Method for regulating and controlling starch-protein composite gel structure based on ice template method

Abstract

The invention discloses a method for regulating and controlling a starch-protein composite gel structure based on an ice template method, which comprises the following steps: adding starch and soybean protein isolate into water, heating a product which is uniformly dispersed and hydrated, and cooling to form a starch / protein composite gel; and freezing the prepared gel under the condition of-18 to-80 DEG C, taking out the gel, recovering the gel to room temperature, and the like. The starch / protein composite gel is prepared by adopting an ice template method, the preparation method is simple, the pore structure morphology of the prepared starch / protein porous composite gel is controllable, the texture property and juiciness of the starch / protein porous composite gel can be regulated and controlled, and a new way is provided for the quality improvement of industrial frozen porous gel. The starch / protein composite gel prepared by freezing at the temperature of-80 DEG C through the method has good texture characteristics, the hardness of the starch / protein composite gel is 555.57, the elasticity of the starch / protein composite gel can reach 0.95, and the chewiness of the starch / protein composite gel can reach 264.26.

Description

Technical Field

[0001] The invention relates to the field of food processing, and specifically discloses a method for regulating the texture of starch-protein composite gel based on an ice template method. Background Art

[0002] Starch and protein are two important sources of energy supply and are widely present in daily food. In the process of food processing, thermal processing is usually required to transform starch and protein raw materials into gel-like foods. The composite gel of starch and protein is not only conducive to the diversification of nutritional sources, but also its texture and digestibility can be regulated by changing the ratio of the two to meet the needs of different groups of people. However, protein-starch gel contains rich carbon and nitrogen sources, which is conducive to the growth of microorganisms, resulting in the problem of food safety of the gel.

[0003] Freezing plays a key role in food preservation and can effectively inhibit the growth of microorganisms, thereby extending the shelf life of food. For gel-like foods, freezing them under certain conditions is not only conducive to improving their food safety, but also helps to improve their texture characteristics, especially elasticity and chewiness. For example, frozen tofu is prepared based on the freezing process. However, the current conventional freezing process does not significantly improve the texture characteristics of the gel, which is far from meeting people's requirements for the texture of starch-protein composite gels. In addition, during the freezing process, the growth of ice crystals will cause the internal structure of the food to be destroyed, resulting in a decrease in its quality after thawing. Prolonging the freezing time and multiple freeze-thaw cycles are conducive to further improving the texture characteristics of the gel, but longer freezing or multiple freeze-thaw cycles will greatly reduce production efficiency and increase production costs. Therefore, it is of great significance to find a method that is efficient and low-cost and can greatly improve the texture characteristics of starch-protein composite gels. Summary of the invention

[0004] In view of the above problems, the present invention proposes a method for regulating the texture of starch-protein composite gel based on ice template method. The present invention specifically selects starch and soy protein isolate as the main food raw materials, forms a porous gel by freezing-thawing on the basis of forming a composite gel through thermal processing.

[0005] In view of the above purpose, the present invention first discloses a method for regulating the texture of starch-protein composite gel based on ice template method, comprising the following steps:

[0006] (1) adding starch and soy protein isolate into water, dispersing them evenly and then subjecting them to hydration treatment;

[0007] (2) heating the product of the hydration treatment in step (1) and cooling it to form a starch / protein composite gel;

[0008] (3) freezing the gel prepared in step (2) at -18 to -80°C, taking it out and returning it to room temperature to obtain a starch / protein porous gel.

[0009] In one embodiment of the present invention, the mass ratio of starch to soy protein isolate in step (1) is 8:1 to 8:4, preferably 8:2.

[0010] In one embodiment of the present invention, the concentration of the starch in water in step (1) is 8 g / mL, and the concentration of the soy protein isolate in water is 1-4 g / mL.

[0011] In one embodiment of the present invention, the temperature of the hydration treatment in step (1) is 2-4°C and the time is 12-18h.

[0012] In one embodiment of the present invention, the heating temperature in step (2) is 85-95°C.

[0013] In one embodiment of the present invention, the heating time in step (2) is 25-35 minutes.

[0014] In one embodiment of the present invention, the cooling in step (2) is performed at 2-4°C.

[0015] In one embodiment of the present invention, the freezing temperature of the gel in step (3) is -80°C.

[0016] In one embodiment of the present invention, the freezing time of the gel in step (3) is 10 s to 5 h, preferably 10 s to 4 h.

[0017] The invention also discloses a starch-protein composite gel prepared according to the method.

[0018] Beneficial effects:

[0019] 1. The raw materials used in the present invention are low in price, widely available, safe and non-toxic, and are all important energy supply food raw materials in daily diet.

[0020] 2. The food hot processing and cold processing are combined, and the whole processing process is simple and easy to operate.

[0021] 3. The present invention adopts the ice template method to prepare starch / protein composite gel. The preparation method is simple. The pore structure morphology of the prepared starch / protein porous composite gel is controllable, and its texture characteristics and juiciness can be regulated, providing a new way to improve the quality of industrial frozen porous gel.

[0022] 4. The starch / protein composite gel prepared by freezing at -80°C using the method of the present invention has good texture characteristics, with a hardness of 555.57 g, an elasticity of 0.95, and a chewiness of 264.26. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the orientation freezing device used in Comparative Examples 3 and 4.

[0024] Figure 2 This is a trend chart of the change in the central temperature of the starch / protein composite gel prepared in Examples 1 to 2 and Comparative Examples 2 to 4 during the freezing process.

[0025] Figure 3 SEM images of the porous starch / protein composite gels prepared in Examples 1 to 2 and Comparative Examples 2 to 4 after freeze-drying, (a) Example 1, (b) Example 2, (c) Comparative Example 2, (d) Comparative Example 4, (e) Comparative Example 3.

[0026] Figure 4 It is the water loss rate of the porous starch / protein composite gel prepared in Comparative Examples 1 to 3 and Examples 1 to 4 during the extrusion process. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the applicant will further explain the present invention in detail below with reference to the embodiments and drawings.

[0028] Test method:

[0029] Texture property test method: TPA mode was used to test the texture property of gel. The test probe used was a P / 25 cylindrical probe with a diameter of 25 mm, the sample size was a 1*1*1 cm cube, the pre-test speed and the test speed were 1 mm / s, and the post-test speed was 2 mm / s.

[0030] Water loss rate test method: compress a gel of size 1*1*1cm by 80% at a speed of 1mm / s, wipe off the precipitated water with filter paper, and divide the mass of the gel before and after compression into m 0 (g) and m 1 (g), water loss rate = (m 0 -m 1 ) / m 0 .

[0031] Example 1

[0032] A method for regulating the texture of starch-protein composite gel based on ice template method, the steps are as follows:

[0033] Accurately weigh 8g starch and 2g soy protein isolate and add them to 100mL deionized water. Stir magnetically and place in a 4℃ environment for hydration for 12h. Heat the obtained starch / protein composite solution at 90℃ for 30min to make it completely gelled, and then cool it to room temperature to obtain a starch / protein composite gel. Then, freeze the composite gel in a -18℃ environment for 4h, and return it to room temperature after freezing to finally obtain a starch / protein porous gel.

[0034] Example 2

[0035] A method for regulating the texture of starch-protein composite gel based on ice template method, the steps are as follows:

[0036] Accurately weigh 8g starch and 2g soy protein isolate and add them to 100mL deionized water. Stir magnetically and place in a 4℃ environment for hydration for 12h. Heat the starch / protein composite solution at 90℃ for 30min to completely gelatinize it, and then cool it to room temperature to obtain a starch / protein composite gel. Then, freeze the composite gel at -80℃ for 1h, and return it to room temperature after freezing to finally obtain a starch / protein porous gel.

[0037] Comparative Example 1

[0038] A starch / protein gel and a preparation method thereof, comprising the following steps:

[0039] Accurately weigh 8g starch and 2g soy protein isolate and add them to 100mL deionized water. Stir evenly with magnetic force and place in a 4℃ environment for hydration for 12h. Heat the starch / protein composite solution at 90℃ for 30min to make it completely gelled, and then cool to room temperature to obtain a starch / protein composite gel. Then, store the composite gel in a 4℃ environment to obtain a starch / protein composite gel.

[0040] Comparative Example 2

[0041] A method for regulating the texture of starch-protein composite gel based on ice template method, the steps are as follows:

[0042] Accurately weigh 8g starch and 2g soy protein isolate and add them to 100mL deionized water. Stir magnetically and place in a 4℃ environment for hydration for 12h. Heat the starch / protein composite solution at 90℃ for 30min to completely gelatinize it, and then cool it to room temperature to obtain a starch / protein composite gel. Then, freeze the composite gel in a -196℃ environment (liquid nitrogen) for 20s, and return it to room temperature after freezing to finally obtain a starch / protein porous gel.

[0043] Comparative Example 3

[0044] A method for regulating the texture of starch-protein composite gel based on ice template method, the steps are as follows:

[0045] Accurately weigh 8g of starch and 2g of soy protein isolate and add them to 100mL of deionized water. After magnetic stirring, place it in a 4℃ environment for hydration for 12h. Heat the starch / protein composite solution at 90℃ for 30min to make it completely gelled, and then cool it to room temperature to obtain a starch / protein composite gel. Then, one side of the composite gel is contacted with a metal plate at -196℃ so that the growth direction of the ice crystals is perpendicular to the metal plate surface to achieve the purpose of oriented freezing. After freezing, return it to room temperature to finally obtain a starch / protein porous gel. The direction of the experimental test is parallel to the growth direction of the ice crystals.

[0046] Comparative Example 4

[0047] A method for regulating the texture of starch-protein composite gel based on ice template method, the steps are as follows:

[0048] Accurately weigh 8g starch and 2g soy protein isolate and add them to 100mL deionized water. After magnetic stirring, place it in a 4℃ environment for hydration for 12h. Heat the starch / protein composite solution at 90℃ for 30min to make it completely gelled, and then cool it to room temperature to obtain a starch / protein composite gel. Then, one side of the composite gel is contacted with a metal plate at -196℃ so that the growth direction of the ice crystals is perpendicular to the metal plate surface to achieve the purpose of oriented freezing. After freezing, return it to room temperature to finally obtain a starch / protein porous gel. The direction of the experimental test is perpendicular to the growth direction of the ice crystals.

[0049] Table 1 shows the texture properties of the porous starch / protein composite gel prepared by Comparative Examples 1 to 4 and Examples 1 to 2. Compared with the starch / protein composite gel refrigerated at 4°C (Comparative Example 1), the composite gel after freezing at -18°C has higher hardness, higher elasticity and chewiness. This may be due to the formation of a macroporous structure, which causes it to store its energy in a deformed pore structure during pressure, thereby showing a certain elasticity. As the freezing temperature drops to -80°C, the hardness and chewiness of the gel are significantly improved, especially the chewiness, which can reach 264.26, but the elasticity changes less. After freezing and thawing at -196°C, the hardness, elasticity and chewiness are reduced, which may be due to the reduction of pore size and pore wall thickness, and the gel structure is easily destroyed. For oriented frozen gels, the hardness and chewiness measured in the parallel direction and the vertical direction are significantly different, which is related to the anisotropic pore morphology. The above results show that compared with unfrozen gels, the gel has higher hardness, elasticity and chewiness after freezing at -80°C.

[0050] Table 1 Texture properties of starch / protein composite gels in Examples 1 to 2 and Comparative Examples 1 to 3

[0051]

[0052] Figure 1 This is a schematic diagram of the orientation freezing device used in Comparative Examples 3 and 4. One side of the metal plate is immersed in -196°C, and the starch / protein composite gel is placed on the other side. Since only the bottom of the gel is frozen, the ice crystals will grow vertically upwards to the metal plate surface, achieving the purpose of orientation freezing.

[0053] Figure 2 The trend diagram of the change of the center temperature of the starch / protein composite gel prepared in Examples 1 to 2 and Comparative Examples 2 to 4 during the freezing process. Under -18°C conditions, the freezing rate is low, and there is an obvious platform in the range of 0-3°C. This is because the liquid water in the gel is converted into ice crystals to release latent heat, resulting in a slight increase in temperature. As the freezing temperature decreases, no obvious platform area of ​​the maximum ice crystal formation zone is observed under -80°C freezing conditions, and the center point temperature quickly drops to below zero. In the lower liquid nitrogen freezing process (-196°C), the time required for the entire gel to freeze is greatly reduced. The above results show that the lower the freezing temperature, the more conducive it is to the rapid conversion of liquid water to ice crystals, and the higher the freezing efficiency, but at lower temperatures, due to the rapid generation and rapid shaping of ice crystals, the size of the ice crystals may be smaller.

[0054] Figure 3 The SEM images of the porous starch / protein composite gel prepared in Examples 1 to 2 and Comparative Examples 2 to 4 after freeze-drying. It can be clearly observed that the starch / protein gels treated under different freezing conditions all present a porous structure. As the freezing temperature decreases, the size of the pores gradually decreases. The morphology of the composite gel after -196°C oriented freezing treatment shows an anisotropic pore structure. When observed in the direction perpendicular (⊥) to the surface of the frozen metal plate, it was found that the pores were regular in shape and circular, while when observed in the direction parallel (∥) to the surface of the frozen metal plate, it was found that the opening of the pores and the growth direction of the pore walls showed consistency.

[0055] Figure 4 It is the water loss rate of the porous starch / protein composite gel prepared in Comparative Examples 1 to 4 and Examples 1 to 2 during the extrusion process. This process can be used to simulate the juiciness of food gels when chewing in the mouth, that is, the greater the water loss rate, the more juice is shown during chewing. Compared with the gels that have not been frozen, all porous gels that have been thawed after freezing have a higher water loss rate. Among them, the composite gel thawed after freezing at -18°C has the highest water loss rate, followed by -80°C and -196°C. Although lower temperatures are conducive to the formation of a denser and smaller pore structure, it has a stronger ability to bind water and cannot be fully released during the extrusion process. The above results show that gels with large pores have a weaker ability to bind water, which is conducive to releasing water under pressure.

[0056] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for regulating the texture of starch-protein composite gel based on ice template method, characterized in that: The steps include: (1) adding starch and soy protein isolate into water, dispersing them evenly and then subjecting them to hydration treatment; (2) heating the product of the hydration treatment in step (1) and cooling it to form a starch / protein composite gel; (3) freezing the gel prepared in step (2) at -18 to -80°C, taking it out and returning it to room temperature to obtain a starch / protein porous gel.

2. The method according to claim 1, characterized in that: The mass ratio of starch to soy protein isolate described in step (1) is 8:1 to 8:

4.

3. The method according to claim 1, characterized in that The concentration of the starch in water in step (1) is 8 g / mL, and the concentration of the soy protein isolate in water is 1-4 g / mL.

4. The method according to claim 1, characterized in that: The temperature of the hydration treatment in step (1) is 2 to 4° C. and the time is 12 to 18 hours.

5. The method according to claim 1, characterized in that The heating temperature in step (2) is 85-95°C.

6. The method according to claim 1, characterized in that The heating time in step (2) is 25-35 min.

7. The method according to claim 1, characterized in that The cooling described in step (2) is carried out at 2-4°C.

8. The method according to claim 1, characterized in that The freezing temperature of the gel in step (3) is -80°C.

9. The method according to claim 1, characterized in that: The freezing time of the gel in step (3) is 10s-5h.

10. The starch / protein porous gel prepared according to the method according to any one of claims 1 to 9.

Images