A modified starch and its heat treatment production method

Abstract

This invention discloses a modified starch and a heat treatment production method, relating to the field of modified starch technology, including: S1, construction and impregnation of a composite modification system; S2, pre-drying lattice activation; S3, solid-phase esterification and cross-linking reaction; this invention achieves deep penetration and uniform grafting of the modifier by controlling moisture pre-activation and gradient temperature solid-phase reaction, resulting in a robust cross-linking network and excellent anti-aging properties, exhibiting high reaction efficiency, excellent high-temperature shear stability and freeze-thaw stability, while maintaining good whiteness and appearance quality.

Description

Technical Field

[0001] This invention relates to the field of modified starch technology, specifically to a modified starch and a heat treatment production method. Background Technology

[0002] Modified starch is a product that uses physical, chemical, or enzymatic methods to change the molecular structure and physicochemical properties of natural starch, thereby adapting it to the requirements of specific industrial applications. Heat treatment is a commonly used preparation process, which usually uses heat energy to drive the modifier to react chemically with starch molecules under specific temperature conditions, so as to improve the gelatinization characteristics, stability and processing adaptability of starch. Its basic principle is to use the energy provided by the heating equipment to overcome the reaction potential barrier, so that the modifier binds to the molecular chain of starch particles, or promotes the formation of cross-linked structures between starch molecular chains.

[0003] However, existing heat treatment preparation technologies still face many challenges in practical applications. On the one hand, in traditional wet processes or reaction systems without precise control, the moisture content in the reaction medium often fails to reach an ideal equilibrium. Excessive moisture can easily induce side reactions such as hydrolysis, leading to the consumption of modifying agents without effective grafting onto the starch. This not only reduces the utilization rate of raw materials but also results in a lower degree of reaction in the final product. On the other hand, conventional dry heating processes are insufficient in heat transfer and reaction uniformity control. Under rapid or continuous high temperatures, the surface of starch granules is prone to changes in properties before the interior, and even surface gelatinization or crusting may occur. This hinders the penetration and diffusion of modifying agents into the granules. This non-uniformity of the reaction leads to large fluctuations in the quality of the modified starch. In practical use, it often exhibits insufficient shear resistance and is prone to aging phenomena such as decreased viscosity, severe water separation, and yellowing when subjected to freeze-thaw cycles or long-term storage, making it difficult to meet the stringent requirements of the high-end food industry for the performance stability of modified starch. Summary of the Invention

[0004] The purpose of this invention is to provide a modified starch and a heat treatment production method, which solves the problems existing in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for producing modified starch by heat treatment, comprising the following steps: S1. Construction and Impregnation of Composite Modification System: Weigh 100 parts by weight of starch matrix material, 0.5-5.0 parts by weight of hydrophobic modifier, 1.0-10.0 parts by weight of polycarboxylic acid crosslinking agent, and 0.1-3.0 parts by weight of catalyst; dissolve or disperse the hydrophobic modifier, polycarboxylic acid crosslinking agent, and catalyst in a solvent, adjust the pH value to 3.0-5.0 using a 1-5wt% hydrochloric acid or sodium hydroxide solution to prepare a homogeneous modification activation solution; under high-speed mechanical shearing conditions, uniformly coat the surface of starch matrix material with the modification activation solution using an atomized spray method, and mix evenly to obtain a starch mixture; S2. Pre-drying lattice activation: The starch mixture is placed in a drying device and dried at varying temperatures within the first preset temperature range. The moisture content is adjusted to 5%-10%, allowing the modifier molecules to penetrate into the amorphous region of the starch granules and be pre-fixed, thus obtaining a pre-activated starch intermediate. S3. Solid-phase esterification and cross-linking reaction: The pre-activated starch intermediate is placed in a fluidized bed reactor and subjected to a gradient heating reaction in a second preset temperature range under a protective atmosphere of nitrogen gas to induce solid-phase esterification and cross-linking, thereby obtaining modified starch.

[0006] Preferably, in step S3, the solid-phase graft copolymerization reaction adopts a gradient temperature control mode, specifically including: Dehydration phase change stage: The reaction temperature is raised to T1 at a heating rate of 2-5℃ / min, and 100℃≤T1≤115℃ is maintained at a constant temperature for 15-30 minutes to remove bound water and form a porous structure. Solid-phase reaction stage: Continue heating to T2, with 120℃≤T2≤150℃, and maintain the constant temperature for 30-60 minutes to initiate the solid-phase esterification crosslinking reaction under the action of the catalyst.

[0007] Preferably, in step S1, the hydrophobic modifier is selected from octenyl succinic anhydride or dodecenyl succinic anhydride; the polycarboxylic acid crosslinking agent is selected from anhydrous citric acid, maleic anhydride or adipic acid; and the catalyst is selected from sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium hypophosphite or urea.

[0008] Preferably, in step S1, the solvent is water, ethanol, or a mixed solution, and the amount of solvent used is 3%-15% of the mass of the starch matrix material; The rotational speed of high-speed mechanical shearing is 800-2000 rpm.

[0009] Preferably, in step S2, the first preset temperature range is 50℃-60℃.

[0010] Preferably, a post-processing step is included after step S3: S4: The modified starch obtained is washed, neutralized, dried and pulverized to remove unreacted residues and adjust the pH value.

[0011] Preferably, in step S1, the starch matrix material is corn starch or tapioca starch.

[0012] A modified starch is also provided, which is prepared by the above-mentioned heat treatment production method of modified starch, with a degree of substitution of 0.007-0.045 and a high temperature shear stability of ≥94%, exhibiting excellent anti-aging properties.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention effectively balances the diffusion and penetration of the modifying agent within the particles and the chemical reaction by precisely controlling the moisture environment in the system before the reaction and using a phased gradient heating strategy. The initial mild heat treatment process constructs suitable mass transfer channels in the starch particle structure, avoiding particle surface closure or crusting caused by sudden temperature changes. This ensures that the modifier can penetrate deeply into the starch particles and undergo uniform chemical grafting, thereby improving reaction efficiency, ensuring the uniformity of the product microstructure, and effectively controlling energy consumption in the production process.

[0014] 2. The present invention has a robust and dense three-dimensional network skeleton, which endows the material with excellent mechanical shear resistance and heat resistance stability. When faced with high-speed mechanical stirring or high-temperature sterilization environments commonly encountered in food processing, it can maintain stable viscosity characteristics and microstructure, overcoming the problems of structural collapse and drastic viscosity drop that are prone to occur in conventional products under harsh processing conditions, thereby ensuring the continuity and reliability of product quality in downstream industrial production.

[0015] 3. This invention successfully introduces modified groups with specific functions into the starch molecular chain. The resulting steric hindrance effectively hinders the rearrangement and association of starch molecules during the aging process, endowing the product with excellent freeze-thaw stability and anti-aging properties. It solves the problems of water separation, layering, and taste deterioration that easily occur in frozen or refrigerated foods during their shelf life. Moreover, the controlled process environment avoids the damage to the matrix caused by high-temperature oxidation, ensuring that the final product has good whiteness and delicate sensory quality, thus broadening its application range in the food industry where color requirements are high. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a correlation analysis diagram of the degree of substitution (DS) and anti-aging performance (water separation rate) of this invention. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0018] Before formal preparation, this invention pre-established a dynamic correlation model between pre-dried moisture content and solid-phase reaction activation energy to determine the optimal drying termination point in step S2. Specifically, multiple groups of starch mixtures coated with the same modified dosage were prepared. At different moisture content points ranging from 3% to 15%, the starting temperature and endothermic peak area of ​​the subsequent esterification reaction were measured using differential scanning calorimetry (DSC). Regression analysis data showed a non-linear U-shaped correlation between moisture content and reaction activation energy. When the moisture content was controlled within the range of 5% to 10%, the amorphous region on the surface of the starch granules was in the critical transition zone from a rubbery to a glassy state. At this point, the diffusion coefficient of the modifier molecules reached its peak, and the required reaction activation energy was lowest. Based on this model, this invention set the moisture control target for step S2 to 5% to 10%, aiming to utilize residual moisture as a molecular lubricant to assist the macromolecular modifier in penetrating into the micropores inside the granules, while avoiding side reactions such as hydrolysis competition caused by excessive moisture.

[0019] Example 1: This embodiment provides a method for producing modified starch through heat treatment, which is the optimal implementation mode of the present invention; S1. Construction and Impregnation of Composite Modification System: Weigh 100 parts by weight of starch matrix material, 0.5 to 5.0 parts by weight of hydrophobic modifier, 1.0 to 10.0 parts by weight of polycarboxylic acid crosslinking agent, and 0.1 to 3.0 parts by weight of catalyst; dissolve or disperse the hydrophobic modifier, polycarboxylic acid crosslinking agent, and catalyst in a solvent, adjust the pH value to 3.0 to 5.0 using 1 mol / L hydrochloric acid or sodium hydroxide solution, and prepare a homogeneous modification activation solution; under high-speed mechanical shearing conditions, use an atomized spraying method to uniformly coat the surface of starch matrix material, and mix evenly to obtain a starch mixture; In step S1 of this embodiment, 100 parts by weight of commercially available food-grade corn starch are selected as the starch matrix material; 2.0 parts by weight of octenyl succinic anhydride is selected as the hydrophobic modifier; 5.0 parts by weight of anhydrous citric acid is selected as the polycarboxylic acid crosslinking agent; and 1.0 part by weight of sodium dihydrogen phosphate is selected as the catalyst. The anhydrous citric acid and sodium dihydrogen phosphate, which are water-soluble components, are dissolved, and the octenyl succinic anhydride, which is the hydrophobic component, is dispersed in water, which is the solvent. The amount of solvent is 8% of the mass of the starch matrix material, which is in the range of 3% to 15%. The pH value is adjusted to 4.0 to prepare a homogeneous modified activation solution. Under the condition that the high-speed mechanical shearing speed is set to 1200 rpm, the operation is carried out by atomization spraying. In this step, the strong centrifugal force generated by the high-speed mechanical shearing, combined with the atomized droplets, overcomes the high viscosity resistance of octenyl succinic anhydride and its poor water solubility, so that it forms a uniform monomolecular layer coating on the surface of starch granules, laying the foundation for the uniformity of subsequent reactions. S2. Pre-drying lattice activation: The starch mixture is placed in a drying device and subjected to variable temperature drying within the first preset temperature range. The drying rate is controlled and the moisture content is adjusted to 5% to 10%, so that the modifier molecules penetrate into the amorphous region of the starch particles and are pre-fixed to obtain a pre-activated starch intermediate. In step S2 of this embodiment, the starch mixture is placed in a fluidized bed drying device and subjected to variable temperature drying at a first preset temperature range of 55°C. The drying rate is strictly controlled and the moisture content is adjusted to 8%. This pre-drying lattice activation step is not a simple physical dehydration, but rather induces the micropores on the surface of the starch particles to open through a gentle thermal field. The modifier molecules attached to the surface are driven by capillary force to penetrate deeply into the amorphous region of the starch particles and pre-fixed, thereby reducing the activation energy of the subsequent solid-phase reaction and preventing the reaction from only stopping at the outermost layer of the particles. S3. Solid-phase esterification and cross-linking reaction: The pre-activated starch intermediate is placed in a fluidized bed reactor. Under a protective atmosphere of nitrogen, a gradient temperature increase reaction is carried out according to the second preset temperature range to induce solid-phase esterification and cross-linking to obtain modified starch. Specifically, it includes: a dehydration phase change stage, in which the reaction temperature is increased to T1 at a heating rate of 2 to 5 °C / min, and T1 satisfies 100 °C ≤ T1 ≤ 115 °C, and the temperature is maintained for 15 to 30 minutes to remove bound water and form a porous structure; a solid-phase reaction stage, in which the temperature is further increased to T2, and T2 satisfies 120 °C ≤ T2 ≤ 150 °C, and the temperature is maintained for 30 to 60 minutes to initiate the solid-phase esterification and cross-linking reaction under the action of a catalyst. The reaction proceeds to the dehydration phase transition stage, where the temperature is increased to T1 (105℃) at a rate of 3℃ / min and maintained at this temperature for 20 minutes. This stage aims to gently remove bound water from the starch granules, preventing the rapid vaporization of water at high temperatures from damaging the granule integrity. Simultaneously, it constructs a porous structure in situ that facilitates reactant transport. The reaction then proceeds to the solid-phase reaction stage, where the temperature is further increased to T2 (130℃) and maintained at this temperature for 45 minutes, meeting the preset reaction time requirements. Under this high-temperature environment, the catalyst sodium dihydrogen phosphate releases a protic acid, which efficiently catalyzes the opening of the anhydride bond in octenyl succinic anhydride and its esterification with the starch hydroxyl groups. Simultaneously, anhydrous citric acid forms diester bonds between starch molecular chains, constructing a modified starch with a three-dimensional network structure. Step S3 is followed by a post-processing step S4: the modified starch is washed, neutralized and dried and pulverized to remove unreacted residues and adjust the pH value. After the reaction in step S3 is completed, step S4 is performed: after the material in the reactor is cooled to room temperature, the modified starch is dispersed in a mixture of water and ethanol and washed, neutralized to neutral with sodium carbonate solution, and then dried and pulverized by airflow to obtain the finished product. The modified starch prepared in this example exhibits excellent thickening stability and anti-aging properties in sauce products, solving the problem of water separation in traditional sauces during shelf life.

[0020] Example 2: This embodiment provides a method for producing modified starch through heat treatment, aiming to explore the reaction efficiency at higher temperature parameters and its applicability to cassava starch matrix; In step S1, the starch matrix material is corn starch or cassava starch; in this embodiment, 100 parts of cassava starch are selected as the starch matrix material; 4.0 parts of dodecenyl succinic anhydride are selected as the hydrophobic modifier; 8.0 parts of maleic anhydride are selected as the polycarboxylic acid crosslinking agent; and 2.5 parts of urea are selected as the catalyst. In step S1, the solvent is water, ethanol, or a mixture thereof, and the amount of solvent used is 3% to 15% of the mass of the starch matrix material; the rotation speed of the high-speed mechanical shearing is 800 to 2000 rpm; the solvent is a mixture of ethanol and water prepared at a mass ratio of 1:1, and the amount used is 12% of the mass of the starch matrix material, and the pH value is adjusted to 3.5; the starch mixture is obtained under the condition of a high-speed mechanical shearing speed of 1800 rpm; the high rotation speed shearing force helps the high viscosity dodecenyl succinic anhydride to be dispersed more finely, while the addition of ethanol reduces the surface tension of the system and promotes the spreading of the hydrophobic modifier on the hydrophilic starch surface; In step S2, the first preset temperature range is 50°C to 60°C; the starch mixture is dried at 60°C in the first preset temperature range, and the moisture content is adjusted to 6% to obtain a pre-activated starch intermediate; the lower moisture content is beneficial to the forward shift of the esterification equilibrium in the subsequent high-temperature reaction, thereby increasing the degree of substitution. In step S3, the solid-phase graft copolymerization reaction is carried out under a protective atmosphere of nitrogen to prevent starch oxidation. During the dehydration phase change stage, the temperature is increased to T1 (115°C) at a rate of 5°C / min and held for 15 minutes. In the solid-phase reaction stage, the temperature is increased to T2 (145°C) and held for 30 minutes. This high-temperature, short-time process utilizes the buffering effect and catalytic ability of ammonia gas generated from the decomposition of urea at high temperatures on the microenvironment pH, promoting the rapid grafting of the hydrophobic modifier and the polycarboxylic acid crosslinking agent onto the starch backbone. After post-treatment in step S4, the modified starch is applied to frozen dough. The introduction of its unique hydrophobic groups endows the product with excellent freeze-thaw stability, effectively inhibiting the damage to the gluten network caused by ice crystal growth.

[0021] Example 3: This embodiment provides a method for producing modified starch by heat treatment, focusing on efficient modification under low chemical load and mild reaction conditions; In step S1, the hydrophobic modifier is selected from octenyl succinic anhydride or dodecenyl succinic anhydride; the polycarboxylic acid crosslinking agent is selected from anhydrous citric acid, maleic anhydride, or adipic acid; the catalyst is selected from sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium hypophosphite, or urea; in step S1, 100 parts of corn starch are selected as the starch matrix material; 0.8 parts of octenyl succinic anhydride are selected as the hydrophobic modifier; 2.0 parts of adipic acid are selected as the polycarboxylic acid crosslinking agent; 0.5 parts of disodium hydrogen phosphate are selected as the catalyst; water is used as the solvent at 3%; hydrochloric acid is used to adjust the pH to 4.5; the high-speed mechanical shearing speed is 900 rpm; the low solvent content combined with high-speed mechanical shearing achieves a near-dry mixing effect, minimizing subsequent drying energy consumption; in the solid-phase reaction stage, the preset reaction time is 30 to 60 minutes; In step S2, the moisture content is adjusted to 9% within the first preset temperature range of 50°C; In step S3, the solid-phase esterification and cross-linking reactions adopt a relatively mild gradient: in the dehydration phase change stage, the temperature is increased to T1 (100℃) at 2℃ / min and held for 30 minutes; in the solid-phase reaction stage, the temperature is increased to T2 (125℃) and held for 60 minutes. The long-term mild reaction is conducive to the full reaction of low doses of adipic acid and the formation of a uniformly distributed cross-linking network. At the same time, nitrogen protection prevents oxidation and yellowing caused by prolonged heating. After the treatment in step S4, the resulting product has high whiteness and a delicate paste texture, which is suitable for dairy product additives with extremely high color requirements.

[0022] Example 4: This embodiment verifies the product performance under extreme process parameters, aiming to prepare highly shear-resistant modified starch; Step S1: Construction and impregnation of the composite modified system; In step S1, 100 parts of cassava starch were selected as the starch matrix material; 5.0 parts of octenyl succinic anhydride were selected as the hydrophobic modifier, which is the upper limit; 10.0 parts of anhydrous citric acid were selected as the polycarboxylic acid crosslinking agent, which is the upper limit; 3.0 parts of sodium hypophosphite were selected as the catalyst; water was used as the solvent, with a dosage of 15% and the pH value adjusted to 3.0; the high-speed mechanical shearing speed was 2000 rpm; the high concentration of modifiers was added to construct an extremely high-density crosslinking network; Step S2: Pre-drying lattice activation; at the first preset temperature range of 58°C, the moisture content is adjusted to 5%, i.e., the lower limit, to obtain the pre-activated starch intermediate; the extremely low moisture content creates conditions for a high degree of substitution reaction, forcing the reaction to shift towards the formation of esters and water; Step S3: Solid-phase graft copolymerization reaction; The solid-phase graft copolymerization reaction was set as follows: the dehydration phase change stage was heated to T1 at 110°C and held for 25 minutes; the solid-phase reaction stage was heated to T2 at 150°C, i.e., the upper limit, and held for 40 minutes; Under this high-temperature and high-concentration system, the hydrophobic modifier and the polycarboxylic acid crosslinking agent underwent strong solid-phase esterification, constructing a robust shear-resistant skeleton; After treatment in step S4, the modified starch exhibited an exceptional viscosity retention rate under industrial-grade high-temperature shear conditions, such as the canning process, demonstrating the synergistic enhancement effect of the dual modifying groups under extreme conditions.

[0023] Example 5: This embodiment provides an implementation method for balanced process parameters, which aims to balance energy consumption and product performance. Step S1: Construction and impregnation of the composite modified system; In step S1, 100 parts of corn starch were selected as the starch matrix material; 3.0 parts of octenyl succinic anhydride were selected as the hydrophobic modifier; 6.0 parts of anhydrous citric acid were selected as the polycarboxylic acid crosslinking agent; 1.5 parts of sodium dihydrogen phosphate were selected as the catalyst; water was used as the solvent at 10%; the pH value was adjusted to 3.8; and the high-speed mechanical shearing speed was 1500 rpm. Step S2: Pre-drying lattice activation; at a first preset temperature range of 52°C, the moisture content is adjusted to 7% to obtain a pre-activated starch intermediate; Step S3: Solid-phase graft copolymerization reaction; The parameters for the solid-phase graft copolymerization reaction are: during the dehydration phase change stage, the temperature is raised to T1 at 108°C and held for 20 minutes; during the solid-phase reaction stage, the temperature is raised to T2 at 135°C and held for 50 minutes. Under this process, the dehydration phase change stage and the solid-phase reaction stage are well coordinated, ensuring both the depth of the reaction and energy consumption control. After processing in step S4, the modified starch obtained has both good emulsifying ability and thermal stability, making it particularly suitable for fillings in baked goods, and can prevent the bursting phenomenon during high-temperature baking.

[0024] Comparative Example 1: This comparative example uses a traditional wet reaction process as a blank control group. The difference from Example 1 is that the pre-drying lattice activation in step S2 and the solid-phase graft copolymerization reaction in step S3 are not performed. The specific operation is as follows: 100 parts of corn starch are dispersed in 150 parts of water, and octenyl succinic anhydride, anhydrous citric acid and catalyst are added in the same amount as in Example 1. The mixture is stirred at 45°C for 12 hours, and then filtered, washed and dried. Due to the lack of high-temperature solid-phase reaction driving force and the presence of a large amount of water, the reversible equilibrium of the esterification reaction shifts towards hydrolysis, which limits the esterification efficiency.

[0025] Comparative Example 2: This comparative example uses a dry process without gradient temperature control to verify the necessity of gradient temperature increase. The difference from Example 1 is that step S3 does not include a dehydration phase change stage, and the temperature is directly and rapidly raised to 130°C for reaction. Due to the lack of a dehydration phase change stage to orderly remove bound water and pre-form a porous structure, the surface water of the starch granules evaporates rapidly in the early stage of the reaction, causing local gelatinization and crusting, which hinders the inward transfer of heat and molecules, resulting in poor product uniformity.

[0026] Comparative Example 3: This comparative example does not add hydrophobic modifiers and aims to verify the contribution of hydrophobic groups to resist aging. The difference from Example 1 is that octenyl succinic anhydride is not added in step S1, and crosslinking modification is carried out only by anhydrous citric acid. Due to the lack of steric hindrance effect caused by the introduction of long-chain hydrophobic groups, starch molecular chains are easy to reassociate after gelatinization and cooling.

[0027] Comparative Example 4: In this comparative example, nitrogen protection was not introduced during the reaction process to verify the effect of atmosphere control on product color. The difference from Example 1 is that the solid-phase graft copolymerization reaction in step S3 was carried out in a normal air atmosphere. Due to the presence of oxygen at high temperature, starch molecules and modifiers underwent partial oxidative degradation, generating colored groups.

[0028] Verification experiment: To verify the technical effects of the method for producing modified starch by heat treatment of the present invention and the resulting product, performance tests were conducted on the starch samples prepared in Examples 1-5 and Comparative Examples 1-4 above.

[0029] Testing standards: Degree of substitution (DS): Determined by acid-base titration, in accordance with GB / T20378-2006 standard, reflecting the efficiency of esterification reaction; Freeze-thaw water separation rate: Prepare a 6% starch paste, freeze it at -18℃ for 24 hours and thaw it at 25℃ for 4 hours five times, then centrifuge it at 3000 rpm for 20 minutes and measure the water separation rate; the lower the water separation rate, the better the anti-aging properties. High-temperature shear stability: Prepare 5% starch milk, use RVA rapid viscometer to shear at 95℃ and 500rpm for 30 minutes, and calculate the percentage ratio of final viscosity to peak viscosity; Whiteness: Measured using an R457 whiteness meter, reflecting the product's appearance quality and degree of oxidation; each sample was tested three times, and the average value was taken.

[0030] Specific testing process: All samples were pretreated and measured strictly according to the above standard methods; in the degree of substitution determination, the samples were washed with ethanol 5 times in advance to thoroughly remove unreacted free acid; in the RVA test, the heating rate and shear rate were kept consistent to ensure the comparability of the data.

[0031] Data table: Table 1. Performance test results of modified starch in each embodiment and comparative example.

[0032] Result analysis components: As shown in Table 1, the modified starch prepared by this invention exhibits excellent performance in all key indicators. Comparing the degree of substitution of 0.018 in Example 1 with that of 0.005 in Comparative Example 1, it can be seen that, under the same raw material feed ratio, the pre-drying lattice activation + solid-phase esterification process adopted in this invention improves the reaction efficiency by more than 3 times. This is because the presence of a large amount of water in the wet process leads to severe hydrolysis side reactions of the esterifying agent. In contrast, step S2 of this invention precisely controls the moisture content to 5%-10%, which not only preserves the solvent channels required for molecular diffusion but also suppresses hydrolysis competition to the greatest extent. In addition, Example 4 achieved a relatively high degree of substitution of 0.042 with a maximum feed amount of 5.0 parts, verifying that in this solid-phase system, as the reactant concentration increases, the catalyst sodium hypophosphite can effectively reduce the activation energy and promote the esterification reaction to proceed in the forward direction. The high-temperature shear stability of Examples 1-5 remained above 94%, with Example 4 reaching as high as 99.3%, while Comparative Example 2 was only 82.1%. This is attributed to the unique gradient temperature control mode in step S3: the dehydration phase change stage gently removes bound water and constructs porous channels, avoiding premature crusting on the surface of starch granules; the subsequent solid-phase reaction stage allows the polycarboxylic acid crosslinking agent to penetrate deep into the particle interior with the assistance of a catalyst to complete dense crosslinking; the high stability of Example 4 proves that even under solid-phase conditions, as long as the process is appropriate, a high dose of crosslinking agent can construct a robust skeleton that can withstand industrial-grade high-temperature shearing. All examples with added hydrophobic modifiers showed excellent performance with freeze-thaw water separation rates below 4.1%. In particular, Example 3, even with only 0.8 parts of the hydrophobic modifier octenyl succinic anhydride, still had a water separation rate as low as 4.1%, far superior to Comparative Example 3 without added hydrophobic modifier. This fully demonstrates that the process of the present invention can uniformly graft trace amounts of hydrophobic groups onto the surface of starch granules, and the resulting steric hindrance effect effectively hinders the rearrangement and hydrogen bond association of amylose molecules, achieving excellent anti-aging capabilities at extremely low chemical costs. Comparing the whiteness of 92.1 in Example 1 with that of 76.4 in Comparative Example 4 confirms the crucial role of nitrogen protection. In high-temperature solid-phase reactions, oxygen is the main cause of starch oxidative browning. By using nitrogen protection throughout the process, the oxidation path is effectively blocked, ensuring that the product can maintain a high whiteness after high-temperature heat treatment, thus meeting the appearance requirements of high-end food additives. In summary, this invention overcomes the shortcomings of uneven reaction in traditional dry methods and low efficiency in wet methods by constructing a composite modification system, implementing pre-drying lattice activation, and employing a gradient temperature-controlled solid-phase esterification reaction, and successfully prepares modified starch with high reaction efficiency, high shear resistance, and excellent anti-aging properties.

[0033] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments that can be applied to other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for producing modified starch through heat treatment, characterized in that, Includes the following steps: S1. Construction and impregnation of the composite modified system: Weigh 100 parts by weight of starch matrix material, 0.5-5.0 parts by weight of hydrophobic modifier, 1.0-10.0 parts by weight of polycarboxylic crosslinking agent, and 0.1-3.0 parts by weight of catalyst; dissolve or disperse the hydrophobic modifier, polycarboxylic crosslinking agent and catalyst in a solvent, and adjust the pH value to 3.0-5.0 using a 1-5wt% hydrochloric acid or sodium hydroxide solution to prepare a homogeneous modified activation solution; Under high-speed mechanical shearing conditions, the modified activating liquid is uniformly coated onto the surface of the starch matrix material by atomized spraying, and the starch mixture is obtained by uniform mixing. S2. Pre-drying lattice activation: The starch mixture is placed in a drying device and dried at varying temperatures within the first preset temperature range. The moisture content is adjusted to 5%-10%, allowing the modifier molecules to penetrate into the amorphous region of the starch granules and be pre-fixed, thus obtaining a pre-activated starch intermediate. S3. Solid-phase esterification and cross-linking reaction: The pre-activated starch intermediate is placed in a fluidized bed reactor and subjected to a gradient heating reaction in a second preset temperature range under a protective atmosphere of nitrogen gas to induce solid-phase esterification and cross-linking, thereby obtaining modified starch.

2. The method for producing modified starch by heat treatment according to claim 1, characterized in that, In step S3, the solid-phase graft copolymerization reaction adopts a gradient temperature control mode, specifically including: Dehydration phase change stage: The reaction temperature is raised to T1 at a heating rate of 2-5℃ / min, and 100℃≤T1≤115℃ is maintained at a constant temperature for 15-30 minutes to remove bound water and form a porous structure. Solid-phase reaction stage: Continue heating to T2, with 120℃≤T2≤150℃, and maintain the constant temperature for 30-60 minutes to initiate the solid-phase esterification crosslinking reaction under the action of the catalyst.

3. The method for producing modified starch by heat treatment according to claim 1, characterized in that, In step S1, the hydrophobic modifier is selected from octenyl succinic anhydride or dodecenyl succinic anhydride; the polycarboxylic acid crosslinking agent is selected from anhydrous citric acid, maleic anhydride or adipic acid; and the catalyst is selected from sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium hypophosphite or urea.

4. The method for producing modified starch by heat treatment according to claim 1, characterized in that, In step S1, the solvent is water, ethanol, or a mixed solution, and the amount of solvent used is 3%-15% of the mass of the starch matrix material; The rotational speed of high-speed mechanical shearing is 800-2000 rpm.

5. The method for producing modified starch by heat treatment according to claim 1, characterized in that, In step S2, the first preset temperature range is 50℃-60℃.

6. The method for producing modified starch by heat treatment according to claim 1, characterized in that, Step S3 is followed by post-processing steps: S4: The modified starch obtained is washed, neutralized, dried and pulverized to remove unreacted residues and adjust the pH value.

7. The method for producing modified starch by heat treatment according to claim 1, characterized in that, In step S1, the starch matrix material is corn starch or tapioca starch.

8. A modified starch, prepared by the heat treatment method of any one of claims 1-7, characterized in that, It has a degree of substitution of 0.007-0.045 and a high-temperature shear stability of ≥94%, exhibiting excellent anti-aging properties.

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