Method for preparing gel based on succinylation modified rice protein alkali heat induction

Abstract

The invention relates to the technical field of food, in particular to a method for preparing gel based on succinylation modified rice protein alkali heat induction. The preparation method comprises the following steps: firstly, acylating rice protein by adopting succinic anhydride to prepare rice protein with different acylation degrees; the influence of different alkaline solutions and alkaline environments with different pH values on the performance of inducing the rice protein to prepare the gel is further investigated. Compared with a traditional alkali heat induction process, the brand new rice protein gel preparation process provided by the invention is milder and safer. The application range of the rice protein in the food industry is expanded, and meanwhile, an important foundation is laid for developing safe, nutritional and palatable foods easy to swallow.

Description

Technical Field

[0001] This invention relates to the field of food technology, specifically to a method for preparing a gel based on alkali-thermal induction of succinylated modified rice protein. Background Technology

[0002] Developing easily swallowable foods based on plant protein is an important direction for addressing the needs of an aging society and specific clinical nutritional requirements. Rice protein is considered an ideal base material due to its low allergenicity, relatively balanced amino acid composition, and neutral odor. However, rice protein suffers from poor solubility and its ability to form gels only under strongly alkaline conditions (pH=10). Therefore, how to modify rice protein to maintain excellent gelling ability within a near-neutral pH range of food systems has become a key technical problem that urgently needs to be solved.

[0003] Currently, most commercially available and research-developed easily swallowable foods rely on whey protein, gelatin, κ-carrageenan, xanthan gum, or similar gel matrices. While these systems can form gels rapidly, they have inherent drawbacks: animal proteins may trigger allergies, and their gels are often hard, brittle, or excessively elastic. However, research on the gelation behavior of plant proteins, especially rice protein systems, is still insufficient. This invention addresses this by succinylated rice protein to enable it to form high-quality gels with precise and controllable texture, stable performance, and safe swallowing properties under mild, weakly alkaline conditions, thus providing a new solution for the development of foods for people with swallowing disorders. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing gels based on alkali-thermal induction of succinylated modified rice protein, so as to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for preparing a gel based on succinylated modified rice protein using alkaline thermal induction, comprising the following steps: Step 1: Rice protein powder was dispersed in deionized water, and the pH was adjusted to 11.0 using sodium hydroxide solution. Succinic anhydride was added, and the mixture was heated and stirred in a water bath. After the reaction was completed, the reaction was stopped in a cold water bath, and the pH of the reaction system was adjusted to 7.0. After dialysis, the mixture was freeze-dried to obtain succinylated rice protein. Step 2: Succinylated rice protein was added to deionized water and magnetically stirred to obtain an aqueous solution of succinylated rice protein. An alkaline solution was added to the aqueous solution of succinylated rice protein and stirred to obtain an alkaline aqueous solution of succinylated rice protein. After the pH of the alkaline aqueous solution of succinylated rice protein stabilized, the solution was capped and heated in a water bath with stirring. After the reaction was completed, the solution was transferred to an ice-water bath and stored overnight to obtain rice protein gel.

[0006] Furthermore, in step 1, the amount of succinic anhydride added is 10-50% of the total mass of rice protein.

[0007] Furthermore, in step 1, the water bath temperature is 40℃; the stirring reaction time is 90 min, during which sodium hydroxide solution is used to control the pH value of the reaction system to 8.5±0.5.

[0008] Furthermore, in step 1, the dialysis treatment temperature is 4°C and the dialysis time is 48 hours.

[0009] Furthermore, in step 2, the alkaline solution is an aqueous solution of sodium hydroxide or an aqueous solution of sodium carbonate.

[0010] Furthermore, in step 2, the pH value of the alkaline aqueous solution of succinylated rice protein is 8-10.

[0011] Furthermore, in step 2, the water bath temperature is 85℃; the stirring reaction time is 30 min.

[0012] Furthermore, in step 2, the overnight storage temperature is 4°C.

[0013] Compared with the prior art, the beneficial effects achieved by the present invention are: 1. This invention uses succinic anhydride to modify rice protein and investigates the quantitative relationship between the amount of succinic anhydride added and the degree of acylation, protein physicochemical properties and gelation properties; 2. This invention innovatively uses Na2CO3 as an alkali inducer to prepare gels, and analyzes the difference in gel strength between Na2CO3 and NaOH as an alkali inducer. Compared with traditional NaOH induction, Na2CO3 has a buffering effect, making the process milder and safer, and providing a new technical path for specific food applications. 3. This invention systematically evaluated the effects of two alkali inducers on gelation properties within the pH range of 8 to 10, providing a basis for selecting appropriate process conditions according to product requirements. Attached Figure Description

[0014] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This describes the effect of the amount of succinic anhydride added on the degree of acylation of rice protein in Experiment 1 of this invention. Figure 2 This refers to the solubility of rice protein with different degrees of acylation in Experiment 1 of this invention; Figure 3 This refers to the free sulfhydryl content of rice proteins with different degrees of acylation in Experiment 1 of this invention; Figure 4-1This refers to the effect of different degrees of acylation on the particle size and polymer dispersion index of rice protein in Experiment 1 of this invention; Figure 4-2 The effect of different degrees of acylation on the Zeta potential of rice protein; Figure 5 These are the Fourier transform infrared (FTIR) characterization results of rice proteins with different degrees of acylation in Experiment 1 of this invention. Figure 6 These are the color difference analysis results of rice protein with different degrees of acylation in Experiment 1 of this invention; among them, the L* value continuously decreased, indicating that the sample gradually darkened; the a* value continuously increased, indicating that the sample was slightly reddish; and the b* value increased significantly, indicating that the sample was significantly yellowish. Figure 7 This refers to the surface hydrophobicity of rice proteins with different degrees of acylation in Experiment 1 of this invention; Figure 8 The gel strength of rice protein with different degrees of acylation in Experiment 2 of this invention; wherein, Figure 8-1 Rice protein gel prepared by induction with NaOH alkaline solution. Figure 8-2 Rice protein gel prepared by induction with Na2CO3 alkaline solution; Figure 9 This refers to the water-holding capacity of rice protein gels with different degrees of acylation in Experiment 2 of this invention; wherein, Figure 9-1 Rice protein gel prepared by induction with NaOH alkaline solution. Figure 9-2 Rice protein gel prepared by induction with Na2CO3 alkaline solution. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] All raw materials used in this invention are commercially available products. Example

[0017] Rice protein powder was dissolved in deionized water to prepare a rice protein aqueous solution (3%, w / v). The pH was adjusted to 11.0 with 2M NaOH solution. Succinic anhydride of 10% of the rice protein mass was added. The mixture was stirred in a water bath at 40°C for 90 min, during which the pH was maintained at 8.5±0.5 with NaOH solution. The reaction was then terminated by rapid cooling in a cold water bath, and the pH was adjusted to 7.0. The mixture was dialyzed at 4°C for 48 h and then lyophilized to obtain succinylated rice protein, denoted as SA-RP 10. Example

[0018] The difference from Example 1 is that 20% of the rice protein content of succinic anhydride is added in this example, and the remaining steps and parameters are the same as in Example 1; the succinylated rice protein obtained is denoted as SA-RP 20. Example

[0019] The difference from Example 1 is that 30% of the rice protein content of succinic anhydride is added in this example, and the remaining steps and parameters are the same as in Example 1; the succinylated rice protein obtained is denoted as SA-RP 30. Example

[0020] The difference from Example 1 is that 40% of the rice protein content of succinic anhydride is added in this example, while the remaining steps and parameters are the same as in Example 1; the succinylated rice protein obtained is denoted as SA-RP 40. Example

[0021] The difference from Example 1 is that succinic anhydride of 50% of the rice protein content is added in this example, while the remaining steps and parameters are the same as in Example 1; the succinylated rice protein obtained is denoted as SA-RP 40.

[0022] Comparative Example 1: Without the addition of succinic anhydride, the remaining steps and parameters were the same as in Example 1, and the resulting product was denoted as RP.

[0023] Experiment 1: The products prepared in Examples 1-5 and Comparative Example 1 were tested and analyzed.

[0024] (1) Determination of acylation The ninhydrin method was used. Samples were separately added to water to prepare corresponding 1.0% (w / v) sample solutions. 1 mL of the sample solution and 1 mL of 2.0% (w / v) ninhydrin solution were thoroughly mixed, heated in a boiling water bath for 15 minutes, and then rapidly cooled in ice water. After cooling, 5 mL of deionized water was added to the mixture. The absorbance of the solution at 570 nm was measured using a microplate reader. The following formula was used to calculate the degree of succinylation: Acylation degree (%) = (A0 - A1) / A0 × 100%; Where A0 is the absorbance of natural rice protein and A1 is the absorbance of succinylated rice protein.

[0025] Succinylation degree determination, such as Figure 1As shown, the degree of succinylation of rice protein gradually increases with the increase of succinic anhydride addition. When the amount of succinic anhydride added reaches 40%, the degree of acylation reaches 58%. Further increasing the amount of succinic anhydride added does not improve the degree of acylation of rice protein. This is because succinylation mainly modifies the lysine residues of proteins. When the reaction proceeds to a certain extent, most of the available amino groups have been acylated, and the available sites are basically exhausted.

[0026] (2) Solubility determination Dissolve the protein sample in deionized water to prepare a 1% (w / v) protein solution, and adjust the pH to 7.0 with 0.1M NaOH and 0.1M HCl. Stir magnetically for 1 hour to ensure complete protein hydration. Then centrifuge (4000 rpm, 15 min) and collect the supernatant. Using bovine serum albumin as a standard curve, collect the supernatant of the protein sample and determine the protein concentration using a BCA kit.

[0027] Solubility (%) = (protein concentration in supernatant) / total protein concentration × 100%; Solubility determination, such as Figure 2 As shown, the solubility of rice protein gradually increased with the increase of succinic anhydride addition. When the succinic anhydride addition reached 40%, the solubility of rice protein reached a plateau, increasing to 36.2%, which is about 6 times the solubility of natural rice protein (6.0%). The main reason is that the succinylation reaction introduces hydrophilic amide groups into the protein, which greatly reduces the exposure of hydrophobic amino groups on the protein surface and reduces its surface hydrophobicity. This enhances the hydrophilicity of the protein. Further increasing the succinic anhydride addition to 50% failed to further increase the protein solubility because the available sites for succinylation had reached saturation, which was also confirmed by the degree of acylation measurement.

[0028] (3) Determination of free thiol groups Ellman's reagent at a concentration of 4 mg / mL was prepared by dissolving 5,5-dithiobis-2-nitrobenzoic acid (DTNB) in Tris-glycine buffer (pH=8.0). 1 mL of the sample solution (5 mg / mL) was added to 5 mL of Tris-glycine buffer containing 8 M urea, followed by 50 μL of Ellman's reagent. The absorbance was measured at 412 nm, and the free thiol content was calculated as follows: Free thiol content (μM / g) = 73.53 × A 412 ×D / C; Among them, A 412 is the absorbance at 412 nm, C is the amount of solids in the protein solution, D is the dilution factor, and 73.53 is the molar extinction coefficient.

[0029] Thiol groups and DTNB can specifically bind to form thionitrobenzoic acid (TNB), which exhibits maximum absorbance at 412 nm. The thiol content in proteins can be calculated by measuring the absorbance of this reaction product at 412 nm. Furthermore, the content of free thiol groups significantly influences the structural properties of proteins.

[0030] Determination of free sulfhydryl content in rice protein, such as Figure 3 As shown, the free sulfhydryl content of acylated rice protein was significantly lower than that of natural rice protein. From RP to SA-RP50, the free sulfhydryl content decreased by a total of 27 μM / g, a reduction of 31.8%, and the decrease was positively correlated with the degree of acylation. This is because free sulfhydryl groups are cross-linked during the succinylation reaction. The decrease in free sulfhydryl content indicates an increase in the degree of cross-linking between protein molecules. The formed disulfide bonds enhance the structural stability of the protein, which affects its functional properties such as solubility, gelation, and emulsification.

[0031] (4) Particle size and potential measurement The particle size, zeta potential, and polymer dispersion index (PDI) of the samples were determined at 25°C using water refractive index (1.33) and particle refractive index (1.46).

[0032] Figure 4-1 and Figure 4-2 The particle size, polymer dispersion index, and potential of the samples are shown. The results indicate that with increasing acylation degree, the particle size and polymer dispersion index of rice protein significantly decreased; compared to natural rice protein, the particle size of the SA-50 group was reduced by 60%. With increasing acylation degree, the absolute value of the zeta potential of the rice protein gradually increased. However, after the addition of succinic anhydride reached 30%, further increases in the amount of succinic anhydride did not affect the potential measurement results. The absolute value of the zeta potential increased from 7.9 mV to 25.8 mV, an increase of approximately 2.7 times. This increase in absolute value is related to the increase in electrostatic repulsion. This is because succinylation introduces a large number of carboxyl groups (-COOH), which carry a negative charge at pH=7.0. The increase in negative charge significantly enhances the electrostatic repulsion between protein molecules, increases the intermolecular distance, and reduces the formation of aggregates. The reduction in particle size and the improvement in distribution uniformity mean that the modified rice protein is easier to dissolve and disperse more uniformly, and can form a more stable structure in food systems. This has a positive impact on the functional properties of the protein. At the same time, smaller particle size also facilitates the digestion and absorption of proteins.

[0033] (5) Fourier transform infrared analysis KBr was placed in an oven and dried at 105℃ for 5 hours. The sample was then mixed with the dried KBr at a ratio of 1:80 (w / w), thoroughly ground, and pressed into a pellet for FTIR analysis. The temperature range was 400–4000 cm⁻¹.-1 The spectrum was obtained by scanning within a certain range, with a spectral resolution of 4 cm⁻¹. -1 The sample was scanned 16 times. The KBr spectrum was used as the background for sample correction.

[0034] Fourier transform infrared results as follows Figure 5 At 3300 cm -1 (NH stretching vibration), 1652 cm -1 (C=O stretching vibration) and 1516 cm -1 The peak value of RP was observed at (CN stretching vibration and NH in-plane bending vibration), where 3300 cm⁻¹ -1 and 1652cm -1 Belongs to the amide I band, 1516 cm -1 It belongs to the amide II band. The results show that the areas of the three characteristic peaks of rice protein increase with increasing acylation degree, which is due to the change in vibrational properties after the amino group is covalently modified by the succinyl group.

[0035] (6) Color difference analysis Colorimeters were used to analyze the color differences between different samples.

[0036] Figure 6 The results of color difference analysis of succinylated rice protein show that the L* value continuously decreases, indicating that the sample gradually darkens; the a* value continuously increases, indicating that the sample is slightly reddish; and the b* value increases significantly, indicating that the sample is significantly yellowish. Overall, succinylation darkens and yellows the rice protein, and the degree of change is positively correlated with the degree of acylation. This is because succinylation induces protein unfolding and denaturation, making some amino sites that are not normally readily involved in the reaction more accessible. Since the reaction is carried out in a 40℃ water bath for 90 minutes, prolonged heating may promote the Maillard reaction. These amino groups react with reducing sugars to form melanoidins, which are brown or yellow. Simultaneously, heating under alkaline conditions (pH=8.5) may cause some amino acids to degrade, producing colored substances; these degradation products are yellow or brown.

[0037] (7) Surface hydrophobicity analysis Dilute the sample to 0.02 mg / mL–0.12 mg / mL with 10 mM phosphate buffer (pH=8.5). Mix 4 mL of protein solution with 20 μL of 8 mM 8-aniline-1-naphthalenesulfonic acid (ANS) solution and react in the dark for 5 min. Detection is performed using a fluorescence spectrophotometer with excitation wavelength set to 390 nm, emission wavelength set to 488 nm, and slit width set to 5 nm. Fluorescence intensity is used to plot protein solution concentration and perform linear regression.

[0038] The slope of the linear regression is used as an exponent of H0, such as Figure 7As shown, H0 is an important parameter for revealing the hydrophobic regions on the protein surface. Succinylation can reduce the H0 of RP, possibly because succinylation alters the tertiary structure of RG, reducing the proportion of hydrophobic regions and increasing electronegativity and charge density, thus affecting the binding of the ANS probe to the hydrophobic sites. Furthermore, steric hindrance may also contribute to the decrease in H0 of succinylated proteins due to structural changes after succinylation. With increasing succinic anhydride addition, the H0 of rice protein gradually decreased, reaching its lowest point at 40%, where succinylation reduced the H0 of rice protein by nearly 4.5 times. Example

[0039] Weigh 2.4g of succinylated rice protein SA-RP 10 and add it to 20ml of deionized water. Stir magnetically for 30min to ensure complete hydration. Add an alkaline solution and stir continuously to adjust the pH to 8, 9, and 10 respectively. After the pH stabilizes, cover with plastic wrap and continue magnetic stirring for 30min. Stop stirring and incubate at 85℃ for 30min, then immediately in an ice-water bath. After cooling, store at 4℃ overnight to obtain rice protein gel. The alkaline solution is a 1M NaOH aqueous solution. Example

[0040] Weigh 2.4g of succinylated rice protein SA-RP 20 and add it to 20ml of deionized water. Stir magnetically for 30 min to ensure complete hydration. Add an alkaline solution and stir continuously to adjust the pH to 8, 9, and 10 respectively. After the pH stabilizes, cover with plastic wrap and continue stirring magnetically for 30 min. Stop stirring and incubate at 85℃ for 30 min, then immediately in an ice-water bath. After cooling, store at 4℃ overnight to obtain rice protein gel. The alkaline solution is a 1M NaOH aqueous solution. Example

[0041] Weigh 2.4g of succinylated rice protein SA-RP 30 and add it to 20ml of deionized water. Stir magnetically for 30 min to ensure complete hydration. Add an alkaline solution and stir continuously to adjust the pH to 8, 9, and 10 respectively. After the pH stabilizes, cover with plastic wrap and continue magnetic stirring for 30 min. Stop stirring and incubate at 85℃ for 30 min, then immediately in an ice-water bath. After cooling, store at 4℃ overnight to obtain rice protein gel. The alkaline solution is a 1M NaOH aqueous solution. Example

[0042] Weigh 2.4g of succinylated rice protein SA-RP 40 and add it to 20ml of deionized water. Stir magnetically for 30 min to ensure complete hydration. Add an alkaline solution and stir continuously to adjust the pH to 8, 9, and 10 respectively. After the pH stabilizes, cover with plastic wrap and continue magnetic stirring for 30 min. Stop stirring and incubate at 85℃ for 30 min, then immediately in an ice-water bath. After cooling, store at 4℃ overnight to obtain rice protein gel. The alkaline solution is a 1M NaOH aqueous solution.

[0043] Example 10: Weigh 2.4g of succinylated rice protein SA-RP 50 and add it to 20ml of deionized water. Stir magnetically for 30 min to ensure complete hydration. Add an alkaline solution and stir continuously to adjust the pH to 8, 9, and 10 respectively. After the pH stabilizes, cover with plastic wrap and continue stirring magnetically for 30 min. Stop stirring and incubate at 85℃ for 30 min, then immediately in an ice-water bath. After cooling, store at 4℃ overnight to obtain rice protein gel. The alkaline solution is a 1M NaOH aqueous solution.

[0044] Example 11: The alkaline solution used in this embodiment is a 1M Na2CO3 aqueous solution, and the remaining steps and parameters are the same as in Example 6.

[0045] Example 12: The alkaline solution used in this example is a 1M Na2CO3 aqueous solution, and the remaining steps and parameters are the same as in Example 7.

[0046] Example 13: The alkaline solution used in this embodiment is a 1M Na2CO3 aqueous solution, and the remaining steps and parameters are the same as in Example 8.

[0047] Example 14: The alkaline solution used in this embodiment is a 1M Na2CO3 aqueous solution, and the remaining steps and parameters are the same as in Example 9.

[0048] Example 15: The alkaline solution used in this example is a 1M Na2CO3 aqueous solution, and the remaining steps and parameters are the same as in Example 10.

[0049] Comparative Example 2: Weigh 2.4g of rice protein RP and add it to 20ml of deionized water. Stir magnetically for 30min to ensure complete hydration. Add an alkaline solution while stirring continuously, adjusting the pH to 8, 9, and 10 respectively. After the pH stabilizes, cover with plastic wrap and continue magnetic stirring for 30min. Stop stirring and incubate at 85℃ for 30min, then immediately in an ice-water bath. After cooling, store at 4℃ overnight to obtain rice protein gel. The alkaline solution is a 1M NaOH aqueous solution.

[0050] Comparative Example 3: Weigh 2.4g of rice protein RP and add it to 20ml of deionized water. Stir magnetically for 30min to ensure complete hydration. Add an alkaline solution and stir continuously to adjust the pH to 8, 9, and 10 respectively. After the pH stabilizes, cover with plastic wrap and continue stirring magnetically for 30min. Stop stirring and incubate at 85℃ for 30min, then immediately in an ice-water bath. After cooling, store at 4℃ overnight to obtain rice protein gel. The alkaline solution is a 1M Na2CO3 aqueous solution.

[0051] Experiment 2: The rice gels prepared in Examples 6-15 and Comparative Examples 1-2 were tested and analyzed.

[0052] (1) Determination of gel strength The gel strength of the gel samples was tested using a texture analyzer equipped with a P / 0.5 probe. The speed before and after the test was 1 mm / s, the deformation distance was 15 mm, and the triggering force was 3 g.

[0053] The results of rice protein gel strength testing are as follows: Figure 8 As shown, the results indicate that gel strength exhibits a significant pH dependence and varies with the type of alkali. Both alkali solutions showed a strong pH dependence; as the pH increased from 8 to 10, the gel strength increased. This is because under high pH conditions, the rates of protein denaturation and cross-linking reactions accelerate. During stirring and water bath time, the high pH system can complete more cross-linking reactions, forming a more complete gel network.

[0054] in, Figure 8-1 The study investigated the gelation of rice protein induced by NaOH. Results showed that natural rice protein could only form a gel at pH 10, while acylated rice protein could form a gel at all pH values. The gel strength gradually increased with increasing succinic anhydride content. However, at pH 10, the gel strength decreased when the succinic anhydride content further increased to 50%. This may be due to the enhanced electrostatic repulsion of the rice protein caused by excessive acylation, resulting in over-stretching of the molecular chains. The highly stretched molecular chains are too flexible, lacking the rigidity and structural stability required to form a rigid network structure.

[0055] Figure 8-2The results showed that natural rice protein could not be induced to form a gel by Na2CO3, while acylated rice protein could be induced to form a gel. With increasing succinic anhydride addition, the gel strength of the rice protein gradually increased, but the absolute value was lower than that of NaOH. This is because the strong alkalinity of NaOH allows the protein to unfold more quickly and fully, thus exposing more reaction sites and forming a denser gel network. Meanwhile, Na2CO3 has a buffering effect, resulting in a more gradual pH change, while NaOH has no buffering capacity and provides more direct pH regulation; therefore, a momentarily high pH may be more conducive to rapid protein unfolding.

[0056] (2) Determination of gel water holding capacity A certain amount of rice protein gel was weighed and placed in a centrifuge tube. After centrifugation at 10000×g for 20 min, the supernatant was removed. The water holding capacity of the protein gel was calculated according to the following formula: Water holding capacity (%) = W1 / W0 × 100%; Where W1 is the total weight after removing the supernatant, and W0 is the sample weight.

[0057] Figure 9 The changes in water holding capacity of rice protein gel induced by NaOH and Na2CO3 were shown, exhibiting a trend similar to that of gel strength, indicating that the mechanical properties of the gel are closely related to its water retention capacity.

[0058] Figure 9-1 These are the results of NaOH-induced protein gel water-holding capacity measurement. For rice protein with the same degree of acylation, the gel water-holding capacity increases with increasing pH. This is because the gel network formed under high pH conditions is denser, with smaller inter-linking point spacing, a tighter network, and smaller gel pore size, effectively trapping water. Simultaneously, under high pH conditions, the protein carries a large number of negative charges, forming a hydration layer around these negative charges. Water molecules in this hydration layer are bound by electrostatic forces, further increasing the gel's water-holding capacity, making it difficult for water to be removed by centrifugation. Under the same pH conditions, the gel water-holding capacity also gradually increases with the degree of acylation of the rice protein.

[0059] Figure 9-2 The results are from the determination of water holding capacity of protein gels induced by Na2CO3. Similar to NaOH-induced gels, the water holding capacity of the gel also increases with increasing pH and degree of acylation.

[0060] in conclusion: (1) This study used succinic anhydride to chemically modify rice protein and systematically evaluated the effects of different succinic anhydride addition amounts (10-50%) on the physicochemical properties of rice protein. As the amount of succinic anhydride added increased, the ε-amino sites of rice protein were gradually occupied, reaching an acylation plateau (≈58%) at 40% addition, indicating that the available lysine residues for modification were close to saturation. Succinylation darkened and yellowed the color of rice protein, and the color difference was positively correlated with the degree of acylation. Succinylation reduced the particle size of rice protein by 60%, decreased the potential by 2.7 times, and transformed the protein conformation from "hydrophobic collapse" to "hydrophilic expansion," reducing surface hydrophobicity by nearly 4.5 times and increasing solubility by about 6 times.

[0061] (2) This study further evaluated the gel-forming ability of succinylated rice protein in different alkaline solutions (NaOH and Na2CO3). The results showed that under the induction of NaOH, natural rice protein could only form a fragile gel under strongly alkaline conditions of pH=10, while the gel strength of SA-RP 40 group reached the peak, which was 3.5 times higher than that of natural protein; the water holding capacity increased by about 40% at the same time. Under Na2CO3 induction, natural rice protein could not gel in the pH range of 8-10, while succinylated rice protein could gel. This indicates that succinylation extends the lower limit of pH tolerance for alkaline-thermal induced gels of rice protein. Although the absolute gel strength was 15-20% lower than that of the NaOH-induced group, the gel water holding capacity of the SA-RP 40 group (85.6%, 88.0%) in the pH range of 9-10 and the gel water holding capacity of the SA-RP 50 group (85.9%, 87.6%, 88.1%) in the pH range of 8-10 were comparable to those of the same modified group induced by NaOH.

[0062] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0063] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a gel based on alkali-thermal induction of succinylated modified rice protein, characterized in that: Includes the following steps: Step 1: Rice protein powder was dispersed in deionized water, and the pH was adjusted to 11.0 using sodium hydroxide solution. Succinic anhydride was added, and the mixture was heated and stirred in a water bath. After the reaction was completed, the reaction was stopped in a cold water bath, and the pH of the reaction system was adjusted to 7.

0. After dialysis, the mixture was freeze-dried to obtain succinylated rice protein. Step 2: Succinylated rice protein was added to deionized water and magnetically stirred to obtain an aqueous solution of succinylated rice protein. An alkaline solution was added to the aqueous solution of succinylated rice protein and stirred to obtain an alkaline aqueous solution of succinylated rice protein. After the pH of the alkaline aqueous solution of succinylated rice protein stabilized, the solution was capped and heated in a water bath with stirring. After the reaction was completed, the solution was transferred to an ice-water bath and stored overnight to obtain rice protein gel.

2. The method for preparing gel based on alkali-thermal induction of succinylated modified rice protein according to claim 1, characterized in that: In step 1, the amount of succinic anhydride added is 10-50% of the total mass of rice protein.

3. The method for preparing gel based on alkali-thermal induction of succinylated modified rice protein according to claim 1, characterized in that: In step 1, the water bath temperature is 40℃; the stirring reaction time is 90 min, and the pH value of the reaction system is controlled at 8.5±0.5 using sodium hydroxide solution.

4. The method for preparing gel based on alkali-thermal induction of succinylated modified rice protein according to claim 1, characterized in that: In step 1, the dialysis temperature is 4℃ and the dialysis time is 48h.

5. The method for preparing a gel based on alkali-thermal induction of succinylated modified rice protein according to claim 1, characterized in that: In step 2, the alkaline solution is an aqueous solution of sodium hydroxide or an aqueous solution of sodium carbonate.

6. The method for preparing a gel based on alkali-thermal induction of succinylated modified rice protein according to claim 1, characterized in that: In step 2, the pH value of the alkaline aqueous solution of succinylated rice protein is 8-10.

7. The method for preparing a gel based on alkali-thermal induction of succinylated modified rice protein according to claim 1, characterized in that: In step 2, the water bath temperature is 85℃; the stirring reaction time is 30 minutes.

8. The method for preparing a gel based on alkali-thermal induction of succinylated modified rice protein according to claim 1, characterized in that: In step 2, the overnight storage temperature is 4°C.

9. The rice protein gel prepared by the method according to any one of claims 1 to 8.

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