Hydrophobic vegetable protein acidic gel and preparation method thereof

Abstract

The invention discloses hydrophobic vegetable protein acidic gel and a preparation method thereof, and belongs to the technical field of food processing. The preparation method of the hydrophobic vegetable protein acidic gel comprises the following steps: mixing a vegetable protein solution with a polysaccharide solution to obtain a mixture, adding acid to adjust the pH value, centrifuging, collecting supernate, dialyzing, and freeze-drying to obtain a freeze-dried sample; adding water into the freeze-dried sample to dissolve the freeze-dried sample to obtain a freeze-dried sample solution, adding gluconic acid-delta-lactone, and standing for acidification to obtain the hydrophobic vegetable protein acidic gel. The hydrophobic vegetable protein acidic gel with different rheological properties and microstructures is obtained by slowly acidifying a vegetable protein-polysaccharide system, and the performance of the gel can be controlled by pH and the concentration and proportion of a protein-polysaccharide compound. In addition, the water holding capacity of the obtained gel can be customized by adjusting the pH value.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to a hydrophobic plant protein acid gel and a preparation method thereof. Background Art

[0002] Gels are popular in food production due to their structural modifications and unique sensory properties. Protein is an important raw material for preparing food-grade gels. Compared with animal proteins, the eco-friendliness, sustainability and wide accessibility of plant proteins have made consumers increasingly inclined to consume plant protein products. However, the strong hydrophobicity of plant proteins leads to their low solubility under neutral conditions. Taking rice protein, a highly hydrophobic plant protein, as an example, its solubility under neutral conditions is only about 1%, which greatly limits its application and development as a gelling agent in the food industry.

[0003] The low solubility of plant protein makes it difficult to form a gel. The existing methods for preparing hydrophobic plant protein gels mainly include: using a co-solvent system to improve the solubility and gel properties of the protein, or using physical modification methods such as ultrasound, high pressure, etc. to pre-treat the protein. Although these methods have their own advantages, they still have some limitations. For example, the co-solvent system may introduce impurities, affecting product quality and safety; the physical modification method has high requirements for equipment and a complex processing process, making it difficult to apply on a large scale. The preparation of complexes using proteins and polysaccharides is an effective means to improve the functional properties of proteins, but there is still a blank in the invention of gel preparation for hydrophobic plant protein-polysaccharide complexes. Summary of the invention

[0004] In view of the deficiencies in the prior art, the present invention provides a hydrophobic plant protein acid gel and a preparation method thereof. The present invention optimizes the polysaccharide complexed with the plant protein and slowly acidifies the plant protein-polysaccharide system to obtain a rice protein acid gel with different rheological properties and microstructures. The performance of the gel can be controlled by pH, the concentration and ratio of the protein-polysaccharide complex. In addition, the water holding capacity of the obtained gel can be customized by adjusting the pH value. The preparation method of the present invention can form a gel within a larger pH range, and the preparation process is easier to control by slowly acidifying the system; the prepared gel solves the problem that the formation of the existing gel and its performance are reduced due to pH changes, and at the same time, provides a theoretical basis for the study of preparing gel from hydrophobic plant protein.

[0005] The technical solution of the present invention is as follows:

[0006] The first aspect of the present invention provides a method for preparing a hydrophobic plant protein acidic gel, the preparation method comprising the following steps:

[0007] S1: The plant protein solution and the polysaccharide solution are mixed to obtain a mixture, and the pH value is adjusted by adding acid, centrifuging, collecting the supernatant, and lyophilizing after dialyzing to obtain a lyophilized sample.

[0008] S2: adding water to dissolve the freeze-dried sample to obtain a freeze-dried sample solution, adding glucono-δ-lactone (GDL), standing and acidifying to obtain a hydrophobic plant protein acid gel.

[0009] Preferably, in step S1, the plant protein is a plant protein having hydrophobic groups on its surface.

[0010] Preferably, in step S1, the plant protein includes at least one of rice protein, quinoa protein and corn protein;

[0011] The purity of the plant protein is 85% to 95%, and the water content is 4.5% to 5.5%.

[0012] Preferably, in step S1, the plant protein solution is prepared by dissolving the plant protein in water to obtain a solution with a concentration of 8 to 12 mg / mL, and adjusting the pH to 12±0.1.

[0013] Preferably, in step S1, the polysaccharide is carboxymethyl cellulose;

[0014] The concentration of the polysaccharide solution is 1 mg / mL, and the pH value is 12±0.1.

[0015] Preferably, in step S1, in the mixture, the mass ratio of the plant protein to the polysaccharide is 6 to 20:1.

[0016] Preferably, in step S1, adjusting the pH value means adjusting the pH value to 8.5-9.5; the centrifugal speed is 8000g-12000g, and the time is 10min-15min; the dialysis time is 22h-26h; the freeze-drying temperature is -85℃--96℃, and the time is 90h-100h.

[0017] Preferably, in step S2, the mass concentration of the freeze-dried sample solution is 1% to 5%.

[0018] Preferably, in step S2, the mass volume ratio of the glucono-δ-lactone to the lyophilized sample solution is 2 to 4:1 in mg / mL;

[0019] The static acidification time is 4 to 6 hours.

[0020] The second aspect of the present invention provides a hydrophobic plant protein acid gel prepared by the preparation method described in the first aspect.

[0021] The beneficial technical effects of the present invention are:

[0022] The present invention optimizes the polysaccharide complexed with the plant protein, and at the same time, by adding GDL to the plant protein-polysaccharide mixture, the pH value is reduced, and the deformation and rearrangement of the plant protein are promoted to form a more stable three-dimensional network structure. The change in the conformation of the plant protein makes it easier to combine with the carboxymethyl cellulose with uniform and dense charge distribution, thereby forming a more stable gel structure. This structure can enhance the water holding capacity of the gel and maintain the freshness and taste of the product; thereby improving the application of plant protein in the food industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The pictures are of the gels prepared in Examples 1-5 of the present invention.

[0024] In the figure: A, gel of Example 1; B, gel of Example 2; C, gel of Example 3; D, gel of Example 4; E, gel of Example 5.

[0025] Figure 2 CLSM images of the gels prepared in Examples 1-5 of the present invention.

[0026] In the figures: A, CLSM image of the gel of Example 1; B, CLSM image of the gel of Example 2; C, CLSM image of the gel of Example 3; D, CLSM image of the gel of Example 4; E, CLSM image of the gel of Example 5.

[0027] Figure 3 The following are pictures of the gels prepared in Examples 6-10 of the present invention.

[0028] In the figure: A, gel of Example 6; B, gel of Example 7; C, gel of Example 8; D, gel of Example 9; E, gel of Example 10.

[0029] Figure 4 CLSM images of the gels prepared in Examples 6-10 of the present invention.

[0030] In the figures: A, CLSM image of the gel of Example 6; B, CLSM image of the gel of Example 7; C, CLSM image of the gel of Example 8; D, CLSM image of the gel of Example 9; E, CLSM image of the gel of Example 10.

[0031] Figure 5 These are pictures of the gels prepared in Examples 11-12 of the present invention and Comparative Example 1.

[0032] In the figure: A, gel of Example 11; B, gel of Example 12; C, gel of Comparative Example 1.

[0033] Figure 6CLSM images of the gels prepared in Examples 11-12 of the present invention and Comparative Example 1 after GDL was added and the gels were acidified to a pH of 5.5.

[0034] In the figures: A, CLSM image of the gel of Example 11; B, CLSM image of the gel of Example 12; C, CLSM image of the gel of Comparative Example 1.

[0035] Figure 7 The water holding capacity of the gels at different pH values ​​in Examples 7 and 10 of the present invention.

[0036] In the figure: A, gel of Example 7; B, gel of Example 10. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below in conjunction with the embodiments.

[0038] The first aspect of the present invention provides a method for preparing a hydrophobic plant protein acidic gel, the preparation method comprising the following steps:

[0039] S1: The plant protein solution and the polysaccharide solution are mixed to obtain a mixture, and the pH value is adjusted by adding acid, centrifuging, collecting the supernatant, and lyophilizing after dialyzing to obtain a lyophilized sample.

[0040] S2: adding water to dissolve the freeze-dried sample to obtain a freeze-dried sample solution, adding glucono-δ-lactone, standing and acidifying, and obtaining a hydrophobic plant protein acid gel.

[0041] It can be understood that the present invention optimizes the polysaccharide complexed with the plant protein, and at the same time, by adjusting the pH to make the charge of the plant protein and the polysaccharide evenly matched, it can increase its solubility in water and avoid precipitation and aggregation. By adding GDL to the plant protein-polysaccharide mixture, the pH value is lowered, the deformation and rearrangement of the plant protein are promoted, and a more stable three-dimensional network structure is formed. The change in the conformation of the plant protein makes it easier to combine with carboxymethyl cellulose, thereby forming a more stable gel structure. This structure can enhance the water holding capacity of the gel and maintain the freshness and taste of the product; and improve the application of plant protein in the food industry.

[0042] In some embodiments, in step S1, the plant protein is a plant protein having a hydrophobic group on the surface, including but not limited to a methyl group, an isopropyl group, and an isobutyl group.

[0043] It is understandable that the plant protein of the present invention is preferably a plant protein with hydrophobic groups on the surface, because its low solubility limits its application in the food industry, but because of its rich nutrition and wide source, it is beneficial to reduce production costs. At the same time, compared with hydrophilic plant protein, the gel it forms is stronger and more elastic, and has greater application potential.

[0044] In some embodiments, in step S1, the plant protein includes at least one of rice protein, quinoa protein, and corn protein.

[0045] In some embodiments, the plant protein used in the present invention is preferably rice protein. Compared with other proteins, rice protein has the advantages of low allergenicity, easy digestion, low pollution and sustainability.

[0046] It is understandable that the present invention does not limit the method for extracting plant protein. Any method that can achieve the effect of the present invention is within the scope of protection of the present invention. Rice protein is used as an example: the rice protein is prepared by the following method: after the rice is ground into powder, it is mixed with deionized water in a mass ratio of 1:8. After stirring for 3h to 4h at pH 12.0 ± 0.1., 10000g is centrifuged for 10min, and the collected supernatant is adjusted to pH 4.5 to precipitate protein. The precipitate is subjected to secondary precipitation, the pH is adjusted to 7.0, and impurities are removed by centrifugation. After washing with deionized water to desalinate, it is obtained by -80°C freeze drying for 96h.

[0047] In some embodiments, in step S1, the purity of the plant protein is 85% to 95%, including but not limited to 85%, 90%, and 95%, and the water content is 4.5% to 5.5%, including but not limited to 4.5%, 5.0%, and 5.5%.

[0048] In some embodiments, in step S1, the plant protein solution is prepared by dissolving the plant protein in water to obtain a solution with a concentration of 8 mg / mL to 12 mg / mL, and adjusting the pH to 12±0.1.

[0049] In some embodiments, in step S1, the polysaccharide is carboxymethyl cellulose.

[0050] It can be understood that the carboxymethyl cellulose has good water solubility and biocompatibility. Compared with other polysaccharides, its charge distribution is more uniform and dense, and it can better produce a strong and effective interaction with the hydrophobic plant protein. Specifically, the carboxyl anions and hydroxyl groups of hydroxymethyl cellulose are combined with the positively charged groups and amino groups of the hydrophobic plant protein through electrostatic interactions. The hydroxyl groups in its molecules can also form hydrogen bonds with the amino groups, carboxyl groups, etc. in the hydrophobic plant protein molecules to form a stable structure, which is conducive to the formation of gel.

[0051] In some embodiments, in step S1, the concentration of the polysaccharide solution is 1 mg / mL, and the pH value is 12±0.1.

[0052] In some embodiments, in step S1, in the mixture, the mass ratio of the plant protein to the polysaccharide is 6 to 20:1, including but not limited to 6:1, 8:1, 10:1, 12:1, 14:1, 16:1, 18:1, and 20:1.

[0053] In some embodiments, in step S1, the dialysis is performed using a recovery cellulose dialysis tube and deionized water for 24 hours.

[0054] In some embodiments, in step S1, the pH value is adjusted to 8.5-9.5; the centrifugal speed is 8000g-12000g, including but not limited to 8000g, 9000g, 10000g, 12000g, and the time is 10min-15min, including but not limited to 10min, 12min, 14min, 15min; the dialysis time is 22h-24h; the freeze-drying temperature is -80℃~-96℃, and the time is 90h~100h.

[0055] It is understandable that during the freeze-drying process, the structure of the rice protein is retained, and the ice crystals sublime to form a porous structure, which increases the contact area with water, making it more soluble in water and facilitating the formation of a stable gel network when preparing the gel.

[0056] In some embodiments, in step S2, the mass concentration of the freeze-dried sample solution is 1% to 5%, including but not limited to 1%, 2%, 3%, 4%, and 5%.

[0057] In some embodiments, in step S2, the mass concentration of the freeze-dried sample solution is 2% to 4%, including but not limited to 2%, 3%, and 4%.

[0058] It can be understood that when the concentration of the freeze-dried sample solution is 2% to 4%, the gel prepared by the present invention has a good self-supporting ability. The quality of the self-supporting ability can be evaluated by the size of its elastic modulus. The gel with a large elastic modulus has a better self-supporting ability. The gel with a high self-supporting ability can maintain the properties of the food and improve the taste of the food.

[0059] In some embodiments, in step S2, the mass volume ratio of the glucono-δ-lactone to the lyophilized sample solution is 2 to 4:1 in mg / mL, including but not limited to 2:1, 3:1, and 4:1.

[0060] In some embodiments, in step S2, the pH of the hydrophobic plant protein acidic gel can be determined by different acidification times.

[0061] The present invention measures the pH of the gel obtained after different acidification times at different glucono-δ-lactone addition amounts and freeze-dried sample solution concentrations, and fits to obtain the logarithmic relationship between the acidification time t and the pH of the obtained gel at specific glucono-δ-lactone addition amounts and freeze-dried sample solution concentrations as follows:

[0062] pH=A×ln(t)+B

[0063] Where: t represents time, in minutes; A and B are coefficients of the relationship, and the values ​​of A and B vary with the concentrations of GDL and RCs (lyophilized sample solution). Exemplarily, when the mass volume ratio of GDL to RCs (lyophilized sample solution) is 2 mg / mL and the concentration of RCs (lyophilized sample solution) is 2%, the pH at different acidification times is measured, and fitting is performed to obtain A as -0.3071 and B as 7.1888. At this time, the logarithmic relationship between the acidification time t and the pH of the obtained gel is: pH = -0.3071 × ln (t) + 7.1888. Therefore, when determining the concentrations of GDL and RCs (lyophilized sample solution), in addition to measuring the pH value during the acidification process in real time, the pH value of the gel at different acidification times can also be directly obtained through the above relationship.

[0064] In some embodiments, in step S2, the static acidification time is 4 hours to 6 hours.

[0065] It is understandable that the pH of the hydrophobic plant protein acidic gel of the present invention can be regulated by the acidification time; the hydrophobic plant protein acidic gel is a pH-controllable gel.

[0066] The second aspect of the present invention provides a hydrophobic plant protein acid gel prepared by the preparation method described in the first aspect.

[0067] It is understood that the performance of the acidic gel prepared by the present invention is flexible to adjust, and the pH of the obtained gel can be controlled by the acidification time, and the self-supporting ability of the obtained gel can be controlled by the RCs concentration, thus solving the problem that the performance of the existing gel decreases due to pH changes.

[0068] The following are specific embodiments.

[0069] Example 1

[0070] A kind of rice protein acid gel, its preparation method is as follows:

[0071] (1) RPs (rice protein, purity of 90.3%, water content of 5.2%) was dispersed in deionized water to obtain a solution with a concentration of 10 mg / mL, and then the pH value was adjusted to 12.0±0.1 and mixed for 1 hour to obtain a RPs solution.

[0072] The carboxymethyl cellulose (CMC) was dissolved in water to obtain a CMC initial solution with a concentration of 1 mg / mL, and then the pH value was adjusted to 12.0±0.1 to obtain a CMC solution.

[0073] (2) The RPs solution was mixed with the CMC solution at a mass ratio of 10:1 between rice protein and hydroxymethyl cellulose, and hydrochloric acid (0.1 M) was slowly added to the mixture under magnetic stirring at 900 r / min until the pH value reached 9.0 ± 0.1. The supernatant collected after centrifugation at 10000 g for 10 min was called RCs, and then dialyzed for 24 h with a dialysis bag with a molecular weight cutoff of 3400 Da to remove salt ions, and then freeze-dried at -80 ° C for 96 h to obtain a freeze-dried sample.

[0074] (3) The freeze-dried sample was dissolved in water to obtain a freeze-dried sample solution with a mass fraction of 1% (called RCs solution). 2 mg of GDL (glucono-δ-lactone) was added to 1 mL of 1% RCs solution and the solution was allowed to stand for acidification for 6 h to prepare a gel. The pH value was measured using an HQ411D laboratory pH / mV meter during the acidification process.

[0075] Example 2

[0076] A rice protein acid gel, the preparation method of which is substantially the same as that of Example 1, except that the concentration of the RCs solution is 2%.

[0077] A kind of rice protein acid gel, its preparation method is as follows:

[0078] (1) RPs (rice protein, purity of 90.3%, water content of 5.2%) was dispersed in deionized water to obtain a solution with a concentration of 10 mg / mL, and then the pH value was adjusted to 12.0±0.1 and mixed for 1 hour to obtain a RPs solution.

[0079] The carboxymethyl cellulose (CMC) was dissolved in water to obtain a CMC initial solution with a concentration of 1 mg / mL, and then the pH value was adjusted to 12.0±0.1 to obtain a CMC solution.

[0080] (2) The RPs solution was mixed with the CMC solution at a mass ratio of 10:1 between rice protein and hydroxymethyl cellulose, and hydrochloric acid (0.1 M) was slowly added to the mixture under magnetic stirring at 900 r / min until the pH value reached 9.0 ± 0.1. The supernatant collected after centrifugation at 10000 g for 10 min was called RCs, and then dialyzed for 24 h with a dialysis bag with a molecular weight cutoff of 3400 Da to remove salt ions, and then freeze-dried at -80 ° C for 96 h to obtain a freeze-dried sample.

[0081] (3) Water was added to the freeze-dried sample to dissolve it, and a freeze-dried sample solution with a mass fraction of 2% (called RCs solution) was obtained. 2 mg of GDL (glucono-δ-lactone) was added to 1 mL of the 2% RCs solution, and the solution was allowed to stand for acidification for 6 h to prepare a gel. During the acidification process, the pH value was measured using an HQ411D laboratory pH / mV meter.

[0082] Example 3

[0083] A rice protein acid gel, the preparation method of which is substantially the same as that of Example 1, except that the concentration of the RCs solution is 3%.

[0084] A kind of rice protein acid gel, its preparation method is as follows:

[0085] (1) RPs (rice protein, purity of 90.3%, water content of 5.2%) was dispersed in deionized water to obtain a solution with a concentration of 10 mg / mL, and then the pH value was adjusted to 12.0±0.1 and mixed for 1 hour to obtain a RPs solution.

[0086] The carboxymethyl cellulose (CMC) was dissolved in water to obtain a CMC initial solution with a concentration of 1 mg / mL, and then the pH value was adjusted to 12.0±0.1 to obtain a CMC solution.

[0087] (2) The RPs solution was mixed with the CMC solution at a mass ratio of 10:1 between rice protein and hydroxymethyl cellulose, and hydrochloric acid (0.1 M) was slowly added to the mixture under magnetic stirring at 900 r / min until the pH value reached 9.0 ± 0.1. The supernatant collected after centrifugation at 10000 g for 10 min was called RCs, and then dialyzed for 24 h with a dialysis bag with a molecular weight cutoff of 3400 Da to remove salt ions, and then freeze-dried at -80 ° C for 96 h to obtain a freeze-dried sample.

[0088] (3) Water was added to the freeze-dried sample to dissolve it, and a freeze-dried sample solution with a mass fraction of 3% (called RCs solution) was obtained. 2 mg of GDL (glucono-δ-lactone) was added to 1 mL of the 3% RCs solution, and the solution was allowed to stand and acidify for 6 h to prepare a gel. During the acidification process, the pH value was measured using an HQ411D laboratory pH / mV meter.

[0089] Example 4

[0090] A rice protein acid gel, the preparation method of which is substantially the same as that of Example 1, except that the concentration of the RCs solution is 4%.

[0091] A kind of rice protein acid gel, its preparation method is as follows:

[0092] (1) RPs (rice protein, purity of 90.3%, water content of 5.2%) was dispersed in deionized water to obtain a solution with a concentration of 10 mg / mL, and then the pH value was adjusted to 12.0±0.1 and mixed for 1 hour to obtain a RPs solution.

[0093] The carboxymethyl cellulose (CMC) was dissolved in water to obtain a CMC initial solution with a concentration of 1 mg / mL, and then the pH value was adjusted to 12.0±0.1 to obtain a CMC solution.

[0094] (2) The RPs solution was mixed with the CMC solution at a mass ratio of 10:1 between rice protein and hydroxymethyl cellulose, and hydrochloric acid (0.1 M) was slowly added to the mixture under magnetic stirring at 900 r / min until the pH value reached 9.0 ± 0.1. The supernatant collected after centrifugation at 10000 g for 10 min was called RCs, and then dialyzed for 24 h with a dialysis bag with a molecular weight cutoff of 3400 Da to remove salt ions, and then freeze-dried at -80 ° C for 96 h to obtain a freeze-dried sample.

[0095] (3) Add water to the freeze-dried sample to dissolve it, and obtain a freeze-dried sample solution with a mass fraction of 4% (called RCs solution). Add 2 mg of GDL (glucono-δ-lactone) to 1 mL of 4% RCs solution, and let it stand for 6 hours to acidify to prepare a gel. During the acidification process, the pH value was measured using an HQ411D laboratory pH / mV meter.

[0096] Example 5

[0097] A rice protein acid gel, the preparation method of which is substantially the same as that of Example 1, except that the concentration of the RCs solution is 5%.

[0098] A kind of rice protein acid gel, its preparation method is as follows:

[0099] (1) RPs (rice protein, purity of 90.3%, water content of 5.2%) was dispersed in deionized water to obtain a solution with a concentration of 10 mg / mL, and then the pH value was adjusted to 12.0±0.1 and mixed for 1 hour to obtain a RPs solution.

[0100] The carboxymethyl cellulose (CMC) was dissolved in water to obtain a CMC initial solution with a concentration of 1 mg / mL, and then the pH value was adjusted to 12.0±0.1 to obtain a CMC solution.

[0101] (2) The RPs solution was mixed with the CMC solution at a mass ratio of 10:1 between rice protein and hydroxymethyl cellulose, and hydrochloric acid (0.1 M) was slowly added to the mixture under magnetic stirring at 900 r / min until the pH value reached 9.0 ± 0.1. The supernatant collected after centrifugation at 10000 g for 10 min was called RCs, and then dialyzed for 24 h with a dialysis bag with a molecular weight cutoff of 3400 Da to remove salt ions, and then freeze-dried at -80 ° C for 96 h to obtain a freeze-dried sample.

[0102] (3) The freeze-dried sample was dissolved in water to obtain a 5% freeze-dried sample solution (called RCs solution). 2 mg of GDL (glucono-δ-lactone) was added to 1 mL of the 5% RCs solution and the solution was allowed to stand for acidification for 6 h to prepare a gel. The pH value was measured using an HQ411D laboratory pH / mV meter during the acidification process.

[0103] Example 6

[0104] A rice protein acid gel, its preparation method is substantially the same as that of Example 1, except that the addition of GDL in step (3) is used. In the present embodiment, step (3) is as follows:

[0105] (3) Water was added to the freeze-dried sample to dissolve it and a 1% mass fraction freeze-dried sample solution (called RCs solution) was obtained. 4 mg of GDL (glucono-δ-lactone) was added to 1 mL of 1% RCs solution and the solution was allowed to stand for 6 h to acidify and prepare a gel. During the acidification process, the pH value was measured using an HQ411D laboratory pH / mV meter.

[0106] Example 7

[0107] A rice protein acid gel, its preparation method is substantially the same as that of Example 2, except that the addition of GDL in step (3) is used. In the present embodiment, step (3) is as follows:

[0108] (3) Water was added to the freeze-dried sample to dissolve it and a 2% freeze-dried sample solution (called RCs solution) was obtained. 4 mg of GDL (glucono-δ-lactone) was added to 1 mL of 2% RCs solution and the solution was allowed to stand for 6 h to acidify and prepare a gel. During the acidification process, the pH value was measured using an HQ411D laboratory pH / mV meter.

[0109] Example 8

[0110] A rice protein acid gel, its preparation method is substantially the same as that of Example 3, except that the addition of GDL in step (3) is used. In the present embodiment, step (3) is as follows:

[0111] (3) The freeze-dried sample was dissolved in water to obtain a freeze-dried sample solution with a mass fraction of 3% (called RCs solution). 4 mg of GDL (glucono-δ-lactone) was added to 1 mL of the 3% RCs solution and the solution was allowed to stand for acidification for 6 h to prepare a gel. The pH value was measured using an HQ411D laboratory pH / mV meter during the acidification process.

[0112] Example 9

[0113] A rice protein acid gel, its preparation method is substantially the same as Example 4, except that the addition of GDL in step (3), in the present embodiment, step (3) is specific as follows:

[0114] (3) The freeze-dried sample was dissolved in water to obtain a freeze-dried sample solution with a mass fraction of 4% (called RCs solution). 4 mg of GDL (glucono-δ-lactone) was added to 1 mL of 4% RCs solution and the solution was allowed to stand for acidification for 6 h to prepare a gel. The pH value was measured using an HQ411D laboratory pH / mV meter during the acidification process.

[0115] Example 10

[0116] A rice protein acid gel, its preparation method is substantially the same as that of Example 5, except that the addition of GDL in step (3) is used. In the present embodiment, step (3) is as follows:

[0117] (3) The freeze-dried sample was dissolved in water to obtain a 5% freeze-dried sample solution (called RCs solution). 4 mg of GDL (glucono-δ-lactone) was added to 1 mL of 5% RCs solution and the solution was allowed to stand for 6 h to acidify to prepare a gel. During the acidification process, the pH value was measured using an HQ411D laboratory pH / mV meter.

[0118] Embodiment 11

[0119] A rice protein acid gel, the preparation method of which is substantially the same as that of Example 7, except that in step (2), the mass ratio of RPs to CMC is changed. In this embodiment, RPs and CMC are mixed in a mass ratio of 20:1.

[0120] Example 12

[0121] A rice protein acid gel, the preparation method of which is substantially the same as that of Example 7, except that in step (2), the mass ratio of RPs to CMC is changed. In this embodiment, RPs and CMC are mixed in a mass ratio of 6:1.

[0122] Comparative Example 1

[0123] A rice protein acid gel, the preparation method of which is substantially the same as that of Example 7, except that in step (2), the mass ratio of RPs to CMC is changed. In this embodiment, RPs and CMC are mixed in a mass ratio of 5:1.

[0124] Test example:

[0125] The pH value and storage modulus of the acid gels of the examples and comparative examples were measured, and their microstructures were observed using a confocal laser microscope.

[0126] The storage modulus was determined by using a DHR-3 rheometer (TA Instruments, DE, USA) with parallel plate geometry (diameter: 40 mm; gap: 1 mm), the temperature was controlled by a Peltier system, and silicone oil was used to prevent dehydration during the measurement. The frequency used in the experiment was 1 Hz and the strain frequency was 1%. After adding GDL for 6 h at 25°C, the storage (G') modulus of the resulting gel was recorded for each embodiment and comparative example. The test results are shown in Table 1.

[0127] The microstructure was observed by confocal laser microscopy, and the specific method was as follows: the protein and CMC in the RCs suspension (1 mL) were stained with 10 μL of 1% (w / v) FITC and CFW, respectively. After adding GDL, the mixture was vortexed, and then the suspension (10 μL) was poured onto a concave slide, covered with a thin sheet, and then sealed. A Nikon C2.5i Eclipse TI2Racon confocal laser scanning microscope (Minato, Tokyo, Japan) was used to observe the microstructure of the gel for 6 hours. The microscopic images of the gels corresponding to each embodiment and comparative example are shown in Figure 2. Figure 2 , 4 , 6, wherein Example 6 measures the CLSM image of the gel prepared by adding GDL and allowing to stand and acidify to a pH of 5.5.

[0128] Table 1: Performance test table of acid gel obtained in Examples 1-5

[0129]

[0130]

[0131] Note: The amount of GDL added in the table refers to the amount of GDL added to 1 mL, 5% RCs solution in step (3).

[0132] Comparing the results of Examples 1-5 in the above table, it can be seen that when the RCs concentration increases in the range of 1% to 5%, gels with different pH values ​​and different storage moduli can be obtained. It can meet the requirements of different pH values, such as in the fields of drug release and biosensing, and can release drugs according to the specific pH value of the intestinal environment.

[0133] The morphology of the gel obtained in Examples 1-5 is as follows Figure 1 Its microstructure is shown in Figure 2 As shown. Figure 1-2 It can be seen that Figure 1 Although 1% RCs can form a gel, it does not form a stable gel. When the concentration increases to 2%, 3%, and 4%, a self-supporting gel is formed. However, when the concentration continues to increase to 5%, the gel loses its self-supporting ability. Figure 2 The CLSM images also show that when the RCs concentration is 1% ( Figure 2 In Figure A), an irregular gel network is formed, while the gels obtained in Examples 2-4 have a regular gel network, and the gel obtained in Example 5 also has a clear gel network, but its self-supporting ability can be seen from its gel morphology diagram.

[0134] Comparing the results of Examples 1-10 in the above table, it can be seen that when the amount of GDL added is 4 mg / mL, gels with different pH and storage modulus can also be obtained with the increase of RCs concentration. Under the same conditions, the storage modulus of the gel obtained when the amount of GDL added is 2 mg / mL is higher than that of 4 mg / mL, and the pH does not change much.

[0135] The morphology of the gel obtained in Examples 6-10 is as follows Figure 3 Its microstructure is shown in Figure 4 As shown. Figure 3 As shown in Figure A, Example 6 increases the amount of GDL added. The gel morphology prepared at 1% RCs concentration is different from that of Example 1, but no stable gel is formed. The complex at this time is not enough to encapsulate the water molecules it contains. This may be because the interaction between the two is weak at this concentration. At a concentration of 1%, the intermolecular interactions (hydrogen bonds, electrostatic effects, etc.) are not enough to maintain the stable structure of the gel. However, Examples 7-10 can all form stable gels ( Figure 3 B, C, D, E), wherein Example 10 increases the amount of GDL added compared to Example 4, and successfully obtains a stable gel. Figure 4 From the CLSM images, it can be seen that when the addition amount of GDL is 4 mg / mL, there are large aggregates in the acid gel prepared by 1% RCs, and there is no complete gel network structure. When the concentration increases to 2%, a uniform gel network appears in the gel. When the concentration increases to 3% and 4%, the gel network begins to break. When the concentration increases to 5%, the rupture phenomenon disappears, and a uniform gel network reappears in the acid gel. Therefore, the water holding capacity of the acid gel prepared with RCs concentrations of 2% and 5% was subsequently measured ( Figure 7). In addition, by comparing the gels prepared with two different GDL addition amounts, it can be seen that the gel prepared with 4 mg / mL GDL addition amount showed a complete gel structure and separated water, indicating that the acidification rate had a significant effect on the formation of the gel. Combined with the CLSM images at the two addition amounts, it can be seen that rapid acidification led to the disordered aggregation of the RC complex.

[0136] The present invention also measured the storage modulus of the gel when the pH reached 5.5 in different RPs and CMC ratios of Examples 11-12 and Comparative Example 1, during the standing process of adding GDL, and the specific test method was basically the same as the above storage modulus test method, except that the storage modulus corresponding to pH reaching 5.5 was tested. The results are shown in Table 2.

[0137] Table 2 Storage modulus of gel at different RPs / CMC ratios

[0138]

[0139] As can be seen from the table above, when RPs / CMC is 20:1, the storage modulus of the gel is the highest. The higher the storage modulus, the stronger the self-supporting ability of the gel. As the proportion of CMC in the system increases, the storage modulus of the gel decreases, indicating that in the composite system, the contribution of protein to the gel strength is relatively large.

[0140] The morphology of the gel obtained in Examples 11-12 and Comparative Example 1 is as follows Figure 5 As shown. Figure 5 It can be seen that Figure A cannot form a stable gel, Figure B can form a stable gel, and Figure C can hardly form a gel. This is because when the polysaccharide ratio is low, the molecular interaction between protein and polysaccharide is weak, and it is difficult to form a continuous three-dimensional network structure. When the polysaccharide ratio is high, the polysaccharide hinders the continuity of the protein phase, thus forming a liquid sample.

[0141] Figure 6 The CLSM images of Examples 11-12 and Comparative Example 1 were measured when GDL was added and the solution was acidified to a pH of 5.5. It can be seen from the figure that when the pH is 5.5, the morphologies of the acidic gels prepared with different RPs / CMC ratios are quite different. When the mass ratio of RPs to CMC is 20:1, the coarsened gel network structure of Figure A confirms the enhancement of the gel strength. When the mass ratio of RPs to CMC is 10:1, the gel network structure of Figure B is stronger. When the mass ratio of RPs to CMC is 5:1, the self-supporting ability of the formed product (Figure C) is weak, and it is basically impossible to form a complete gel.

[0142] The present invention also tested the water holding capacity of the acidic gel obtained in Example 7 and Example 10. The specific determination method is: 2 g of gel samples with different pH values ​​were taken in a centrifuge tube to determine their water holding capacity. The water holding capacity was determined based on the gel weight before and after centrifugation at 6000×g for 10 minutes. The water holding capacity (WHC) was calculated by the following formula:

[0143]

[0144] Among them, M 1 is the amount of water in the gel before centrifugation (g) and M 2 is the amount of water lost during centrifugation. All measurements were performed in triplicate.

[0145] Test results such as Figure 7 As shown in the figure, when the pH is 6.0, the water holding capacity of the gel of Example 7 is better, and the water holding capacity of the gel of Example 10 becomes weaker as the pH increases. The present invention can obtain the pH required for preparing the gel according to the requirements of the water holding capacity, and then prepare gels with different water holding capacities by controlling the acidification time.

[0146] The above is only a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims

1. A method for preparing a hydrophobic plant protein acid gel, characterized in that: The preparation method comprises the following steps: S1: mixing the plant protein solution and the polysaccharide solution to obtain a mixture, adding acid to adjust the pH value, centrifuging, collecting the supernatant, dialyzing and freeze-drying to obtain a freeze-dried sample; S2: adding water to dissolve the freeze-dried sample to obtain a freeze-dried sample solution, adding glucono-δ-lactone, standing and acidifying, and obtaining a hydrophobic plant protein acid gel.

2. The preparation method according to claim 1, characterized in that: In step S1, the plant protein is a plant protein having hydrophobic groups on the surface.

3. The preparation method according to claim 1, characterized in that: In step S1, the plant protein includes at least one of rice protein, quinoa protein, and corn protein; The purity of the plant protein is 85% to 95%, and the water content is 4.5% to 5.5%.

4. The preparation method according to claim 1, characterized in that: In step S1, the plant protein solution is prepared by dissolving the plant protein in water to obtain a solution with a concentration of 8 mg / mL to 12 mg / mL, and adjusting the pH to 12±0.

1.

5. The preparation method according to claim 1, characterized in that: In step S1, the polysaccharide is carboxymethyl cellulose; The concentration of the polysaccharide solution is 1 mg / mL, and the pH value is 12±0.

1.

6. The preparation method according to claim 1, characterized in that: In step S1, in the mixture, the mass ratio of the plant protein to the polysaccharide is 6 to 20:

1.

7. The preparation method according to claim 1, characterized in that: In step S1, the acid addition to adjust the pH refers to adjusting the pH value to 8.5-9.5; the centrifugal speed is 8000g-12000g, and the time is 10min-15min; the dialysis time is 22-26h; the freeze-drying temperature is -85℃--96℃, and the time is 90-100h.

8. The preparation method according to claim 1, characterized in that: In step S2, the mass concentration of the freeze-dried sample solution is 1% to 5%.

9. The preparation method according to claim 1, characterized in that: In step S2, the mass volume ratio of the glucono-δ-lactone to the freeze-dried sample solution is 2 to 4:1 in mg / mL; and the static acidification time is 4 to 6 hours.

10. A hydrophobic plant protein acid gel prepared by the preparation method according to any one of claims 1 to 9.

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