阅读说明：本技术 一种大豆分离蛋白膜的制备方法 (Preparation method of soybean protein isolate membrane ) 是由 夏楠 杨丽军 张冬冬 张爽 徐迪 苏超 王杰 于 2021-08-25 设计创作，主要内容包括：本发明公开了一种大豆分离蛋白膜的制备方法,配制一定浓度的大豆分离蛋白溶液并调节pH至12,水浴加热后冷却至室温；将乙二胺四乙酸二酐按照一定比例向蛋白溶液中缓慢添加,保持混合体系pH始终为12并持续搅拌3h,随后将pH调节为7；使用8000-14000的透析袋在4℃下透析24h,结束后冷冻干燥。制备改性大豆分离蛋白溶液,水浴条件下加入甘油,调节至一定pH,超声脱泡后倒入模具中,45℃真空干燥24h得大豆分离蛋白膜。本发明开发出一种通过接枝改性制备出高质量大豆分离蛋白膜的方法,步骤简单,成本较低,在新型塑料开发及食品包装等方面具有一定的应用价值。(The invention discloses a preparation method of a soy protein isolate membrane, which comprises the steps of preparing a soy protein isolate solution with a certain concentration, adjusting the pH value to 12, heating in a water bath, and cooling to room temperature; slowly adding ethylenediamine tetraacetic dianhydride into the protein solution according to a certain proportion, keeping the pH of the mixed system at 12 all the time, continuously stirring for 3h, and then adjusting the pH to 7; dialyzing at 4 deg.C for 24h with 8000-. Preparing a modified soy protein isolate solution, adding glycerol under the condition of water bath, adjusting to a certain pH value, pouring into a mould after ultrasonic defoaming, and carrying out vacuum drying at 45 ℃ for 24 hours to obtain the soy protein isolate membrane. The invention develops a method for preparing the high-quality soybean protein isolate membrane by graft modification, has simple steps and lower cost, and has certain application value in the aspects of novel plastic development, food packaging and the like.)

1. A preparation method of a soy protein isolate membrane is characterized in that a carboxyl grafting technology is adopted to combine with a method of changing pH and temperature, natural soy protein isolate and ethylene diamine tetraacetic dianhydride in a certain proportion are taken as substrates, and modified soy protein isolate is prepared by carboxyl grafting modification; the method comprises the following steps of taking modified soybean protein isolate as a main raw material, adding a proper amount of glycerol, and casting to form a membrane to prepare the soybean protein isolate membrane:

1) preparing a soy protein isolate solution with a concentration of 4% (w/v) by using distilled water, adjusting the pH value to 12, heating in a water bath at 65 ℃ for 30min, and cooling to room temperature; the method comprises the following steps of adding ethylene diamine tetraacetic dianhydride into a protein solution according to a certain addition amount compared with the mass of the isolated soy protein, keeping the pH of a mixed system to be 12 all the time, continuously stirring for 3 hours, and then adjusting the pH to be 7; the obtained protein mixed solution is dialyzed for 24 hours at 4 ℃ by using a dialysis bag of 8000-; freeze-drying the dialyzed protein solution for 24 hours, and grinding to obtain modified soybean protein isolate;

2) preparing a modified soy protein isolate solution with the concentration of 6% (w/v), adding 4% (v/v) glycerol under the condition of water bath at 60 ℃, adjusting the pH value to 8, pouring the solution into a mould after ultrasonic defoaming, and performing vacuum drying at 45 ℃ for 24 hours to obtain the target soy protein isolate membrane.

2. The method of claim 1, wherein in step 1), ethylenediaminetetraacetic dianhydride is slowly added to the protein solution in an amount of 5%, 10%, 15%, 20% and 30% by weight of the mass of the soy protein isolate.

Technical Field

The invention belongs to the technical field of food processing, and particularly relates to a preparation method of a soybean protein isolate membrane.

Background

In recent years, soy protein isolate has attracted much attention due to its excellent nutritional value and functional properties, and there are many types of related products, such as emulsions, gels, and the like. The soybean protein isolate has a complex structure, contains a large amount of polar amino acids and hydrophobic groups, and can form strong hydrogen bonds, ionic bonds, hydrophobic interaction, disulfide bonds and the like among molecules so as to maintain stability, so the soybean protein isolate is an ideal material for preparing a protein membrane. However, most of natural isolated soy protein molecules are compact and disordered, polypeptide chains are bent and folded, hydrophobic groups are wrapped by hydrophilic shells and are easily interfered by external environmental factors, and the membrane products with stable structures are not easily formed.

At present, the research on improving the quality of the soybean protein isolate membrane is more, and the method is roughly divided into three directions, namely, suitable membrane preparation conditions (selecting a membrane preparation method, controlling temperature, pH and other influencing factors) are respectively searched; preparing various composite membrane products such as a protein-polysaccharide composite membrane and the like; the toughness of the film is improved by adding a plasticizer, a cross-linking agent and the like in the film preparation process. The method can improve the stability and other qualities of the protein film to a certain extent, but the research on changing the protein structure and preparing the protein film by chemical grafting modification is less, and the quality of the protein film can be further improved by the novel soybean protein isolate film prepared by the method, so that a new thought is provided for the development of the fields of novel plastic development, food packaging and the like.

Disclosure of Invention

The invention provides a method for preparing a novel soybean protein isolate membrane by modifying soybean protein isolate, which has the defects of disordered structure, poor hydrophobicity and the like and is difficult to prepare a high-quality membrane product.

The invention provides a method for preparing a novel soybean protein isolate membrane with high strength, high barrier property, high stability and low air permeability on the basis of the original protein membrane preparation process from the viewpoint of improving the molecular structure of the soybean protein isolate and enhancing the intermolecular force. The method has the advantages of simple and clear operation steps, easy realization and low cost.

In the invention, a carboxyl grafting technology is combined with a method for changing pH and temperature, natural soybean protein isolate and ethylenediamine tetraacetic dianhydride in a certain proportion are taken as substrates, and the modified soybean protein isolate is prepared by carboxyl grafting modification. The novel soybean protein isolate membrane is prepared by taking modified soybean protein isolate as a main raw material, adding a proper amount of glycerol and adopting a casting film forming method.

The quality of the protein film mainly depends on several indexes of tensile strength, elongation, barrier property and stability. Wherein, higher tensile strength and elongation are favorable for the protein film to resist external pressure and maintain the integrity of the film, the higher the barrier property is, oxygen, water vapor and other pollutants can be better blocked outside, the stability is the storage property of the film, and is the basis that other film properties can play a role in a certain period. However, these indices are closely related to the structure of the protein itself. The natural soybean protein isolate has large molecular weight, high structural disorder degree, most of hydrophobic groups are wrapped by hydrophilic shells, the storage stability is poor, and the membrane product with stable structure is not easy to form. Therefore, from the microscopic viewpoint, it is theoretically possible to improve the molecular structure of protein and enhance intermolecular interactions to prepare a novel soybean protein film.

The novel soybean protein isolate membrane prepared by graft modification has certain application value in the aspects of novel plastic development, food packaging and the like, and further expands the application range of the soybean protein in the food field.

The purpose of the invention is realized by the following technical scheme, which comprises the following steps:

1) preparing a soy protein isolate solution with a concentration of 4% (w/v) by using distilled water, adjusting the pH value to 12, heating in a water bath at 65 ℃ for 30min, and cooling to room temperature; the method comprises the following steps of slowly adding ethylenediamine tetraacetic dianhydride into a protein solution according to the addition amount of 5%, 10%, 15%, 20% and 30% of the weight of the soybean protein isolate, keeping the pH of a mixed system to be 12 all the time, continuously stirring for 3 hours, and then adjusting the pH to be 7; the obtained protein mixed solution is dialyzed for 24 hours at 4 ℃ by using a dialysis bag of 8000-; and (4) freeze-drying the dialyzed protein solution for 24 hours, and grinding to obtain the modified isolated soy protein.

2) Preparing a modified soy protein isolate solution with the concentration of 6% (w/v), adding 4% (v/v) glycerol under the condition of water bath at 60 ℃, adjusting the pH value to 8, pouring the solution into a mould after ultrasonic defoaming, and performing vacuum drying at 45 ℃ for 24 hours to obtain the target soy protein isolate membrane.

The novel isolated soy protein membrane prepared by the method has the advantages of 95MPa of tensile strength, 8% of elongation at break, 0.018 mu m/(Pa & S) of air permeability and good storage stability.

Advantageous effects

1) The solubility and the emulsibility of the soybean protein isolate prepared by the method are enhanced, the macromolecular structure of the protein is depolymerized, and the hydrophobicity of the protein is improved due to the exposure of hydrophobic groups. The reaction of ethylenediamine tetraacetic dianhydride with free amino groups on the protein introduces a large number of carboxyl groups to the protein. The protein membrane prepared by the soybean protein isolate can form a relatively compact structure, the mechanical property of the protein membrane is obviously improved, the air permeability is low, and the protein membrane is a novel high-quality protein membrane.

2) The invention has low cost, clear working procedures and lower cost, and the performance of the produced soybean protein isolate membrane is obviously improved, thereby having certain application value in the aspects of novel plastic development, food packaging and the like.

Drawings

FIG. 1 shows the high-quality soy protein isolate membrane prepared in each example and comparative example-A at 4000-400cm^-1Infra-red spectrogram in the range. Wherein the abscissa represents the wavelength and the ordinate represents the transmittance of the sample at the corresponding wavelength.

Fig. 2 is a graph of tensile strength and elongation at break properties of high quality soy protein isolate membranes prepared in each of the examples and comparative example one. In which the abscissa represents the sample number in each of the control and the embodiment, the left ordinate represents the tensile strength of the sample even when the tensile strength is deformed, in MPa, and the right ordinate represents the elongation at break of each sample, i.e., the elongation at break of the film sample.

Fig. 3 is a graph comparing air permeability and light transmittance properties of high quality soy protein isolate membranes prepared in each example and comparative example one. Wherein the abscissa represents the sample number in each control and example, the left ordinate represents the air permeability of the sample, and the right ordinate represents the light transmittance of each sample.

Detailed Description

The technical solution of the present invention is specifically described below with reference to the accompanying drawings.

FIG. 1 shows the high-quality soy protein isolate membrane prepared in each example and comparative example-A at 4000-400cm^-1An infrared spectrogram in a range; wherein the abscissa represents the wavelength and the ordinate represents the transmittance of the sample at the corresponding wavelength. In this plot, the samples of each example set were at 3286.06cm^-1Blue shift, decrease in hydrophilic O-H elongation, intermolecular association, 1534.66cm^-1The peak of the vibration is sharp, the intensity is increased, and the peak is 1123.54cm^-1A peak is added to form a new amido bond. The results show that a large amount of carboxyl groups are grafted to the isolated soy protein by the treatment of the ethylenediamine tetraacetic dianhydride.

FIG. 2 is a graph showing tensile strength and elongation at break properties of high quality soy protein isolate films prepared in each of the examples and comparative example one; in which the abscissa represents the sample number in each of the control and the embodiment, the left ordinate represents the tensile strength of the sample even when the tensile strength is deformed, in MPa, and the right ordinate represents the elongation at break of each sample, i.e., the elongation at break of the film sample. In fig. 3, the tensile strength and elongation at break of the comparative example one are small, the strength of the film is low, and the film is easy to break, and both properties are greatly improved compared with the film sample of the example two.

FIG. 3 is a graph showing air permeability and light transmittance properties of high quality soy protein isolate membranes prepared in each of the examples and comparative example one; wherein the abscissa represents the sample number in each control and example, the left ordinate represents the air permeability of the sample, and the right ordinate represents the light transmittance of each sample. In fig. 2, the air permeability is the highest and the light transmittance is the lowest in the first control example, and when the film sample is used as a packaging material, the packaged article is liable to react with external environments such as oxygen, water vapor and the like, so that the shelf life is shortened, and in addition, the appearance is poor; the air permeability is reduced to the minimum, the light transmittance is improved, and the treatment has important significance for improving the storage and quality guarantee period of the articles and prolonging the service life of the film samples.

The first embodiment is as follows: preparing a soy protein isolate solution with a concentration of 4% (w/v) using distilled water and adjusting the pH to 12, heating in a water bath at 65 ℃ for 30min and cooling to room temperature. Ethylenediamine tetraacetic dianhydride was slowly added to the protein solution at an addition amount of 5% compared with the protein mass, the pH of the mixed system was kept at 12 all the time and stirring was continued for 3 hours, and then the pH was adjusted to 7. Dialyzed at 4 ℃ for 24h using 8000-. Preparing a modified soy protein isolate solution with the concentration of 6% (w/v), adding 4% (v/v) glycerol under the condition of water bath at 60 ℃, adjusting the pH to 9, pouring into a mould after ultrasonic defoaming, and performing vacuum drying at 45 ℃ for 24 hours to obtain the soy protein isolate membrane. The properties of the product are shown in figures 1, 2 and 3.

Example two: preparing a soy protein isolate solution with a concentration of 4% (w/v) using distilled water and adjusting the pH to 12, heating in a water bath at 65 ℃ for 30min and cooling to room temperature. Ethylenediamine tetraacetic dianhydride was slowly added to the protein solution at an addition amount of 15% compared with the protein mass, the pH of the mixed system was kept at 12 all the time and stirring was continued for 3 hours, and then the pH was adjusted to 7. Dialyzed at 4 ℃ for 24h using 8000-. Preparing a modified soy protein isolate solution with the concentration of 6% (w/v), adding 4% (v/v) glycerol under the condition of water bath at 60 ℃, adjusting the pH to 9, pouring into a mould after ultrasonic defoaming, and performing vacuum drying at 45 ℃ for 24 hours to obtain the soy protein isolate membrane. The properties of the product are shown in figures 1, 2 and 3.

Example three: preparation of a 4% (w/v) Soy protein isolate solution using distilled water

Adjusting pH to 12, heating in water bath at 65 deg.C for 30min, and cooling to room temperature. Ethylenediamine tetraacetic dianhydride was slowly added to the protein solution at an addition amount of 30% compared with the protein mass, the pH of the mixed system was kept at 12 all the time and stirring was continued for 3 hours, and then the pH was adjusted to 7. Dialyzed at 4 ℃ for 24h using 8000-. Preparing a modified soy protein isolate solution with the concentration of 6% (w/v), adding 4% (v/v) glycerol under the condition of water bath at 60 ℃, adjusting the pH to 9, pouring into a mould after ultrasonic defoaming, and performing vacuum drying at 45 ℃ for 24 hours to obtain the soy protein isolate membrane. The properties of the product are shown in figures 1, 2 and 3.

Comparative example one: preparing a soy protein isolate solution with a concentration of 4% (w/v) using distilled water and adjusting the pH to 12, heating in a water bath at 65 ℃ for 30min, cooling to room temperature, and freeze-drying for 24 h. And then preparing a freeze-dried soy protein isolate solution with the concentration of 6% (w/v) by using distilled water, adding 4% (v/v) of glycerol under the condition of water bath at 60 ℃, adjusting the pH to 9, pouring the mixture into a mould after ultrasonic defoaming, and performing vacuum drying at 45 ℃ for 24 hours to obtain the soy protein isolate membrane. The properties of the product are shown in figures 1, 2 and 3.

The peeling properties of the soybean protein isolate films prepared in comparative example one and each example are shown in table 1. Among them, the film peeling process of example two and example three is easier, the film integrity is higher, and the film peeling condition of comparative example one is less ideal.

TABLE 1

The invention provides a method for preparing a novel soybean protein isolate membrane with high strength, high barrier property, high stability and low air permeability on the basis of the original protein membrane preparation process from the viewpoint of improving the molecular structure of the soybean protein isolate and enhancing the intermolecular force.

In the invention, a carboxyl grafting technology is combined with a method for changing pH and temperature, natural soybean protein isolate and ethylenediamine tetraacetic dianhydride in a certain proportion are taken as substrates, and the modified soybean protein isolate is prepared by carboxyl grafting modification. The novel soybean protein isolate membrane is prepared by taking modified soybean protein isolate as a main raw material, adding a proper amount of glycerol and adopting a casting film forming method.