Method for improving emulsibility of soybean protein isolate through cooperation of alkaline pH shift and oxidized cellulose nanocrystals

Abstract

The invention relates to a method for improving the emulsibility of soybean protein isolate by synergism of alkaline pH shift and oxidized cellulose nanocrystals, and belongs to the technical field of protein modification. The method comprises the following steps: (1) preparing a soybean protein isolate (SPI) solution; (2) preparing an alkaline pH shift soybean protein isolate (MSPI) solution; (3) preparation of oxidized cellulose nanocrystals (DCNC); and (4) preparing the SPI / MSPI-DCNC compound. The SPI is modified through the synergistic effect of alkaline pH shift and oxidized cellulose nanocrystals, the emulsibility of the SPI is greatly improved, and the method has very important significance for expanding the application field of the SPI.

Description

Technical Field

[0001] This invention relates to the treatment of alkaline pH shift with the synergistic addition of oxidized cellulose nanocrystals, belonging to the field of protein modification technology. Background Technology

[0002] Soy protein isolate (SPI), as an important plant protein resource, is widely used in the food industry due to its rich nutritional value and various functional properties. Because of its hydrophilic and lipophilic structure, SPI can adsorb at the oil-water interface, inhibiting oil droplet aggregation and thus stabilizing the solution. Therefore, SPI is often used in emulsification systems. However, SPI molecules adsorbed at the interface mainly form an interfacial film through weak non-covalent interactions (such as hydrogen bonds and hydrophobic interactions). This film is soft and lacks viscoelasticity, making it difficult to effectively resist deformation caused by environmental factors such as collisions, which can lead to droplet aggregation and destabilize the system.

[0003] Alkaline pH shifting is a physical modification method for unfolding protein structures. It involves exposing the protein solution to extremely alkaline conditions, causing the protein molecules to unfold and their structure to expand, exposing embedded functional groups. When the pH is adjusted back to neutral, the protein partially refolds, forming a more flexible "molten" or unfolded structure different from its native state. This process effectively improves the emulsifying properties of proteins, and is gentle, green, and efficient. However, alkaline pH shifting alone has limited effect on improving the strength of the SPI interfacial film and the long-term stability of the system; therefore, it must be combined with other modification methods.

[0004] Proteins are complexed with polysaccharides, and the hydrophilicity and steric effects of polysaccharides can improve the emulsifying properties of proteins. Cellulose nanocrystals (CNCs) have attracted much attention due to their unique nanoscale size, high specific surface area, and modifiability. Oxidation of CNCs with sodium periodate oxidizes the hydroxyl groups in CNCs to aldehyde groups. The aldehyde groups in oxidized cellulose nanocrystals (DCNCs) can covalently cross-link with the free amino groups in SPIs to form Schiff bases, preventing droplet aggregation and improving emulsifying performance. Under alkaline pH shift conditions, the SPI structure unfolds, allowing for better cross-linking with DCNCs and forming a strong interpenetrating network, which further enhances the long-term stability of the complex.

[0005] Currently, there is limited research on the improvement of soy protein isolate emulsifying properties through alkaline pH shift combined with DCNC. This invention utilizes alkaline pH shift combined with DCNC to enhance the emulsifying properties of soy protein isolate and determines the optimal DCNC concentration. This is expected to yield soy protein isolate with better emulsifying properties, broadening its application in the food industry. Summary of the Invention

[0006] This invention provides a method for improving the emulsifying properties of soy protein isolate by synergistic alkaline pH shift and oxidized cellulose nanocrystals, with the aim of further enhancing the emulsifying properties of soy protein isolate and broadening its application in the food industry.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for improving the emulsificability of soy protein isolate by synergistic alkaline pH shift and oxidized cellulose nanocrystals, the method comprising the following steps: (1) Preparation of soy protein isolate (SPI) solution: Disperse SPI powder in deionized water to prepare a solution with a protein concentration of 2%, and stir at room temperature until it is completely dissolved to obtain the SPI solution; (2) Preparation of alkaline pH-shifted soy protein isolate (MSPI) solution: Take half of the SPI solution obtained in step (1), add NaOH (2 M) to adjust the pH to 12, stir for 1-2 h, then adjust the pH back to 7.0 with HCl (2 M), stir for 2 h, and that is the MSPI solution; (3) Preparation of oxidized cellulose nanocrystals (DCNC): Add an appropriate amount of NaIO4 to the cellulose nanocrystal (CNC) dispersion, stir for 6 h at 40°C in the dark, add ethylene glycol to terminate the reaction, continue stirring for 2 h, dialyze with deionized water until pH is 7.0, and freeze dry to obtain oxidized cellulose nanocrystal (DCNC) powder. (4) Preparation of SPI / MSPI-DCNC complex: Add 0.5%, 1.0%, 1.5% and 2.0% DCNC to the SPI solution obtained in step (1) and the MSPI solution obtained in step (2), respectively, and stir at room temperature for 2 h to obtain the SPI / MSPI-DCNC complex.

[0008] The preferred conditions are that the optimal alkaline pH shift condition is pH 12, and the optimal stirring time during the shift process is 1 hour. The preferred condition is that the optimal oxidation method is sodium periodate oxidation. The preferred condition is that the optimal stirring time during the room temperature dissolution process is 2 hours; The preferred condition is that the optimal DCNC addition concentration is 1.5%.

[0009] The MSPI produced by the method of this invention exhibits better emulsifying properties. Preferably, a DCNC concentration of 1.5% is added to the MSPI solution, at which point the emulsifying activity is 52.47 m. 2 The emulsification stability was 63.70 min / g.

[0010] The above preparation method can obtain MSPI emulsions with good emulsification properties, further expanding the application value of SPI. Attached Figure Description

[0011] Appendix Figure 1 Flowchart of this method; Appendix Figure 2 Alkaline pH shift synergistically enhances the emulsifying activity of oxidized cellulose nanocrystal soy protein isolate; Appendix Figure 3 Alkaline pH shift synergistically enhances the emulsification stability of oxidized cellulose nanocrystal soy protein isolate. Detailed Implementation

[0012] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0013] A method for improving the emulsifying properties of soy protein isolate by alkaline pH shifting in conjunction with oxidized cellulose nanocrystals, the method comprising the following steps: (1) Preparation of soy protein isolate (SPI) solution: dispersing SPI powder in deionized water to prepare a solution with a protein concentration of 2%, and stirring at room temperature until completely dissolved, which is the SPI solution; (2) Preparation of alkaline pH shifted soy protein isolate (MSPI) solution: taking half of the SPI solution obtained in step (1), adding NaOH (2 M) to adjust the pH to 12, stirring for 1-2 h, then adjusting the pH back to 7.0 with HCl (2 M), and stirring for 2 h, which is the MSPI solution; (3) Preparation of oxidized cellulose nanocrystals (DCNC): adding an appropriate amount of NaIO4 to the cellulose nanocrystal (CNC) dispersion, stirring at 40℃ in the dark for 6 h, adding ethylene glycol to terminate the reaction, and continuing to stir for 2 h. After h, the solution was dialyzed with deionized water until the pH was 7.0, and then freeze-dried to obtain oxidized cellulose nanocrystals (DCNC) powder; (4) Preparation of SPI / MSPI-DCNC complex: DCNC with concentrations of 0.5%, 1.0%, 1.5% and 2.0% was added to the SPI solution obtained in step (1) and the MSPI solution obtained in step (2), respectively, and stirred at room temperature for 2 h to obtain the SPI / MSPI-DCNC complex.

[0014] In Implementation Case 1, 8 g of SPI powder was dispersed in 400 mL of deionized water to prepare a 2% protein concentration solution. The solution was stirred at room temperature until completely dissolved, thus obtaining the SPI solution. 200 mL of this SPI solution was taken, and NaOH (2 M) was added to adjust the pH to 12. After stirring for 1 h, the pH was adjusted back to 7.0 with HCl (2 M), and stirred for 2 h, resulting in the MSPI solution. At this point, the emulsifying activity of SPI / MSPI was 19.83 m... 2 / g and 38.53 m 2 / g, with emulsification stability of 39.20 min and 53.53 min, respectively.

[0015] In Implementation Case 2, 8 g of SPI powder was dispersed in 400 mL of deionized water to prepare a 2% protein concentration solution. The solution was stirred at room temperature until completely dissolved, yielding the SPI solution. 200 mL of this SPI solution was taken, and NaOH (2M) was added to adjust the pH to 12. After stirring for 1 h, the pH was adjusted back to 7.0 with HCl (2M) and stirred for 2 h to obtain the MSPI solution. 3.6 g of NaIO4 was added to 400 mL of CNC (containing 200 g of an 8% solids aqueous solution) dispersion. The mixture was stirred at 40°C in the dark for 6 h, and 12 mL of ethylene glycol was added to terminate the reaction. Stirring was continued for 2 h, and the mixture was dialyzed with deionized water until the pH reached 7.0. The resulting DCNC powder was freeze-dried. 2 g of DCNC powder was dispersed in the SPI / MSPI solution to prepare a 0.5% DCNC concentration solution. The mixture was stirred at room temperature until completely dissolved, yielding the SPI / MSPI-DCNC complex. The emulsifying activity of the samples at this point was 25.63 m... 2 / g and 42.30 m 2 / g, with emulsification stability of 43.27 min and 56.30 min, respectively.

[0016] In Implementation Case 3, 8 g of SPI powder was dispersed in 400 mL of deionized water to prepare a 2% protein concentration solution. The solution was stirred at room temperature until completely dissolved, yielding the SPI solution. 200 mL of this SPI solution was taken, and NaOH (2M) was added to adjust the pH to 12. After stirring for 1 h, the pH was adjusted back to 7.0 with HCl (2M) and stirred for 2 h to obtain the MSPI solution. 3.6 g of NaIO4 was added to 400 mL of CNC (containing 200 g of an 8% solids aqueous solution) dispersion. The mixture was stirred at 40°C in the dark for 6 h, and 12 mL of ethylene glycol was added to terminate the reaction. Stirring was continued for 2 h, and the mixture was dialyzed with deionized water until the pH reached 7.0. The resulting DCNC powder was freeze-dried. 4 g of DCNC powder was dispersed in the SPI / MSPI solution to prepare a 1.0% DCNC concentration solution. The mixture was stirred at room temperature until completely dissolved, yielding the SPI / MSPI-DCNC complex. The emulsifying activity of the samples at this point was 31.23 m... 2 / g and 47.27 m 2 / g, with emulsification stability of 45.40 min and 58.43 min, respectively.

[0017] In Implementation Case 4, 8 g of SPI powder was dispersed in 400 mL of deionized water to prepare a 2% protein concentration solution. The solution was stirred at room temperature until completely dissolved, yielding the SPI solution. 200 mL of this SPI solution was taken, and NaOH (2M) was added to adjust the pH to 12. After stirring for 1 h, the pH was adjusted back to 7.0 with HCl (2M) and stirred for 2 h to obtain the MSPI solution. 3.6 g of NaIO4 was added to 400 mL of CNC (containing 200 g of an 8% solids aqueous solution) dispersion. The mixture was stirred at 40°C in the dark for 6 h, and 12 mL of ethylene glycol was added to terminate the reaction. Stirring was continued for 2 h, and the mixture was dialyzed with deionized water until the pH reached 7.0. The resulting DCNC powder was freeze-dried. 6 g of DCNC powder was dispersed in the SPI / MSPI solution to prepare a 1.5% DCNC concentration solution. The mixture was stirred at room temperature until completely dissolved, yielding the SPI / MSPI-DCNC complex. The emulsifying activity of the samples at this point was 35.27 m... 2 / g and 52.47 m 2 / g, with emulsification stability of 53.50 min and 63.70 min, respectively.

[0018] In Implementation Case 5, 8 g of SPI powder was dispersed in 400 mL of deionized water to prepare a 2% protein concentration solution. The solution was stirred at room temperature until completely dissolved, yielding the SPI solution. 200 mL of this SPI solution was taken, and NaOH (2M) was added to adjust the pH to 12. After stirring for 1 h, the pH was adjusted back to 7.0 with HCl (2M) and stirred for 2 h to obtain the MSPI solution. 3.6 g of NaIO4 was added to 400 mL of CNC (containing 200 g of an 8% solids aqueous solution) dispersion. The mixture was stirred at 40°C in the dark for 6 h, and 12 mL of ethylene glycol was added to terminate the reaction. Stirring continued for 2 h, and the mixture was dialyzed with deionized water until the pH reached 7.0. The resulting DCNC powder was freeze-dried. 8 g of DCNC powder was dispersed in the SPI / MSPI solution to prepare a 2.0% DCNC concentration solution. The mixture was stirred at room temperature until completely dissolved, yielding the SPI / MSPI-DCNC complex. The emulsifying activity of the samples at this point was 32.33 m... 2 / g and 47.57 m 2 / g, emulsification stability was 47.33 min and 61.33 min, respectively.

Claims

1. A method for improving the emulsifying properties of soy protein isolate by synergistic alkaline pH shift and oxidized cellulose nanocrystals, the method comprising the following steps: (1) Preparation of soy protein isolate (SPI) solution: Disperse SPI powder in deionized water to prepare a solution with a protein concentration of 2%, and stir at room temperature until it is completely dissolved to obtain the SPI solution; (2) Preparation of alkaline pH-shifted soy protein isolate (MSPI) solution: Take half of the SPI solution obtained in step (1), add NaOH (2 M) to adjust the pH to 12, stir for 1-2 h, then adjust the pH back to 7.0 with HCl (2 M), stir for 2 h, and that is the MSPI solution; (3) Preparation of oxidized cellulose nanocrystals (DCNC): Add an appropriate amount of NaIO4 to the cellulose nanocrystal (CNC) dispersion, stir for 6 h at 40°C in the dark, add ethylene glycol to terminate the reaction, continue stirring for 2 h, dialyze with deionized water until pH is 7.0, and freeze dry to obtain oxidized cellulose nanocrystal (DCNC) powder. (4) Preparation of SPI / MSPI-DCNC complex: Add 0.5%, 1.0%, 1.5% and 2.0% DCNC to the SPI solution obtained in step (1) and the MSPI solution obtained in step (2), respectively, and stir at room temperature for 2 h to obtain the SPI / MSPI-DCNC complex.

2. The method for improving the emulsifying properties of soy protein isolate by alkaline pH shifting synergistically with oxidized cellulose nanocrystals, as described in claim 1, is characterized in that... The optimal alkaline pH shift condition is pH 12, and the optimal stirring time during the shift process is 1 h.

3. The method for improving the emulsifying properties of soy protein isolate by alkaline pH shifting synergistically with oxidized cellulose nanocrystals, as described in claim 1, is characterized in that... The best oxidation method is sodium periodate oxidation.

4. The method for improving the emulsifying properties of soy protein isolate by alkaline pH shifting synergistically with oxidized cellulose nanocrystals, as described in claim 1, is characterized in that... The optimal stirring time during room temperature dissolution is 2 hours.

5. The method for improving the emulsifying properties of soy protein isolate by alkaline pH shifting synergistically with oxidized cellulose nanocrystals, as described in claim 1, is characterized in that... The optimal concentration of DCNC is 1.5%.

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