Preparation method of enhanced whey protein isolate-corn protein gel ground

Abstract

The invention relates to the field of food engineering, in particular to modified composite whey protein isolate-corn protein gel as well as a preparation method and a product thereof. The preparation method comprises the following steps: mixing and stirring different amounts of whey protein isolate and water, adjusting the pH value to 12 by using NaOH, adding corn protein, standing to form gel, soaking in hydrochloric acid to adjust the pH value, flushing, refrigerating and the like. A large number of experiments show that when the mass ratio of whey protein isolate to corn protein is 8: 2, the gel has the best properties such as strength, moisture retention capacity and rheological property. The protein proportion is accurately controlled, the gel structure and functional characteristics are optimized, technical support and theoretical basis are provided for development of novel functional gel in the food industry, and the method can be used for development of food additives for improving food texture and taste.

Description

Technical Field

[0001] The invention relates to the field of food science and technology, and in particular to a preparation method for enhancing the texture of whey protein isolate-zein gel. Background Art

[0002] Amidst the booming food industry, plant-based proteins are gaining popularity due to their health, environmental benefits, and diverse functionality. Whey protein isolate, a globular protein derived from milk, is widely used in the food industry due to its excellent nutritional value, emulsifying activity, and gelling properties. Upon heating, its molecules denature and aggregate, forming a three-dimensional network gel structure that significantly improves food texture and moisture retention. Zein, the core storage protein of corn, is renowned for its biocompatibility and solubility in specific alcohols and alkaline solutions. Zein, in combination with whey protein isolate, creates a high-performance composite gel system under alkaline conditions.

[0003] As a common protein modification technique, pH shift has shown great potential in the preparation of gels of whey protein isolate and zein. By precisely controlling the pH value, the protein is first placed in a strong alkaline environment to unfold its structure, allowing the two protein molecules to interact after unfolding to form a gel, and then the pH is adjusted back to neutral. In the preparation of composite gels of whey protein isolate and zein, precise control of pH shift is particularly critical. When the pH value of the treatment environment changes from neutral to alkaline, it will significantly change the molecular conformation and interaction pattern of the two proteins, thereby affecting the texture, elasticity and stability of the final gel.

[0004] This invention focuses on the pH-treated gel preparation technology for whey protein isolate and zein, aiming to rapidly form a gel product and optimize gel quality by controlling the different ratios of whey protein isolate and zein. This allows the resulting composite gel to achieve ideal texture uniformity, moisture retention, and appearance, providing a higher-quality gel product option for the plant-based food sector. This is expected to promote the widespread application of plant protein gels in the food industry, bringing consumers innovative foods that combine taste and nutrition, while also helping companies improve production efficiency and product quality, enhancing their market competitiveness. Summary of the Invention

[0005] The present invention aims to overcome the limitations of zein gelation by modifying zein through alkali treatment to improve its rapid-setting properties. The present invention also aims to effectively improve the gelation properties of zein and whey protein isolate, while removing residual residues through reagent neutralization. This simple and convenient method can meet the needs of large-scale production. This method significantly promotes the development of the zein processing industry.

[0006] This invention modulates the gel properties by adjusting the mass ratio of whey protein isolate to zein. It was found that an 8:2 ratio achieved optimal overall gel performance. At this ratio, the gel's strength, water retention, and rheological properties were significantly improved. The invention also reveals the effect of zein on the secondary and tertiary structures of whey protein isolate and how this influence can be used to improve the gel's properties and functionality by adjusting the protein mass ratio.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a whey protein isolate-zein gel with enhanced texture, characterized by comprising the following steps:

[0009] (1) Treatment of whey protein isolate solution: Different amounts of whey protein isolate (1.0, 0.9, 0.8, 0.7, 0.6, and 0.5 g) were mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0010] (2) Alkaline pH treatment of zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, different amounts of zein (0, 0.1, 0.2, 0.3, 0.4, and 0.5 g) were added and stirred at room temperature for another 3 min.

[0011] (3) The mixture was allowed to stand for 2 h to obtain a composite gel. The gel sample was then immersed in 0.1 M HCl for 12 h to adjust the pH to approximately 6.8. Afterwards, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C for further analysis.

[0012] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0013] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0014] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0015] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0016] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0017] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0018] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0019] The experimental conditions for measuring protein solubility in step (5) are as follows: first, each sample group is diluted to 10 mg / mL with phosphate buffer (0.01 M, pH 7.0), then centrifuged at 8000 rpm for 10 min at room temperature, and the supernatant is retained for later use. The protein concentration in the supernatant is determined by the Lowry method. The protein solubility formula is as follows:

[0020]

[0021] The experimental conditions for measuring the surface hydrophobicity of the protein in step (5) are as follows: each group of samples is diluted to (0.0625, 0.125, 0.25, 0.5 and 1 mg / mL) with 0.1 M phosphate buffer solution (pH 7.0), 40 μL of 8 mM 8-anilino-1-naphthalenesulfonic acid (ANS) solution is added to 4 mL of the diluted solution, and the reaction is completed after waiting for 20 minutes in the dark. The excitation wavelength and emission wavelength are set to 335 nm and 600 nm, respectively, and the surface hydrophobicity is measured using a fluorescence spectrophotometer. The slope of the fluorescence intensity curve in the initial stage is the surface hydrophobicity index (H0) of the protein.

[0022] The experimental conditions for measuring the free thiol groups of the protein in step (6) are as follows: a UV spectrophotometer is required. First, a Tris-Gly buffer solution is prepared, which comprises 0.086M Tris, 0.09M Gly and 0.004M EDTA (ethylenediaminetetraacetic acid) (pH 8.0). Then, Ellman (5,5'-dithiobis(2-nitropropene, DTNB) is prepared. 2mL of whey protein isolate-zein solution (200mg / mL) is dispersed in 4mL of Tris-Gly buffer and mixed. The mixture is then mixed with 50μL of Ellman's reagent and incubated at room temperature in the dark for 1h. Finally, the absorbance at 412nm is measured. The free thiol content is calculated as follows:

[0023]

[0024] Among them A 412 is the absorbance at 412 nm, D is the dilution factor, C is the protein concentration (mg / mL), 73.53 is 10 6 / (1.36×10 4 ) is calculated, where the molar extinction coefficient is 1.36×10 4 m -1 cm -1 .

[0025] In the step (7) of measuring protein, the freeze-dried gel sample is broken to obtain a flat sample cross section, and then the sample is fixed on a sample stage with conductive glue, the sample is sprayed with gold, and then observed and photographed using a scanning electron microscope at a voltage of 20 kV.

[0026] The rheological test conditions for the composite gel in step (8) are as follows: the sample is tested using a 40 mm stainless steel disc and an MCR302 rheometer. The sample is positioned between a conical plate and a platform with a gap of 1 mm. The changes in the elastic modulus (G') and the viscosity modulus (G") are monitored within a certain strain range. When the frequency is swept from 0.1 to 10 Hz, the changes in G' and G" with frequency are recorded.

[0027] The test conditions for measuring the composite gel strength in step (9) are as follows: the gel sample is carefully removed from the beaker and then subjected to texture profile analysis (TPA) using a food physical property analyzer. The experimental parameters are set as follows: probe model P / 36R, pre- and post-test speeds of 1.0 mm / s, deformation ratio of 30%, and trigger force of 2 g.

[0028] The experimental conditions for measuring the composite gel strength in step (10) are as follows: samples of composite proteins with different proportions are placed on a glass plate, and photographs are taken to record the gel state.

[0029] The whey protein isolate-corn protein composite gel prepared by the preparation method has good solubility and surface hydrophobicity, moderate free thiol content, delicate and orderly structure, excellent water retention capacity and rheological properties.

[0030] One of the purposes of the present invention is to provide a rapid and novel method for preparing protein gel.

[0031] The second object of the present invention is to provide a whey protein isolate-zein gel product with excellent texture. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a technical flow chart of the present invention;

[0033] Figure 2 The protein solubility and surface hydrophobicity of whey protein isolate-zein mixed gels with different mass ratios are shown;

[0034] Figure 3 The free sulfhydryl content of whey protein isolate-zein mixed gels with different mass ratios is shown;

[0035] Figure 4 Scanning electron microscopy (SEM) images of whey protein isolate-zein mixed gels with different mass ratios are shown;

[0036] Figure 5 The rheological properties of whey protein isolate-zein mixed gels with different mass ratios are shown;

[0037] Figure 6 The changes in water distribution of whey protein isolate-zein mixed gels with different mass ratios are shown;

[0038] Figure 7 The gel strength of whey protein isolate-zein mixed gels with different mass ratios is shown;

[0039] Figure 8 Shows the appearance of whey protein isolate-zein mixed gels with different mass ratios. DETAILED DESCRIPTION

[0040] The following is a further description of specific embodiments with reference to the accompanying drawings.

[0041] A method for preparing a whey protein isolate-zein gel with enhanced texture, characterized by comprising the following steps:

[0042] (1) Treatment of whey protein isolate solution: Different amounts of whey protein isolate (1.0, 0.9, 0.8, 0.7, 0.6, and 0.5 g) were mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0043] (2) Alkaline pH treatment of zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, different amounts of zein (0, 0.1, 0.2, 0.3, 0.4, and 0.5 g) were added and stirred at room temperature for 3-5 min.

[0044] (3) The mixture was allowed to stand for 2 h to obtain a composite gel. The gel sample was then immersed in 0.1 M HCl for 12 h to adjust the pH to approximately 6.8. Afterwards, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C for further analysis.

[0045] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0046] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0047] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0048] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0049] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0050] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0051] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0052] The experimental conditions for measuring protein solubility in step (5) are as follows: first, each sample group is diluted to 10 mg / mL with phosphate buffer (0.01 M, pH 7.0), then centrifuged at 8000 rpm for 10 min at room temperature, and the supernatant is retained for later use. The protein concentration in the supernatant is determined by the Lowry method. The protein solubility formula is as follows:

[0053]

[0054] The experimental conditions for measuring the surface hydrophobicity of the protein in step (5) are as follows: each group of samples is diluted to (0.0625, 0.125, 0.25, 0.5 and 1 mg / mL) with 0.1 M phosphate buffer solution (pH 7.0), and then 4 mL of the diluted solution is added with 40 μL of 8 mM 8-anilino-1-naphthalenesulfonic acid (ANS) solution. The reaction is completed after waiting for 20 minutes in the dark. The excitation wavelength and emission wavelength are set to 335 nm and 600 nm, respectively, and the surface hydrophobicity is measured using a fluorescence spectrophotometer. The slope of the fluorescence intensity curve in the initial stage is the surface hydrophobicity index (H0) of the protein.

[0055] The experimental conditions for measuring the free thiol groups of the protein in step (6) are as follows: a UV spectrophotometer is required. First, a Tris-Gly buffer solution is prepared, which comprises 0.086M Tris, 0.09M Gly and 0.004M EDTA (ethylenediaminetetraacetic acid) (pH 8.0). Then, Ellman (5,5'-dithiobis(2-nitropropene, DTNB) is prepared. 2mL of whey protein isolate-zein solution (200mg / mL) is dispersed in 4mL of Tris-Gly buffer and mixed. The mixture is then mixed with 50μL of Ellman's reagent and incubated at room temperature in the dark for 1h. Finally, the absorbance at 412nm is measured. The free thiol content is calculated as follows:

[0056]

[0057] Among them A 412 is the absorbance at 412 nm, D is the dilution factor, C is the protein concentration (mg / mL), 73.53 is 10 6 / (1.36×10 4 ) is calculated, where the molar extinction coefficient is 1.36×10 4 m -1 cm -1 .

[0058] In the step (7) of measuring protein, the freeze-dried gel sample is broken to obtain a flat sample cross section, and then the sample is fixed on a sample stage with conductive glue, the sample is sprayed with gold, and then observed and photographed using a scanning electron microscope at a voltage of 20 kV.

[0059] The rheological test conditions for the composite gel in step (8) are as follows: the sample is tested using a 40 mm stainless steel disc and an MCR302 rheometer. The sample is positioned between a conical plate and a platform with a gap of 1 mm. The changes in the elastic modulus (G') and the viscosity modulus (G") are monitored within a certain strain range. When the frequency is swept from 0.1 to 10 Hz, the changes in G' and G" with frequency are recorded.

[0060] The test conditions for measuring the composite gel strength in step (9) are as follows: the gel sample is carefully removed from the beaker and then subjected to texture profile analysis (TPA) using a food physical property analyzer. The experimental parameters are set as follows: probe model P / 36R, pre- and post-test speeds of 1.0 mm / s, deformation ratio of 30%, and trigger force of 2 g.

[0061] The experimental conditions for measuring the composite gel strength in step (10) are as follows: samples of composite proteins with different proportions are placed on a glass plate, and photographs are taken to record the gel state.

[0062] The whey protein isolate-corn protein composite gel prepared by the preparation method has good solubility and surface hydrophobicity, moderate free thiol content, delicate and orderly structure, excellent water retention capacity and rheological properties.

[0063] Example 1

[0064] (1) Treatment of whey protein isolate solution: 1.0 g of whey protein isolate was mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0065] (2) Alkaline pH treatment of the corn protein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2M NaOH and stirred at room temperature for 3 minutes. Then, 0g of corn protein was added and stirred at room temperature for 3-5 minutes.

[0066] (3) The mixture was allowed to stand for 2 h to obtain a composite gel, and then the gel sample was immersed in 0.1 M HCl for 12 h to adjust the pH to about 6.8. After that, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C before further analysis.

[0067] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0068] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0069] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0070] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0071] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0072] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0073] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0074] Example 2

[0075] (1) Treatment of whey protein isolate solution: 0.9 g of whey protein isolate was mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0076] (2) Alkaline pH treatment of the zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, 0.1 g of zein was added and stirred at room temperature for 3-5 min.

[0077] (3) The mixture was allowed to stand for 2 h to obtain a composite gel. The gel sample was then immersed in 0.1 M HCl for 12 h to adjust the pH to approximately 6.8. Afterwards, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C for further analysis.

[0078] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0079] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0080] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0081] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0082] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0083] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0084] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0085] Example 3

[0086] (1) Treatment of whey protein isolate solution: 0.8 g of whey protein isolate was mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0087] (2) Alkaline pH treatment of the zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, 0.2 g of zein was added and stirred at room temperature for 3-5 min.

[0088] (3) The mixture was allowed to stand for 2 h to obtain a composite gel, and then the gel sample was immersed in 0.1 M HCl for 12 h to adjust the pH to about 6.8. After that, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C before further analysis.

[0089] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0090] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0091] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0092] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0093] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0094] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0095] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0096] Example 4

[0097] (1) Treatment of whey protein isolate solution: 0.7 g of whey protein isolate was mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0098] (2) Alkaline pH treatment of the zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, 0.3 g of zein was added and stirred at room temperature for 3-5 min.

[0099] (3) The mixture was allowed to stand for 2 h to obtain a composite gel, and then the gel sample was immersed in 0.1 M HCl for 12 h to adjust the pH to about 6.8. After that, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C before further analysis.

[0100] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0101] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0102] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0103] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0104] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0105] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0106] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0107] Example 5

[0108] (1) Treatment of whey protein isolate solution: 0.6 g of whey protein isolate was mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0109] (2) Alkaline pH treatment of the zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, 0.4 g of zein was added and stirred at room temperature for 3-5 min.

[0110] (3) The mixture was allowed to stand for 2 h to obtain a composite gel, and then the gel sample was immersed in 0.1 M HCl for 12 h to adjust the pH to about 6.8. After that, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C before further analysis.

[0111] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0112] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0113] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0114] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0115] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0116] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0117] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0118] Example 6

[0119] (1) Treatment of whey protein isolate solution: 0.5 g of whey protein isolate was mixed with 5 mL of distilled water and magnetically stirred for 30 min;

[0120] (2) Alkaline pH treatment of the zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, 0.5 g of zein was added and stirred at room temperature for 3-5 min.

[0121] (3) The mixture was allowed to stand for 2 h to obtain a composite gel, and then the gel sample was immersed in 0.1 M HCl for 12 h to adjust the pH to about 6.8. After that, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C before further analysis.

[0122] (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis;

[0123] (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer;

[0124] (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel;

[0125] (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4);

[0126] (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3);

[0127] (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3);

[0128] (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

[0129] By attaching Figure 2 It is clear that the protein ratio significantly affects the solubility of the total complex protein. When the ratio of whey protein isolate to corn protein is 8:2, a balance is achieved between the two molecules, which can effectively stabilize the solubility of the complex protein. Figure 2 The results showed that the overall surface hydrophobicity continued to increase with the decrease of whey protein isolate content. These results indicate that adjusting the protein ratio can regulate the solubility and surface hydrophobicity of composite proteins, thereby affecting their gelation. Figure 3 The results showed that the free thiol content of WZ7-3, WZ6-4 and WZ5-5 was still higher than that of WPI, WZ9-1 and WZ8-2. This was mainly because the amount of whey protein isolate was insufficient to fully interact with zein. In addition, under alkaline conditions, zein unfolded for a long time, causing some of its rigid structures to break and protein molecular subunits to depolymerize, thereby increasing the content of free thiol groups. Figure 4 Compared with pure whey protein isolate gel, WZ8-2 gel showed a more uniform network structure without obvious granular structure, which indicated complete gelation. Figure 5 It shows that G′ is always higher than G″, which indicates that the composite system exhibits gel-like behavior in the entire test frequency range. For the WZ8-2 composite gel, the G′ value reaches the maximum value, and with the increase of zein concentration, the G′ increment of whey protein isolate-zein composite gel gradually decreases. Figure 6 The relaxation time of the composite protein emulsion gel at different whey protein isolate-zein ratios is shown, and WZ8-2 has the strongest ability to retain water. Figure 8The gel-like paste produced by WZ5-5 was not self-supporting, and the WZ8-2 formulation showed a significant increase in gel strength compared to the control group using pure whey protein isolate. WZ8-2 significantly enhanced the gel texture and the Figure 7 Visual assessment was consistent.

[0130] The pH treatment and the 8:2 ratio provide the whey protein isolate-corn protein composite gel with good solubility and surface hydrophobicity, moderate free thiol content, a fine and orderly structure, excellent water retention capacity and rheological properties.

Claims

1. A method for preparing a whey protein isolate-zein gel with enhanced texture, characterized in that Overcoming the limitations of corn protein gelation, alkali treatment of corn protein is used to modify and improve its rapid coagulation properties. At the same time, the whey protein isolate-corn protein composite gel produced has excellent structure, water retention capacity and rheological properties. (1) Treatment of whey protein isolate solution: Different amounts of whey protein isolate (1.0, 0.9, 0.8, 0.7, 0.6, and 0.5 g) were mixed with 5 mL of distilled water and magnetically stirred for 30 min; (2) Alkaline pH treatment of zein solution: The pH of the whey protein isolate solution was adjusted to 12.0 with 2 M NaOH and stirred at room temperature for 3 min. Then, different amounts of zein (0, 0.1, 0.2, 0.3, 0.4, and 0.5 g) were added and stirred at room temperature for another 3 min. (3) The mixture was allowed to stand for 2 h to obtain a composite gel, and then the gel sample was immersed in 0.1 M HCl for 12 h to adjust the pH to about 6.

8. After that, it was thoroughly rinsed with distilled water for 30 min and stored in a refrigerator at 4 °C before further analysis. (4) A portion of the gel sample formed above was freeze-dried, ground into powder and stored in a refrigerator at 4°C before further analysis; (5) after re-dissolving the protein powder samples treated in step (4), the solubility and surface hydrophobicity of different samples were analyzed using an ultraviolet spectrophotometer and a fluorescence spectrophotometer; (6) re-dissolving the protein powder sample treated in step (4), and analyzing the free thiol content of the mixed gel; (7) analyzing a scanning electron microscope (SEM) image of the freeze-dried mixed gel obtained in step (4); (8) analyzing the rheological properties of the mixed gel of the protein sample treated in step (3); (9) analyzing the gel strength of the mixed gel of the protein sample treated in step (3); (10) Analyze the appearance of the mixed gel of the protein sample treated in step (3).

2. The method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein: The experimental conditions for measuring protein solubility in step (5) are as follows: dilute each sample to 10 mg / mL, centrifuge at 8000 rpm for 10 min at room temperature, take the supernatant, and measure the protein concentration in the supernatant. The protein solubility formula is as follows:

3. The method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein: The experimental conditions for measuring the surface hydrophobicity of the protein in step (5) are as follows: each group of samples is diluted to (0.0625, 0.125, 0.25, 0.5 and 1 mg / mL) with 0.1 M phosphate buffer solution (pH 7.0), 40 μL of 8 mM 8-anilino-1-naphthalenesulfonic acid (ANS) solution is added to 4 mL of the diluted solution, and the reaction is completed after waiting for 20 minutes in the dark. The excitation wavelength and emission wavelength are set to 335 nm and 600 nm, respectively, and the surface hydrophobicity is measured using a fluorescence spectrophotometer. The slope of the fluorescence intensity curve in the initial stage is the surface hydrophobicity index (H0) of the protein.

4. The method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein: The experimental conditions for measuring the free thiol groups of proteins in step (6) are as follows: a UV spectrophotometer is required. First, a Tris-Gly buffer solution is prepared, and then Ellman (5,5'-dithiobis, DTNB) is prepared. 2 mL of a whey protein isolate-zein mixed solution (200 mg / mL) is dispersed in 4 mL of Tris-Gly buffer, and then mixed with 50 μL of Ellman's reagent. The mixture is incubated at room temperature in the dark for 1 hour, and finally the absorbance at 412 nm is measured. The free thiol content is calculated as follows: -SH(μmol / g)=(73.53×A 412 ×D) / C Among them A 412 is the absorbance at 412 nm, D is the dilution factor, C is the protein concentration (mg / mL), 73.53 is 10 6 / (1.36×10 4 ) is calculated, where the molar extinction coefficient is 1.36×10 4 m -1 cm -1 .

5. The method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein: In the step (7) of measuring protein, the freeze-dried gel sample is broken to obtain a flat sample cross section, and then the sample is fixed on a sample stage with conductive glue and subjected to gold spraying treatment; and then the sample is observed and photographed using a scanning electron microscope at a voltage of 20 kV.

6. The method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein: The test conditions for measuring the rheological properties of the composite gel in step (8) are as follows: a 40 mm stainless steel disc and an MCR302 rheometer are used to test the sample. The sample is located between the conical plate and the platform with a gap of 1 mm. The changes in the elastic modulus (G') and the viscosity modulus (G") are monitored. When the frequency is scanned from 0.1 to 10 Hz, the changes in G' and G" with frequency are recorded.

7. The method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein: The test conditions for measuring the composite gel strength in step (9) are as follows: after carefully removing the gel sample from the flat-bottom beaker, a texture profile analysis (TPA) is performed using a food property tester. The experimental parameters are set as follows: probe model P / 36R, pre- and post-test speeds of 1.0 mm / s, deformation ratio of 30%, and trigger force of 2 g.

8. The method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein: The experimental conditions for measuring the composite appearance in step (10) are as follows: samples of composite proteins with different ratios are placed on a glass plate, and photographs are taken to record the gel state.

9. A method for preparing a whey protein isolate-zein gel with enhanced texture according to claim 1, wherein the whey protein isolate-zein composite gel has good solubility and surface hydrophobicity, a moderate free thiol content, a fine and orderly structure, excellent water retention capacity and rheological properties.

Images