A compound modified protein ingredient for improving the cooking quality of rice noodles and a preparation method thereof

Abstract

The present application relates to the field of food processing technology, and particularly to a compound modified protein ingredient for improving the cooking quality of rice noodles and a preparation method thereof.The present application uses mung bean protein and black bean protein as raw materials, which are respectively modified by ultrasonic wave and glutamine transaminase, and then compounded in proportion to obtain the compound modified protein ingredient.The compound modified protein ingredient prepared by the present application has a significantly reduced particle size, enhanced structure flexibility and improved emulsification stability.Adding the compound modified protein ingredient to the rice flour system can significantly reduce the peak viscosity, disintegration value and retrogradation value of the rice flour, and improve the hot paste stability;the broken noodle rate of the prepared rice noodles can be reduced to 2.54% or less, the cooking loss rate can be reduced to 5.38% or less, the elasticity can be improved to 0.86 or more, and the cohesiveness and resilience are significantly improved, and the protein digestion rate is increased to 87% or more.The present application effectively solves the problems of poor cooking quality, single nutrition and insufficient storage stability of traditional rice noodles.

Description

Technical Field

[0001] This invention relates to the field of food processing technology, specifically to a compound modified protein ingredient for improving the cooking quality of rice noodles and its preparation method. Background Technology

[0002] Rice noodles are a representative traditional staple food in southwestern and southern my country, beloved by consumers for their smooth, chewy texture and easy digestibility. However, traditional rice noodles are mostly made from refined indica rice, which typically contains less than 7% protein, resulting in a limited nutritional profile. Furthermore, pure starch-based rice noodles generally suffer from high breakage rates, significant cooking losses, poor rehydration, and insufficient elasticity during cooking, severely hindering quality improvement and industrial development. Currently, methods for improving rice noodle quality mainly include physical modification, aging, fermentation, and the addition of quality improvers. Among these, adding exogenous proteins is a relatively effective method. Exogenous proteins contain abundant active groups that can interact with starch molecules through hydrogen bonds, hydrophobic interactions, and electrostatic interactions, promoting the formation of a protein-starch complex network structure. This improves the gel strength, tissue stability, and cooking stability of the rice noodle system, addressing issues such as easy breakage, high cooking losses, and insufficient taste.

[0003] Existing research indicates that adding plant proteins such as soy protein isolate, mung bean protein, and black bean protein to rice flour systems can alter the gelatinization properties of starch, reduce peak viscosity and disintegration value, improve the thermal stability of the starch system, and enhance the structural strength of rice noodles to some extent. However, natural plant proteins typically suffer from drawbacks such as compact molecular structure, high aggregation degree, and insufficient exposure of internal active groups. This results in limited effective binding sites between protein and starch molecules, insufficient protein-starch interaction, and difficulty in fully realizing their role in improving the quality of rice noodles.

[0004] Therefore, reducing the breakage rate and cooking loss of rice noodles, improving their texture and edible quality remain urgent technical problems to be solved in the field of rice noodle quality improvement. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a compound modified protein ingredient for improving the cooking quality of rice noodles and its preparation method.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for preparing a compound modified protein ingredient to improve the cooking quality of rice noodles includes the following steps:

[0008] (1) Using mung bean protein and black bean protein as raw materials, they were dissolved in deionized water and hydrated to prepare mung bean protein solution and black bean protein solution respectively;

[0009] (2) The mung bean protein solution and the black bean protein solution were subjected to ultrasonic treatment to obtain ultrasonically treated protein solutions. The ultrasonically treated protein solutions were then added to transglutaminase for enzymatic hydrolysis. After the reaction was completed, the solutions were subjected to enzyme inactivation treatment and freeze-dried to obtain modified mung bean protein and modified black bean protein, respectively.

[0010] (3) The modified mung bean protein and the modified black bean protein are compounded to obtain the compound modified protein ingredient.

[0011] Furthermore, the mass fraction of the mung bean protein solution and the black bean protein solution is 5%.

[0012] Furthermore, in step (2), the conditions for ultrasonic treatment are an ultrasonic power of 200-600W, a treatment time of 10-30 min, and a temperature of 15-20℃.

[0013] Furthermore, in step (2), the enzymatic hydrolysis specifically includes: preheating the protein solution after ultrasonic treatment in a water bath at 40-50℃, adding transglutaminase, and reacting at 40-50℃ and 80-100 rpm for 20-40 min.

[0014] Furthermore, the amount of transglutaminase added was 5-15 U / g, based on the mass of mung bean protein and black bean protein, respectively.

[0015] Furthermore, the amount of transglutaminase added was 10 U / g and 15 U / g, respectively, based on the mass of mung bean protein and black bean protein.

[0016] Furthermore, in step (3), the mass ratio of modified mung bean protein to modified black bean protein is 3:7 to 7:3.

[0017] Furthermore, in step (3), the mass ratio of modified mung bean protein to modified black bean protein is 6:4.

[0018] The present invention also provides the application of the compound modified protein ingredient prepared by the preparation method of the compound modified protein ingredient for improving the cooking quality of rice noodles in food processing.

[0019] The beneficial effects of adopting the above technical solution include:

[0020] This invention modifies mung bean protein and black bean protein using ultrasound-assisted transglutaminase (TGT) treatment. Utilizing ultrasound-assisted TGT hydrolysis, the proteins are moderately modified to regulate their structural and functional properties. The effects of ultrasound power and enzyme dosage on the secondary and tertiary structures, particle size, foaming properties, foam holding capacity, emulsifying activity, and emulsifying stability of the proteins are investigated. The preparation conditions of the modified proteins are optimized, and the resulting modified proteins are compounded in specific proportions to prepare a compound modified protein formulation. The compound modified protein formulation prepared using this method exhibits significantly reduced particle size, enhanced structural flexibility, and significantly improved emulsifying stability. When added to rice flour, it significantly reduces the peak viscosity, disintegration value, and retrogradation value of the rice flour. Specifically, modified mung bean protein reduces the peak viscosity by 496.33 cP and the disintegration value by 314.67 cP, while modified black bean protein reduces the disintegration value by 260.33 cP. The resulting protein-starch gel system consistently exhibits a higher storage modulus than loss modulus, with elasticity being the dominant characteristic. The resulting compound modified protein rice noodles exhibited a breakage rate reduced to 2.54% and a cooking loss rate reduced to 5.38%, representing reductions of 90.1% and 79.1% respectively compared to traditional rice noodles. Elasticity was improved to over 0.86, with significantly enhanced cohesion and resilience. Relative crystallinity increased to 23.94%, an increase of 88.4% compared to traditional rice noodles. Protein digestibility increased to over 87%, an increase of 83.3% compared to traditional rice noodles (48%). The predicted glycemic index (eGI) decreased from 71.72 to 56.71, a reduction of 21.0%. After 12 months of storage at 37℃ and 75% relative humidity, the increase in moisture content and fatty acid value was minimal, demonstrating significantly better storage stability than traditional rice noodles. The invention utilizes mung bean protein and black bean protein as raw materials, which are widely available and highly safe. Combined with ultrasound-assisted enzyme modification technology, it offers advantages such as mild reaction conditions, controllable process, and environmental friendliness, making it highly valuable for application and promotion. Attached Figure Description

[0021] Figure 1 The diagrams show the secondary structure packing diagrams of the modified proteins of this invention, where: A is the secondary structure packing diagram of modified MBP with different ultrasonic powers; B is the secondary structure packing diagram of modified MBP with different enzyme addition amounts; C is the secondary structure packing diagram of modified BBP with different ultrasonic powers; and D is the secondary structure packing diagram of modified BBP with different enzyme addition amounts.

[0022] Figure 2 The images show the fluorescence spectra of the modified proteins of this invention, where: A is the fluorescence spectrum of modified MBP with different ultrasonic powers; B is the fluorescence spectrum of modified MBP with different enzyme addition amounts; C is the fluorescence spectrum of modified BBP with different ultrasonic powers; and D is the fluorescence spectrum of modified BBP with different enzyme addition amounts.

[0023] Figure 3The emulsifying properties and emulsification stability of the modified protein of this invention are as follows: A represents the emulsifying properties and emulsification stability of modified MBP with different ultrasonic powers; B represents the emulsifying properties and emulsification stability of modified MBP with different enzyme addition amounts; C represents the emulsifying properties and emulsification stability of modified BBP with different ultrasonic powers; and D represents the emulsifying properties and emulsification stability of modified BBP with different enzyme addition amounts.

[0024] Figure 4 The images show the gelatinization curves of the modified protein-rice flour of this invention, where: A is the gelatinization curve of modified MBP-RF with different ultrasonic powers; B is the gelatinization curve of modified MBP-RF with different enzyme addition amounts; C is the gelatinization curve of modified BBP-RF with different ultrasonic powers; and D is the gelatinization curve of modified BBP-RF with different enzyme addition amounts.

[0025] Figure 5 The rheological properties of the modified protein-rice flour of the present invention are shown in the figures: A represents the rheological properties of modified MBP-RF with different ultrasonic powers; B represents the rheological properties of modified MBP-RF with different enzyme addition amounts; C represents the rheological properties of modified BBP-RF with different ultrasonic powers; D represents the rheological properties of modified BBP-RF with different enzyme addition amounts; the numbers 1 and 2 represent the G' and G” values, respectively.

[0026] Figure 6 The cooking characteristics of the modified protein-rice noodles of this invention are as follows: A represents the cooking characteristics of modified MBP-RNs with different ultrasonic powers; B represents the cooking characteristics of modified MBP-RNs with different enzyme addition amounts; C represents the cooking characteristics of modified BBP-RNs with different ultrasonic powers; and D represents the cooking characteristics of modified BBP-RNs with different enzyme addition amounts.

[0027] Figure 7 The short-range order of the modified protein-rice noodles of the present invention is defined as follows: A represents the short-range order of modified MBP-RNs with different ultrasonic powers; B represents the short-range order of modified MBP-RNs with different enzyme addition amounts; C represents the short-range order of modified BBP-RNs with different ultrasonic powers; and D represents the short-range order of modified BBP-RNs with different enzyme addition amounts.

[0028] Figure 8 The long-range order of the modified protein-rice noodles of the present invention is shown in the following figures: A represents the long-range order of modified MBP-RNs with different ultrasonic powers; B represents the long-range order of modified MBP-RNs with different enzyme addition amounts; C represents the long-range order of modified BBP-RNs with different ultrasonic powers; and D represents the long-range order of modified BBP-RNs with different enzyme addition amounts.

[0029] Figure 9 The microstructure of the modified MBP-RNs with different ultrasonic powers according to the present invention;

[0030] Figure 10 The microstructures of the modified MBP-RNs with different enzyme addition amounts of the present invention are shown.

[0031] Figure 11 The microstructure of modified BBP-RNs with different ultrasonic powers according to the present invention;

[0032] Figure 12 The microstructures of modified BBP-RNs with different enzyme addition amounts according to the present invention;

[0033] Figure 13 The XRD diffraction pattern of the modified protein rice noodles of this invention is shown below.

[0034] Figure 14 This is the microstructure of the compound modified protein rice noodles of the present invention;

[0035] Figure 15 Sensory evaluation of the compound modified protein rice noodles of this invention;

[0036] Figure 16 The protein digestibility of the compound modified protein rice noodles of this invention;

[0037] Figure 17 The starch hydrolysis rate of the compound modified protein rice noodles of this invention;

[0038] Figure 18 The storage stability of the compound modified protein ingredients of the present invention is defined as follows: A represents the change in moisture content of the compound modified protein ingredients during storage; B represents the change in fatty acid value of the compound modified protein ingredients during storage. Detailed Implementation

[0039] 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.

[0040] Unless otherwise specified, the reagents and materials used in this invention are all conventional reagents and materials in the art, which can be obtained commercially or prepared using conventional methods. Unless otherwise specified, the experimental methods used in this invention are all conventional experimental methods in the art.

[0041] In this invention, mung bean protein and black bean protein were purchased from Jushengyuan Biotechnology Co., Ltd., food grade, with a protein purity of ≥90%; transglutaminase (TG enzyme) was purchased from Shanghai Yuanye Biotechnology Co., Ltd., food grade, with an enzyme activity of 50 U / g; and indica rice was purchased from Jiangxi Wufeng Food Co., Ltd., food grade.

[0042] Example 1

[0043] 1.1 Experimental Methods

[0044] Weigh appropriate amounts of mung bean protein (MBP) and black bean protein (BBP), dissolve them in deionized water, hydrate for 4-8 h, and prepare a protein solution with a mass fraction of 5% (w / v). Then store it at 4℃ for later use. Ultrasonic-assisted enzymatic hydrolysis modification treatment was used. Two types of modification conditions were set for each protein sample: (1) Under the condition of fixed TG enzyme addition of 10 U / g (based on protein mass), different ultrasonic power gradients were set, namely 0 W, 200 W, 400 W and 600 W; (2) Under the condition of fixed ultrasonic power of 400 W, different enzyme addition gradients were set, namely 0 U / g, 5 U / g, 10 U / g and 15 U / g.

[0045] Ultrasonic treatment: A probe-type ultrasonic cell disruptor was used. The beaker containing the protein solution was placed in an ice-water bath, and the temperature was maintained at 15-20℃ throughout the process. The ultrasonic parameters were set to 2 seconds of operation and 2 seconds of interval, and the total ultrasonic treatment time was 10-30 minutes.

[0046] Enzymatic hydrolysis: The protein solution after ultrasonic treatment was preheated in a 45℃ water bath. TG enzyme was added according to the set enzyme amount (enzyme activity = 50 U / g), and quickly mixed. The mixture was then placed in a constant temperature water bath shaker and subjected to enzymatic hydrolysis at 40-50℃ and 80-100 rpm for 20-40 min. After the reaction, the solution was immediately placed in a 90℃ water bath for 10 min to inactivate the enzyme, followed by cooling in an ice-water bath to obtain the enzymatic hydrolysate. The hydrolysate was pre-frozen at -20℃ for 48 h, then freeze-dried in a freeze dryer for 48 h, followed by lyophilization in a freeze dryer for 48 h. The lyophilized samples were pulverized and passed through a 100-mesh sieve to obtain uniform modified protein powder. Each sample was labeled with a sample number and sealed for storage at -20℃ for later use. Detailed sample naming is shown in Table 1.

[0047] Table 1. Sample Nomenclature of Modified Proteins

[0048]

[0049] 1.2 Performance Testing

[0050] The modified protein samples prepared under the above different conditions were analyzed for structural characteristics and functional properties.

[0051] (1) Determination of the secondary structure of the modified protein: The secondary structure of the modified protein was detected by Fourier transform infrared spectroscopy (FTIR). 2.0 mg of the modified protein sample was accurately weighed and mixed thoroughly with 200 mg of KBr powder. The mixture was then scanned across the entire wavelength range of FTIR, from 4000 to 450 cm⁻¹. -1 The scanning rate is 4 cm. -1 The spectrum obtained after baseline correction and deconvolution was 1047 cm⁻¹. -1 1022cm -1 and 995cm -1 The absorbance value at the specified location was used to calculate the content of α-helix, β-sheet, β-turn, and random coil using Peakfit.

[0052] (2) Determination of the tertiary structure of modified protein: The tertiary structure of modified protein was determined by fluorescence spectrophotometer. The modified protein was dissolved in deionized water to prepare a protein sample solution with a concentration of 1.0 mg / mL. The test parameters were: excitation wavelength of fluorescence spectrum of 280 nm, scanning emission spectrum range of 300-500 nm, and excitation and emission slit width of 5 nm.

[0053] (3) Determination of modified protein particle size: Accurately weigh 0.250 g of modified protein sample, add deionized water to make up to 25 mL, place on a magnetic stirrer to fully hydrate for 4 h, centrifuge at 3000 × g for 10 min, take 1 mL of supernatant and make up to 10 mL of deionized water; use a laser particle size analyzer to determine the particle size and dispersion of the sample, select water as the optical model for light scattering, with a refractive index of 1.000.

[0054] (4) Determination of foaming and foam holding capacity of modified protein: After weighing the modified protein sample, deionized water was added and hydrated for 6 hours to prepare a solution with a concentration of 10 mg / mL. The liquid level at this time was recorded as H1. The protein solution was dispersed at 1000 r / min for 2 min, and the foam height was measured at 0 min (H2) and after standing for 30 min (H3). The foaming and foam stability were calculated according to the following formula:

[0055] ;

[0056] ;

[0057] (5) Determination of emulsifying activity and emulsion stability: The emulsifying activity index (EAI) and emulsifying stability index (ESI) of the modified protein were determined. Soybean oil was used as the oil phase, and 10 mg / mL modified protein sample solution was used as the aqueous phase. The mixture was stirred and mixed at 10000 r / min for 2 min with an oil-water volume ratio of 1:9. 50 μL of the bottom sample was taken and 10 mL of 0.1% (w / v) SDS solution was added. The absorbance was measured at 500 nm. The emulsifying activity and emulsion stability were calculated according to the following formula:

[0058] ;

[0059] ;

[0060] In the formula: D2 represents the dilution; C2 represents the protein concentration in the solution (g / mL); I is the optical path length (I=0.01); φ is the oil phase percentage (φ=0.1); A0 and A 60 These correspond to the absorbance values ​​of the emulsion after standing for 0 and 60 minutes, respectively.

[0061] 1.4 Experimental Results

[0062] (1) Secondary structure of modified protein: Results are attached. Figure 1 As shown, ultrasound-assisted enzyme modification can alter the secondary structure composition of MBP and BBP proteins. With increasing ultrasound power from 0 W to 600 W, the β-sheet content of MBP first increased and then decreased. Specifically, the β-sheet content in the 0 W, 200 W, 400 W, and 600 W treatment groups was 37%, 39.5%, 36.33%, and 35.85%, respectively, while the β-turn content increased from 24.77% to 25.87%. This indicates that ultrasound modification disrupts the ordered structure in MBP, causing the peptide chains to unfold and rearrange, forming more β-turn structures. With increasing enzyme addition from 0 U / g to 15 U / g, the β-sheet content decreased from 37.95% to 36.34%, while the β-turn and α-helix contents increased from 24.69% and 17.53% to 25.2% and 18.32%, respectively. As the ultrasonic power increases, the β-fold content of BBP first decreases and then increases (32.99% at 0 W, 31.89% at 200 W, 33.18% at 400 W, and 32.85% at 600 W), while the β-turn and α-helix contents fluctuate slightly, and the random coil content remains stable.

[0063] The β-sheet content of BBP rebounded after ultrasonic treatment, possibly because the initial amino acid composition and structure of BBP are more stable. After ultrasonic treatment disrupts part of the β-sheet, the peptide chain refolds to form a new ordered structure, resulting in a partial recovery of the β-sheet content. With increasing TG addition, the β-turn of BBP-10U decreased to 26.83%, then increased to 27.26%. The β-sheet content increased to 33.36% at an enzyme addition of 5 U / g, then decreased to 33.06%. The contents of α-helices and random coils fluctuated within a small range. The results indicate that moderate ultrasonic modification and enzymatic modification can disrupt the ordered β-sheet structure and increase disordered structures such as β-turns and random coils. The increase in disordered structures makes the protein easier to unfold, exposes hydrophobic groups, improves structural flexibility, and comprehensively improves the protein's solubility, water retention, and emulsion stability.

[0064] (2) Tertiary structure of modified protein: Results are attached. Figure 2 As shown, the fluorescence emission wavelength range of all modified protein samples covered 300 nm to 460 nm. The fluorescence intensity of MBP was significantly lower than that of the modified protein. max The fluorescence intensity was approximately 340 nm, indicating that Trp residues were primarily encapsulated within the hydrophobic core of the protein, effectively shielding fluorescence. As the ultrasonic power increased, the protein structure unfolded, exposing the Trp residues to a polar aqueous environment. The surrounding dielectric constant was low, limiting non-radiative transition channels and significantly increasing fluorescence intensity. However, when the ultrasonic power reached 600 W, the protein molecules may re-aggregate, and the Trp residues were once again encapsulated in the hydrophobic region, resulting in a rebound in fluorescence intensity. With increasing TG enzyme addition, the intensity of MBP-0U significantly increased, followed by decreases in MBP-5U and MBP-10U, and an increase in MBP-15U. This may be because enzyme treatment induced the exposure of tryptophan residues to a polar aqueous environment, allowing their excited state to be more efficiently inactivated via non-radiative pathways through hydrogen bonding with water molecules, leading to a decrease in fluorescence intensity. Excessive enzymatic digestion (15 U / g) may cause small peptide aggregation, allowing the Trp residues to re-enter the hydrophobic microenvironment, resulting in a rebound in fluorescence intensity.

[0065] The fluorescence intensity of BBP is significantly higher than that of MBP, λ maxThe fluorescence intensity was 360 nm, indicating that the initial microenvironment of Trp residues in BBP was more hydrophobic, making fluorescence easier to excite. With increasing ultrasonic power, the fluorescence intensity first increased and then decreased: the intensity of BBP-0W and BBP-200W gradually increased, while the intensity of BBP-400W and BBP-600W significantly decreased. The results show that moderate ultrasonic modification and enzymatic modification can significantly improve fluorescence intensity by disrupting the higher-order structure of the protein, exposing Trp residues to a hydrophobic microenvironment; while higher-intensity modification may lead to the exposure of Trp residues to a polar environment, causing fluorescence quenching, or it may induce peptide aggregation, causing the Trp residues to re-enter a hydrophobic microenvironment, resulting in a partial recovery of fluorescence intensity.

[0066] (3) Particle size of modified protein: The results are shown in Table 2. The average particle size of MBP is 296.90 nm, and the dispersion is as high as 60.9, indicating that MBP is easy to polymerize and the particle size distribution is uneven. The particle size of MBP-0W decreased to 70.53 nm, and the dispersion decreased to 40.88. With increasing ultrasonic power, the particle size increased, while the dispersion initially increased and then decreased. Specifically, the particle size of MBP-600W increased to 113.13 nm, indicating that increased ultrasonic power caused the dissociated small particles to re-aggregate due to hydrophobic interactions, leading to an increase in particle size. (Ultrasonic treatment mechanically disrupts the protein aggregation structure, resulting in a decrease in dispersion and a more uniform particle size distribution.) After TG modification, the particle size of MBP further changed: MBP-0U decreased to 102.37 nm, and MBP-5U further decreased to 90.34 nm. Subsequently, the particle size of MBP-10U and MBP-15U increased to 123.3 nm. The dispersion fluctuated within a small range (56.6-65.63), but remained lower than that of MBP overall. The results show that appropriate enzyme treatment can alter the protein aggregation state. The average particle size of BBP was 519.33 nm. The average particle size was nm, with a dispersion of only 0.75, indicating that it exists as large aggregated particles in its natural state, but the particle size distribution is relatively uniform. After ultrasonic treatment, the average particle size continued to decrease, with BBP-0W decreasing to 234.33 nm, BBP-200W decreasing to 205.77 nm, BBP-400W rising back to 215.18 nm, and BBP-600W further decreasing to 189.43 nm, which is consistent with the effect of ultrasonic treatment on MBP; the dispersion of BBP-200W decreased to 0.17, and increased with increasing ultrasonic power, but was still significantly lower than that of BBP ( p < 0.05). The results show that the aggregated structure is more easily and completely disintegrated under ultrasonic action, and the particle size distribution is more uniform.

[0067] The particle size of BBP-0U decreased to 170.93 nm. After TG modification, the particle size of BBP-5U, BBP-10U, and BBP-15U rebounded to 200.7 nm, with a continuous decrease in dispersion, indicating that the enzymatically modified BBP has a more uniform particle size distribution. The results show that moderate ultrasonic modification and enzymatic modification can effectively reduce protein particle size, destroy aggregate structures, and reduce dispersion, resulting in a more uniform particle size distribution.

[0068] Table 2 Particle size of modified protein

[0069]

[0070] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0071] (4) Foaming and foam holding properties of modified proteins: The results are shown in Table 3. The foaming property of MBP was 33.35%, and the foam holding property was 16.70%. As the ultrasonic power increased from 0 W to 600 W, the foaming property of MBP-0W increased significantly to 55.57%, and the foam holding property increased to 50.08%. The foaming property of MBP-200W decreased to 30.55%, but the foam holding property was the highest among all modified proteins (72.77%), indicating that although ultrasonic treatment reduced the adsorption rate of the protein, the resulting interfacial film was more stable. Subsequently, the foaming properties of MBP-400W and MBP-600W gradually increased to 48.52% and 41.67%, respectively, while the foam holding properties decreased to 50.08% and 46.67%, respectively. It is speculated that this was because excessive ultrasonic treatment caused the dissociated small peptides to re-aggregate, partially restoring the protein's adsorption capacity, but the stability of the interfacial film decreased. After TG modification, the foaming performance of MBP was further improved. MBP-0U achieved foaming and foam holding properties of 55.56% and 50.00%, respectively, while MBP-5U achieved a foam holding property of 56.25%, demonstrating good foam stability. This is because although enzyme catalysis reduced the adsorption rate, it enhanced the stability of the interfacial film.

[0072] The foaming property of BBP was 31.49%, and its foam holding capacity was 18.22%. After ultrasonic treatment, the foaming properties of BBP-0W, BBP-200W, and BBP-400W decreased to 11.16%, 17.16%, and 6.07%, respectively, while the foam holding capacity remained at around 50%. After TG modification, the foaming properties of BBP-0U, BBP-5U, and BBP-10U decreased to 24.33%, 16.68%, and 6.1%, respectively, while the foam holding capacity increased to 22.24%, 16.67%, and 50.05%, respectively.

[0073] Table 3. Foaming and foam-holding properties of modified proteins

[0074]

[0075] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0076] (5) Emulsifying activity and emulsion stability: Results are attached. Figure 3 As shown, ultrasound-assisted enzyme modification effectively improves the emulsification properties of mung bean protein (MBP) and black bean protein (BBP). The EAI of unmodified MBP is 16.77 m² / g, and the ESI is 28.69%. As the ultrasound power increases from 0 W to 600 W, the EAI first decreases and then increases: the EAI of MBP-0W decreases to 9.03 m² / g, while the EAI of MBP-200W, MBP-400W, and MBP-600W increase to 12.62 m² / g, 11.39 m² / g, and 12.62 m² / g, respectively. The ESI shows a trend of first increasing and then decreasing, indicating that appropriate ultrasound treatment can improve the protein molecular structure and enhance its interfacial stability. With increasing enzyme addition, the EAI of MBP-5U decreased to 11.05 m² / g, while that of MBP-15U increased to 12.13 m² / g. At enzyme addition levels of 5 U / g and 10 U / g, the initial cross-linking masked some hydrophobic groups, reducing the protein's adsorption efficiency at the oil-water interface. However, when the enzyme addition increased to 15 U / g, the excessive cross-linking formed soluble or insoluble aggregates, potentially increasing particle stabilization and thus emulsifying activity. The ESI initially increased and then decreased, reaching a peak of 78.07% with MBP-10U and decreasing to 68.19% with MBP-15U. This indicates that appropriate enzyme addition (10 U / g) can induce moderate cross-linking of proteins, forming a structurally stable interfacial film with suitable adsorption capacity, thereby significantly improving emulsifying stability.

[0077] For BBP, its emulsifying properties also changed significantly after ultrasonic treatment. When the ultrasonic power was increased to 200 W, the EAI of BBP decreased to 21.62 m² / g. After further increasing the ultrasonic power to 400 W, the EAI increased further, and the ESI reached its maximum value of 86.89%. After TG modification, both the EAI and ESI of BBP showed a trend of first increasing and then decreasing, indicating that moderate enzymatic hydrolysis can significantly improve interfacial adsorption and stabilization capacity. Further enzymatic hydrolysis leads to peak interfacial membrane stability, while excessive enzymatic hydrolysis causes small peptide aggregation, destroying the compactness of the interfacial membrane and causing a decrease in ESI.

[0078] Example 2

[0079] Rice was ground in a grinder and passed through a 100-mesh sieve. The final moisture content of the rice flour was adjusted to 35% (w / w, on a dry basis). Modified protein was added at a rate of 5% (w / w) and thoroughly mixed. Extrusion was performed using a twin-screw extruder and a 1.5 mm aperture rice noodle die. The extruder had three temperature control zones, set at 60℃, 90℃, and 95℃ respectively. Extrusion began when all three zones reached 85℃. After the temperatures in all three zones stabilized, the extruded rice noodles were collected and aged in a constant temperature and humidity chamber at 15℃ and 80% humidity for 12 hours, followed by drying at 25℃ and 30% humidity for 2 hours. The dried rice noodles were then stored at 4℃. The rice flour samples were named after the modified protein, RNs.

[0080] 2.1 Performance Testing

[0081] (1) Determination of the gelatinization characteristics of rice flour with added modified protein: Take 3.0 g of each group of rice flour samples and 25 mL of deionized water and put them into an aluminum box. The torque is 700 cmg. The heating program is 10℃ / min to heat from 50℃ to 95℃ and hold for 3 min. Then, cool to 50℃ at the same heating rate and hold for 2 min. Measure the peak viscosity (PV), valley viscosity (TV), disintegration value (BD), final viscosity (FV), retrogradation value (SB), peak time (PTe) and peak temperature (PT).

[0082] (2) Determination of rheological properties of rice flour with modified protein: Each group of rice flour samples was placed on the MCR rheometer testing platform for rheological frequency scanning to determine gel strength. The test probe was PP50, the pre-test speed was 0.5 mm / s, the test speed was 5.0 mm / s, the compression distance was 1.0 mm, the trigger force was 5.0 g, and the compression interval was 2 s. The ratios of storage modulus (G') and loss modulus (G") to frequency were collected.

[0083] (3) Determination of the textural properties of rice noodles with modified protein: The textural properties of the modified protein rice noodles were determined using a texture analyzer. During the test, hardness, adhesiveness, elasticity, etc., were measured using a P / 36R probe. The test parameters were as follows: speed before test was 2.0 mm / s, test speed was 1.0 mm / s, speed after test was 5.0 mm / s, deformation was 50%, holding time was 5.0 s, and applied force was 0.098 N.

[0084] (4) Determination of breakage rate: Take the rice noodles from each group that have completed extrusion, aging, and drying, place them in 500 mL of boiling water and cook for 10 minutes. After draining, remove the excess water and absorb any remaining moisture with filter paper. Place them on a plate, and separate the rice noodles with a length less than 10 cm and those longer than 10 cm, and weigh them separately. The breakage rate is calculated using the following formula:

[0085] ;

[0086] In the formula: BR is the breakage rate of rice noodles; m1 is the mass of rice noodles with a length of less than 10 cm; m2 is the mass of rice noodles with a length of more than 10 cm.

[0087] (5) Determination of cooking loss rate: Take the rice noodles that have been extruded, aged and dried in each group, put them in 1000 mL of boiling water and cook for 10 min. Collect all the cooking liquid and transfer it to a 500 mL beaker that has been pre-weighed. Evaporate to constant weight at 100℃ and weigh the resulting residue. Calculate the cooking loss rate according to the following formula.

[0088] ;

[0089] In the formula: LS is the cooking loss rate; m1 is the mass of the evaporation residue; m2 is the sample mass.

[0090] (6) Color determination of rice noodles with added modified protein: The color of each group of rice noodle samples was measured using a colorimeter, and the color of each group of rice noodle samples was recorded. L * , a * , b * value. L * Indicates the brightness of a color (0-100), where 0 represents black and 100 represents white; a * This represents the redness or greenness of a color, where a positive value represents red and a negative value represents green. b * The value represents the yellow-blue tint of a color, where a positive value represents yellow and a negative value represents blue. Whiteness W is calculated using the following formula.

[0091] ;

[0092] In the formula: W represents whiteness; L * Brightness; a * Indicates the red-green hue of a color; b * It indicates the yellow-blue tint of the color.

[0093] (7) Determination of thermodynamic properties of rice noodles with modified protein: 2.0 mg of each group of rice noodle samples were weighed and added to deionized water to prepare a suspension with a mass ratio of 1:3. The suspension was placed in a DSC crucible and then stored at 4°C overnight. The test conditions were set to heat the samples from 30°C to 120°C at a rate of 10°C / min to measure the enthalpy change curve and obtain the initial temperature (T) at which the sample gelatinized. o Peak temperature (T) p ), termination temperature (T) c The gelatinization enthalpy (ΔH) was measured using an empty crucible as a control.

[0094] (8) Determination of short-range ordering of rice noodles with modified protein: The rice noodle samples of each group were ground and passed through a 120-mesh sieve. 2.0 mg of each group's rice noodle sample was mixed evenly with 200 mg of KBr powder, and the mixture was scanned in the full band using a Fourier transform infrared spectrometer. The infrared spectrometer scanning range was 4000-400 cm⁻¹. -1 Scan rate: 4 cm -1 An average of 32 scans were performed.

[0095] (9) Long-range order determination: The dried rice noodle samples were ground and passed through a 100-mesh sieve and equilibrated at 26℃ for 24 h. X-ray diffraction (XRD) was performed using an X-ray diffractometer with an angle range of 2θ = 5-50° and a scanning speed of 8° / min. The relative crystallinity (RC) was calculated.

[0096] (10) The determination of microstructure includes the following steps: slice each group of rice noodle samples, fix the cross-section facing upward on the sample stage, spray gold, and then use a scanning electron microscope (SEM) to observe the micro-particle morphology of the rice noodles at 1500, 2500 and 4000 magnification respectively.

[0097] 2.2 Test Results

[0098] (1) Gelatinization characteristics of rice flour with added modified protein: The results are presented in the appendix. Figure 4As shown in Table 4, the gelatinization curves of indica rice flour and the mixed rice flour with modified protein exhibit typical starch gelatinization characteristics: the viscosity remains at a very low level in the initial heating stage, begins to rise rapidly at about 200 s, reaches the gelatinization PV at about 400 s, then the viscosity decreases slightly during the hot gelatinization stability stage, and increases significantly again during the cooling and retrogradation process. Compared with RF, the gelatinization initiation time of the MBP groups treated with different ultrasonic powers did not change significantly, and the PV was significantly reduced, with MBP400W-RF having the lowest PV. The viscosity during the cooling and retrogradation stage was also significantly lower than that of RF. The PV of rice flour in the MBP groups treated with different amounts of TG enzyme first decreased and then increased, with the PV of MBP10U-RF and SB decreasing to the lowest. The PV of all modified BBP-RF was significantly reduced, with BBP5U-RF having the lowest PV.

[0099] Compared to RF, all modified groups showed varying degrees of reduction in PV, TV, FV, BD, and SB, while PT significantly increased. In the U-MBP group, as the ultrasonic power increased from 0 W to 600 W, the PV value first decreased and then increased, with MBP400W-RF reaching the lowest value of 2391.67 cP, a decrease of 496.33 cP compared to MBP0W-RF. In the E-MBP group, PV decreased to the lowest level at an enzyme addition of 10 U / g and increased at 15 U / g. The U-BBP and E-BBP groups showed similar trends, with BBP600W-RF's PV decreasing to 2808.33 cP, and BBP5U-RF's PV being the lowest in the E-BBP group at 2487.33 cP. These results indicate that the modification treatment may significantly inhibit gelatinization by affecting starch-water interactions, limiting starch chain extension and amylose dissolution. TV represents the lowest viscosity of starch gelatinized at high temperatures. The TV of all modified groups was lower than that of the original protein-RF. The TV of MBP400W-RF and MBP15U-RF decreased to 2039 cP and 1904 cP, respectively, while the TV of BBP600W-RF and BBP15U-RF were 2302 cP and 2266.67 cP, respectively. The results indicate that the modification treatment enhanced the viscosity stability of the system at high temperatures. This may be because the modified protein exposed active groups, forming a denser network structure, which enhanced its interaction with starch, thereby inhibiting the excessive expansion and rupture of starch granules and improving the thermal stability of the system.

[0100] BD reflects the degree of viscosity decay of starch under high-temperature shear; the lower the BD value, the stronger the thermal paste stability of the starch. The BD value of MBP400W-RF (352.33 cP) is 47.18% lower than that of RF (667 cP), and the BD value of MBP10U-RF is significantly lower. p(< 0.05), the BD values ​​of BBP400W-RF and BBP5U-RF also decreased to 506.67 cP and 407.67 c, respectively.

[0101] SB reflects the degree of viscosity retrogradation of starch during cooling. In the U-MBP group, MBP0W-RF had the lowest SB value (2408.67 cP). With increasing ultrasonic power, the SB value of MBP600W-RF increased to 2552.67 cP. The SB value of MBP15U-RF (1766 cP) was the lowest in the E-MBP group, decreasing by 700 cP compared to RF. The SB values ​​of both the U-BBP and E-BBP groups were significantly lower than those of RF. p < 0.05), and the SB values ​​of BBP400W-RF and BBP5U-RF were 2263 cP and 2035 cP, respectively, indicating that appropriate ultrasonic treatment may promote the formation of protein networks and slow down starch retrogradation.

[0102] The PT values ​​of both the U-MBP and U-BBP groups reached their maximum values ​​at an ultrasonic power of 400 W, while those of both the E-MBP and E-BBP groups reached their maximum values ​​at an enzyme addition of 10 U / g. This indicates that moderate modification increased the gelatinization initiation temperature and delayed the starch gelatinization process, likely due to the increased energy required for gelatinization resulting from the formation of the protein-starch complex. Excessive modification, on the other hand, may have disrupted the complex structure and reduced thermal stability. The results show that ultrasound-assisted TG enzyme treatment generally reduces PV, TV, and BD, inhibiting swelling and disintegration during starch gelatinization. Moderate ultrasound (and enzymatically modified MBP and BBP) can both inhibit starch granule gelatinization swelling, reduce peak viscosity and retrogradation value, and simultaneously improve thermal gelatinization stability by forming a stable complex system with starch.

[0103] Table 4 Gelatinization characteristics of modified protein-rice flour

[0104]

[0105] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0106] (2) Rheological properties of rice flour with added modified protein: The results are presented in the appendix. Figure 5 As shown, the G' values ​​of the four modified protein-rice flour systems were significantly higher than RF, and increased with increasing angular frequency, indicating that the elasticity of the starch gel was improved after modification. Figure 5In group A, the G' value of MBP400W-RF was the highest across the entire angular frequency range. In group C, the G' value of BBP400W-RF was also the highest across the entire angular frequency range, indicating that ultrasonic treatment can significantly enhance the elastic network structure of the protein-starch gel. In group B, the G' value of MBP10U-RF was significantly higher than that of RF. In group D, the G' value continued to increase with increasing enzyme addition, and the G' value of BBP15U-RF was significantly higher than that of other groups and RF, indicating that increasing enzyme addition can strengthen the elastic structure of the protein-starch gel. The G'' values ​​of all four modified protein-starch gel systems were higher than those of RF, and showed an increasing trend with increasing angular frequency, indicating that the viscosity of the system was also improved after modification. The results show that both ultrasonic and enzymatic modification treatments can increase the G' and G'' values ​​of protein-starch gels, and the G' value is always higher than the G'' value, indicating that the modified protein-starch gel is still mainly elastic.

[0107] (3) Texture properties of rice noodles with added modified protein: The results are shown in Table 5. The hardness, chewiness, and adhesiveness of MBP-RNs were 2278.69 g, 1024.55 g, and 1303.83 g, respectively, which were lower than those of RNs. However, the elasticity, cohesion, and resilience were higher than those of RNs, indicating that the addition of MBP can effectively reduce the hardness of rice noodles and improve their elasticity. In the U-MBP group, with the increase of ultrasonic power, the hardness, chewiness, and adhesiveness continued to decrease significantly, while the elasticity, cohesion, and resilience increased significantly. Among them, the elasticity of MBP400W-RNs increased to 0.86, the cohesion of MBP200W-RNs increased to 0.69, and the resilience of MBP600W-RNs increased to 0.49. In the E-MBP group, as the enzyme addition increased from 0 U / g to 15 U / g, elasticity, cohesiveness, and resilience first increased and then decreased, reaching their maximum at an enzyme addition of 10 U / g. This indicates that moderate enzymatic hydrolysis of MBP generates small peptides that form a more uniform complex network with starch, significantly improving the textural properties of rice noodles. The hardness, chewiness, and adhesiveness of BBP-RNs decreased to 1489.93 g, 780.57 g, and 930.65 g, respectively, while elasticity, cohesiveness, and resilience increased to 0.84, 0.62, and 0.43, respectively, showing better improvement than the MBP group.

[0108] The results showed that appropriate ultrasound-assisted TG-modified protein can effectively regulate the textural properties of rice noodles, reduce hardness, chewiness and adhesiveness, and improve elasticity and resilience, making the rice noodles more elastic. At the same time, the increase in cohesion indicates that the denser the internal structure, the less likely the rice noodles are to break and the less likely they are to be lost during steaming. This result is consistent with the conclusion on steaming characteristics, that is, the formation of protein-starch complex improves the textural properties of rice noodles.

[0109] Table 5. Texture properties of modified protein-rice noodles

[0110]

[0111] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0112] (4) Rice noodles with added modified protein: Results are as follows Figure 6 As shown, the addition of unmodified protein already had a significant quality improvement effect. BBP-RNs reduced the cooking loss rate to 10.47% and the breakage rate to 4.46%, while MBP-RNs reduced them to 14.68% and 11.48%, respectively. This indicates that protein can enhance the network structure of starch gel by interacting with starch, thereby reducing the dissolution of soluble substances and the breakage of rice noodles during cooking. The cooking loss rate and breakage rate of all modified groups were significantly reduced ( p < 0.05). As the ultrasonic power increased from 0 W to 400 W, the cooking loss rate and breakage rate of both the U-MBP and E-BBP groups decreased significantly, with MBP400W-RNs and BBP400W-RNs reaching the lowest values. When the ultrasonic power increased to 600 W, the cooking loss rate of BBP600W-RNs increased to 8.93% and the breakage rate increased to 3.92%, while that of MBP600W-RNs increased to 10.23% and 5.94%, respectively. With increasing TG enzyme addition, the cooking loss rates of MBP10U-RNs and BBP10U-RNs decreased to 7.81% and 9.87%, respectively, and the breakage rates decreased to 2.63% and 4.82%, respectively. When the enzyme addition increased to 15 U / g, the cooking loss rate and breakage rate increased. The cooking loss rate of MBP15U-RNs increased to 11.71%, and the breakage rate increased to 9.09%, while that of BBP15U-RNs increased to 9.53% and 3.77%, respectively. The results indicate that moderate ultrasonic treatment or enzymatic hydrolysis can significantly improve the cooking stability of rice noodles and effectively reduce the cooking loss rate and breakage rate; however, excessive modification treatment can degrade the cooking quality. This conclusion is consistent with the results showing improved cohesion and resilience in textural properties, confirming that the addition of modified protein to form a dense and stable protein-starch complex network can improve the cooking characteristics of rice noodles.

[0113] (5) Rice noodle color with added modified protein: The results of rice noodle color with different ultrasonic power and enzyme addition amounts of modified MBP and BBP are shown in Table 6. In the U-MBP group, as the ultrasonic power increased from 0 W to 400 W, L The * value increased from 51.61 to 54.48, and the W value increased from 49.08 to 51.89, significantly higher than RNs ( p< 0.05), while at 600 W L * and W values ​​decreased. In the E-MBP group, when the enzyme addition was 10 U... L The * and W values ​​reached their highest levels (54.48, 51.89), then decreased to 46.89 and 44.05 at 15 U. This may be because ultrasonic treatment or enzymatic hydrolysis unfolds the protein structure, reducing the scattering of light by protein aggregation, thereby improving brightness and whiteness. Excessive modification, however, may lead to an increase in protein degradation products or Maillard reaction products, reducing whiteness. The BBP600W-RNs in the U-BBP group... L The * value was 51.98, and the W value was 47.96, significantly higher than that of BBP-RNs ( p <0.05), in the E-BBP group, BBP5U-RNs L The * and W values ​​were the lowest, at 32.64 and 31.73 respectively, indicating that low enzyme addition levels may lead to a significant decrease in brightness and whiteness due to protein browning or pigment release. In the U-BBP group, as the ultrasonic power increased from 0 W to 600 W, the rice noodles... L The * and W values ​​increased significantly, with BBP600W-RNs achieving the highest luminance and whiteness. In the E-BBP group, BBP0U-RNs... L * and W values ​​are the highest, but as the amount of enzyme added increases, BBP-5U's... L The * and W values ​​decreased significantly, BBP10U-RNs increased, but BBP15U-RNs decreased again, indicating that the effect of enzyme treatment on color is not linear. a The * value reflects the redness of the sample, and the RNs a * Value is -1.19 (greenish), for MBP200W-RNs and MBP600W-RNs a * Values ​​are 0.28 and 0.18 (reddish) respectively, for MBP0U-RNs and MBP5U-RNs. a * Values ​​were 0.77 and 0.74 (significantly reddish), respectively. In the U-BBP group, BBP600W-RNs... a The value is 1.65, for BBP5U-RNs. a The * value was 1.41, which was significantly higher than RNs, indicating that the modification treatment increased the redness of the rice noodles. This may be due to the release of pigments from the protein or the occurrence of Maillard reaction promoted by ultrasound or enzymatic hydrolysis. Moderate modification can control the redness within an acceptable range. b The * value reflects the yellowness of the sample; all modified groups b * values ​​were all significantly higher than RNs ( p < 0.05), MBP600W-RNs b*The value of 17.06 is the highest in the U-MBP group, and the highest for MBP15U-RNs. b The value is 17.62 for BBP600W-RNs. b *Value is 20, BBP15U-RNs b The value of 15.56 indicates that the modification treatment generally improved the yellowness of the rice noodles.

[0114] Table 6. Color of Modified Protein-Rice Noodles

[0115]

[0116] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0117] (6) Thermodynamic properties of rice noodles with modified protein: The results are shown in Table 7. In the U-MBP group, as the ultrasonic power increased from 0 W to 400 W, T0 decreased from 80.84℃ to 65.22℃, and T... p The temperature dropped from 109.08℃ to 89.85℃, T c The temperature dropped from 138.09℃ to 115.91℃, significantly lower than that of RNs ( p < 0.05), while at 600 W, all temperatures increased; in the E-MBP group, when the enzyme addition was 10 U / g, T0 and T p and T c The temperatures dropped to their lowest levels (65.22℃, 89.85℃, 115.91℃), with a slight increase at 15 U / g. This indicates that moderate ultrasonic or enzymatic modification of MBP and starch formed a complex system, altering the thermal response characteristics of the starch crystallization region, lowering the temperatures required for gelatinization initiation and peak, thus shifting the phase transition temperature range forward and prolonging the gelatinization process. Excessive modification may have led to protein aggregation, increasing thermal stability and causing an increase in gelatinization temperature. The T0 and T2 values ​​of BBP600W-RNs... p and T c The T0 and T2 values ​​of BBP15U-RNs were 77.42℃, 107.27℃, and 132.25℃, respectively. p and T c The temperatures were 62.77℃, 99.3℃, and 128.29℃, respectively, all significantly lower than those of RNs and BBP-RNs ( ). p < 0.05), indicating that the modified BBP formed a thermally stable composite crystalline region with starch. ΔH reflects the heat absorbed or released during the starch phase transition and is directly related to crystallinity and structural order. The ΔH of the protein-added and modified protein groups was significantly higher than that of RNs (22.02 J / g). p< 0.05). The ΔH values ​​of MBP400W-RNs, MBP10U-RNs, BBP600W-RNs, and BBP15U-RNs were 143.42 J / g, 112.66 J / g, and 112.93 J / g, respectively. This indicates that the crystalline structure of rice starch was disrupted after extrusion, and the amorphous region increased. At the same time, the interaction between the modified protein and rice flour hindered the water absorption and swelling of the starch granules, requiring a higher temperature for gelatinization and more heat absorption during the phase transition.

[0118] Table 7 Thermodynamic properties of modified protein-rice noodles

[0119]

[0120] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0121] (7) Short-range ordering of rice noodles with added modified protein: Results are attached. Figure 7 As shown, compared with RNs, the rice noodle sample with added modified protein showed better performance at 1047 cm⁻¹. -1 The absorption peak intensity at 1022 cm⁻¹ has generally increased, while the intensity at 1022 cm⁻¹ has increased. -1 The relatively small changes indicate that the addition of modified protein promoted the ordered arrangement of starch molecular chains to some extent, thereby improving the short-range order of the system. Figure 7 A and Figure 7 As can be seen from C, with the increase of ultrasonic power, 1047 cm -1 The absorption peak gradually increases, indicating that ultrasonic treatment helps improve the molecular ordered structure of the system. Meanwhile, under different enzyme addition conditions ( Figure 7 B and Figure 7 D), as the amount of enzyme added increases, 1047 cm -1 The significantly enhanced absorption peak intensity indicates that the modified protein after enzyme treatment further promoted the ordered rearrangement of starch molecular chains, thereby improving the short-range order of the system. FTIR results show that appropriate ultrasonic treatment and enzyme treatment can effectively promote the interaction between protein and starch, improve the order of the rice noodle system, and thus facilitate the formation of a more stable and dense structural network.

[0122] (8) Long-range order of rice noodles with added modified protein: Results are attached. Figure 8 As shown, each sample at 13 ° and 20 °All samples exhibited distinct diffraction peaks, consistent with the characteristic diffraction peaks of a typical V-shaped starch crystal structure, indicating that starch and protein formed a protein-starch complex structure during processing. Compared to the relative crystallinity of RNs (12.71%), the RC values ​​of all samples significantly increased after the addition of modified protein, suggesting that the addition of modified protein promotes the rearrangement of starch molecular chains and the formation of a more stable crystal structure. Figure 8 A and Figure 8 As shown in Figure C, the relative crystallinity of the samples increased significantly with increasing ultrasonic power. The crystallinity of MBP600W-RNs and BBP600W-RNs increased to 23.66% and 22.14%, respectively, representing increases of 86.15% and 74.19% compared to RNs. This indicates that ultrasonic treatment can promote partial disruption of protein structure through cavitation, exposing more hydrophobic groups, thereby forming a more ordered complex structure with starch chains through hydrophobic interactions, promoting the ordered arrangement of starch molecules during gelatinization and retrogradation. When the ultrasonic power is too high, the trend of increasing crystallinity weakens, possibly because excessive mechanical action can lead to the destruction of some ordered structures. Figure 8 B and Figure 8 As shown in D, with the increase of enzyme addition, the relative crystallinity of the samples was significantly higher than that of RNs. The crystallinity of MBP10U-RNs reached the highest value of 23.52%, indicating that the addition of protein helps to stabilize the arrangement structure of starch molecular chains.

[0123] (9) Microstructure of rice noodles with added modified protein: Results are attached. Figure 9-12 As shown, RNs exhibit a relatively loose porous structure with obvious pores and irregular gaps. The structure is unevenly distributed, and the pore size is relatively large. This is a typical structure of starch-based rice noodles, mainly because the gel network structure formed by starch during gelatinization, aging, and drying is not dense enough. After some water evaporates, more voids remain in the system, resulting in a relatively loose internal structure. Figure 9In the study, significant changes in the internal structure of the modified protein-rice noodles were observed. Compared to RNs, the internal porosity of the MBP0W-RNs sample was significantly reduced, and the network structure gradually became more continuous and smooth. With increasing ultrasonic power (200 W, 400 W, and 600 W), the internal structure of the rice noodles gradually transformed from a loose porous structure to a denser layered or fibrous network structure, with a significant reduction in pore size and enhanced structural uniformity. This indicates that ultrasonic treatment can promote the unfolding of protein molecules through cavitation and mechanical shearing effects, and enhance the interaction between protein and starch, enabling the protein and starch molecules to form a more stable composite network structure, thereby improving the structural density of the system. However, under higher power conditions, obvious pores or structural breakage were still observed in some areas, indicating that excessively strong ultrasonic waves may damage the already formed network structure. Figure 11 In the modified protein-rice noodles, the structure of the modified protein-rice noodles showed increased density, indicating that ultrasonic treatment also promoted the interaction between BBP and starch. However, compared with group A, the network structure of group C samples was slightly coarser overall, with relatively obvious pores, which may be related to the differences in molecular structure and functional properties of MBP and BBP. With the increase of TG enzyme addition, the internal structure of the modified protein-rice noodles gradually changed from a relatively loose porous structure to a more uniform and dense network structure. Figure 10 and Figure 12 The relatively uniform pore distribution indicates that enzyme catalysis can enhance the flexibility of protein structure, making it easier to participate in the formation of network structure and interact with starch molecules, which is conducive to the formation of stable complex structure.

[0124] The results showed that the addition of modified protein could significantly change the microstructure of the rice noodle system, gradually transforming it from a relatively loose porous structure into a denser and more continuous network structure. This is consistent with the conclusion that short-range order and long-range order are reduced. This structural change indicates that a strong interaction has formed between the protein and starch, thereby enhancing the structural stability of the system and helping to improve the textural and cooking properties of rice noodles.

[0125] Example 3

[0126] Based on the experimental results of Examples 1 and 2, modified MBP prepared under conditions of 400 W ultrasonic power and 10 U / g TG enzyme addition, and modified BBP prepared under conditions of 400 W ultrasonic power and 15 U / g TG enzyme addition were selected for compounding. Using rice flour mass as the basis, the total added amount of the compounded modified protein was 5% (w / w). The modified MBP and modified BBP were mixed at mass ratios of 3:7, 4:6, 5:5, 6:4, and 7:3 to obtain the compounded modified protein ingredients. These compounded modified protein ingredients were used for rice noodle processing. Compounded modified protein rice noodles were prepared using a twin-screw extruder. Rice noodles prepared with different proportions of compounded modified protein ingredients were named Compound Modified Protein Rice Noodles I, II, III, IV, and V, respectively.

[0127] Rice was pulverized and passed through a 100-mesh sieve to obtain rice flour. The obtained rice flour was then processed into rice noodle samples (RNs) using a twin-screw extruder as a control group.

[0128] 3.1 Performance Testing

[0129] (1) Determination of breakage rate: Take rice noodle samples from each group and cook them in 500 mL of boiling water for 10 min. After taking them out, drain the water and use filter paper to absorb the residual water on the surface. Place them on a disk, pick out rice noodles with a length of less than 10 cm and more than 10 cm, weigh them separately, and calculate the breakage rate.

[0130] (2) Determination of cooking loss rate: Take rice noodles from each group and cook them in 1000 mL of boiling water for 10 min. Collect all the cooking liquid and transfer it to a 500 mL beaker that has been pre-weighed. Evaporate the liquid to constant weight at 100℃, weigh the residue, and calculate the cooking loss rate.

[0131] (3) Texture characteristics determination: The texture characteristics of each group of rice noodle samples were determined using a texture analyzer. A P / 36R probe was used for the test. The test parameters were: speed before test 2.0 mm / s, test speed 1.0 mm / s, speed after test 5.0 mm / s, deformation 50%, holding time 5.0 s, and applied force 0.098 N.

[0132] (4) Long-range ordering determination: The rice noodle samples of each group were ground and passed through a 120-mesh sieve. 2.0 mg of each group of modified protein rice noodle samples was mixed with 200 mg of KBr powder and the mixture was scanned in the full band using a Fourier transform infrared spectrometer. The infrared spectrometer scanning range was 4000-400 cm⁻¹. -1 Scan rate: 4 cm -1 An average of 32 scans were performed.

[0133] (5) Microstructure determination: Each group of rice noodle samples were sliced, fixed on the sample stage with the cross-section facing upwards, and sputtered with gold. The micro-particle morphology of the rice noodles was observed by SEM at 1500, 2500 and 4000 magnification respectively.

[0134] (6) Sensory evaluation: The evaluation panel consisted of 20 appropriately trained evaluators, half male and half female. The samples were transferred to plastic cups and provided to the evaluators in random order. Evaluation indicators included odor (0-20 points), taste (0-40 points), and appearance (0-40 points).

[0135] (7) Protein digestibility determination: 4.0 g of each group of rice noodle samples were placed into 50 mL centrifuge tubes, with 3 parallel samples in each treatment group. Artificial simulated gastric and intestinal digestive fluids were added sequentially for digestion. The entire digestion process was carried out in a constant temperature shaking water bath at 37℃ with a shaking speed of 180 r / min. After digestion, the samples were placed in a 90℃ water bath for 5 min to inactivate enzymes and terminate the reaction. The digestibility was calculated using the following formula.

[0136] ;

[0137] In the formula: W0 and W T These represent the protein content (g / 100 g) of the samples before and after digestion, respectively.

[0138] (8) Determination of in vitro starch digestibility: Accurately weigh 0.2 g of each group of rice noodle samples and white bread control samples, mix with 5 mL of sodium acetate buffer (pH 7.0), and heat in a 95℃ constant temperature water bath for 20 min to fully gelatinize. After naturally cooling to room temperature, add α-amylase and saccharifying enzyme sequentially to a concentration of 300 U / mL and 20 U / mL, respectively, and carry out enzymatic hydrolysis under a 37℃ constant temperature shaking water bath. Maintain uniform shaking during the reaction to ensure complete enzymatic hydrolysis. The glucose equivalent (DE) at different time points (0 min, 10 min, 20 min, 30 min, 60 min, 90 min, 120 min and 180 min) was determined by the 3,5-dinitrosalicylic acid (DNS) method. The specific operation is as follows: Centrifuge the enzymatically hydrolyzed mixture at 1700 ×g for 5 min, take the supernatant and react with DNS colorimetric reagent, place it in a 100℃ boiling water bath for color development, and heat in a boiling water bath for 10 min. After color development, the absorbance of the solution was immediately measured at the characteristic wavelength of 510 nm using a UV-Vis spectrophotometer, and the DE value was calculated. A hydrolysis kinetic curve was established, and the area under the curve (AUC) was obtained by integration to determine the hydrolysis index (HI). The GI value of the sample was then calculated based on the established mathematical model. All samples were measured three times.

[0139] The calculation formula is as follows:

[0140] ;

[0141] ;

[0142] In the formula: HI is the hydrolysis index; AUC is the area under the curve calculated from the sample hydrolysis rate curve; GI is the glycemic index; 39.71 and 0.549 are constants and coefficients for calculating the GI value.

[0143] (9) Storage stability test:

[0144] Moisture content determination: Accurately weigh 3.0g of each group of rice noodle samples and use a halogen moisture meter to determine the moisture content of the samples. All samples were measured in triplicate and the average value was taken.

[0145] The fatty acid value of the samples was determined according to GB / T 5510-2024 "Grain and Oil Inspection - Determination of Fatty Acid Value of Grains and Their Products". 10.00 g of crushed and sieved rice noodle sample was accurately weighed and placed in a stoppered conical flask. 50 mL of anhydrous ethanol was added, and the flask was sealed and placed on a constant-temperature shaker for 30 min for extraction. After extraction, the extract was filtered through rapid filter paper to obtain a clear extract. 25 mL of the filtrate was accurately transferred to a conical flask, and 2–3 drops of phenolphthalein indicator were added. Titration was performed with 0.01 mol / L potassium hydroxide standard titration solution until the solution turned slightly red and did not fade within 30 seconds, which was the titration endpoint. The volume of standard solution consumed was recorded. A blank control experiment was set up to eliminate reagent error. The fatty acid value of the samples was calculated based on the titration data. Three parallel experiments were performed for all samples, and the average value of the parallel determinations was taken.

[0146] (10) The compound modified protein rice noodles with the best overall performance were selected as the experimental group, while single modified protein rice noodles, unmodified rice noodles, and commercially available rice noodles were used as the control group. The cooking characteristics and texture characteristics of different rice noodle samples were compared and analyzed according to the above-mentioned methods for determining the breakage rate, cooking loss rate, and textural properties.

[0147] 3.2 Experimental Results

[0148] (1) Determination of breakage rate and cooking loss rate: The results are shown in Table 8. After adding the compound modified protein ingredients, both indicators of all compound modified protein rice noodle samples decreased significantly. p< 0.05), and as the proportion of BBP decreased (the compound ratio increased from 3:7 to 7:3), the breakage rate and cooking loss rate continued to decrease. Among them, the breakage rate and cooking loss rate of compound modified protein rice noodles I (MBP:BBP=3:7) were 12.15% and 10.73%, respectively, which were 56.3% and 58.3% lower than RNs. The breakage rate and cooking loss rate of compound modified protein rice noodles V (MBP:BBP=7:3) decreased to 2.74% and 5.91%, respectively, compared with RNs. RNs decreased by 90.1% and 77.0% respectively. The modified protein rice noodles IV (MBP:BBP=6:4) showed the most stable cooking characteristics, with both indicators reaching the lowest values ​​(2.54% and 5.38%). The results indicate that the modified protein ingredients significantly reduced the breakage rate and cooking loss rate of rice noodles. Moreover, this synergistic strengthening effect became more significant as the proportion of MBP increased. The cooking stability of the rice noodles was optimal when the ratio of modified mung bean protein to modified black bean protein was 6:4.

[0149] Table 8. Cooking characteristics of compound modified protein rice noodles

[0150]

[0151] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0152] (2) Texture properties determination: The results are shown in Table 9. After adding the compound modified protein ingredients, the texture properties of the compound modified protein rice noodles showed a regular change: the hardness decreased continuously and then rebounded as the proportion of BBP decreased. The hardness of compound modified protein rice noodles III (MBP:BBP=5:5) dropped to 1724.50 g, which was the lowest value among all samples. Subsequently, the hardness of compound modified protein rice noodles IV and V rebounded to 2133.77 g and 2164.93 g, respectively. The absolute value of adhesiveness first decreased and then increased. The absolute value of adhesiveness of compound modified protein rice noodles III was the lowest, at only 9.5 g. Elasticity and cohesion increased with the increase of MBP proportion. The elasticity of compound modified protein rice noodles IV reached 0.86, and the cohesion of compound modified protein rice noodles III reached 0.69. The trend of chewiness and adhesiveness was consistent with that of hardness, and both dropped to the lowest value (1005.53 g) at compound modified protein rice noodles III. After a period of decline (from 1181.50 g to 1234.30 g), the chewiness and adhesiveness of the modified protein rice noodles V increased to 1234.30 g and 1455.17 g, respectively; the resilience of the modified protein rice noodles III reached 0.4, the highest among all groups. These trends indicate that the combination of modified MBP and BBP can synergistically regulate the textural properties of rice noodles. The addition of BBP mainly reduces the hardness and adhesiveness of the rice noodles, while modified MBP mainly improves the elasticity, cohesion, and resilience of the rice noodles. The ratio of the two optimizes the texture of the rice noodles. When the ratio of modified mung bean protein to modified black bean protein is 5:5, the rice noodles have the lowest hardness, the weakest stickiness, and the best cohesion and resilience. When the ratio is 7:3, the chewiness and adhesiveness of the rice noodles are the best.

[0153] Table 9. Texture properties of compound modified protein rice noodles

[0154]

[0155] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0156] (3) Long-range order determination: The results are attached. Figure 13As shown, the relative crystallinity of the blank control group RNs was only 12.71%, and the diffraction peak intensity was low, indicating that the crystalline structure of pure starch-based rice noodles was relatively loose and the long-range order was weak. After adding compound modified protein ingredients, the diffraction peak intensity of all compound modified protein rice noodle samples was significantly improved, and the characteristic peaks at 13° and 20° diffraction angles were significantly enhanced. The relative crystallinity also showed a regular change: the RC of compound modified protein rice noodle I was 22.03%. As the proportion of MBP increased, the RC first increased and then decreased. Among them, the RC of compound modified protein rice noodle III (MBP:BBP=5:5) reached 23.94%, which was the highest value among all samples. Subsequently, the RC of compound modified protein rice noodles IV and V decreased to 23.57% and 22.81%, respectively, but were still much higher than those of the blank control group RNs. This indicates that the combination of modified MBP and BBP can promote the orderly arrangement of starch molecules through intermolecular forces such as hydrogen bonds and hydrophobic interactions, thereby enhancing the crystallinity and structural order of the rice noodle system.

[0157] (4) Microstructure determination: The results are attached. Figure 14 As shown, the cross-sectional surface of RNs is relatively rough, and the microstructure exhibits a large number of irregular pores without a clear continuous network structure, indicating that the microstructure of pure starch-based rice noodles lacks structural support and has poor density. After adding compound modified protein ingredients, the number of cross-sectional pores in compound modified protein rice noodles I (MBP:BBP=3:7) decreased, and the fibrous structure began to cross-link, but some large pores still existed. With the increase of modified MBP, the micropores of compound modified protein rice noodles II and III further decreased, and the degree of cross-linking of the network structure continued to increase. Among them, the microstructure of compound modified protein rice noodles III (MBP:BBP=5:5) was the most dense, with uniform pore distribution and extremely small pore size, forming a continuous and compact three-dimensional network. The microstructure of compound modified protein rice noodles IV and V still maintained high density, with only a few micropores. This result is consistent with the results measured by XRD, which showed an increase in relative crystallinity, enhanced structural integrity in cooking characteristics, and improved cohesion and elasticity in textural characteristics. From the overall cross-sectional morphology, the surfaces of all the modified protein rice noodles were smoother and more regular than those of RNs, and the uniformity of the cross-section remained stable with the increase of the modified MBP blending ratio. This indicates that the blending of modified MBP and BBP can form a cross-linked network through intermolecular hydrogen bonds and hydrophobic interactions, filling the pores in the starch matrix and thus improving the density of the rice noodle microstructure. When the blending ratio of modified mung bean protein and modified black bean protein is 5:5, the cross-linking effect between protein and starch reaches its optimal level, and the density and continuity of the micronetwork are the strongest. Even when the proportion of MBP is further increased, the cross-linking of protein and starch molecules can still maintain the density of the structure.

[0158] (5) Sensory evaluation: Results are attached. Figure 15As shown, the blank control RNs scored low in odor, structure, gloss, and smoothness, but high in viscosity and hardness, resulting in poor overall sensory performance. After adding the compound modified protein, the sensory evaluation indicators of all compound modified protein rice noodle samples significantly improved. Regarding odor, the overall scores of all compound modified protein rice noodle samples were at a high level, indicating that the addition of the compound modified protein ingredient did not have a significant negative impact on the aroma of the rice noodles. Among them, compound modified protein rice noodles II and III had higher odor scores, possibly due to a more balanced protein blend ratio, which reduced the potential beany smell from the soy protein. Regarding color, the color score of the compound modified protein rice noodles gradually increased with the increase in the modified MBP content. Compound modified protein rice noodles II and IV had higher color scores, while compound modified protein rice noodles I and V had relatively lower scores, which may be related to the darker color of the rice noodles when the modified MBP content is higher. In terms of structural properties, the modified protein rice noodles II, III, and IV scored higher, indicating that the addition of modified protein ingredients can promote the formation of a protein-starch complex network, thereby improving the integrity and stability of the rice noodle structure. Meanwhile, in terms of gloss, modified protein rice noodle IV scored higher, indicating that the addition of modified protein ingredients can make the surface structure of the rice noodles more uniform and dense, thus improving the surface gloss. Among the texture-related indicators, there were significant differences in viscosity, hardness, and smoothness. Specifically, modified protein rice noodles II and III scored higher in viscosity and smoothness, indicating that the addition of modified protein ingredients can enhance the network structure of the rice noodles and improve the elasticity of the starch gel system. In terms of hardness, all modified protein rice noodle samples were generally higher than the control group, indicating that modified protein ingredients help enhance the structural strength of the rice noodles. This is mainly because proteins can interact with starch molecules to form a more stable three-dimensional network structure, thereby improving the structural support capacity of the samples. Based on a comprehensive analysis of various sensory indicators, the overall sensory scores of the compound modified protein rice noodles IV and III are relatively high, indicating that within this compound ratio range, MBP and BBP can form a relatively ideal synergistic effect, thereby improving the overall quality of the rice noodles.

[0159] (6) Protein digestibility determination: Results are attached. Figure 16 As shown, the protein digestibility of RNs was significantly low, at only 48.18%. This is because pure starch-based rice noodles have extremely low protein content and lack protein structures that are easily broken down by digestive enzymes. Compared with RNs, the protein digestibility of each compound modified protein rice noodle sample was significantly improved. p< 0.05). The results showed that the protein digestibility of all compound modified protein rice noodles increased significantly after the addition of the compound modified protein ingredients. The protein digestibility of compound modified protein rice noodles I was 66.89%, which was 18.71% higher than that of RNs. As the proportion of modified MBP increased, the digestibility of compound modified protein rice noodles II and III continued to increase, reaching 73.81% and 78.46%, respectively. The protein digestibility of compound modified protein rice noodles IV was the highest (87.04%). When the proportion of modified MBP increased to 7:3, the protein digestibility of compound modified protein rice noodles V decreased to 79.06%, but it was still significantly higher than that of other groups.

[0160] (7) In vitro starch digestibility determination: Results are provided in Appendix Figure 17 It was found that the starch hydrolysis rate of each sample gradually increased with the extension of hydrolysis time. In the initial stage of digestion (0-30 min), the starch hydrolysis rate of all samples increased rapidly. This was mainly because the surface structure of starch granules was relatively loose, making them easily acted upon by digestive enzymes in the early stages of digestion, resulting in a high initial hydrolysis rate. Compared with RNs, the overall starch hydrolysis rate of each compound modified protein rice noodle sample was lower, indicating that the addition of compound modified protein ingredients inhibited the enzymatic hydrolysis process of starch to some extent. Especially in the middle and late stages of digestion (120-180 min), the hydrolysis rate of compound modified protein rice noodles was significantly lower than that of RNs. This indicates that the addition of compound modified protein ingredients can form a protein-starch complex network structure, creating a certain spatial barrier on the surface of starch granules, thereby reducing the contact between starch and digestive enzymes. Among the modified protein rice noodles with different blending ratios, modified protein rice noodle IV showed a lower starch hydrolysis rate overall, indicating that under this blending ratio, the composite structure formed between modified MBP and BBP was more stable, and its encapsulation and protection of starch molecules was more significant. Modified protein ingredients not only increase the protein content of rice noodles but also reduce the starch digestion rate to some extent. Modified protein rice noodle IV had a lower starch hydrolysis rate and the highest protein digestibility. The HI, pGI, and eGI results of the modified protein rice noodle samples are shown in Table 10. The HI, pGI, and eGI of RNs were 73.69, 79.17, and 71.72, respectively, all at a high level, indicating that pure starch-based rice noodles easily cause a rapid increase in postprandial blood glucose. Compared with RNs, the HI, pGI, and eGI values ​​of each modified protein rice noodle sample were significantly lower (…). p< 0.05 indicates that the compound modified protein ingredients can effectively reduce the starch digestion rate of rice noodles, thereby reducing their GI value. The HI, pGI, and eGI of compound modified protein rice noodles I decreased to 63.23, 73.42, and 62.7, respectively, which were 14.2%, 7.3%, and 12.6% lower than RNs. As the proportion of modified MBP increased, the indicators of compound modified protein rice noodles II and III continued to decrease. The HI, pGI, and eGI of compound modified protein rice noodles IV reached the lowest values ​​(56.28, 69.61, and 56.71), which were 23.6%, 12.1%, and 21.0% lower than RNs, respectively. When the ratio was further increased to 7:3, the three indicators of compound modified protein rice noodles V all rebounded (57.87, 70.48, and 58.08), but were still significantly lower than other groups. This trend is highly consistent with the changes in starch hydrolysis rate, indicating that the compound modified protein ingredients inhibit the rate and extent of starch hydrolysis by constructing a physical barrier of the protein-starch complex network, thereby reducing the HI, pGI, and eGI of rice noodles. The inhibitory effect on glycemic index is strongest when the protein ratio is 6:4. However, when the proportion of modified MBP is too high, the aggregation of protein molecules may slightly weaken the barrier effect, leading to a slight increase in the indicators. Overall, a 6:4 ratio of modified mung bean protein to modified black bean protein is the best in reducing the glycemic index.

[0161] Table 10 HI, pGI, and eGI of compound modified protein rice noodles

[0162]

[0163] Note: Values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same column show significant differences. p < 0.05).

[0164] (8) Storage stability test: Results are attached. Figure 18As shown, the moisture content of the samples showed a continuous upward trend with prolonged storage time. The initial moisture content of the compound modified protein ingredients was 2.94 g / 100g, which increased to 4.37 g / 100g and 4.49 g / 100g at 9 and 12 months, respectively, with a total increase of 1.55 g / 100g during the entire storage period, representing an increase of 52.7%. In terms of phased changes, the period from 0 to 6 months was the period of rapid moisture increase, with an increase of 1.21 g / 100g during this stage, accounting for 78.1% of the total increase; from 6 to 12 months, the increase in moisture level tended to be slower, with an increase of only 0.34 g / 100g, accounting for 21.9% of the total increase. This trend indicates that the compound protein ingredients modified by ultrasound-assisted TG enzyme have strong hygroscopicity in the early stages of storage. After 6 months of storage, the moisture absorption rate slowed down significantly. This is presumably because a hydration layer gradually formed on the surface of the protein particles. At the same time, the ε-(γ-glutamyl) lysine cross-links formed by TG enzyme catalysis constructed a stable three-dimensional network structure, which to some extent inhibited further penetration and diffusion of moisture.

[0165] From the perspective of fatty acid values, the total fatty acid value increased by 0.53 mg / 100g during the entire storage period, representing an increase of 12.3%. This indicates that a slow lipid hydrolysis reaction occurred during storage, producing free fatty acids. Looking at the phased changes, the fatty acid value increased by 0.30 mg / 100g from 0-6 months, accounting for 56.6% of the total increase; and by 0.23 mg / 100g from 6-12 months, accounting for 43.4% of the total increase, with a relatively gradual rate of increase overall. Considering the changes in moisture content and fatty acid values, although the moisture content increased due to physical hygroscopicity during the 12-month accelerated storage period, the increase in fatty acid values ​​was minimal, with a generally gradual change and no obvious oxidative rancidity or quality deterioration. This indicates that rice noodles with the added compound modified protein ingredients have good long-term storage stability and can maintain their functional properties under normal temperature conditions.

[0166] (9) Comprehensive comparison of the cooking and textural properties of commercially available rice noodles, single-modified protein rice noodles, unmodified protein rice noodles, and compound modified protein rice noodles: The results are shown in Table 11. In terms of cooking properties, commercially available rice noodles had the highest breakage rate (27.80%) and cooking loss rate (25.73%), indicating the worst quality. After adding protein, both indicators decreased significantly. The breakage rates of BBP-RNs and BBP15U-RNs decreased to 4.46% and 3.77%, respectively, and the cooking loss rates were 10.47% and 9.53%, respectively, showing better resistance to cooking. This indicates that BBP modification can effectively inhibit the swelling and disintegration of starch granules due to its strong hydrophobic interaction. Compared with rice noodles prepared with unmodified MBP, the breakage rate of MBP10U-RNs decreased from 11.48% to 4.82%, and the cooking loss rate decreased from 14.68% to 9.87%. The modified protein rice noodles IV (MBP:BBP=6:4) exhibited the lowest breakage rate (2.54%) and cooking loss rate (5.38%) among all samples, significantly superior to any single modified protein group. This indicates a strong synergistic effect between the MBP and BBP blend in inhibiting the dissolution of soluble substances during starch gelatinization. The two components form a denser and more continuous gel network barrier through complementary hydrogen bonds and hydrophobic interactions.

[0167] In terms of texture, the commercially available rice noodles have the highest hardness (2460.20 g), but their elasticity (0.81), cohesion (0.53), and resilience (0.33) are all relatively low, resulting in a hard texture and loose structure. The addition of a single modified protein significantly altered the texture: MBP10U-RNs showed a decrease in hardness to 1126.01 g, an increase in elasticity to 0.86, an increase in cohesion to 0.62, and an increase in resilience to 0.44, but a significant decrease in chewiness (601.27 g) and adhesiveness (701.48 g), indicating that excessive softening resulted in a lack of chewiness and structural support in the rice noodles; BBP15U-RNs showed a further decrease in hardness to 790.76 g, with the highest elasticity (0.91) and cohesion (0.82) among all samples, and the best resilience (0.62), but its chewiness (589.74 g) and adhesiveness (644.78 g) were still relatively low, indicating that while using modified BBP alone gave the rice noodles excellent softness and elasticity, it sacrificed necessary toughness and shear resistance, which may result in an overly soft and glutinous texture. In comparison, the hardness (2133.77 g) of the compound modified protein rice noodles IV was moderately lower than that of commercially available rice noodles, but still remained at a high level. Its chewiness (1165.69 g) and adhesiveness (1349.74 g) were significantly higher than all single-modification groups, while its elasticity (0.86), cohesion (0.63), and resilience (0.34) remained within the ideal range. The results indicate that the flexible unfolded structure of MBP in the compound system is responsible for filling network pores, absorbing stress, and improving viscoelasticity, while the rigid cross-linking of BBP provides structural support and resistance to deformation. The 6:4 ratio of MBP to BBP avoids excessive softening caused by MBP alone and compensates for the insufficient chewiness of BBP alone. This allows the rice noodles to maintain high structural strength while possessing good elasticity and cohesion, thus giving them a smooth, chewy, and high-quality texture.

[0168] Based on comprehensive cooking and texture data, the compound modified protein rice noodles IV achieved the lowest cooking loss and breakage rate without relying on excessive reduction of hardness, while maintaining the best chewing performance. This fully demonstrates that the compound modified protein technology enhances the gel network through intermolecular synergy, significantly improving the cooking quality of rice noodles.

[0169] Table 11 Cooking and textural properties of commercially available rice noodles, single-modified protein rice noodles, and compound-modified protein rice noodles

[0170]

[0171] Note: Numerical values ​​represent the mean ± standard deviation of three replicate experiments. Values ​​labeled with different letters in the same row show significant differences. p < 0.05).

Claims

1. A method for preparing a compound modified protein ingredient to improve the cooking quality of rice noodles, characterized in that, Includes the following steps: (1) Using mung bean protein and black bean protein as raw materials, they were dissolved in deionized water and hydrated to prepare mung bean protein solution and black bean protein solution respectively; (2) The mung bean protein solution and the black bean protein solution were subjected to ultrasonic treatment to obtain ultrasonically treated protein solutions. The ultrasonically treated protein solutions were then added to transglutaminase for enzymatic hydrolysis. After the reaction was completed, the solutions were subjected to enzyme inactivation treatment and freeze-dried to obtain modified mung bean protein and modified black bean protein, respectively. (3) The modified mung bean protein and the modified black bean protein are compounded to obtain the compound modified protein ingredient.

2. The preparation method according to claim 1, characterized in that, In step (1), the hydration time is 4-8 h, and the mass fraction of the mung bean protein solution and black bean protein solution is 5%.

3. The preparation method according to claim 1, characterized in that, In step (2), the ultrasonic treatment conditions are: ultrasonic power of 200-600W, treatment time of 10-30 min, and temperature of 15-20℃.

4. The preparation method according to claim 1, characterized in that, In step (2), the enzymatic hydrolysis specifically includes: preheating the protein solution after ultrasonic treatment in a water bath at 40-50℃, adding transglutaminase, and reacting at 40-50℃ and 80-100rpm for 20-40 min.

5. The preparation method according to claim 4, characterized in that, The amount of transglutaminase added was 5-15 U / g, based on the mass of mung bean protein and black bean protein, respectively.

6. The preparation method according to claim 4, characterized in that, The amount of transglutaminase added was 10 U / g and 15 U / g, respectively, based on the mass of mung bean protein and black bean protein.

7. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of modified mung bean protein to modified black bean protein is 3:7~7:

3.

8. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of modified mung bean protein to modified black bean protein is 6:

4.

9. The application of the compound modified protein ingredient prepared by the method for improving the cooking quality of rice noodles according to claims 1-8 in food processing.

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