A highly soluble carboxylated guar gum, its preparation method and application

Abstract

This invention belongs to the field of carboxylated curdlan gum preparation, and discloses a highly soluble carboxylated curdlan gum, its preparation method, and its applications. The preparation method of this invention includes the following steps: mixing curdlan gum, a metal ion salt, and a free radical quencher solution to obtain curdlan gel; adding hydrogen peroxide solution to the curdlan gel, stirring the reaction, and separating to obtain carboxylated curdlan gum. The carboxylated curdlan gum preparation method provided by this invention is green and environmentally friendly; it can react under mild conditions and obtain carboxylated curdlan gum with high carboxyl content and low degradation in a short time, and has broad application prospects.

Description

Technical Field

[0001] This invention belongs to the field of carboxylated gellan gum preparation, and specifically relates to a highly soluble carboxylated gellan gum, its preparation method, and its application. Background Technology

[0002] Glide gum is a neutral, linear β-(1→3)-D-glucan derived from bacteria. Its unique, stable, and highly ordered triple helix structure endows it with excellent gelling properties and bioactivity. However, due to the large number of hydroxyl groups on the molecular chain forming extensive intramolecular and intermolecular hydrogen bonds, glide gum is insoluble in most organic solvents and aqueous solutions. At the same time, the extremely strong intermolecular forces also lead to the tendency of glide gum particles to aggregate, making it difficult to disperse evenly. This greatly limits the practical application of glide gum.

[0003] Oxidating the hydroxyl groups of gluconolactone to carboxyl groups can greatly improve its water solubility and bioactivity. The resulting carboxyl groups also have high reactivity and electrolyte properties, making them highly valuable for applications. However, traditional oxidation methods are inefficient and require stringent conditions. Chinese patent publication CN110872360A uses hydrogen peroxide to oxidize gluconolactone, but this requires oxidation under alkaline conditions at a temperature of 50–60°C and involves relatively complex procedures.

[0004] The hydrogen peroxide / metal ion catalytic oxidation reaction can generate highly reactive oxygen species with extremely high oxidation potentials, which can efficiently and selectively oxidize the C6 hydroxyl groups in natural polysaccharides to carboxyl groups. Chinese patent publication CN105111321A uses hydrogen peroxide and ferric sulfate to prepare a carboxyl starch with a high carbonization rate. Chinese patent publication CN104017090A uses hydrogen peroxide and metal salts to prepare carboxyl cellulose with different oxidation degrees. Therefore, it has the potential to oxidize gum arabic, and compared to the TEMPO oxidation system, it is lower in cost, simpler to operate, and more environmentally friendly and low-carbon.

[0005] However, the excessive oxidizing power of hydroxyl radicals can trigger hydrogen abstraction reactions that indiscriminately attack the carboxylated gum molecular chains. The acidic environment produced by oxidation inevitably leads to the hydrolysis of glycosidic bonds, resulting in a significant decrease in the average molecular weight of the final product, destruction of the pyran ring structure, and the mixing of a large number of small molecule polysaccharides, which affects the bioactivity of carboxylated carboxylated gum and reduces its stability. Summary of the Invention

[0006] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing highly soluble carboxylated gellan gum.

[0007] The method of this invention uses environmentally friendly reagents and regulates the reaction process by adding a free radical quencher to control the oxidation effect of hydroxyl radicals and inhibit the hydrolysis of gellan gum to a certain extent. Thus, under mild conditions, highly soluble and antibacterial carboxylated gellan gum can be obtained rapidly and efficiently.

[0008] Another object of the present invention is to provide highly soluble carboxylated guar gum prepared by the above method.

[0009] Another object of the present invention is to provide the application of the above-mentioned highly soluble carboxylated guar gum in hydrogel materials, food or antimicrobial materials.

[0010] The objective of this invention is achieved through the following solution:

[0011] A method for preparing highly soluble carboxylated guar gum includes the following steps:

[0012] (1) Mix kelp, metal ion salt and free radical quencher solution to obtain kelp gel;

[0013] (2) Add hydrogen peroxide solution to the gel in step (1), stir to react, separate, and obtain carboxylated gel.

[0014] The metal ions in step (1) include at least one of copper ions, cobalt ions, manganese ions, chromium ions, and zinc ions; preferably at least one of copper ions and zinc ions.

[0015] The free radical quencher in step (1) includes at least one of ethanol, ethylene glycol, glycerol, isopropanol, and tert-butanol; preferably at least one of ethanol and glycerol.

[0016] In step (1), the volume ratio of free radical quencher to water in the free radical quencher solution is 20-100:80-0.

[0017] The ratio of the amount of guar gum to the free radical quencher solution in step (1) is 1g:5-10mL.

[0018] The mass ratio of the metal ion salt and guar gum in step (1) is 1 to 100:10000, preferably 5 to 20:10000.

[0019] The stirring temperature in step (1) is 20-40℃; the stirring time is 10-30 min; and the stirring speed is 300-500 rpm.

[0020] In step (2), the mass ratio of hydrogen peroxide to the kerogen gel in step (1) is 10-100:100; preferably 10-50:100.

[0021] The reaction in step (2) is carried out at a temperature of 20–40°C for 1–6 hours.

[0022] The solid obtained in step (2) is first washed with water and then with ethanol, and then dried at 60-80°C to constant weight.

[0023] The highly soluble carboxylated gelatin was prepared by the above method.

[0024] Applications of the aforementioned highly soluble carboxylated guar gum in hydrogel materials, food, or antimicrobial materials.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0026] (1) The method for preparing carboxylated guar gum provided by the present invention uses hydrogen peroxide as an oxidant and metal ions as a catalyst to generate oxygen free radicals with high oxidation activity, selectively oxidizing the hydroxyl group at the C6 position of guar gum to a carboxyl group, and the byproducts generated during the reaction are water and oxygen, which is green and environmentally friendly.

[0027] (2) The method for preparing carboxylated gellan gum provided by the present invention effectively inhibits the formation of metal peroxide precipitates through the coordination of metal ions with gellan gum and achieves in-situ catalytic oxidation. It can react under mild conditions (30°C) and obtain carboxylated gellan gum with high carboxyl content and low degradation in a short time (3h), which is fast and efficient.

[0028] (3) The method for preparing carboxylated sorbent gum provided by the present invention inhibits the excessive oxidation of hydroxyl radicals by using a free radical quencher, thereby reducing the ring-opening and chain-breaking effects caused by hydroxyl radicals attacking glycosidic bonds during the oxidation process, and obtaining high-quality carboxylated sorbent gum. It also has high water solubility and can be used in hydrogel material applications.

[0029] (4) The carboxyl ketorum prepared by the present invention has a high carboxyl content and solubility, which is conducive to penetrating the interior of bacteria and changing their environment, affecting the growth and reproduction of bacteria. Therefore, it has excellent antibacterial properties against Staphylococcus aureus and Escherichia coli, and can be applied in the fields of food and antibacterial materials. Attached Figure Description

[0030] Figure 1 The infrared spectra are of gellan gum and carboxylated gellan gum obtained in Example 1.

[0031] Figure 2 The photoelectron spectra are those of kelden gum and carboxylated kelden gum obtained in Example 1.

[0032] Figure 3 The NMR carbon spectra are of kelden gum and carboxylated kelden gum obtained in Example 1.

[0033] Figure 4 The carboxyl content of the carboxylated gums obtained in Example 1 and Comparative Example 5 changes over time.

[0034] Figure 5 The results of liquid chromatography-mass spectrometry testing of carboxylated guar gum obtained in Example 1 and Comparative Example 1 are shown.

[0035] Figure 6 The changes in the solubility of carboxylated gellan gum, the gellan gum obtained in Examples 1-2 and Comparative Example 1, in water.

[0036] Figure 7 The results show the antibacterial properties of carboxylated gellan gum, the carboxylated gellan gum obtained in Example 1 and Comparative Examples 1-4.

[0037] Figure 8 The carboxylated guar gum obtained in Example 1 and Comparative Example 1 enhances the mechanical properties of ionic hydrogels. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0039] Unless otherwise specified, all reagents used in the examples are commercially available.

[0040] All reagents provided in this invention were purchased from Shanghai Anaiji Chemical Co., Ltd. or Guangzhou Chemical Reagent Factory, and Kederan gel was purchased from Guangzhou Huaxi Biotechnology Co., Ltd.

[0041] Example 1

[0042] 100g of gellan gum, 60mg of copper chloride, 40mg of zinc chloride, 250mL of deionized water, and 250mL of ethanol were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion of the gellan gum. Then, 35g of a 30wt% hydrogen peroxide solution was added to the gellan gum, stirred thoroughly, and reacted at 30℃ for 3h. After the reaction was complete, the resulting product was separated, washed repeatedly with deionized water and ethanol, and dried in a 60℃ oven to constant weight to obtain carboxylated gellan gum E1OC-1.

[0043] Example 2

[0044] 100g of currant, 60mg of copper chloride, 40mg of zinc chloride, and 500mL of ethanol were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion of the currant. Then, 35g of a 30wt% hydrogen peroxide solution was added to the currant, stirred thoroughly, and reacted at 30℃ for 3h. After the reaction was complete, the resulting product was separated, washed repeatedly with deionized water and ethanol, and dried in a 60℃ oven to constant weight to obtain carboxylated currant E2OC-1.

[0045] Example 3

[0046] 100g of currant, 60mg of copper chloride, 40mg of zinc chloride, 250mL of deionized water, and 250mL of ethanol were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion of the currant. Then, 140g of a 30wt% hydrogen peroxide solution was added to the currant, stirred thoroughly, and reacted at 30℃ for 3h. After the reaction was complete, the resulting product was separated, washed repeatedly with deionized water and ethanol, and dried in a 60℃ oven to constant weight to obtain carboxylated currant E3OC-1.

[0047] Comparative Example 1

[0048] 100g of gellan gum, 60mg of copper chloride, 40mg of zinc chloride, and 500mL of deionized water were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion of the gellan gum. Then, 35g of a 30wt% hydrogen peroxide solution was added to the gellan gum, stirred thoroughly, and reacted at 30℃ for 3h. After the reaction was complete, the resulting product was separated, washed repeatedly with deionized water and ethanol, and dried in a 60℃ oven to constant weight to obtain carboxylated gellan gum OC-1.

[0049] Comparative Example 2

[0050] 100g of gellan gum, 60mg of copper chloride, 40mg of zinc chloride, and 500mL of deionized water were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion of the gellan gum. Then, 70g of a 30wt% hydrogen peroxide solution was added to the gellan gum, and the mixture was stirred until homogeneous. The mixture was then reacted at 30℃ for 3h. After the reaction was complete, the product was separated using a high-speed centrifuge and washed repeatedly with deionized water and ethanol. The product was then dried in a 60℃ oven to constant weight to obtain carboxylated gellan gum OC-2.

[0051] Comparative Example 3

[0052] 100g of gellan gum, 60mg of copper chloride, 40mg of zinc chloride, and 500mL of deionized water were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion of the gellan gum. Then, 140g of a 30wt% hydrogen peroxide solution was added to the gellan gum, stirred thoroughly, and reacted at 30℃ for 3h. After the reaction was complete, the resulting product was separated, washed repeatedly with deionized water and ethanol, and dried in a 60℃ oven to constant weight to obtain carboxylated gellan gum OC-3.

[0053] Comparative Example 4

[0054] 100g of gellan gum, 60mg of copper chloride, 40mg of zinc chloride, and 500mL of deionized water were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion of the gellan gum. Then, 210g of a 30wt% hydrogen peroxide solution was added to the gellan gum, stirred thoroughly, and reacted at 30℃ for 3h. After the reaction was complete, the resulting product was separated, washed repeatedly with deionized water and ethanol, and dried in a 60℃ oven to constant weight to obtain carboxylated gellan gum OC-4.

[0055] Comparative Example 5

[0056] 100g of gellan gum and 500mL of deionized water were mixed and stirred at 500rpm for 30min at 30℃ to ensure uniform dispersion. Then, 60mg of copper chloride and 40mg of zinc chloride were added to 35g of 30wt% hydrogen peroxide solution, and then added to the gellan gum. After stirring until homogeneous, the mixture was reacted at 30℃ for 3h. After the reaction was complete, the resulting product was separated, washed repeatedly with deionized water and ethanol, and dried in a 60℃ oven to constant weight to obtain carboxylated gellan gum BE1OC-1.

[0057] Figure 1 The infrared spectra of carboxylated collamer (CUR) and the carboxylated collamer (E1OC-1) prepared in Example 1 are shown. The carboxylated collamer has an infrared spectrum at 1734 cm⁻¹. -1 A significant new characteristic peak appeared nearby, which corresponds to the stretching vibration of the carboxyl group C=O. The peak intensity of the characteristic peak increased with the increase of carboxyl content, confirming that the oxidation successfully introduced the carboxyl group into the structure of the gellan gum. Apart from this, there were no other significant changes.

[0058] Figure 2 The photoelectron spectra of kellan gum and the carboxylated kellan gum prepared in Example 1 are shown. The intensity of the C characteristic peak is used as a reference. The decrease in the ratio of the CO to the C characteristic peak area indicates a significant reduction in C-OH, which means that the hydroxyl groups are oxidized to carboxyl groups.

[0059] Figure 3The images show the carbon NMR spectra of gellan gum and the carboxylated gellan gum prepared in Example 1. The intensity of the C6 characteristic peak in the carboxylated gellan gum spectrum is relatively reduced, and new characteristic signals appear, indicating that some hydroxyl groups at the C6 position are oxidized to carboxyl groups.

[0060] Figure 4 The carboxyl content of the carboxylated gelatin prepared in Example 1 and Comparative Example 5 changes over time. In comparison, copper ions react with hydrogen peroxide to form a brownish-yellow copper peroxide precipitate, while adding them first to gelatin allows for coordination inhibition of precipitate formation and achieves in-situ catalysis, thereby achieving a higher carboxyl content in a shorter time and improving reaction efficiency.

[0061] Figure 5 The results of liquid chromatography-mass spectrometry (LC-MS) analysis of carboxylated curdlan gum prepared in Example 1 and Comparative Example 1 show that ethanol, as a quencher of hydroxyl radicals, can effectively inhibit the activity of hydroxyl radicals, thereby reducing hydrolysis, chain scission, and ring opening of curdlan gum during the oxidation process, and achieving the preparation of high-quality oxidized curdlan gum.

[0062] Figure 6 The changes in the solubility of pure gluconol, carboxylated glucon prepared in Examples 1-2, and Comparative Example 1 in water are shown. Compared to pure gluconol, the carboxylated glucon obtained in Examples 1-2 has a smaller particle size and a larger specific surface area, making it easier for the solvent to penetrate the interior of the carboxylated glucon (OC). Furthermore, the oxidation of hydroxyl groups to carboxyl groups increases the polarity of the oxidized glucon molecules, making it easier for them to interact with solvent molecules to form a stable solution, ultimately resulting in higher solubility of the carboxylated glucon.

[0063] Table 1. Carboxyl content of carboxylated curd gums prepared in Examples 1-3 and Comparative Examples 1-4

[0064]

[0065] From Examples 1 and 3 in Table 1, it is shown that by adjusting the amount of hydrogen peroxide added, the present invention can obtain gellan gum with a higher carboxyl content.

[0066] Figure 7 The results show the antibacterial properties of carboxylated collan gum, as well as the carboxylated collan gum prepared in Examples 1 and 1-4. Pure collan gum did not show significant inhibition zones against Staphylococcus aureus and Escherichia coli. However, with the introduction of carboxyl groups, carboxylated collan gum exhibited a significant antibacterial effect, and the diameter of the inhibition zone around the carboxylated collan gum increased with increasing carboxyl content, indicating its excellent antibacterial activity.

[0067] Figure 8The carboxylated gel prepared in Example 1 and Comparative Example 1 enhances the mechanical properties of polyacryloyloxyethyltrimethylammonium chloride ion hydrogel, indicating that E1OC-1, with its greater macromolecular components and more complete molecular chain structure, is a better physical crosslinking agent for hydrogel macromolecules.

[0068] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing carboxylated colloidal gum, characterized in that, Includes the following steps: (1) Mix guar gum, metal ion salt, and free radical quencher solution to obtain guar gum gel; (2) Add hydrogen peroxide solution to the gel in step (1), stir to react, separate, and obtain carboxylated gel.

2. The method for preparing carboxylated colloidal gum according to claim 1, characterized in that: The metal ion mentioned in step (1) is at least one of copper ion and zinc ion.

3. The method for preparing carboxylated colloidal gum according to claim 1, characterized in that: The free radical quencher mentioned in step (1) is at least one of ethanol and glycerol.

4. The method for preparing carboxylated colloidal gum according to claim 1, characterized in that: In step (1), the volume ratio of free radical quencher to water in the free radical quencher solution is 20~100:80~0; In step (1), the ratio of the amount of guar gum to the free radical quencher solution is 1g:5~10mL.

5. The method for preparing carboxylated colloidal gum according to claim 1, characterized in that: The mass ratio of the metal ion salt and guar gum in step (1) is 5~20:10000.

6. The method for preparing carboxylated colloidal gum according to claim 1, characterized in that: The stirring temperature in step (1) is 20~40℃; the stirring time is 10~30 min.

7. The method for preparing carboxylated colloidal gum according to claim 1, characterized in that: In step (2), the mass ratio of hydrogen peroxide to the kerogen gel in step (1) is 10~50:

100.

8. The method for preparing carboxylated colloidal gum according to claim 1, characterized in that: The reaction in step (2) is carried out at a temperature of 20-40°C for 1-6 hours.

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