Method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp

Abstract

The present invention provides a method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp. The present invention uses kelp as a raw material. While extracting the seaweed iodine, the by-product generated by the extraction of the seaweed iodine can also be used as a raw material. The high-purity mannitol is extracted by a Soxhlet extraction combined with ultrasonic oscillation method. Therefore, while producing qualified seaweed iodine solution, the by-product mannitol can be purified and comprehensively utilized, thereby maximizing resource utilization.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and particularly relates to a method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp. Background Art

[0002] The natural iodine cycle makes the ocean a major source of iodine. Seaweed, particularly kelp, is the richest source of iodine. Kelp has the ability to concentrate iodine from the ocean, resulting in high iodine concentrations. For example, kelp generally contains between 0.2% and 0.8%, with some reaching over 1%. Studies have shown that iodine in seaweed exists in both organic and inorganic forms, with organic iodine being directly absorbed and utilized by the human body. Compared to inorganic iodine, organic iodine is more stable and less toxic, leading to increasing research on its use for iodine supplementation. Studies on the iodine supplementation effects of kelp's bioactive iodine in animals have shown that active iodine is safer than inorganic iodine and can also prevent and treat hyperiodine-induced goiter. Some experts suggest replacing imported inorganic iodine with organic iodine from kelp. Research on the chemical speciation and preparation methods of iodine in kelp could provide a theoretical basis for more effective utilization of kelp's iodine. The development and application of independent bioactive iodine in kelp would have broad market prospects and far-reaching social benefits.

[0003] Seaweed iodine is made from kelp through physical processing techniques such as water extraction, purification, and concentration. It is rich in kelp's natural components, such as iodine, mannitol, and soluble fucoidan, and has a unique kelp flavor. Based on its raw material source and to distinguish it from mineral iodine, it is named seaweed iodine. On December 21, 2018, the state issued the "National Food Safety Standard for Seaweed Iodine GB1903.39-2018," which clearly states that "this standard applies to seaweed iodine, a food nutritional supplement made from kelp through extraction, purification, concentration, sterilization, and filling." It also stipulates the content standards: a dark brown, viscous liquid with a unique kelp flavor and no odor, an iodine (I) content of 3.0-5.0%, a fucoidan content greater than 0.3%, and a mannitol content greater than or equal to 7.0%. In fact, when using kelp as a raw material to extract seaweed iodine, a large amount of sodium chloride and mannitol mixture is produced. If this part of solid waste is discarded, it will not only cause a waste of resources, but is also more likely to cause further environmental pollution problems. Mannitol is an important fine chemical product widely used in medicine, food, chemical industry and related fields. With the continuous deepening of scientific research, the application field of mannitol is also constantly expanding. Therefore, how to effectively separate and extract the mannitol byproduct from the salt-containing solid mixture to achieve the required purity of the mannitol product during the seaweed iodine extraction process is an attractive separation technology.

[0004] A Chinese patent (Patent No. CN200510044407.5) discloses a method for extracting mannitol from kelp. However, this method is only applicable to extracting mannitol after extracting elemental iodine from kelp. It is not suitable for separating and extracting mannitol products with the required purity from byproducts containing large amounts of salt and sugar during the seaweed iodine extraction process. A Chinese patent (Patent No. CN201110043272.6) discloses an integrated reaction and separation method and apparatus for producing mannitol. This method is used for purifying mannitol produced by electrolysis of glucose, but is not suitable for separating and extracting mannitol products with the required purity from byproducts containing large amounts of salt and sugar during the seaweed iodine extraction process. Traditional kelp mannitol production technologies generally use evaporation crystallization and electrodialysis reverse osmosis. Evaporation crystallization is suitable for solutions with high mannitol content (above 15%) and low salt content and requires a large amount of energy. Electrodialysis reverse osmosis: It requires a large amount of electricity and membrane materials. The operating cost of this technology is still relatively high, and it does not fundamentally change the problem of the existing high cost of mannitol production. Summary of the Invention

[0005] In response to the above problems, the present invention provides a method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp. While using kelp as a raw material to extract seaweed iodine, the present invention can also use the by-products produced by the extraction of seaweed iodine as raw materials to extract high-purity mannitol by Soxhlet extraction combined with ultrasonic oscillation. This allows the by-product mannitol to be purified and comprehensively utilized while producing qualified seaweed iodine solution, thereby maximizing resource utilization.

[0006] The present invention is achieved through the following technical solutions.

[0007] A method for continuously extracting seaweed iodine and mannitol from kelp is characterized by comprising the following steps:

[0008] 1) chopping the dried kelp and soaking it in water, centrifuging it after the soaking is completed, collecting the centrifugal supernatant and the soaking liquid, combining them, filtering them, and collecting the filtrate to obtain the kelp extract;

[0009] 2) adding 2‰ to 5‰ of sodium hydroxide and 3‰ to 6‰ of calcium hydroxide based on the mass of the kelp extract to the kelp extract obtained in step (1), stirring evenly and then slowly introducing 80% to 95% pure carbon dioxide gas into the kelp extract, stopping the aeration after the system is saturated, and then continuing to stir for 15 to 30 minutes and then standing for 8 to 24 hours, then filtering the kelp extract with a sieve, and collecting the filter residue and filtrate separately for later use;

[0010] 3) adjusting the pH of the filtrate obtained in step (2) to 7 with hydrochloric acid, filtering, collecting the filtrate and concentrating it under reduced pressure and vacuum, stopping the concentration when solid precipitation occurs, cooling, filtering to remove most of the salt, adding anhydrous ethanol to the filtrate until a large amount of solid precipitation occurs, filtering again, and further concentrating the filtrate. Monitoring the iodine content in the concentrate. When the iodine content in the concentrate reaches 3.0% to 5.0%, stopping the concentration, crystallizing the concentrate, and then collecting the crystallization supernatant and crystal precipitate separately for later use;

[0011] 4) centrifuging the crystal precipitate obtained in step (3), collecting the centrifugal precipitate and the centrifugal supernatant respectively, combining the centrifugal supernatant with the crystallization supernatant obtained in step (3) to obtain a seaweed iodine solution, concentrating the seaweed iodine solution and then drying it to obtain the target product seaweed iodine;

[0012] 5) drying and crushing the centrifugal precipitate obtained in step (4), and then performing Soxhlet extraction with ethanol as the extraction solvent. After the extraction is completed, the sample at the bottom of the flask is allowed to stand for crystallization, and then poured out and filtered to obtain crude mannitol;

[0013] 6) The crude mannitol obtained in step (5) is added to water, heated to boiling to dissolve it, and kept boiling for 5 to 10 minutes, then cooled and crystallized under constant stirring, and the crystals are washed with anhydrous ethanol to obtain the target product mannitol.

[0014] As a specific technical solution, in step (1), the mass ratio of dry kelp to water during soaking is 1:7-12 kg / kg, the soaking time is 36-48 hours, and the soaking temperature is 10-40°C.

[0015] As a specific technical solution, in step (3), the parameters of reduced pressure vacuum concentration are vacuum degree -0.09 to -0.05 Map and temperature 60 to 70°C.

[0016] As a specific technical solution, in step (3), during the reduced pressure vacuum concentration, the pH of the concentrate is monitored, and when the pH of the concentrate is greater than 7, the pH of the concentrate is adjusted to 7 with hydrochloric acid.

[0017] As a specific technical solution, in step (4), the crystallization conditions are: crystallization for more than 12 hours, and the crystallization temperature is 5-15°C.

[0018] As a specific technical solution, in step (5), the parameters of Soxhlet extraction are: solid-liquid ratio 1:3-10 g / ml, ethanol mass concentration 90-100%, and extraction time 5-24 h.

[0019] As a specific technical solution, in step (5), the parameters of Soxhlet extraction are: solid-liquid ratio 1:6 g / ml, ethanol mass concentration 95%, and extraction time 12 h.

[0020] As a specific technical solution, during Soxhlet extraction, ultrasonic vibration treatment is simultaneously applied to the material in the extraction cylinder.

[0021] As a specific technical solution, the parameters of the ultrasonic oscillation treatment are power 100-1000W and frequency 20-25KHz.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1) The present invention can not only extract seaweed iodine from kelp as a raw material, but also use the by-products produced by the seaweed iodine extraction as raw materials to extract high-purity mannitol by using a Soxhlet extraction combined with ultrasonic oscillation method, so that while producing qualified seaweed iodine solution, the by-product mannitol can be purified and comprehensively utilized to maximize resource utilization.

[0024] 2) In the prior art, the byproducts produced by extracting seaweed iodine from kelp as raw material contain mannitol, a large amount of salt and sugars. Since mannitol, sodium chloride and some sugar substances are all relatively water-soluble, if only the conventional Soxhlet extraction method is used, that is, 90% to 100% ethanol is used as a solvent for reflux extraction, the solubility of mannitol is very limited, and thus it is impossible to extract a mannitol crude product with higher purity, which will increase the difficulty and cost of subsequent purification. Therefore, the present invention combines ultrasonic vibration on the basis of traditional Soxhlet extraction, utilizing the mechanical effect and cavitation effect of ultrasound, thereby increasing the penetration of the extraction solvent and increasing the dissolution rate and efficiency of mannitol in the byproduct, and combining the continuous circulation reflux of the extraction solvent, finally extracting a mannitol crude product with higher purity, and after further purification, the mannitol crude product can obtain a mannitol fine product with a content of up to 97.77%. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure is a liquid chromatogram of centrifugal precipitate, crude mannitol, centrifugal precipitate after Soxhlet extraction, and target product mannitol;

[0026] Figure 2 Schematic diagram of the present invention wherein ultrasonic vibration treatment is simultaneously applied to the material in the extraction cylinder during Soxhlet extraction. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific embodiments. It should be pointed out that the following embodiments are merely illustrative of the present invention in the form of examples, but the scope of protection of the present invention is not limited thereto. All equivalent replacements made by those skilled in the art to the present invention in the spirit of the present invention fall within the scope of protection of the present invention.

[0028] Example 1

[0029] A method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp, comprising the following steps:

[0030] (1) chopping the dried kelp into pieces and soaking them in water, centrifuging the pieces after the soaking, collecting the centrifugal supernatant and the soaking liquid, combining them, filtering them, and collecting the filtrate to obtain the kelp extract;

[0031] (2) adding 2‰ to 5‰ of sodium hydroxide and 3‰ to 6‰ of calcium hydroxide based on the mass of the kelp extract to the kelp extract obtained in step (1), stirring evenly and then slowly introducing 80% to 95% pure carbon dioxide gas into the kelp extract, stopping the aeration after the system is saturated, and then continuing to stir for 15 to 30 minutes and then standing for 8 to 24 hours, and then filtering the kelp extract with a sieve, collecting the filter residue and the filtrate separately for later use;

[0032] (3) adjusting the pH of the filtrate obtained in step (2) to 7 with hydrochloric acid, filtering, collecting the filtrate and concentrating it under reduced pressure and vacuum, stopping the concentration when solid precipitation occurs, cooling, filtering to remove most of the salt, adding anhydrous ethanol to the filtrate until a large amount of solid precipitation occurs, filtering again, and further concentrating the filtrate. Monitoring the iodine content in the concentrate. When the iodine content in the concentrate reaches 3.0% to 5.0%, stopping the concentration, crystallizing the concentrate, and then collecting the crystallization supernatant and crystallization precipitate separately for later use;

[0033] (4) centrifuging the crystal precipitate obtained in step (3), collecting the centrifugal precipitate and the centrifugal supernatant respectively, combining the centrifugal supernatant with the crystallization supernatant obtained in step (3) to obtain a seaweed iodine solution, concentrating the seaweed iodine solution and then drying it to obtain the target product seaweed iodine;

[0034] (5) drying and crushing the centrifugal precipitate obtained in step (4), and then performing Soxhlet extraction using ethanol as the extraction solvent. After the extraction is completed, the sample at the bottom of the flask is allowed to stand for crystallization, and then poured out and filtered to obtain crude mannitol;

[0035] (6) Add the crude mannitol obtained in step (5) into water, heat to boiling to dissolve it, keep boiling for 5 to 10 minutes, then cool and crystallize under continuous stirring, take the crystals and wash them with anhydrous ethanol to obtain the target product mannitol.

[0036] Example 2

[0037] A method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp, comprising the following steps:

[0038] (1) 1 kg of dried kelp (purchased from Rongcheng City, Shandong Province, with a water content of 12.8%) was cut into small pieces of about 7-8 cm × 3-4 cm with scissors, and then soaked in water at a mass ratio of 1:10 kg / kg for 48 h at a water temperature of 18°C. After soaking, the kelp was removed and added to a centrifuge for thorough centrifugation. The supernatant was collected and combined with the soaking liquid, and then the combined liquid was filtered with a 120-mesh sieve, and the filter residue was discarded. The filtrate was collected to obtain a total of 6.3 kg of kelp extract.

[0039] (2) adding 2‰ of sodium hydroxide and 3‰ of calcium hydroxide based on the mass of the kelp extract to the kelp extract obtained in step (1), stirring evenly and then slowly introducing carbon dioxide gas with a purity of 80% to 95% into the kelp extract, stopping the aeration after the system is saturated, and then continuing to stir for 15 to 30 minutes and then standing for 8 to 24 hours, and then filtering the kelp extract with a sieve, collecting the filter residue and the filtrate separately for later use;

[0040] (3) The filtrate obtained in step (2) is adjusted to pH 7 with hydrochloric acid, and then filtered. The filtrate is collected and concentrated under reduced pressure and vacuum, and the vacuum degree is controlled to be ≤-0.08 Map, and the temperature is 60-70° C. The pH value of the system is continuously monitored. When the pH value of the system is greater than 7, the pH is continued to be adjusted to 7 with 20% dilute hydrochloric acid, and the iodine content in the concentrate is monitored at the same time. When the iodine content in the concentrate reaches 3.2%, the concentration is stopped, and the concentrate is transferred to a turnover barrel for crystallization treatment. The crystallization is allowed to stand for more than 12 hours at a crystallization temperature of 5-15° C., and then the supernatant is poured out, and the crystallization supernatant and crystallization precipitate are collected separately for later use;

[0041] (4) centrifuging the crystal precipitate obtained in step (3) in a flat centrifuge using an 800-mesh filter bag, collecting the centrifugal precipitate and the centrifugal supernatant, combining the centrifugal supernatant with the crystallization supernatant obtained in step (3) to obtain a seaweed iodine solution, concentrating the seaweed iodine solution and then drying it to obtain the target product seaweed iodine, and simultaneously obtaining 377.97 g of a centrifugal precipitate containing substances such as sodium chloride, mannitol, and fucoidan (i.e., a by-product);

[0042] (5) The centrifugal precipitate obtained in step (4) is placed in a blast drying oven and dried at 70°C. When the sample weight loss is less than or equal to 0.5%, it is taken out and placed at room temperature to cool. The dried product is then crushed with a grinder to obtain 167.7g of a dried sample for later use. The sample is then wrapped with filter paper and added to the extraction cylinder of a Soxhlet extractor. 95% ethanol, which is 5 times the weight of the centrifugal precipitate, is added. A condenser is connected and the sample is heated to reflux. During the reflux process, ultrasonic vibration treatment is applied to the material in the extraction cylinder. After heating and reflux for 2h, white solid precipitation can be seen at the bottom of the flask. The reflux is continued for 10-12h. When the by-product in the filter paper cylinder of the Soxhlet extractor does not contain mannitol or the mannitol content is very low, the reflux can be stopped. After the extraction is completed, the sample at the bottom of the flask is allowed to stand for crystallization for more than 12h. The crystallization temperature is 5-15°C. Filtering is performed to obtain 21.95g of crude mannitol. The mannitol content is 69.43% after testing. In this step, the ultrasonic vibration treatment is applied as follows: Figure 2 As shown, a medium container 1 is fixedly installed on one side of the extraction cylinder 3 of a traditional Soxhlet extractor, an ultrasonic generator vibrator 2 is suspended in the medium container 1, and clean water is filled in the medium container 1 as an ultrasonic transmission medium. The filling height of the clean water should be higher than the ultrasonic generator vibrator 2. The medium container 1 is made of glass and can be integrally formed with the extraction cylinder 3 or detachably fixed to the extraction cylinder 3. Based on the above arrangement, the ultrasonic wave generated by the ultrasonic generator vibrator 2 is sequentially transmitted to the medium container 1, the extraction cylinder 3, the extraction solvent in the extraction cylinder 3, and the sample in the filter paper bag through the clean water. In this way, the mechanical effect and cavitation effect of the ultrasonic wave, combined with the continuous circulation and reflux of the extraction solvent, can greatly improve the extraction efficiency and extraction yield. According to tests, in the preparation of crude mannitol, compared with not applying ultrasonic vibration treatment, the use of ultrasonic vibration treatment in the Soxhlet extraction process can shorten the drawer time by 20% to 40% and increase the extraction yield by 10% to 17%.

[0043] (6) The crude mannitol obtained in step (5) was added to 17.56 g of water (the mass ratio of the crude mannitol to water was 1:1.036), heated to boiling to dissolve it, and kept boiling for 5 to 10 minutes. Then, the mixture was cooled and crystallized under constant stirring. The crystals were washed with anhydrous ethanol to obtain the target product mannitol. The purity of the mannitol was 97.77% after testing.

[0044] Take the same mass of the centrifugal precipitate obtained in step (4), the crude mannitol obtained in step (5), the centrifugal precipitate after Soxhlet extraction in step (5), and the target product mannitol obtained in step (6) as samples, and use liquid chromatography to determine the mannitol contained therein. The chromatographic detection results are shown in FIG. Figure 1 ,Depend on Figure 1It can be seen that after the centrifugal precipitate (i.e., the by-product) is extracted by Soxhlet extraction, the mannitol content in the centrifugal precipitate is significantly reduced, and the obtained crude mannitol contains 69.43% mannitol, while the target product mannitol contains 97.77% mannitol. Therefore, the method of the present invention can utilize the by-product generated by extracting seaweed iodine as a raw material, and use Soxhlet extraction combined with ultrasonic oscillation to extract high-purity mannitol.

[0045] Example 3

[0046] High-purity mannitol was prepared by the method of Example 2, and the Soxhlet extraction process in step (5) was optimized, that is, L9 (3 3 The effects of three key factors in Soxhlet extraction, namely A (ethanol concentration), B (solid-to-liquid ratio), and C (extraction time), on the extraction of mannitol were investigated using orthogonal design to determine the optimal extraction conditions. The factor levels are shown in Table 1, and the results are shown in Table 2.

[0047] Table 1 Orthogonal experimental factor level table

[0048]

[0049] Table 2 Orthogonal test results

[0050]

[0051]

[0052] Table 2 shows that the optimal Soxhlet extraction process combination is A3B2C2, which includes an ethanol concentration of 95%, a solid-liquid ratio of 1:6 g / mL, and an extraction time of 12 hours. Because the optimal process parameter combination was not among the nine groups in the orthogonal design, three parallel validation experiments were conducted using the process parameters of the optimal A3B2C2 combination. The results are shown in Table 3. Table 3 shows that the average mannitol extraction yield was 10.86%, exceeding that of the nine groups in the orthogonal design, and the extraction results were stable.

[0053] Table 3 Optimal parameter combination verification experiment

[0054] Sample number Mannitol extraction rate (%) 1 10.65 2 10.70 3 10.68 average value 10.68

[0055] Therefore, in the present invention, the optimal process for Soxhlet extraction of mannitol is as follows: ethanol concentration is 95%, solid-liquid ratio is 1:6 g / mL, and extraction time is 12 h. Under these conditions, the extraction rate of mannitol can reach 10.68%.

Claims

1. A method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp, characterized in that The steps include: (1) Cut the dried kelp into pieces and soak it in water. After soaking, centrifuge the mixture, collect the supernatant from the centrifuge and combine it with the soaking liquid, then filter it and collect the filtrate to obtain the kelp extract; (2) Add 2‰ to 5‰ of sodium hydroxide and 3‰ to 6‰ of calcium hydroxide to the kelp extract obtained in step (1), based on the mass of the kelp extract, stir evenly, and slowly introduce 80% to 95% purity carbon dioxide gas into the kelp extract. Stop aeration after the system is saturated, continue stirring for 15 to 30 minutes, and then let it stand for 8 to 24 hours. Then, filter the kelp extract with a sieve, and collect the filter residue and filtrate separately for later use. (3) The filtrate obtained in step (2) is adjusted to pH 7 with hydrochloric acid, and then filtered. The filtrate is collected and concentrated under reduced pressure. The concentration is stopped when solid precipitation occurs. The filtrate is cooled and filtered to remove most of the salt. Anhydrous ethanol is added to the filtrate until a large amount of solid precipitation occurs. The filtrate is filtered again and the filtrate is further concentrated. The iodine content in the concentrate is monitored. When the iodine content in the concentrate reaches 3.0% to 5.0%, the concentration is stopped and the concentrate is crystallized. The crystallization supernatant and the crystal precipitate are collected and set aside. (4) centrifuging the crystal precipitate obtained in step (3), collecting the centrifugal precipitate and the centrifugal supernatant respectively, and combining the centrifugal supernatant with the crystallization supernatant obtained in step (3) to obtain the target product seaweed iodine solution; (5) The centrifugal precipitate obtained in step (4) is dried and crushed, and then subjected to Soxhlet extraction using ethanol having a mass concentration of 90% to 100% as an extraction solvent. After the extraction is completed, the sample at the bottom of the flask is allowed to stand for crystallization, and then poured out and filtered to obtain a crude mannitol product; wherein, during the Soxhlet extraction, ultrasonic vibration treatment is simultaneously applied to the material in the extraction cylinder, and the parameters of the ultrasonic vibration treatment are power 100 to 1000 W and frequency 20 to 25 kHz; (6) The crude mannitol obtained in step (5) is added to water, heated to boiling to dissolve it, and kept boiling for 5 to 10 minutes. Then, the water is cooled and crystallized under continuous stirring. The crystals are washed with anhydrous ethanol to obtain the target product mannitol.

2. The method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp according to claim 1, wherein: In the step (1), the mass ratio of the dried kelp to water during soaking is 1:7-12 kg / kg, the soaking time is 36-48 h, and the soaking temperature is 10-40°C.

3. The method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp according to claim 1, wherein: In the step (3), the parameters of the reduced pressure vacuum concentration are: vacuum degree -0.09 to -0.05 Map, and temperature 60 to 70°C.

4. The method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp as claimed in claim 1, characterized in that: In the step (3), during the reduced pressure vacuum concentration, the pH of the concentrate is monitored, and when the pH of the concentrate is greater than 7, the pH of the concentrate is adjusted to 7 with hydrochloric acid.

5. The method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp as claimed in claim 1, characterized in that: In the step (4), the crystallization conditions are: crystallization for more than 12 hours, and the crystallization temperature is 5-15°C.

6. The method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp as claimed in claim 1, characterized in that: In the step (5), the parameters of the Soxhlet extraction are a material-liquid ratio of 1:3 to 10 g / ml and an extraction time of 5 to 24 h.

7. The method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp according to claim 6, characterized in that: In step (5), the parameters of Soxhlet extraction are: solid-liquid ratio 1:6 g / ml, ethanol mass concentration 95%, and extraction time 12 h.

8. The method for continuously extracting seaweed iodine solution and high-purity mannitol from dried kelp according to claim 1, wherein: In the step (6), the mass ratio of crude mannitol to water is 1:0.8-1.2.

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