Vegetable protein thermal reversible hydrogel and preparation method thereof

Abstract

The invention discloses plant protein thermal reversible hydrogel and a preparation method thereof, and belongs to the technical field of protein gel preparation. The preparation method of the vegetable protein reversible hydrogel comprises the following steps: hydrating a vegetable protein solution overnight, adjusting the pH value, stirring at room temperature, adding ethanol to obtain a vegetable protein-ethanol mixed solution, heating for reaction, and cooling in an ice bath to obtain the vegetable protein thermal reversible hydrogel. According to the preparation method disclosed by the invention, the concentration of protein and ethanol is reduced, the thermal reversible vegetable protein gel can be successfully prepared under the condition of low protein concentration, and the prepared vegetable protein thermal reversible hydrogel has a wide application prospect in the field of foods, can be used as a substitute of gelatin for healthy foods, and has a wide application prospect. Or the solid beverage can be used as a novel vegetable protein alcohol solid beverage, and can also be used as a steady-state delivery system of functional active ingredients.

Description

Technical Field

[0001] The invention belongs to the technical field of protein gel preparation, and in particular relates to a plant protein thermoreversible hydrogel and a preparation method thereof. Background Art

[0002] Thermoreversible gel is a kind of gel that changes from sol to gel as the temperature decreases, and can be converted from gel to sol again when heated again. This temperature-sensitive reversible transformation property has brought innovative applications in many fields. In the food field, thermoreversible gel can melt in the mouth and is widely used in the production of puddings, desserts, yogurt-like dairy products, beverages and condiments. Although protein-based thermoreversible gels have many advantages and potential application prospects, most of the current research on thermoreversible gels is based on animal protein and cannot meet the needs of fast food lovers. As a substitute for animal protein, plant-derived protein plays an increasingly important role in the human diet, and the demand for plant protein is also increasing day by day.

[0003] At present, the preparation of plant gels mostly adopts heating, pH shift, adding polysaccharides and other methods, but the hydrogels obtained cannot meet the reversibility requirements. There are also pea proteins extracted by ammonium sulfate precipitation to prepare thermoreversible hydrogels, but their pH range is between 2.8-4.2, which can only be applied to acidic foods. At the same time, the extraction method is cumbersome and not suitable for industrial production. Therefore, it is urgent to develop plant protein gels that can achieve reversibility and have a wider range of applicability. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention provides a plant protein thermoreversible hydrogel and a preparation method thereof. The present invention obtains a thermoreversible plant protein gel with a low protein concentration by adding ethanol to compound with a plant protein solution and controlling the relative amounts of reactants and reaction conditions. The preparation method of the present invention reduces the concentrations of protein and ethanol, and can successfully prepare a thermoreversible plant protein gel at a low protein concentration. The preparation process is simple and the raw materials are safe. The prepared plant protein thermoreversible hydrogel has broad application prospects in the food field, and can be used as a substitute for gelatin for healthy food, or as a new type of plant protein alcohol solid beverage, and can also be used as a steady-state delivery system for functional active ingredients.

[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 plant protein thermoreversible hydrogel, the preparation method comprising the following steps:

[0007] After the plant protein solution is hydrated overnight, the pH value is adjusted to 7.0, and after stirring at room temperature for 5-30 minutes, ethanol is added to obtain a plant protein-ethanol mixed solution. After heating for reaction, the mixed solution is cooled in an ice bath to obtain a plant protein thermoreversible hydrogel.

[0008] Preferably, the plant protein comprises at least one of peanut protein, soy protein, pea protein, chickpea protein, oat protein, quinoa protein and potato protein.

[0009] Preferably, the vegetable protein solution is obtained by mixing vegetable protein with water.

[0010] Preferably, the concentration of the vegetable protein solution is 6-20% (w / v).

[0011] Preferably, the method further comprises stirring the vegetable protein solution at room temperature for 1-3 hours before hydrating overnight.

[0012] Preferably, the overnight hydration is standing at 4°C overnight.

[0013] Preferably, the ethanol is edible ethanol.

[0014] Preferably, in the vegetable protein-ethanol mixture, the concentration of the ethanol is 5-50% (v / v), and the concentration of the vegetable protein is 3-20% (w / v).

[0015] Preferably, the heating reaction is carried out at a temperature of 80-95°C and a time of 5-15 minutes.

[0016] The second aspect of the present invention provides a plant protein thermoreversible hydrogel prepared by the preparation method of the first aspect, wherein the plant protein thermoreversible hydrogel can be reversibly cycled 5-15 times.

[0017] The beneficial technical effects of the present invention are:

[0018] The present invention prepares a low-protein-concentration plant protein thermoreversible gel under neutral conditions by adding ethanol to a plant protein solution. The preparation method is simple. The prepared thermoreversible gel is physically cross-linked through hydrogen bonds. The hydrogen bonds are destroyed at high temperatures and re-formed during cooling, thereby achieving a thermoreversible effect. The plant protein thermoreversible gel prepared by the present invention has a high similarity to gelatin and can be used as a substitute for gelatin used in health foods. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a photo of the peanut protein gel prepared according to an embodiment of the present invention.

[0020] Figure 2 This is a photograph of a product prepared in a comparative example of the present invention.

[0021] Figure 3 This is a heating reversible cycle diagram of the peanut protein gel of Example 8 of the present invention.

[0022] In the figure: a is peanut protein gel; b is peanut protein sol after the first heating; c is peanut protein gel after cooling; d is peanut protein sol obtained after the second heating; e is peanut protein gel obtained after cooling; f is peanut protein sol obtained after the fifth heating; g is peanut protein gel obtained after cooling.

[0023] Figure 4 This is a diagram of the peanut protein gel prepared in Example 8 of the present invention being repeatedly extruded after being heated.

[0024] Figure 5 This is a frequency scanning diagram of the peanut protein gel prepared with 5% peanut protein and different ethanol concentrations according to the present invention.

[0025] Figure 6 This is a temperature scan diagram of the peanut protein gel prepared in Example 8 of the present invention.

[0026] Figure 7 This is a urea temperature scanning diagram of the peanut protein gel prepared in Example 8 of the present invention.

[0027] Figure 8 This is a diagram of the preparation and reversible process of soybean protein gel in Example 22 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0029] The present invention provides a method for preparing a thermoreversible plant protein gel. By adding ethanol to a protein solution, a thermoreversible plant protein gel with a low protein concentration can be prepared, which can be used as a gelatin substitute for various foods in the vegetarian, halal and Jewish markets. At the same time, the low protein concentration also provides the possibility of using it as an additive in healthy foods.

[0030] It is understood that the edible ethanol used in the present invention has a small polarity and a low dielectric constant, and can easily destroy non-covalent interactions (such as hydrogen bonds or hydrophobic interactions). When present in a protein solution, it can reduce the hydrophobicity of the non-polar groups buried in the protein core, thereby causing partial unfolding of the protein molecules and promoting protein denaturation and aggregation. Ethanol treatment can effectively denature proteins, change the secondary structure of proteins and induce protein aggregation. Compared with heating, acid denaturation or a combination of heating and low pH, the denaturation effect of ethanol is much greater.

[0031] The first aspect of the present invention provides a method for preparing a plant protein thermoreversible hydrogel, comprising the following steps:

[0032] After the plant protein solution is hydrated overnight, the pH value is adjusted to 7.0, and after stirring at room temperature for 5-30 minutes, ethanol is added to obtain a plant protein-ethanol mixed solution. After heating for reaction, the mixed solution is cooled in an ice bath to obtain a plant protein thermoreversible hydrogel.

[0033] In the present invention, the effect of ethanol on the hardness of the protein gel is mainly due to hydrogen bonds. The gel is physically cross-linked through hydrogen bonds. The hydrogen bonds will be destroyed at high temperatures and will be re-formed during the cooling process, thereby achieving the transformation of sol and gel. The thermoreversible gel of the present invention has a high similarity with gelatin. The preparation of the thermoreversible gel has the opportunity to replace the existing gelatin.

[0034] It can be understood that the present invention uses plant protein solution as raw material and, by adding ethanol, can prepare a thermoreversible plant protein hydrogel at a lower protein concentration and in a shorter heating time. This method not only has cheap and readily available raw materials, thus saving costs, but is also a plant-based product of non-animal origin, and is suitable for all vegetarian, kosher and halal foods.

[0035] In some embodiments, the plant protein includes at least one of peanut protein, soy protein, pea protein, chickpea protein, oat protein, and quinoa protein.

[0036] In some embodiments, the plant protein solution is obtained by mixing plant protein with water.

[0037] In some embodiments, the mass concentration of the plant protein solution is 6-20% (w / v), including but not limited to 6% (w / v), 8% (w / v), 10% (w / v), 12% (w / v), 14% (w / v), 16% (w / v), 18% (w / v), 20% (w / v), preferably 8-12% (w / v).

[0038] In some embodiments, the method further comprises stirring the plant protein solution at room temperature for 1-3 hours before hydrating overnight, including but not limited to 1 hour, 2 hours, and 3 hours.

[0039] In some embodiments, the hydration overnight is standing at 4°C overnight.

[0040] In some embodiments, the ethanol is edible ethanol.

[0041] In some embodiments, in the plant protein-ethanol mixture, the concentration of ethanol is 5-50% (v / v), including but not limited to 6% (v / v), 10% (v / v), 15% (v / v), 20% (v / v), 25% (v / v), 30% (v / v), 35% (v / v), 40% (v / v), 45% (v / v), 50% (v / v), preferably 6-50% (v / v), and the concentration of plant protein is 3-20%, including but not limited to 3% (w / v), 4% (w / v), 5% (w / v), 6% (w / v), 7% (w / v), 9% (w / v), 10% (w / v), 12% (w / v), 14% (w / v), 16% (w / v), 18% (w / v), 20% (w / v); preferably 4-7% (w / v).

[0042] It is to be understood that, in the present invention, the concentration of ethanol in the vegetable protein-ethanol mixture refers to the volume proportion of ethanol in the mixture, and the concentration of vegetable protein is the percentage of the mass of vegetable protein to the volume of the mixture.

[0043] In some embodiments, the temperature of the heating reaction is 80-95°C, including but not limited to 80°C, 85°C, 90°C, 95°C, and the time is 5-15min, including but not limited to 5min, 7min, 9min, 10min, 12min, 14min, 15min.

[0044] It is understandable that when the heating temperature exceeds 95° C., ethanol will evaporate during the reaction, which is not conducive to controlling the formation of gel.

[0045] The second aspect of the present invention provides a plant protein thermoreversible hydrogel prepared by the preparation method of the first aspect. The plant protein thermoreversible hydrogel can be reversibly cycled 5-10 times. After multiple reversible cycles, the physical properties of the hydrogel only change slightly, and its key performance indicators such as strength, elasticity and water absorption are still within a relatively ideal range.

[0046] It can be understood that “w:v” mentioned in the present invention represents the ratio of mass g to volume mL.

[0047] The present invention will be further described below by way of examples and the like.

[0048] Embodiment 1:

[0049] Thermoreversible peanut protein gel is prepared as follows:

[0050] (1) Extraction of peanut protein

[0051] Peanut protein was extracted by alkali dissolution and acid precipitation. The specific method is as follows: peanut protein powder and distilled water were mixed in a ratio of 1:10 (w:v), pH was adjusted to 9.0 with 6mol / L NaOH, and stirred at room temperature for 2h to ensure full dissolution. Centrifuge at 4000rpm for 15min, adjust the pH of the supernatant to 4.5 with 6mol / L HCl, let stand for 1h, centrifuge at 4000rpm for 15min, mix the precipitate with distilled water in a ratio of 1:4 (w:v), adjust pH to 7.0 with 6mol / L HCl, obtain peanut protein raw material liquid, freeze-dry, obtain peanut protein powder, and set aside.

[0052] (2) Preparation of Peanut Protein Thermoreversible Gel

[0053] The peanut protein powder prepared in step (1) is diluted with water to obtain a 10% w / v peanut protein dilution, stirred at room temperature for 2 hours, and then hydrated at 4°C overnight to obtain a peanut protein solution, the pH of which is adjusted to 7.0, and stirred at room temperature for 10 minutes, and then 50% (v / v) edible ethanol is added to obtain a vegetable protein-ethanol mixed solution, so that the concentration of peanut protein in the mixed solution is 4% (w / v) and the concentration of ethanol is 8% (v / v), and the mixed solution is heated at 85°C for 10 minutes. After the heating is completed, it is immediately placed in an ice water bath and cooled to induce gelation to form a peanut protein thermoreversible gel.

[0054] Example 2

[0055] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 4% (w / v) and the concentration of ethanol is 9% (v / v).

[0056] Example 3

[0057] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 4% (w / v) and the ethanol concentration is 20% (v / v).

[0058] Example 4

[0059] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 4% (w / v) and the concentration of ethanol is 40% (v / v).

[0060] Example 5

[0061] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 4% (w / v) and the concentration of ethanol is 45% (v / v).

[0062] Example 6

[0063] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 4% (w / v) and the ethanol concentration is 50% (v / v).

[0064] Example 7

[0065] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 5% (w / v) and the concentration of ethanol is 8% (v / v).

[0066] Example 8

[0067] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 5% (w / v) and the concentration of ethanol is 10% (v / v).

[0068] Example 9

[0069] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 5% (w / v) and the concentration of ethanol is 40% (v / v).

[0070] Example 10

[0071] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 5% (w / v) and the ethanol concentration is 45% (v / v).

[0072] Embodiment 11

[0073] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 5% (w / v) and the concentration of ethanol is 50% (v / v).

[0074] Example 12

[0075] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 6% (w / v) and the ethanol concentration is 8% (v / v).

[0076] Example 13

[0077] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 6% (w / v) and the ethanol concentration is 20% (v / v).

[0078] Embodiment 14

[0079] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 6% (w / v) and the ethanol concentration is 40% (v / v).

[0080] Embodiment 15

[0081] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 6% (w / v) and the concentration of ethanol is 45% (v / v).

[0082] Example 16

[0083] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 6% (w / v) and the ethanol concentration is 50% (v / v).

[0084] Embodiment 17

[0085] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 7% (w / v) and the concentration of ethanol is 8% (v / v).

[0086] Embodiment 18

[0087] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 7% (w / v) and the concentration of ethanol is 10% (v / v).

[0088] Embodiment 19

[0089] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 7% (w / v) and the ethanol concentration is 40% (v / v).

[0090] Embodiment 20

[0091] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the peanut protein concentration is 7% (w / v) and the ethanol concentration is 45% (v / v).

[0092] Embodiment 21

[0093] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this example, the concentration of peanut protein is 7% (w / v) and the concentration of ethanol is 50% (v / v).

[0094] Embodiment 22

[0095] The soy protein thermoreversible gel is prepared as follows:

[0096] (1) Extraction of soybean protein

[0097] Soy protein was extracted by alkali dissolution and acid precipitation. Defatted soybean meal and distilled water were mixed in a ratio of 1:10 (w:v), pH was adjusted to 9.0 with 6mol / L NaOH, and stirred at 50°C for 50min to ensure full dissolution. Centrifuged at 4000rpm for 15min, the pH of the supernatant was adjusted to 4.5 with 6mol / L HCl, allowed to stand at room temperature for 30min, and centrifuged at 4000rpm for 15min. The precipitate was mixed with distilled water in a ratio of 1:4 (w:v), adjusted to pH 7.0 with 6mol / L HCl, and freeze-dried to obtain soy protein powder, which was stored for later use.

[0098] (2) Preparation of soy protein thermoreversible gel

[0099] Soy protein powder was dissolved in water to obtain a 15% w / v soy protein solution. The soy protein solution was stirred at room temperature for 2 hours and hydrated overnight at 4°C. The soy protein solution was adjusted to pH 7.0 and stirred at room temperature for 10 minutes. 50% (v / v) edible ethanol was added to make the concentration of the mixed protein solution 7% (w / v) and the concentration of ethanol 25% (v / v). The solution was heated at 85°C for 30 minutes and immediately placed in an ice water bath after heating to induce gel formation. The gel was subjected to multiple heating cycles to study its cyclic performance.

[0100] Embodiment 23

[0101] Thermoreversible peanut protein gel is prepared as follows:

[0102] (1) Extraction of peanut protein

[0103] The preparation method is the same as that of Example 1.

[0104] (2) Preparation of Peanut Protein Thermoreversible Gel

[0105] The peanut protein powder prepared in step (1) is diluted with water to obtain a 6% (w / v) peanut protein dilution, stirred at room temperature for 1 hour, hydrated overnight at 4°C to obtain a peanut protein solution, adjusted to pH 7.0, stirred at room temperature for 10 minutes, and then added with 50% (v / v) edible ethanol to obtain a vegetable protein-ethanol mixed solution, so that the concentration of peanut protein in the mixed solution is 3% (w / v), and the concentration of ethanol is 20% (v / v), heated at 80°C for 15 minutes, and immediately placed in an ice water bath after heating, and cooled to induce gelation to form a peanut protein thermoreversible gel. Experiments have found that peanut protein gel can be well formed, and the obtained gel has thermoreversibility.

[0106] Embodiment 24

[0107] Thermoreversible peanut protein gel is prepared as follows:

[0108] (1) Extraction of peanut protein

[0109] The preparation method is the same as that of Example 1.

[0110] (2) Preparation of Peanut Protein Thermoreversible Gel

[0111] The peanut protein powder prepared in step (1) is diluted with water to obtain a 10% w / v peanut protein dilution, stirred at room temperature for 2 hours, hydrated overnight at 4°C to obtain a peanut protein solution, adjusted to pH 7.0, stirred at room temperature for 10 minutes, then added with 50% (v / v) edible ethanol to obtain a vegetable protein-ethanol mixed solution, so that the concentration of peanut protein in the mixed solution is 6% (w / v) and the concentration of ethanol is 7% (v / v), heated at 95°C for 5 minutes, immediately placed in an ice water bath after heating, and cooled to induce gelation to form a peanut protein thermoreversible gel. The experiment found that the peanut protein gel formed had a good morphology and was reversible.

[0112] Comparative Example 1:

[0113] The same as Example 1, except that the concentration of peanut protein was changed.

[0114] (1) Preparation of peanut protein raw material liquid

[0115] The preparation method is the same as step (1) of Example 1.

[0116] (2) Preparation of Peanut Protein Thermoreversible Gel

[0117] After the peanut protein solution prepared in step (1) is thawed, water is added to dilute it to a 10% w / v peanut protein diluent, and after stirring at room temperature for 2 hours, it is hydrated overnight at 4°C to obtain a peanut protein solution. The peanut protein solution is adjusted to pH 7.0 and stirred at room temperature for 10 minutes, and then 50% (v / v) edible ethanol is added to make the concentration of ethanol in the mixed solution 5% (v / v) and the concentration of the peanut protein solution 2% (w / v). The mixture is heated at 85°C for 10 minutes, and immediately placed in an ice water bath after heating to cool and induce gel formation. The experiment found that when the protein concentration was 2% (w / v) and the ethanol concentration was 5% (v / v), gel could not be formed.

[0118] Comparative Example 2:

[0119] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this comparative example, the peanut protein concentration is 2% (w / v) and the ethanol concentration is 45% (v / v). In this case, no gel can be formed.

[0120] Comparative Example 3:

[0121] The preparation method of the peanut protein thermoreversible gel is basically the same as that of Example 1, except that in this comparative example, the peanut protein concentration is 7% (w / v) and the ethanol concentration is 5% (v / v). At this time, no gel can be formed.

[0122] Comparative Example 4

[0123] Peanut protein gel, the preparation method thereof is as follows:

[0124] (1) Preparation of peanut protein

[0125] Peanut protein was extracted by alkali dissolution and acid precipitation. The specific method is: peanut protein powder and distilled water were mixed in a ratio of 1:10 (w:v), pH was adjusted to 9.0 with 6mol / L NaOH, and stirred at room temperature for 2h to ensure full dissolution. Centrifuged at 4000rpm for 15min, the pH of the supernatant was adjusted to 4.5 with 6mol / L HCl, allowed to stand for 1h, and centrifuged at 4000rpm for 15min. The resulting precipitate was peanut protein.

[0126] (2) Preparation of Peanut Protein Gel

[0127] Ethanol was added to the peanut protein prepared in step (1) to obtain a vegetable protein-ethanol mixed solution, so that the concentration of the protein in the mixed solution was 4% (w / v), and the mixture was heated at 85° C. for 10 min. After the heating was completed, the mixture was immediately placed in an ice water bath. No gel was formed after cooling, because the addition of ethanol to the peanut protein could not dissolve the peanut protein, and no gel could be formed after heating.

[0128] Comparative Example 5

[0129] Peanut protein gel, the preparation method thereof is as follows:

[0130] (1) Prepare peanut protein raw material liquid according to the method described in Example 1

[0131] (2) Preparation of Peanut Protein Thermoreversible Gel

[0132] After the peanut protein raw material liquid prepared in step (1) was thawed, water was added to dilute it to a 10% (w / v) peanut protein diluent, and after stirring at room temperature for 2 hours, it was hydrated at 4°C overnight to obtain a peanut protein solution, the pH was adjusted to 7.0, and stirred at room temperature for 10 minutes, and then heated at 85°C for 10 minutes. After the heating was completed, it was immediately placed in an ice water bath and cooled to induce, but no gel was formed. This shows that gel cannot be formed when ethanol is not added.

[0133] Comparative Example 6

[0134] Peanut protein gel, the preparation method thereof is as follows:

[0135] (1) Prepare peanut protein raw material liquid according to the method described in Example 1

[0136] (2) Preparation of Peanut Protein Gel

[0137] After the peanut protein raw material liquid prepared in step (1) was thawed, water was added to dilute it to a 10% (w / v) peanut protein diluent, and after stirring at room temperature for 2 hours, it was hydrated at 4°C overnight to obtain a peanut protein solution, and stirred at room temperature for 10 minutes, and then 50% (v / v) edible ethanol was added to obtain a vegetable protein-ethanol mixed solution, so that the protein concentration in the mixed solution was 4% (w / v) and the ethanol concentration was 8% (v / v), and heated at 85°C for 10 minutes. After heating, it was immediately placed in an ice water bath and cooled, but gel was not successfully prepared. The experiment found that gel could not be prepared under acidic conditions.

[0138] Test example:

[0139] (1) Characterization of protein gel

[0140] The morphologies of the gels prepared in the examples and comparative examples were tested by photographing, as shown in FIG. Figure 1 , Figure 2 As shown. Figure 1 It can be seen that the gel obtained in the embodiment of the present invention has a better morphology. Figure 2 It can be seen that Comparative Examples 1-3 cannot form gel.

[0141] (2) Rheological test of protein gel

[0142] 1) Frequency sweep

[0143] The protein gel was subjected to frequency scanning using an interfacial rheometer MCR302 under the following conditions: the angular frequency was set to 1 Hz, the strain amplitude was set to 1%, and the gel sample was subjected to frequency scanning measurement (0.1-100 rad / s) at 25°C, and the storage modulus (G') and loss modulus (G") were recorded. Figure 5 This is a frequency scan of a gel prepared from peanut protein with a protein concentration of 5% and different concentrations of ethanol. In the figure, PPI represents peanut protein and E represents ethanol, such as G'PPI 5％ -E 8％ G"PPI represents the storage modulus of the gel with a peanut protein concentration of 5% and an ethanol concentration of 8%, i.e., the storage modulus of the gel corresponding to Example 7; 5％ -E 8％ is the loss modulus of the gel corresponding to Example 7; similarly G'PPI 5％ -E 10％ G"PPI is the storage modulus of the gel corresponding to Example 8; 5％ -E 10％ is the loss modulus of the gel corresponding to Example 8; G'PPI5％ -E 40％ G"PPI is the storage modulus of the gel corresponding to Example 9; 5％ -E 40％ is the loss modulus of the gel corresponding to Example 9; G'PPI 5％ -E 45％ G"PPI is the storage modulus of the gel corresponding to Example 10; 5％ -E 45％ is the loss modulus of the gel corresponding to Example 10; G'PPI 5％ -E 50％ G"PPI is the storage modulus of the gel corresponding to Example 11; 5％ -E 50％ is the loss modulus of the gel corresponding to Example 11. As can be seen from the figure, in all cases, the storage modulus (G') value is greater than the loss modulus (G"), which indicates that the peanut protein ethanol gel is solid, and as the ethanol concentration increases, the G' of the gel increases.

[0144] 2) Temperature scanning

[0145] The temperature of the protein gel prepared by the present invention was scanned using an interfacial rheometer (MCR302). The specific method is: during the first heating and cooling process, the rate was set from 25-85°C at a rate of 5°C / min and maintained for 10min, and then cooled from 85°C to 4°C at a rate of 5°C / min, and the storage modulus and loss modulus were measured during this process. After cooling at 4°C for 30min, a second heating and cooling cycle was performed under the same conditions. The angular frequency was set to 1Hz and the strain amplitude was set to 1%. Figure 6 This is a temperature scan of the protein gel (Example 8) obtained when the protein concentration is 5% and the ethanol concentration is 10%. During the initial heating process, the temperature increased from 25°C to 85°C, and the storage modulus (G') remained unchanged. During the second heating period, the G' value first decreased and then returned to the original value before cooling. This result shows that the heating process has limited effect on the establishment of the gel network. On the contrary, when the temperature was reduced from 85°C to 4°C, the protein solution gelled during the cooling process, and G' increased rapidly. The G' value of the gel was not affected by the extended cooling at 4°C, indicating that the gel network was mainly formed through the cooling process. In the second heating stage, the G' value decreased, and the formed gel turned back to a liquid state, indicating that the gel network constructed by hydrogen bonds was destroyed, resulting in a significant decrease in viscoelasticity. As the second cooling stage progressed, the G' value increased, and the protein suspension once again turned into a solid gel state, proving that the peanut protein ethanol gel has a thermoreversible gel ability.

[0146] 2. Intermolecular forces

[0147] The specific test method is: add 3M urea to the protein-ethanol mixed solution of Example 8, stir until completely dissolved, and then perform a heating temperature scan. The specific parameters are the same as the temperature scan in the rheology test.

[0148] Figure 7 This is a urea temperature scanning diagram of a protein gel (Example 8) with a protein concentration of 5% and an ethanol concentration of 10%. It can be seen from this figure that the loss modulus (G") is greater than the storage modulus (G'), and the added urea destroys the hydrogen bond, resulting in the inability to form a gel, indicating that the main force of the protein ethanol gel of the present invention is the hydrogen bond.

[0149] (2) Thermal reversibility of protein gel

[0150] Figure 8 The figure shows the preparation of soybean protein ethanol gel and its thermal reversible process. As can be seen from the figure, the successful preparation of soybean protein ethanol gel shows that the method of the present invention is universal and can be applied to multiple plant proteins.

[0151] Figure 3 This is a reversible test diagram of the gel prepared in Example 8 of the present invention. The gel prepared in Example 8 was heated to obtain a sol, then cooled to obtain a gel, and then the heating-cooling process was repeated. As can be seen from the figure, the gel prepared in Example 8 still has a relatively good morphology after being reversible for 5 times, indicating that the gel prepared in the example has a relatively good stability in at least 5 reversible experiments.

[0152] Figure 4 This is a diagram of repeated extrusion of the peanut protein gel prepared in Example 8 of the present invention after heating. As can be seen from the figure, after the peanut protein gel is heated to 85°C to obtain a sol, it is squeezed out with a syringe to write, cooled, and then the written gel is heated again to obtain a sol, and then squeezed out again. The extruded liquid can be used for writing again, indicating that the gel prepared in the example is reusable.

[0153] (3) Performance test of protein gel

[0154] The mechanical properties of the gels prepared in Examples 1-21 were measured and the results are shown in the following table.

[0155] The test method is as follows: cylindrical composite gels with a height of 10 mm and a diameter of 20 mm were prepared and stored in a refrigerator at 4°C overnight. Then, the hardness, elasticity, cohesion, stickiness and chewiness of the gels were measured using a texture analyzer (TA-XT plus, Stable MicroSystems Ltd., England) equipped with a P / 0.5 probe. Parameters: The speed was set to 1 mm / s before and after the test, and the test speed was set to 1 mm / s. The sample was compressed by 50% at a trigger force of 5 g.

[0156] Table 1 Properties of the gels prepared in Example

[0157]

[0158]

[0159] As can be seen from the above table, the gel prepared in the embodiment of the present invention can not only achieve thermal reversibility, but also has excellent mechanical properties. In addition, the gel of the present invention can be prepared at a lower protein concentration and ethanol concentration, avoiding the effect of ethanol on the human body and the limitation of high protein in health food.

[0160] The gel prepared by the invention has good mechanical properties, excellent chewiness and viscosity while ensuring the gel morphology, and has low ethanol content and low protein concentration, which is more conducive to use in food, especially vegetarian food, halal food and kosher food.

[0161] 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 plant protein thermoreversible hydrogel, characterized in that: The preparation method comprises the following steps: After the plant protein solution is hydrated overnight, the pH value is adjusted to 7.0, and after stirring at room temperature for 5-30 minutes, ethanol is added to obtain a plant protein-ethanol mixed solution. After heating for reaction, the mixed solution is cooled in an ice bath to obtain a plant protein thermoreversible hydrogel.

2. The preparation method according to claim 1, characterized in that: The plant protein includes at least one of peanut protein, soy protein, pea protein, chickpea protein, oat protein, quinoa protein and potato protein.

3. The preparation method according to claim 1, characterized in that: The vegetable protein solution is obtained by mixing vegetable protein with water.

4. The preparation method according to claim 3, characterized in that: The concentration of the vegetable protein solution is 6-20% (w / v).

5. The preparation method according to claim 1, characterized in that: The method further comprises stirring the vegetable protein solution at room temperature for 1-3 hours before hydration overnight.

6. The preparation method according to claim 1, characterized in that: The overnight hydration means standing at 4°C overnight.

7. The preparation method according to claim 1, characterized in that: The ethanol is edible ethanol.

8. The preparation method according to claim 1, characterized in that: In the vegetable protein-ethanol mixed solution, the concentration of the ethanol is 5-50% (v / v), and the concentration of the vegetable protein is 3-20% (w / v).

9. The preparation method according to claim 1, characterized in that: The temperature of the heating reaction is 80-95° C. and the time is 5-15 minutes.

10. A plant protein thermoreversible hydrogel prepared by the preparation method according to any one of claims 1 to 9, characterized in that: The plant protein thermoreversible hydrogel can be reversibly cycled 5-15 times.

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