Method for improving stability of soybean protein isolate-konjac mannan emulsion

Abstract

The invention discloses a preparation method for improving the stability of soybean protein isolate-konjac mannan emulsion, and belongs to the technical field of application of vegetable protein structures. The method comprises the following steps: (1) fully dissolving a soybean protein isolate solution with a certain concentration, and fully hydrating; (2) adding a certain amount of konjac mannan, and reacting at high temperature; and (3) adding six different sodium salt ions into the soybean protein isolate-konjac mannan compound. And (4) respectively mixing the samples in the steps (1), (2) and (3) with sunflower seed oil, and shearing at a high speed to obtain the emulsion. Six sodium salt ions are introduced, the emulsion particle size of the soybean protein isolate-konjac mannan compound is reduced through the Hough-Merster effect, the stability of the emulsion is improved, and under the freezing condition, the emulsion also shows higher freeze injury resistance and emulsion cracking resistance. The method has a certain reference value for the food industry.

Description

Technical Field

[0001] This invention relates to a method for preparing soybean protein isolate-konjac mannan emulsion with improved stability, belonging to the field of plant protein structure application technology. Background Technology

[0004] Konjac glucomannan precisely compensates for the shortcomings of soy protein isolate in long-term emulsification stability. While soy protein isolate can quickly adsorb at the oil-water interface to form an emulsion layer, the interfacial film strength is limited, and oil droplet aggregation easily occurs during heat treatment or long-term storage. In contrast, konjac glucomannan, after dissolving, forms a high-viscosity pseudoplastic fluid. Instead of adsorbing at the interface, it constructs a strong three-dimensional network structure in the aqueous phase, significantly enhancing the overall stability of the emulsion in synergy with soy protein isolate, enabling it to withstand more stringent food processing conditions and shelf-life testing.

[0005] Introducing sodium salt into an emulsion system containing soy protein isolate and konjac mannan directly manifests the Hofmeister effect as a significant improvement in product texture and stability. The addition of sodium salt promotes a more compact protein molecular structure and creates a stronger synergistic effect with the three-dimensional network formed by konjac polysaccharides in the aqueous phase. This ultimately results in increased emulsion viscosity, a finer and more uniform texture, and long-term stability without separation, effectively extending the product's shelf life and improving the final taste experience.

[0006] The addition of sodium salt to the soy protein isolate-konjac mannan system is significant for improving the emulsifying properties of soy protein isolate. This improvement mainly stems from the synergistic effect of the three components. While soy protein isolate itself possesses emulsifying capabilities, its adsorption and film stability at the interface are often insufficient. When konjac mannan is introduced, as a hydrophilic high-molecular-weight polysaccharide, it can significantly increase the viscosity of the aqueous phase, enhancing the long-term stability of the emulsion by inhibiting the movement and aggregation of oil droplets, i.e., preventing flocculation through steric hindrance. The addition of sodium salt is crucial; it weakens the electrostatic repulsion between soy protein isolate and konjac mannan molecules through electrostatic shielding, promoting a tighter complexation and forming a denser and more robust interfacial adsorption layer. This complex can more effectively reduce interfacial tension at the oil-water interface and form an interfacial film with stronger mechanical strength, thereby significantly improving the emulsifying activity and emulsifying stability of the emulsion. Ultimately, this system achieves a synergistic enhancement of the emulsifying properties of soybean protein through the combined improvement of a stable interfacial layer formed between proteins and polysaccharides under salt ion mediation and bulk viscosity. Summary of the Invention

[0008] This invention aims to improve the emulsifying properties of konjac glucomannan-soy protein isolate composite emulsions by adding sodium salts. Results show a significant improvement, resulting in enhanced storage stability under refrigeration conditions. This invention utilizes sodium salts to enhance the stability of soybean protein isolate-konjac glucomannan emulsions, providing a theoretical basis for the high-value utilization of soybean protein.

[0009] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0010] Step 1: Dissolve soy protein isolate in deionized water at an initial concentration of 40 g / L, stir magnetically for 3 h, and hydrate at 4℃ for 12 h. Step 2: Add konjac mannan to the soy protein isolate solution at a concentration of 4 g / L. Stir thoroughly. After mixing evenly, heat at 85℃ for 2 h. Immediately cool in an ice-water bath for 10-20 min after heating. This is designated SPI-G. Step 3: Add six sodium salts—Na₂CO₃, Na₂SO₄, CH₃COONa (NaAc), NaCl, NaI, and NaSCN—to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L. Step 4: Adjust the pH of the above eight samples to 7.00 ± 0.02 using 1 mol / L NaOH or HCl solution. Name these as the anionic fractions of the respective sodium salts. Step 5: Mix the above eight samples with sunflower seed oil and shear.

[0011] According to claim 1, the method for preparing a soy protein isolate-konjac mannan emulsion with improved stability is characterized in that the soy protein isolate in step one is extracted by alkali dissolution and acid precipitation, and after thorough impurity removal and process optimization, the extraction rate is 20% and the purity is 91-93%.

[0012] According to claim 1, the method for preparing a soy protein isolate-konjac mannan emulsion with improved stability is characterized in that, in step three, after the six sodium salts are stirred evenly, magnetic stirring is continued for more than 1 hour to ensure that the sodium salts fully interact with the solution system.

[0013] According to claim 1, the method for preparing a soy protein isolate-konjac mannan emulsion with improved stability is characterized in that, in step four, after adjusting the pH of the solution, deionized water is added to achieve the following final concentrations: soy protein isolate 30 g / L, konjac mannan 3 g / L, and the molar concentrations of various sodium salts 100 mmol / L.

[0014] According to claim 1, the method for preparing a soybean protein isolate-konjac mannan emulsion with improved stability is characterized in that the volume ratio of the emulsion to sunflower seed oil in step five is 3:1, and the final shear rate is selected as 12000 rpm. Attached Figure Description

[0015] Figure 1 This is the overall invention process diagram;

[0016] Figure 2 These are comparative photographs of the microstructure of the emulsions in Examples 1-8 and Comparative Examples 1-2 of the present invention;

[0017] Figure 3 This is a comparison of the emulsion particle size in Examples 1-8 and Comparative Examples 1-2 of the present invention;

[0018] Figure 4 This is a comparison of the emulsification activity index and emulsification stability index of the emulsions in Examples 1-8 and Comparative Examples 1-2 of the present invention;

[0019] Figure 5 This is a comparison of the centrifugal stability of the emulsions in Examples 1-8 and Comparative Examples 1-2 of the present invention;

[0020] Figure 6 These are comparative photographs of the storage stability and freeze-thaw stability of Examples 1-8 and Comparative Examples 1-2 of the present invention;

[0021] Figure 7 These are comparative photographs of the storage stability and freeze-thaw stability of Examples 1-8 and Comparative Examples 1-2 of the present invention. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0023] Step 1: Dissolve soy protein isolate in deionized water at an initial concentration of 40 g / L, stir magnetically for 3 h, and hydrate at 4℃ for 12 h. This is denoted as SPI. Step 2: Add konjac mannan to the soy protein isolate solution at a concentration of 4 g / L. Stir thoroughly. After mixing evenly, heat at 85℃ for 2 h. Then, rapidly cool in an ice-water bath for 10-20 min. This is denoted as SPI-G. Step 3: Add six sodium salts—Na₂CO₃, Na₂SO₄, CH₃COONa, NaCl, NaI, and NaSCN—to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L. Step 4: Adjust the pH of the above eight samples to 7.00 ± 0.02 using 1 mol / L NaOH or HCl solution. Name these as the anionic fractions of the respective sodium salts. Step 5: Mix the above eight samples with sunflower seed oil and shear.

[0024] Example 1:

[0025] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This solution was denoted as SPI. The pH of the SPI solution was adjusted to 7.00 ± 0.02, resulting in a final SPI concentration of 30 g / L. SPI was then mixed with sunflower seed oil at a volume ratio of 3:1 and sheared at a shear rate of 12000 rpm at room temperature for 3 min.

[0026] Example 2:

[0027] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This solution is denoted as SPI. Konjac mannan was added to the soy protein isolate solution at a concentration of 4 g / L. The mixture was stirred thoroughly. After homogenization, the solution was heated at 85 ℃ for 2 h. Following heating, the solution was rapidly cooled in an ice-water bath for 10–20 min. This solution is denoted as SPI-G. The pH of the SPI-G solution was adjusted to 7.00 ± 0.02, resulting in a final SPI concentration of 30 g / L and a konjac mannan concentration of 3 g / L. The SPI-G solution was mixed with sunflower seed oil at a volume ratio of 3:1 and sheared at a shear rate of 12000 rpm at room temperature for 3 min.

[0028] Example 3:

[0029] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This is denoted as SPI. Konjac mannan was added to the soy protein isolate solution at a concentration of 4 g / L. The mixture was stirred thoroughly. After homogenization, it was heated at 85 ℃ for 2 h. Following heating, it was rapidly cooled in an ice-water bath for 10–20 min. This is denoted as SPI-G. The final SPI concentration was 30 g / L, and the konjac mannan concentration was 3 g / L. Na₂CO₃ was added to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L, and the pH of the sample solution was adjusted to 7.00 ± 0.02. The final SPI concentration was 30 g / L, the konjac mannan concentration was 3 g / L, and the molar concentration of sodium salt was 100 mmol / L. The above solution was mixed with sunflower seed oil at a volume ratio of 3:1, and sheared at a shear rate of 12,000 rpm at room temperature for 3 min.

[0030] Example 4:

[0031] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This is denoted as SPI. Konjac mannan was added to the soy protein isolate solution at a concentration of 4 g / L. The mixture was stirred thoroughly. After homogenization, it was heated at 85 ℃ for 2 h. Following heating, it was rapidly cooled in an ice-water bath for 10–20 min. This is denoted as SPI-G. The final SPI concentration was 30 g / L, and the konjac mannan concentration was 3 g / L. Na₂SO₄ was added to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L, and the pH of the sample solution was adjusted to 7.00 ± 0.02. The final SPI concentration was 30 g / L, the konjac mannan concentration was 3 g / L, and the molar concentration of sodium salt was 100 mmol / L. The above solution was mixed with sunflower seed oil at a volume ratio of 3:1, and sheared at a shear rate of 12,000 rpm at room temperature for 3 min.

[0032] Example 5:

[0033] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This is denoted as SPI. Konjac mannan was added to the soy protein isolate solution at a concentration of 4 g / L. The mixture was stirred thoroughly. After thorough mixing, it was heated at 85 ℃ for 2 h. Following heating, it was rapidly cooled in an ice-water bath for 10–20 min. This is denoted as SPI-G. The final SPI concentration was 30 g / L, and the konjac mannan concentration was 3 g / L. CH3COOH was added to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L, and the pH of the sample solution was adjusted to 7.00 ± 0.02. The final SPI concentration was 30 g / L, the konjac mannan concentration was 3 g / L, and the molar concentration of sodium salt was 100 mmol / L. The above solution was mixed with sunflower seed oil at a volume ratio of 3:1, and sheared at a shear rate of 12,000 rpm at room temperature for 3 min.

[0034] Example 6:

[0035] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This is denoted as SPI. Konjac mannan was added to the soy protein isolate solution at a concentration of 4 g / L. The mixture was stirred thoroughly. After homogenization, it was heated at 85 ℃ for 2 h. Following heating, it was rapidly cooled in an ice-water bath for 10–20 min. This is denoted as SPI-G. The final SPI concentration was 30 g / L, and the konjac mannan concentration was 3 g / L. NaCl was added to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L, and the pH of the sample solution was adjusted to 7.00 ± 0.02. The final SPI concentration was 30 g / L, the konjac mannan concentration was 3 g / L, and the molar concentration of sodium salt was 100 mmol / L. The above solution was mixed with sunflower seed oil at a volume ratio of 3:1, and sheared at a shear rate of 12,000 rpm at room temperature for 3 min.

[0036] Example 7:

[0037] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This is denoted as SPI. Konjac mannan was added to the soy protein isolate solution at a concentration of 4 g / L. The mixture was stirred thoroughly. After homogenization, it was heated at 85 ℃ for 2 h. Following heating, it was rapidly cooled in an ice-water bath for 10–20 min. This is denoted as SPI-G. The final SPI concentration was 30 g / L, and the konjac mannan concentration was 3 g / L. NaI was added to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L, and the pH of the sample solution was adjusted to 7.00 ± 0.02. The final SPI concentration was 30 g / L, the konjac mannan concentration was 3 g / L, and the molar concentration of sodium salt was 100 mmol / L. The above solution was mixed with sunflower seed oil at a volume ratio of 3:1, and sheared at a shear rate of 12,000 rpm at room temperature for 3 min.

[0038] Example 8:

[0039] Soy protein isolate was dissolved in deionized water at an initial concentration of 40 g / L, magnetically stirred for 3 h, and hydrated at 4 ℃ for 12 h. This is denoted as SPI. Konjac mannan was added to the soy protein isolate solution at a concentration of 4 g / L. The mixture was stirred thoroughly. After homogenization, it was heated at 85 ℃ for 2 h. Following heating, it was rapidly cooled in an ice-water bath for 10–20 min. This is denoted as SPI-G. The final SPI concentration was 30 g / L, and the konjac mannan concentration was 3 g / L. NaSCN was added to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L, and the pH of the sample solution was adjusted to 7.00 ± 0.02. The final SPI concentration was 30 g / L, the konjac mannan concentration was 3 g / L, and the molar concentration of sodium salt was 100 mmol / L. The above solution was mixed with sunflower seed oil at a volume ratio of 3:1, and sheared at a shear rate of 12,000 rpm at room temperature for 3 min.

[0040] Comparative analysis of the above examples reveals that different sodium salts significantly improved the effects of soybean protein isolate-konjac mannan emulsions. The particle size of the emulsions decreased significantly, and the distribution became more uniform. Figure 2 The reduction in droplet size is due to the Hofmeister effect, which enhances hydrophobic interactions between oil droplets, thereby reducing their volume. The emulsifying activity index and emulsifying stability index also increased. Figure 4Sodium salts, at appropriate concentrations, can induce a slight "salt-dissolving" effect. Ions interact with the surfaces of protein and polysaccharide molecules, as well as water molecules. This slightly increases the hydrophobic interactions between the protein and polysaccharide, subtly altering the protein's conformation and making its structure slightly "relaxed." This relaxed state actually facilitates the protein's unfolding and rearrangement at the oil-water interface, thus more effectively reducing interfacial tension and further promoting emulsifying activity. Regarding centrifugal stability, the sample with added sodium salt was significantly higher than the soy protein isolate-konjac mannan sample, and the soy protein isolate sample also showed significant improvement after the addition of polysaccharide. Sodium ions in the sodium salt reduce the intramolecular and intermolecular electrostatic repulsion of the protein-polysaccharide complex through electrostatic shielding, making its structure more compact. Figure 5 This compact structure enhances the stability of the complex itself and the strength of the interfacial film formed at the oil-water interface, thus better resisting the enormous shear forces and aggregation tendency generated during centrifugation, which macroscopically manifests as improved centrifugal stability. Polysaccharide molecules bind to proteins adsorbed on the interface through electrostatic interactions or covalent linkages, forming a thicker and more stable three-dimensional protective layer on the oil droplet surface, generating a strong steric hindrance effect and effectively preventing the oil droplets from agglomerating under centrifugal force. The above trend was also observed in the storage stability at 4°C over 14 days, as well as the freeze-thaw stability (frozen at -20°C for 22 hours, thawed at room temperature for 2 hours, constituting one freeze-thaw cycle, repeated four times). Figure 6 () Figure 7Regarding storage stability, this denser structure and more robust interfacial film more effectively resist oil droplet aggregation (due to enhanced steric hindrance) and Ostwald ripening (due to the enhanced barrier effect of the interfacial film on mass diffusion). Simultaneously, electrostatic shielding helps suppress unfavorable phase separation during storage, maintaining system homogeneity. The polysaccharides dissolved in the aqueous phase significantly increase system viscosity, effectively slowing down the Brownian motion, rising, or settling velocities of oil droplets caused by density differences, thus greatly delaying stratification. Furthermore, the polysaccharides adsorbed on the protein-coated oil droplet surface form a thick, three-dimensional protective layer, generating strong steric hindrance and preventing oil droplets from aggregating or merging due to collisions during long-term storage. For freeze-thaw stability, the key to improvement lies in the enhanced ability of the compacted complex structure to bind water and resist ice crystal destruction. During freezing, the formed, more robust interfacial film protects oil droplets from being punctured by growing ice crystals and is less prone to denaturation and aggregation due to rapid increases in local solute concentration. After thawing, the system can thus better recover its original state, preventing water separation, layering, and textural damage. The role of polysaccharides is particularly crucial for freeze-thaw stability. During freezing, polysaccharides, due to their strong water-holding capacity, effectively bind a large amount of free water, inhibiting the excessive growth and distribution of ice crystals, thereby reducing the mechanical penetration and damage of ice crystals to the protein interface membrane and the oil droplets they encapsulate. Furthermore, some polysaccharides can form a gel network structure under low-temperature, high-concentration conditions. This network can physically fix and isolate oil droplets, preventing them from approaching each other, thus maintaining structural integrity after freeze-thaw cycles and preventing water separation and oil layer separation.

Claims

1. A method for preparing a soy protein isolate-konjac mannan emulsion by improving its stability, characterized in that... The method steps are as follows: Step 1: Dissolve soy protein isolate in deionized water at an initial concentration of 40 g / L, stir magnetically for 3 h, and hydrate at 4 ℃ for 12 h. This is denoted as SPI. Step 2: Add konjac mannan to the soy protein isolate solution at a concentration of 4 g / L. Stir thoroughly. After stirring evenly, heat at 85 ℃ for 2 h. After heating, quickly cool in an ice-water bath for 10-20 min. This is denoted as SPI-G. Step 3: Add six sodium salts—Na2CO3, Na2SO4, CH3COONa, NaCl, NaI, and NaSCN—to the soy protein isolate-konjac mannan system at a concentration of 133.3 mmol / L. Step 4: Adjust the pH of the above eight samples to 7.00 ± 0.02 using 1 mol / L NaOH or HCl solution. Name these as the anionic fractions of the respective sodium salts. Step 5: Mix the above eight samples with sunflower seed oil and shear.

2. The preparation method of soybean protein isolate-konjac mannan emulsion with improved stability according to claim 1, characterized in that... The soy protein isolate described in step one is extracted by alkali dissolution and acid precipitation. After thorough impurity removal and process optimization, the extraction rate is 20% and the purity is 91-93%.

3. The preparation method of soybean protein isolate-konjac mannan emulsion with improved stability according to claim 1, characterized in that... As described in step three, after the six sodium salts are thoroughly mixed, they should continue to be magnetically stirred for more than 1 hour to ensure that the sodium salts and the solution system react fully.

4. The preparation method of soybean protein isolate-konjac mannan emulsion with improved stability according to claim 1, characterized in that... After adjusting the pH of the solution described in step four, deionized water should be added to achieve the following final concentrations: soy protein isolate 30 g / L, konjac mannan 3 g / L, and various sodium salts 100 mmol / L.

5. The preparation method of soybean protein isolate-konjac mannan emulsion with improved stability according to claim 1, characterized in that... The emulsion described in step five is mixed with sunflower seed oil in a volume ratio of 3:1, and the final shear rate is selected as 12000 rpm.

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