Genipin modified ginkgo protein and whey protein composite gel and preparation method thereof

Abstract

The invention discloses genipin modified ginkgo protein and whey protein composite gel and a preparation method thereof, and belongs to the field of functional food. The method comprises the following steps: (1) uniformly mixing a prepared ginkgo protein solution and a prepared whey protein solution, and adjusting the pH value to obtain composite sol; (2) adding a genipin reagent into the composite sol, carrying out a cross-linking reaction, and after the reaction is completed, adjusting the pH value again to obtain a genipin-treated composite sol; and (3) carrying out thermal induction gel formation on the genipin-treated composite sol, taking out and cooling to obtain the genipin-modified ginkgo protein and whey protein composite gel. Animal protein and plant protein are combined through the cross-linking agent genipin, so that the prepared composite gel is more nutritional, pollution to the environment is reduced, application in food production is facilitated, meanwhile, the composite gel treated with the cross-linking agent genipin has more diversified functional characteristics, and the composite gel is suitable for being applied to food production. And the food can be provided for people with different requirements.

Description

Technical Field

[0001] The invention belongs to the field of functional foods, and particularly relates to a genipin-modified ginkgo protein and whey protein composite gel and a preparation method thereof. Background Art

[0002] The kernel of the ginkgo seed is commonly known as the white nut, and its kernel is the edible part. Compared with the ginkgo leaf, the ginkgo seed has a long history of use as food and medicine. Studies have shown that ginkgo seeds contain 9%-13% crude protein; the amino acid composition is diverse, and it is a high-quality protein. China's annual production of ginkgo nuts is huge, providing sufficient raw materials for protein supply, and it is a resource library with great development potential. In the early research process, it was found that the gelation of ginkgo protein (GSPI) was weak, which seriously limited its application in the food industry.

[0003] Whey protein (WPI) is a natural byproduct of cheese production and was once considered an environmental pollutant due to its limited use. Whey protein isolate is mainly composed of 60-70% β-lactoglobulin, α-lactalbumin and bovine serum albumin. Whey protein isolate has high nutritional value and biological activity. Due to its excellent functional properties, it is widely used to improve the processing characteristics of food. However, the production of whey protein isolate requires more greenhouse gas emissions and a larger land area, so plant protein is used to partially replace animal protein in food formulas in many productions. Past studies have found that the functional properties of plant protein alone are relatively simple and have certain limitations. Therefore, the function and scope of use of plant protein gel can be improved by processing multiple proteins. A large number of experiments have shown that the nutritional value of animal protein and plant protein is higher than that of single protein products. Although the existing, simple protein mixture has improved the functional properties of single protein to a certain extent, there is still a lot of room for improvement. Summary of the invention

[0004] Purpose of the invention: In order to solve the technical problems existing in the prior art, the first purpose of the present invention is to provide a method for preparing a composite gel of genipin-modified ginkgo protein and whey protein having diverse gel properties, both texture and elastic viscosity, rich in nutrition, and capable of meeting the edible needs of different groups of people. The second purpose of the present invention is to provide a method for preparing the above-mentioned composite gel of genipin-modified ginkgo protein and whey protein.

[0005] Technical solution: The method for preparing the composite gel of genipin-modified ginkgo protein and whey protein of the present invention comprises the following steps:

[0006] (1) mixing the prepared ginkgo protein solution and whey protein solution uniformly, and adjusting the pH to obtain a GSPI / WPI composite sol;

[0007] (2) adding genipin reagent to the GSPI / WPI composite sol to carry out a cross-linking reaction, and adjusting the pH again after the reaction is complete to obtain a GSPI / WPI composite sol treated with genipin;

[0008] (3) The GSPI / WPI composite sol treated with genipin is subjected to thermal induction gelation, and then taken out and cooled to obtain a composite gel of genipin-modified ginkgo protein and whey protein.

[0009] Furthermore, in step (1), the preparation method of the ginkgo protein solution is: dissolving the ginkgo protein powder in a solvent, stirring the solution sufficiently and then standing the solution to obtain the solution.

[0010] Furthermore, the preparation method of the whey protein solution is: dissolving whey protein powder in a solvent, stirring the solution sufficiently and then standing the solution to obtain the whey protein solution.

[0011] Furthermore, the mass concentration of the ginkgo protein solution is 100-140 g / L, and the mass concentration of the whey protein solution is 100-140 g / L; the volume ratio of the ginkgo protein solution to the whey protein solution is 0.1-1:1; and the pH adjustment range is 5.0±0.1.

[0012] Furthermore, in step (2), the mass concentration of the genipin reagent added in the GSPI / WPI composite sol is 1-5 g / L; the conditions of the cross-linking reaction are: continuous stirring at a speed of 300-500 rpm for 3-5 hours at room temperature; and the pH adjustment range is: 4.0-6.0.

[0013] Furthermore, in step (3), the conditions for heat-induced gelation are: reaction at 85-95° C. for 25-45 min.

[0014] The invention provides a composite gel of genipin-modified ginkgo protein and whey protein prepared by the preparation method.

[0015] Principle of the invention: The present invention mixes animal protein and plant protein to form a dual-protein system. The two proteins form polymers through disulfide bonds, hydrophobic interactions, hydrogen bonds and electrostatic interactions, and are further cross-linked with different concentrations of genipin to obtain different microstructures at different pH values, thereby improving the gel properties. Genipin is a green biocrosslinker with active groups such as ester groups and hydroxyl groups. After cross-linking with biomacromolecules with primary amine groups, it can form a polymer network with strength and biocompatibility, thereby achieving intramolecular or intermolecular covalent crosslinking. Genipin reacts with free amino groups in proteins to form stable covalent bonds, and reacts with primary amino groups to generate blue compounds. The complex coagulation system between the two charged proteins exhibits unique functional properties such as gelation, emulsification, and ligand binding, and the addition of genipin further repairs the gel properties of the protein, which also gives this protein complex a unique advantage in the food field.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the present invention modifies the ginkgo protein and whey protein composite gel by different genipin concentrations, and the hardness of the prepared ginkgo protein and whey composite protein gel increases with the increase of genipin concentration at pH 4.0 and pH 5.0, and the elasticity is also improved. At pH 6.0, the gel hardness is weak and the chewiness is also low, which is suitable for elderly people with bad teeth. The gel has diversified properties and is suitable for people with different needs, and is more conducive to food production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the solubility analysis of the ginkgo whey protein composite gel modified with different genipin concentrations in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3;

[0018] Figure 2 It is a schematic diagram of the polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the ginkgo whey protein composite gel modified with different genipin concentrations in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3;

[0019] Figure 3 It is a schematic diagram of the texture profile analysis of the ginkgo whey protein composite gel modified with different genipin concentrations in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3;

[0020] Figure 4 It is a schematic diagram of the water holding capacity analysis of ginkgo whey protein composite gel modified with different genipin concentrations in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3;

[0021] Figure 5 Schematic diagram of scanning electron microscopy of ginkgo whey protein composite gel modified with different genipin concentrations in Examples 1 to 9 of the present invention and Comparative Examples 1 to 3. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described below in conjunction with embodiments and drawings.

[0023] Example 1: The method for preparing the composite gel of genipin-modified ginkgo protein and whey protein provided by the present invention comprises the following steps:

[0024] (1) After uniformly mixing a prepared ginkgo protein solution with a mass concentration of 120 g / L and a whey protein solution with a mass concentration of 120 g / L in a volume ratio of 1:1, adjusting the pH to 5.0 to obtain a GSPI / WPI composite sol, wherein the preparation method of the ginkgo protein solution is: dissolving ginkgo protein powder in a ratio of 120 g / L in water, stirring evenly, and standing in a refrigerator for hydration for 24 hours, and the preparation method of the whey protein solution is: dissolving whey protein powder in a ratio of 120 g / L in water, stirring evenly, and standing in a refrigerator for hydration for 24 hours, and the GSPI / WPI composite sol is obtained;

[0025] (2) adding 1 g / L genipin reagent to the GSPI / WPI composite sol, and performing a cross-linking reaction for 4 h. After the reaction is complete, adjusting the pH to 4.0 again to obtain a genipin-treated GSPI / WPI composite sol;

[0026] (2) The GSPI / WPI composite sol treated with genipin was subjected to thermal induction gelation and heated in a 90°C water bath for 30 min. After the reaction was completed, the sol was taken out and cooled to obtain a composite gel of genipin-modified ginkgo protein and whey protein.

[0027] Example 2: The difference from Example 1 is that in step (2), the pH is adjusted to 5.0.

[0028] Example 3: The difference from Example 1 is that in step (2), the pH is adjusted to 6.0.

[0029] Example 4: The difference from Example 1 is that in step (2), the mass concentration of the genipin reagent is 3 g / L.

[0030] Example 5: The difference from Example 1 is that in step (2), the mass concentration of the genipin reagent is 5 g / L.

[0031] Example 6: The difference from Example 2 is that in step (2), the mass concentration of the genipin reagent is 3 g / L.

[0032] Example 7: The difference from Example 2 is that in step (2), the mass concentration of the genipin reagent is 5 g / L.

[0033] Example 8: The difference from Example 3 is that in step (2), the mass concentration of the genipin reagent is 3 g / L.

[0034] Example 9: The difference from Example 3 is that in step (2), the mass concentration of the genipin reagent is 5 g / L.

[0035] Comparative Example 1: The difference from Example 1 is that in step (2), no genipin reagent is added.

[0036] Comparative Example 2: The difference from Example 2 is that in step (2), no genipin reagent is added.

[0037] Comparative Example 3: The difference from Example 3 is that in step (2), no genipin reagent is added.

[0038] The materials obtained from Examples 1 to 9 and Comparative Examples 1 to 3 were subjected to performance tests, including:

[0039] (1) The GSPI / WPI composite sol treated with genipin was diluted to 10 mg / mL with a citrate phosphate buffer of the corresponding pH. After centrifugation at 5000 g and 25°C for 10 minutes, the protein concentration in the supernatant was determined using a biuret reagent. The protein solubility was expressed as the percentage of the protein concentration (mg / mL) in the supernatant to the initial total protein concentration (10 mg / mL).

[0040] (2) The GSPI / WPI composite sol sample (2 g / L) of the corresponding pH was mixed with the same volume of sample buffer (4% SDS, 20% glycerol and 0.125 mol / L Tris-HCl, pH 6.8) to prepare two samples with and without the addition of 5% β-mercaptoethanol (β-ME). The prepared mixed solution was boiled for 3 minutes and cooled to room temperature for use. SDS-PAGE was performed in the prepared 5% (v / v) polyacrylamide stacking gel and 12% (v / v) separating gel, and the sample volume in each well was 15 μL.

[0041] (3) The texture characteristics of the composite gel were determined by using a texture analyzer with two downward pressures, using a P / 0.5 cylindrical probe. The probe speeds were set to 1.0, 2.0, and 5.0 mm / s before, during, and after the test, respectively; the downward pressure distance was 7.0 mm, and the trigger force was 5.0 g. The gel texture was calculated according to the Bourne definition, which mainly included the hardness, elasticity, cohesion, adhesiveness, chewiness, and resilience of the composite gel.

[0042] (4) Take an appropriate amount of composite gel (5.0 g) in a centrifuge tube containing filter paper, centrifuge at 3000g for 20 minutes, and then record the mass of the gel after centrifugation. The water holding capacity (WHC) is calculated as follows:

[0043] WHC(%)=(m2-m0) / (m1-m0)×100

[0044] Where: m1 is the mass of the composite gel, centrifuge tube and filter paper; m0 is the mass of the centrifuge tube and filter paper; m2 is the mass of the composite gel removed after centrifugation.

[0045] (5) The microstructure of the GSPI / WPI composite gel at different pH values ​​after genipin treatment was observed by Quanta-200 scanning electron microscope (SEM) at an electron acceleration voltage of 20 kV at two scales: 5 μm and 50 μm. The cross section of the gel was fixed and gold-sprayed before analysis.

[0046] The above test results are as follows Figure 1-Figure 5 shown.

[0047] like Figure 1 As shown, at pH 4.0 and pH 5.0, the solubility of GSPI / WPI decreased with the increase of genipin concentration; at pH 6.0, the solubility of GSPI / WPI increased with the increase of genipin concentration.

[0048] like Figure 2 As shown, under non-reducing conditions, the main bands observed were G1 and G2 for GSPI, and β-lactoglobulin and α-lactoglobulin for WPI. At all pH values, a large amount of protein aggregates were observed at the top of the stacking gel. When β-ME was added, G1 was observed to split into G3 and G4. Protein aggregates with larger molecular weight could not enter the stacking gel, and the presence of β-ME caused the stacking gel to disappear. With the increase of genipin concentration, the β-lactoglobulin band of WPI weakened.

[0049] like Figure 3 As shown in the figure, at pH 4.0 and pH 5.0, the hardness of the GSPI / WPI composite gel increased with the increase of genipin concentration, and the viscosity and chewiness were positively correlated with the hardness. The cohesion and recovery also showed an upward trend; at pH 6.0, the hardness decreased with the increase of genipin concentration, and the gel texture properties showed a downward trend, with poor texture performance.

[0050] like Figure 4 As shown, at pH 4.0, the water holding capacity of GSPI / WPI gel increased with the increase of genipin concentration; at pH 5.0, the water holding capacity of GSPI / WPI gel fluctuated with the increase of genipin concentration and showed a downward trend; at pH 6.0, the water holding capacity of GSPI / WPI gel decreased with the increase of genipin concentration.

[0051] like Figure 5As shown in the figure, the GSPI / WPI protein gel, without the addition of genipin, mainly presents a spherical three-dimensional network structure. With the increase of genipin concentration, at pH 4.0 and pH 5.0, GSPI / WPI aggregates to form larger polymers, while at pH 6.0, the protein structure changes significantly and becomes smoother.

Claims

1. A method for preparing a composite gel of genipin-modified ginkgo protein and whey protein, characterized in that: The following steps are involved: (1) mixing the prepared ginkgo protein solution and whey protein solution uniformly, and adjusting the pH to obtain a GSPI / WPI composite sol; (2) adding genipin reagent to the GSPI / WPI composite sol to carry out a cross-linking reaction, and adjusting the pH again after the reaction is complete to obtain a GSPI / WPI composite sol treated with genipin; (3) The GSPI / WPI composite sol treated with genipin is subjected to thermal induction gelation, and then taken out and cooled to obtain a composite gel of genipin-modified ginkgo protein and whey protein.

2. The method according to claim 1, characterized in that In step (1), the preparation method of the ginkgo protein solution is: dissolving the ginkgo protein powder in a solvent, stirring the solution sufficiently and then standing the solution to obtain the solution.

3. The method according to claim 1, characterized in that In step (1), the whey protein solution is prepared by dissolving whey protein powder in a solvent, stirring the solution sufficiently and then standing the solution to obtain the whey protein solution.

4. The method according to claim 1, characterized in that: In step (1), the mass concentration of the ginkgo protein solution is 100-140 g / L, and the mass concentration of the whey protein solution is 100-140 g / L; the volume ratio of the ginkgo protein solution to the whey protein solution is 0.1-1:

1.

5. The method according to claim 1, characterized in that In step (1), the pH is adjusted within a range of 5.0±0.

1.

6. The method according to claim 1, characterized in that In step (2), the mass concentration of the genipin reagent added in the GSPI / WPI composite sol is 1-5 g / L.

7. The method according to claim 1, characterized in that In step (2), the conditions for the cross-linking reaction are: continuous stirring at a rotation speed of 300-500 rpm for 3-5 hours at room temperature.

8. The method according to claim 1, characterized in that In step (2), the pH is adjusted in the range of 4.0-6.

0.

9. The method according to claim 1, characterized in that: In step (3), the conditions for heat-induced gelation are: reaction at 85-95° C. for 25-45 min.

10. A composite gel of genipin-modified ginkgo protein and whey protein prepared by the preparation method according to any one of claims 1 to 9.

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