Method for preparing oxidized starch by accurately controlling oxidation of starch particles

Abstract

The invention discloses a method for preparing oxidized starch by accurately controlling oxidation of starch granules, which comprises the following steps: firstly, pre-oxidizing a starch suspension with ozone gas, and then, carrying out pulsed electric field and ozone treatment, so that dissolved ozone molecules are promoted to be decomposed and converted into more active oxygen free radicals with higher oxidation efficiency; further, the advanced oxidation process of the ozone-oxidized starch is realized, so that the production efficiency of the ozone-oxidized starch is improved; meanwhile, the free radical strengthening process is quantificationally controllable by regulating and controlling parameters of the pulsed electric field, free radicals are uniformly oxidized on the surface layers of charged particles under the induction of polarization of the electric field, the oxidation depth of the particles is improved, and the integrity of the starch particle structure is kept on the basis of ensuring that the oxidation degree of starch is improved; and thus, the oxidation effect is accurately controlled. The obtained product can be used as a high-concentration and low-viscosity thickener and binder to be applied to the fields of food, building, papermaking, textile and the like.

Description

Technical field:

[0001] The present invention relates to the technical field of starch modification, and in particular to a method for preparing oxidized starch by precisely controlling the oxidation of starch granules. Background technology:

[0002] Modified starch is a natural starch that has its properties changed by physical, chemical and enzymatic means. Oxidation is one of the common chemical methods used to modify the properties of natural starch. At the same time, oxidized starch is one of the modified starches with the largest production volume and the widest application range. It can be used in many fields such as food, construction, papermaking, textiles, etc. At present, the most commonly used oxidant in the industrial production of oxidized starch is alkaline sodium hypochlorite. Although it has mature process research and production practice, it will produce wastewater with high salt content, high COD and high treatment costs, which limits its production cost; hydrogen peroxide, as another excellent oxidant, faces problems such as insufficient oxidation stability, insufficient oxidation degree, the need to add catalysts and their residues; other oxidants such as potassium permanganate, chlorine dioxide, ammonium sulfate and other chemical reagents have problems such as complex processes, high wastewater treatment costs, and environmental pollution.

[0003] Ozone is a substance with very active reaction activity, with a high standard redox potential (2.07V). It can directly attack organic matter through electrophilic reaction, and can also decompose in water to produce active oxygen free radicals with hydroxyl free radicals (·OH) as the main body, and attack organic matter more efficiently through indirect free radical reaction. Under normal temperature and pressure, the half-life of ozone decomposition in water is only 5 to 10 minutes, and it is easier to decompose under heating conditions, so there is no problem of residual oxidant. Chinese invention patent CN110183540A discloses a method for preparing modified starch by ozone oxidation. However, the above-mentioned prior art has certain limitations: although the process of single ozone gas oxidation is simple and pollution-free, it is obviously inferior to liquid phase ozone mass transfer in terms of ozone gas mass transfer oxidation efficiency, and it is impossible to achieve ozone advanced oxidation, starch oxidation efficiency is low, and starch is insoluble in water and easy to agglomerate, making oxidation uneven; it is urgent to further solve the problems of low oxidation efficiency, uneven oxidation, and unsuitability for food-grade industrial applications. Summary of the invention:

[0004] The purpose of the present invention is to provide a method for preparing oxidized starch by accurately controlling the oxidation of starch granules, which solves the problems of low ozone oxidation efficiency and uneven oxidation in the prior art.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing oxidized starch by precisely controlling the oxidation of starch granules, the method comprising the following steps:

[0007] (1) Pre-oxidation of starch suspension: Prepare a starch suspension with a mass fraction of 5-30%, place it in a jacketed reactor, stir it evenly, and keep its temperature at 5°C through cooling circulating water. Then introduce ozone gas into the starch suspension, with an ozone concentration of 40-105 mg / L, preferably 90-105 mg / L, and a gas flow rate of 1-4 L / min, preferably 1-2 mL / min. The pre-oxidation process lasts for 10 min to accumulate a certain concentration of dissolved ozone in the suspension;

[0008] (2) Pulse electric field assisted treatment: Feed the pre-oxidized starch suspension obtained in step (1) into the pulse electric field treatment chamber through a constant-speed peristaltic pump; during the reaction, continuously introduce ozone gas into the starch suspension in the reactor, and at the same time start the pulse electric field for assisted treatment; the specific conditions for pulse electric field treatment are: electric field strength 2-10 kV / cm, preferably 4-8 kV / cm, frequency 25-200 Hz, preferably 50-100 Hz, pulse width 5-10 μs, and the assisted treatment time is 10-30 min;

[0009] (3) Drying and degassing: Filter the starch suspension after pulse electric field assisted treatment in step (2), wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a blast drying oven at 50°C for 12 h, and then degas and dry it in a vacuum drying oven at 50°C for 24 h to obtain the final product.

[0010] Preferably, in step (2), the constant-speed peristaltic pump makes the starch suspension pass through the pulse electric field at a constant flow rate of 400 mL / min.

[0011] The beneficial effects of the present invention are as follows:

[0012] 1) The present invention first pre-oxidizes the starch suspension with ozone gas, and then combines the pulse electric field with ozone treatment. By strengthening the free radical chain reaction process, it promotes the decomposition of dissolved ozone molecules and converts them into more active oxygen free radicals with stronger oxidation efficiency, thereby realizing the advanced oxidation process of ozone oxidation of starch. This is beneficial for further oxidation of carbonyl groups (aldehyde groups, ketone groups) in the oxidized starch product to carboxyl groups, increasing the carboxyl group content, the proportion of carboxyl group content, and the overall oxidation degree (carboxyl group content + carbonyl group content). The carboxyl group content and the starch solubility are improved, thus improving the production efficiency of ozone oxidized starch.

[0013] 2) The present invention can also polarize starch molecules through the polarization effect of the electric field to endow the surface layer of starch particles with polarized charges, activate the reaction sites, and accelerate the oxidation reaction of active oxygen hydroxyl free radicals at these activated sites. Thus, it realizes the directional attack of active oxygen on the activated reaction sites and induces the uniform attack of oxidants on the starch surface layer, significantly increasing the oxidation uniformity on the particle surface.

[0014] 3) By controlling the electric field strength at 2-10 kV / cm, the frequency at 25-200 Hz, and the pulse width at 5-10 μs, the present invention aids in removing starch channel proteins, thereby opening starch pores, increasing the particle oxidation depth by approximately 56%, and having a synergistic treatment duration of 30 min. On the basis of ensuring an increase in starch oxidation degree, the integrity of the starch granule structure is maintained.

[0015] 4) The present invention is simple, efficient, operationally controllable, free of additional additives, green, and energy-saving. It provides innovative technical guidance for ozone-oxidized starch production, and at the same time expands the practical application of pulsed electric fields in the synergistic treatment of the modified starch field. The obtained products can be used as thickeners and binders with high concentration and low viscosity in many fields such as food, construction, papermaking, and textiles.

[0016] In summary, the present invention first pre-oxidizes a starch suspension with ozone gas, and then performs pulsed electric field-assisted ozone treatment, which not only promotes the decomposition of dissolved ozone molecules and converts them into more active oxygen free radicals with stronger oxidation efficiency, thereby realizing the advanced oxidation process of ozone-oxidized starch, and improving the production efficiency of ozone-oxidized starch; at the same time, by regulating the pulsed electric field parameters, the enhanced free radical process can be quantitatively controlled, and under the induction of the electric field polarization effect, the free radicals are uniformly oxidized on the surface layer of charged particles, and at the same time the particle oxidation depth increases. On the basis of ensuring an increase in starch oxidation degree, the integrity of the starch granule structure is maintained, thereby realizing the precise control of the oxidation effect. The obtained products can be used as thickeners and binders with high concentration and low viscosity in many fields such as food, construction, papermaking, and textiles. Description of the Drawings:

[0017] Figure 1 Shows the influence of pulsed electric field-assisted ozone on the total oxidation degree of oxidized starch at different field strengths (2-15 kV / cm) and different frequencies (25-300 Hz). Among them, (A) shows the influence of pulsed electric field-assisted ozone on the total oxidation degree of oxidized starch at different field strengths (2-15 kV / cm), and (B) shows the influence of pulsed electric field-assisted ozone on the total oxidation degree of oxidized starch at different frequencies (25-300 Hz).

[0018] Figure 2 In (A), the secondary integral map obtained by using DMPO to capture the hydroxyl free radicals generated in the examples and comparative examples after 30 s of treatment and measured and calculated by an electron paramagnetic resonance spectrometer (EPR) is shown, and the integral value can relatively reflect the content of the captured hydroxyl free radicals. Figure 2 In (B), a comparison graph of the ozone concentration of each example and comparative example at the end of the reaction under different electric field parameters and treatment conditions is shown.

[0019] Figure 32D planar (first row) / 3D stereoscopic (second row) laser confocal images and laser intensity distribution maps of particles (third row) of Examples 1-3 and Comparative Examples 1, 3, and 4 after staining with APTS (sodium 8-aminopyrene-1,3,6-trisulfonate) dye can reflect the degree of oxidative modification of starch granules, including the uniformity, depth, and intensity of granule oxidation.

[0020] Figure 4 For the two-dimensional signal intensity map at 1400 cm -1 collected by a Raman spectrometer for Examples 1-3 and Comparative Examples 1, 3, and 4, which reflects the carboxylate signal intensity within a 6×6 μm range on the surface of oxidized starch granules, can illustrate the uniformity and intensity of granule oxidation. Specific implementation method:

[0021] The following is a further description of the present invention, rather than a limitation to the present invention.

[0022] Example 1

[0023] The specific steps of this example are as follows:

[0024] (1) Pre-oxidation of starch suspension: Place 400 mL of a starch suspension with a mass fraction of 10% (w / w) in a jacketed reactor. After cooling to 5 °C, introduce ozone gas with a concentration of 105 mg / L into the starch suspension. Set the gas flow rate to 1 L / min and the duration to 10 min.

[0025] (2) Synergistic treatment with pulsed electric field: Feed the pre-oxidized starch suspension obtained in step (1) into the pulsed electric field treatment chamber through a constant-speed peristaltic pump. During the reaction, continuously introduce ozone gas into the starch suspension in the reactor, and at the same time start the pulsed electric field for synergistic treatment. The pulsed electric field treatment conditions are: electric field strength 2 kV / cm, frequency 100 Hz, pulse width 10 μs, and synergistic treatment time 30 min.

[0026] (3) Drying and degassing: Filter the starch suspension after synergistic treatment, wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a blast drying oven at 50 °C for 12 h, and then degas and dry it in a vacuum drying oven at 50 °C for 24 h to obtain the final product.

[0027] Example 2

[0028] Referring to Example 1, the difference lies in that the pulsed electric field strength in step (2) is 8 kV / cm.

[0029] The specific steps of this example are as follows:

[0030] (1) Pre-oxidation of starch suspension: Place 400 mL of a 10% (w / w) starch suspension in a jacketed reactor. After cooling to 5 °C, introduce ozone gas with a concentration of 105 mg / L into the starch suspension. Set the gas flow rate at 1 L / min and the duration at 10 min.

[0031] (2) Synergistic treatment with pulsed electric field: Feed the pre-oxidized starch suspension obtained in step (1) into the pulsed electric field treatment chamber through a constant-speed peristaltic pump. During the reaction, continue to introduce ozone gas into the starch suspension in the reactor, and at the same time, start the pulsed electric field for synergistic treatment. The pulsed electric field treatment conditions are: electric field strength 8 kV / cm, frequency 100 Hz, pulse width 10 μs, and synergistic treatment time 30 min.

[0032] (3) Drying and degassing: Filter the starch suspension after synergistic treatment by suction filtration. Wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a blast drying oven at 50 °C for 12 h, and then degas and dry it in a vacuum drying oven at 50 °C for 24 h to obtain the final product. The test results are shown in Table 1 below.

[0033] Example 3

[0034] Refer to Example 1, the difference is that the pulsed electric field strength in step (2) is 10 kV / cm.

[0035] The specific steps of this example are as follows:

[0036] (1) Pre-oxidation of starch suspension: Place 400 mL of a 10% (w / w) starch suspension in a jacketed reactor. After cooling to 5 °C, introduce ozone gas with a concentration of 105 mg / L into the starch suspension. Set the gas flow rate at 1 L / min and the duration at 10 min.

[0037] (2) Synergistic treatment with pulsed electric field: Feed the pre-oxidized starch suspension obtained in step (1) into the pulsed electric field treatment chamber through a constant-speed peristaltic pump. During the reaction, continue to introduce ozone gas into the starch suspension in the reactor, and at the same time, start the pulsed electric field for synergistic treatment. The pulsed electric field treatment conditions are: electric field strength 10 kV / cm, frequency 100 Hz, pulse width 10 μs, and synergistic treatment time 30 min.

[0038] (3) Drying and degassing: Filter the starch suspension after synergistic treatment by suction filtration. Wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a blast drying oven at 50 °C for 12 h, and then degas and dry it in a vacuum drying oven at 50 °C for 24 h to obtain the final product. The test results are shown in Table 1 below.

[0039] Example 4

[0040] Referring to Example 2, the difference is that the pulsed electric field frequency is lower, which is 25 Hz.

[0041] The specific steps of this example are as follows:

[0042] (1) Pre-oxidation of starch suspension: Place 400 mL of a 10% (w / w) starch suspension in a jacketed reactor. After cooling to 5 °C, introduce ozone gas with a concentration of 105 mg / L into the starch suspension, set the gas flow rate to 1 L / min, and the duration to 10 min.

[0043] (2) Pulsed electric field co-treatment: Feed the pre-oxidized starch suspension obtained in step (1) into the pulsed electric field treatment chamber through a constant-speed peristaltic pump. During the reaction, continue to introduce ozone gas into the starch suspension in the reactor, and at the same time start the pulsed electric field for co-treatment. The pulsed electric field treatment conditions are: electric field strength 8 kV / cm, frequency 25 Hz, pulse width 10 μs, and co-treatment time 30 min.

[0044] (3) Drying and degassing: Filter the starch suspension after co-treatment by suction filtration, wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a blast drying oven at 50 °C for 12 h, and then degas and dry it in a vacuum oven at 50 °C for 24 h to obtain the final product. The test results are shown in Table 1 below.

[0045] Example 5

[0046] Referring to Example 2, the difference is that the pulsed electric field frequency is higher, which is 200 Hz.

[0047] The specific steps of this example are as follows:

[0048] (1) Pre-oxidation of starch suspension: Place 400 mL of a 10% (w / w) starch suspension in a jacketed reactor. After cooling to 5 °C, introduce ozone gas with a concentration of 105 mg / L into the starch suspension, set the gas flow rate to 1 L / min, and the duration to 10 min.

[0049] (2) Pulsed electric field co-treatment: Feed the pre-oxidized starch suspension obtained in step (1) into the pulsed electric field treatment chamber through a constant-speed peristaltic pump. During the reaction, continue to introduce ozone gas into the starch suspension in the reactor, and at the same time start the pulsed electric field for co-treatment. The pulsed electric field treatment conditions are: electric field strength 8 kV / cm, frequency 200 Hz, pulse width 10 μs, and co-treatment time 30 min.

[0050] (3) Drying and degassing: The starch suspension after co-treatment was filtered by suction, and the filter cake was washed twice with distilled water and ethanol respectively. Then the obtained filter cake was dispersed in a blast drying oven at 50 °C for 12 h, and then degassed and dried in a vacuum drying oven at 50 °C for 24 h to obtain the final product. The test results are shown in Table 1 below.

[0051] Examples 6 - 8:

[0052] Referring to Example 1, the difference is that the pulsed electric field intensities in step (2) are 4 kV / cm, 6 kV / cm, and 12 kV / cm respectively.

[0053] Examples 9 - 10:

[0054] Referring to Example 2, the difference is that the pulsed electric field frequencies in step (2) are 50 Hz and 300 Hz respectively.

[0055] Comparative Example 1:

[0056] Referring to Example 2, the difference is that in step (2), the pulsed electric field was not turned on and no pulsed electric field co-treatment was carried out. That is, the pulsed electric field intensity was 0 kV / cm and the pulsed electric field frequency was 0 Hz.

[0057] The specific steps of this comparative example are as follows:

[0058] (1) Oxidation of starch suspension: 400 mL of a starch suspension with a mass fraction of 10% (w / w) was placed in a jacketed reactor. After cooling to 5 °C, ozone gas with a concentration of 105 mg / L was introduced into the starch suspension. The gas flow rate was set at 1 L / min and the duration was 10 min. Subsequently, the starch suspension was pumped into the pulsed electric field treatment chamber at a constant speed of 400 mL / min by a peristaltic pump without pulsed electric field treatment and continued to be treated for 30 min.

[0059] (2) Drying and degassing: The starch suspension after co-treatment was filtered by suction, and the filter cake was washed twice with distilled water and ethanol respectively. Then the obtained filter cake was dispersed in a blast drying oven at 50 °C for 12 h, and then degassed and dried in a vacuum drying oven at 50 °C for 24 h to obtain the final product. The test results are shown in Table 1 below.

[0060] Comparative Example 2:

[0061] Referring to Example 2, the difference is that the sequence of steps (1) and (2) is different.

[0062] The specific steps of this comparative example are as follows:

[0063] (1) Pulse electric field pretreatment: Place 400 mL of a starch suspension with a mass fraction of 10% (w / w) in a jacketed reactor. After cooling to 5 °C, pump the starch suspension into the pulse electric field treatment chamber at a constant rate of 400 mL / min using a peristaltic pump. The pulse electric field treatment conditions are: electric field strength 8 kV / cm, frequency 100 Hz, pulse width 10 μs, and treatment time 30 min.

[0064] (2) Oxidation of the starch suspension: Turn off the pulse electric field and maintain the peristaltic pump circulation. Introduce ozone gas with a concentration of 105 mg / L into the suspension, set the flow rate at 1 L / min, and the duration at 40 min.

[0065] (3) Drying and degassing: Filter the treated starch suspension by suction, wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a blast drying oven at 50 °C for 12 h, and then degas and dry it in a vacuum drying oven at 50 °C for 24 h to obtain the final product. The test results are shown in Table 1 below.

[0066] Comparative Example 3

[0067] Refer to Example 1, the difference is that the pulse electric field strength is higher, at 15 kV / cm.

[0068] The specific steps of this comparative example are as follows:

[0069] (1) Pre-oxidation of the starch suspension: Place 400 mL of a starch suspension with a mass fraction of 10% (w / w) in a jacketed reactor. After cooling to 5 °C, introduce ozone gas with a concentration of 105 mg / L into the starch suspension, set the gas flow rate at 1 L / min, and the duration at 10 min.

[0070] (2) Pulse electric field co-treatment: Pump the pre-oxidized starch suspension obtained in step (1) into the pulse electric field treatment chamber through a constant-speed peristaltic pump. During the reaction, continue to introduce ozone gas into the starch suspension in the reactor, and at the same time start the pulse electric field for co-treatment. The pulse electric field treatment conditions are: electric field strength 15 kV / cm, frequency 100 Hz, pulse width 10 μs, and co-treatment time 30 min.

[0071] (3) Drying and degassing: Filter the starch suspension after co-treatment by suction, wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a blast drying oven at 50 °C for 12 h, and then degas and dry it in a vacuum drying oven at 50 °C for 24 h to obtain the final product. The test results are shown in Table 1 below.

[0072] Comparative Example 4:

[0073] Refer to Example 2, the difference is that there is no pre-oxidation of the starch suspension in step (1).

[0074] The specific steps of this comparative example are as follows:

[0075] (1) Treatment with pulsed electric field alone: Place 400 mL of a starch suspension with a mass fraction of 10% (w / w) in a jacketed reactor. After cooling to 5 °C, pump the starch suspension into the pulsed electric field treatment chamber at a constant rate of 400 mL / min using a peristaltic pump. The pulsed electric field treatment conditions are: electric field strength 8 kV / cm, frequency 100 Hz, pulse width 10 μs, and treatment time 30 min.

[0076] (2) Drying and degassing: Filter the starch suspension treated with pulsed electric field, wash the filter cake twice with distilled water and ethanol respectively, then disperse the obtained filter cake in a 50 °C forced air oven and dry for 12 h, and then degas and dry in a 50 °C vacuum oven for 24 h to obtain the final product.

[0077] Performance testing:

[0078] Test the products obtained in the examples and comparative examples. The results are shown in Table 1 and Figures 1-4 as follows. The methods for measuring free radicals and starch solubility in the solution of Table 1, and the method for measuring the internal structure of starch granules using a laser confocal microscope (Zeiss LSM 800, Germany) are as follows:

[0079] I. Measurement of free radicals in solution

[0080] Measure the free radicals generated when pure water / ozone water is treated with pulsed electric field of different electric field strengths in the form of DMPO spin adducts.

[0081] Take 1 mL of pure water / saturated ozone water and add it to a small treatment chamber. Add 10 μL of DMPO as a spin trap, and apply pulsed electric field of different electric field strengths for 30 s. Then, aspirate 10 μL of the solution with a capillary and place it in an EPR quartz tube with an inner diameter of 4 mm. The EPR-200M spectrometer is set as follows: modulation amplitude 2 G, modulation frequency 100 kHz, time constant 200 ms, conversion time 100 ms, center magnetic field 3500 G, scan width 100 G, and microwave power 1 mW.

[0082] II. Measurement of starch solubility

[0083] The test is carried out at a high concentration of 10% (w / w). Mix 2 g of starch sample with 20 g of distilled water in a pre-weighed centrifuge tube, heat at 95 °C for 30 minutes, and stir constantly to prevent agglomeration. After cooling, centrifuge the sample at 8000 rpm for 30 minutes. Then, transfer the supernatant to a pre-weighed petri dish and dry at 105 °C for 8 hours. The calculation formula is solubility (%) = (mass of soluble starch / sample mass) × 100%.

[0084] III. Laser Confocal Imaging

[0085] The internal structure of starch granules was measured using a laser confocal microscope (Zeiss LSM 800, Germany). 10 mg of starch sample was taken and mixed with 15 μL of APTS solution (10 mmol / L, 15% w / v glacial acetic acid) and 15 μL of sodium bromohydrogenate (1 mol / L), and incubated in the dark at 30 °C for 18 h. The sample was washed 5 times with distilled water and then dispersed into 100 μL (50%, v / v) glycerol-water mixture. A drop of the suspended starch granules was pipetted onto a glass slide and covered with a coverslip. Then it was observed under a 63× oil immersion lens. The excitation wavelength for the test was 488 nm. Finally, the fluorescence intensity distribution data of the starch granules were obtained using Zess Zein 3.9 software.

[0086] Table 1 Data table of the effects of different electric field parameters and treatment methods on the physicochemical properties of starch and the reaction environment

[0087]

[0088]

[0089] Note: "Total oxidation degree" is expressed as the sum of the contents of carbonyl (aldehyde group, ketone group) and carboxyl group; "Carboxyl ratio" is expressed as the value of the carboxyl group content divided by the total oxidation degree; Determination of carboxyl group content: It was determined by referring to the method of national standard GB / T20374-2006; Determination of carbonyl group content: It was determined by referring to the method of national standard GB / T14454.13-2008; The content of dissolved ozone in water (mg / L) was detected by a portable ozone water concentration detector (electrode method).

[0090] Conclusion:

[0091] (1) Example 2, Comparative Example 1 and Comparative Example 4, combined with the data in Table 1 and Figure 2By comparison, it can be seen that the combined treatment of pulsed electric field and ozone in the present invention can expose more reactive sites of starch molecules, improve the deep oxidation effect to a certain extent, significantly increase the carboxyl content, the proportion of carboxyl content, the overall oxidation degree content, and the solubility of starch, and also significantly increase the free radical signal intensity and the dissolved ozone concentration. The carboxyl content of starch increases, the overall oxidation degree content increases, the proportion of carboxyl content increases, the solubility increases, and the free radical signal intensity and the dissolved ozone concentration also increase. In Comparative Example 1, the PEF equipment protected by the present invention was not used for treatment, and only ozone treatment was carried out alone. The carboxyl content in the obtained product was only 0.1666%, the proportion in the overall oxidation degree was only 22.58%, and the starch solubility was only 32.81%. From Comparative Example 4, it can be seen that pulsed electric field treatment alone cannot oxidize and modify starch, and cannot make starch have good solubility at high concentrations. Under the treatment conditions of this comparative example, only a small amount of free radicals can be generated, which is sufficient to promote the occurrence of free radical chain reactions but not sufficient to oxidize starch. Comparing Example 2 and Comparative Example 1, it can be seen that after adding pulsed electric field combined treatment, the carboxyl content of starch increases, the overall oxidation degree content increases, the proportion of carboxyl content increases, the solubility increases, and the free radical signal intensity and the dissolved ozone concentration also increase. It can be seen that pulsed electric field treatment can expose more reactive sites of starch molecules, improve the oxidation effect to a certain extent. However, when the pulsed electric field is only used as a pretreatment, it cannot play the role of promoting the generation of active oxygen free radicals, while pulsed electric field combined treatment has a significant effect of strengthening free radical attack.

[0092] (2) By comparing Example 2 and Comparative Example 2 combined with the data in Table 1, it can be seen that pre-oxidizing the starch suspension with ozone first and then treating it with an electric field is more conducive to playing the role of pulsed electric field in promoting the generation of active oxygen free radicals, promoting the increase of dissolved ozone concentration, thereby realizing the advanced oxidation process of ozone oxidizing starch, and being beneficial to further oxidizing the carbonyl group in the oxidized starch product to carboxyl group, so that the carboxyl content increases, the overall oxidation degree content increases, the proportion of carboxyl content increases, and the starch solubility increases, thus improving the production efficiency of ozone-oxidized starch.

[0093] (3) Examples 1 - 3, Examples 6 - 10, Comparative Example 1 and Comparative Example 3 combined with Table Figure 1From the comparison between (A) and (B), it can be seen that the electric field strength is 2 - 10 kV / cm, preferably 4 - 8 kV / cm, and the frequency is 25 - 200 Hz, preferably 50 - 100 Hz. The electric field strength used in Comparative Example 3 is 15 kV / cm, which exceeds 10 kV / cm, and the overall oxidation degree and starch solubility of the obtained product do not continue to increase with the increase of the field strength. Although within the range of the electric field strength of 2 - 8 kV / cm, the carboxyl content, carbonyl content, total oxidation degree, carboxyl ratio, and solubility of starch all gradually increase, when the electric field strength increases from 8 kV / cm to 15 kV / cm, the amount of free radicals generated and ozone concentration during the reaction process both decrease significantly, resulting in a decrease in the oxidation effect of the synergistic treatment. Therefore, the preferred electric field strength treatment condition of the present invention is 4 - 8 kV / cm. Increasing the pulsed electric field frequency can effectively enhance the oxidation effect, and the amount of free radicals generated and ozone concentration during the reaction process both increase. However, when the frequency exceeds 100 Hz, the effect of the pulsed electric field promoting the conversion of ozone into free radicals may reach saturation, and the oxidation gain brought by further increasing the pulsed electric field frequency is not significant. Therefore, in view of the need to save energy, the preferred electric field frequency treatment condition of the present invention is 50 - 100 Hz.

[0094] (4) Examples 1 - 5 and Comparative Examples 1 - 4 combined with Table 1, Figure 2 (A), Figures 3-4 It can be seen that by regulating the pulsed electric field parameters, the process of strengthening free radicals can be quantitatively controlled. Under the induction of the electric field polarization effect, free radicals are uniformly oxidized on the surface layer of charged particles, and at the same time, the oxidation depth of the particles is increased. While ensuring the increase of the starch oxidation degree, the integrity of the starch particle structure is maintained, thereby achieving precise control of the oxidation effect. Figure 2 (A) is the second integral value of the EPR free radical signal of Examples 1 - 5 and Comparative Examples 1 - 4. It can be seen from the figure that Examples 2 and 5 with appropriate electric field strength and electric field frequency have stronger free radical signals, while the free radical signals of Example 1 with a low electric field strength, Comparative Example 3 with a high electric field strength, and Example 4 with a low electric field frequency are quite different from those of Examples 2 and 5. This shows that within the preferred electric field parameter range of the present invention, the conversion of ozone into free radicals can be better promoted, thereby strengthening the attack of free radicals. In addition, combined with the data of the carboxyl content ratio in Table 1, it can also be shown that the present invention can change the attack intensity of free radicals by adjusting the electric field parameters (field strength, frequency), so as to precisely control the carboxyl content ratio of oxidized starch. Figure 3 are the 2D plane (first row) / 3D stereo (second row) laser confocal images and the laser intensity distribution maps of the particles (third row) of Examples 1 - 3 and Comparative Examples 1, 3, and 4 after being stained with APTS (8 - aminopyrene - 1,3,6 - trisulfonic acid trisodium salt) dye. Figure 3From the analysis of the modified situation of the first - row 2D plan view of the granular single - layer, it can be seen that the oxidation area at the edge of the particles in Example 2 is more complete and the degree of oxidation is higher. From Figure 3 From the analysis of the modified situation of the overall particles in the second - row 3D stereogram, it can be seen that the oxidation area of the particles in Example 2 is evenly distributed and the degree of oxidation is higher. From Figure 3 From the laser - intensity distribution map in the third row, it can be seen that the oxidation depth of the particles in Example 2 is deeper. Compared with Comparative Example 1, the oxidation depth of the particles is increased by about 56%. These changes indicate that the pulsed - electric - field synergistic treatment method adopted in the present invention can improve the uniformity, depth, and degree of oxidation of particle modification during ozone oxidation. Figure 4 It is the two - dimensional Raman map of the oxidized starch for Examples 1 - 3 and Comparative Examples 1, 3, and 4. Comparative Example 4 shows that there are a small amount of carboxylate groups on the surface of the original starch. Comparative Example 1 shows that a large - area oxidation region appears on the particle surface after ozone oxidation, but the uniformity is poor. Compared with Comparative Example 1, Examples 1 - 3 have a more significant oxidation effect, with a higher degree of oxidation and better uniformity on the particle surface layer. Example 2 has a more concentrated and uniform high - intensity oxidation region compared with Examples 1 and 3, indicating that the electric field has an induction - oxidation effect under specific electric - field parameters.

[0095] The present invention prepares oxidized starch through the synergistic treatment of pulsed electric field and ozone, strengthens the free - radical reaction in the modification process, successfully improves the oxidation efficiency of ozone, realizes the controllable adjustment of the modification ratio of carboxyl / carbonyl functional groups. At the same time, the directional attack of the oxidant induced by the pulsed electric field can improve the degree, depth, and uniformity of the surface - layer oxidation modification of the particles. These characteristics provide a new guiding scheme for the industrial application of ozone - oxidized starch production; the present invention provides a method for preparing oxidized starch without additional substances, which helps to realize green and intelligent processing and reduce wastewater pollution.

[0096] The above has made a detailed description of the present invention and described the embodiments. However, the present invention is not limited thereto. Those of ordinary skill in the art can obviously make various formal changes and innovations according to the above description. As long as they do not depart from the scope protected by the claims of the present invention, they are all protected.

Claims

1. A method for preparing oxidized starch by precisely controlling the oxidation of starch granules, characterized in that: The method comprises the following steps: (1) Pre-oxidation of starch suspension: A starch suspension with a mass fraction of 5-30% is prepared, placed in a jacketed reactor, stirred evenly, and cooled by circulating water to a temperature of 5° C. Ozone gas is introduced into the starch suspension, with an ozone concentration of 40-105 mg / L and a gas flow rate of 1-4 L / min. The pre-oxidation process lasts for 10 minutes, so that a certain concentration of dissolved ozone accumulates in the suspension; (2) Pulsed electric field synergistic treatment: the pre-oxidized starch suspension obtained in step (1) is introduced into the pulsed electric field treatment chamber through a constant speed peristaltic pump; during the reaction process, ozone gas is continuously introduced into the starch suspension in the reactor, and the pulsed electric field is started for synergistic treatment; the specific conditions of the pulsed electric field treatment are: electric field intensity 2-10 kV / cm, frequency 25-200 Hz, pulse width 5-10 μs, and synergistic treatment time 10-30 min; (3) Drying and degassing: The starch suspension treated by the pulse electric field in step (2) is filtered, and the filter cake is washed twice with distilled water and ethanol respectively. The obtained filter cake is then dispersed in a 50° C. forced air oven and dried for 12 h, and then degassed and dried in a 50° C. vacuum oven for 24 h to obtain the final product.

2. The method according to claim 1, characterized in that The ozone concentration in step (1) is 90-105 mg / L.

3. The method according to claim 1, characterized in that The ozone gas flow rate in step (1) is 1-2 mL / min.

4. The method according to claim 1, characterized in that: The specific conditions of the pulse electric field treatment in step (2) are: the electric field strength is 4-8 kV / cm and the frequency is 50-100 Hz.

5. The method according to claim 1, characterized in that In step (2), the constant speed peristaltic pump causes the starch suspension to pass through the pulsed electric field at a constant flow rate of 400 mL / min.

6. The use of the oxidized starch obtained by the method according to claim 1, characterized in that: As a high-concentration, low-viscosity thickener and adhesive, it is used in food, construction, papermaking, and textile fields.

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