Modified starch hydrogel, and preparation method and application thereof

Abstract

This invention provides a modified starch hydrogel, its preparation method, and its applications, belonging to the field of starch gel technology. The modified starch hydrogel comprises natural starch, water, and a polyhydroxy compound; the water, polyhydroxy compound, and natural starch are cross-linked to form a honeycomb network structure. The modified starch hydrogel provided by this invention has a honeycomb network structure. Compared to pure starch hydrogel, the modified starch hydrogel provided by this invention has a denser gel network structure, smaller pore size, and thicker pore walls, thus exhibiting excellent mechanical properties. Furthermore, the modified starch hydrogel provided by this invention does not use chemical reagents, will not cause harm to the human body, and will not cause environmental pollution.

Description

Technical Field

[0001] This invention belongs to the field of starch gel technology, specifically relating to a modified starch hydrogel, its preparation method, and its application. Background Technology

[0002] Hydrogels are three-dimensional network structures composed of hydrophilic polymer chains cross-linked through physical or chemical means. They possess a variety of tunable physical and chemical properties and hold significant promise for applications in tissue engineering, drug delivery, biosensors, and intelligent robotics. Starch, as a natural biomacromolecule, contains numerous hydroxyl groups and can interact with water molecules via hydrogen bonds, exhibiting excellent cross-linking capabilities. This makes it one of the ideal materials for preparing hydrogels.

[0003] However, natural starch hydrogels generally suffer from poor mechanical properties, high brittleness, and low tensile strength. Arayaphan et al. discovered that a biodegradable double-network hydrogel with excellent mechanical properties can be prepared by free radical polymerization of cassava starch and polyvinyl alcohol using the crosslinking agent polyacrylic acid. He et al. prepared a strong and tough hydrogel with a multi-scale anisotropic structure using directional freezing and salting-out methods.

[0004] Although the above methods can improve the mechanical properties of starch hydrogels, the chemical reagents are toxic, which is harmful to the human body and causes environmental pollution. In addition, salt ions will diffuse outward in the water environment, causing serious damage to the gel structure. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a modified starch hydrogel, its preparation method, and its applications. The modified starch hydrogel provided by this invention does not use chemical reagents or salts and also possesses excellent mechanical properties.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a modified starch hydrogel comprising natural starch, water, and a polyhydroxy compound; wherein the water, the polyhydroxy compound, and the natural starch are cross-linked to form a honeycomb network structure.

[0008] Preferably, the polyhydroxy compound includes one or more of glycerol, glucose alcohol, sucrose, erythritol, xylitol, maltitol, D-mannitol, and sorbitol; the mass of the polyhydroxy compound is 2-8% of the mass of the modified starch hydrogel; and the mass of the water is 52-58% of the mass of the modified starch hydrogel.

[0009] Preferably, the natural starch includes one or more of potato starch, corn starch, wheat starch, sweet potato starch, cassava starch, indica rice flour, mung bean starch, and pea starch; the natural starch includes amylose and amylopectin; the mass of the amylose is 20-25% of the mass of the starch; and the mass of the natural starch is 40% of the mass of the modified starch hydrogel.

[0010] This invention provides a method for preparing the modified starch hydrogel described above, comprising the following steps:

[0011] A starch hydrogel and an aqueous solution of a polyhydroxy compound are mixed and subjected to a hydrothermal toughening treatment, in which part of the water in the starch hydrogel is replaced by the polyhydroxy compound to obtain a modified starch hydrogel; the temperature of the hydrothermal toughening treatment is 25-135℃.

[0012] Preferably, the wet heat toughening treatment time is 15 to 120 minutes.

[0013] Preferably, the mass ratio of the starch hydrogel to the aqueous solution of the polyhydroxy compound is (1-1.25):15; and the mass concentration of the polyhydroxy compound in the aqueous solution is 25-100%.

[0014] Preferably, the mass concentration of water molecules in the starch hydrogel is 60%.

[0015] Preferably, after completing the wet heat toughening treatment, the product is further immersed in water; the immersion temperature is 0-5°C, the number of immersions is 1-5, and the immersion time for each immersion is 5-30 minutes.

[0016] Preferably, the preparation of the starch hydrogel includes: gelatinizing a starch slurry to obtain the starch hydrogel; the gelatinization power is 500-800W and the time is 3-4min.

[0017] This invention provides the application of the modified starch hydrogel described in the above-described scheme or the modified starch hydrogel prepared by the preparation method described in the above-described scheme in food.

[0018] This invention provides a modified starch hydrogel comprising natural starch, water, and a polyhydroxy compound; the water, polyhydroxy compound, and natural starch are cross-linked to form a honeycomb network structure. The modified starch hydrogel provided by this invention has a honeycomb network structure, and compared to pure starch hydrogel, the modified starch hydrogel provided by this invention has a denser gel network structure, smaller pore size, and thicker pore walls, thus exhibiting superior mechanical properties.

[0019] Furthermore, the modified starch hydrogel provided by this invention does not use chemical reagents, will not cause harm to the human body or environmental pollution.

[0020] This invention provides a method for preparing the modified starch hydrogel described above. The invention places pure starch hydrogel in an aqueous solution of a polyhydroxy compound. During the hydrothermal toughening process, the free movement of macromolecules optimizes the interactions between polymers (polymer being amylose) or between polymers and solvents (solvent being an aqueous solution of the polyhydroxy compound), increasing the crystalline domains of the polymer or reducing the average distance between adjacent structural domains in the starch hydrogel, thereby enhancing the gel network structure within the starch hydrogel. The hydrothermal toughening process provides a freer, looser environment for macromolecular movement, increasing the entanglement density between molecular chains and making the starch hydrogel network structure more compact and stable. The combination of solvent displacement and hydrothermal toughening significantly improves the toughness and mechanical properties of the starch hydrogel. These superior mechanical properties are mainly attributed to the synergistic effect of the high crystallinity and molecular chain entanglement in the starch hydrogel.

[0021] Furthermore, the modified starch hydrogel provided by this invention does not use salt. During gelatinization (a physical change), the double helix structure in the amylose molecular chain dissociates. During the hydrogelatinization process, the hydroxyl groups on the amylose molecular chain interact with the hydroxyl groups on the polyhydroxy compound (such as glycerol) molecules to form strong hydrogen bonds. Polyhydroxy compounds are miscible with water; excess polyhydroxy compounds can displace a large number of water molecules from the starch gel without significantly altering its morphology and structure. Therefore, the preparation method provided by this invention does not cause severe damage to the gel structure.

[0022] Furthermore, when the soaking temperature is high enough to break the polyhydroxy compound molecules and starch molecular chains, prolonged soaking will displace the polyhydroxy compounds, but this will cause starch swelling and severely damage the starch gel network. The present invention controls the soaking temperature at 0-5°C, which will not cause serious damage to the gel network structure of the modified starch hydrogel.

[0023] This invention provides the application of the modified starch hydrogel described above in food preparation. Compared with gels prepared from ordinary starch and water, the modified starch hydrogel provided by this invention has the advantages of higher toughness and density, smaller pores, thicker pore walls, higher hardness, and a more chewy texture. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.

[0025] Figure 1 This is a schematic diagram of the preparation process of the modified starch hydrogel of the present invention;

[0026] Figure 2 PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 PSgel@Glycerol in Example 24 100-90 Storage modulus (G'), loss modulus (G") (A.), and loss factor tanδ (B) of the sample; in the figure, solid represents G' and hollow represents G";

[0027] Figure 3 Stress-strain curves of modified starch hydrogel samples of Comparative Examples 8–12 at -30℃ (A.) and modified starch hydrogel samples of Comparative Examples 13–17 at -18℃ (B.) for 15 min, 30 min, 60 min, 90 min and 120 min.

[0028] Figure 4 The stress-strain curves of the modified starch hydrogel samples of Comparative Examples 18-22 at 4°C (C.) and the modified starch hydrogel samples of Examples 32-36 at 25°C (D.) for 15 min, 30 min, 60 min, 90 min and 120 min are shown.

[0029] Figure 5 The stress-strain curves of the modified starch hydrogel samples of Examples 37-41 at 50°C (E.) and the modified starch hydrogel samples of Examples 42-46 at 100°C (F.) for 15 min, 30 min, 60 min, 90 min and 120 min are shown.

[0030] Figure 6 Stress-strain curves of the modified starch hydrogel samples of Examples 47-51 treated at 120℃ (G.) and the modified starch hydrogel samples of Examples 52-56 treated at 135℃ (H.) for 15 min, 30 min, 60 min, 90 min and 120 min.

[0031] Figure 7 PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 PSgel@Glycerol in Example 24 100-90 The stretching curve (A.) and shear curve (B.);

[0032] Figure 8Stress-strain curves of sweet potato starch (A.) from Example 25 and mung bean starch (B.) from Example 26 were measured based on a solvent displacement synergistic hydrothermal toughening treatment method.

[0033] Figure 9 Stress-strain curves of rice flour (C.) from Example 27 and cassava starch (D.) from Example 28 were obtained based on a solvent displacement synergistic hydrothermal toughening treatment method.

[0034] Figure 10 Stress-strain curves of pea starch (E.) from Example 29 and wheat starch (F.) from Example 30 were measured based on a solvent displacement synergistic hydrothermal toughening treatment method.

[0035] Figure 11 The stress-strain curve of corn starch (G.) in Example 31 was measured based on the solvent displacement synergistic hydrothermal toughening treatment method;

[0036] Figure 12 PSgel@Control (top left image) for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 (Top row, right image) and PSgel@Glycerol from Example 24 100-90 (Bottom row) SEM images of the cross-section;

[0037] Figure 13 PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 PSgel@Glycerol in Example 24 100-90 Fourier transform infrared spectrum of the sample (A.) and short-range order plot (B.);

[0038] Figure 14 PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 PSgel@Glycerol in Example 24 100-90 X-ray diffraction pattern of the sample. Detailed Implementation

[0039] This invention provides a modified starch hydrogel comprising natural starch, water, and a polyhydroxy compound; wherein the water, the polyhydroxy compound, and the natural starch are cross-linked to form a honeycomb network structure.

[0040] Unless otherwise specified, all materials and equipment used in this invention are commercially available.

[0041] In this invention, the polyhydroxy compound preferably includes one or more of glycerol, glucosyl alcohol, sucrose, erythritol, xylitol, maltitol, D-mannitol, and sorbitol; the mass of the polyhydroxy compound is preferably 2-8% of the mass of the modified starch hydrogel, and in the embodiments of this invention, it can specifically be 2%, 3%, 4%, 5%, 6%, 7%, or 8%; the mass of the water is preferably 52-58% of the mass of the modified starch hydrogel, and in the embodiments of this invention, it can specifically be 52%, 53%, 54%, 55%, 56%, 57%, or 58%.

[0042] In this invention, the natural starch preferably includes one or more of potato starch, corn starch, wheat starch, sweet potato starch, cassava starch, indica rice flour, mung bean starch, and pea starch; the starch preferably includes amylose and amylopectin; the mass of the amylose is preferably 20-25% of the mass of the starch; and the mass of the natural starch is preferably 40% of the mass of the modified starch hydrogel.

[0043] The modified starch hydrogel provided by this invention has a honeycomb network structure. Compared with pure starch hydrogel, the modified starch hydrogel provided by this invention has a denser gel network structure, smaller pore size, and thicker pore wall, thus exhibiting excellent mechanical properties.

[0044] Furthermore, the modified starch hydrogel provided by this invention does not use chemical reagents, will not cause harm to the human body or environmental pollution.

[0045] This invention provides a method for preparing the modified starch hydrogel described above, comprising the following steps:

[0046] A starch hydrogel and an aqueous solution of a polyhydroxy compound are mixed and subjected to a wet heat toughening treatment, in which part of the water in the starch hydrogel is replaced by the polyhydroxy compound to obtain a modified starch hydrogel.

[0047] In this invention, the preparation of the starch hydrogel preferably includes: gelatinizing a starch slurry to obtain the starch hydrogel.

[0048] In this invention, the starch slurry is preferably obtained by mixing natural starch and water. The mass ratio of natural starch to water is preferably 2:3. The starch slurry is preferably gelatinized in a silicone mold. The gelatinization power is preferably 500-800W, and in specific embodiments, it can be 500W, 550W, 600W, 650W, 700W, 750W, or 800W; the gelatinization time is preferably 3-4 minutes, and in specific embodiments, it can be 3 minutes or 4 minutes. The mass concentration of water molecules in the starch hydrogel is preferably 60%.

[0049] In this invention, during the gelatinization process of starch slurry, the double helix structure in the amylose molecular chain dissociates.

[0050] After gelatinization, the present invention preferably cools the gelatinized sample to room temperature and then demolds it to obtain the starch hydrogel.

[0051] In this invention, the preferred mass ratio of the starch hydrogel to the aqueous solution of the polyhydroxy compound is (1-1.25):15. In the embodiments of this invention, it can be 1:15, 1.1:15, 1.2:15 or 1.25:15.

[0052] In this invention, the mass concentration of the polyhydroxy compound in the aqueous solution is 25% to 100%, and in the embodiments of this invention, it can specifically be 25%, 30%, 50%, 60%, 75%, 80%, or 100%.

[0053] In this invention, a mixture of starch hydrogel and an aqueous solution of a polyhydroxy compound is preferably placed in a sealed retort bag for wet heat toughening treatment. In this invention, the temperature of the wet heat toughening treatment is 25–135°C, and in specific embodiments, it can be 25°C, 30°C, 50°C, 60°C, 100°C, 120°C, or 135°C; the preferred time for the wet heat toughening treatment is 15–120 min, and in specific embodiments, it can be 15 min, 20 min, 30 min, 50 min, 60 min, 80 min, 90 min, 100 min, or 120 min.

[0054] After completing the aforementioned wet heat toughening treatment, the present invention preferably further includes immersing the obtained product in water; the immersion temperature is preferably 0-5°C, and in the embodiments of the present invention, it can specifically be 0°C, 1°C, 2°C, 3°C, 4°C, or 5°C; the number of immersions is preferably 1-5 times, and in the embodiments of the present invention, it can specifically be 1 time, 2 times, 3 times, 4 times, or 5 times; the immersion time for a single immersion is preferably 5-30 minutes, and in the embodiments of the present invention, it can specifically be 5 minutes, 10 minutes, 20 minutes, or 30 minutes. In the present invention, the immersion preferably uses an ice-water mixture; the mass ratio of the sample to the volume ratio of the ice-water mixture is preferably 1 g: 20 mL.

[0055] This invention uses soaking to wash away polyhydroxy compounds that did not participate in the reaction (i.e., did not bind with natural starch during the wet heat toughening process).

[0056] After the soaking is completed, the present invention preferably uses filter paper to absorb the moisture on the surface of the soaked sample to obtain the modified starch hydrogel.

[0057] This invention places pure starch hydrogel in an aqueous solution of a polyhydroxy compound. During the hydrothermal toughening process, the free movement of macromolecules optimizes the interactions between polymers (amylose) or between polymers and solvents (aqueous solutions of the polyhydroxy compound). This increases the crystalline domains of the polymers or reduces the average distance between adjacent structural domains in the starch hydrogel, thereby enhancing the gel network structure within the hydrogel. The hydrothermal toughening process provides a freer, looser environment for macromolecular movement, increasing the entanglement density between molecular chains and making the starch hydrogel network structure more compact and stable. The combination of solvent displacement and hydrothermal toughening significantly improves the toughness and mechanical properties of the starch hydrogel. These superior mechanical properties are mainly attributed to the synergistic effect of the high crystallinity and molecular chain entanglement in the starch hydrogel.

[0058] The modified starch hydrogel provided by this invention does not use salt. Furthermore, during the gelatinization process (a physical change), the double helix structure in the amylose molecular chain dissociates. During the hydrogelatinization process, the hydroxyl groups on the amylose molecular chain interact with the hydroxyl groups on the polyhydroxy compound (such as glycerol) molecules to form strong hydrogen bonds. The polyhydroxy compound is miscible with water; an excess of the polyhydroxy compound can displace a large number of water molecules from the starch gel without significantly altering its morphology and structure. Therefore, the preparation method provided by this invention does not cause severe damage to the gel structure.

[0059] When the soaking temperature is high enough to break the polyhydroxy compound molecules and starch molecular chains, prolonged soaking will displace the polyhydroxy compounds, but this will cause starch swelling and severely damage the starch gel network. The present invention controls the soaking temperature at 0-5°C, which will not cause serious damage to the gel network structure of the modified starch hydrogel.

[0060] This invention provides the application of the modified starch hydrogel described in the above-described scheme or the modified starch hydrogel prepared by the preparation method described in the above-described scheme in food. Compared with gels prepared from ordinary starch and water, the modified starch hydrogel provided by this invention has the advantages of higher toughness and density, smaller pores, thicker pore walls, higher hardness, and a more chewy texture.

[0061] Figure 1 The preparation process of starch hydrogels, such as... Figure 1 As shown, the present invention sequentially performs gelatinization, solvent replacement + wet heat toughening treatment and soaking and washing of potato starch solution to obtain the final sample, namely the modified starch hydrogel.

[0062] To further illustrate the present invention, a modified starch hydrogel, its preparation method, and its application are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0063] In the examples, potato starch was purchased from Gansu Lantian Potato Industry Development Co., Ltd., and glycerin (food grade) was purchased from Beijing Qingyuan Food Additives Co., Ltd.; all water used in the experiment was deionized water; the high-temperature retort pouches were from Xizhilong, with specifications GWZZD.

[0064] Examples 1-4

[0065] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0066] 12g of PSgel@Control sample was placed in a high-temperature retort bag containing 180g of glycerol aqueous solution with mass concentrations of 25%, 50%, 75% and 100% respectively, and subjected to wet heat toughening treatment at 100℃ for 90min.

[0067] Take 12g of the sample after the wet heat toughening treatment, soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min, repeat three times, and use filter paper to absorb the excess water on the surface to obtain the modified starch hydrogel.

[0068] Comparative Example 1

[0069] The preparation steps are the same as in Example 1, except that the mass concentration of glycerol in the glycerol water solution is 0%.

[0070] Tensile property tests of modified starch hydrogel samples in Examples 1-4 and the sample obtained in Comparative Example 1

[0071] Take 4g of PSgel@Glycerol sample and boil it in 200mL of boiling water at 100℃ until the optimal rehydration time (40s, optimal rehydration time: the time when the sample is boiled in boiling water until there is no white core inside the starch gel). The tensile properties of the sample are then measured.

[0072] The test conditions are as follows: Use friction paper to wrap one end of the starch gel, and wrap the other end with friction paper at a distance of 1 cm. Clamp both ends with clamps to fix one end, and stretch the other end at a constant speed in the horizontal direction. When the starch gel breaks, stop stretching and record the stretching length.

[0073] The tensile strain of the samples was determined based on the change in stretching length. By comparing the tensile strain lengths of starch hydrogels soaked in different glycerol concentrations, it was concluded that the gel obtained by soaking in 100% glycerol concentration had the best tensile properties. Therefore, 100% glycerol concentration was selected for subsequent experiments to prepare modified starch hydrogels. All test samples were completed within 15 minutes after reaching the optimal rehydration time.

[0074] Examples 5-9

[0075] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0076] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 25℃, 50℃, 100℃, 120℃ and 135℃ for 90min respectively.

[0077] Take 12g of the sample after the wet heat toughening treatment, soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min, repeat three times, and use filter paper to absorb the excess water on the surface to obtain the modified starch hydrogel.

[0078] Comparative Examples 2-4

[0079] The only difference from Example 5 is that the damp heat toughening treatment is replaced by the freeze aging treatment or the low temperature aging treatment, that is, the damp heat toughening treatment is carried out at -30°C and -18°C respectively (Comparative Examples 2 and 3), and the low temperature aging treatment is carried out at 4°C (Comparative Example 4).

[0080] Tensile property tests of the modified starch hydrogels obtained in Examples 5-9 and the samples obtained in Comparative Examples 2-4

[0081] Following the testing method in Example 1, it was determined that a temperature of 100°C was optimal for the wet heat toughening treatment. Therefore, subsequent experiments used a temperature of 100°C to prepare the required modified starch hydrogel. All test samples were tested within 15 minutes after reaching the optimal rehydration time.

[0082] Examples 10-14

[0083] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0084] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 100℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0085] Take 12g of the sample after the wet heat toughening treatment, soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min, repeat three times, and use filter paper to absorb the excess water on the surface to obtain the modified starch hydrogel.

[0086] Tensile property tests of the modified starch hydrogels obtained in Examples 10-14

[0087] Following the testing method in Example 1, it was determined that a wet heat toughening treatment time of 90 minutes yielded the best results. Therefore, a time of 90 minutes was selected for subsequent experiments to prepare the desired modified starch hydrogel. All test samples were tested within 15 minutes after reaching the optimal rehydration time.

[0088] Examples 15-18

[0089] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0090] Place 12g of PSgel@Control in a high-temperature retort bag containing 180g of glycerin (glycerin mass concentration is 100%) and perform wet heat toughening treatment at 100℃ for 90min;

[0091] Take 12g of the processed sample and soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 5min, 10min, 20min and 30min respectively. Repeat this process three times. Use filter paper to absorb the excess water on the surface to obtain the modified starch hydrogel.

[0092] Comparative Example 5

[0093] The only difference from Example 15 is that the soaking and washing time is 0 minutes, that is, no soaking is performed.

[0094] Tensile property tests of the modified starch hydrogels obtained in Examples 15-18 and the sample obtained in Comparative Example 5

[0095] Following the testing method in Example 1, it was determined that immersion in water for 10 minutes yielded the best results. Therefore, a 10-minute soaking time was selected for subsequent experiments to prepare the desired modified starch hydrogel. All test samples were completed within 15 minutes after reaching the optimal rehydration time.

[0096] Examples 19-23

[0097] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0098] Place 12g of PSgel@Control in a high-temperature retort bag containing 180g of glycerin (glycerin mass concentration is 100%) and perform wet heat toughening treatment at 100℃ for 90min;

[0099] After the sample has undergone wet heat toughening treatment, take 12g of the sample and soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min. Repeat this process 1, 2, 3, 4 and 5 times. Use filter paper to absorb the excess water on the surface to obtain the modified starch hydrogel.

[0100] Tensile property tests of the modified starch hydrogels obtained in Examples 19-23

[0101] Following the testing method in Example 1, it was determined that soaking and washing with water three times yielded the best results. Therefore, subsequent experiments used soaking and washing with water three times to prepare the desired modified starch hydrogel. All test samples were tested within 15 minutes after reaching the optimal rehydration time.

[0102] Example 24

[0103] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0104] 12g of PSgel@Control sample was placed in a high-temperature retort bag containing 180g (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 100℃ for 90min.

[0105] After the sample has undergone wet heat toughening treatment, take 12g of the sample and soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min. Repeat this process three times. Use filter paper to absorb the excess water from the surface to obtain the modified starch hydrogel, in which the water content is 54wt.%, the glycerol content is 6wt.%, and the starch content is 40wt.%.

[0106] Comparative Example 6

[0107] The only difference from Example 24 is that the PSgel@Control sample was placed in a high-temperature retort bag (containing no water or glycerin) and subjected to a wet heat toughening treatment at 100°C for 90 minutes to obtain the sample (without soaking or washing), denoted as PSgel@Control. 100-90 .

[0108] Comparative Example 7

[0109] Potato starch and deionized water were mixed at a mass ratio of 2:3 and stirred until homogeneous to obtain a starch slurry. 4 mL of the starch slurry was poured into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smoothed evenly. The mold was then steamed in a steamer (500 W) for 4 minutes. After cooling to room temperature, the mold was demolded to obtain a pure starch hydrogel, denoted as PSgel@Control, in which the water content was 60 wt.%.

[0110] Examples 25-31

[0111] Sweet potato starch, mung bean starch, rice flour, tapioca starch, pea starch, wheat starch, corn starch, and deionized water were mixed in a mass ratio of 2:3 and stirred evenly to obtain a starch slurry. 4 mL of the starch slurry was poured into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smoothed evenly. The mold was then steamed in a steamer (500 W) for 4 minutes. After cooling to room temperature, the mold was demolded to obtain a pure starch hydrogel, denoted as PSgel@Control.

[0112] Place 12g of PSgel@Control in a high-temperature retort bag containing 180g of glycerin (glycerin mass concentration is 100%) and perform wet heat toughening treatment at 100℃ for 90min;

[0113] Take 12g of the sample after the wet heat toughening treatment, soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min, repeat three times, and use filter paper to absorb the excess water on the surface to obtain the modified starch hydrogel.

[0114] Comparative Examples 8–12

[0115] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0116] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to freeze aging treatment at -30℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0117] After freeze-aging, take 12g of the sample and immerse it in 240mL of deionized water (a mixture of ice and water at 0°C) for 10 minutes. Repeat this process three times. Blot away excess water with filter paper to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. -30-15 PSgel@Glycerol -30-30 PSgel@Glycerol -30-60 PSgel@Glycerol -30-90 and PSgel@Glycerol -30-120 .

[0118] Comparative Examples 13–17

[0119] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0120] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to freeze aging treatment at -18℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0121] After freeze-aging, take 12g of the sample and immerse it in 240mL of deionized water (a mixture of ice and water at 0°C) for 10 minutes. Repeat this process three times. Blot away excess water with filter paper to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. -18-15 PSgel@Glycerol -18-30 PSgel@Glycerol -18-60 PSgel@Glycerol -18-90 and PSgel@Glycerol -18-120 .

[0122] Comparative Examples 18–22

[0123] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0124] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to low-temperature aging treatment at 4℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0125] Take 12g of the processed sample and immerse it in 240mL of deionized water (a mixture of ice and water at 0°C) for 10 minutes. Repeat this process three times. Blot away excess water with filter paper to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. 4-15 PSgel@Glycerol 4-30 PSgel@Glycerol 4-60 PSgel@Glycerol 4-90 and PSgel@Glycerol 4-120 .

[0126] Examples 32-36

[0127] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0128] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 25℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0129] After the wet heat toughening treatment, take 12g of the sample and immerse it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min. Repeat this process three times. Blot away excess water with filter paper to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. 25-15 PSgel@Glycerol 25-30 PSgel@Glycerol 25-60 PSgel@Glycerol 25-90 and PSgel@Glycerol 25-120 .

[0130] Examples 37-41

[0131] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0132] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 50℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0133] After the wet heat toughening treatment, take 12g of the sample and soak it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min. Repeat this process three times. Use filter paper to absorb excess water from the surface to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. 50-15 PSgel@Glycerol 50-30 PSgel@Glycerol 50-60 PSgel@Glycerol 50-90 and PSgel@Glycerol 50-120 .

[0134] Examples 42-46

[0135] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0136] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 100℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0137] After the wet heat toughening treatment, take 12g of the sample and immerse it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min. Repeat this process three times. Blot away excess water with filter paper to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. 100-15 PSgel@Glycerol 100-30 PSgel@Glycerol 100-60 PSgel@Glycerol 100-90 and PSgel@Glycerol 100-120 .

[0138] Examples 47-51

[0139] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0140] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 120℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0141] After the sample underwent moist heat toughening treatment, 12g of the sample was immersed and washed in 240mL of deionized water (a mixture of ice and water at 0°C) for 10 minutes. This process was repeated three times. Excess water was then absorbed from the surface using filter paper to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. 120-15 PSgel@Glycerol 120-30PSgel@Glycerol 120-60 PSgel@Glycerol 120-90 and PSgel@Glycerol 120-120 .

[0142] Examples 52-56

[0143] Mix potato starch and deionized water at a mass ratio of 2:3 and stir well to obtain a starch slurry. Pour 4 mL of the starch slurry into a rectangular silicone mold measuring 80 mm (length) × 20 mm (width) × 2 mm (thickness) and smooth it evenly. Then, steam the mold in a steamer (500 W) for 4 minutes. After cooling to room temperature, demold to obtain pure starch hydrogel, denoted as PSgel@Control.

[0144] 12g of PSgel@Control was placed in a high-temperature retort bag containing 180g of glycerol (glycerol mass concentration of 100%) and subjected to wet heat toughening treatment at 135℃ for 15min, 30min, 60min, 90min and 120min respectively.

[0145] After the wet heat toughening treatment, take 12g of the sample and immerse it in 240mL of deionized water (a mixture of ice and water at 0℃) for 10min. Repeat this process three times. Blot away excess water with filter paper to obtain the modified starch hydrogel, denoted as PSgel@Glycerol. 135-15 PSgel@Glycerol 135-30 PSgel@Glycerol 135-60 PSgel@Glycerol 135-90 and PSgel@Glycerol 135-120 .

[0146] Rheological property determination of high-toughness starch hydrogel

[0147] The rheological properties of starch hydrogels were determined using a previously reported method (Feng et al., 2023) with slight modifications, and an interfacial rheometer (Anton Paar MCR102) was used. The test conditions were as follows: test plate diameter 50 mm; test rotor model PP50; gap between rotor and plate 2 mm; test strain 1%; angular frequency range 0.1-100 rad / s. The storage modulus (G') and loss modulus (G'') of the hydrogel were measured as a function of angular frequency (ω). Figure 2 As shown, these are PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6. 100-90 PSgel@Glycerol in Example 24100-90 Storage modulus (G'), loss modulus (G") (A.), and loss factor tanδ (B) of the sample; in the figure, solid represents G' and hollow represents G''.

[0148] G' and G" are used to evaluate the rheological behavior of hydrogel networks. G' is the energy elastically stored in the specimen during periodic stress application, and G" represents the energy lost in the specimen. tanδ reflects the relative contributions of the elastic and viscous components to the viscoelastic properties of the specimen.

[0149] Figure 2 Figure A shows the function curves of G' and G" of starch hydrogels as a function of frequency. From the curves, we can see that G' of all samples is significantly higher than the corresponding G" across the entire frequency scanning range. This indicates that all samples in this frequency range are elastic gels rather than viscous sols, exhibiting a strong gel network structure or solid-like behavior. As the frequency increased from 1 rad / s to 100 rad / s, the G' and G" values ​​of all samples gradually increased without significant crossover, indicating that gel properties dominate within this frequency range. Within the 1–100 rad / s frequency scan range, the viscoelastic modulus of all samples increased with increasing frequency, demonstrating a frequency-dependent viscoelastic modulus. This phenomenon is attributed to the strong hydrogen bond interaction between the hydroxyl groups (OH) in the glycerol molecule and the hydroxyl groups (C-OH) on the starch molecular chain during solvent displacement with water in the starch hydrogel. Furthermore, during the hydrothermal toughening process, high temperatures promote free movement between macromolecules, causing the weak cross-linking points between molecular chains to dissociate. The dissociated molecular chains, in the presence of glycerol macromolecules, form new strong hydrogen bonds or tighter helical structures, resulting in a conformational change and the formation of a highly entangled gel network. Consequently, the network structure in the starch gel becomes more compact and stable, thereby increasing the gel modulus. Solvent displacement combined with hydrothermal toughening significantly enhances the solid-state behavior of starch-based hydrogels. Compared to PSgel@Control, PSgel@Glycerol… 100-90 The G' value of the sample increased by 138.9% at 10 rad / s. This further indicates that the gel network of the starch hydrogel was significantly enhanced.

[0150] tanδ, the ratio of G′ to G″, can be used to reflect the damping characteristics of a sample. Figure 2 As shown in Figure B, the tanδ of all samples ranged from 0.1 to 0.25, indicating that G' plays a dominant role in determining the rheological behavior of the gel (Gao et al., 2023). According to related studies, when tanδ < 0.1, the gel exhibits relatively robust characteristics, while when 0.1 < tanδ < 1, the gel exhibits a weak gel state (Mauro et al., 2023). Figure 2 As can be seen in B, with increasing frequency, PSgel@Glycerol 100-90 The increasing tanδ value of the sample indicates that the sample gradually tends to be a weak gel. This may be attributed to the water absorption and swelling phenomenon that occurred during the second solvent replacement process, which damaged the network structure and affected its mechanical properties.

[0151] Determination of tensile and shear properties of high-toughness starch hydrogels

[0152] Following a previously reported method (Gao et al., 2023) with slight modifications, the tensile and shear properties of all rehydrated gel samples were determined using a texture analyzer (TA.XTPlus, Stable Micro Systems, Surrey, UK). The tensile property test parameters were as follows: trigger force of 5g, stop sampling point at the "target position," and speeds set to 3, 1, and 3 mm² before, during, and after the test, respectively, with a strain height of 10 mm. Sample parameters were set to a width of 2 mm, a length of 18 mm, and a stress area of ​​36 m². 2 The shear performance test parameters were set as follows: the speeds before, during, and after the test were set to 2 mm / s, 0.17 mm / s, and 10 mm / s, respectively; the deformation degree was 80%; and the strain height was 10 mm. Tensile and shear data are the average of 10 measurements. The stress-strain curve, toughness, textural hardness, and chewing hardness of the samples can be obtained using the TPA program. All samples were tested within 15 minutes after reaching the optimal cooking time.

[0153] Figures 3-6 The stress-strain curves of pure starch hydrogel samples after hydrothermal toughening treatment at different temperatures for different times are shown. Figure 3 Stress-strain curves of modified starch hydrogel samples of Comparative Examples 8–12 at -30℃ (A.) and modified starch hydrogel samples of Comparative Examples 13–17 at -18℃ (B.) for 15 min, 30 min, 60 min, 90 min and 120 min. Figure 4 The stress-strain curves of the modified starch hydrogel samples of Comparative Examples 18-22 at 4°C (C.) and the modified starch hydrogel samples of Examples 32-36 at 25°C (D.) for 15 min, 30 min, 60 min, 90 min and 120 min are shown. Figure 5 The stress-strain curves of the modified starch hydrogel samples of Examples 37-41 at 50°C (E.) and the modified starch hydrogel samples of Examples 42-46 at 100°C (F.) for 15 min, 30 min, 60 min, 90 min and 120 min are shown. Figure 6Stress-strain curves of the modified starch hydrogel samples from Examples 47-51 treated at 120°C (G.) and the modified starch hydrogel samples from Examples 52-56 treated at 135°C (H.) for 15 min, 30 min, 60 min, 90 min, and 120 min. From... Figures 3-6 As shown in Figures A through H, the stress and strain of the hydrogel gradually increase with increasing temperature and time. However, when the temperature exceeds 100℃ and the time exceeds 90 min, the stress and strain of the sample gradually decrease. This phenomenon can be attributed to the following factors: First, excessively high temperatures can destroy the cross-linking bonds in the molecular chains, resulting in numerous cracks and damage to the cross-linking structure inside the gel, leading to uneven stress during stretching. Second, excessively high temperatures can cause inter-chain breakage due to excessive and violent movement of macromolecular chain segments. This chain breakage can damage the three-dimensional network structure of the gel, thereby weakening the tensile properties of the gel network. Third, at high temperatures, glycerol macromolecules redistribute within the gel and aggregate at the cross-linking points of the molecular chains to form high-hardness crystalline domains. As the temperature gradually increases, glycerol molecules collide with starch molecules too frequently, weakening the interaction force between them, which in turn damages the network structure of the gel and deteriorates its tensile properties. Based on the above research results, we found that the gel exhibits optimal stress and strain when the hydrothermal toughening treatment condition is 100℃ for 90 min. Therefore, this condition was selected for subsequent experimental samples.

[0154] Figure 7 PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 PSgel@Glycerol in Example 24 100-90 The tensile (A.) and shear curves (B.) are shown. Typically, natural starch hydrogels suffer from high brittleness (i.e., low toughness) and poor tensile properties. In this invention, the hydrogel prepared based on a solvent displacement synergistic hydrothermal toughening strategy exhibits excellent tensile and shear properties. From... Figure 7 As can be seen in Figure A, compared with the control group, PSgel@Glycerol 100-90 The tensile strains of the samples ranged from 334.35% (PSgel@Control) to 221.87% (PSgel@Control). 100-90 The percentage increased to 479.72% (PSgel@Glycerol). 100-90 The tensile stress ranged from 383 Pa (PSgel@Control) and 572.83 Pa (PSgel@Control). 100-90 Increased to 795 Pa (PSgel@Glycerol) 100-90 ).from Figure 7 As can be seen in B, PSgel@Glycerol100-90 The shear stresses of the samples ranged from 760.70 Pa (PSgel@Control) to 1452.70 Pa (PSgel@Control). 100-90 Increased to 2407 Pa (PSgel@Glycerol) 100-90 Table 1 shows the PSgel@Control for Comparative Example 7 and Comparative Example 6. 100-90 PSgel@Glycerol in Example 24 100-90 Shear characteristic data.

[0155] Table 1PSgel@Control, PSgel@Control 100-90 and PSgel@Glycerol 100-90 shear properties

[0156] sample Toughness (g / sec) Texture hardness (g) Chewing hardness (g) Chewing properties (g / sec) PSgel@Control <![CDATA[6.4443±0.11 c ]]> <![CDATA[42.9747±1.85 c ]]> <![CDATA[316.7053±12.18 c ]]> <![CDATA[713.3717±12.62 c ]]> <![CDATA[PSgel@Control 100-90 ]]> <![CDATA[12.2420±0.47 b ]]> <![CDATA[59.5900±2.96 b ]]> <![CDATA[658.4627±23.49 b ]]> <![CDATA[1116.2707±75.32 b ]]> <![CDATA[PSgel@Glycerol 100-90 ]]> <![CDATA[20.9603±1.72 a ]]> <![CDATA[90.7090±5.25 a ]]> <![CDATA[881.6790±70.43 a ]]> <![CDATA[1740.5823±60.28 a ]]>

[0157] Data are expressed as mean ± standard deviation (n=3). Statistically significant differences were found between the means labeled with different letters (a–c) within the same column (p<0.05).

[0158] As shown in Table 1, compared with the control group, PSgel@Glycerol 100-90 The toughness of the samples ranged from 6.4443 g / sec (PSgel@Control) to 12.2420 g / sec (PSgel@Control). 100-90 The concentration significantly increased to 20.9603 g / sec (PSgel@Glycerol). 100-90 Chewing hardness increased from 316.7053g and 658.4627g to 881.6790g, and textural hardness increased from 42.9747g and 59.5900g to 90.7090g; PSgel@Glycerol 100-90The excellent mechanical properties of the sample may be attributed to the increased polymer chain entanglement and crystalline domains. Previous studies have found that hydrothermal toughening can induce high entanglement of macromolecular chains in the amorphous region and increase crystallinity in the crystalline region. In the amorphous phase, when highly entangled molecular chains are stretched, the entanglement points on the molecular chains act like a sliding chain, transmitting tension to other chains along the direction of the molecular chains. The entire gel network contains many entanglement points, which can increase the tensile tension on the molecular chains. Therefore, a large amount of energy is required to untangle these entanglement points during stretching, resulting in large tensile stress. At the same time, a higher stretching rate is required to straighten the coiled macromolecular chains, which in turn leads to high tensile strain. In the crystalline phase (starch is divided into crystalline and amorphous regions, and the crystalline phase can also be called the crystalline region), from a physical perspective, dense crystalline domains can act as closely packed cross-linking points to enhance the strength of the hydrogel. The higher the crystallinity, the stronger the gel, the greater the energy required to break the double helix structure, and the greater the force required to destroy the ordered arrangement of macromolecular chains. This further clarifies the reason for the increase in tensile stress and strain. Furthermore, due to the synergistic effect of high entanglement within the molecular chains and the expansion of crystalline domains, when shear compression encounters crystalline molecular chains, the pinning effect (where the sample remains relatively stable in its position or state under external force, without significant change; due to the increased internal crystalline domains, the stress increases when shear compression reaches a specific strain level) leads to a corresponding increase in the shear stress required to achieve a specific shear deformation. Therefore, PSgel@Glycerol 100-90 The toughness, chewing hardness, and textural hardness of the samples were also significantly enhanced.

[0159] In short, the synergistic effect of the highly entangled molecular chains and dense crystalline domains in the hydrogel is the key to PSgel@Glycerol's success. 100-90 The reason for its high strength, toughness and tensile properties.

[0160] Determination of textural properties of high-toughness starch hydrogels

[0161] Based on the previously reported method (Jia et al., 2022), some modifications were made. A texture analyzer (TA.XTPlus, Stable Micro Systems, Surrey, UK) was used to determine the textural properties of all rehydrated gel samples. The test conditions were as follows: TPA program was used with a P / 36R probe, and compression-decompression cycle mode was employed. Analysis was stopped at the "target position". The speed before and after the test was set to 5 mm / s, the speed during the test was set to 1 mm / s, the contact force was 5 g, the deformation degree was set to 30%, the strain height was set to 10 mm, and the sample length, width, and thickness were set to 20 mm and 20 mm, respectively. The gel hardness, elasticity, adhesion, cohesion, and resilience parameters were determined according to the TPA program. The textural data are the average of 10 measurements. All samples were completed within 15 min after reaching the optimal cooking time. Table 2 shows the PSgel@Control of Comparative Example 7 and PSgel@Control of Comparative Example 6. 100-90 PSgel@Glycerol in Example 24 100-90 The textural properties of the sample include indicators such as gel hardness, viscosity, elasticity, and chewiness.

[0162] Table 2PSgel@Control, PSgel@Control 100-90 and PSgel@Glycerol 100-90 Texture properties

[0163]

[0164] As shown in Table 2, compared with the control group, PSgel@Glycerol 100-90 The gel hardness of the samples ranged from 1653.6763 g (PS gel@Control) to 1578.1617 g (PS@Control). 100-90 Increased to 2092.449g (PSgel@Glycerol) 100-90 This may be attributed to the fact that the wet heat toughening treatment intensifies the free movement of macromolecules, causing rearrangement between starch molecular chains. Weak cross-linking points between chains dissociate and recombine to form new strong cross-linking points. Furthermore, the strong hydrogen bond interaction between glycerol macromolecules and starch macromolecules, formed through hydroxyl groups, further enhances the strength of the gel network, resulting in a denser and more stable gel network structure and increasing gel hardness. Adhesion increased from -279.1840 g·s (PSgel@Control) to -65.384 g·s (PSgel@Glycerol). 100-90This is attributed to the esterification reaction between glycerol macromolecules and starch molecules under high-temperature conditions, forming ester bonds and creating a sticky starch gel on the gel surface. Glycerol acts as a plasticizer, making the molecular chains of the starch gel more flexible and malleable, with a looser molecular structure, and allowing the surface to interact more easily with water, thus producing an adhesive feel. Elasticity increased from 0.8890 and 0.9537 to 0.9617, possibly due to the strong hydrogen bonding between glycerol and starch molecules, and the fact that hydrothermal treatment promotes cross-linking and recombination of molecular chains, improving the stability of the gel network and thus enhancing the gel's elasticity. Chewability increased from 1401.3163 g / sec and 1281.4927 g / sec to 1802.4277 g / sec, possibly related to the gel's high toughness. Texture results further demonstrate that solvent displacement synergistic hydrothermal toughening treatment is an effective method for improving the mechanical properties of starch gels.

[0165] Determination of Crystallinity of High-Toughness Starch Gel

[0166] The relative crystallinity (RC) of all samples was measured by X-ray diffraction (XRD, AxSD8Advance, Bruker, Karlsruhe, Germany). The moisture content of each powder sample was increased to 25% at room temperature, and then the samples were stored at 4°C for 24 hours to allow for moisture equilibration. Test parameters were set as follows: speed 1° / min, step size 0.01° / min, scan range 5–40°, 40 mA, 40 kV, Cu-kα radiation (K = 1.54). The RC value is the ratio of the crystallized peak area (Ac) to the total peak area (A) between 5° and 28° (2θ).

[0167] To further understand the synergistic effect of solvent substitution and hydrothermal toughening treatment on gel crystallization properties, we conducted X-ray diffraction studies. Figure 14 PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 PSgel@Glycerol in Example 24 100-90 The X-ray diffraction pattern of the sample. (e.g.) Figure 14 As shown, all samples exhibited typical type B crystallization, with characteristic peaks at 17°, 20°, and 23°. Significant differences in the peak intensities were observed among the different samples, with PSgel@Glycerol showing the most pronounced peaks. 100-90 The crystallization peak intensity is the strongest, PSgel@Control 100-90The crystallization peak intensity was weak, while the PSgel@Control sample had almost no crystallization peak, with crystallinity of 8.92%, 3.35%, and 0.95%, respectively. This indicates that solvent displacement-assisted hydrothermal toughening treatment can promote crystal formation and increase crystalline domains. This is because high temperature promotes the dissociation and rearrangement of the starch double helix structure, and the dissociation and rearrangement of weak crosslinking sites form strong crosslinking sites. In addition, the strong hydrogen bonds formed between glycerol molecules and starch molecular chains further enhance the recrystallization degree of starch.

[0168] Fourier transform infrared spectroscopy determination of high-toughness starch hydrogel

[0169] Infrared spectra of all samples were obtained using a Fourier Transform Infrared (FTIR) spectrometer manufactured by Thermo Scientific, USA, with a scanning range of 400–4000 cm⁻¹. -1 64 scans, with a resolution of 4cm. -1 Each spectrum used air as a background. Spectra were smoothed and baseline corrected using OMNIC 8.0 software, within the range of 950–1150 cm⁻¹. -1 Perform Fourier deconvolution within the range. Analyze R... 1047 / 1022 The absorbance at a certain point was used to investigate the changes in the short-range ordered structure of starch in the sample.

[0170] Figure 13 PSgel@Control for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 PSgel@Glycerol in Example 24 100-90 Fourier transform infrared spectrum of the sample (A.) and short-range spectral density plot (B.). For example... Figure 13 As shown in Figure A, the overall shape of the infrared spectra of all samples is similar, indicating that no new compounds were formed after solvent displacement and hydrothermal toughening treatment. In all samples, the infrared spectra in the 3000-3700 cm⁻¹ range show similar patterns. -1 A significant broadband band was observed within the range, associated with OH stretching vibrations and intermolecular hydrogen bonds in the pyranose ring. Compared to the control group (PSgel@Control, PSgel@Control...) 100-90 Compared to PSgel@Glycerol 100-90 The sample's wideband wavelength starts from 3358.67 cm⁻¹ -1 and 3298.16cm -1 Reduced to 3278.63cm -1 The wavelength shift from a wide band to a low frequency band indicates a significant enhancement of hydrogen bonding interactions within the starch gel. Figure 13 B shows the R values ​​of all samples obtained after performing Fourier deconvolution on the FTIR spectra. 1047 / 1022 Value. 1047cm-1 The absorbance at 1022 cm⁻¹ is related to the ordered double helix (crystalline region). -1 The absorbance at a certain point indicates the changes in the amorphous region and disordered double helix of starch. 1047 / 1022 The value can represent the short-range ordered structure of starch, mainly reflecting the configuration of starch molecular chains. It reflects the local organization of the crystal array formed by helices, depending on the arrangement of the double helix. Compared with the control group (PSgel@Control and PSgel@Control...) 100-90 Compared to PSgel@Glycerol 100-90 The short-range order of the samples increased from 0.3773 and 0.3883 to 0.4141, indicating that the wet heat toughening treatment can promote the rearrangement of the double helix in starch, change the conformation of the macromolecular chain, enhance the hydrogen bonding interaction in starch gel, and reorganize the crystalline domains.

[0171] Scanning electron microscopy determination of high-toughness starch hydrogel

[0172] Cross-sections of the samples were analyzed using a scanning electron microscope (SEM, S-4800, Hitachi Instruments Ltd, Tokyo, Japan). All samples were thoroughly frozen in liquid nitrogen at -198°C for 2 min, then immediately transferred to -80°C and freeze-dried for 72 h. The network structure of the freeze-dried samples was observed using a scanning electron microscope at 5 kV and 10 μA.

[0173] Figure 12 PSgel@Control (top left image) for Comparative Example 7 and PSgel@Control for Comparative Example 6 100-90 (Top row, right image) and PSgel@Glycerol from Example 24 100-90 (Bottom row) SEM images of the cross-section. As shown in the figure, all samples have a porous structure, exhibiting a honeycomb-like appearance, but with different pore sizes and pore densities. Compared with the control group (PSgel@Control, PSgel@Control...) 100-90 Compared to PSgel@Glycerol 100-90 The sample has a denser gel network structure, smaller pore size, and thicker pore walls. Specific data are listed in Table 3.

[0174] Table 3PSgel@Control, PSgel@Control 100-90 and PSgel@Glycerol 100-90 Pore ​​characteristics

[0175]

[0176] Data are expressed as mean ± standard deviation (n=3). Statistically significant differences were found between means labeled with different letters (ac) within the same column (p<0.05).

[0177] As shown in Table 3, compared with the control group, the pore size of the starch gel decreased from 0.0715 μm and 0.0523 μm to 0.0227 μm, the pore wall thickness increased from 0.1534 μm and 0.2224 μm to 0.4349 μm, and the number of pores increased from 1564.33 / μm. 2 and 1218 / μm 2 Reduced to 1017.67 / μm 2 The porosity decreased from 25.26% and 16.79% to 6.47%, indicating that the hydrothermal toughening treatment can significantly improve the porosity properties of starch gel. This phenomenon is attributed to the fact that the hydrothermal toughening treatment process promotes the migration of starch molecular chains, the high degree of entanglement and reorganization between molecular chains, and the hydrogen bonding interaction between glycerol molecules and starch molecular chains enhances the reorganization of crystalline domains.

[0178] Universality testing

[0179] Different types of starch, including corn starch, wheat starch, sweet potato starch, cassava starch, indica rice flour, mung bean starch, and pea starch, were selected and their universality was determined using the method according to the present invention. Figures 8-11 It can be seen that, compared with the control group (PSgel@Control, PSgel@Control) 100-90 Compared to the control group, the tensile stress and tensile strain of the sample were significantly higher, indicating that the method has universality.

[0180] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A modified starch hydrogel, comprising natural starch, water, and a polyhydroxy compound; wherein the water, the polyhydroxy compound, and the natural starch are cross-linked to form a honeycomb network structure; wherein the polyhydroxy compound comprises one or more of glycerol, glucose alcohol, sucrose, erythritol, xylitol, maltitol, D-mannitol, and sorbitol; The preparation method of the modified starch hydrogel includes the following steps: A starch hydrogel and an aqueous solution of a polyhydroxy compound are mixed and subjected to a wet heat toughening treatment, in which part of the water in the starch hydrogel is replaced by the polyhydroxy compound to obtain a modified starch hydrogel. The preparation of the starch hydrogel includes: gelatinizing a starch slurry to obtain the starch hydrogel; The starch slurry is obtained by mixing natural starch and water; the temperature of the wet heat toughening treatment is 25~135℃; After completing the wet heat toughening treatment, the product is further immersed in water; the immersion temperature is 0~5℃, the number of immersions is 1~5 times, and the immersion time for each immersion is 5~30 minutes.

2. The modified starch hydrogel according to claim 1, characterized in that, The mass of the polyhydroxy compound is 2-8% of the mass of the modified starch hydrogel; the mass of the water is 52-58% of the mass of the modified starch hydrogel.

3. The modified starch hydrogel according to claim 1 or 2, characterized in that, The natural starch includes one or more of potato starch, corn starch, wheat starch, sweet potato starch, cassava starch, indica rice flour, mung bean starch, and pea starch; the natural starch includes amylose and amylopectin; the mass of the amylose is 20-25% of the mass of the starch; the mass of the natural starch is 40% of the mass of the modified starch hydrogel.

4. A method for preparing the modified starch hydrogel according to any one of claims 1 to 3, comprising the following steps: A starch hydrogel and an aqueous solution of a polyhydroxy compound are mixed and subjected to a wet heat toughening treatment, in which part of the water in the starch hydrogel is replaced by the polyhydroxy compound to obtain a modified starch hydrogel. The preparation of the starch hydrogel includes: gelatinizing a starch slurry to obtain the starch hydrogel; The starch slurry is obtained by mixing natural starch and water; the temperature of the wet heat toughening treatment is 25~135℃; After completing the wet heat toughening treatment, the product is further immersed in water; the immersion temperature is 0~5℃, the number of immersions is 1~5 times, and the immersion time for each immersion is 5~30 minutes.

5. The preparation method according to claim 4, characterized in that, The wet heat toughening treatment time is 15~120 min.

6. The preparation method according to claim 4 or 5, characterized in that, The mass ratio of the starch hydrogel to the aqueous solution of the polyhydroxy compound is (1~1.25):15; the mass concentration of the polyhydroxy compound in the aqueous solution is 25~100%.

7. The preparation method according to claim 6, characterized in that, The starch hydrogel has a water molecule concentration of 60%.

8. The preparation method according to claim 4, characterized in that, The gelatinization process involves a power of 500-800W and a time of 3-4 minutes.

9. The application of the modified starch hydrogel according to any one of claims 1 to 3 or the modified starch hydrogel prepared by the preparation method according to any one of claims 4 to 8 in food.

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