Preparation method of high-stability etherified cross-linked starch and etherified cross-linked starch

Abstract

The invention belongs to the technical field of starch processing, and particularly discloses high-stability etherified cross-linked starch which is prepared by the steps of swelling inhibition, etherification, cross-linking, antibacterial compounding, dispersion and film formation, vacuum devolatilization, drying and the like. The invention also discloses high-stability etherified cross-linked starch, which is prepared from the following raw materials: edible starch, an etherifying agent, a swelling inhibitor, a composite cross-linking agent, an antibacterial agent and a dispersing agent. The etherified modified starch with high stability, high safety and multiple functions is successfully prepared through a fine process and optimization of the sequence and conditions of swelling inhibition, etherification, cross-linking, compounding and dispersion, and the problem of how to prepare the etherified modified starch through compounding of a cross-linking agent and precise process control on the premise of ensuring food safety (ethylene oxide residue is not detected) is solved. The viscosity, shear resistance, acid and alkali resistance and film-forming property of a starch product are greatly improved, and the technical problem that safety, functions and stability are difficult to consider in a traditional process is solved.

Description

Technical Field

[0001] This invention belongs to the field of starch processing technology, specifically a method for preparing highly stable etherified cross-linked starch and the etherified cross-linked starch itself. Background Technology

[0002] The cross-linking reaction is a reaction in which the hydroxyl groups of starch form diether bonds or diester bonds with etherifying agents having binary or multi-functional groups, bridging two or more starch molecules together to form a multidimensional network structure. In starch granules, the molecules are bonded together by hydrogen bonds to form the granular structure. When heated in hot water, the strength of these hydrogen bonds weakens, causing the granules to absorb water and swell, increasing their viscosity to its maximum value, indicating that the swelling granules have reached maximum hydration. Further heating causes the hydrogen bonds to break, the granules to break apart, and the viscosity to decrease. The strength of cross-linking chemical bonds is much higher than that of hydrogen bonds; they enhance the strength of the granular structure and inhibit granule swelling, breakage, and viscosity decrease.

[0003] As the degree of cross-linking increases, the number of cross-linked chemical bonds between starch molecules increases. With approximately 100 AGU (glucose dehydrated units), if there is only one cross-linked bond, the cross-linking completely inhibits the swelling of the particles in boiling water, preventing gelatinization. Cross-linked starch exhibits many properties superior to starch. Firstly, cross-linked starch increases gelatinization temperature and viscosity; its shear resistance is significantly improved compared to starch paste, where viscosity is greatly reduced by shear force, while low-degree cross-linking enhances stability. Furthermore, cross-linked starch demonstrates significantly better acid and alkali resistance than starch.

[0004] Existing starch crosslinking technologies have the following drawbacks: 1. Component redundancy and safety risks: Traditional hydroxyethyl crosslinked starch preparation relies on chloroethanol (chloroethyl ether residue), phosphorus oxychloride (chlorine residue), and a phosphate buffer system (increasing sodium content), leading to food safety hazards and environmental pressures. For example, the method described in CN107502227B uses propylene oxide etherification + industrial crosslinking agents, resulting in halogenated hydrocarbon residues that fail to meet food safety requirements. 2. Poor functional synergy: Single crosslinking agents (such as sodium trimetaphosphate) require sodium phosphate to maintain pH, but phosphates compete with starch for reaction, reducing crosslinking efficiency; plasticizing components (such as polycaprolactone) have poor compatibility with starch, affecting biodegradability. Some schemes attempting to eliminate crosslinking agents and rely entirely on physical components (such as gelatin and chitosan), while offering higher safety, have limited physical network strength. These networks are prone to collapse under high temperature, high shear, or extreme pH conditions, resulting in insufficient viscosity stability, boiling resistance, and freeze-thaw stability, making it difficult to meet the demands of harsh industrial applications. 3. High process complexity: The stepwise addition of multiple components (such as phosphate buffer first, followed by chloroethanol etherification) leads to instability of the reaction system and large fluctuations in the degree of substitution of the product.

[0005] Therefore, developing a food-grade, safe, streamlined, and multifunctional modified starch to meet the stringent performance requirements of frozen foods for high water retention and biodegradable packaging materials has become an urgent need for the food industry. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing highly stable hydroxyethyl crosslinked starch. Through refined processing and optimization of the sequence and conditions of "swelling inhibition → etherification → crosslinking → compounding → dispersion", a highly stable, highly safe, and multifunctional etherified modified starch is successfully prepared. This method solves the problem of how to significantly improve the viscosity, shear resistance, acid and alkali resistance, and film-forming properties of starch products through the compounding of crosslinking agents and precise process control, while ensuring food safety (no ethylene oxide residue was detected). It also solves the technical problem of the difficulty in balancing "safety, function, and stability" in traditional processes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing highly stable etherified modified starch includes the following steps: (a) Edible starch and swelling inhibitor are suspended in water to form a premixed system; the swelling inhibitor preferentially penetrates the gaps between starch particles, increases the ionic strength of the system, inhibits excessive swelling of starch under alkaline conditions, and avoids uneven subsequent reactions; (b) First, add an alkaline agent to the system in step (a) to adjust the pH value to 10.5-11.0, and then slowly introduce the etherifying agent to carry out the etherification reaction to prevent excessive local substitution. (c) Without separating the product, the composite crosslinking agent is directly added to the system of step (b) to carry out the crosslinking reaction; (d) The cross-linked product is cooled to 38-42℃, the pH value is adjusted to 6.5-7.0 with citric acid, and then the antibacterial agent is added to carry out the compound reaction; the antibacterial agent is added at low temperature to prevent the antibacterial agent molecules from being degraded at high temperature and to ensure antibacterial activity; weakly acidic conditions promote electrostatic adsorption; (e) Finally, add the dispersant at room temperature to avoid premature addition of the dispersant and competition for reaction with the etherifying agent; disperse the film under ultrasonic conditions for 5-15 minutes to ensure that the dispersant coats the starch granules. (f) Vacuum devolatilization and drying.

[0008] Preferably, in step (a), the water temperature is 35-40°C, the suspension mass concentration is 35-40%, and the stirring speed is 100-300 rpm.

[0009] Preferably, in step (a), the ionic strength of the premixed system is ≥0.6 mol / L.

[0010] Preferably, in step (b), the flow rate of ethylene oxide is ≤0.5 L / h·kg starch to avoid the formation of the byproduct ethylene glycol.

[0011] Preferably, in step (b), the etherification reaction is carried out at a temperature of 45–50°C for 4–6 hours, and the molar degree of substitution is controlled to be MS = 0.08–0.15.

[0012] Preferably, in step (c), the order of adding the composite crosslinking agent is as follows: first, sodium hexametaphosphate is added to chelate metal ions and activate the crosslinking activity of sodium trimetaphosphate; then, sodium trimetaphosphate is added to avoid excessively rapid hydrolysis of sodium trimetaphosphate at high temperatures.

[0013] Preferably, in step (c), when the temperature is increased from 50°C in the etherification stage to 55°C in the crosslinking stage, the rate must be ≤2°C / min to prevent the reaction system from changing abruptly and causing uneven crosslinking.

[0014] Preferably, sodium hexametaphosphate is dissolved at <40°C; otherwise, it is easily hydrolyzed to produce orthophosphate, resulting in a bitter taste.

[0015] Preferably, in step (c), the crosslinking reaction is carried out at a temperature of 50-55°C for 1.5-2 hours, and the degree of crosslinking is controlled to be 0.3%-0.5%.

[0016] Preferably, in step (a), the edible starch is tapioca starch. Potato starch or corn starch can also be used as a substitute, provided that the linear content is 15-35% to provide hydroxyl reaction sites; and the content of free hydroxyl / glucose units is ≥8 to provide higher reactivity.

[0017] Preferably, in step (a), the swelling inhibitor is sodium sulfate. Potassium sulfate can also be used as a substitute, provided that the ionic strength is ≥0.6 mol / L, which can improve the ionic strength of the system, inhibit excessive swelling of starch or rupture of protein by absorbing water, thereby maintaining structural stability, preventing excessive gelatinization of particles in starch modification, and avoiding products that are sticky or soft. The addition amount must be ≤1.0%, otherwise it will mask the original flavor of the food and affect its texture.

[0018] Preferably, in step (b), the etherifying agent is ethylene oxide. Propylene oxide can also be used as a substitute, provided that MS = 0.08–0.15 is met to provide low-temperature water retention.

[0019] Preferably, in step (c), the composite crosslinking agent is composed of sodium trimetaphosphate and sodium hexametaphosphate. Sodium trimetaphosphate contains multiple POP bonds and can form phosphodiester bonds with starch hydroxyl groups under alkaline conditions, enhancing the molecular network strength, improving the elasticity and chewiness of the food, and providing acid and heat resistance. Sodium hexametaphosphate can chelate metal ions, inhibit protein aggregation, and promote uniform moisture distribution. Sodium trimetaphosphate alone can easily lead to excessive hardness, while sodium hexametaphosphate alone provides insufficient structural support. In the starch crosslinking of this invention, sodium trimetaphosphate enhances elasticity, and sodium hexametaphosphate improves dispersibility. The combination of the two can optimize the crosslinking network density and result in a more balanced taste.

[0020] Preferably, in step (d), the antibacterial agent is carboxymethyl chitosan, which contains bifunctional groups of carboxyl (-COOH) and amino (-NH2), has electrostatic adsorption capacity, and provides plasticizing, antibacterial and degradable properties.

[0021] Preferably, in step (e), the dispersant is polyvinylpyrrolidone. Polyvinylpyrrolidone has ≥3 hydrogen bond donors / acceptors per repeating unit, enabling it to bind with starch hydroxyl groups via hydrogen bonds, thereby improving the tensile strength of the film.

[0022] Preferably, in step (f), vacuum devolatilization is performed: the product obtained in step (e) is adjusted to pH 5-6 with 0.5-1.5% citric acid; the devolatilization temperature is 75-85℃, the vacuum degree is -0.1-0.05MPa, and the time is 0.5-1.5h. Adjusting the pH and devolatilizing the material after the dispersion and film-forming reaction can decompose unreacted etherifying agents, further reducing etherifying agent residue.

[0023] Preferably, in step (f), drying: the devolatilized material is dried to a moisture content of ≤14%, and then pulverized through a 100-mesh sieve to obtain the finished product.

[0024] A highly stable etherified modified starch, the raw material for preparation comprises the following components in parts by weight: 100 parts edible starch, 3.5–5.2 parts etherifying agent, 0.5–0.8 parts swelling inhibitor; 0.4–0.75 parts composite crosslinking agent, 1.5–2.5 parts antibacterial agent, and 0.5–0.8 parts dispersant.

[0025] Preferably, the edible starch is tapioca starch, but potato starch or corn starch can also be used as substitutes.

[0026] Preferably, the swelling inhibitor is sodium sulfate, but potassium sulfate can also be used as a substitute.

[0027] Preferably, the etherifying agent is ethylene oxide, but propylene oxide can also be used as a substitute.

[0028] Preferably, the composite crosslinking agent is composed of sodium trimetaphosphate and sodium hexametaphosphate.

[0029] Preferably, in the composite crosslinking agent, the mass ratio of sodium trimetaphosphate to sodium hexametaphosphate is 2:1–4:1; if the ratio exceeds this range, the degree of crosslinking will be insufficient.

[0030] Preferably, the antibacterial agent is carboxymethyl chitosan.

[0031] Preferably, the dispersant is polyvinylpyrrolidone.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention, through refined processes and optimization of the sequence and conditions of "swelling inhibition → etherification → crosslinking → compounding → dispersion", successfully prepared a highly stable, highly safe, and multifunctional etherified modified starch. Its comprehensive performance is significantly better than that of commercially available products, solving the technical problem of balancing "safety, function, and stability" in traditional processes. It is suitable for various food applications such as yogurt, sauces, and edible films.

[0033] This invention employs an innovative formula with a "swelling inhibition + compound cross-linking + antibacterial + dispersion" system, strictly controlling the amount added, achieving multi-functional synergy, and containing no toxic chemical cross-linking agents throughout the process. Ethylene oxide residue was "not detected," further improving "safety, functionality, and stability."

[0034] This invention differs significantly from physical methods that completely abandon crosslinking agents. We have innovatively discovered that by carefully selecting safe, food-grade phosphate crosslinking agents (sodium trimetaphosphate and sodium hexametaphosphate) and strictly controlling their addition order, reaction pH, and temperature, a dense, uniform, and stable covalent crosslinking network can be constructed. The structural strength of this network far exceeds that of networks constructed by physical forces, effectively inhibiting the expansion, cracking, and retrogradation of starch granules during high temperatures, shearing, or freeze-thaw processes. This results in products with extremely high viscosity stability, excellent film-forming properties, and strong processing resistance. This invention does not simply use crosslinking agents; rather, it solves the problem of safely using crosslinking agents while maximizing their effectiveness through process innovation, making it particularly suitable for fields with extremely stringent requirements for stability and processing performance, such as sauces, soups, and edible packaging films. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention. The following embodiments are used to illustrate the technical solutions described in claims 1-10, with each processing group tested in parallel three times, and the data averaged.

[0036] In the following examples / comparative examples of the present invention, all raw materials used were commercially available.

[0037] A method for preparing highly stable etherified modified starch includes the following steps: (a) Edible starch and swelling inhibitor are suspended in water to form a premixed system; (b) First, add an alkaline agent to the system in step (a) to adjust the pH value to 10.5-11.0, and then slowly introduce the etherifying agent to carry out the etherification reaction; (c) Without separating the product, the composite crosslinking agent is directly added to the system of step (b) to carry out the crosslinking reaction; (d) The cross-linked product is cooled to 38-42℃, the pH value is adjusted to 6.5-7.0 with citric acid, and then an antibacterial agent is added to carry out the compound reaction; (e) Finally, add the dispersant at room temperature and disperse it into a film under ultrasonic conditions for 5-15 minutes. (f) Vacuum devolatilization: The product obtained in step (e) is added with citric acid at a mass concentration of 0.5-1.5% to adjust the pH value to 5-6; the product is then devolatilized at 75-85℃ and a vacuum degree of -0.1-0.05MPa for 0.5-1.5 hours; drying: the devolatilized material is dried until the moisture content is ≤14%, and then pulverized through a 100-mesh sieve to obtain the finished product.

[0038] In some embodiments, in step (a), the temperature of the water is 35-40°C, the mass concentration of the suspension is 35-40%, and the stirring speed is 100-300 rpm.

[0039] In some embodiments, in step (a), the ionic strength of the premixed system is ≥0.6 mol / L.

[0040] In some embodiments, in step (b), the flow rate of ethylene oxide is ≤0.5 L / h·kg starch.

[0041] In some embodiments, in step (b), the etherification reaction is carried out at a temperature of 45–50°C for 4–6 hours, and the molar substitution degree is controlled to be MS = 0.08–0.15.

[0042] In some embodiments, in step (c), the order of adding the composite crosslinking agent is as follows: first add sodium hexametaphosphate, then add sodium trimetaphosphate.

[0043] In some embodiments, sodium hexametaphosphate is first dissolved at <40°C.

[0044] In some embodiments, in step (c), the crosslinking reaction is carried out at a temperature of 50-55°C for 1.5-2 hours, and the degree of crosslinking is controlled to be 0.3%-0.5%.

[0045] A highly stable etherified modified starch, the raw material for preparation comprises the following components in parts by weight: 100 parts edible starch, 3.5–5.2 parts etherifying agent, 0.5–0.8 parts swelling inhibitor; 0.4–0.75 parts composite crosslinking agent, 1.5–2.5 parts antibacterial agent, and 0.5–0.8 parts dispersant.

[0046] In some embodiments, the edible starch is tapioca starch, but potato starch or corn starch can also be used as substitutes.

[0047] In some embodiments, the swelling inhibitor is sodium sulfate, but potassium sulfate can also be used as a substitute.

[0048] In some embodiments, the etherifying agent is ethylene oxide, but propylene oxide can also be used as a substitute.

[0049] In some embodiments, the composite crosslinking agent is composed of sodium trimetaphosphate and sodium hexametaphosphate, with a mass ratio of sodium trimetaphosphate to sodium hexametaphosphate of 2:1–4:1.

[0050] In some embodiments, the antibacterial agent is carboxymethyl chitosan.

[0051] In some embodiments, the dispersant is polyvinylpyrrolidone.

[0052] In some embodiments, in step (d), citric acid with a mass concentration of 0.5-1.5% is added to adjust the pH value to 5-6 before devolatilization; the devolatilization temperature is 75-85℃, the vacuum degree is -0.1--0.05MPa, and the time is 0.5-1.5h. Adjusting the pH value and devolatilizing the material after the composite reaction can decompose unreacted etherifying agent and further reduce etherifying agent residue.

[0053] Example 1 Referring to the raw material formulation and preparation method provided above, and according to the raw material components and dosage ratios shown in Table 1, different treatment groups were set up with the specific composition of the crosslinking agent as a variable to investigate the effect of this variable on the properties of the prepared high-stability hydroxyethyl crosslinked starch.

[0054] Table 1 (Unit: copies)

[0055] Example 2 Referring to the raw material formulation and preparation method provided above, and according to the raw material components and dosage ratios shown in Table 2, different treatment groups were set up with the mass ratio of sodium trimetaphosphate and sodium hexametaphosphate in the composite binder as a variable, and the effect of this variable on the properties of the prepared high-stability hydroxyethyl cross-linked starch was investigated.

[0056] Table 2 (Unit: copies)

[0057] Example 3 Referring to the raw material formula and preparation method provided above, and according to the raw material components and dosage ratios shown in Table 3, different treatment groups were set up with the amount of swelling inhibitor added as a variable to investigate the effect of this variable on the properties of the prepared high-stability hydroxyethyl cross-linked starch.

[0058] Table 3 (Unit: copies)

[0059] Example 4 Referring to the raw material formulation and preparation method provided above, and following the process method shown in Table 4, different treatment groups were set up with the order of addition of sodium trimetaphosphate and sodium hexametaphosphate in the composite crosslinking agent as variables, and the effect of this variable on the properties of the prepared high-stability hydroxyethyl crosslinked starch was investigated.

[0060] Table 4

[0061] Example 5 Referring to the raw material formulation and preparation method provided above, and following the process method shown in Table 5, different treatment groups were set up with the overall process sequence, i.e. the order in which each raw material was added, as a variable, to investigate the effect of this variable on the properties of the prepared high-stability hydroxyethyl cross-linked starch.

[0062] Table 5

[0063] Comparative Example Commercially available hydroxypropyl starch (Ingredion, USA, model PURITY® Gum 1773) is a representative product of hydroxypropyl cross-linked starch widely used in yogurt, and was therefore selected as a comparative example to demonstrate the advantages of the present invention.

[0064] Performance testing experiment 1. Method for detecting residual ethylene oxide 1.1 Chromatographic conditions and methods Chromatographic column: DB-624 capillary column (30.0m × 250μm × 1.4μm). Column temperature: 80℃, injection port temperature: 250℃. Detector temperature: 200℃. Flow rate: Nitrogen 3mL / min, Hydrogen 40mL / min, Air 450mL / min, FID detection.

[0065] Method: The headspace method was selected according to the pharmacopoeia. The headspace sampler was heated for 5 minutes at a temperature of 80℃.

[0066] 1.2 Method and Steps Weigh 0.1g of ethylene oxide and dilute it with water to prepare aqueous solutions of ethylene oxide with concentrations of 100ppm and 1ppm.

[0067] 1.2.1 Repeatability Add 1 mL of the 100 ppm ethylene oxide to a 20 mL headspace vial (with 4 mL of water already added), seal the vial, and prepare 5 aliquots. Inject each aliquot into a headspace sampler under the above chromatographic conditions. The RSD of the 5 injections, based on peak area, is 2.5%. The theoretical plate number of the ethylene oxide peak is 65191.

[0068] 1.2.2 Minimum Detection Concentration 1 mL of the 1 ppm ethylene oxide was added to a 20 mL headspace vial (with 4 mL of water already added), the vial was sealed, and then injected into a headspace sampler. The lowest detectable concentration of ethylene oxide was found to be 0.3 ppm (S / N > 3).

[0069] 1.3 Determination of Ethylene Oxide Residue in Samples Preparation of the reference solution: Accurately weigh 0.1 g of ethylene oxide into a 100 mL volumetric flask, dilute with water to the mark and shake well; then pipette 10 mL into the 100 mL volumetric flask, dilute with water to the mark, and shake well. Take 1 mL of the above solution, add 4 mL of water, and add to a 20 mL headspace vial.

[0070] Preparation of the test solution: Accurately weigh about 1.0 g of the sample, place it in a 20 mL headspace vial, add 5 mL of water, and shake well.

[0071] Assay: Inject the above reference standard and test sample vials into the headspace sampler, record the chromatogram, measure the peak area, and calculate the peak area using the external standard method. Each sample is tested in parallel 3 times, and the average value is taken.

[0072] 2. Viscosity Measurement According to GB12098-89 method, the viscosity of a 6% cross-linked starch paste was determined using an NDJ-1 type rotational viscometer. A ×1 type rotor was used, with a rotation speed of 120 r / min. Each sample was tested in triplicate, and the average value was taken.

[0073] 3. Degree of crosslinking determination (Expressed as sedimentation volume) Accurately weigh 0.5 g of oven-dry sample into a 100 mL beaker, and add 25 mL of distilled water using a pipette to prepare a 2% starch solution. Place the beaker in a water bath at 82℃-85℃, stir slightly, and keep warm for 2 min. Remove and cool to room temperature. Pour 10 mL of the paste into two graduated centrifuge tubes, symmetrically place them into a centrifuge sedimentation unit, start the sedimentation unit, and slowly accelerate to 4000 rpm. Use a stopwatch to time the process for 2 min, then stop. Remove the centrifuge tubes and pour the supernatant into another centrifuge tube of the same volume. The volume read (mL) is the sedimentation volume. Perform three parallel determinations on the same sample, and take the average value of the results.

[0074] 4. Determination of swelling degree Starch was suspended in water and heated at 85°C with stirring for 30 minutes. It was then centrifuged at 2000 rpm for 15 minutes. The sediment that settled was the expanded starch. The supernatant was separated and dried to obtain the amount of water-soluble starch. The solubility was calculated, and the expansion degree was calculated from the mass of the expanded starch. Each sample was tested in triplicate, and the average value was taken.

[0075] 5. Freeze-thaw property test Prepare a 7% starch slurry by stirring in boiling water for 20 minutes. Adjust the volume to the original concentration with water. Weigh a certain amount of the slurry and place it in a refrigerator at -5℃ to -10℃ for 24 hours. After thawing naturally, centrifuge at 3000 r / min for 20 minutes, weigh the precipitate, and calculate the water separation rate. Each sample is tested in triplicate, and the average value is taken.

[0076] 6. Film-forming property test A 6% paste was used to coat the film, and the film-forming properties were observed. Each sample was tested in triplicate, and the average value was taken.

[0077] 7. Determination of molar substitution degree Bromine single-tube absorption assay. Each sample was tested in triplicate, and the average value was taken.

[0078] 8. Gel hardness determination TA.XTC-18 Texture Analyzer, Shanghai Baosheng Industrial Development Co., Ltd.

[0079] The parameters are as follows: SP / 0.5 probe, compressive deformation 30%, pre-test speed 1mm / s, test speed 1mm / s, post-test speed 1mm / s, trigger point value 5gf. Each sample was tested in parallel 3 times, and the average value was taken.

[0080] 9. Antibacterial performance test Dissolve the culture medium formula in Table 5 in 250 mL of distilled water, adjust the pH to 7.2 with sodium hydroxide solution, and prepare a solid culture medium.

[0081] Table 6: Culture Medium Formulation

[0082] Methods: Liquid culture media were prepared in the same manner. After preparation, *Escherichia coli* and *Staphylococcus aureus* were inoculated onto the media and cultured at 37°C for 12 hours to allow the bacteria to enter a stable logarithmic growth phase, yielding bacterial suspensions of *E. coli* and *S. aureus* for later use. Solid culture media were sterilized by high-temperature steam and cooled to 60°C. 0.4 mL of *E. coli* and *S. aureus* bacterial suspension were evenly spread on the surface of each solid culture medium. Using an inoculation loop, the bacterial suspension was evenly dotted onto the center of a membrane. Each culture dish was divided into two equal portions. One sample (20 mm × 20 mm) was placed in each portion using tweezers, and antibacterial tests were performed. The same sample was tested three times in parallel on each culture medium. *E. coli* was cultured at 37°C in an inverted state for 1 day, and *S. aureus* was cultured under the same conditions for 5 hours. Observe the growth of each bacterial species and measure the diameter of the inhibition zone. Compare the colony diameter (D) with the blank control plate. Evaluate the antibacterial performance of the two membranes by the size of the inhibition zone diameter, and calculate the inhibition rate using the following formula: Antibacterial rate = (Dd) / D × 100% In the formula, D is the diameter of the inhibition zone of the tested sample, in mm; d is the diameter of the inhibition zone in the distilled water blank, in mm.

[0083] 10. Application stability test Yogurt sample preparation: skim milk powder → preparation of 25% milk powder solution by mass → purification → ingredient addition (adding different mass fractions of acetylated cross-linked starch) → filtration → preheating → high pressure homogenization → sterilization → cooling → inoculation → packaging → fermentation → cooling and ripening → finished product.

[0084] After the yogurt samples were prepared, they were stored at (4±1)℃, and the stratification was observed after 30 days of storage.

[0085] 11. The test results are shown in Table 7-11.

[0086] Table 7: Test Results of Each Process in Example 1

[0087] As shown in Table 7: In Treatment 1-1, the combination of sodium trimetaphosphate and sodium hexametaphosphate outperformed the comparative sample in terms of viscosity, degree of crosslinking, and antibacterial rate, demonstrating its optimal overall performance. It exhibits zero residue, high viscosity, low water separation rate, low gel hardness, and high antibacterial activity. Sodium trimetaphosphate provides crosslinking strength, while sodium hexametaphosphate improves dispersibility; the two synergistically optimize the network structure. Treatment 1-2, containing only sodium trimetaphosphate, resulted in excessive crosslinking, leading to slight brittleness. Treatment 1-3, containing only sodium hexametaphosphate, suffered from insufficient crosslinking, resulting in a loose structure and decreased performance. Treatment 1-4, lacking any crosslinking agent, exhibited the worst performance, confirming the necessity of crosslinking.

[0088] Table 8: Test Results of Each Process in Example 2

[0089] As shown in Table 8: In treatments 2-3, the optimal performance was achieved with a sodium trimetaphosphate to sodium hexametaphosphate ratio of 4:1, indicating that appropriately increasing the proportion of sodium trimetaphosphate helps to form a denser and more stable network structure. In treatments 2-5, an excessively high ratio led to over-crosslinking and a harder texture; in treatment 2-1, an excessively low ratio resulted in insufficient crosslinking and decreased performance.

[0090] Table 9: Test Results of Each Process in Example 3

[0091] As shown in Table 9: Treatment 3-1 used 0.5 parts of sodium sulfate, resulting in balanced performance. Treatment 3-2, without the addition of inhibitors, experienced a comprehensive decline in performance due to excessive swelling. Treatment 3-3 used 2 parts of sodium sulfate; although the salt effect inhibited swelling and improved some properties, the excessive salt content affected the flavor, confirming that 0.5 parts was the optimal addition amount.

[0092] Table 10: Test Results of Each Process in Example 4

[0093] As shown in Table 10: Treatment 4-1, which involves adding sodium hexametaphosphate first and then sodium trimetaphosphate, yields the best performance. Sodium hexametaphosphate first chelates metal ions and creates the reaction conditions for sodium trimetaphosphate; the two work synergistically to form a uniform network. Compared to treatment 4-1, treatment 4-2 reverses the order of adding sodium hexametaphosphate and sodium trimetaphosphate, while treatment 4-3 adds both sodium hexametaphosphate and sodium trimetaphosphate simultaneously. All of these methods result in uneven cross-linking and decreased performance.

[0094] Table 11: Test Results of Each Process in Example 5

[0095] As shown in Table 11: Treatment 5-1 exhibits the best overall process performance of this invention. Compared to treatments 5-2 and 5-4, the addition of sodium sulfate before etherification effectively inhibits swelling and ensures reaction uniformity. Compared to treatment 5-3, etherification followed by crosslinking is more conducive to network construction. In treatment 5-5, the premature addition of the antibacterial agent leads to its inactivation.

[0096] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing highly stable etherified cross-linked starch, characterized in that, Includes the following steps: (a) Edible starch and swelling inhibitor are suspended in water to form a premixed system; (b) An etherifying agent is introduced into the system of step (a) to carry out an etherification reaction; (c) Add a composite crosslinking agent to the system of step (b) to carry out a crosslinking reaction; (d) Add an antibacterial agent to the crosslinking product of step (c) to carry out a composite reaction; (e) Finally, add the dispersant and disperse to form a film; (f) Vacuum devolatilization and drying.

2. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (b), the etherification reaction is carried out at a temperature of 45–50°C for 4–6 hours.

3. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (c), the crosslinking reaction is carried out at a temperature of 50-55°C for 1.5-2 hours.

4. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (d), the temperature of the composite reaction is 38-42°C and the time is 0.5-1 hour.

5. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (a), the swelling inhibitor is sodium sulfate or potassium sulfate.

6. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (c), the composite crosslinking agent is a combination of sodium trimetaphosphate and sodium hexametaphosphate.

7. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (b), the etherifying agent is ethylene oxide or propylene oxide.

8. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (c), the antibacterial agent comprises carboxymethyl chitosan.

9. The method for preparing highly stable etherified cross-linked starch as described in claim 1, characterized in that: In step (d), the dispersant comprises polyvinylpyrrolidone.

10. A highly stable etherified cross-linked starch, characterized in that, The raw materials, by weight, comprise the following components: 100 parts edible starch, 3.5–5.2 parts etherifying agent, 0.5–0.8 parts swelling inhibitor, 0.4–0.75 parts composite crosslinking agent, 1.5–2.5 parts antibacterial agent, and 0.5–0.8 parts dispersant.

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