Method for optimizing gelatinization and rheological properties of wheat starch based on addition of modified pectin

Abstract

The invention relates to a method for optimizing gelatinization and rheological properties of wheat starch based on addition of modified pectin, and belongs to the technical field of food processing and starch modification. In order to solve the technical problems that existing wheat starch is low in gelatinization temperature and poor in thermal stability, and rheological properties are difficult to accurately regulate and control, the modified pectin with low esterification degree, high molecular weight and high amidation degree is prepared through a specific process, and natural pectin is subjected to low-temperature deesterification and segmented amidation treatment, so that the modified pectin is obtained. Controlling the esterification degree to be lower than 10%, the molecular weight to be greater than 100 kDa and the amidation degree to be higher than 50%, and then forming a three-dimensional composite network structure with wheat starch according to the mass ratio of (1: 4)-(1: 9) through high-speed shearing and ultrasonic synergistic treatment. According to the method, the starch gelatinization temperature is remarkably increased, the thermal stability and shear thinning recovery capacity of a system are improved, the method is suitable for improving the quality of cooked wheaten food products such as noodles and baked products, and the texture characteristics and processing adaptability of the products can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and more particularly to a method for optimizing the gelatinization and rheological properties of wheat starch by adding modified pectin. Background Art

[0002] Starch, an important natural high-molecular-weight polysaccharide, is widely used in food processing. Its gelatinization and rheological properties are crucial for food quality and processing performance. However, during complex processing, starch's molecular structure is easily damaged, resulting in changes in its physical and chemical properties, which limits its application in certain foods. Studies have shown that the gelatinization and rheological properties of starch are not only influenced by its own structure (such as the ratio of amylose to amylopectin) but are also closely related to the synergistic effects of exogenous additives. How to scientifically regulate the gelatinization and rheological properties of starch has become an important research direction in the field of starch modification.

[0003] Currently, common starch modification methods include physical modification, chemical modification, and enzymatic modification. For example, physical modification through heat-shearing methods can change the crystal structure of starch to improve its application performance, and chemical modification (such as acetylation and phosphation) can significantly enhance the cold water solubility and thermal stability of the starch system. However, these methods often have certain limitations. For example, the chemical modification process may introduce harmful residues, and physical modification can easily lead to excessive damage to the starch structure, thereby reducing its functional properties. In addition, traditional single modification methods mainly focus on improving a specific property of starch, and lack effective methods for multi-dimensional and multi-property synergistic optimization. Therefore, the development of green, controllable and efficient modification technologies has become a key issue in starch functionalization research.

[0004] Pectin, a natural functional polysaccharide, has been widely used in the food industry due to its excellent gelation and rheological properties. However, pectin currently exists mostly as an emulsifying thickener or gelling agent, failing to fully explore its potential in regulating starch properties. Pectin has a complex chemical structure, and its functional properties vary significantly due to differences in key parameters such as degree of esterification, molecular weight, and degree of amidation. For example, the effects of pectins of varying degrees of esterification on the gelatinization, viscoelastic properties, and gelation behavior of starch systems are not yet clearly defined; molecular weight, to a certain extent, determines the distribution of pectin in starch systems and the strength of its interaction with starch molecules; and changes in the degree of amidation may regulate pectin's hydration capacity, gel network stability, and synergistic interaction with starch molecules.

[0005] Based on this, research has shown that pectin can significantly improve the gelatinization properties of starch by changing the water distribution in the system and strengthening the physical and chemical cross-linking between starch molecules, while optimizing the rheological behavior of starch molecules and affecting the gel properties of amylose and amylopectin. However, current research has mostly focused on the mechanism of action of a single pectin structure on starch properties, lacking the ability to explore the effects of fine-grained pectin structure modification on starch properties. Summary of the Invention

[0006] One object of the present invention is to provide a method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin. By regulating the esterification degree, molecular weight and amidation degree of pectin, a synergistic network of pectin and starch can be accurately constructed, thereby significantly improving the gelatinization and rheological properties of starch.

[0007] In order to achieve these objects and other advantages of the present invention, according to one aspect of the present invention, the present invention provides a method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin, comprising the following steps: Step 1: Prepare modified pectin: Take natural pectin and adjust its initial esterification degree, molecular weight and amidation degree so that the esterification degree is less than 10%, the molecular weight is greater than 100 kDa and the amidation degree is greater than 50%; Step 2: Constructing a starch-pectin composite system: Mixing the modified pectin obtained in step 1 with wheat starch in a mass ratio of 1:4-1:9 to form a composite network structure.

[0008] Preferably, the preparation of the modified pectin comprises the following steps: Step a, molecular weight protection stage: dissolving natural pectin in ultrapure water to form a pectin solution with a mass concentration of 2%-4%, and precooling at 2-6°C; Step b, deesterification stage: the pre-cooled pectin solution is mixed with an ammonia-isopropanol solution having a concentration of 3.5-4.5 mol / L, and reacted under magnetic stirring to reduce the degree of esterification to less than 10%; Step c, amidation stage: adding a 0.5-1.5 mol / L HCl-isopropanol solution to the deesterified solution, adjusting the pH to 3.8-4.2 under magnetic stirring, and increasing the degree of amidation to above 50%; Step d, post-treatment: filtration using an ultrafiltration membrane with a molecular weight cutoff of 100 kDa, washing the precipitate with isopropanol solution multiple times to remove unreacted reagents and low molecular weight pectin, and vacuum drying to finally obtain modified pectin with a molecular weight greater than 100 kDa.

[0009] Preferably, in step a, the natural pectin is mixed with 40-50°C ultrapure water, stirred at 800-1200 rpm / min using a magnetic stirrer for 30-60 min until completely dissolved, and then cooled to 2-6°C at a rate of 0.5-1°C / min and allowed to stand at a constant temperature for 1-2 h to form a homogeneous pre-cooled solution without gel lumps.

[0010] Preferably, step b further comprises dynamically regulating the reaction parameters according to the initial degree of esterification DE0 of the natural pectin, the volume ratio of the ammonia-isopropanol solution to the pre-cooled pectin solution is calculated according to formula 1: (0.05×DE0+0.75), wherein DE0 in the formula is the percentage value of the degree of esterification, the reaction temperature is maintained at 2-6°C, and the stirring rate is set according to the DE0 value: When DE0≥70%, the stirring rate is 500-600 rpm / min; When 50%≤DE0<70%, the stirring rate is 400-500 rpm / min; When DE0 < 50%, the stirring rate is 200-300 rpm / min; The degree of esterification was monitored in real time during the reaction, and the deesterification stage was completed when the degree of esterification was lower than 10%.

[0011] Preferably, the HCl-isopropanol solution in step c is added dropwise to the deesterified solution in batches, specifically: First addition: Based on the initial amidation degree DA0 of natural pectin, the droplet acceleration rate is calculated according to the formula V1=0.4×DA0+6. A 1.3-1.5 mol / L high-concentration HCl-isopropanol solution is used, and the magnetic stirring speed is simultaneously started to 300-500 rpm / min until the pH of the system drops to 5.8-6.2. Second addition: switch to a 1.0-1.2 mol / L medium-concentration HCl-isopropanol solution, reduce the drop rate to 4-6 mL / min, and increase the stirring speed to 800-1000 rpm / min until the pH drops to 4.5-5.0; Final addition: Use a 0.5-0.8 mol / L low-concentration HCl-isopropanol solution, reduce the drop rate to 0.5-0.7 mL / min, maintain the stirring speed at 800-1000 rpm / min, and adjust the pH to 3.8-4.2; Wherein, DA0 is the percentage value of the degree of amidation, and V1 is the dropwise acceleration rate of the HCl-isopropanol solution, mL / min.

[0012] Preferably, the preparation process of the ammonia-isopropanol solution is: Precool anhydrous isopropanol to -5-0°C and mix with 25-28% concentrated ammonia water to a final concentration of 3.5-4.5 mol / L to form an initial ammonia-isopropanol solution; The initial ammonia-isopropanol solution is placed in a high-pressure homogenizer and subjected to shearing treatment at 2000-2500 rpm / min under a pressure of 10-15 MPa for 5-8 minutes to uniformly disperse the ammonia molecules in the form of nanoclusters; Aging at 2-5°C for 12-24 h forms a homogeneous ammonia-isopropanol solution without stratification.

[0013] Preferably, the preparation process of the HCl-isopropanol solution is: Precool anhydrous isopropyl alcohol to -10~-5℃ and place it in a jacketed reactor with a -15℃ coolant circulating in the jacket; Dry HCl gas was introduced at a rate of 0.2-0.4 L / min and stirred at 1000 rpm / min to prepare an HCl-isopropanol solution with a concentration of 0.5-1.5 mol / L. During the stirring process, when the solution temperature is higher than -3°C, the enhanced cooling and intermittent aeration mode is triggered until the temperature drops below -5°C.

[0014] Preferably, the enhanced cooling and intermittent introduction mode is as follows: when the solution temperature is higher than -3°C, the jacket coolant temperature is reduced to -25°C, the stirring speed is increased by 10-20%, and the introduction of HCl gas is suspended. When the temperature drops to -5°C, HCl gas is introduced at a low speed of 0.1 L / min for 5 min, and then the original introduction rate is restored.

[0015] Preferably, the specific process of constructing the starch-pectin composite system in step 2 is: Place modified pectin and wheat starch in a high-speed shear mixer at a mass ratio of 1:4-1:9, control the mixing temperature to 25-30°C, and stir at a speed of 2000-3000 rpm / min for 10-15 minutes to form a primary dispersion system; Transfer the primary dispersion system to an ultrasonic treatment tank and apply ultrasonic treatment at a frequency of 20-40 kHz and a power density of 5-10 W / cm² for 20-30 minutes at 40-50°C to promote the formation of a three-dimensional network structure between the pectin molecular chains and starch granules through hydrogen bonding and hydrophobic interactions; The mixed solution after ultrasonic treatment was allowed to stand at 4-6°C for 2-4 h to allow the composite network structure to fully self-assemble, and finally a homogeneous starch-pectin composite system was obtained.

[0016] The present invention has at least the following beneficial effects: First, the present invention breaks through the limitations of traditional single parameter regulation and optimizes starch gelatinization and rheological properties by regulating fine structures such as pectin esterification degree, molecular weight and amidation degree. A more continuous and orderly composite gel network structure can be formed between low-esterification pectin and starch, thereby improving the thermal stability of starch. Compared with low-molecular-weight pectin, high-molecular-weight pectin is more hydrophilic, which reduces the adsorption of water molecules by starch and thus increases the gelatinization temperature. The amidated groups in high-amidation pectin can be tightly bound to starch through hydrogen bonds and hydrophobic interactions. This synergistic regulation mechanism not only simplifies the modification process, but also improves the modification effect, creating a new idea for starch modification technology.

[0017] Second, the present invention optimizes starch gelatinization and rheological properties through the multi-dimensional synergistic effects of pectin esterification, molecular weight, and degree of amidation, without relying on complex chemical modifications or the addition of external stabilizers. Compared to traditional modification methods, the present invention effectively simplifies the production process, avoids the use of chemical reagents, and reduces production costs. Furthermore, it avoids the risk of potentially harmful residues, improving the safety and green nature of food products and providing an environmentally friendly and efficient solution for industrial applications.

[0018] Third, the present invention significantly improves the gelatinization behavior and rheological properties of starch through the optimized combination of multiple pectin parameters. The modified starch system exhibits improved thermal stability, shear stability, and storage stability, meeting the requirements of various food processing techniques. Furthermore, the modified starch exhibits excellent water retention, gel strength, and thixotropy, making it suitable for a wide range of food applications.

[0019] Fourth, the present invention uses a deesterification process with low-temperature molecular weight protection and dynamic regulation to precisely control the degree of esterification to below 10% while avoiding β-elimination reaction, so that the modified pectin retains the chain length advantage of molecular weight >100 kDa and significantly increases the density of carboxylic acid groups, providing sufficient reaction sites for subsequent amidation; the segmented gradient amidation treatment is combined with the synergistic adjustment of HCl-isopropanol concentration and drop rate to achieve an amidation degree >50% while inhibiting molecular chain cross-linking, thereby enhancing the hydrogen bonding ability between pectin and starch; the nano-dispersion and low-temperature stable preparation of ammonia / hydrochloric acid isopropanol solution ensures the high reactivity and dispersion uniformity of the reagents, avoiding molecular weight loss caused by local over-reaction; the spatiotemporal coordination of high-speed shear and ultrasonic treatment in the construction of the composite system promotes the directional adsorption of pectin molecular chains on the surface of starch granules, forming a three-dimensional network structure with both thermal stability and shear responsiveness, effectively overcoming the technical bottlenecks of traditional modified pectin molecular weight-functional group synergistic optimization and unstable composite system structure.

[0020] Other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is the gelatinization characteristic curve of the starch composite system of each embodiment; Figure 2 is the gelatinization characteristic curve of the starch composite system of each comparative example; Figure 3 is the storage modulus curve of the starch composite system; Figure 4 This is the loss modulus curve of the starch composite system. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can implement the invention with reference to the description.

[0023] It should be understood that terms such as “having”, “including” and “comprising” used herein do not preclude the existence or addition of one or more other elements or combinations thereof.

[0024] The present invention provides a method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin, comprising the following steps: Step 1: Prepare modified pectin: Take natural pectin and adjust its initial esterification degree, molecular weight and amidation degree so that the esterification degree is less than 10%, the molecular weight is greater than 100 kDa and the amidation degree is greater than 50%; Step 2: Constructing a starch-pectin composite system: The modified pectin obtained in Step 1 is mixed with wheat starch in a mass ratio of 1:4-1:9 to form a composite network structure. In this technical solution, the pectin's degree of esterification (less than 10%), molecular weight (greater than 100 kDa), and degree of amidation (greater than 50%) are controlled to produce a modified pectin with a low degree of esterification, high molecular weight, and rich in amide groups. The low degree of esterification reduces hydrophobic interactions between pectin molecules and enhances hydrogen bonding with starch. The high molecular weight pectin provides a long-chain backbone, promoting the formation of a stable three-dimensional network structure. The amide groups introduced by the high degree of amidation bind tightly to starch through hydrogen bonding and hydrophobic interactions, significantly increasing the starch gelatinization temperature while also improving the thermal stability and shear recovery of the system. After mixing the modified pectin with wheat starch in a mass ratio of 1:4-1:9, a uniform three-dimensional composite network structure is formed through physical treatment (such as high-speed shearing and ultrasonic treatment). This structure effectively limits excessive expansion of starch granules, increases the gelatinization temperature, and enhances the structural stability of the system under high temperature or shear stress. The composite system exhibits significantly increased storage modulus (G′) and decreased loss modulus (G″), demonstrating excellent elastic recovery properties, making it suitable for foods such as noodles and baked goods that require high processing adaptability and texture. This method optimizes starch properties through targeted regulation of pectin's natural structure and physical compounding techniques, without relying on chemical cross-linking agents or complex modification processes. This avoids the introduction of harmful reagents, aligning with the green development trend of the food industry. It also reduces production costs and process complexity, demonstrating its high potential for industrial application.

[0025] In one of the technical solutions, the preparation of the modified pectin comprises the following steps: Step a, molecular weight protection stage: dissolving natural pectin in ultrapure water to form a pectin solution with a mass concentration of 2%-4%, and precooling at 2-6°C; Step b, deesterification stage: the pre-cooled pectin solution is mixed with an ammonia-isopropanol solution having a concentration of 3.5-4.5 mol / L, and reacted under magnetic stirring to reduce the degree of esterification to less than 10%; Step c, amidation stage: adding a 0.5-1.5 mol / L HCl-isopropanol solution to the deesterified solution, adjusting the pH to 3.8-4.2 under magnetic stirring, and increasing the degree of amidation to above 50%; Step d, post-treatment: Filter through an ultrafiltration membrane with a molecular weight cutoff of 100 kDa, wash the precipitate multiple times with isopropanol solution to remove unreacted reagents and low-molecular-weight pectin, and vacuum dry to ultimately obtain modified pectin with a molecular weight greater than 100 kDa. In this technical solution, first, in the molecular weight protection stage, low-temperature dissolution and pre-cooling treatment are used to inhibit the degradation of pectin chains and maintain its high molecular weight characteristics; then, in the deesterification stage, ester groups are selectively removed, reducing the degree of esterification and releasing more active carboxylic acid groups, enhancing the potential for intermolecular interactions; in the amidation stage, amide groups are introduced through gradient regulation to enhance hydrogen bonding ability and further optimize the functional group distribution; in the post-treatment stage, ultrafiltration technology is used to accurately screen and retain high-molecular-weight components, remove low-molecular-weight fragments and impurities, and ensure product purity. The modified pectin reduces intermolecular repulsion due to its low degree of esterification, provides structural support due to its high molecular weight, and strengthens the binding effect due to its high degree of amidation. It forms a dense three-dimensional network with wheat starch, significantly increasing the gelatinization temperature, enhancing thermal stability, and improving rheological recovery properties. The overall process avoids the use of harmful reagents through low-temperature control and physical purification, improving the functional properties of starch while taking into account production safety and efficiency.

[0026] In one of the technical solutions, in step a, natural pectin is mixed with 40-50°C ultrapure water, stirred at 800-1200 rpm / min using a magnetic stirrer for 30-60 minutes until completely dissolved, then cooled to 2-6°C at a rate of 0.5-1°C / min and allowed to stand at a constant temperature for 1-2 hours to form a homogeneous pre-cooled solution without gel clumps. In this technical solution, step a ensures the homogeneity and stability of the pectin solution by the following operations: first, natural pectin is mixed with moderately heated ultrapure water, and medium-high-speed stirring with a magnetic stirrer is used to promote the full dispersion and dissolution of the pectin molecules; then, a gradient cooling control is used to avoid molecular chain aggregation or gelation caused by sudden temperature changes, and finally, the solution is allowed to stand in a low-temperature environment to fully stabilize. This process, through the coordinated regulation of temperature, stirring rate, and time, not only ensures the complete dissolution of the pectin, but also effectively inhibits the formation of gel clumps, laying the foundation for the uniformity of subsequent reactions and the retention of high-molecular-weight pectin.

[0027] In one technical solution, step b further includes dynamically controlling the reaction parameters based on the initial degree of esterification DE0 of the natural pectin. The volume ratio of the ammonia-isopropanol solution to the pre-cooled pectin solution is calculated according to Formula 1: (0.05×DE0+0.75), where DE0 in the formula is the percentage value of the degree of esterification. The reaction temperature is maintained at 2-6°C, and the stirring rate is set according to the DE0 value: When DE0≥70%, the stirring rate is 500-600 rpm / min; When 50%≤DE0<70%, the stirring rate is 400-500 rpm / min; When DE0 < 50%, the stirring rate is 200-300 rpm / min; The degree of esterification is monitored in real time during the reaction. The deesterification stage is complete when the degree of esterification falls below 10%. In this technical solution, the volume ratio of the ammonia-isopropanol solution to the pectin solution and the stirring rate are dynamically adjusted based on the initial degree of esterification (DE0) of the natural pectin, achieving precise adaptation of reaction parameters. High-DE0 pectin (DE0 ≥ 70%) requires more ammonia-isopropanol reagent for the deesterification reaction due to its high ester content. The volume ratio formula (1:(0.05 × DE0 + 0.75)) ensures that the reagent addition amount matches the reaction requirements. Low-DE0 pectin (DE0 < 50%) reduces reagent usage, avoiding waste and side reactions. The stirring rate is adjusted gradually with the DE0 (500-600 rpm to 200-300 rpm), ensuring a rapid reaction for highly active pectins while preventing molecular chain breakage due to excessive shearing in low-activity pectins, thus balancing reaction efficiency and product molecular weight. The reaction temperature is strictly controlled between 2-6°C. This low temperature inhibits potential β-elimination reactions during the deesterification process and slows thermal motion of the molecular chains, preventing local overheating and molecular weight loss caused by vigorous reactions. The low temperature, combined with staged stirring, ensures a uniform and gentle reaction system, maintaining the structural stability of high-molecular-weight pectin. The degree of esterification is monitored in real time during the deesterification process (e.g., by acid-base titration), and the reaction is terminated immediately if the measured value falls below 10%. This strategy avoids the potential for underreaction (excessive residual ester groups) or overreaction (excessive molecular chain degradation) associated with traditional fixed-time methods, ensuring that the modified pectin achieves the desired degree of esterification and providing a structurally uniform intermediate for the subsequent amidation step. Dynamic matching of the volume ratio and stirring rate (e.g., high DEO with high stirring speed) promotes full contact between the ammonia-isopropanol reagent and the pectin molecules, eliminating reaction inhomogeneities caused by local concentration differences. For example, high DE0 pectin enhances mass transfer efficiency and accelerates ester hydrolysis through high stirring rates (500-600 rpm); low DE0 pectin uses low rotation speeds (200-300 rpm) to reduce mechanical shear damage to the molecular chains while maintaining sufficient mixing of the reaction system. In summary, this technical solution achieves high efficiency, uniformity, and controllability in the deesterification process through DE0-dependent dynamic parameter regulation, low-temperature reaction protection, and real-time endpoint monitoring. Ultimately, a pectin intermediate with a low degree of esterification (<10%) and a high molecular weight (>100 kDa) is obtained, laying the structural foundation for the subsequent construction of a high-performance starch-pectin composite system.

[0028] In one of the technical solutions, the HCl-isopropanol solution in step c is added dropwise to the deesterified solution in batches, specifically: First addition: Based on the initial amidation degree DA0 of natural pectin, the droplet acceleration rate is calculated according to the formula V1=0.4×DA0+6. A 1.3-1.5 mol / L high-concentration HCl-isopropanol solution is used, and the magnetic stirring speed is simultaneously started to 300-500 rpm / min until the pH of the system drops to 5.8-6.2. Second addition: switch to a 1.0-1.2 mol / L medium-concentration HCl-isopropanol solution, reduce the drop rate to 4-6 mL / min, and increase the stirring speed to 800-1000 rpm / min until the pH drops to 4.5-5.0; Final addition: Use a 0.5-0.8 mol / L low-concentration HCl-isopropanol solution, reduce the drop rate to 0.5-0.7 mL / min, maintain the stirring speed at 800-1000 rpm / min, and adjust the pH to 3.8-4.2; In the formula, DA0 represents the percentage of amidation, and V1 represents the addition rate of the HCl-isopropanol solution (mL / min). In this technical solution, a high-concentration HCl-isopropanol solution is used for the initial addition. The addition rate is dynamically controlled using the formula (V1 = 0.4 × DA0 + 6), combined with medium-to-low speed stirring to ensure a smooth initial initiation of the amidation reaction. High-concentration reagents are rapidly introduced into the acidic environment, but by limiting the addition rate (e.g., a lower DA0 leads to a slower rate), localized pH drops that could lead to excessive protonation or cross-linking of the molecular chains are avoided. For the second and final additions, the HCl concentration (from 1.0-1.2 mol / L to 0.5-0.8 mol / L) and addition rate (from 4-6 mL / min to 0.5-0.7 mL / min) are gradually reduced, while the stirring speed (800-1000 rpm) is simultaneously increased to enhance system mixing efficiency and gradually fine-tune the pH to the target range (3.8-4.2). This gradient design balances reaction rate with product stability, minimizing the risk of side reactions. The initial addition rate formula (V1 = 0.4 × DA0 + 6) is dynamically adjusted based on the initial degree of amidation (DA0) of the natural pectin. When the DA0 is low (e.g., 2%-5%), the addition rate is reduced accordingly (e.g., 6.8-8 mL / min) to avoid excessive reagent accumulation due to insufficient initial reaction activity. When the DA0 is high, the addition rate is appropriately increased to match the reaction requirements. This formula quantifies the correlation between DA0 and reaction rate to ensure uniform introduction of amidated groups and minimize the formation of localized crosslinking or unreacted regions. A low stirring speed (300-500 rpm) is used during the initial addition to minimize shear damage to the molecular chains caused by the vigorous mixing of high-concentration HCl while allowing the reagent to diffuse gradually into the reaction system. During the second and final additions, the speed is increased (800-1000 rpm), combined with low- to medium-concentration HCl solutions, to accelerate reagent dispersion and pH equilibrium, thereby avoiding localized over-acidification that could lead to molecular chain breakage. Staged pH control (5.8-6.2 → 4.5-5.0 → 3.8-4.2) promotes the orderly replacement of carboxylic acid groups with amide groups by gradually acidifying the reaction environment, ensuring uniform distribution of functional groups. A combination of a low addition rate (final addition 0.5-0.7 mL / min) and high stirring speed enables precise control near the reaction endpoint (pH 3.8-4.2), avoiding side reactions such as excess HCl residue or excessively low pH (e.g., pectin chain hydrolysis). The staged addition strategy reduces transient overload of reagents, and combined with a low temperature (2-6°C), further inhibits β-elimination reactions and maintains the integrity of the pectin molecular weight (>100 kDa). In summary, this technical solution achieves efficient control of the amidation reaction by batch-by-batch gradient adjustment of HCl concentration, addition rate, and stirring intensity, combined with a dynamic formula to adapt initial conditions. The resulting modified pectin has a high degree of amidation (>50%) and intact molecular chains, significantly enhancing its hydrogen bonding ability with starch, providing a structural foundation for functional optimization of the composite system.

[0029] In one of the technical solutions, the preparation process of the ammonia-isopropanol solution is: Precool anhydrous isopropanol to -5-0°C and mix with 25-28% concentrated ammonia water to a final concentration of 3.5-4.5 mol / L to form an initial ammonia-isopropanol solution; The initial ammonia-isopropanol solution is placed in a high-pressure homogenizer and subjected to shearing treatment at 2000-2500 rpm / min under a pressure of 10-15 MPa for 5-8 minutes to uniformly disperse the ammonia molecules in the form of nanoclusters; Aging at 2-5°C for 12-24 hours forms a homogeneous, layer-free ammonia-isopropanol solution. In this technical solution, anhydrous isopropanol is precooled to -5-0°C, significantly reducing its volatility and suppressing localized temperature rise caused by exothermic mixing, thereby preventing the escape of ammonia molecules or oxidation of the isopropanol. The solution is then mixed with 25-28% concentrated aqueous ammonia to a final concentration of 3.5-4.5 mol / L. The low temperature maintains the chemical activity balance of the reagents, ensuring the alkalinity required for the deesterification reaction while avoiding the risk of side reactions introduced by excess ammonia, thereby ensuring the stability and controllability of the initial solution. The solution is then treated in a high-pressure homogenizer (10-15 MPa pressure, 2000-2500 rpm shear rate) for 5-8 minutes. The high shear force and cavitation effect fragment the ammonia molecules into nanoscale clusters (particle size <100 nm). The nano-dispersed ammonia clusters significantly increase the reaction contact area, improving the efficiency of ester hydrolysis in the subsequent deesterification reaction. Furthermore, the uniform dispersion reduces local concentration variations, preventing uneven reactions or excessive degradation caused by ammonia molecular aggregation. The homogenized solution is then aged at 2-5°C for 12-24 hours. The low temperature suppresses molecular thermal motion, allowing the nano-ammonia clusters to gradually distribute evenly throughout the system through Brownian motion, eliminating microbubbles and undispersed particles. The aging process promotes thermodynamic equilibrium, forming a homogeneous ammonia-isopropanol solution free of stratification and precipitation. This provides a highly uniform reaction medium for the subsequent deesterification reaction, significantly improving reaction reproducibility and product consistency. This formulation process combines low-temperature precooling to suppress volatilization, high-pressure homogenization to achieve nano-scale dispersion, and low-temperature aging to eliminate microscopic inhomogeneities. These three factors work synergistically to ensure the high stability, activity, and uniformity of the ammonia-isopropanol solution. The resulting solution precisely supports the deesterification reaction, reducing the degree of esterification while preserving the integrity of the pectin molecular chains, laying a solid foundation for subsequent amidation and starch composite system construction.

[0030] In one of the technical solutions, the preparation process of the HCl-isopropanol solution is: Precool anhydrous isopropyl alcohol to -10~-5℃ and place it in a jacketed reactor with a -15℃ coolant circulating in the jacket; Dry HCl gas was introduced at a rate of 0.2-0.4 L / min and stirred at 1000 rpm / min to prepare an HCl-isopropanol solution with a concentration of 0.5-1.5 mol / L. During stirring, if the solution temperature rises above -3°C, enhanced cooling and intermittent aeration are triggered until the temperature drops below -5°C. In this technical solution, anhydrous isopropyl alcohol is pre-cooled to -10--5°C, and a -15°C coolant is circulated through the jacketed reactor. This significantly reduces the exothermic effect of HCl gas dissolution, minimizing solvent volatilization and gas escape. The low temperature slows the thermal motion of HCl molecules, increasing their solubility in isopropyl alcohol and ensuring precise control of the target concentration (0.5-1.5 mol / L) while avoiding side reactions (such as molecular chain degradation or solvent oxidation) caused by localized temperature spikes. The solution is stirred at 1000 rpm / min, combined with an HCl gas aeration rate of 0.2-0.4 L / min. The synergistic effects of strong shear and gas dispersion promote uniform dissolution of HCl molecules in the isopropyl alcohol, resulting in a homogeneous solution free of bubbles and localized excess concentrations. When the solution temperature exceeds -3°C, enhanced cooling (e.g., the jacket coolant temperature is reduced to -25°C) and intermittent gas flow (gas flow is suspended) is triggered to rapidly cool the solution to below -5°C. This prevents uneven dissolution or runaway reactions caused by temperature fluctuations and ensures stable solution concentration. The enhanced cooling mode rapidly absorbs the heat of reaction through extreme low temperatures, inhibiting thermal degradation of the molecular chains. Intermittent HCl flow prevents excess gas accumulation during the temperature rise phase and reduces the risk of undissolved HCl escape. This dynamic switching between these two modes balances reaction rate and temperature control, maintaining a low solution temperature while protecting the integrity of the pectin molecular chains and providing a highly active and structurally stable acidic medium for the subsequent amidation reaction. This preparation process achieves high homogeneity and stability of the HCl-isopropanol solution through the synergistic effect of low-temperature pre-cooling, efficient stirring, and dynamic temperature control. The low temperature and enhanced cooling mode effectively suppress side reactions, ensuring precise control of solution concentration and providing reliable acidic reaction conditions for the subsequent amidation stage, ultimately improving the uniformity of the functional group distribution of the modified pectin and the performance of the composite system.

[0031] In one technical solution, the enhanced cooling and intermittent gas flow mode specifically involves: when the solution temperature rises above -3°C, the jacket coolant temperature is lowered to -25°C, the stirring speed is increased by 10-20%, and the HCl gas flow is suspended. Once the temperature returns to -5°C, HCl gas is introduced at a low rate of 0.1 L / min for 5 minutes before returning to the original flow rate. In this technical solution, this enhanced cooling and intermittent gas flow mode dynamically responds to changes in solution temperature to ensure the stability and controllability of the reaction system. When the temperature exceeds a set threshold, the jacket coolant temperature is rapidly lowered and the stirring speed is increased to accelerate heat dissipation and suppress temperature rise. The HCl gas flow is also suspended to prevent further exacerbation of temperature fluctuations caused by the reaction exotherm. Once the temperature returns to a safe range, the gas flow is resumed at a low rate, maintaining the necessary reaction progress while preventing temperature rebound. This mode, through a "cooling-pause-slow resumption" cycle, balances reaction rate and temperature control, reducing the risk of molecular chain breakage or localized overreaction caused by heat accumulation, and ensuring the structural integrity and functional uniformity of the product.

[0032] In one of the technical solutions, the specific process of constructing the starch-pectin composite system in step 2 is: Place modified pectin and wheat starch in a high-speed shear mixer at a mass ratio of 1:4-1:9, control the mixing temperature to 25-30°C, and stir at a speed of 2000-3000 rpm / min for 10-15 minutes to form a primary dispersion system; Transfer the primary dispersion system to an ultrasonic treatment tank and apply ultrasonic treatment at a frequency of 20-40 kHz and a power density of 5-10 W / cm² for 20-30 minutes at 40-50°C to promote the formation of a three-dimensional network structure between the pectin molecular chains and starch granules through hydrogen bonding and hydrophobic interactions; The ultrasonically treated mixture is allowed to stand at 4-6°C for 2-4 hours to allow the composite network structure to fully self-assemble, ultimately yielding a homogeneous starch-pectin composite system. In this technical solution, modified pectin and wheat starch are mixed at a mass ratio of 1:4-1:9 at 25-30°C and high-speed shearing at 2000-3000 rpm. The strong shear force breaks up the aggregated starch granules and promotes full contact between the pectin molecular chains and the starch surface. Moderate heating softens the starch granule surface, enhancing the pectin's adsorption and penetration capacity, forming a primary dispersion system and providing a homogenous foundation for subsequent network construction. The primary dispersion system is transferred to an ultrasonic treatment tank at 40-50°C and subjected to high-frequency ultrasound at 20-40 kHz. Ultrasonic cavitation generates microjets and localized high pressure, further expanding the pectin molecular chains and exposing more hydrogen bonds and hydrophobic sites. Simultaneously, high-frequency vibrations weaken the crystalline regions of the starch granules, strengthening their interfacial bonding with the pectin. Gentle heating at 40-50°C reduces the system's viscosity, accelerating the directional alignment of the molecular chains and forming a continuous three-dimensional network framework. After ultrasonic treatment, the mixture is allowed to stand at 4-6°C for 2-4 hours. The low temperature inhibits molecular thermal motion, allowing pectin chains and starch granules to gradually self-assemble through hydrogen bonding, hydrophobic interactions, and physical entanglement. During the standing process, internal stress in the network structure is slowly released, and micro-area heterogeneity is eliminated through molecular rearrangement, ultimately forming a homogeneous and dense composite system, significantly improving its thermal stability (high-temperature shear resistance) and rheological recovery (increased elastic modulus). The temporal and spatial coordination of high-speed shearing and ultrasonic treatment achieves macroscopic uniform dispersion while strengthening microscopic molecular interactions. Low-temperature standing improves the network structure through thermodynamic relaxation. This composite system has an increased gelatinization temperature and shortened recovery time after shear thinning, making it suitable for pasta products such as noodles and baked goods that must withstand high-temperature processing and mechanical shear. Physical modification is employed throughout the process, avoiding the introduction of chemical reagents, meeting the green requirements of the food industry. The well-defined process parameters and universal equipment make it suitable for large-scale production.

[0033] <Example 1> A method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin comprises the following steps: Step 1: Take natural apple pectin (initial degree of esterification DE0 = 73%, degree of amidation DA0 = 2%, molecular weight 150 kDa), add ultrapure water to prepare a 3% mass concentration solution, stir until completely dissolved, and cool to 4°C to obtain a homogeneous pre-cooled solution.

[0034] Step 2: The pre-cooled pectin solution was mixed with a 4.0 mol / L ammonia-isopropanol solution at a fixed volume ratio of 1:3, and samples were taken every 15 minutes to detect the degree of esterification. When the DE was detected to be below 10%, 1.0 mol / L HCl-isopropanol solution was immediately added dropwise and stirred. When the pH value reached 4.0, the addition was stopped, and the solution was filtered through an ultrafiltration membrane with a molecular weight cutoff of 100 kDa. The precipitate was washed three times with 60% isopropanol solution, and then dried to obtain the modified pectin.

[0035] Step 3: Use a vortex mixer to fully mix the modified pectin and wheat starch in a mass ratio of 1:6 to obtain a starch-pectin composite network structure.

[0036] <Example 2> A method for optimizing the gelatinization and rheological properties of wheat starch by adding modified pectin, which differs from Example 1 in that: Step 1: Take natural apple pectin (initial degree of esterification DE0 = 73%, degree of amidation DA0 = 2%, molecular weight 150 kDa), mix it with 45℃ ultrapure water, use a magnetic stirrer at 1000 rpm / min for 45 minutes until it is completely dissolved, then cool it to 4℃ at a rate of 0.8℃ / min and keep it at a constant temperature for 1.5 hours to form a homogeneous pre-cooled solution without gel clumps.

[0037] The remaining steps are the same as in Example 1.

[0038] <Example 3> A method for optimizing the gelatinization and rheological properties of wheat starch by adding modified pectin, which differs from Example 2 in that: Step 2: The precooled pectin solution was mixed and stirred with a 4.0 mol / L ammonia-isopropanol solution. The volume ratio of the ammonia-isopropanol solution to the precooled pectin solution was calculated according to the formula: 1: (0.05 × DE0 + 0.75) = 1: 4.4. The reaction temperature was maintained at 4°C, and the stirring rate was set to 550 rpm / min based on the initial esterification degree DE0 = 73%. The esterification degree was detected every 15 minutes. When the DE was detected to drop below 10%, 1.0 mol / L HCl-isopropanol solution was immediately added dropwise and stirred. The addition was stopped when the pH value reached 4. The solution was filtered using an ultrafiltration membrane with a molecular weight cutoff of 100 kDa, the precipitate was washed 3 times with 60% isopropanol solution, and then dried to obtain modified pectin.

[0039] The remaining steps are the same as in Example 2.

[0040] <Example 4> A method for optimizing the gelatinization and rheological properties of wheat starch by adding modified pectin, which differs from Example 3 in that: Step 2: The pre-cooled pectin solution was mixed with a 4.0 mol / L ammonia-isopropanol solution and stirred. The volume ratio of the ammonia-isopropanol solution to the pre-cooled pectin solution was calculated according to the formula: 1: (0.05 × DE0 + 0.75) = 1: 4.4. The reaction temperature was maintained at 4°C, and the stirring rate was set to 550 rpm / min based on the initial esterification degree DE0 = 73%. Samples were taken every 15 minutes to detect the esterification degree. When the DE was detected to drop below 10%, 1.0 mol / L HCl-isopropanol solution was immediately added dropwise in batches: First addition: Based on the initial amidation degree of natural pectin (DA0) = 2%, the droplet acceleration rate is calculated according to the formula: V1 = 0.4 × DA0 + 6 = 6.8 mL / min. A 1.5 mol / L high-concentration HCl-isopropanol solution is used, and the magnetic stirring speed is simultaneously started at 400 rpm / min until the pH of the system drops to 6.0. Second addition: switch to 1.2 mol / L medium-concentration HCl-isopropanol solution, reduce the drop rate to 5 mL / min, and increase the stirring speed to 800 rpm / min until the pH drops to 5.0; Final addition: Use a 0.6 mol / L low-concentration HCl-isopropanol solution, reduce the drop rate to 0.6 mL / min, maintain the stirring speed at 800 rpm / min, and adjust the pH to 4.0; stop adding HCl-isopropanol solution, filter using an ultrafiltration membrane with a molecular weight cutoff of 100 kDa, wash the precipitate three times with 60% isopropanol solution, and then dry to obtain modified pectin.

[0041] The remaining steps are the same as in Example 3.

[0042] <Example 5> A method for optimizing the gelatinization and rheological properties of wheat starch by adding modified pectin differs from Example 4 in that: The ammonia-isopropanol solution used was prepared as follows: anhydrous isopropanol was precooled to -3°C and mixed with 26% concentrated aqueous ammonia to a final concentration of 4.0 mol / L to form an initial ammonia-isopropanol solution. The initial ammonia-isopropanol solution was placed in a high-pressure homogenizer and sheared at 2500 rpm / min for 6 min under a pressure of 12 MPa to uniformly disperse the ammonia molecules in the form of nanoclusters. The solution was then aged at 3°C ​​for 16 h to form a homogeneous ammonia-isopropanol solution without stratification.

[0043] The HCl-isopropanol solution used was prepared as follows: anhydrous isopropanol was precooled to -8°C and placed in a jacketed reactor with a -15°C coolant circulating through the jacket. Dry HCl gas was introduced at a rate of 0.3 L / min with stirring at 1000 rpm / min to achieve a 1.0 mol / L HCl-isopropanol solution. During stirring, when the solution temperature rose above -3°C, enhanced cooling and intermittent addition were activated. When the solution temperature was higher than -3°C, the jacket coolant temperature was lowered to -25°C, the stirring speed was increased to 1200 rpm / min, and the introduction of HCl gas was suspended. After the temperature dropped to -5°C, HCl gas was introduced at a low speed of 0.1 L / min for 5 min, and then the original introduction rate was restored until the temperature dropped below -5°C.

[0044] The remaining steps are the same as in Example 4.

[0045] <Example 6> A method for optimizing the gelatinization and rheological properties of wheat starch by adding modified pectin differs from Example 5 in that: Step 3: Place the modified pectin and wheat starch in a high-speed shear mixer at a mass ratio of 1:6, control the mixing temperature to 28°C, and stir at 2500 rpm for 12 minutes to form a primary dispersion system; The primary dispersion system was transferred to an ultrasonic treatment tank and subjected to ultrasonic treatment at a frequency of 30 kHz and a power density of 8 W / cm² for 25 minutes at 45°C to promote the formation of a three-dimensional network structure between the pectin molecular chains and starch granules through hydrogen bonding and hydrophobic interactions. The mixed solution after ultrasonic treatment was allowed to stand at 5°C for 3 h to allow the composite network structure to fully self-assemble, and finally a homogeneous starch-pectin composite system was obtained.

[0046] The remaining steps are the same as in Example 5.

[0047] Comparative Example 1 Natural apple pectin (initial esterification degree DE0 = 73%, amidation degree DA0 = 2%, molecular weight 150 kDa) was taken and thoroughly mixed with wheat starch in a mass ratio of 1:6 using a vortex mixer to obtain a starch-pectin composite network system.

[0048] Comparative Example 2 The difference from Example 1 is that in step 2, when it is detected that the DE drops to 30%, HCl-isopropanol solution is immediately added dropwise to carry out the amidation stage.

[0049] The remaining steps are the same as in Example 1.

[0050] Comparative Example 3 Gelatin with a molecular weight of 150 kDa was taken and thoroughly mixed with wheat starch in a mass ratio of 1:6 using a vortex mixer to obtain a starch-gelatin composite system.

[0051] Comparative Example 4 Xanthan gum with a molecular weight of 150 kDa was taken and thoroughly mixed with wheat starch in a mass ratio of 1:6 using a vortex mixer to obtain a starch-xanthan gum composite system.

[0052] Comparative Example 5 Gum arabic with a molecular weight of 150 kDa was taken and thoroughly mixed with wheat starch in a mass ratio of 1:6 using a vortex mixer to obtain a starch-gum arabic composite system.

[0053] Comparative Example 6 Carrageenan with a molecular weight of 150 kDa was taken and mixed with wheat starch in a mass ratio of 1:6 using a vortex mixer to obtain a starch-carrageenan composite system.

[0054] <Determination of Degree of Esterification, Degree of Amidation, and Molecular Weight> The modified pectins in Examples 1 to 6 and Comparative Example 2 were taken and their esterification degree, amidation degree and molecular weight were measured respectively.

[0055] 1. Determination of degree of esterification (DE) Method: Acid-base titration (refer to GB 25533-2010) Procedure: Accurately weigh 0.5 g of pectin sample and dissolve it in 50 mL of deionized water. Heat to 60°C and stir to dissolve. Add 5 drops of phenolphthalein indicator and titrate with 0.1 mol / L NaOH standard solution until it turns pink (pH ≈ 8.3). Record the volume V1 (free carboxylic acid titration value). Add 20 mL of 0.5 mol / L NaOH solution and saponify in a boiling water bath for 30 min. After cooling, back-titrate with 0.1 mol / L HCl until it becomes colorless. Record the volume V2 (total carboxylic acid titration value). Calculation: DE(%)=(1-V1 / V2)×100.

[0056] 2. Determination of degree of amidation (DA) Method: Kjeldahl nitrogen determination with FTIR verification (refer to ISO 1871:2009) Steps: Weigh 0.2 g of pectin sample and determine the total nitrogen content using a Kjeldahl nitrogen analyzer; calculate the degree of amidation based on the molar ratio of carboxylic acid and amide groups in the pectin molecule: DA (%) = amide nitrogen content / total nitrogen content × 100; By FTIR (wave number range 4000-400 cm -1) to verify the characteristic peak of the amide group (1650 cm -1 , C=O stretching vibration; 1550 cm -1 , NH bending vibration).

[0057] 3. Molecular weight (Mw) determination method Methods: Gel permeation chromatography coupled with multi-angle light scattering (GPC-MALS) Instruments and parameters: Chromatographic column: TSKgel GMPWXL (7.8 mm × 300 mm); Mobile phase: 0.1 mol / L NaNO3 solution (containing 0.02% NaN3), flow rate 0.6 mL / min; Detector: DAWN HELEOS II MALS (wavelength 658 nm), Optilab T-rEX differential refractive index detector; Data processing: ASTRA software was used to calculate the weight-average molecular weight (Mw).

[0058] The test results are shown in Table 1.

[0059] Table 1. Comparison of esterification degree, amidation degree and molecular weight determination results DE(%) DA(%) Mw(kDa) Initial value 73.0 2.0 150 Example 1 8.2 57.2 188 Example 2 7.8 55.1 182 Example 3 9.5 58.5 185 Example 4 8.5 60.4 188 Example 5 6.9 57.2 182 Example 6 7.2 58.6 186 Comparative Example 2 30.1 36.7 175 Table 1 shows the evolution of the degree of esterification, degree of amidation, and molecular weight of the modified pectins. The initial natural pectin had a DE of 73.0%, a DA of 2.0%, and a Mw of 150 kDa, indicating a high degree of esterification, a low degree of amidation, and a medium molecular weight. After modification, the DE of Examples 1 to 6 was significantly reduced to below 10% (6.9% to 9.5%), while the DA increased to 55% to 60%, and the Mw increased to 182 to 188 kDa. This change is attributed to a synergistic effect of the process: the deesterification stage uses an ammonia-isopropanol solution to selectively remove ester groups, releasing carboxylic acid groups, which provide reactive sites for the subsequent amidation stage. The staged addition of HCl-isopropanol solution converts carboxylic acid groups into amide groups, significantly increasing the DA. Simultaneously, the ultrafiltration membrane (molecular weight cutoff 100 kDa) effectively removes low-molecular-weight pectin fragments (<100 kDa), retaining and concentrating high-molecular-weight components, resulting in an increase in Mw. Comparative Example 2 failed to meet deesterification standards, resulting in insufficient carboxylic acid groups and limited amidation efficiency. Furthermore, some molecular chains may have had an Mw lower than that of the examples due to incomplete reaction or degradation. The data demonstrate that the modification process, through precise control of ester removal, amide introduction, and molecular weight screening, achieves targeted optimization of pectin structure, laying the chemical foundation for constructing functionally enhanced starch-pectin composite systems.

[0060] <Starch gelatinization measurement> The starch composite system in each embodiment and comparative example was heat treated by gradually increasing the temperature using a rapid viscosity analyzer to induce starch gelatinization. The heating program was as follows: the composite system was kept at 50°C for 1 minute, then heated from 50°C to 95°C at a heating rate of 12°C / min, and then cooled to 50°C at the same rate and held for 2 minutes. The gelatinization curve (e.g. Figure 1 and Figure 2 The gelatinization parameters were recorded (as shown in Table 2).

[0061] Table 2. Comparison of gelatinization parameters Depend on Figure 1 As can be seen from the gelatinization test curve in Figure 2 and the gelatinization parameters in Table 1, the gelatinization viscosity and gelatinization problems of the starch composite system in Examples 1-6 have been significantly improved and enhanced. And compared with Comparative Examples 1-6, Examples 1-6 are more effective in optimizing the gelatinization of starch. This shows that the low-ester, high-amide, high-molecular-weight apple pectin prepared by the present invention can form relatively dense hydrogen bonds with starch, thereby forming a more stable composite gel network structure. The presence of low-ester, high-amide, high-molecular-weight apple pectin will also limit the adsorption of water molecules by starch, and ultimately increase the gelatinization temperature of starch.

[0062] <Starch rheology measurement method> The storage modulus (G′) and loss modulus (G″) of the starch composite system in each embodiment and comparative example after heat treatment were measured using a rheometer. A dynamic frequency sweep program was used, the strain was set to 1%, and the frequency sweep range was 0.1 Hz to 10 Hz. The storage modulus curve and loss modulus curve of the starch composite system were obtained, and the results are shown in FIG. Figure 3 and 4 shown.

[0063] Depend on Figure 3 and 4 It can be seen that the starch G′ and G″ added with low-ester, high-amide, high-molecular-weight apple pectin are both higher than those of Comparative Examples 1-6, and exhibit a typical weak gel system. This indicates that the density and viscoelasticity of the starch gel network are greatly improved after the addition of pectin prepared by this invention. The presence of low-ester, high-amide, high-molecular-weight apple pectin promotes the aggregation of wheat starch granules, strengthens the connection between starch granules, and strengthens the gel network of the composite system.

[0064] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin, characterized in that: The following steps are involved: Step 1: Prepare modified pectin: Take natural pectin and adjust its initial esterification degree, molecular weight and amidation degree so that the esterification degree is less than 10%, the molecular weight is greater than 100 kDa and the amidation degree is greater than 50%; Step 2: Constructing a starch-pectin composite system: Mixing the modified pectin obtained in step 1 with wheat starch in a mass ratio of 1:4-1:9 to form a composite network structure.

2. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin according to claim 1, wherein: The preparation of the modified pectin comprises the following steps: Step a, molecular weight protection stage: dissolving natural pectin in ultrapure water to form a pectin solution with a mass concentration of 2%-4%, and precooling at 2-6°C; Step b, deesterification stage: the pre-cooled pectin solution is mixed with an ammonia-isopropanol solution having a concentration of 3.5-4.5 mol / L, and reacted under magnetic stirring to reduce the degree of esterification to less than 10%; Step c, amidation stage: adding a 0.5-1.5 mol / L HCl-isopropanol solution to the deesterified solution, adjusting the pH to 3.8-4.2 under magnetic stirring, and increasing the degree of amidation to above 50%; Step d, post-treatment: filtration using an ultrafiltration membrane with a molecular weight cutoff of 100 kDa, washing the precipitate multiple times with isopropanol solution to remove unreacted reagents and low molecular weight pectin, and vacuum drying to finally obtain modified pectin with a molecular weight greater than 100 kDa.

3. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin as claimed in claim 2, wherein: In step a, natural pectin is mixed with 40-50°C ultrapure water, stirred at 800-1200 rpm / min using a magnetic stirrer for 30-60 minutes until completely dissolved, and then cooled to 2-6°C at a rate of 0.5-1°C / min and kept at a constant temperature for 1-2 hours to form a homogeneous pre-cooled solution without gel lumps.

4. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin as claimed in claim 2, wherein: The step b further includes dynamically regulating the reaction parameters according to the initial degree of esterification DE0 of the natural pectin. The volume ratio of the ammonia-isopropanol solution to the pre-cooled pectin solution is calculated according to Formula 1: (0.05×DE0+0.75), wherein DE0 in the formula is the percentage value of the degree of esterification. The reaction temperature is maintained at 2-6°C, and the stirring rate is set according to the DE0 value: When DE0≥70%, the stirring rate is 500-600 rpm / min; When 50%≤DE0<70%, the stirring rate is 400-500 rpm / min; When DE0 < 50%, the stirring rate is 200-300 rpm / min; The degree of esterification was monitored in real time during the reaction, and the deesterification stage was completed when the degree of esterification was lower than 10%.

5. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin as claimed in claim 4, characterized in that: In step c, the HCl-isopropanol solution is added dropwise to the deesterified solution in batches, specifically: First addition: Based on the initial amidation degree of natural pectin (DA0), the droplet acceleration rate is calculated according to the formula V1=0.4×DA0+6. A 1.3-1.5 mol / L high-concentration HCl-isopropanol solution is used, and the magnetic stirring speed is simultaneously started to 300-500 rpm / min until the pH of the system drops to 5.8-6.

2. Second addition: switch to a 1.0-1.2 mol / L medium-concentration HCl-isopropanol solution, reduce the drop rate to 4-6 mL / min, and increase the stirring speed to 800-1000 rpm / min until the pH drops to 4.5-5.0; Final addition: Use a 0.5-0.8 mol / L low-concentration HCl-isopropanol solution, reduce the drop rate to 0.5-0.7 mL / min, maintain the stirring speed at 800-1000 rpm / min, and adjust the pH to 3.8-4.2; Wherein, DA0 is the percentage value of the degree of amidation, and V1 is the dropwise acceleration rate of the HCl-isopropanol solution, mL / min.

6. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin as claimed in claim 2, wherein: The preparation process of the ammonia-isopropanol solution is: Precool anhydrous isopropanol to -5-0°C and mix with 25-28% concentrated ammonia water to a final concentration of 3.5-4.5 mol / L to form an initial ammonia-isopropanol solution; The initial ammonia-isopropanol solution is placed in a high-pressure homogenizer and subjected to shearing treatment at 2000-2500 rpm / min under a pressure of 10-15 MPa for 5-8 minutes to uniformly disperse the ammonia molecules in the form of nanoclusters; Aging at 2-5°C for 12-24 h forms a homogeneous ammonia-isopropanol solution without stratification.

7. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin as claimed in claim 2, wherein: The preparation process of the HCl-isopropanol solution is as follows: Precool anhydrous isopropyl alcohol to -10~-5℃ and place it in a jacketed reactor with a -15℃ coolant circulating in the jacket; Dry HCl gas was introduced at a rate of 0.2-0.4 L / min and stirred at 1000 rpm / min to prepare an HCl-isopropanol solution with a concentration of 0.5-1.5 mol / L. During the stirring process, when the solution temperature is higher than -3°C, the enhanced cooling and intermittent aeration mode is triggered until the temperature drops below -5°C.

8. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin as claimed in claim 7, wherein: The enhanced cooling and intermittent introduction mode is specifically as follows: when the solution temperature is higher than -3°C, the jacket coolant temperature is reduced to -25°C, the stirring speed is increased by 10-20%, and the introduction of HCl gas is suspended. After the temperature drops to -5°C, HCl gas is introduced at a low speed of 0.1 L / min for 5 minutes, and then the original introduction rate is restored.

9. The method for optimizing the gelatinization and rheological properties of wheat starch based on the addition of modified pectin according to claim 1, wherein: The specific process of constructing the starch-pectin composite system in step 2 is as follows: Place modified pectin and wheat starch in a high-speed shear mixer at a mass ratio of 1:4-1:9, control the mixing temperature to 25-30°C, and stir at a speed of 2000-3000 rpm / min for 10-15 minutes to form a primary dispersion system; Transfer the primary dispersion system to an ultrasonic treatment tank and apply ultrasonic treatment at a frequency of 20-40 kHz and a power density of 5-10 W / cm² for 20-30 minutes at 40-50°C to promote the formation of a three-dimensional network structure between the pectin molecular chains and starch granules through hydrogen bonding and hydrophobic interactions; The mixed solution after ultrasonic treatment was allowed to stand at 4-6°C for 2-4 h to allow the composite network structure to fully self-assemble, and finally a homogeneous starch-pectin composite system was obtained.

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