Method for preparing chitosan oligosaccharide by oxidizing agent enhanced electrochemical degradation of chitosan

Abstract

The invention discloses a method for preparing chitosan oligosaccharide by oxidizing agent enhanced electrochemical degradation of chitosan, and belongs to the technical field of natural high-molecular polysaccharide. The method comprises the following steps: S1, dissolving chitosan powder in an acidic aqueous solution to obtain a chitosan solution; s2, adding an oxidizing agent and an electrolyte into the chitosan solution to obtain a mixed solution, then immersing the positive electrode and the negative electrode into the mixed solution, switching on a power supply, and carrying out an electrochemical coupling oxidizing agent degradation reaction; s3, after the reaction is completed, the pH value of the mixed solution is adjusted to 8-10, and the chitosan oligosaccharide is obtained after separation, washing and drying. The method disclosed by the invention is low in cost, free of biological enzyme addition, free of heating and high in degradation rate, and chitosan oligosaccharide with specific molecular weight can be prepared by simply adjusting the current density and the reaction time so as to meet different application requirements. And secondly, the method disclosed by the invention still has relatively high degradation efficiency under the condition of no heating.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural polymer polysaccharides, and particularly relates to a method for preparing chitosan oligosaccharide by enhancing electrochemical degradation of chitosan with an oxidant. Background Art

[0002] Chitosan oligosaccharide (oligomeric β-(1-4)-2-amino-2-deoxy-D-glucose) is a low-molecular-weight chitosan. Due to its excellent physical, chemical, and biological properties, it is widely used in fields such as food, medicine, daily chemicals, agriculture, materials, and environmental protection. For example, medical research shows that chitosan oligosaccharide has various effects such as improving intestinal flora, regulating blood lipids, and enhancing immunity. Chitosan oligosaccharide is also regarded as an ideal raw material for food preservative additives due to its excellent antibacterial properties and higher water solubility characteristics.

[0003] Currently, the main production method of chitosan oligosaccharide is to degrade chitosan, and the degradation methods mainly involve three categories: physical degradation, chemical degradation, and biological degradation. Physical degradation methods include ultrasonic degradation, microwave degradation, γ-ray degradation, photo degradation, thermal degradation, etc. It mainly uses methods such as microwave and ray to break the glycosidic bonds in chitosan. However, this process has high requirements for equipment, and the degree of polymerization of the obtained chitosan oligosaccharide product is uncertain, making it difficult to apply industrially. Chemical degradation methods mainly include acid degradation and oxidative degradation. It mainly uses oxidants or acid solutions to break glycosidic bonds under high temperature and high pressure conditions. However, acid degradation requires the use of a large amount of acid-base reagents, which is easy to cause environmental pollution. The reaction needs to be carried out under high temperature and high pressure conditions, and part of the product is damaged during the reaction. Oxidative degradation requires the use of a large amount of oxidants, and the reaction also needs to be carried out under high temperature conditions. The heating oxidation has poor selectivity and many by-products. The core of biological degradation lies in relying on enzymatic reactions to convert chitosan into chitosan oligosaccharide. However, this process requires the use of highly specific enzymes or non-specific enzymes, with high production costs, relatively complex processes, and low degradation efficiency. Electrochemical degradation has the advantages of being convenient to control and environmentally friendly. The main problem with using electrochemistry for the degradation of macromolecular chitosan is the slow degradation rate and low conversion rate of chitosan oligosaccharide. Chinese Patent CN103755832A discloses a method for degrading chitosan. In this method, a chitosan solution is added to an electrolytic cell, and lithium chloride is used as a supporting electrolyte. Chitosan is electrolyzed under the conditions of pH 4-4.5 and temperature 50-70°C. This method can effectively degrade chitosan, but this method also requires heating. In summary, the above degradation methods respectively have some problems to be improved, such as high requirements for equipment, high production costs, slow degradation rate, the need to use biological enzymes, the need to heat, and easy generation of by-products.

[0004] Therefore, it is of great significance to provide a method for degrading chitosan to prepare chitosan oligosaccharide that is convenient to control, does not require the addition of biological enzymes, does not require heating, has a fast degradation rate, and a high conversion rate of chitosan oligosaccharide. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned prior art, one of the objectives of the present invention is to provide a method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan. The method of the present invention has low cost, does not require the addition of biological enzymes, does not require heating, has a fast degradation rate and a high conversion rate of chitosan oligosaccharide, and is expected to achieve rapid and efficient conversion of chitosan oligosaccharide.

[0006] To achieve the above objective, the specific technical solution of the present invention is as follows:

[0007] A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan, comprising the following steps:

[0008] S1. Dissolve chitosan powder in an acidic aqueous solution to obtain a chitosan solution;

[0009] S2. Add an oxidant and an electrolyte to the chitosan solution to obtain a mixed solution, then immerse the anode and cathode in the mixed solution, and perform an electrochemical coupling oxidant degradation reaction after connecting the power supply;

[0010] S3. After the reaction is completed, adjust the pH value of the mixed solution to 8-10, and obtain the chitosan oligosaccharide after separation, washing and drying.

[0011] Preferably, the concentration of chitosan in the chitosan solution is 1 wt% - 5 wt%.

[0012] Preferably, the oxidant is an H2O2 solution with a mass fraction of 10% - 30%, and the volume ratio of the H2O2 solution to the chitosan solution is (0.04 - 0.08):100.

[0013] Preferably, the electrolyte is NaCl, and the concentration of NaCl in the mixed solution is 5 - 20 g / L.

[0014] Preferably, both the anode and cathode are graphite electrodes and / or carbon-based conductive materials.

[0015] Preferably, the temperature of the electrochemical coupling oxidant degradation reaction is 20 - 30 °C, the current density is 0.2 - 1.0 A / dm 2 , and the time is 1 - 3 h. More preferably, the temperature of the electrochemical coupling oxidant degradation reaction is 25 °C, the current density is 1.0 A / dm 2 , and the time is 3 h.

[0016] Preferably, the acidic aqueous solution is a 0.1 - 0.5 mol / L acetic acid-sodium acetate buffer solution.

[0017] Preferably, in step S3, the pH value of the mixed solution is adjusted to 8 - 10 by using a sodium hydroxide solution or an ammonia water solution.

[0018] Preferably, the drying method is vacuum drying, and the drying temperature is 50-70 °C.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] (1) The methods for oxidatively degrading chitosan in the prior art all require heating. Hydrogen peroxide, an oxidant, generates hydroxyl radicals under heating conditions. Its oxidation ability is very strong, with poor selectivity and a short quenching time. In the method of the present invention, chloride ions and oxidants in the electrolyte react during electrolysis to generate chlorine-containing radicals with moderate oxidation ability and a long quenching time, improving selectivity and degradation rate.

[0021] (2) The method of the present invention can prepare chitosan oligosaccharides with a specific molecular weight by simply adjusting the current density and reaction time to meet different application needs, with good selectivity.

[0022] (3) In the method of the present invention, the oxidant undergoes an electrochemical reaction on the electrode surface to generate reactive oxygen species. The reactive oxygen species preferentially attack the β-(1,4)-glycosidic bond of the chitosan molecule to break it, and at the same time, the sugar ring structure is not damaged. This chain-breaking method does not cause a change in the basic structure of the chitosan molecule.

[0023] (4) The method of the present invention has low cost, does not require the addition of biological enzymes, does not require heating, has a fast degradation rate, and a high conversion rate of chitosan oligosaccharides, and is expected to achieve rapid and efficient conversion of chitosan oligosaccharides. Description of the Drawings

[0024] Figure 1 It is the infrared absorption spectrum of the chitosan raw material and the product of electrochemically degrading chitosan of the present invention. Detailed Embodiments

[0025] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

[0026] The present invention provides a method for preparing chitosan oligosaccharides by enhancing the electrochemical degradation of chitosan with an oxidant, comprising the following steps:

[0027] S1. Dissolve chitosan powder in an acidic aqueous solution to obtain a chitosan solution;

[0028] S2. Add an oxidant and an electrolyte to the chitosan solution to obtain a mixed solution, then immerse the anode and cathode in the mixed solution, and turn on the power supply to carry out an electrochemical coupling oxidant degradation reaction;

[0029] S3. After the reaction is completed, adjust the pH value of the mixed solution to 8 - 10, and obtain the chitosan oligosaccharide after separation, washing, and drying.

[0030] The concentration of chitosan in the chitosan solution is 1wt% - 5wt%. For example, it can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, etc.

[0031] The oxidant is a H2O2 solution with a mass fraction of 10% - 30%, and the volume ratio of the H2O2 solution to the chitosan solution is (0.04 - 0.08):100. For example, the mass fraction of the H2O2 solution can be 10%, 15%, 20%, 25%, 30%, etc.; the volume ratio of the H2O2 solution to the chitosan solution can be 0.04:100, 0.05:100, 0.06:100, 0.07:100, 0.08:100, etc.

[0032] The electrolyte is NaCl, and the concentration of NaCl in the mixed solution is 5 - 20 g / L. For example, the concentration of NaCl in the mixed solution can be 5 g / L, 10 g / L, 15 g / L, 20 g / L, etc.

[0033] The acidic aqueous solution is a 0.1 - 0.5 mol / L acetic acid - sodium acetate buffer solution. For example, the acidic aqueous solution can be a 0.1mol / L acetic acid - sodium acetate buffer solution, a 0.2mol / L acetic acid - sodium acetate buffer solution, a 0.5mol / L acetic acid - sodium acetate buffer solution, etc.

[0034] The raw materials used in the examples and comparative examples of the present invention can all be obtained commercially. The molecular weight of chitosan is 4.0×10 5 ~ 4.1×10 5 .

[0035] Example 1

[0036] This example provides a method for preparing chitosan oligosaccharide by enhancing the electrochemical degradation of chitosan with an oxidant, including the following steps:

[0037] S1. Weigh 10 g of chitosan powder and dissolve it in 1 L of 0.1 M acetic acid - sodium acetate buffer solution (pH 3.5), and stir until the chitosan is completely dissolved to obtain a chitosan solution;

[0038] S2. Take 200 mL of the above chitosan solution, add 0.12 mL of a 30% mass fraction H2O2 solution and 2 g of NaCl, continue to stir to obtain a mixed solution, and then immerse two graphite electrodes with an effective area of 20 cm 2 into the mixed solution, and set the current density to 1.0 A / dm by chronopotentiometry2 Electrochemically degrade for 3 h at room temperature (25 °C), and continuously stir using a magnetic stirrer during electrolysis;

[0039] S3. After the electrolysis reaction ends, adjust the pH value of the electrolytic solution to be between 8 and 10 with NaOH solution; then perform suction filtration on the solution, wash the filter residue with distilled water 2 - 3 times first, and then wash it with absolute ethanol 2 - 3 times. Place the filter residue in a vacuum drying oven at 60 °C for drying to obtain chitosan oligosaccharide.

[0040] Example 2

[0041] The method of this example is basically the same as that of Example 1, except that the current density in step S2 is 0.8 A / dm 2 .

[0042] Example 3

[0043] The method of this example is basically the same as that of Example 1, except that the degradation time in step S2 is 2 h.

[0044] Example 4

[0045] The method of this example is basically the same as that of Example 1, except that the current density in step S2 is 0.8 A / dm 2 , and the degradation time is 2 h.

[0046] Comparative Example 1

[0047] This comparative example provides a method for preparing chitosan oligosaccharide by electrochemically degrading chitosan, including the following steps:

[0048] S1. Weigh 10 g of chitosan powder and dissolve it in 1 L of acetic acid - sodium acetate buffer solution with a concentration of 0.1 M (pH 3.5), and stir until the chitosan is completely dissolved to obtain a chitosan solution;

[0049] S2. Take 200 mL of the above - mentioned chitosan solution, add 2 g of NaCl, and continue to stir to obtain a mixed solution. Then immerse two graphite electrodes with an effective area of 20 cm 2 into the mixed solution, and set the current density to 1.0 A / dm 2 by chronopotentiometry, electrochemically degrade for 3 h at room temperature (25 °C), and continuously stir using a magnetic stirrer during electrolysis;

[0050] S3. After the electrolysis reaction ends, adjust the pH value of the electrolytic solution to be between 8 and 10 with NaOH solution; then perform suction filtration on the solution, wash the filter residue with distilled water 2 - 3 times first, and then wash it with absolute ethanol 2 - 3 times. Place the filter residue in a vacuum drying oven at 60 °C for drying to obtain chitosan oligosaccharide;

[0051] That is, compared with Example 1, hydrogen peroxide is not added in this comparative example.

[0052] Comparative Example 2

[0053] This comparative example provides a method for preparing chitosan oligosaccharide by oxidative degradation of chitosan, including the following steps:

[0054] S1. Weigh 10 g of chitosan powder and dissolve it in 1 L of acetic acid-sodium acetate buffer solution with a concentration of 0.1 M (pH 3.5), and stir until the chitosan is completely dissolved to obtain a chitosan solution;

[0055] S2. Take 200 mL of the above chitosan solution, add 0.12 mL of H2O2 solution with a mass fraction of 30% and 2 g of NaCl, continue to stir, and then electrochemically degrade for 3 h at room temperature (25 °C), during which an electromagnetic stirrer is continuously used for stirring;

[0056] S3. After the oxidative degradation is completed, adjust the pH value of the electrolytic solution to be between 8 and 10 with NaOH solution; then filter the solution, wash the filter with distilled water 2 - 3 times first, and then wash it with absolute ethanol 2 - 3 times, and place the filter in a vacuum drying oven at 60 °C to dry to obtain chitosan oligosaccharide;

[0057] That is, compared with Example 1, this comparative example does not adopt an electrochemical reaction.

[0058] The molecular weights of the chitosan oligosaccharide solutions obtained in Examples 1 - 4 and Comparative Examples 1 - 2 were detected, and the detection results are shown in Table 1.

[0059] Table 1 Degradation effects of chitosan oligosaccharides in Examples 1 - 4 and Comparative Examples 1 - 2

[0060]

[0061] It can be seen from the data in Table 1 that the method of the present invention can prepare chitosan oligosaccharides with specific molecular weights by simply adjusting the current density and reaction time to meet different application requirements. Secondly, the method of the present invention still has a high degradation efficiency without heating.

[0062] By comparing Example 1 with Comparative Examples 1 - 2, it can be found that compared with the single electrochemical and oxidative degradation methods, the effect of the present invention using electrochemical coupling with an oxidant to degrade chitosan has been significantly improved.

[0063] In summary, the electrodes used in the method of the present invention can be reused. The electrochemical method has low cost and is environmentally friendly, without heating, without adding extra specific enzymes, and can adjust the molecular weight of the chitosan oligosaccharide prepared by the electrochemical method according to the electrolysis parameters (current density, time), meeting the requirements under different applications, and can be widely used in the preparation of chitosan oligosaccharide.

[0064] Figure 1 FIG. is the infrared absorption spectrum of the chitosan raw material and the product of electrochemically degraded chitosan of the present invention; it can be seen from the figure that the chitosan molecules are generally very similar before and after degradation, indicating that the functional groups and structural units of the electrochemically degraded chitosan product have basically not changed compared with the raw material.

[0065] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing chitosan oligosaccharide by electrochemically degrading chitosan with enhanced oxidant, characterized in that, It includes the following steps: S1. Dissolve chitosan powder in an acidic aqueous solution to obtain a chitosan solution; S2. Add an oxidant and an electrolyte to the chitosan solution to obtain a mixed solution, then immerse the anode and cathode in the mixed solution, and carry out an electrochemical coupling oxidant degradation reaction after turning on the power supply; S3. After the reaction is completed, adjust the pH value of the mixed solution to 8-10, and obtain the chitosan oligosaccharide after separation, washing and drying.

2. The method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that, The concentration of chitosan in the chitosan solution is 1wt% - 5wt%.

3. A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that, The oxidant is a H2O2 solution with a mass fraction of 10% - 30%, and the volume ratio of the H2O2 solution to the chitosan solution is (0.04 - 0.08):

100.

4. A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that, The electrolyte is NaCl, and the concentration of NaCl in the mixed solution is 5 - 20g / L.

5. A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that, Both the anode and cathode are graphite electrodes and / or carbon-based conductive materials.

6. A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that, The temperature of the electrochemical coupling oxidant degradation reaction is 20~30 °C, the current density is 0.2~1.0 A / dm 2 , and the time is 1~3 h.

7. A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that The temperature of the electrochemically coupled oxidant degradation reaction is 25 °C, the current density is 1.0 A / dm 2 , and the time is 3 h.

8. A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that The acidic aqueous solution is a 0.1 - 0.5 mol / L acetic acid-sodium acetate buffer solution.

9. A method for preparing chitosan oligosaccharide by oxidant-enhanced electrochemical degradation of chitosan according to claim 1, characterized in that, In step S3, the pH value of the mixed solution is adjusted to 8 - 10 using a sodium hydroxide solution or an ammonia water solution.

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