (a high-temperature and high-pressure resistant flexible plastic bag), and tightly sealing the five-layer polyethylene plastic bag by a vacuum packaging machine without air bubbles. Carrying out high-pressure field pretreatment on the sealed solution at the temperature of 25 ℃ and under the pressure of 100MPa to obtain a modified and pretreated soybean protein isolate solution;

the modified and pretreated soy protein isolate solution is analyzed, the content of free lyophobic radicals is 3.43 mu mol/mL, the fluorescence intensity is 761.8a.u., and the enthalpy value is 263.78J/g.

Freeze-drying the modified and pretreated soy protein isolate solution at-50 ℃ to obtain freeze-dried SPI;

adding distilled water into the lyophilized SPI to prepare a lyophilized SPI solution with the mass concentration of 9mg/100mL, and stirring for 1h at room temperature. Adding TGase in 20U/mL solution, stirring at 800r/min, and rapidly stirring for 10s to obtain a mixture; in the mixture, the concentration of TGase is 30U/g, and the mass concentration of SPI is 9mg/100 mL;

reacting the mixture at 40 deg.C for 2h, inactivating at 90 deg.C for 10min, and standing overnight at 4 deg.C to obtain super water-holding soy protein isolate gel.

The texture property parameters of the obtained soybean protein isolate gel are shown in Table 1, and the scanning electron microscope image of the super water-holding soybean protein isolate gel is shown in FIG. 6.

Example 2

A method for preparing super water-holding soy protein isolate gel, which is the same as example 1, except that:

the pressure adopted by the high-pressure field pretreatment is 200MPa, and the modified and pretreated soy protein isolate solution obtained in the example is analyzed, so that the content of free lyophobic radicals is 3.53 mu mol/mL, the fluorescence intensity is 754.4a.u., and the enthalpy value is 262.36J/g.

The texture characteristics of the soy protein isolate gel obtained in this example are shown in Table 1, and the SEM image of the ultra-water-retained soy protein isolate gel is shown in FIG. 7.

Example 3

A method for preparing super water-holding soy protein isolate gel, which is the same as example 1, except that:

the pressure adopted by the high-pressure field pretreatment is 300MPa, and the modified and pretreated soy protein isolate solution obtained in the example is analyzed, so that the content of free lyophobic radicals is 3.67 mu mol/mL, the fluorescence intensity is 715.7a.u., and the enthalpy value is 271.46J/g.

The texture characteristics of the soy protein isolate gel obtained in this example are shown in Table 1, and the SEM image of the ultra-water-retained soy protein isolate gel is shown in FIG. 8.

Example 4

A method for preparing super water-holding soy protein isolate gel, which is the same as example 1, except that:

the pressure adopted by the high-pressure field pretreatment is 400MPa, and the modified and pretreated soy protein isolate solution obtained in the example is analyzed, so that the content of free lyophobic radicals is 4.01 mu mol/mL, the fluorescence intensity is 689.9a.u., and the enthalpy value is 275.37J/g.

The texture characteristics of the soy protein isolate gel obtained in this example are shown in Table 1, and the SEM image of the ultra-water-retained soy protein isolate gel is shown in FIG. 9.

Example 5

A method for preparing super water-holding soy protein isolate gel, which is the same as example 1, except that:

the pressure adopted by the high-pressure field pretreatment is 500MPa, and the modified and pretreated soy protein isolate solution obtained in the example is analyzed, so that the content of free lyophobic radicals is 3.76 mu mol/mL, the fluorescence intensity is 782.9a.u., and the enthalpy value is 236.94J/g.

The texture characteristics of the soy protein isolate gel obtained in this example are shown in Table 1, and the SEM image of the ultra-water-retained soy protein isolate gel is shown in FIG. 10.

Comparative example 1

A method for preparing a soy protein isolate gel, which is the same as example 1, except that: no high pressure field pretreatment was performed. The scanning electron microscope image of the obtained soybean protein isolate gel is shown in FIG. 11, and the texture parameters of the soybean protein isolate gel are shown in Table 1.

The comparison of the free thiol content of the modified and pretreated soybean protein isolate obtained in the above examples 1 to 5 and comparative example 1 is shown in fig. 1, and it can be known that the free thiol content of the soybean protein isolate is increased after the ultrahigh pressure pretreatment, which indicates that the high pressure pretreatment field has an effect on the modification of the soybean protein isolate, and can increase the reactive functional group free mercapto group on the surface of the soybean protein isolate, thereby affecting the gel property of the subsequent soybean protein isolate.

As shown in FIG. 2, the particle size comparison graph of the modified and pretreated soybean protein isolates obtained in examples 1 to 5 and comparative example 1 shows that, compared with the particle size in comparative example 1, the particle size distribution of the soybean protein isolate which is not subjected to high pressure field pretreatment is small, and after the ultrahigh pressure treatment, the intermolecular expansion of the soybean protein isolate can be increased to form small aggregates and the average particle size can be increased when the soybean protein isolate is treated at 100 to 300 MPa. When the soybean protein isolate is treated under 400-500 MPa, the structure of the soybean protein isolate is seriously damaged due to overlarge strength, and the average particle size is reduced.

As is apparent from FIG. 3, the comparison of the fluorescence intensities of the modified pretreated soybean protein isolates obtained in examples 1 to 5 and comparative example 1 is shown in FIG. 3, and it is understood from FIG. 3 that the fluorescence intensity after the high pressure field pretreatment is higher than that of the untreated soybean protein isolate (comparative example 1). The fluorescence intensity decreases and then increases with the increase of the ultrahigh pressure intensity, and reaches the lowest at 400MPa and the highest at 500 MPa. The reason may be that the ultra-high pressure treatment destroys the protein structure, resulting in different extended and folded structures of the protein, thereby weakening the quenching effect of the solvent.

By comparing the water-holding capacities of the super water-holding soybean protein isolate gel obtained in examples 1 to 5 and comparative example 1, and referring to FIG. 4, it is illustrated that the water-holding capacities of the soybean protein isolate gels of examples 1 to 5 are improved to various degrees compared to comparative example 1. The soybean protein isolate is treated in the range of 100-400 MPa, the water holding capacity of the formed soybean protein isolate gel is in an increasing trend, and the water holding capacity of the gel reaches 92.27% at the maximum under 400MPa, which is 1.28 times that of the gel which is not treated.

By comparing the free water content (i.e., the water not bound into the network structure during the process of the soy protein isolate gel, attached to the surface of the soy protein isolate gel) of the super water-holding soy protein isolate gel obtained in examples 1-5 and comparative example 1, the comparison graph shown in FIG. 5 shows that the free water ratio is minimized to 94.48% at 400MPa with the increase of pressure in the range of 100-400 MPa, and the free water content is reduced because the more secondary structure of the soy protein isolate is opened and the free thiol content is increased, resulting in the increase of the water binding capacity.

By comparing the electron microscope images of examples 1 to 5 with that of comparative example 1, it can be seen that the surface structure of the soybean protein isolate gel formed in comparative example 1 is dense and curly in a lump shape, while the surface structure of the soybean protein isolate gel formed after the pressure treatment at 100 to 500MPa (examples 1 to 5) is changed loosely, and the gel surface structure is looser and the degree of crushing is increased with the increase of pressure, so that the high-pressure field pretreatment can promote the development of the soybean protein isolate structure and TGase crosslinking.

Comparative example 2

A method for preparing a soy protein isolate gel, which is the same as example 4, except that:

after the pretreatment of the high pressure field, the step 4 of freeze-drying is not carried out, but the obtained modified and pretreated soybean protein isolate solution is subjected to high-speed concentration treatment, the mass fraction of the soybean protein isolate is calculated by concentrating the discharged water, and the enzyme adding amount is determined by calculating the content of the substrate. After high-speed concentration, protein may be aggregated, and even after re-suspension, the protein is not uniform, so that the protein cannot be fully crosslinked after TGase is added, thereby affecting the texture characteristics and the micro-morphology of the gel of the soybean protein isolate. The obtained soybean protein isolate gel has the texture characteristic parameters shown in table 1, the gel strength is insufficient, the water holding capacity is low, the soybean protein isolate gel is observed to have uneven distribution of gaps, and each parameter has a difference with most parameters compared with the super water holding soybean protein isolate gel obtained in example 4.

TABLE 1 texture Properties of Soy protein isolate gels

Example 6

A method for preparing super water-holding soy protein isolate gel comprises the following steps:

the method comprises the following steps of (1) extruding the soybean protein isolate by adopting a screw at the temperature of 25 ℃, and carrying out high-pressure field pretreatment, wherein the method specifically comprises the following steps: placing the soybean protein powder in an automatic feeder, wherein the rotation speed of a screw is 200r/min, the temperature is 150 ℃, the water content is 20 percent, and the pressure of a machine head is 20MPa, so as to obtain the modified and pretreated soybean protein isolate;

placing the modified and pretreated soybean protein isolate into a hot air drying system for drying treatment; crushing and sieving the soybean protein isolate by a 100-mesh sieve to obtain a soybean protein isolate pretreatment sample, and preparing a modified and pretreated soybean protein isolate solution with the mass concentration of 5%;

freeze-drying the modified and pretreated isolated soy protein solution at-50 ℃ to obtain freeze-dried SPI;

adding distilled water into the lyophilized SPI to prepare a lyophilized SPI solution with the mass concentration of 10mg/100mL, and stirring for 1h at room temperature. Adding catalase in a solution of 30U/mL, stirring at 900r/min, and quickly stirring for 8s to obtain a mixture; in the mixture, the concentration of catalase is 30U/g, and the mass concentration of SPI is 10mg/100 mL;

reacting the mixture at 35 deg.C for 1h, inactivating at 90 deg.C for 15min, and standing overnight at 4 deg.C to obtain super water-holding soy protein isolate gel.

Example 7

A method for preparing super water-holding soy protein isolate gel comprises the following steps:

weighing and dissolving soybean protein isolate powder in distilled water to prepare a 10% soybean protein isolate solution, placing the soybean protein isolate solution under the condition of 25 ℃ and the pressure of 120MPa for homogenizing for 10-30 min, carrying out high-pressure field pretreatment, and cooling to obtain a modified pretreated soybean protein isolate solution;

freeze-drying the modified and pretreated soy protein isolate solution at-55 ℃ to obtain freeze-dried SPI;

and adding distilled water into the freeze-dried SPI to prepare a freeze-dried SPI solution with the mass concentration of 9mg/100mL, and stirring for 2h at room temperature. Adding 10U/mL solution of horseradish peroxidase, stirring at 700r/min, and rapidly stirring for 15s to obtain a mixture; in the mixture, the concentration of horseradish peroxidase is 0.3U/g, and the mass concentration of SPI is 9mg/100 mL;

reacting the mixture at 45 deg.C for 0.5h, inactivating at 110 deg.C for 10min, and standing overnight at 5 deg.C to obtain super water-holding soybean protein isolate gel.

Example 8

A method for preparing super water-holding soy protein isolate gel comprises the following steps:

weighing soybean protein isolate powder, dissolving the soybean protein isolate powder in distilled water to prepare a soybean protein isolate solution with the mass fraction of 5%, firstly, placing the solution at 80 ℃ for constant temperature treatment for 2h, then, placing the sealed solution at 100MPa pressure at room temperature for 20min for homogenization, carrying out high-pressure field pretreatment, and cooling to obtain a modified pretreated soybean protein isolate solution;

freeze-drying the modified and pretreated soy protein isolate solution at-54 ℃ to obtain freeze-dried SPI;

and adding distilled water into the freeze-dried SPI to prepare a freeze-dried SPI solution with the mass concentration of 9mg/100mL, and stirring for 2h at room temperature. Adding glutathione peroxidase in 30U/mL solution, stirring at 850r/min for 12s to obtain a mixture; in the mixture, the concentration of glutathione peroxidase is 20U/g, and the mass concentration of SPI is 9mg/100 mL;

reacting the mixture at 35 deg.C for 3h, inactivating at 100 deg.C for 12min, and standing overnight at 5 deg.C to obtain super water-holding soy protein isolate gel.

Example 9

A method for preparing super water-holding soy protein isolate gel comprises the following steps:

weighing soybean protein isolate powder, dissolving the soybean protein isolate powder in distilled water to prepare a soybean protein isolate solution with the mass fraction of 8%, regulating the pH value of the solution to 3 by using a hydrochloric acid solution, dissolving the soybean protein isolate for 1h, washing the solution with secondary water to the pH value of 7.0-7.4, then placing the sealed solution at the room temperature under the pressure of 10MPa for 30min for homogenization, carrying out high-pressure field pretreatment, and cooling to obtain a modified pretreated soybean protein isolate solution;

freeze-drying the modified and pretreated soy protein isolate solution at-60 ℃ to obtain freeze-dried SPI;

and adding distilled water into the freeze-dried SPI to prepare a freeze-dried SPI solution with the mass concentration of 9mg/100mL, and stirring for 2h at room temperature. Adding tyrosinase in 20U/mL solution, stirring at 750r/min, and rapidly stirring for 10s to obtain a mixture; in the mixture, the concentration of tyrosinase is 10U/g, and the mass concentration of SPI is 9mg/100 mL;

reacting the mixture at 40 deg.C for 2h, inactivating at 100 deg.C for 10min, and standing overnight at 4 deg.C to obtain super water-holding soy protein isolate gel.

Example 10

A method for preparing super water-holding soy protein isolate gel comprises the following steps:

the method comprises the following steps of (1) extruding the soybean protein isolate by adopting a screw at the temperature of 25 ℃, and carrying out high-pressure field pretreatment, wherein the method specifically comprises the following steps: placing the soybean protein powder in an automatic feeder at the screw rotation speed of 300r/min, the temperature of 140 ℃, the water content of 15 percent and the head pressure of 10MPa to obtain the modified and pretreated soybean protein isolate;

placing the modified and pretreated soybean protein isolate into a hot air drying system for drying treatment; crushing and sieving the soybean protein isolate by a 100-mesh sieve to obtain a soybean protein isolate pretreatment sample, and preparing a modified and pretreated soybean protein isolate solution with the mass concentration of 10%;

freeze-drying the modified and pretreated isolated soy protein solution at-56 ℃ to obtain freeze-dried SPI;

adding distilled water into the lyophilized SPI to prepare a lyophilized SPI solution with the mass concentration of 10mg/100mL, and stirring for 1h at room temperature. Adding catechol oxidase in 30U/mL solution, stirring at 900r/min, and rapidly stirring for 8s to obtain a mixture; in the mixture, the concentration of the catechol oxidase is 30U/g, and the mass concentration of the SPI is 10mg/100 mL;

reacting the mixture at 35 deg.C for 1h, inactivating at 90 deg.C for 15min, and standing overnight at 4 deg.C to obtain super water-holding soy protein isolate gel.

Example 11

A method for preparing super water-holding soy protein isolate gel comprises the following steps:

weighing soybean protein isolate powder, dissolving the soybean protein isolate powder in distilled water to prepare a soybean protein isolate solution with the mass fraction of 8%, adjusting the pH of the soybean protein isolate solution to 2 by using hydrochloric acid solution to dissolve the soybean protein isolate for 1h, washing the soybean protein isolate solution with secondary water to the pH value of 7.0-7.4, then placing the sealed solution at the pressure of 100MPa for 30min at room temperature, carrying out high-pressure field pretreatment, and cooling to obtain a modified pretreated soybean protein isolate solution;

freeze-drying the modified and pretreated soy protein isolate solution at-52 ℃ to obtain freeze-dried SPI;

adding distilled water into the lyophilized SPI to prepare a lyophilized SPI solution with the mass concentration of 10mg/100mL, and stirring for 2h at room temperature. Adding laccase in 20U/mL solution, stirring at 800r/min, and rapidly stirring for 10s to obtain a mixture; in the mixture, the concentration of the laccase is 10U/g, and the mass concentration of the SPI is 10mg/100 mL;

reacting the mixture at 40 deg.C for 2h, inactivating at 100 deg.C for 10min, and standing overnight at 4 deg.C to obtain super water-holding soy protein isolate gel.