Porous phosphate chestnut starch and preparation method and application thereof

文档序号:266804 发布日期:2021-11-19 浏览:35次 中文

阅读说明:本技术 一种多孔磷酸酯板栗淀粉及其制备方法和应用 (Porous phosphate chestnut starch and preparation method and application thereof ) 是由 呼娜 王硕 唐二军 袁淼 于 2021-09-26 设计创作,主要内容包括:本发明涉及化合物制备技术领域,尤其涉及一种多孔磷酸酯板栗淀粉及其制备方法和应用,该制备方法首先将板栗淀粉酶解成多孔结构,并通过磷酸盐对板栗淀粉进行改性,在此基础上通过对原料的筛选以及工艺的设计,最终制得了一种高取代度,高透明度且絮凝能力突出的多孔磷酸酯板栗淀粉,为天然高分子絮凝剂在废水处理中的应用提供了更加优良的选择。(The invention relates to the technical field of compound preparation, in particular to porous phosphate chestnut starch and a preparation method and application thereof.)

1. The preparation method of the porous phosphate chestnut starch is characterized by comprising the following steps:

s1: mixing the Chinese chestnut starch and a disodium hydrogen phosphate-citric acid buffer solution uniformly, emulsifying and stirring to prepare a starch emulsion, adding a compound amylase into the starch emulsion, and performing enzymolysis on the Chinese chestnut starch to obtain porous Chinese chestnut starch;

s2: and uniformly mixing the porous Chinese chestnut starch with a phosphate solution, emulsifying, stirring, centrifugally drying until the water content is 5% -10%, performing esterification, washing to remove unreacted phosphate, and drying the obtained product to obtain the porous phosphate Chinese chestnut starch.

2. The method for preparing the porous phosphate chestnut starch according to claim 1, wherein the temperature of the emulsification stirring process in S1 is 55-60 ℃ and the time is 30-40 min; and/or

The temperature of the emulsification stirring process in the S2 is 50-55 ℃, and the time is 40-45 min.

3. The method for preparing porous phosphate chestnut starch according to claim 1, wherein the pH of the disodium hydrogen phosphate-citric acid solution in S1 is 5.0-5.6, and the mass concentration of starch in the starch emulsion is 20-25%.

4. The method for preparing porous phosphate chestnut starch according to claim 3, wherein the composite amylase in S1 is a mixture of alpha-amylase and glucoamylase DE, and the mass ratio of the alpha-amylase to the glucoamylase DE is 1:1-1.2, and the dosage of the compound amylase is 1248u-1560u/g of Chinese chestnut starch.

5. The preparation method of the porous phosphate chestnut starch as claimed in claim 3, wherein the enzymolysis temperature in S1 is 55-62 ℃, the enzymolysis time is 7-9h, and after the enzymolysis is finished, absolute ethyl alcohol is added to inactivate enzyme.

6. The method for preparing the porous phosphate chestnut starch according to claim 1, wherein the phosphate solution in S2 is orthophosphate solution with a mass concentration of 45% -55%, NaOH and phosphoric acid solution are used for adjusting the pH of reaction solution to 5.6-6.0 in the esterification reaction process, and the mass ratio of the porous chestnut starch to phosphate radical in the modified solution is 1: 1.8-2.

7. The method for preparing porous phosphate chestnut starch as claimed in claim 1, wherein the esterification reaction in S2 is carried out at 140-150 ℃ under normal pressure for 150 min.

8. The method for preparing a porous phosphate chestnut starch according to claim 1, wherein the detergent for washing to remove unreacted phosphate in S2 is a 50% ethanol solution, and the freeze-drying time of the product after washing is 14-20 h.

9. A porous phosphate chestnut starch, which is prepared by the preparation method of the porous phosphate chestnut starch of any one of claims 1 to 8.

10. The use of the chestnut starch of claim 9 in the preparation of polymeric flocculant.

Technical Field

The invention relates to the technical field of compound production, in particular to porous phosphate chestnut starch and a preparation method and application thereof.

Background

China is the biggest Chinese chestnut producing country in the world, more than half of Chinese chestnuts come from China all over the world, the yield is higher, defective products generated in the process of producing and selling the Chinese chestnuts are larger, according to statistics, the defective Chinese chestnuts generated due to the defects of damage, worm damage, unqualified sizes and the like are hundreds of thousands of tons every year, and the Chinese chestnuts are directly discarded, so that the environment is polluted, and the resource waste is caused.

The starch is a green and environment-friendly natural polymer material, is renewable and degradable, and is an excellent flocculant in the field of wastewater treatment, the Chinese chestnut starch is an important constituent substance of Chinese chestnuts and accounts for 40-60% of the dry weight of the Chinese chestnuts, and the recovery and preparation of the starch in the waste Chinese chestnuts into the flocculant is a feasible treatment mode, but the flocculant prepared by the natural Chinese chestnut starch has low flocculation capacity and poor wastewater treatment capacity, and the transparency and the flocculation capacity of the modified Chinese chestnut starch cannot meet the requirements of industrial production due to the low substitution degree, so that the substitution degree of the modified Chinese chestnut starch is improved, the transparency and the flocculation capacity of the modified Chinese chestnut starch are improved, and the application value of the Chinese chestnut starch in the industrial production is very important.

Disclosure of Invention

Aiming at the technical problems of low transparency and apparent viscosity of Chinese chestnut starch, low substitution degree of the existing modified Chinese chestnut starch and poor transparency and flocculation capability in the prior art, the invention provides a preparation method of porous phosphate Chinese chestnut starch, which realizes the modification of the Chinese chestnut starch by phosphoric acid through the design of the process, and the prepared porous phosphate Chinese chestnut starch has high substitution degree, high transparency and outstanding flocculation capability and can be used as a natural polymer flocculant for wastewater treatment.

In order to achieve the purpose of the invention, the embodiment of the invention adopts the following technical scheme:

the embodiment of the invention provides a preparation method of porous phosphate chestnut starch, which specifically comprises the following steps:

s1: uniformly mixing the Chinese chestnut starch and a disodium hydrogen phosphate-citric acid buffer solution, emulsifying and stirring to obtain a starch emulsion, slowly adding a compound amylase into the obtained starch emulsion, and performing enzymolysis on the Chinese chestnut starch to obtain porous Chinese chestnut starch;

s2: and uniformly mixing the obtained porous chestnut starch with a phosphate solution, emulsifying, stirring, centrifugally drying until the water content is 5-10%, performing esterification reaction, washing to remove unreacted phosphate, and drying the obtained product to obtain the porous phosphate chestnut starch.

Compared with the prior art, the preparation method of the porous phosphate chestnut starch provided by the invention comprises the steps of firstly carrying out enzymolysis on chestnut starch by using the compound amylase, wherein the compound amylase acts on irregular parts and amorphous areas on the surface of the starch to destroy hydrogen bonds of a dimensional space spiral structure in starch molecule particles, so that the starch forms a porous structure with a concave surface; on one hand, the porous structure can enable water molecules to enter the starch granules more easily, and reduce the forming difficulty of a uniform hydration system of starch paste, thereby improving the light transmittance and flocculation performance of the starch; on the other hand, the crystalline region and the amorphous region of the starch can be exposed, so that hydroxyl in the starch is easier to be substituted by a substituent group, the substitution degree is improved, and the improvement on the transparency and the flocculation performance is promoted to a certain extent; and then, the enzymatic Chinese chestnut starch is modified by utilizing phosphate groups, the phosphate groups not only have excellent cation adsorption capacity, but also have the advantages that the self-hydrophilic performance promotes the improvement of the light transmittance of the starch, the larger steric hindrance can weaken the binding force among starch molecules, the gaps among the starch molecules are enlarged, the transparency is further improved, and the finally prepared porous phosphate starch has the characteristics of high substitution degree and high transparency and has outstanding flocculation performance.

Preferably, the temperature in the emulsification and stirring process in S1 is 55-60 ℃, and the time is 30-40 min; the temperature of the emulsification and stirring process in the S2 is 50-55 ℃, and the time is 40-45 min.

Preferably, the pH of the disodium hydrogen phosphate-citric acid solution in the S1 is 5.0-5.6, the mass concentration of starch in the starch emulsion is 20% -25%, the composite amylase is a mixture of alpha-amylase and saccharifying enzyme DE, and the mass ratio is 1:1-1.2, and the dosage of the compound amylase is 1248u-1560u/g of Chinese chestnut starch.

The starch solution with the mass concentration of 20-25% is helpful for the dispersion of the composite amylase and the sufficient contact with the starch. Saccharifying enzyme DE in the composite amylase belongs to exonucleases, alpha-1, 4 and alpha-1, 6 glycosidic bonds can be cut randomly, irregular parts on the surfaces of starch granules and amorphous areas easy to hydrolyze are subjected to enzymolysis, and sunken pores appear on the surfaces of the starch granules; alpha-amylase belongs to incision enzyme, can randomly hydrolyze alpha-1, 4 glycosidic bonds, provides a new non-reducing end for saccharifying enzyme to further hydrolyze starch, and is synergistic with other enzymes, so that hydrolysis is gradually promoted to the interior of starch, and finally a hollow structure is formed in the starch, namely a porous structure of the starch. The optimized compound amylase proportion and enzymolysis conditions are combined, the using amount of the compound amylase is reduced, the enzymolysis reaction is controlled within 9 hours, and the enzymolysis efficiency is accelerated.

Preferably, the enzymolysis temperature of the chestnut starch in S1 is 55-62 ℃, the enzymolysis time is 7-9h, after the enzymolysis is finished, absolute ethyl alcohol is added into the reaction solution for enzyme deactivation, and the porous chestnut starch is obtained after centrifugal washing and drying until the water content of the starch is 3% -5%.

The absolute ethyl alcohol has lower destructiveness to the structure of the porous Chinese chestnut starch, is beneficial to protecting the integrity of the porous Chinese chestnut starch granules, and has certain promotion effect for improving the substitution degree, the transparency and the flocculation performance of the porous phosphate Chinese chestnut starch product.

Preferably, the phosphate solution in the S2 is orthophosphate solution with the mass concentration of 45-55%, NaOH and phosphoric acid solution are used for adjusting the pH of the reaction solution to 5.6-6.0 in the esterification reaction process, and the mass ratio of the porous Chinese chestnut starch to the phosphate radical in the mixed modified solution is 1: 1.8-2.

The optimized phosphate group is easier to perform substitution reaction with hydroxyl in the porous Chinese chestnut starch, and the optimized pH value of the solution and the raw material ratio are combined, so that the phosphate esterification modification process of the porous Chinese chestnut starch is smoother, and the quality of a reaction product is better.

Preferably, the esterification reaction in S2 is carried out in a normal pressure environment at 140-150 ℃ for 150 min.

Under the temperature of 140-150 ℃, the reaction rate is high even under the normal pressure condition, the reaction can be completed within the time of 140-150min, the reaction process is more stable, the efficiency is higher, and the substitution degree of the product is higher.

Preferably, the detergent for washing to remove unreacted phosphate in S2 is 50% ethanol solution, and the time for freeze-drying the product after washing is 14-20 h.

Further, the invention also provides porous phosphate chestnut starch prepared by the method.

Further, the invention also provides application of the porous phosphate chestnut starch in preparation of a polymeric flocculant.

Drawings

FIG. 1 is an infrared spectrum of chestnut starch and porous phosphate chestnut starch in example 1 of the present invention;

FIG. 2 is an X-ray diffraction pattern of chestnut starch, porous chestnut starch and porous phosphate chestnut starch according to example 1 of the present invention;

FIG. 3 is a scanning electron microscope image of chestnut starch in example 1 of the present invention;

FIG. 4 is a scanning electron microscope image of the starch of the porous chestnut in example 1 of the present invention;

FIG. 5 is a scanning electron microscope image of a chestnut starch of porous phosphate in example 1 of the present invention;

FIG. 6 is a standard graph showing the phosphorus content obtained in the test examples of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The starch is a green and environment-friendly natural polymer material, is renewable and degradable, and is an excellent flocculant in the field of wastewater treatment, the Chinese chestnut starch is one of the starches, the content of the starch in the Chinese chestnut can reach 40% -60% of the dry weight of the Chinese chestnut, the preparation of the waste water flocculant from the starch in the waste Chinese chestnut is a limited measure for avoiding the accumulation of the waste Chinese chestnut and protecting the environment, but due to the defects of low transparency and poor flocculation capability of the Chinese chestnut starch, the flocculant taking the natural Chinese chestnut starch as a main raw material has poor treatment capability on the wastewater, and the application value of the Chinese chestnut starch in industrial production is seriously reduced.

In order to improve the transparency and flocculation capacity of the Chinese chestnut starch, improve the application value of the Chinese chestnut starch in wastewater treatment, provide a new choice for raw materials of a natural polymeric flocculant and realize high-value recovery of waste Chinese chestnuts, the application provides a preparation method of the porous phosphate Chinese chestnut starch, which specifically comprises the following steps:

s1: uniformly mixing the Chinese chestnut starch and a disodium hydrogen phosphate-citric acid buffer solution, emulsifying and stirring to obtain a starch emulsion, slowly adding a compound amylase into the obtained starch emulsion, and performing enzymolysis on the Chinese chestnut starch to obtain porous Chinese chestnut starch;

s2: and uniformly mixing the obtained porous chestnut starch with a phosphate solution, emulsifying, stirring, centrifugally drying until the water content is 5-10%, performing esterification reaction, washing to remove unreacted phosphate, and drying the obtained product to obtain the porous phosphate chestnut starch.

According to the preparation method of the porous phosphate chestnut starch, the chestnut starch is subjected to enzymolysis by using amylase, and the amylase acts on irregular parts and amorphous areas on the surface of the starch to destroy hydrogen bonds of a dimensional space spiral structure in starch molecule particles, so that the starch forms a porous structure with a concave surface; on one hand, the porous structure can enable water molecules to enter the starch granules more easily, and reduce the forming difficulty of a uniform hydration system of starch paste, thereby improving the light transmittance and flocculation performance of the starch; on the other hand, the crystalline region and the amorphous region of the starch can be exposed, so that hydroxyl in the starch is fully contacted with phosphate groups, and the substitution degree of the phosphate groups in starch molecules reaches more than 0.2, thereby improving the cation adsorption capacity of the Chinese chestnut starch and ensuring that the Chinese chestnut starch has outstanding flocculation performance; on the other hand, the hydrophilicity of the phosphate group has a certain promotion effect on the improvement of the light transmittance of the starch, the larger steric hindrance of the phosphate group can weaken the binding force among starch molecules, increase the gaps among the starch molecules and further improve the transparency.

The pore-forming uniformity and the particle integrity of the porous Chinese chestnut starch are necessary conditions for improving the substitution degree of phosphate modified Chinese chestnut starch, improving the transparency and improving the flocculation performance of the phosphate modified Chinese chestnut starch, and the inventor researches the concentration of a starch solution, the components, the proportion and the dosage of a composite amylase, and finds that the optimal enzymolysis effect can be achieved by adopting the starch solution with the mass concentration of 20-25 percent to react with the composite amylase consisting of alpha-amylase and glucoamylase DE with the mass ratio of 1:1-1.2 under the condition that the total enzyme dosage is 1248u-1560u/(g of Chinese chestnut starch): the reaction time is shorter, the pore forming rate and the pore forming quality are higher, and the starch granules are more complete.

The post-treatment process after the enzymolysis reaction also protects the structure of the porous starch granules, avoids damaging the porous starch granules and influences subsequent esterification modification, and therefore, the anhydrous ethanol is adopted to inactivate the composite amylase after the enzymolysis reaction.

The raw materials and the proportion of phosphate groups for modifying the porous Chinese chestnut starch are the precondition for ensuring the substitution degree, the transparency and the flocculation performance of the porous phosphate Chinese chestnut starch, the inventor researches that the solution for providing the phosphate groups adopts orthophosphate solution with the mass concentration of 45-55 percent, sodium hydroxide solution or phosphoric acid solution is used for adjusting the pH of reaction liquid to be 5.6-6.0 in the esterification reaction process, and the mass ratio of the effective phosphate groups before modification to the porous Chinese chestnut starch is 1.8-2: 1.

the process control of the phosphate group to the modification of the porous chestnut starch is a key factor for determining the substitution degree, the transparency and the flocculation performance of the porous phosphate chestnut starch, and through the research of the inventor, the phosphate group is suitable for the modification process of the porous chestnut starch at the normal pressure of 140-150 ℃, the reaction time is 140-150min, the reaction is more stable, the efficiency is higher, and the substitution degree of the product is higher.

Further, in order to ensure the purity of the porous phosphate chestnut starch, after the reaction is finished, unreacted phosphate is washed and removed by adopting a 50% ethanol solution, and the obtained product is freeze-dried for 14 hours to obtain the porous phosphate chestnut starch.

The present invention will be further illustrated by the following examples, wherein the chestnut starch material used in the following examples has a moisture content of 5-10% and a particle size of 100 mesh or less.

Example 1

The embodiment provides a porous phosphate chestnut starch, and the preparation method of the porous phosphate chestnut starch comprises the following steps:

s1: uniformly mixing Chinese chestnut starch and disodium hydrogen phosphate-citric acid buffer solution with the pH value of 5.6, magnetically stirring for 30min at 55 ℃ to prepare starch emulsion with the starch content of 20%, slowly adding compound amylase consisting of alpha-amylase and glucoamylase DE in a mass ratio of 1:1 into the starch emulsion to carry out enzymolysis on the starch, wherein the using amount of the compound amylase is 1248u/(g of Chinese chestnut starch), carrying out enzymolysis reaction for 9h at 60 ℃, adding 95% ethanol solution which is 3 times of the volume of the starch emulsion into reaction liquid after the reaction is finished to inactivate the enzyme, centrifuging, washing and drying until the water content of a dry starch base is 3% -5%, thus obtaining porous Chinese chestnut starch;

s2: taking the mass ratio of 0.9: NaH of 12PO4·2H2O and Na2HPO4·12H2O, adding water, heating and dissolving under the condition of ultrasonic waves to prepare a phosphate solution with the mass fraction of 50%, uniformly mixing the porous Chinese chestnut starch obtained in the step S1 with a phosphate solution (the mass ratio of the porous Chinese chestnut starch to phosphate radicals in the phosphate solution is 1:2) to prepare a modified solution with the starch milk concentration of 20%, magnetically stirring for 40min at the temperature of 50 ℃, centrifugally treating and freeze-drying after uniformly mixing until the moisture content of the porous starch is 5%, carrying out esterification reaction for 150min in a drying oven at the temperature of 150 ℃, adjusting the pH of the reaction solution to be 5.6-6.0 by using phosphoric acid and sodium hydroxide, washing by using an ethanol solution with the volume of 50% which is 3 times of the volume of the porous Chinese chestnut starch after the reaction is finished, removing unreacted phosphate, centrifuging and freeze-drying for 14h to obtain the porous phosphate Chinese chestnut starch.

Example 2

The embodiment provides a porous phosphate chestnut starch, and the preparation method of the porous phosphate chestnut starch comprises the following steps:

s1: uniformly mixing Chinese chestnut starch and disodium hydrogen phosphate-citric acid buffer solution with the pH value of 5.3, magnetically stirring for 35min at 57 ℃ to prepare starch emulsion with the starch content of 23%, slowly adding composite amylase consisting of alpha-amylase and glucoamylase DE in a mass ratio of 1:1.1 into the starch emulsion to carry out enzymolysis on the starch, wherein the using amount of the composite amylase is 1400u/(g of Chinese chestnut starch), carrying out enzymolysis reaction for 7.5h at 58 ℃, adding 95% ethanol solution which is 3 times of the volume of the starch emulsion into reaction liquid after the reaction is finished to inactivate the enzyme, centrifuging, washing and drying until the water content of a dry starch base is 3% -5%, so as to obtain porous Chinese chestnut starch;

s2: taking the mass ratio of 0.9: NaH of 12PO4·2H2O and Na2HPO4·12H2O, adding water, heating and dissolving under the condition of ultrasonic waves to prepare a phosphate solution with the mass fraction of 45%, uniformly mixing the porous Chinese chestnut starch obtained in the step S1 with the phosphate solution (the mass ratio of the porous Chinese chestnut starch to phosphate radicals in the phosphate solution is 1:1.8), preparing a modified solution with the starch milk concentration of 20%, magnetically stirring for 40min at the temperature of 55 ℃, centrifugally treating and freeze-drying after uniformly mixing until the moisture content of the porous starch is 5%, carrying out esterification reaction for 150min in a drying oven at the temperature of 150 ℃, adjusting the pH of the reaction solution to be 5.6-6.0 by using phosphoric acid and sodium hydroxide during the reaction process, washing by using an ethanol solution with the volume of 50% which is 3 times of that of the porous Chinese chestnut starch after the reaction is finished, removing unreacted phosphate, centrifuging and freeze-drying for 14h to obtain the porous phosphate Chinese chestnut starch.

Example 3

The embodiment provides a porous phosphate chestnut starch, and the preparation method of the porous phosphate chestnut starch comprises the following steps:

s1: uniformly mixing Chinese chestnut starch and disodium hydrogen phosphate-citric acid buffer solution with the pH value of 5.5, magnetically stirring for 30min at 60 ℃ to prepare starch emulsion with the starch content of 25%, slowly adding composite amylase consisting of alpha-amylase and glucoamylase DE in a mass ratio of 1:1.1 into the starch emulsion to carry out enzymolysis on the starch, wherein the using amount of the composite amylase is 1390u/(g of Chinese chestnut starch), carrying out enzymolysis reaction for 9h at 55 ℃, adding 95% ethanol solution which is 3 times of the volume of the starch emulsion into reaction liquid after the reaction is finished to inactivate the enzyme, centrifuging, washing and drying until the water content of a dry starch base is 3% -5%, thus obtaining porous Chinese chestnut starch;

s2: taking the mass ratio of 0.9: NaH of 12PO4·2H2O and Na2HPO4·12H2O, adding water, heating and dissolving under the condition of ultrasonic waves to prepare a phosphate solution with the mass fraction of 45%, uniformly mixing the porous Chinese chestnut starch obtained in the step S1 with a phosphate solution (the mass ratio of the porous Chinese chestnut starch to phosphate radicals in the phosphate solution is 1:2) to prepare a modified solution with the starch milk concentration of 20%, magnetically stirring for 45min at the temperature of 53 ℃, centrifugally treating and freeze-drying after uniformly mixing until the moisture content of the porous starch is 5%, carrying out esterification reaction for 150min in a drying oven at the temperature of 148 ℃, adjusting the pH of the reaction solution to 5.6-6.0 by using phosphoric acid and sodium hydroxide during the esterification reaction, washing by using an ethanol solution with the volume of 50% which is 3 times of the volume of the porous Chinese chestnut starch after the reaction is finished, removing unreacted phosphate, centrifuging and freeze-drying for 15h to obtain the porous phosphate Chinese chestnut starch.

To better illustrate the characteristics of the porous phosphate chestnut starch prepared by the method for preparing porous phosphate chestnut starch according to the embodiment of the present invention, infrared spectroscopy analysis, X-ray diffraction analysis and scanning electron microscope analysis were performed on the porous phosphate chestnut starch and the raw chestnut starch prepared in example 1.

The results of the infrared spectroscopic analysis are shown in FIG. 1, and the infrared spectroscopic curve of the chestnut starch with porous phosphate is 859.44cm-1A new diffraction absorption peak appears nearby, and the peak is P-O-C symmetric expansion and contraction; at 3413cm-1At OH group-The absorption peak of (a) is decreased, indicating that the hydroxyl group in the starch reacts with the phosphate group, so that the number of hydroxyl groups is decreased.

The result of the X-ray diffraction analysis is shown in figure 2, compared with the X-ray diffraction curve of the original Chinese chestnut starch, the X-ray diffraction curve of the porous Chinese chestnut starch has the advantages that the diffraction peak at 15.4 degrees disappears, the diffraction peak at 17.04 degrees weakens, the condition that part of crystalline regions are damaged by the enzymolysis reaction of the composite amylase is shown, the diffraction peak at 22.90 degrees widens, the proportion of the crystalline regions is increased, the condition that the amorphous regions are damaged by the enzymolysis reaction is shown, and the damage degree to the crystalline regions is limited; compared with the X-ray diffraction curve of the porous Chinese chestnut starch, the X-ray diffraction curve of the phosphate porous Chinese chestnut starch has a small diffraction peak at 23 degrees and has new diffraction peaks at 31.28 degrees, 31.48 degrees and 32.86 degrees, which indicates that a new crystallization area appears under the action of phosphate groups. The X-ray diffraction analysis result shows that the original crystal form of the starch is destroyed, the porous structure increases the area of phosphate reaction, the crystalline region and the amorphous region are exposed due to the porous structure, hydroxyl in the original starch is replaced by phosphate, the structure of the starch hydrogen bond is destroyed, the steric hindrance of the group is large, the acting force of the starch intermolecular hydrogen bond is greatly weakened, the stable double-helix structure of the starch is destroyed, and the amorphous region is formed.

The results of SEM analysis are shown in FIGS. 3-5, in which FIG. 3 is SEM analysis of raw chestnut starch, FIG. 4 is SEM analysis of porous chestnut starch, and FIG. 5 is SEM analysis of porous chestnut starch. Comparing fig. 3-5, it can be known that the raw chestnut starch has smooth surface, no edges and corners, and no cracks; the shapes are complex and various, and are mostly oval, triangular and pear-shaped; the surface of the porous Chinese chestnut starch obtained after enzymolysis treatment is sunken and has obvious holes, and the specific surface area is obviously increased compared with the original Chinese chestnut starch; the starch granules of the porous phosphate chestnut starch have the adhesion phenomenon, and the surface of the granules has depressions, damages and fractures because the starch granules have unique laminated structures, wherein the inner layer is mainly a non-crystalline region with relatively loose structure, and the outer layer is a crystalline region with compact structure. During the esterification process, the binding force of interlayer particles of the starch laminated structure is weakened, an amorphous region is damaged, and lattice defects are generated, so that the crystallinity is reduced. Meanwhile, the surface layer of the starch granules is also subjected to a certain rotting candle effect, so that the starch granules are adhered and are not independent granules, and the phosphate groups are further proved to be introduced into the starch molecules from the side surface.

In order to better illustrate the technical solution of the present invention, further comparison is made below by means of a comparative example and an example of the present invention.

Comparative example 1

This comparative example provides a porous phosphate corn starch prepared in a manner consistent with example 3, except that the chestnut starch used was replaced with an equal amount of corn starch, and the remaining preparation and processing parameters were consistent with example 3.

Comparative example 2

Compared with the preparation method of example 3, the preparation method of the porous phosphate chestnut starch comprises the following specific reaction parameters except for S1:

mixing Chinese chestnut starch and disodium hydrogen phosphate-citric acid buffer solution with the pH value of 5.5 uniformly, magnetically stirring for 30min at 60 ℃ to prepare starch emulsion with the starch content of 25%, slowly adding composite amylase consisting of alpha-amylase and glucoamylase DE in a mass ratio of 1:1 into the starch emulsion to carry out enzymolysis on the starch, wherein the using amount of the composite amylase is 800u/(g of Chinese chestnut starch), carrying out enzymolysis reaction for 6h at 55 ℃, adding 95% ethanol solution which is 3 times of the volume of the starch emulsion into reaction liquid after the reaction is finished to inactivate the enzyme, centrifuging, washing and drying until the water content of a dry starch base is 3% -5%, thus obtaining the porous Chinese chestnut starch. The remaining preparation and process parameters were in accordance with example 3.

Comparative example 3

Compared with the preparation method of example 3, the preparation method of the porous phosphate chestnut starch comprises the following specific reaction parameters except for S2: taking the mass ratio of 0.9: NaH of 12PO4·2H2O and Na2HPO4·12H2And O, adding water to dissolve the mixture into a phosphate solution with the mass fraction of 45%, uniformly mixing the porous Chinese chestnut starch obtained in the S1 with a phosphate solution (the mass ratio of the porous Chinese chestnut starch to phosphate radicals in the phosphate solution is 1:2.5) to prepare a modified solution with the starch milk concentration of 20%, magnetically stirring for 45min at the temperature of 53 ℃, after uniform mixing, centrifugally treating, freeze-drying until the moisture content of the porous starch is 5%, performing esterification reaction for 150min in an oven at the temperature of 155 ℃, adjusting the pH of the phosphate solution to 5.6 by using phosphoric acid and a sodium hydroxide solution in the reaction process, washing with an ethanol solution with the volume of 50% which is 3 times of that of the porous Chinese chestnut starch after the reaction is finished, removing unreacted phosphate, centrifuging, and freeze-drying for 14h to obtain the porous phosphate Chinese chestnut starch. The rest(s)The preparation and process parameters remained the same as in example 3.

Comparative example 4

This comparative example provides a phosphate chestnut starch, which was prepared by a method that does not include step S1, as compared to example 3, i.e., a conventional chestnut starch was directly used for an esterification reaction with a phosphate solution, and the remaining preparation method and process parameters were kept consistent with example 3.

Example of detection

The porous phosphate starch obtained in example 3 and comparative examples 1 to 4 is taken, and the reference numbers of sample 1, sample 2, sample 3, sample 4 and sample 5 are sequentially carried out, and the following schemes are adopted to respectively test the performances of the 5 samples:

measurement of degree of Mono-and substitution

(1) Drawing a phosphorus standard curve: accurately weighing 0.5g of anhydrous potassium dihydrogen phosphate, dissolving in water, accurately diluting to 100mL, taking 10mL of the solution, accurately diluting to 100mL with distilled water, taking 10mL of the solution, and accurately diluting to 100mL with distilled water to obtain a standard phosphorus solution with the phosphorus content of 10 mu g/mL.

Accurately sucking 0, 2, 3, 4, 5 and 6mL of the standard phosphorus solution, respectively placing the standard phosphorus solution into a 50mL volumetric flask, sequentially adding 10mL of 26% sulfuric acid solution, 5mL of 2% ammonium molybdate solution and 2mL of 5% ascorbic acid solution, uniformly mixing, heating in a boiling water bath for 10min, rapidly cooling to fix the volume, measuring the absorbance at 825nm, and drawing a standard curve of the phosphorus content by using the obtained data, wherein as shown in FIG. 6, the linear equation of the standard curve of the phosphorus content is as follows: 0.00922x-0.124, R2=0.9993

(2) Determination of total phosphorus in the sample: accurately weighing 1.0g of sample, placing into a 50ml Kai's bottle, adding 15ml of H2SO4-HNO3Digesting the mixed solution until the liquid is clear, adding 10mL of water for dilution, cooling, transferring the mixed solution to a 100mL volumetric flask for constant volume, accurately measuring 1mL of the mixed solution, putting the measured solution into a 50mL volumetric flask, adding 10mL of water for uniformly mixing, sequentially adding 10mL of 26% sulfuric acid solution, 5mL of 2% ammonium molybdate solution and 2mL of 5% ascorbic acid solution, uniformly mixing, heating in a boiling water bath for 10min, rapidly cooling for constant volume, measuring the absorbance at 825nm for constant volumeAnd substituting the obtained absorbance value into a standard curve equation of the phosphorus content to calculate the total phosphorus content in the sample.

(3) And (3) measuring free phosphorus in the sample, accurately weighing 2.0g of the sample, putting the sample into a 50ml beaker, dissolving the sample by using 1mol/l of dilute hydrochloric acid, washing all the samples into a 250ml volumetric flask by using distilled water, fully shaking up, fixing the volume, filtering, taking 10ml of filtrate into the 50ml volumetric flask, carrying out color reaction, measuring absorbance, and calculating the content of the free phosphorus in the sample according to a standard curve of the measured value of the absorbance and the content of the phosphorus.

(4) Calculating the degree of substitution of each sample using a degree of substitution formula, wherein: bound phosphorus being total phosphorus-free phosphorus

Mass fraction of P-free phosphorus in the formula; DS-degree of substitution for samples, the degree of substitution for each sample is shown in Table 1:

second, determination of transparency

Preparing a sample into a starch emulsion with the mass fraction of 1%, heating and stirring the starch emulsion in a boiling water bath for 35min, keeping the original volume to obtain a corresponding starch paste liquid, cooling the starch paste liquid to room temperature, measuring the light transmittance of the starch paste liquid by using a 1cm cuvette under the wavelength of 620nm, taking distilled water as a blank control experiment, wherein the light transmittance of each sample is shown in table 1:

thirdly, testing flocculation performance

The results are shown in table 1, in which a 50mg/L lead nitrate solution prepared in a laboratory was taken, the pH was adjusted to 5 with 1mol/L concentrated nitric acid, 0.04g of a sample was added to 100ml of the lead nitrate solution having a pH of 5, the mixture was stirred at 25 ℃ for 1 hour, and the amount of lead ions adsorbed by the sample was calculated from the change in the concentration of lead ions. The calculation method of the adsorption quantity comprises the following steps:

calculation of the amount of adsorption q (mg/g):

in the formula, C0The initial concentration (mg/L) of the lead ion solution; c is the concentration (mg/L) of the lead ion solution after 1h of adsorption; v is the solution volume (L); w is the sample mass (g).

TABLE 1

From the data in table 1, it can be seen that: the degree of substitution of the porous phosphate chestnut starch provided by the embodiment of the invention is more than 0.2, the transmittance of the chestnut starch is higher than that of the original starch after the chestnut starch is subjected to porous esterification modification, the transmittance of the porous phosphate chestnut starch prepared by the method is higher than that of the porous corn starch, the adsorption capacity of the porous phosphate chestnut starch on heavy metal ions is stronger, the porous phosphate chestnut starch is pollution-free to the environment, and the porous phosphate chestnut starch can be used as a natural polymeric flocculant to treat industrial wastewater.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.

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