High g type / high m type sodium alginate and a method for preparing the same

Abstract

The application discloses high-G type / high-M type sodium alginate and a preparation method thereof, and selects Chinese cultivated kelp Laminaria japonica (LJ) or wild kelp of Chile Lessonia flavicans (LF) as raw materials, the raw materials are sequentially subjected to cleaning, drying, crushing, and sieving to obtain seaweed powder; the seaweed powder is subjected to decolorization by using ethanol, and after the decolorization is completed, the seaweed powder is sequentially subjected to filtering and drying to obtain decolorized seaweed powder; the decolorized seaweed powder is subjected to acid pretreatment by using hydrochloric acid to obtain seaweed filter residue; sodium carbonate solution is added to the seaweed filter residue to leach the seaweed powder, the supernatant is collected after the seaweed powder is left to stand overnight and filtering; the supernatant is left to stand and precipitate by adding ethanol, and the milk-white flocculent precipitate is collected by filtering, and the milk-white flocculent precipitate is subjected to washing and drying to obtain high-G type or high-M type sodium alginate. The method can effectively remove impurities such as pigments and proteins, and improve the extraction rate and product purity; the obtained product is stable in structure, excellent in thermal stability, and controllable in rheological performance, and can be applied to the fields of biological medical materials such as temperature-sensitive gels, pH response microspheres and soft tissue repair.

Description

Technical Field

[0001] This invention relates to sodium alginate and its preparation method, specifically to a high-G / high-M type sodium alginate and its directional preparation method, belonging to the field of marine biomass polysaccharide extraction and purification technology. Background Technology

[0002] Sodium alginate is a natural anionic polysaccharide extracted from brown algae, composed of β-D-mannuronic acid (M unit) and α-L-guluronic acid (G unit) linked by 1,4-glycosidic bonds. In recent years, sodium alginate has been widely used in food, medicine, tissue engineering, smart gels and other fields due to its abundant sources, low price, and good biocompatibility.

[0003] Sodium alginate with high G-unit content readily forms high-strength gels, making it suitable as a support material. Sodium alginate with high M-unit content exhibits good flexibility and solubility, making it suitable for flexible carriers and sustained-release systems. Existing sodium alginate extraction technologies generally suffer from the following drawbacks: the M / G ratio is uncontrollable, making it difficult to obtain high-G or high-M products; decolorization is poor, resulting in high protein impurities, affecting subsequent biomedical applications; the alkaline extraction process is crude, leading to low extraction rates and poor batch stability; and there is a lack of systematic control over structure, thermal properties, and rheological behavior, making it difficult to meet the needs of smart materials.

[0004] Therefore, developing a method for the targeted preparation of high-G / high-M sodium alginate with stable process, high extraction rate, and high purity is of great significance for promoting the high-value utilization of marine polysaccharides in biomedical materials. Summary of the Invention

[0005] The technical problem this invention aims to solve is the shortcomings of existing sodium alginate extraction processes, such as the inability to directionally control the M / G unit ratio, low product purity, insufficient extraction rate, and poor batch stability. This invention provides a high-G / high-M type sodium alginate and its preparation method. This invention uses kelp and LF algae as raw materials to prepare high-M / high-G type sodium alginate. Through a combination of ethanol fractionation decolorization, acidic pretreatment, and gentle sodium carbonate extraction, impurities such as pigments and proteins are effectively removed, improving the extraction rate and product purity. The resulting product has a stable structure, excellent thermal stability, and controllable rheological properties, and can be used as a raw material in the fields of thermosensitive gels, pH-responsive microspheres, and soft tissue repair materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention first provides a method for preparing high-G / high-M sodium alginate, the process flow diagram of which is shown below. Figure 1 As shown, it includes the following steps:

[0008] (1) Raw material pretreatment:

[0009] Chinese farmed kelp Laminaria japonica (LJ) or Chilean wild giant kelp Lessoniaflavicans (LF) were selected as raw materials. The raw materials were washed, dried, crushed and sieved to obtain algae powder.

[0010] (2) Ethanol decolorization:

[0011] The algal powder obtained in step (1) was treated with anhydrous ethanol as the decolorizing agent. The ethanol concentration was 90% to 100% by volume, the liquid-to-solid ratio (volume / mass, v / w) was 2:1 to 4:1, and the decolorization time was 2 to 4 h. After decolorization, the algal powder was filtered, and the filter residue was collected and dried naturally under room temperature conditions to obtain decolorized algal powder.

[0012] (3) Acid pretreatment:

[0013] Add deionized water to the decolorized algae powder obtained in step (2), stir and disperse evenly, adjust the pH of the system to 0.5~1.5 with HCl, stir for 1~3 hours at room temperature for acid treatment; after the acid treatment is completed, filter and discard the supernatant, collect the filter residue, rinse the filter residue with deionized water until the pH reaches 3.5~4.5, drain the water and obtain algae filter residue;

[0014] (4) Alkali extraction:

[0015] Add sodium carbonate solution to the algal residue obtained in step (3) to extract algal powder. The sodium carbonate concentration is 0.4-0.6 mol / L, the liquid-to-solid ratio (v / w, volume / mass) is 40:1-60:1, let stand overnight at room temperature, filter after extraction, and collect the supernatant.

[0016] (5) Alcohol precipitation:

[0017] Add anhydrous ethanol to the supernatant obtained in step (4) until the final ethanol volume concentration of the system reaches 65%~75%. After stirring evenly, let it stand at room temperature for 0.5~1.5h. After standing, filter and collect the milky white flocculent precipitate.

[0018] (6) Washing and drying:

[0019] The milky white flocculent precipitate obtained in step (5) was washed successively with methanol and acetone. After washing, it was dried at room temperature to obtain high G-type or high M-type sodium alginate.

[0020] In the above technical solution, the specific operation process of the raw material pretreatment in step (1) is as follows: after comparing more than 10 different kinds of brown algae raw materials from different production areas in the world, kelp LJ and giant kelp LF are selected as the preferred raw materials. They are rinsed with clean water 2 to 4 times to remove mud and impurities, and then dried at 60 to 70°C for 12 to 36 hours. The dried material is then crushed and passed through a 30 to 50 mesh sieve to obtain algae powder. It is preferred to dry at 65°C for 24 hours and then crush it and pass it through a 40 mesh sieve.

[0021] In the above technical solution, in step (2), the ethanol decolorization is preferably performed with an ethanol volume concentration of 100% and a liquid-to-solid ratio of 2:1 when the raw material is kelp LJ, and a decolorization time of 3 h; when the raw material is giant kelp LF, the ethanol volume concentration is preferably 100%, the liquid-to-solid ratio is preferably 2:1, and the decolorization time is preferably 2 h; after decolorization, the solid and liquid are preferably separated by sieving through a 20-mesh sieve, the filter residue is collected, and the residue is naturally dried in a ventilated environment at room temperature for 24 h to obtain decolorized algal powder. The three influencing factors, ethanol concentration, liquid-to-solid ratio, and decolorization time, were determined to have the optimal extraction parameters through single-factor experiments and orthogonal experiments.

[0022] In the above technical solution, in step (3), during acid pretreatment, it is preferable to use HCl to adjust the pH of the system to 1.0±0.1, stir for 2 hours at room temperature for acid treatment, and rinse the filter residue with deionized water until the pH reaches 4.0±0.1.

[0023] In the above technical solution, in step (4), during alkaline extraction, the sodium carbonate concentration is preferably 0.6 mol / L, the liquid-to-solid ratio is preferably 60:1, and the extraction is preferably carried out at room temperature for 12 hours. After extraction, the solution is preferably filtered through a 20-mesh sieve, and the supernatant is collected. The sodium carbonate concentration and liquid-to-solid ratio are the optimal extraction parameters determined through single-factor experiments and orthogonal experiments.

[0024] In the above technical solution, in step (5), during alcohol precipitation, anhydrous ethanol is added to the supernatant, preferably until the ethanol concentration in the system is 70%, and the preferred standing time is 1 hour.

[0025] In the above technical solution, in step (6), the obtained milky white flocculent precipitate is first washed with methanol for 5 minutes, filtered, then washed with acetone for 5 minutes, filtered, and the precipitate obtained after washing is dried at room temperature for 12 hours to obtain high G-type or high M-type sodium alginate.

[0026] The second objective of this invention is to provide a high-M type sodium alginate, which is prepared from Chinese farmed kelp Laminaria japonica using the above-mentioned preparation method.

[0027] The third objective of this invention is to provide a high-G sodium alginate, which is prepared from wild Chilean giant kelp Lessoniaflavicans using the above-mentioned preparation method.

[0028] Compared with existing technologies, it has the following characteristics:

[0029] 1. Directional controllability: High-G type and high-M type sodium alginate can be stably prepared separately.

[0030] 2. High extraction rate: The extraction rates of kelp (LJ) and giant kelp (LF) can reach 59.19% and 60.13%, respectively.

[0031] 3. High purity and good decolorization effect: Pigments and protein impurities are thoroughly removed.

[0032] 4. Well-defined performance: The structure, thermal properties, and rheological characteristics are predictable, making it suitable for high-end medical materials.

[0033] 5. Mild process: No high temperature and high pressure required, suitable for large-scale production. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the preparation method of high G-type / high M-type sodium alginate of the present invention;

[0035] Figure 2 To verify the Fourier transform infrared spectra of high G-type and high M-type sodium alginate in Example 1;

[0036] Figure 3 To verify the 1H NMR spectra of high G-type and high M-type sodium alginate in Example 2, where a is the 1H NMR spectrum of high G-type sodium alginate (LF-SA) and b is the 1H NMR spectrum of high M-type sodium alginate (Kelp-SA).

[0037] Figure 4 To verify the X-ray diffraction patterns of high-G and high-M sodium alginate in Example 3. Detailed Implementation

[0038] The following describes in detail the specific embodiments of the technical solution of the present invention, but the present invention is not limited to the following description:

[0039] The present invention will now be described in conjunction with specific embodiments:

[0040] Example 1: Preparation of high-M type sodium alginate

[0041] A method for preparing high-M type sodium alginate includes the following steps:

[0042] (1) Raw material pretreatment:

[0043] By comparing the content of mannulic acid and guluronic acid in the brown algae raw material, the target brown algae raw material was finally selected as Chinese farmed kelp, Laminaria japonica (LJ). 500 g of raw material dry powder was selected, rinsed three times with clean water to remove mud and impurities, spread evenly in an enamel dish, and placed in a 65 ℃ constant temperature drying oven to dry for 24 h until completely dry. The dried kelp was then put into a multi-functional pulverizer to be pulverized, and all of it was passed through a 40 mesh standard sieve. The kelp powder was collected, sealed and stored in the dark for later use.

[0044] (2) Ethanol decolorization

[0045] Accurately weigh 100 g of kelp LJ powder, add 200 mL of 100% anhydrous ethanol at a liquid-to-solid ratio of 2:1 (v / w), place in a 2 L beaker, and decolorize at room temperature for 3 h under magnetic stirring. After decolorization, filter through a 20-mesh sieve to separate the solid and liquid, collect the filter residue, and air dry at room temperature for 24 h to obtain decolorized kelp powder.

[0046] (3) Acid pretreatment

[0047] Transfer all the decolorized kelp LJ powder to a 1 L beaker, add 500 mL of deionized water, and stir to disperse evenly; slowly add hydrochloric acid to adjust the pH of the system to 1.0, and perform acid treatment by magnetic stirring at room temperature for 2 h; after the treatment is completed, filter and discard the supernatant, retain the filter residue, rinse the filter residue with deionized water until the pH reaches 4.0, and drain the water.

[0048] (4) Alkali extraction

[0049] Add 6000 mL of 0.6 mol / L sodium carbonate solution (liquid-solid ratio 60:1) to the acid-treated filter residue, stir well, and allow to stand at room temperature for 12 h for extraction. After extraction, filter under pressure through a 20-mesh sieve, collect the pale yellow, clear supernatant, and discard the filter residue.

[0050] (5) Alcohol precipitation

[0051] Under stirring conditions, anhydrous ethanol was slowly added to the supernatant until the final ethanol volume fraction of the system reached 70%. After stirring evenly, the mixture was allowed to stand at room temperature for 1 hour to allow sodium alginate to completely flocculate and precipitate. After standing, the milky white flocculent precipitate was collected by filtration.

[0052] (6) Washing and drying

[0053] The precipitate was first washed with 50 mL of methanol for 5 min by stirring and then filtered; then washed with 50 mL of acetone for 5 min by stirring and then filtered to remove residual pigments and small molecule impurities; the washed precipitate was spread on a clean tray and dried at room temperature and normal pressure for 12 h to obtain a light yellow powder of high M-type sodium alginate, abbreviated as Kelp-SA.

[0054] Example 2: Preparation of high-G sodium alginate

[0055] A method for preparing high-G sodium alginate includes the following steps:

[0056] (1) Raw material pretreatment:

[0057] By comparing the content of mannulic acid and guluronic acid in the brown algae raw material, the target brown algae raw material was finally selected as Chilean wild giant kelp Lessonia flavicans (LF). 500 g of raw material dry powder was selected, rinsed three times with clean water to remove mud and impurities, spread evenly in an enamel dish, and placed in a constant temperature drying oven at 65 ℃ for 24 h until completely dry. The dried giant kelp LF was then put into a multi-functional pulverizer and pulverized. All of it was passed through a 40-mesh standard sieve, and the seaweed powder was collected, sealed and stored in the dark for later use.

[0058] (2) Ethanol decolorization

[0059] Accurately weigh 100 g of giant kelp LF algae powder, add 200 mL of 100% anhydrous ethanol at a liquid-to-solid ratio of 2:1 (v / w), place in a 2 L beaker, and decolorize at room temperature for 2 h under magnetic stirring. After decolorization, filter through a 20-mesh sieve to separate the solid and liquid, collect the filter residue, and air dry at room temperature for 24 h to obtain decolorized seaweed powder.

[0060] (3) Acid pretreatment

[0061] Transfer all the decolorized seaweed powder to a 1 L beaker, add 500 mL of deionized water, and stir to disperse evenly; slowly add hydrochloric acid to adjust the pH of the system to 1.0, and perform acid treatment by magnetic stirring at room temperature for 2 h; after the treatment is completed, filter and discard the supernatant, retain the filter residue, rinse the filter residue with deionized water until the pH reaches 4.0, and drain the water.

[0062] (4) Alkali extraction

[0063] Add 6000 mL of 0.6 mol / L sodium carbonate solution (liquid-solid ratio 60:1) to the acid-treated filter residue, stir well, and allow to stand at room temperature for 12 h for extraction. After extraction, filter under pressure through a 20-mesh sieve, collect the pale yellow, clear supernatant, and discard the filter residue.

[0064] (5) Alcohol precipitation

[0065] Under stirring conditions, anhydrous ethanol was slowly added to the supernatant until the final ethanol volume fraction of the system reached 70%. After stirring evenly, the mixture was allowed to stand at room temperature for 1 hour to allow sodium alginate to completely flocculate and precipitate. After standing, the milky white flocculent precipitate was collected by filtration.

[0066] (6) Washing and drying

[0067] The precipitate was first washed with 50 mL of methanol for 5 min by stirring and then filtered; then washed with 50 mL of acetone for 5 min by stirring and then filtered to remove residual pigments and small molecule impurities; the washed precipitate was spread on a clean tray and dried at room temperature and normal pressure for 12 h to obtain powdered high-G sodium alginate, abbreviated as LF-SA.

[0068] Verification Example 1: Fourier Transform Infrared Spectroscopic Characterization of High-G / High-M Sodium Alginate

[0069] Spectroscopic-grade potassium bromide (KBr) was dried in a drying oven at 110 °C for 4 h. The KBr was thoroughly ground in an agate mortar, compressed into tablets using a tableting mold, and subjected to background scanning on a Fourier transform infrared spectrometer (NICOLET iS10). Then, appropriate amounts of samples (Kelp-SA from Example 1 and LF-SA from Example 2) and potassium bromide were taken at a mass ratio of 1:100, thoroughly ground and mixed uniformly, and then compressed into tablets. Specifically, the scanning range was set to 4000-400 cm⁻¹. -1 The number of scans was 64, and the resolution was 1.0 cm. -1 .

[0070] Infrared spectral results as follows Figure 2 As shown, sodium alginate extracted from kelp (LJ) and giant kelp (LF) exhibits similar infrared spectra, both displaying typical characteristics of sodium alginate. However, differences exist in the position and intensity of characteristic peaks, indicating structural differences. The absorption peak in the 3000-3600 cm⁻¹ range is attributed to the OH stretching vibration. The significantly broadened peak shape of Kelp-SA indicates stronger intramolecular and intermolecular hydrogen bonding, a typical spectral characteristic of the M unit. Furthermore, Kelp-SA shows a CH stretching vibration absorption peak at 2924 cm⁻¹, a characteristic peak of the M unit. Studies indicate that sodium alginate with high G content has a higher carboxyl vibration frequency, and the asymmetric carboxyl (OCO) stretching vibration peak of LF-SA is located at 1612.20 cm⁻¹. -1 Kelp-SA is located at 1604.68 cm. -1 This indicates that LF-SA may be high-G type sodium alginate. 1400-1450 cm -1 The region represents the symmetrical carboxyl stretching vibration; the symmetrical carboxyl peak in LF-SA is located at 1403.92 cm⁻¹. -1 The peak of Kelp-SA is located at 1432.85 cm⁻¹. -1 The peak position of Kelp-SA shifts to higher wavenumbers, reflecting the electronic effects and steric hindrance characteristics of the carboxyl group in the M unit. LF-SA peaks at 1100.19 cm⁻¹ -1There is a distinct β-1,4-glycosidic bond vibration peak at 1036.55 cm⁻¹, while the corresponding peak of Kelp-SA is shifted to 1036.55 cm⁻¹. -1 800-950 cm -1 The characteristic peaks of the sugar ring also differ in the region; the peak of LF-SA is located at 812.84 cm⁻¹. -1 Kelp-SA is located at 823.45 cm. -1 These differences stem from the different sugar ring conformations of the G and M units. Therefore, based on the above differences in characteristic peaks, LF-SA is identified as high-G type sodium alginate, and Kelp-SA as high-M type sodium alginate.

[0071] Verification Example 2: 1H NMR Characterization of High G-type / High M-type Sodium Alginate

[0072] Add 0.1 g of the obtained sodium alginate (Kelp-SA in Example 1 and LF-SA in Example 2) to 100 mL of deionized water to prepare a sodium alginate solution with a concentration of 1 mg / mL. Adjust the pH of the solution to 5.6 and incubate at 100 °C for 1 h. Continue to adjust the pH to 3.8 and incubate at 100 °C for 30 min. Adjust the pH to 7-8 with NaOH and perform a single lyophilization in a vacuum freeze dryer. Dissolve the lyophilized sodium alginate sample in 5 mL of 99%~99.9% D2O and lyophilize again. Weigh 10~12 mg of the lyophilized sodium alginate sample and dissolve it in 1 mL of 99.9% D2O until completely dissolved. Pipette 0.7 mL of the sodium alginate sample into a clean disposable centrifuge tube, add 20 μL of 0.3 mol / L triethylenetetraminehexaacetic acid (TTHA), and mix well. 600 μL of sample was pipetted into an NMR sample tube, and 500 μL of the supernatant was transferred to an NMR tube. The proton NMR spectrum was detected using an Agilent 500 MHz NMR spectrometer, and the data was processed using MestReNova 9.0 software.

[0073] The results of the proton nuclear magnetic resonance spectrum are as follows: Figure 3The diagram shows the differences in molecular structure and unit composition between the two sodium alginate samples: LF-SA exhibits a distinct characteristic signal of hydrogen at the C1 position of guluronic acid (G unit) near 4.95 ppm, with a signal intensity higher than that of mannulic acid (M unit) at 4.55 ppm. Simultaneously, the hydrogen signals at the C2-C5 positions in the 3.0-4.5 ppm range show a continuous and uniform stepwise distribution, without obvious signal concentration or absence, indicating a high content of G units in the LF-SA molecular chain and the absence of obvious unit aggregation, proving that LF-SA is a high-G type sodium alginate. The 1H NMR spectrum of Kelp-SA exhibits typical characteristics of high mannulic acid. Kelp-SA shows a high-intensity single peak at 4.65 ppm, attributed to the characteristic signal of mannulic acid H1, with a signal intensity much higher than that of guluronic acid H1 at 5.04 ppm. Furthermore, the hydrogen signal in the 3.0-4.0 ppm range is mainly concentrated at the characteristic chemical shifts of the C2-C5 positions of mannuronic acid (M unit), while the signal of the C2-C5 positions of guluronic acid (G unit) is significantly weakened and dispersed. These spectroscopic characteristics indicate that mannuronic acid dominates in the Kelp-SA molecular chain, and the M units exist in a blocky form of long chain segments, while the G units are only dispersed and interspersed between the M units as short chain segments. This confirms that Kelp-SA is a high-M type sodium alginate.

[0074] Verification Example 3: X-ray diffraction characterization of high-G / high-M type sodium alginate

[0075] The crystal structure of the samples (Kelp-SA in Example 1 and LF-SA in Example 2) was determined by X-ray diffraction (XRD) with a scanning diffraction angle 2θ ranging from 5° to 60°, a scanning speed of 5° / min, and an accelerating voltage of 40 kV.

[0076] The results are as follows Figure 4As shown, the XRD patterns of both Kelp-SA and LF-SA exhibit broad diffraction peaks without sharp characteristic peaks, indicating that they are both semi-crystalline or low-crystallinity polysaccharide materials. This is a typical characteristic of sodium alginate, stemming from the combination of locally ordered arrangement of its linear polysaccharide chains and its overall amorphous morphology. LF-SA has a sharp small peak at 2θ=11.28° and a main diffraction peak near 20°, which is a typical diffraction feature of sodium alginate, corresponding to the locally ordered arrangement of mannuronic acid (M) and guluronic acid (G) units in its molecular chain. Kelp-SA's main diffraction peak is also located near 20°, but the peak shape is wider, and there is no sharp small peak at 2θ≈10°. Its overall diffraction intensity is significantly higher than that of LF-SA, indicating that LF-SA has a higher proportion of locally ordered structures and slightly stronger crystallinity. The peak positions of the two samples are close, indicating that their basic polysaccharide chain backbone structures are consistent. The differences in peak shape and intensity reflect their differences in molecular chain regularity and aggregation state, which may stem from differences in raw material sources, leading to changes in the proportion of uronic acid units, chain length, and intermolecular forces.

[0077] The above examples are merely illustrative of the technical concept and features of this invention and should not be construed as limiting the scope of protection of this invention. All equivalent transformations or modifications made based on the essence of this invention should be included within the scope of protection of this invention.

Claims

1. A method for preparing high-G / high-M sodium alginate, characterized in that, Includes the following steps: (1) Raw material pretreatment: Selected Chinese farmed kelp Laminaria japonica (LJ) or Chilean wild giant kelp Lessonia flavicans (LF) is used as raw material. The raw material is washed, dried, crushed and sieved in sequence to obtain algae powder. (2) Ethanol decolorization: The algae powder obtained in step (1) was treated with anhydrous ethanol as the decolorizing agent. The ethanol concentration was 90% to 100% by volume, the liquid-solid ratio was 2:1 to 4:1, and the decolorization time was 2 to 4 hours. After decolorization, the algae powder was filtered, and the filter residue was collected and dried naturally under room temperature conditions to obtain decolorized algae powder. (3) Acid pretreatment: Add deionized water to the decolorized algae powder obtained in step (2), stir and disperse evenly, adjust the pH of the system to 0.5~1.5 with HCl, stir for 1~3 hours at room temperature for acid treatment; after the acid treatment is completed, filter and discard the supernatant, collect the filter residue, rinse the filter residue with deionized water until the pH reaches 3.5~4.5, drain the water and obtain algae filter residue; (4) Alkali extraction: Add sodium carbonate solution to the algal residue obtained in step (3) to extract algal powder. The sodium carbonate concentration is 0.4-0.6 mol / L and the liquid-solid ratio is 40:1-60:

1. Let it stand overnight at room temperature. After extraction, filter and collect the supernatant. (5) Alcohol precipitation: Add anhydrous ethanol to the supernatant obtained in step (4) until the final ethanol volume concentration of the system reaches 65%~75%. After stirring evenly, let it stand at room temperature for 0.5~1.5h. After standing, filter and collect the milky white flocculent precipitate. (6) Washing and drying: The milky white flocculent precipitate obtained in step (5) was washed successively with methanol and acetone. After washing, it was dried at room temperature to obtain high G-type or high M-type sodium alginate.

2. The preparation method according to claim 1, characterized in that, In step (1), the specific operation process of the raw material pretreatment is as follows: select kelp LJ and giant kelp LF as raw materials, rinse with clean water 2 to 4 times to remove mud and impurities, and then dry at 60 to 70°C for 12 to 36 hours. After the dried material is crushed, it is passed through a 30 to 50 mesh sieve to obtain algae powder.

3. The preparation method according to claim 1, characterized in that, In step (2), the ethanol decolorization is carried out with the following conditions: when the raw material is kelp LJ, the volume concentration of ethanol is 100%, the liquid-to-solid ratio is 2:1, and the decolorization time is 3 h; when the raw material is giant kelp LF, the volume concentration of ethanol is 100%, the liquid-to-solid ratio is 2:1, and the decolorization time is 2 h; after decolorization, the solid and liquid are separated by sieving through a 20-mesh sieve, the filter residue is collected, and the residue is naturally dried in a ventilated environment at room temperature for 24 h to obtain decolorized algae powder.

4. The preparation method according to claim 1, characterized in that, In step (3), during acid pretreatment, the pH of the system is adjusted to 1.0±0.1 with HCl, and the system is stirred for 2 hours at room temperature for acid treatment. The filter residue is then rinsed with deionized water until the pH reaches 4.0±0.

1.

5. The preparation method according to claim 1, characterized in that, In step (4), the sodium carbonate concentration is 0.6 mol / L and the liquid-to-solid ratio is 60:1 during alkaline extraction. The mixture is allowed to stand at room temperature for 12 hours overnight. After extraction, the mixture is filtered through a 20-mesh sieve and the supernatant is collected.

6. The preparation method according to claim 1, characterized in that, In step (5), during alcohol precipitation, anhydrous ethanol is added to the supernatant until the ethanol concentration in the system is 70%, and the standing time is 1 hour.

7. The preparation method according to claim 1, characterized in that, In step (6), the obtained milky white flocculent precipitate is first washed with methanol for 5 min, filtered, then washed with acetone for 5 min, filtered, and the precipitate obtained after washing is dried at room temperature for 12 h to obtain high G-type or high M-type sodium alginate.

8. A high-M type sodium alginate, characterized in that, Therefore, Chinese kelp farming Laminaria japonica The product is prepared from kelp using the preparation method described in any one of claims 1-7.

9. A high-G type sodium alginate, characterized in that, It is wild giant kelp from Chile Lessonia flavicans It is obtained by preparing it from raw materials using the preparation method described in any one of claims 1-7.

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