Extraction method of laminarin

Abstract

The invention discloses an extraction method of laminarin. The method comprises the following steps: 1) pretreating wet kelp by adopting steam explosion, drying and crushing to obtain powder; 2) carrying out first extraction on the powder by adopting a first organic solvent, and carrying out solid-liquid separation to obtain a first precipitate; (3) carrying out secondary extraction on the first precipitate and an inorganic solvent, and carrying out solid-liquid separation to obtain supernate; 4, the supernate and a second organic solvent are subjected to third extraction and solid-liquid separation, a second precipitate is obtained, and the laminarin is obtained.By means of the extraction method, the extraction rate of the laminarin can be increased, the molecular weight of the laminarin can be reduced, and the uronic acid content can be increased.

Description

Technical Field

[0001] This invention belongs to the field of marine plant extraction technology, specifically relating to a method for extracting kelp polysaccharides. Background Technology

[0002] Kelp is a perennial edible and economically important seaweed, widely used in the food and pharmaceutical industries due to its rich content of carbohydrates, vitamins, and minerals. Kelp polysaccharides are one of the important bioactive substances in kelp, possessing multiple benefits. Kelp polysaccharides can scavenge free radicals and resist oxidation, delaying aging; they can also help regulate blood sugar and lipids, aiding in metabolic balance; and they can promote the proliferation of beneficial bacteria in the intestines, maintaining intestinal microecological balance. Currently, the main extraction methods for kelp polysaccharides include water extraction, acid extraction, alkali extraction, enzyme extraction, and ultrasound-assisted extraction. Water extraction is low-cost but has a low extraction rate; acid-alkali extraction has relatively high extraction efficiency but introduces chemical reagents, posing safety risks; enzyme extraction has minimal environmental impact but requires stringent reaction conditions and is costly; ultrasound-assisted extraction has a relatively high extraction rate but is difficult to scale up. Therefore, the low extraction rate of kelp polysaccharides currently hinders the industrialization of kelp. Therefore, exploring an economical, safe, and high-extraction-rate method for preparing kelp polysaccharides is crucial for the development of kelp in the food and pharmaceutical fields.

[0003] Steam explosion technology is a novel physical modification technique that utilizes a combination of high-temperature, high-pressure steam and instantaneous decompression to disrupt the physicochemical structure of materials. It is widely used in natural product extraction and food processing. Steam explosion achieves efficient material crushing through "steam energization-pressure release," combining physical crushing with mild chemical modification. It avoids the damage to active ingredients caused by strong chemical reagents or extreme temperatures, making it particularly suitable for extraction processes requiring preservation of natural product activity. It is currently one of the most efficient technologies in biomass pretreatment and natural product extraction. However, the impact of steam explosion pretreatment on the extraction rate and structure of kelp polysaccharides remains unclear, limiting the diversification of kelp products and the industrial application of kelp polysaccharides. Therefore, researching the optimal parameters for steam explosion extraction of kelp polysaccharides and the impact of steam explosion on the structure of kelp polysaccharides is crucial.

[0004] CN102367283B discloses a kelp polysaccharide, its extraction method, and its application. The extraction method involves: pulverizing kelp, adding water, and extracting at 105–125°C for 2–5 hours; filtering to obtain an extract; concentrating the extract to a solid content of 35–45%; adding ethanol to the concentrate, mixing thoroughly, and allowing it to stand at 0–4°C for 4–12 hours; filtering to precipitate the polysaccharide; and freeze-drying to obtain the kelp polysaccharide. The kelp polysaccharide is prepared into a solution at 0.01–1.0% of the tobacco weight and added to the tobacco or filter tip by spraying. This effectively reduces the free radical content in mainstream cigarette smoke, with a reduction of over 18%. However, this patent uses a hot water extraction method to extract the kelp polysaccharide, which suffers from a low extraction rate.

[0005] CN101785562B discloses a method for the complete utilization of kelp biomass to prepare various products. The method involves cutting kelp into small segments and subjecting them to steam explosion treatment at 0.6-1.5 MPa for 2-20 minutes, followed by digestion with sodium carbonate solution to produce sodium alginate, dietary fiber, iodine, pigments, and other products. This patent utilizes steam explosion technology to extract kelp components primarily composed of sodium alginate, while also considering other byproducts (iodine, mannitol, etc.). It does not address polysaccharides or their activity. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for extracting kelp polysaccharides to solve the problems in the prior art.

[0007] To achieve the above and other related objectives, the present invention is obtained through the following technical solution.

[0008] One objective of this invention is to provide a method for extracting kelp polysaccharides, comprising the following steps: 1) Wet kelp was pretreated by steam explosion, dried, and pulverized to obtain powder; 2) The powder is subjected to a first extraction with a first organic solvent, followed by solid-liquid separation to obtain a first precipitate; 3) The first precipitate and inorganic solvent are subjected to a second extraction to separate the solid and liquid, and a supernatant is obtained; 4) The supernatant and the second organic solvent are subjected to a third extraction, and solid-liquid separation is performed to obtain the second precipitate, which is the kelp polysaccharide.

[0009] In some embodiments, in 1), the pressure of the steam explosion pretreatment is 0.8 MPa.

[0010] In some embodiments, in 1), the steam explosion pretreatment time is 45 seconds.

[0011] In some embodiments, in 1), the particle size of the powder is 200 mesh.

[0012] In some embodiments, in step 2), the first organic solvent is ethanol. This application utilizes ethanol as the first organic solvent, which not only performs extraction but also decolorizes and degreases.

[0013] In some embodiments, in step 2), the mass ratio of the powder to the first organic solvent is 1 mg:(5-15) mL. Preferably, it is 1 g:10 mL (w / v).

[0014] In some embodiments, in step 2), the temperature of the first extraction is 50-70°C. Preferably, it is 60°C.

[0015] In some embodiments, in 3), the inorganic solvent is selected from water. The use of water extraction after alcohol extraction in this application is mainly for precipitating polysaccharides to separate water-soluble small molecule impurities. In alcohol extraction, the polarity difference of ethanol is used to reduce the solubility of polysaccharides in the solvent, while simultaneously making it easier for lipid-soluble impurities and small molecule organic matter to dissolve.

[0016] In some embodiments, in step 3), the mass ratio of the first precipitate to the inorganic solvent is 1 mg: (40-60) mL. Preferably, it is 1 g: 50 mL (w / v).

[0017] In some embodiments, in step 3), the temperature of the second extraction is 80-100°C. Preferably, it is 90°C.

[0018] In some embodiments, in step 4), the second organic solvent is selected from ethanol. This application uses ethanol as the second organic solvent to achieve the precipitation of polysaccharide alcohols.

[0019] In some embodiments, in step 4), the volume ratio of the supernatant to the second organic solvent is 1:(2-4). Preferably, it is 1 mL:3 mL.

[0020] In some embodiments, in step 4), the temperature of the third extraction is 2-6°C. Preferably, it is 4°C.

[0021] In some embodiments, the molecular weight of the kelp polysaccharide is <10 × 10⁻⁶. 5 Da.

[0022] In some embodiments, the kelp polysaccharide comprises mannulic acid.

[0023] In some embodiments, the content of mannuronic acid is >49% based on the total mass of kelp polysaccharides.

[0024] In some embodiments, the kelp polysaccharide comprises 24.01 wt% fucose, 0.42 wt% rhamnose, 5.58 wt% galactose, 0.53 wt% glucose, 1.82 wt% xylose, 3.57 wt% mannose, 5.45 wt% guluronic acid, 8.64 wt% glucuronic acid, and 49.98 wt% mannuronic acid.

[0025] Using the kelp polysaccharide extracted in this application as a carbon source, Lactobacillus rhamnosus (LGG) can be inoculated to achieve rapid proliferation of LGG and high production of lactic acid and acetic acid.

[0026] Compared with the prior art, the present invention has the following beneficial effects: 1) The extraction method of the present invention, which combines steam explosion with secondary organic solvent (alcohol extraction) and primary water extraction, yields a high extraction rate of kelp polysaccharides, which is 3.06 times higher than that of the traditional water extraction method. 2) The extraction method of the present invention, which combines steam explosion with secondary organic solvent (alcohol extraction) and primary water extraction, has a significant decolorizing effect on kelp.

[0027] 3) This invention breaks through the limitations of traditional extraction methods that rely on high temperature or chemical reagents. It is the first to use steam explosion as a pretreatment method for kelp polysaccharide extraction. It achieves efficient extraction through physical action, avoids chemical residues and structural damage, and is low in cost, making it suitable for large-scale production.

[0028] 4) The extraction method of this invention can efficiently disrupt the cell wall structure of kelp through the physical action of instantaneous high-pressure release, making the polysaccharides more easily soluble and preserving their natural structure. This avoids the glycosidic bond breakage caused by high-temperature water extraction, thereby reducing the molecular weight of kelp polysaccharides, increasing uronic acid content, and promoting the production of acetic acid and lactic acid by *Lactobacillus rhamnosus* LGG. Therefore, compared with water extraction, it has a greater potential effect on promoting the bioactivity of kelp polysaccharides, achieving a dual positive impact on extraction efficiency and bioactivity. Attached Figure Description

[0029] Figure 1 The graph shows the effect of steam explosion pressure, time, and particle size on the extraction rate of kelp polysaccharides in Example 2.

[0030] Figure 2 denoted as , where a represents steam-exploded kelp polysaccharide; b represents water-extracted kelp polysaccharide.

[0031] Figure 3This is the monosaccharide composition of the kelp polysaccharide in Example 3. Wherein, STD: standard curve; LJP: water-extracted kelp polysaccharide; LJPS: steam-exploded kelp polysaccharide; mannuronic acid: Man-UA, fucose: Fuc, galactose: Gal, glucuronic acid: Glc-UA, mannose: Man, xylose: Xyl, glucose: Glc, guluronic acid: Gul-UA, rhamnose: Rha, arabinose: Ara, fructose: Fru, Gal-UA: galacturonic acid, Rib: ribose.

[0032] Figure 4 The graph shows the effect of the extraction method of the present invention used in Example 3 on the promotion of lactic acid production by LGG by kelp polysaccharides.

[0033] Figure 5 The graph shows the effect of the extraction method of the present invention used in Example 3 on the content of acetic acid produced by LGG from kelp polysaccharides. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the described contents. Unless otherwise specified, the methods in this embodiment are operated according to conventional methods, and the reagents used are conventional reagents unless otherwise specified.

[0035] The following embodiments of this application do not restrict the use of kelp, which can be obtained through commercial channels such as Walmart, and can be either wet or dried kelp.

[0036] The LGG strain used in this application was purchased from the Culture Collection Library (CICC), and its 16S rRNA sequence is as follows.ACTTAGACGGCTCGCTCCCTAAAAGGGTTACGCCACCGGCTTCGGGTGTTACAAACTCTCATGGTGTGACGGGCGGTGTGTACAAGGCCCGGGAACGTATTCACCGCGGCGTGCTGATCCGCGATTACTAGCGATTCCGACTTCGTGTAGGCGAGTTGCAGCCTACAGTCCGAACTGAGAATGGCTTTAAGAGATTAGCTTGACCTCGCGGTCTCGCAACTCGTTGTACCATCCATTGTAGCACGTGTGTAGCCCAGGTCATAAGGGGCATGATGATTTGACGTCATCCCCACCTTCCTCCGGTTTGTCACCGGCAGTCTTACTAGAGTGCCCAACTAAATGCTGGCAACTAGTCATAAGGGTTGCGCTCGTTGCGGGACTTAACCCAACATCTCACGACACGAGCTGACGACAACCATGCACCACCTGTCATTTTGCCCCCGAAGGGGAAACCTGATCTCTCAGGTGATCAAAAGATGTCAAGACCTGGTAAGGTTCTTCGCGTTGCTTCGAATTAAACCACATGCTCCACCGCTTGTGCGGGCCCCCGTCAATTCCTTTGAGTTTCAACCTTGCGGTCGTACTCCCCAGGCGGAATGCTTAATGCGTTAGCTGCGGCACTGAAGGGCGGAAACCCTCCAACACCTAGCATTCATCGTTTACGGCATGGACTACCAGGGTATCTAATCCTGTTCGCTACCCATGCTTTCGAGCCTCAGCGTCAGTTACAGACCAGACAGCCGCCTTCGCCACTGGTGTTCTTCCATATATCTACGCATTTCACCGCTACACATGGAGTTCCACTGTCCTCTTCTGCACTCAAGTTTTCCCAGTTTCCGATGCACTTCCTCGGTTAAGCCGAGGGCTTTCACATCAGACTTAAAAAACCGCCTGCGCTCGCTTTACGCCCAATAAATCCGGATAACGCTTGCCACCTACGTATTACCGCGGCTGCTGGCACGTAGTTAGCCG。 Example 1 This embodiment provides a method for extracting kelp polysaccharides, including the following steps: 1. Soak dried kelp, wash and tear it into pieces, then put it into a steam explosion chamber (QBS-200, Qingzheng Ecological Technology Co., Ltd., China) and pre-treat the kelp at 0.8 MPa for 45 seconds. Dry, crush and pass through a 200-mesh sieve to obtain kelp powder.

[0037] 2. Weigh 40 g of kelp powder and defatt it with anhydrous ethanol (1:10, w / v) at 60℃ for 3 h, then centrifuge at 4000 r / min for 20 min to obtain the precipitate.

[0038] 3. Mix the precipitate with deionized water at a mass-to-volume ratio of 1g:50mL at 90℃ for 3 h, and centrifuge at 4000 r / min for 20 min to obtain the supernatant.

[0039] 4. Add three volumes of pre-cooled ethanol (95%, v / v) to the supernatant and incubate overnight at 4°C. Filter the mixture through a filter cloth and centrifuge the collected alcohol precipitate at 4000 r / min for 20 min. Then, dissolve the precipitate uniformly in deionized water and freeze-dry under vacuum to obtain kelp polysaccharide.

[0040] Example 2 In this Example 2, the steam explosion pressure, steam explosion time, and particle size were selected; all other parameters were the same as in Example 1. These include: 2.1 Single-factor experiment 2.1.1 Screening of Steam Explosion Pressure X1 Shredded kelp was placed under steam at pressures of 0, 0.2, 0.4, 0.6, 0.8, and 1.0 MPa for 45 seconds to investigate the effect of steam explosion pressure X1 on kelp polysaccharides.

[0041] 2.1.2 Screening of Steam Explosion Time X2 Shredded kelp was placed under 0.8 MPa and steam-exploded for 0, 15, 30, 45, 60 and 75 s to investigate the effect of steam explosion time X2 on kelp polysaccharides.

[0042] 2.1.3 Screening of kelp particle size X3 Shredded kelp was subjected to steam explosion treatment at 0.8 MPa for 45 s, dried, and then pulverized into 40, 80, 120, 160, and 200 mesh sizes to investigate the effect of particle size X3 on kelp polysaccharides.

[0043] The effects of single-factor factors X1, X2, and X3 on kelp polysaccharides were examined by calculating the extraction rate.

[0044] Each single-factor experiment included a control group C. The control group C differed from Example 1 in that it did not undergo steam explosion, but was otherwise the same as Example 1, namely, only alcohol extraction + water extraction + alcohol extraction (also referred to as water extraction in this application).

[0045] Extraction rate of kelp polysaccharides: The ratio of the mass of kelp polysaccharides after vacuum freeze-drying to the mass of kelp powder obtained by passing through a sieve of the corresponding mesh size. Results are shown below. Figure 1 .

[0046] from Figure 1 As shown in Figure a, the extraction rate of kelp polysaccharides showed a trend of first increasing and then decreasing with the increase of steam explosion pressure. The extraction rates of kelp polysaccharides were relatively high at steam explosion pressures of 0.6 MPa, 0.8 MPa and 1.0 MPa. In particular, at 0.8 MPa, the extraction rate of kelp polysaccharides reached 133.2 mg / g, which was 2.31 times that of the 57.7 mg / g of kelp polysaccharides obtained from control group C.

[0047] from Figure 1 As shown in b, the extraction rate of kelp polysaccharides was relatively high at steam explosion times of 45s, 60s, and 75s. At a steam explosion time of 45s, the yield of kelp polysaccharides reached the maximum of 171.3 mg / g, which was 2.97 times higher than that of the control group C.

[0048] from Figure 1 As shown in Figure c, the extraction rate of kelp polysaccharides increases with increasing particle size. The extraction rates of kelp polysaccharides are relatively high at 120 mesh, 160 mesh, and 200 mesh, and smaller particle size is associated with higher polysaccharide yield. The maximum yield of LJP at 200 mesh is 176.8 mg / g, which is 3.06 times higher than that of the control group C.

[0049] 2.2 Orthogonal Experiment To further investigate the effects of steam explosion pressure, time, and particle size on the extraction rate of seaweed polysaccharides, an orthogonal experiment was designed, and a three-factor, three-level L9 (3) model was constructed. 3 The specific experimental parameters and ranges are shown in Table 1. The kelp polysaccharide pretreated by steam explosion was named LJPS.

[0050] Table 1. Factors and levels of orthogonal experiments An orthogonal experiment was conducted to investigate the extraction rate of kelp polysaccharides. The results are shown in Tables 2 and 3.

[0051] Table 2 Orthogonal Experiment L9 (3) 3 result Table 3. Results of variance and significance analysis As shown in Tables 2 and 3, the yield of kelp polysaccharides reached its maximum of 181.53 mg / g (equivalent to an extraction rate of 18.15%) when the steam explosion pressure was 0.8 MPa, the steam explosion time was 45 s, and the particle size was 200 mesh, which is 3.15 times that of water extraction (Table 2). Interestingly, the orthogonal experimental results indicate that the maximum extraction rate of kelp polysaccharides is lower than that of the single-factor experiment.

[0052] In summary, steam explosion technology can significantly improve the extraction rate of kelp polysaccharides, which is 3.15 times that of water extraction. The optimal parameters are a steam explosion pressure of 0.8 MPa, a steam explosion time of 45 s, and a material particle size of 200 mesh.

[0053] Example 3 In this embodiment, the molecular weight and monosaccharide composition of the kelp polysaccharide obtained in Example 1 were characterized, including: 3.1 Molecular weight Kelp polysaccharides obtained by steam explosion treatment and water extraction were dissolved in 0.1 mol / L NaNO3 solution, respectively. The molecular weight of the kelp polysaccharides was determined using a high-performance liquid chromatograph (HPLC) equipped with an Ultrahydrogel™ Linear column (300 mm × 7.8 mmid). The parameters were: mobile phase 0.1 mol / L NaNO3, flow rate 0.5 mL / min, and column temperature maintained at 40℃.

[0054] 3.2 Monosaccharide Composition 5 mg of steam-explosion-treated kelp polysaccharide and water-extracted kelp polysaccharide were accurately weighed into clean chromatographic vials. 1 mL of 2 mol / L trifluoroacetic acid solution was added, and the mixture was heated at 121 °C for 2 h. The mixture was dried under nitrogen, washed with 99.99% methanol, and dried again. This washing process was repeated 2-3 times. Finally, the dried sample was dissolved in sterile water and transferred to a chromatographic vial for analysis. The sample was then analyzed using high-performance anion exchange chromatography (HPLC) with a CarboPac PA-20 anion exchange column (150 mm × 3 mm, 6.5 μm) and a pulsed amperometric detector (Dionex ICS 5000+) at a flow rate of 0.5 mL / min and an injection volume of 5 μL.

[0055] The molecular weight detection results are shown below. Figure 2 The results of the polysaccharide content test are shown below. Figure 3 .

[0056] from Figure 2As shown in section a, the molecular weight of kelp polysaccharide obtained using the method of this application is 9.56 × 10⁻⁶. 5 Compared to water extraction, steam explosion pretreatment can reduce the molecular weight of kelp polysaccharides. It has been reported that lower molecular weight polysaccharides can relatively enhance their bioactivity.

[0057] from Figure 2 As shown in b, the molecular weight of kelp polysaccharide obtained by water extraction is 1.012 × 10⁻⁶. 6 Da.

[0058] from Figure 3 It is known that the monosaccharide composition of the kelp polysaccharide (LJPS) obtained in this application is as follows: fucose 24.01 wt%, rhamnose 0.42 wt%, galactose 5.58 wt%, glucose 0.53 wt%, xylose 1.82 wt%, mannose 3.57 wt%, guluronic acid 5.45 wt%, glucuronic acid 8.64 wt%, and mannuronic acid 49.98 wt%.

[0059] from Figure 3 As can be seen from the data, the monosaccharide composition of kelp polysaccharide (LJP) obtained by water extraction is as follows: 34.56 wt% mannuronic acid, 30.55 wt% fucose, 10.63 wt% galactose, 7.52 wt% glucuronic acid, 6.66 wt% mannose, 3.74 wt% xylose, 3.62 wt% glucose and 2.72 wt% guluronic acid.

[0060] 3.3 Effects of extracted kelp polysaccharides on acetic acid and lactic acid production by Lactobacillus rhamnosus (LGG) LGG was activated twice in MRS broth until the OD of the bacterial culture was reached. 600 The value was 0.3177. The culture was then divided into two groups. One group was inoculated with bacterial culture at a volume ratio of 1:50 into MRS medium containing 1 wt% LJP as the carbon source. The other group was inoculated with bacterial culture at a volume ratio of 1:50 into MRS medium containing 1 wt% LJP as the carbon source. The contents of acetic acid and lactic acid were observed at 0, 12, and 24 hours of fermentation. The composition of the MRS medium was: peptone 10 g / L, beef extract 8 g / L, yeast extract 4 g / L, glucose 20 g / L, dipotassium hydrogen phosphate 2 g / L, diammonium hydrogen citrate 2 g / L, sodium acetate 5 g / L, magnesium sulfate 0.2 g / L, manganese sulfate 0.04 g / L, agar 14 g / L, and Tween 80 1 g / L.

[0061] (1) Determination of lactic acid: The lactic acid content in the fermentation broth was analyzed using a glucose / lactic acid analyzer (BIOSEM C-line, EKF Diagnostic, Germany). Specifically, 10 μL of the fermentation sample was diluted with solvent (EKF Diagnostic, Germany), and the lactic acid content was determined through the automatic detection channel.

[0062] (2) Determination of acetic acid: The concentration of acetic acid produced by LGG was determined using a gas chromatography-mass spectrometry system equipped with an Agilent DB-FFAP column (30m×0.250×mm×0.25μm). During the entire fermentation process, 200μL of fermentation broth was collected at 0, 12, and 24 hours, respectively. The fermentation broth was then mixed with 200μL of 15% phosphoric acid and extracted with anhydrous diethyl ether. The supernatant was then used to determine the acetic acid concentration using gas chromatography-mass spectrometry. The column temperature program was set as follows: initial temperature 90℃, increased to 120℃ at 10℃ / min, then increased to 245℃ at 25℃ / min, and held at 245℃ for 2 min.

[0063] from Figure 4 It can be seen that both LJP and LJPS can promote lactic acid production by LGG. The lactic acid content in the LJPS group reached its peak at 12 hours, reflecting that LGG achieves rapid proliferation using LJPS. When using LGG for fermentation, the lactic acid content in the LJP group also reached its highest value at 12 hours.

[0064] from Figure 5 It can be seen that the acetic acid content reached its highest level at the end of fermentation using LGG in both the LJP and LJPS groups. Notably, the acetic acid content in the LJPS group was higher than that in the LJP group at 24 hours of fermentation. In summary, the results indicate that LGG can effectively metabolize LJPS to produce lactic acid and acetic acid.

[0065] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: after steam explosion, water extraction was performed first, followed by alcohol extraction, without performing a first alcohol extraction.

[0066] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 was directly extracted with alcohol after steam explosion, without water extraction.

[0067] The extraction rate and color difference composition obtained by using the gas explosion + alcohol extraction method are shown in Table 3.

[0068] The products obtained in Example 1, Water Extraction Method, Comparative Example 1, and Comparative Example 2 of this application were subjected to color difference detection using an ADCI-60-C fully automatic colorimeter manufactured by Beijing Chentek Instrument Technology Co., Ltd. The average initial L, a, b values ​​and ΔE value of the samples were recorded, and the results are shown in Table 3.

[0069] The extraction rates of the products obtained from Examples 1, 2, 3, and 4 of this application, using water extraction, comparative example 1, and comparative example 2, are shown in Table 3.

[0070] In a colorimeter, L represents lightness / darkness (black and white), a represents red / green, and b represents yellow / blue.

[0071] The L value represents the brightness of a color, ranging from 0 to 100. 0 represents black, and 100 represents white.

[0072] The a value represents the redness or greenness of a color; a positive value indicates a reddish tint, while a negative value indicates a greenish tint.

[0073] The b-value represents the yellow-blue tint of a color; a positive value indicates a yellowish tint, while a negative value indicates a bluish tint.

[0074] The larger the difference in ΔE between other methods and the method of Embodiment 1 of this application, the greater the difference in decolorization between the other methods and the method of this application when extracting kelp polysaccharides; the smaller the difference in ΔE, the smaller the color difference. Generally, when ΔE < 1, the color difference is difficult for the human eye to perceive; when ΔE = 1-3, the color difference can be perceived; when ΔE > 3, the color difference is very obvious.

[0075] Table 3 Table 3 shows that the ΔE difference between the water extraction method and the method of this application is >3, indicating a significant color difference between the kelp polysaccharides obtained by the two methods, with the kelp polysaccharides obtained by the method of this application being lighter in color. The ΔE difference between Comparative Example 1 and the method of this application is 1-3, indicating a color difference between the kelp polysaccharides obtained by Comparative Example 1 and the method of this application, with the kelp polysaccharides obtained by the method of this application being lighter in color. Comparative Example 2 only used one alcohol extraction and did not use water extraction, resulting in a larger ΔE, indicating a poorer decolorization effect. In summary, the method of this application not only has a high extraction rate but also a good decolorization effect on kelp.

[0076] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for extracting kelp polysaccharides, characterized in that, Includes the following steps 1) Wet kelp was pretreated by steam explosion, dried, and pulverized to obtain powder; 2) The powder is subjected to a first extraction with a first organic solvent, followed by solid-liquid separation to obtain a first precipitate; 3) The first precipitate and inorganic solvent are subjected to a second extraction to separate the solid and liquid, and a supernatant is obtained; 4) The supernatant and the second organic solvent are subjected to a third extraction, and solid-liquid separation is performed to obtain the second precipitate, which is the kelp polysaccharide.

2. The method as described in claim 1, characterized in that, In step 1), the pressure of the steam explosion pretreatment is 0.8 MPa; And / or, in 1), the steam explosion pretreatment time is 45s; In and / or, in 1), the particle size of the powder is 200 mesh.

3. The method as described in claim 1, characterized in that, In step 2), the first organic solvent is ethanol; In and / or 2), the temperature of the first extraction is 50-70°C; preferably 60°C.

4. The method as described in claim 1, characterized in that, In step 3), the inorganic solvent is selected from water; In and / or 3), the temperature of the second extraction is 80-100°C; preferably 90°C.

5. The method as described in claim 1, characterized in that, In step 4), the second organic solvent is selected from ethanol; And / or, in 4), the temperature of the third extraction is 2-6°C.

6. The method as described in claim 1, characterized in that, In step 2), the mass ratio of the powder to the first organic solvent is 1 mg: (5-15) mL; preferably 1 g: 10 mL. In and / or 3), the mass-to-volume ratio of the first precipitate to the inorganic solvent is 1 mg:(40-60) mL; preferably 1 g:50 mL. In and / or 4), the volume ratio of the supernatant to the second organic solvent is 1:(2-4); preferably 1:

3.

7. The method as described in claim 1, characterized in that, The solid-liquid separation is performed by centrifugation.

8. The method as described in claim 1, characterized in that, The molecular weight of the kelp polysaccharide is <10×10. 5 Da.

9. The method as described in claim 1, characterized in that, The kelp polysaccharide contains mannouronic acid.

10. The method as described in claim 9, characterized in that, Based on the total mass of kelp polysaccharides, the content of mannuronic acid is >49%.

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