Soy protein emulsion gel product and preparation method thereof

Abstract

The present invention provides a soy protein emulsion gel product and a preparation method thereof, belonging to the technical field of plant protein processing. Using soy protein as raw material, the invention first enzymatically hydrolyzes and heat-treats soy protein to obtain soy protein with different 7S / 11S ratios and soluble aggregate contents. Oil is then added and emulsified to prepare a soy protein emulsion. On this basis, glucono-δ-lactone is used to prepare an acid-induced emulsion gel. This method achieves the preparation of a soy protein emulsion gel with excellent textural properties and microstructure, broadening the application of soy protein in food and related fields.

Description

Technical Field

[0001] The invention belongs to the technical field of plant protein processing, and particularly relates to a soybean protein emulsion gel product and a preparation method thereof. Background Art

[0002] Soy protein, a high-quality plant protein with high nutritional value and excellent functional properties, has become a hot topic in the food industry for basic research and application development. Gelation properties are one of the most important functional properties of soy protein. With the growing interest and preference for plant-based foods, acid-induced gels of soy protein emulsions prepared from soy protein have gradually become a popular innovative product in the plant-based food market. However, these products have texture issues (such as a hard texture and a strong grainy feel), which seriously affect the consumer's sensory experience.

[0003] The tribological properties of a gel reflect its smoothness and largely determine its palatability. Fat droplets in an emulsion gel can be released from the gel matrix during chewing and adhere to the oral surface, thereby reducing friction and improving the gel's mouthfeel. Water holding capacity is also an important indicator for evaluating the textural properties of a gel. Currently, finding a method for preparing acid-induced soy protein emulsion gels with favorable textural properties (low hardness, high water holding capacity, and low friction coefficient) remains an unresolved issue.

[0004] Research on improving the textural properties of acid-induced gels of soy protein emulsions has primarily focused on modifying processing conditions (e.g., heating and homogenization) and adding polysaccharides, while the effects of protein components on gel properties have been less explored. The ratio of 7S to 11S components in soy protein significantly influences the textural properties and structure of acid-induced gels of soy protein emulsions. The complex separation and purification steps of the 11S and 7S components of soy protein, coupled with high production costs, significantly limit the methods of compounding 7S and 11S soy proteins. Therefore, the effects of enzymatic hydrolysis of soy protein with different proteases on the textural properties of acid-induced gels of soy protein emulsions and the influence of oil content in soy protein emulsions on gel properties were investigated. This study aims to address gaps in existing research and broaden the application of soy protein in food and related fields. Summary of the Invention

[0005] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of this application to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions should not be used to limit the scope of the present invention.

[0006] In view of the above problems and / or the problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the object of the present invention is to provide a method for preparing acid-induced gel of soy protein emulsion, which improves the gel properties by two methods: (1) hydrolyzing soy protein with different proteases to change the molecular weight of soy protein and adjust the 11S / 7S ratio of soy protein; and (2) changing the oil content of the acid-induced gel of soy protein emulsion.

[0008] A method for preparing acid-induced gel of soybean protein emulsion comprises the following steps:

[0009] (1) Enzymatic hydrolysis: dispersing soybean protein in water to prepare a protein solution, adding protease, adjusting the enzymatic hydrolysis conditions, and performing enzymatic hydrolysis to obtain an enzymatically hydrolyzed soybean protein solution;

[0010] (2) Heating: adjusting the pH of the enzymatically hydrolyzed soy protein solution obtained in step (1) to 7.0, heating, and cooling to obtain a heated soy protein solution;

[0011] (3) Emulsification: adding vegetable oil to the soy protein solution prepared in step (2), shearing and homogenizing to obtain a soy protein emulsion;

[0012] (4) Acidification: Add glucono-δ-lactone to the soybean protein emulsion prepared in step (3), acidify, and obtain an acid-induced gel of the soybean protein emulsion.

[0013] Furthermore, the soy protein in step (1) is soy protein isolate.

[0014] Furthermore, the mass proportion of soybean protein in the protein solution in step (1) is 2%-5%.

[0015] Furthermore, the protease in step (1) includes one or more of flavor protease and neutral protease.

[0016] Furthermore, in step (1), the amount of protease used is 300-900 U / g soybean protein.

[0017] Furthermore, the enzymatic hydrolysis conditions in step (1) are: enzymatic hydrolysis pH is 7.0-7.5, and enzymatic hydrolysis temperature is 55-65°C.

[0018] Furthermore, the enzymatic hydrolysis time in step (1) is 10-30 min.

[0019] Furthermore, the heating in step (2) is heating at 95-100° C. for 10 to 15 minutes.

[0020] Furthermore, the vegetable oil in step (3) includes one or more of soybean oil, peanut oil, and sunflower oil.

[0021] Furthermore, the amount of vegetable oil used in step (3) is 2 to 10% of the total mass of the soybean protein emulsion.

[0022] Furthermore, the shearing in step (3) is performed at a rotation speed of 12000 to 14000 rpm for 2 to 4 minutes.

[0023] Furthermore, the homogenization in step (3) is carried out 1 to 2 times at 35-40 MPa.

[0024] Furthermore, the amount of glucono-δ-lactone used in step (4) is 0.6%-0.8% of the total mass of the soy protein emulsion.

[0025] Furthermore, the acidification in step (4) is carried out at room temperature for 8-10 hours, and the pH at the end of the acidification is 4.4-4.6.

[0026] The application of the preparation method of the present invention in the field of protein processing.

[0027] The present invention provides a soybean protein emulsion acid-induced gel prepared according to the method.

[0028] The invention provides application of the soy protein emulsion acid-induced gel in the food field.

[0029] Furthermore, the acid-induced gel of the soy protein emulsion has good textural properties including low hardness, low friction coefficient, and high water holding capacity.

[0030] Furthermore, the low hardness has a hardness range of less than 100g; the low friction coefficient has a friction coefficient of less than 0.1 when the rolling rate is 10mm / s; the higher water holding capacity has a water holding capacity greater than 70% when the centrifugal force is 2000g, and a water holding capacity range greater than 40% when the centrifugal force is 4000g.

[0031] Beneficial effects of the present invention:

[0032] (1) The present invention prepares a soy protein emulsion acid-induced gel with good textural properties by controlling the enzymatic hydrolysis conditions, providing a basis for the further development of plant-based protein products.

[0033] (2) The present invention optimizes the type of protease and controls the 7S / 11S ratio of soy protein after enzymatic hydrolysis, thereby preparing soy protein with a relatively suitable 7S / 11S ratio (approximately 2:5). The acid-induced gel of the soy protein emulsion prepared with the soy protein emulsion has low hardness and low friction coefficient while also having high water holding capacity. This provides a foundation for further developing soy protein products and expanding the application of soy protein in the market.

[0034] (3) The present invention optimizes the oil content in the soy protein emulsion based on the optimization of suitable proteases (flavor protease, neutral protease), and prepares the soy protein emulsion acid-induced gel with better texture properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The microstructure of acid-induced gel of soy protein emulsion after enzymatic hydrolysis with different proteases. DETAILED DESCRIPTION

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0037] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0038] Secondly, the term "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0039] Analytical methods

[0040] 1. Determination of protein content: semi-micro Kjeldahl method (GB5009.5-2016).

[0041] 2. Determine the activity of bromelain, neutral protease, flavor protease, and pepsin according to industry standard NY / T 4306-2023. One unit (U) of enzyme activity is defined as the amount of protease required to hydrolyze casein to produce 1 μg of tyrosine per minute.

[0042] 3. Determination of soluble aggregate content in enzymatically hydrolyzed soy protein: Size exclusion high-performance liquid chromatography (SMELC) analysis was performed. The sample was diluted to 5 mg / mL with ultrapure water, filtered through a 0.45 μm aqueous membrane filter, and analyzed by size exclusion chromatography. The column used was a KW-804 protein gel column (300 × 8.0 mm), with a flow rate of 1 mL / min, UV detection at 214 nm, an injection volume of 20 μL, and a column temperature maintained at 25°C.

[0043] 4. Determination of subunit composition (7S / 11S ratio) after soybean protein hydrolysis: SDS-PAGE analysis was performed using 3% and 12.5% ​​stacking and separating gel concentrations, respectively. The sample protein concentration was adjusted to 1 mg / mL before loading. After electrophoresis, fixation was performed in the fixative for 2 h, staining was performed in the staining solution for 4 h, and decolorization was performed in the destaining solution for 4 h. The gel was photographed, processed, and analyzed using Image Lab software.

[0044] 5. Determination of the texture of acid-induced soy protein emulsion gels: After storing 20 g of the prepared gel at 4°C overnight, the gel was removed and allowed to equilibrate at room temperature for at least 30 minutes. The texture of the acid gel was then determined using a physical property analyzer (SMS, UK). A P25 probe was used, with a deformation of 30%, a trigger force of 5 g, and pre-, mid-, and post-measurement speeds of 1 mm / s, 0.5 mm / s, and 1 mm / s, respectively.

[0045] 6. Determination of the friction coefficient of acid-induced soy protein emulsion gels: The friction coefficient of emulsion gels prepared after hydrolysis with different proteases was measured using a microtraction force tester (PCS Instruments, UK). The sliding rate was set between 1 mm / s and 1000 mm / s, the rolling-slip ratio was 50%, the load was 2 N, and the test temperature was 37°C.

[0046] 7. Determination of Water Holding Capacity of Acid-Induced Soy Protein Emulsion Gels: Approximately 5 g of soy protein gel was placed in a 10 mL centrifuge tube and centrifuged at 2000 g and 4000 g, respectively, for 15 min at 25°C. After aspirating the supernatant, the tube was inverted, drained, and weighed. The water holding capacity was calculated according to Equation 1.

[0047]

[0048] Where W1 refers to the mass of the gel after removing water after centrifugation, and W refers to the mass of the gel

[0049] 8. Determination of the microstructure of acid-induced gel of soy protein emulsion: The microstructure was observed using a laser confocal microscope (CLSM, LSM-710).

[0050] Example 1

[0051] (1) Enzymatic hydrolysis: Soy protein isolate was dispersed in water at a ratio of 3% (w / w), and the mixture was stirred thoroughly to obtain a soy protein solution. Neutral protease was added to the solution at a protease dosage of 700 U / g soy protein. After the enzymatic hydrolysis was completed, an enzymatic hydrolyzed soy protein solution was obtained. The enzymatic hydrolysis conditions were as follows: enzymatic hydrolysis pH 7.5, enzymatic hydrolysis temperature 60°C, and enzymatic hydrolysis time 15 min.

[0052] (2) Heating: The pH of the enzymatically hydrolyzed soybean protein solution prepared in step (1) was adjusted to 7.0, heated at 95° C. for 15 min, and then cooled to obtain a heated soybean protein solution.

[0053] (3) Emulsification: 3% (w / w) soybean oil was added to the heated soybean protein solution obtained in step (2), sheared at 14,000 rpm for 2 min, and homogenized once at 40 MPa to obtain a soybean protein emulsion.

[0054] (4) Acidification: 0.75% (w / w) glucono-δ-lactone was added to the soy protein emulsion prepared in step (3), and acidified for 8 h at room temperature. The acidification end point was 4.5, thereby obtaining an acid-induced gel of the soy protein emulsion.

[0055] The enzymatically hydrolyzed soy protein prepared in Example 1 had a 7S / 11S ratio of 2:5 and a soluble aggregate content of 34.9%. The prepared soy protein emulsion gel had a hardness of 89.20±3.16 g, friction coefficients measured at rolling speeds of 10 mm / s and 100 mm / s were 0.0370±0.0054 and 0.0182±0.0028, respectively, and water holding capacities measured at centrifugal forces of 4000 g and 2000 g were 51.42%±0.41% and 74.01%±0.95%, respectively.

[0056] Example 2

[0057] (1) Enzymatic hydrolysis: Soy protein isolate was dispersed in water at a ratio of 3% (w / w), and stirred thoroughly to obtain a soy protein solution. Flavor protease was added to the solution at a protease dosage of 700 U / g soy protein. After the enzymatic hydrolysis was completed, an enzymatic hydrolyzed soy protein solution was obtained. The enzymatic hydrolysis conditions were as follows: enzymatic hydrolysis pH 7.5, enzymatic hydrolysis temperature 60°C, and enzymatic hydrolysis time 15 min.

[0058] Steps (2) to (4) in Example 2 remain consistent with those in Example 1.

[0059] The enzymatically hydrolyzed soy protein prepared in Example 2 had a 7S / 11S ratio of 2:5 and a soluble aggregate content of 50.19%. The prepared soy protein emulsion gel had a hardness of 76.17±1.52g, friction coefficients measured at rolling speeds of 10 mm / s and 100 mm / s were 0.0335±0.0031 and 0.0174±0.0013, respectively, and water holding capacities measured at centrifugal forces of 4000g and 2000g were 54.71%±0.49% and 78.03%±2.40%, respectively.

[0060] Comparative Example 1

[0061] (1) Dispersion: Disperse the soy protein isolate in water at a ratio of 3% (w / w), and stir thoroughly to obtain a soy protein solution.

[0062] (2) Heating: The pH of the soybean protein solution obtained in step (1) was adjusted to 7.0, heated at 95° C. for 15 min, and then cooled to obtain a heated soybean protein solution.

[0063] (3) Emulsification: 3% (w / w) soybean oil was added to the heated soybean protein solution obtained in step (2), sheared at 14,000 rpm for 2 min, and homogenized once at 40 MPa to obtain a soybean protein emulsion.

[0064] (4) Acidification: 0.75% (w / w) glucono-δ-lactone was added to the soy protein emulsion prepared in step (3), and acidified for 8 h at room temperature. The acidification end point was 4.5, thereby obtaining an acid-induced gel of the soy protein emulsion.

[0065] The soy protein prepared in Comparative Example 1 had a 7S / 11S ratio of 3:5 and a soluble aggregate content of 36.48%. The prepared soy protein emulsion gel had a hardness of 172.98±1.26g, friction coefficients of 0.1103±0.0112 and 0.0224±0.0018 at rolling rates of 10 mm / s and 100 mm / s, respectively, and water holding capacities of 52.23%±0.18% and 73.06%±0.71% at centrifugal forces of 4000g and 2000g, respectively.

[0066] Comparative Example 2

[0067] (1) Enzymatic hydrolysis: Soy protein isolate was dispersed in water at a ratio of 3% (w / w), and the mixture was stirred thoroughly to obtain a soy protein solution. Papain was added to the solution at a protease dosage of 700 U / g soy protein. After the enzymatic hydrolysis was completed, an enzymatic hydrolyzed soy protein solution was obtained. The enzymatic hydrolysis conditions were as follows: enzymatic hydrolysis pH 7.5, enzymatic hydrolysis temperature 60°C, and enzymatic hydrolysis time 15 min.

[0068] In Comparative Example 2, steps (2) to (4) are consistent with those in Example 1.

[0069] The enzymatically hydrolyzed soy protein prepared in Comparative Example 2 had a 7S / 11S ratio of 0 and a soluble aggregate content of 0%. The prepared soy protein emulsion gel had a hardness of 9.79±0.11 g, friction coefficients of 0.0341±0.0032 and 0.0223±0.0018 at rolling speeds of 10 mm / s and 100 mm / s, respectively, and water holding capacities of 32.60%±0.41% and 60.02%±2.59% at centrifugal forces of 4000 g and 2000 g, respectively.

[0070] Comparative Example 3

[0071] (1) Enzymatic hydrolysis: Soy protein isolate was dispersed in water at a ratio of 3% (w / w), and the mixture was stirred thoroughly to obtain a soy protein solution. Bromelain was added to the solution at a protease dosage of 700 U / g soy protein. After the enzymatic hydrolysis, an enzymatic hydrolyzed soy protein solution was obtained. The enzymatic hydrolysis conditions were as follows: enzymatic hydrolysis pH 7.5, enzymatic hydrolysis temperature 60°C, and enzymatic hydrolysis time 15 min.

[0072] In Comparative Example 3, steps (2) to (4) are consistent with those in Example 1.

[0073] The enzymatically hydrolyzed soy protein prepared in Comparative Example 3 had a 7S / 11S ratio of 1.3:5 and a soluble aggregate content of 7.29%. The prepared soy protein emulsion gel had a hardness of 74.75±2.37 g, friction coefficients of 0.0306±0.0011 and 0.0271±0.0081 at rolling rates of 10 mm / s and 100 mm / s, respectively, and water holding capacities of 36.84%±0.74% and 64.59%±2.23% at centrifugal forces of 4000 g and 2000 g, respectively.

[0074] Comparative Example 4

[0075] (1) Enzymatic hydrolysis: Soy protein isolate was dispersed in water at a ratio of 3% (w / w), and stirred thoroughly to obtain a soy protein solution. Pepsin was added to the solution at a protease dosage of 700 U / g soy protein. After the enzymatic hydrolysis was completed, an enzymatic hydrolyzed soy protein solution was obtained. The enzymatic hydrolysis conditions were as follows: enzymatic hydrolysis pH 2, enzymatic hydrolysis temperature 37°C, and enzymatic hydrolysis time 15 min.

[0076] In Comparative Example 4, steps (2) to (4) are consistent with those in Example 1.

[0077] The enzymatically hydrolyzed soy protein prepared in Comparative Example 4 had a 7S / 11S ratio of 5.5:1 and a soluble aggregate content of 17.79%. The prepared soy protein emulsion gel had a hardness of 23.30±1.39 g, friction coefficients of 0.0474±0.0033 and 0.0246±0.0030 at rolling speeds of 10 mm / s and 100 mm / s, respectively, and water holding capacities of 45.37%±4.2% and 39.92%±0.48% at centrifugal forces of 4000 g and 2000 g, respectively.

[0078] Table 1 Effect of enzymatic hydrolysis on the texture properties of acid-induced gel of soy protein emulsion

[0079]

[0080] A comprehensive comparison of the above examples and comparative examples is shown in Table 1. Compared with comparative example 1, the hardness of the gels prepared in Examples 1-2 was reduced by 48.43% and 55.97% respectively, and the friction coefficient was reduced by 66.46% and 69.63% respectively, and the water holding capacity (2000g) was also slightly improved. Although the hardness and friction coefficient of the gels prepared in Comparative Examples 2-4 were greatly reduced, their water holding capacity was also reduced. At the same time, the microscopic results ( Figure 1 Observations showed that the microstructures of the gels prepared in Examples 1, 2, and Comparative Example 1 were uniform, dense, and had small pores. In contrast, the gels prepared in Comparative Examples 2-4 had looser structures and larger pores. This indicates that treating soy protein with neutral protease and flavor protease can significantly improve the texture of acid-induced gels of soy protein emulsions.

[0081] Furthermore, the ratio of 7S / 11S in soy protein has a great influence on the texture properties and microstructure of soy protein gel. As shown in Table 2, the 7S / 11S ratio in the soy protein after enzymatic hydrolysis in Example 1 and Example 2 is 2:5, and the soluble aggregate content is 34.9% and 50.19%, respectively. In contrast, in Comparative Examples 2 to 4, the soluble aggregate content is greatly reduced (0 to 17.79%), and the 7S / 11S ratio is either too high (5.5:1) or too low (1.3:5), indicating that the 11S or 7S components in the soy protein are over-hydrolyzed, producing a large number of small peptide chains. During the heating process, these peptide chains will form a large number of insoluble aggregates under the conditions of hydrophobic forces, disulfide bonds and other forces, which is not conducive to the mutual cross-linking of proteins during the acidification process, resulting in the formation of a gel with an uneven network structure and weak water retention. Therefore, when using enzymatic hydrolysis to improve the texture properties of acid-induced gel of soy protein emulsion, it is necessary to select a suitable protease and control the 7S / 11S ratio of soy protein after enzymatic hydrolysis to about 2:5.

[0082] Table 2 Effect of enzymatic hydrolysis on the soluble aggregate content and 7S / 11S ratio of soybean protein

[0083]

[0084] Example 3

[0085] To further enhance the beneficial effects of the enzymatic hydrolysis method of the present invention on improving the textural properties of acid-induced gels of soy protein emulsions, this example investigates the effect of oil content on the textural properties of acid-induced gels of soy protein emulsions. Compared to Example 2, this example maintains the same parameters as Example 2, except that in step (4), "adding 3% (w / w) soybean oil" is replaced with "adding 0%, 1%, 2%, 3%, 5%, 7%, 10%, and 13% (w / w) soybean oil, respectively." The results are shown in Table 3.

[0086] Table 3 Effect of oil content on acid-induced gelation of soybean protein emulsion

[0087]

[0088]

[0089] As can be seen from Table 3, the higher the oil content of the acid-induced gel of soy protein emulsion, the higher its hardness and water holding capacity, and the lower its friction coefficient. This may be because when the oil content increases, the solid content of the gel increases, resulting in an increase in the water holding capacity and hardness of the gel. At the same time, more oil droplets can be released from the gel matrix, which reduces the friction coefficient of the gel. Therefore, to further improve the textural properties of the gel, it is necessary to control the oil content of the gel. In this example, the water holding capacity of the gel with a 1% oil content measured at a centrifugal force of 2000g was only 51.26±0.66%, and the hardness of the gel with a 13% oil content was 117.46±5.36g. Excessive hardness or too low water holding capacity will deteriorate the sensory perception of the gel. Therefore, the optimal oil content range in this example is 2%-10%.

[0090] The embodiments provided above are not intended to limit the scope of the present invention, nor are the steps described to limit their execution order. Any obvious improvements to the present invention made by those skilled in the art in combination with existing common knowledge are also within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing acid-induced gel of soybean protein emulsion, characterized in that: The following steps are involved: (1) Enzymatic hydrolysis: Soy protein is dispersed in water to prepare a protein solution, protease is added, and the enzymatic hydrolysis conditions are adjusted to obtain an enzymatic hydrolyzed soy protein solution; the soy protein is soy protein isolate; the protease is flavor protease or neutral protease; the amount of protease is 300-900 U / g soy protein; the enzymatic hydrolysis pH is 7.0-7.5, the enzymatic hydrolysis temperature is 55-65°C, and the enzymatic hydrolysis time is 10-30 min; (2) Heating: adjusting the pH of the enzymatically hydrolyzed soy protein solution obtained in step (1) to 7.0, heating, and cooling to obtain a heated soy protein solution; (3) Emulsification: adding vegetable oil to the heated soy protein solution obtained in step (2), shearing and homogenizing to obtain a soy protein emulsion; the amount of vegetable oil used is 2-10% of the total mass of the soy protein emulsion; (4) Acidification: Add glucono-δ-lactone to the soybean protein emulsion prepared in step (3) and acidify to obtain an acid-induced gel of the soybean protein emulsion.

2. The method according to claim 1, wherein The mass proportion of soy protein in the protein solution in step (1) is 2%-5%.

3. The method according to claim 1, wherein The heating in step (2) is heating at 95-100°C for 10-15 minutes.

4. The method according to claim 1, wherein The vegetable oil in step (3) includes one or more of soybean oil, peanut oil, and sunflower oil.

5. The method according to claim 1, wherein The shearing rate and time in step (3) are 12000~14000rpm, 2-4min respectively; the homogenization pressure and number of times in step (3) are 35~40MPa, 1-2 times respectively.

6. The method according to claim 1, wherein The amount of glucono-δ-lactone used in step (4) is 0.6%-0.8% of the total mass of the soy protein emulsion; the acidification in step (4) is acidification at room temperature for 8-10 hours, and the acidification end point pH is 4.4-4.

6.

7. A soy protein emulsion acid-induced gel prepared according to the method according to any one of claims 1 to 6.

8. Use of the acid-induced gel of soybean protein emulsion according to claim 7 in the food field.

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