Preparation method of dihydroxy propyl etherified starch

Abstract

The invention provides a preparation method of dihydroxy propyl etherified starch, which comprises the following steps: sequentially adding a starch raw material and pure water to prepare a starch emulsion, then adding anhydrous sodium sulfate into the starch emulsion, and stirring for 8-15 minutes at a constant speed in a constant-temperature oil bath to obtain a mixture; dropwise adding a NaOH solution into the mixture to adjust the pH value, then adding glyceryl ether, and stirring and reacting for 0.5-2 hours at a constant speed in a constant-temperature oil bath; after the reaction is completed, dropwise adding an HCl solution, adjusting the pH value, and then centrifugally washing and drying to obtain the product. Glycerol ether is adopted as an etherifying agent to modify the starch raw material, the dosage of glycerol ether and etherification time are controlled to prepare the dihydroxy propyl etherified starch, the gelatinization temperature of the starch is remarkably reduced through dihydroxy propyl etherification modification, and the film-forming property of the starch is improved.

Description

Technical Field

[0001] The invention relates to the technical field of starch etherification, and in particular to a method for preparing dihydroxypropyl etherified starch. Background Art

[0002] Starch with high amylose content has good film-forming properties, but the high energy required to destroy the tight amylose structure results in a gelatinization temperature greater than 130°C, requiring the use of a high-temperature, high-pressure reactor for gelatinization. At the same time, when the pure starch paste is dried at a temperature below 80°C, the starch molecular chains and the starch molecules and water molecules rearrange their orientations, and aggregate to form microcrystalline bundles through intramolecular and intermolecular hydrogen bond interactions. The retrogradation phenomenon is obvious, affecting the starch's ability to form a complete, smooth, and uniform film.

[0003] Nowadays, starch is etherified to lower its gelatinization temperature while improving its film-forming properties. While etherification modification does not affect the amylose content in starch granules, the larger groups introduced disrupt hydrogen bonds within and between starch molecules, increasing steric hindrance, lowering the gelatinization temperature and increasing the hydrophilicity of the starch. Commonly used etherifying agents include ethylene oxide, propylene oxide, methyl chloride, and ethyl chloride. However, these etherification reactions require demanding reaction conditions, and the hydroxypropyl groups formed with starch contain only one hydroxyl group, resulting in lower hydrophilicity and functionalization potential. This results in lower solubility of the etherified starch, and the solubility of the etherified starch prepared using these etherifying agents is highly dependent on heating.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] A first object of the present invention is to provide a method for preparing dihydroxypropyl etherified starch. By using glycerol ether as an etherifying agent, better etherification modification of starch is achieved. While introducing more hydroxyl groups, the starch etherification can be carried out under lower reaction temperature and pH conditions, thereby reducing energy consumption and the generation of side reactions. As a result, the prepared etherified starch has higher hydrophilicity and can be dissolved in cold water. At the same time, by controlling the amount of glycerol ether and the etherification time, the etherification level of the starch is increased, and the gelatinization temperature of the dihydroxypropyl etherified starch after etherification modification is significantly reduced, thereby improving film-forming properties.

[0006] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A method for preparing dihydroxypropyl etherified starch comprises the following steps: Adding starch raw material and pure water in sequence to prepare starch emulsion, then adding anhydrous sodium sulfate to the starch emulsion and stirring at a constant speed for 8 minutes to 15 minutes in a constant temperature oil bath to obtain a mixture; NaOH solution was added dropwise to the mixture to adjust the pH, and then glycerol ether was added. The mixture was stirred at a constant speed in a constant temperature oil bath for 0.5-2 h; After the reaction is completed, HCl solution is added dropwise, the pH is adjusted, and the mixture is centrifuged, washed, and dried to obtain the product.

[0007] Preferably, as a further specific embodiment, the added amount of the glycerol ether is 5%-40% of the mass of the starch raw material.

[0008] Preferably, as a further specific embodiment, the added amount of the glycerol ether is 30% of the mass of the starch raw material.

[0009] In the present invention, glycerol ether is used as an etherifying agent to achieve etherification modification of starch, so that the prepared dihydroxypropyl etherified starch has higher hydrophilicity and film-forming properties. Compared with the method of using propylene oxide as an etherifying agent commonly used in the prior art to achieve etherification modification of starch, the present invention has milder conditions. This is because when propylene oxide is used as an etherifying agent, since the boiling point of propylene oxide itself is only 34°C, it is usually a volatile gas at room temperature. Therefore, in order to enable propylene oxide and starch to react better, the etherification process usually needs to be carried out under pressurized conditions, which makes the operation complicated. When propylene oxide is used as an etherifying agent, a high-concentration alkaline solution is usually required for catalysis, but the strong alkaline propylene oxide is not suitable for the reaction between propylene oxide and starch. The environment is prone to starch degradation or over-substitution, thereby affecting the utilization rate of the etherifying agent. In addition, when propylene oxide is used to etherify starch, it shows high temperature sensitivity to the etherification temperature. If the temperature is not properly controlled, side reactions will be triggered. More importantly, when propylene oxide is used as an etherifying agent to etherify starch, the hydroxypropyl-O-CH2-CHOH-CH3 generated contains only one hydroxyl group, so its hydrophilicity and functionalization potential are low, and the solubility of the generated etherified starch is extremely dependent on heating. It has poor solubility under cold water conditions, which limits the application range of the etherified starch. In order to solve the above problems, the inventors have found through a series of creative work that when glycerol ether is used as an etherifying agent to etherify starch, The obtained dihydroxy etherified starch has more excellent performance and milder reaction conditions. This is because glycerol ether has higher reaction activity and milder reaction conditions than propylene oxide. The epoxy ring of glycerol ether has greater tension than propylene oxide, and the three-membered epoxy ring structure it contains is more reactive than propylene oxide, so that it can be efficiently ring-opened at lower temperature and milder alkaline conditions. Glycerol ether itself is liquid and has a higher boiling point than propylene oxide, so that it can react at normal pressure, thereby reducing energy consumption and side reactions. At the same time, since dihydroxy groups can be introduced during the etherification reaction of glycerol ether and starch, the prepared etherified starch has more excellent properties. Yes, after glycerol ether reacts with starch, dihydroxypropyl starch ether is generated, and its structure is Starch-O-CH2-CH(OH)-CH2OH. It has one more hydroxyl group than the traditional hydroxypropyl-O-CH2-CHOH-CH3, which makes it more hydrophilic and can be dissolved in cold water, thus avoiding its solubility from being dependent on heating conditions. The remaining hydroxyl groups can be further cross-linked, esterified or grafted with other functional groups, thereby further expanding its application scenarios. In addition, when glycerol ether is used for etherification modification, fewer by-products are produced and the product purity is higher. This is because glycerol ether has a high reaction activity, which can reduce the dependence on strong alkaline catalysts or high temperatures, thereby reducing starch degradation and the occurrence of side reactions.In summary, the present invention adopts glycerol ether as an etherifying agent to carry out starch etherification, thereby introducing more hydroxyl groups and being able to carry out the reaction at lower reaction temperature and pH conditions, thereby reducing energy consumption and the generation of side reactions, so that the prepared etherified starch has higher hydrophilicity and can be dissolved under cold water conditions. At the same time, by controlling the amount of glycerol ether and the etherification time, the etherification level of the starch is increased, so that the gelatinization temperature of the dihydroxypropyl etherified starch after etherification modification is significantly reduced, and the film-forming performance is improved.

[0010] Among them, the amount of glycerol ether is very important for the present invention, because the amount of glycerol ether is a key factor affecting the etherification reaction efficiency, substitution degree and product performance. For the present invention, when the amount of glycerol ether added is 5%-40% of the mass of the starch raw material, preferably, when the amount of glycerol ether added is 30% of the mass of the starch raw material, the effect achieved is excellent. This is because an increase in the amount of glycerol ether increases the probability of etherification of hydroxyl groups on starch molecules, thereby increasing the substitution degree and further improving the solubility of etherified starch. However, when the glycerol ether is excessive, the growth trend of the substitution degree gradually stabilizes, and the excess glycerol ether may self-polymerize or over-hydrolyze, thereby reducing the effective utilization rate.

[0011] Preferably, as a further specific embodiment, the starch raw material includes any one of pea native starch, potato native starch or corn native starch; the amylose of the pea native starch is 30%-40%; the amylose of the potato native starch is 15%-25%; and the amylose of the corn native starch is 40%-70%.

[0012] Preferably, as a further specific embodiment, the linearity of the pea native starch is 33%; the linearity of the potato native starch is 23%; and the linearity of the corn native starch is 50% or 70%.

[0013] Preferably, as a further specific embodiment, the starch raw material is native corn starch, and the linearity of the native corn starch is 50%.

[0014] In the present invention, the inventors have conducted a series of creative work to explore the effects of dihydroxypropyl etherification modification on the physical and chemical properties of starches from different sources and with different structures. For the present invention, when the starch raw material is selected as any one of pea native starch, potato native starch or corn native starch, and the linearity of the pea native starch is 30%-40%; the linearity of the potato native starch is 15%-25%; and the linearity of the corn native starch is 40%-70%, the effects that can be achieved are excellent. This is because the highly branched structure of high-branched starch such as potato native starch or corn native starch exposes more amorphous regions and free hydroxyl groups, making it easier for glycerol ether to contact reaction sites and the reaction rate is faster. In the present invention, when the starch raw material is corn native starch and the linearity of the corn native starch is 50%, the etherified starch effect is excellent. This is because the hydroxyl groups of corn native starch with 50% linearity are more easily exposed than those of pea native starch and potato native starch, making it The probability of contact with glycerol ether is higher, thereby making the accessibility of reaction sites better. Although amylose is more likely to form double helical crystals, the proportion of amorphous regions of high-amylose corn starch is higher in comparison, making its etherifying agent easier to penetrate, resulting in better starch etherification effect. As the linearity of corn native starch gradually increases, it is easy to cause large steric hindrance and internal hydroxyl groups to be wrapped, making it difficult for glycerol ether to reach the reaction sites. At the same time, when the amount of etherifying agent and the etherification reaction time are constant, the size of the starch linearity affects the etherification level to a certain extent. When the starch linearity is within the range provided by the present invention, the degree of starch etherification is excellent. In the etherification reaction provided by the present invention, if the starch linearity is too high, it may form uneven substitution during the etherification reaction because the reaction difference between its linear region and crystalline region is large, so that the product may show the coexistence of local high substitution and unreacted regions. If the starch linearity is low, the branched structure may lead to a low overall substitution degree due to steric hindrance, and the reaction efficiency is low.

[0015] Preferably, as a further specific embodiment, after adding anhydrous sodium sulfate, the temperature of the constant temperature oil bath is 40°C-50°C; Preferably, the temperature of the constant temperature oil bath is 45°C.

[0016] In the present invention, the etherification reaction is heated by using an oil bath, which is more suitable for the preparation of dihydroxypropyl etherified starch than traditional water bath heating. This is because the present invention mainly uses glycerol ether as an etherifying agent to achieve starch etherification. The presence of hydroxyl groups in glycerol ether enables it to form strong hydrogen bonds with water molecules, making it more soluble in water. Therefore, in order to avoid the introduction of additional moisture and the resulting hydrolysis of glycerol ether, the present invention uses an oil bath to create an anhydrous environment, inhibiting the hydrolysis of glycerol ether and improving the reaction selectivity. In addition, starch easily forms a high-viscosity slurry under alkaline conditions. Traditional water bath heating is prone to uneven heat transfer, resulting in local overheating or uneven distribution of glycerol ether. When heating in an oil bath, the convection makes heating more efficient, making it suitable for heating high-viscosity systems and ensuring uniform reaction. In addition, the reaction time of the present invention is long and the reaction process is relatively sensitive to the reaction temperature. The oil bath has small temperature fluctuations and is suitable for long-term constant temperature reactions. The water bath is prone to temperature fluctuations due to water evaporation, which may lead to uneven substitution degree, increased side reactions, or starch degradation. Preferably, as a further specific embodiment, the mass concentration of the HCl solution is 0.5%-1.5%; Preferably, the mass concentration of the HCl solution is 1%.

[0017] In the present invention, hydrochloric acid is used to quickly terminate the reaction, and the pH is quickly reduced to neutral or weakly acidic by neutralizing the alkali in the etherification reaction system, thereby immediately stopping the ring-opening and etherification reaction of the glycerol ether, thereby ensuring that the degree of substitution meets the expectations. Therefore, the amount of hydrochloric acid used is limited in the present invention. When the mass concentration of the HCl solution is 0.5%-1.5%, preferably the mass concentration of the HCl solution is 1%, the effect that can be achieved is excellent. This is because the amount of hydrochloric acid used has an important influence on the reaction termination effect, product properties and subsequent treatment. Excessive hydrochloric acid will make the overall reaction system acidic, thereby causing starch to hydrolyze in an acidic environment, or may cause the hydroxypropyl ether bond in the dihydroxypropyl etherified starch to break at extreme pH; and if the amount of hydrochloric acid used is insufficient, it will not be able to completely neutralize the alkaline catalyst, so that the residual base will continue to catalyze the ring-opening of the glycerol ether, resulting in an uncontrollable increase in the degree of substitution or an increase in side reactions.

[0018] Preferably, as a further specific embodiment, the pH is 10-11 after adding NaOH solution dropwise to the mixture.

[0019] In the present invention, when glycerol ether is used as an etherifying agent, since glycerol ether contains both epoxy and hydroxyl groups in its molecule compared to propylene oxide, and the ring-opening activity of epoxy groups is significantly higher than that of propylene oxide, propylene oxide needs to be catalyzed by a strong base when performing starch etherification, while glycerol ether can achieve efficient ring opening in a relatively mild alkaline environment. Glycerol ether is easily hydrolyzed under strong alkaline conditions, thereby reducing the etherification efficiency. In addition, a strongly alkaline environment will cause starch degradation. Therefore, in summary, when glycerol ether is used as an etherifying agent, selecting a pH environment of 10-11 can significantly inhibit the hydrolysis of glycerol ether, thereby improving the utilization rate of glycerol ether, and the weak alkaline environment is milder and can protect the integrity of the starch skeleton.

[0020] Preferably, as a further specific embodiment, the pH is 6 after the HCl solution is added dropwise.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for preparing dihydroxypropyl etherified starch, which uses glycerol ether as an etherifying agent to achieve better etherification modification of starch, introduces more hydroxyl groups and can etherify starch at lower reaction temperature and pH conditions, thereby reducing energy consumption and the generation of side reactions, so that the prepared etherified starch has higher hydrophilicity and can be dissolved in cold water. At the same time, by controlling the amount of glycerol ether and the etherification time, the etherification level of starch is higher, so that the gelatinization temperature of the dihydroxypropyl etherified starch after etherification modification is significantly reduced, and the film-forming performance is improved. DETAILED DESCRIPTION

[0022] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, those skilled in the art will understand that the embodiments described below are part of the embodiments of the present invention, not all of them, and are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0023] In order to more clearly illustrate the technical solutions of the present invention, specific embodiments are provided below for illustration.

[0024] Example 1 The preparation process of a dihydroxypropyl etherified starch of the present invention is as follows: The main raw materials and chemical reagents required for the experiment are shown in Table 1 below: Table 1 Main raw materials and chemical reagents required for the experiment

[0025] The experimental instruments and equipment required for the experiment are shown in Table 2 below Table 2 Main instruments and equipment required for the experiment

[0026] The preparation process is as follows: In a clean, dry 250 mL three-necked flask, weigh 40 g of native potato starch (15% amylose) and 60 g of pure water to prepare a 40% starch emulsion. Add 5.6 g of anhydrous sodium sulfate and stir uniformly in a 40°C oil bath for 8 minutes to ensure uniform mixing. Slowly add a certain amount of 0.5 wt% NaOH solution dropwise to adjust the emulsion's pH to 10. Quickly add 2 g of glycerol ether and seal the container. Then, the mixture was stirred at a constant speed in a 40°C constant temperature oil bath for 0.5 h; After the reaction was completed, a certain amount of 0.5 wt% HCl solution was slowly added dropwise to adjust the pH to 6 to terminate the reaction; The product was then centrifuged at 8000 rpm in a high-speed centrifuge for 5 min, washed twice with pure water, and then washed twice with 95 wt% ethanol solution. The product was moved to a 40°C forced air drying oven and dried for 24 h, and then dried at 105°C for 2 h to obtain dry dihydroxypropyl etherified starch.

[0027] Example 2 The preparation process is as follows: In a clean, dry 250 mL three-necked flask, weigh 20 g of native potato starch (40% amylose) and 80 g of pure water to prepare a 20% starch emulsion. Add 4.2 g of anhydrous sodium sulfate and stir uniformly in a 50°C oil bath for 15 minutes to ensure uniform mixing. Slowly add a certain amount of 1.5 wt% NaOH solution dropwise to adjust the emulsion's pH to 11. Quickly add 8 g of glycerol ether and seal the container. Then, the mixture was stirred at a constant speed in a 50°C oil bath for 2 h; After the reaction was completed, a certain amount of 1.5 wt% HCl solution was slowly added dropwise to adjust the pH to 6 to terminate the reaction; The product was then centrifuged at 8000 rpm in a high-speed centrifuge for 5 min, washed twice with pure water, and then washed twice with 95 wt% ethanol solution. The product was moved to a 40°C forced air drying oven and dried for 24 h, and then dried at 105°C for 2 h to obtain dry dihydroxypropyl etherified starch.

[0028] Example 3 The preparation process is as follows: In a clean, dry 250 mL three-necked flask, weigh 30 g of native corn starch (50% amylose) and 70 g of pure water to prepare a 30% starch emulsion. Add 4.8 g of anhydrous sodium sulfate and stir uniformly in a 45°C oil bath for 10 minutes to ensure uniform mixing. Slowly add a 1 wt% NaOH solution dropwise to adjust the emulsion's pH to 11. Quickly add 9 g of glycerol ether and seal the container. Then, the mixture was stirred at a constant speed in a 45°C constant temperature oil bath for 2 h; After the reaction was completed, a certain amount of 1 wt% HCl solution was slowly added dropwise to adjust the pH to 6 to terminate the reaction; The product was then centrifuged at 8000 rpm in a high-speed centrifuge for 5 min, washed twice with pure water, and then washed twice with 95 wt% ethanol solution. The product was moved to a 40°C forced air drying oven and dried for 24 h, and then dried at 105°C for 2 h to obtain dry dihydroxypropyl etherified starch.

[0029] Experimental Example 1 Determination of molar substitution (MS) of etherified starch 1.1 The molar substitution degree of the dihydroxyetherified starch obtained in Example 1-3 was determined. The specific steps of the determination were the same as those in Experimental Example 1.2. The specific test results are shown in Table 1 below: Table 1 Test results

[0030] 1.2 Based on the preparation method in Example 3, the molar substitution degree of glycidyl etherified starch with different starch structures and different glycerol ether dosages was determined. The specific parameters changed are shown in Table 2, and the specific determination method is as follows: (1) Preparation of internal standard solution Weigh 2.5 g of toluene into a 100 mL volumetric flask and dilute to the mark with o-xylene. Invert the flask repeatedly to mix evenly. Calculate the exact concentration of the toluene solution based on the actual amount weighed.

[0031] (2) Preparation of standard solution Weigh 65 mg of adipic acid into a 5 mL reaction vial. Use a pipette to accurately add 2.0 mL of internal standard solution and 2.0 mL of hydroiodic acid. Accurately weigh the reaction vial. Use a syringe to add 15 µL of isopropyl iodide to the reaction vial. Accurately weigh the reaction vial. Mix thoroughly and set aside in a dark place until ready to use.

[0032] (3) Preparation of sample solution Weigh 65 mg of sample into a 5 mL reaction vial. Add 65 mg of adipic acid. Use a pipette to accurately add 2.0 mL of internal standard solution and 2.0 mL of hydroiodic acid. Accurately weigh the reaction vial. Mix thoroughly and place the reaction vial in a 150°C metal bath thermostat for 1 hour. After the reaction, cool to room temperature and weigh again. Ensure the weight loss does not exceed 10 mg.

[0033] (4) Measurement method Inject 2 µL of the upper layer of the standard solution into a gas chromatograph and record the chromatogram. Repeat this procedure five times. The relative standard deviation (RSD) of the peak area ratio of isopropyl iodide to toluene should be no greater than 5%. Similarly, inject 2 µL of the upper layer of the sample solution into a gas chromatograph and record the chromatogram. Calculate the dihydroxypropyl content using the internal standard method.

[0034] (5) Calculation process In percentage terms, the dihydroxypropyl content (K2) is calculated according to formula (1-1): (1-1) Where: K2 is the percentage of dihydroxypropyl (%); is the ratio of the molecular weight of dihydroxypropyl to the molecular weight of isopropyl iodide ( =0.5353); Q2 is the mass ratio of isopropyl iodide to toluene (2 mL internal standard solution) in the standard solution; A3 is the peak area ratio of isopropyl iodide to toluene in the standard solution; A4 is the peak area ratio of isopropyl iodide to toluene in the sample solution; W is the mass of toluene in 2 mL internal standard solution (g); W2 is the dry basis mass of etherified starch in the sample solution (g); The specific measurement results are shown in Table 2 below: Table 2 Molar substitution degree of dihydroxypropyl etherified starch

[0035] Experimental Example 2 Preparation of dihydroxypropyl etherified starch film and its performance determination (1) Preparation process of dihydroxypropyl etherified starch film Weigh a certain amount of the dried starch obtained from 1-1#-3-8# in Experimental Example 1 and pure water to prepare a 10% starch emulsion. Add 2 wt% glycerol, 33 wt% sorbitol, 0.6 wt% polyvinyl alcohol, and 0.04 wt% anhydrous calcium chloride, relative to the dry weight of the starch. Gradually heat to 110°C in an oil bath. Stir at a constant temperature of 400 rpm for 1 hour to fully gelatinize the starch. Slowly cool. Pour the gelatinized film-forming solution onto a preheated smooth glass plate. Use a doctor blade to control the film thickness to a uniform thickness. Dry completely in a 45°C oven, then remove the film. Store in a desiccator containing a saturated sodium bromide solution at a relative humidity of 56%. After drying, it was visible to the naked eye that the etherification modification significantly improved the film-forming ability of the starch film. In particular, for high-amylose corn starch, the unmodified native starch has a high gelatinization temperature due to its high amylose content, and the starch failed to fully gelatinize at 110°C. High-amylose starch also has strong retrogradation properties. During the film-forming process at a lower temperature (45°C), the amylose molecules in the starch granules will quickly rearrange and crystallize, making the starch film brittle and even unable to form a complete film. However, the etherification reaction of the present invention, which introduces dihydroxypropyl groups, significantly reduces the gelatinization temperature, allowing the modified starch to fully gelatinize at 110°C. Furthermore, the increased steric hindrance of the starch molecular chains makes it difficult for the amylose molecules to orient and retrograde during the film-forming process, allowing them to form a solid gel network structure at lower temperatures, resulting in better film-forming properties.

[0036] (2) Determination of transparency of etherified starch film Scanning electron microscopy (SEM) images of native starch and dihydroxypropyl-etherified starch obtained with 1-1#-3-8# in Experimental Example 1 revealed that, compared to native starch, the surface of the etherified starch granules exhibited small depressions and protrusions. Furthermore, as the amount of etherifying agent increased, the volume of the starch granules increased. This may be due to the low accessibility of the etherifying agent and the large size of the dihydroxypropyl groups. The etherification modification increased the steric hindrance between starch molecular chains and reduced hydrogen bonding interactions between starch molecules, resulting in an overall increase in starch granule volume. Furthermore, aggregation occurred at the sites of dihydroxypropyl group insertion, resulting in an uneven surface and even small protrusions. Before etherification modification, the surface of low-amylose pea starch and potato starch particles was smooth and uniformly round. However, after modification, wrinkles or protrusions appeared on the particle surface due to particle expansion and group aggregation. Before modification, high-amylose corn starch particles were irregular polygons, and even had small holes of different sizes, depths and distributions on the surface. After modification, the small holes were squeezed out and disappeared due to particle expansion, so the surface of the etherified starch remained relatively smooth.

[0037] (3) Determination of mechanical properties of etherified starch films The etherified starch obtained by 1-1#-3-8# in Experimental Example 1 was measured, and it can be seen that the dihydroxypropyl etherified starch film obtained by etherification modification with glycerol ether in the present invention, in addition to potato starch, low-amylose pea starch and high-amylose corn starch, has significantly improved tensile strength or elongation at break after etherification modification.

[0038] This is because the insertion of larger dihydroxypropyl groups into starch molecules increases the distance between starch molecules, reduces hydrogen bonding interactions within and between starch molecules, increases the flexibility of starch macromolecules, and exerts a certain internal plasticizing effect on the starch film, resulting in greater strength and toughness of the prepared film. However, due to the low amylose content of potato starch, the vicinal diol structure of the dihydroxypropyl group actually increases hydrogen bonding between starch molecular chains, resulting in uneven crystallization within the starch film and significantly weakened mechanical properties. This is consistent with the results of retrogradation, relative crystallinity, and transparency.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing dihydroxypropyl etherified starch, characterized in that: The following steps are involved: Adding starch raw material and pure water in sequence to prepare starch emulsion, then adding anhydrous sodium sulfate to the starch emulsion and stirring at a constant speed for 8 minutes to 15 minutes in a constant temperature oil bath to obtain a mixture; NaOH solution was added dropwise to the mixture to adjust the pH, and then glycerol ether was added. The mixture was stirred at a constant speed in a constant temperature oil bath for 0.5-2 h; After the reaction is completed, HCl solution is added dropwise, the pH is adjusted, and the mixture is centrifuged, washed, and dried to obtain the product.

2. The method for preparing dihydroxypropyl etherified starch according to claim 1, wherein The added amount of the glycerol ether is 5%-40% of the mass of the starch raw material.

3. The method for preparing dihydroxypropyl etherified starch according to claim 2, wherein: The added amount of the glycerol ether is 30% of the mass of the starch raw material.

4. The method for preparing dihydroxypropyl etherified starch according to claim 1, wherein The starch raw material includes any one of pea native starch, potato native starch or corn native starch; the linearity of the pea native starch is 30%-40%; the linearity of the potato native starch is 15%-25%; and the linearity of the corn native starch is 40%-70%.

5. The method for preparing dihydroxypropyl etherified starch according to claim 4, characterized in that: The linearity of the pea native starch is 33%; the linearity of the potato native starch is 23%; and the linearity of the corn native starch is 50% or 70%.

6. The method for preparing dihydroxypropyl etherified starch according to claim 5, characterized in that: The starch raw material is native corn starch, and the linearity of the native corn starch is 50%.

7. The method for preparing dihydroxypropyl etherified starch according to claim 1, characterized in that: After adding anhydrous sodium sulfate, the temperature of the constant temperature oil bath is 40°C-50°C; Preferably, the temperature of the constant temperature oil bath is 45°C.

8. The method for preparing dihydroxypropyl etherified starch according to claim 1, wherein The mass concentration of the HCl solution is 0.5%-1.5%; Preferably, the mass concentration of the HCl solution is 1%.

9. The method for preparing dihydroxypropyl etherified starch according to claim 1, characterized in that: The pH was 10-11 after adding NaOH solution dropwise to the mixture.

10. The method for preparing dihydroxypropyl etherified starch according to claim 1, characterized in that: After the reaction was completed, the pH was 6 after HCl solution was added dropwise.

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