Seaweed iodine salt and preparation method thereof

Abstract

The present invention belongs to the technical field of salt manufacturing, and specifically relates to a seaweed iodized salt and a preparation method thereof. The seaweed iodized salt, measured by weight, comprises 100 to 150 parts of iodine-free salt, 0.1 to 0.5 parts of seaweed iodine crystals, and an appropriate amount of ammonium ferric citrate. The seaweed iodized salt prepared by the present invention meets the iodine content standard for edible salt, and the organic iodine content in the prepared seaweed iodine crystals is relatively high. The iodine-containing amino acids in the organic iodine can be directly absorbed by the human body and are not limited by the amount of protein intake. Inorganic iodine also has good stability in this system and is not easily decomposed at high temperatures, thus meeting actual cooking needs. The seaweed iodized salt prepared by the present application has a wide economic value and is suitable for large-scale promotion and production.

Description

Technical Field

[0001] The invention belongs to the technical field of salt manufacturing, and particularly relates to seaweed iodized salt and a preparation method thereof. Background Art

[0002] Seaweed iodized salt is a new generation of iodized salt made from natural biological seaweed through scientific processing. It not only contains inorganic iodine that is easily absorbed by the human body, but is also rich in organic iodine. It is an ideal natural seasoning iodine supplement. Moreover, the iodine amino acids such as monoiodotyrosine and 3.5-diiodotyrosine in organic iodine are not only easily absorbed by the human body, but also iodine amino acids may protect the myocardium by increasing the activity of ATPase. At higher doses, organic iodine containing iodine amino acids is safer and more reliable than inorganic iodine. Therefore, compared with some inorganic iodized salts, seaweed iodized salt will not cause adverse reactions such as hyperiodine goiter when the dose is slightly excessive.

[0003] However, existing technologies, while organic iodine from seaweed is easier to store and utilize, it is difficult to extract. While inorganic iodine is easily absorbed by the human body, it is less stable and prone to redox reactions, producing elemental iodine that sublimes, affecting the stability of the resulting seaweed iodine salt. Furthermore, the extraction process for seaweed iodine is complex, and it's difficult to completely remove heavy metals from the seaweed, impacting the product's yield. Summary of the Invention

[0004] The present invention aims to provide a seaweed iodized salt and a preparation method thereof. The seaweed iodized salt not only has an iodine content that meets national standards, but also has a high organic iodine content and good inorganic iodine stability. At the same time, the seaweed iodized salt has a low heavy metal content, meets national edible salt requirements, and has good edible value.

[0005] The invention discloses iodized seaweed salt, wherein the raw materials for its preparation comprise, by weight, 100-150 parts of iodine-free salt, 0.1-0.5 parts of seaweed iodine crystals, and an appropriate amount of ammonium ferric citrate.

[0006] The preparation method of seaweed iodine crystals comprises the following steps:

[0007] S1. Rinse the seaweed material with deionized water 2-3 times, dry it at 50-70°C, and grind it through a 40-mesh sieve to obtain seaweed powder;

[0008] S2, mixing the seaweed powder with the buffer solution, stirring evenly, adjusting the pH to 7-8, adding the enzyme, ultrasonicating, centrifuging, and vacuum filtering to obtain a filtrate, repeating the above operation with the residue, combining the filtrates, and concentrating the filtrates under reduced pressure to dryness to obtain a crude seaweed extract;

[0009] S3. Dissolve the crude seaweed extract in water, pass it through an anion separation column at a flow rate of 2.5 to 3.5 BV / h, and elute it step by step with the mobile phase for 40 to 70 minutes. Collect the eluate, let it stand for 20 to 30 hours, then filter it with a ceramic membrane, collect the filtrate, and concentrate it under reduced pressure to dryness to obtain seaweed iodine crystals.

[0010] Preferably, the seaweed material is one or more of Nostoc, Laver, Kelp, Sea Cabbage, and Undaria pinnatifida; more preferably, it is Kelp.

[0011] Preferably, the solid-liquid ratio of the seaweed powder and the buffer solution is 1 g: 15-25 mL.

[0012] Preferably, the buffer solution is NaH2PO4 solution.

[0013] Preferably, the concentration of NaH2PO4 in the buffer solution is 0.1 to 0.2 mol / L.

[0014] Preferably, the added amount of the enzyme is 0.2% to 0.5% of the seaweed powder; more preferably, it is 0.4%.

[0015] Preferably, the enzyme is trypsin and a complex protease.

[0016] Preferably, the mass ratio of trypsin to compound protease is (2-4):1; more preferably, it is 3:1.

[0017] Preferably, the trypsin activity is ≥15000 U / g.

[0018] In some preferred embodiments, the trypsin is purchased from Hunan Yunbang Pharmaceutical Co., Ltd.

[0019] Preferably, the enzyme activity of the composite protease is ≥40,000 U / g.

[0020] In some preferred embodiments, the composite protease is purchased from Shandong Aicai Biotechnology Co., Ltd.

[0021] The specific conditions of the ultrasonic treatment are: ultrasonic power of 100-150W, ultrasonic time of 8-12h, and ultrasonic temperature of 45-55°C.

[0022] The inventors discovered that treating seaweed with specific enzymes and buffers under ultrasonic conditions can increase the iodine content in seaweed iodine crystals. This may be because, under specific buffer solutions and ultrasonic treatment conditions, inorganic iodine can be leached from the seaweed matrix. The combination of ultrasonic treatment and enzymes accelerates the breakdown of plant cell walls, reduces the transfer resistance of active ingredients, and promotes the extraction and separation of organic iodine. The combined effect significantly increases iodine content. The specific ultrasonic conditions and enzymes act synergistically, increasing enzyme catalytic activity, helping to break down plant cell walls and reduce the mass transfer resistance of organic iodine. They also increase the solubility and diffusion coefficient of organic iodine, thereby facilitating its extraction. However, controlled conditions are required during the actual preparation process. Prolonged ultrasonic treatment times may cause the decomposition of iodine amino acids and the loss of potassium iodide. Excessively high temperatures can affect both enzyme activity and the stability of inorganic iodine, thereby reducing iodine extraction efficiency. If the enzyme dosage is too high, the seaweed cell walls will be more thoroughly broken. In this case, the buffer solution will not only leach iodine but also dissolve excessive impurities, affecting product purity and stability.

[0023] Preferably, the solid-liquid ratio of the seaweed crude extract and water is 1 g: 10-20 mL.

[0024] Preferably, the bonded phase of the anion separation column is quaternary ammonium, the particle size is 4 to 6 μm, and the number of theoretical plates of a chromatographic column is ≥10,000.

[0025] In some preferred embodiments, the anion separation column is purchased from Lisenok Scientific Instruments (Shanghai) Co., Ltd., Shodex IC S I-504E.

[0026] The inventors discovered that by selecting a specific anion separation column, they could improve iodine separation efficiency, thereby increasing the iodine content in seaweed iodine crystals. This is likely due to the quaternary ammonium groups not only having strong ion exchange capacity, effectively adsorbing iodide ions, thereby improving separation efficiency and selectivity, but also having high chemical stability, ensuring stable separation. Furthermore, selecting a specific particle size for the separation column increases its contact area with the solution, thereby increasing the amount of iodine adsorbed.

[0027] Preferably, the mobile phase is (NH4)2CO3 / NaOH solution.

[0028] Preferably, the concentration of (NH4)2CO3 in the mobile phase is 0.01 to 0.02 mol / L.

[0029] Preferably, the pH of the mobile phase is 8-10.

[0030] Preferably, the specific steps of the stepwise elution are: the flow rate of the mobile phase is 0.6-1.0 mL / min for the first 20-30 minutes, and the flow rate is 1.1-1.3 mL / min thereafter.

[0031] In some preferred embodiments, the use of a specific eluent can further improve the collection rate of organic iodine, thereby increasing the iodine amino acid content in seaweed iodine salt. This may be because ammonium carbonate dissociates into carbonate ions or bicarbonate ions at a specific pH. These ions can compete with the anions of organic and inorganic iodine adsorbed on the anion separation column, displacing iodine ions from the resin and eluting with the eluent. Due to the dissociation characteristics of ammonium carbonate and its exchange capacity with the resin, it can effectively elute the iodine ions adsorbed on the resin. After extensive experiments, the inventors found that selecting a specific mobile phase concentration and pH can increase the elution rate of organic iodine. This may be because in a specific mobile phase solution, organic iodine can not only be completely separated from the anion separation column but also remain in the mobile phase solution for a longer period of time. However, excessively high ammonium carbonate concentrations not only reduce the retention time of iodine amino acids but also easily form deposits on the separation column, causing blockage or corrosion, thereby affecting the separation efficiency of the anion separation column. Furthermore, during the elution process, the flow rate of the mobile phase also has a significant impact on the separation efficiency of iodine ions. At low flow rates, the retention time of iodide ions is prolonged, and the separation time is too long, preventing some iodide ions from being eluted. At high flow rates, the resolution may be reduced, and high flow rates can also lead to excessive column pressure, shortening the life of the anion exchange column. The inventors have discovered that a step-by-step elution method can separate inorganic and organic iodine while shortening the separation time and minimizing damage to the anion exchange column, thus avoiding damage to the anion exchange column that could affect the iodine separation capacity during industrial use.

[0032] Preferably, the transmembrane pressure difference during the filtration in step S3 is 0.05 to 0.15 MPa.

[0033] The preparation method of the modified ceramic membrane comprises the following steps:

[0034] B1. Hydrolyze the silane coupling agent in an 80 wt% ethanol aqueous solution and heat it to 55-65° C. Immerse the ceramic membrane in the solution for 2-4 hours, rinse with deionized water, and dry at 100-120° C. for 3-5 hours to obtain a silane coupling agent-modified ceramic membrane.

[0035] B2. Polyvinyl alcohol is prepared into a polyvinyl alcohol aqueous solution with a mass concentration of 0.5% to 2%, graphene oxide is added thereto and evenly dispersed to obtain a mixed solution, and a silane coupling agent-modified ceramic membrane is completely immersed in the mixed solution by a vacuum migration method. After vacuum treatment for 20 to 30 minutes, the membrane is taken out and heat-treated at 100 to 200° C. for 1 to 3 hours to obtain the obtained product.

[0036] In some preferred embodiments, the eluate is filtered through a ceramic membrane. Suspended matter, colloids, bacteria, viruses, etc. larger than the membrane pore size are trapped on one side of the membrane, thereby ensuring the purity and stability of the seaweed iodine crystals. Moreover, the ceramic membrane filtration process is gentle and does not introduce harmful chemicals. It can maximize the activity of iodine in the seaweed iodine crystals and reduce their degradation and loss during the extraction process. However, the filtration time is long, and some impurities may clog the pores, resulting in limited purification effect and inability to remove heavy metals in seaweed substances. The inventors have discovered that constructing a new graphene oxide film on the surface of the ceramic membrane can improve the stability of the modified ceramic membrane while also increasing the adsorption capacity of heavy metals in the eluate, thereby improving the purity of the prepared seaweed iodine crystals and making their heavy metal content lower than the national standard. This may be because graphene oxide has a large specific surface area and abundant adsorption sites, and contains active functional groups such as hydroxyl and carboxyl groups, so it can effectively adsorb heavy metal ions, organic pollutants, etc. in water. In addition, the layered structure of graphene oxide also provides it with more adsorption space, making its adsorption capacity relatively large. This greatly improves the purity of the final seaweed iodine, but the adhesion effect between graphene oxide and the ceramic membrane is poor.

[0037] Preferably, the volume ratio of the silane coupling agent to the ethanol aqueous solution is 1:30-50; more preferably, it is 1:40.

[0038] Preferably, the silane coupling agent is 3-aminopropyltrimethoxysilane and γ-mercaptopropyltrimethoxysilane.

[0039] Preferably, the mass ratio of 3-aminopropyltrimethoxysilane to γ-mercaptopropyltrimethoxysilane is 1:(5-7); more preferably, it is 1:6.

[0040] Through a large number of experiments, the inventors found that by selecting two silane coupling agents to modify the ceramic membrane, functional groups such as amino and thiol groups were grafted on the surface of the ceramic membrane. These functional groups can react with the epoxy groups on the graphene oxide, so that the graphene oxide can adhere to the ceramic membrane, thereby improving the adsorption effect of the ceramic membrane; at the same time, by controlling the particle size and other properties of the ceramic membrane and graphene oxide, the prepared modified ceramic membrane can be used for precision filtration, further improving the purity of the final seaweed iodine crystals.

[0041] Preferably, the separation pore size of the ceramic membrane is 0.4-0.5 μm, the material is Al2O3-ZrO2, and it is purchased from Beijing Dopson Membrane Application Engineering Technology Co., Ltd.

[0042] Preferably, the polyvinyl alcohol has a degree of alcoholysis ≥ 99% and an ash content ≤ 0.5%, and a viscosity of a 4 wt % aqueous solution thereof is 15-25 CP.

[0043] In some preferred embodiments, the polyvinyl alcohol is purchased from Japan Kuraray polyvinyl alcohol 80-18.

[0044] Preferably, the graphene oxide includes single-layer graphene oxide and multi-layer graphene oxide.

[0045] Preferably, the weight ratio of the single-layer graphene oxide to the multi-layer graphene oxide is 1:(0.5-2); more preferably, it is 1:1.

[0046] Preferably, the average thickness of the single-layer graphene oxide is 0.5 to 1.2 nm, and the diameter is 4 to 7 μm.

[0047] Preferably, the multilayer graphene oxide has an average thickness of 1 to 3 nm, a diameter of 4 to 7 μm, and 2 to 5 layers.

[0048] In some preferred embodiments, the single-layer graphene oxide and the multi-layer graphene oxide are both purchased from Zhejiang Zhiti Nano Micro New Materials Co., Ltd.

[0049] Preferably, the solid-to-liquid ratio of the graphene oxide to the polyvinyl alcohol aqueous solution is 1-10 g:100 mL.

[0050] In order to improve the filtering effect and stability of ceramic membrane, two specific graphene oxides are selected to be modified. This may be because on the one hand, specific single-layer graphene oxide and multi-layer graphene oxide are selected, and their diameters are similar and the thickness difference is not much, so there is a certain compatibility effect between the two. On the one hand, the complementarity on the number of layers is realized, and the high activity of the single-layer graphene oxide is retained, and the mechanical properties of the product are improved. On the other hand, the single-layer and multi-layer graphene oxides of similar size are intertwined and stacked to form a stable three-dimensional network structure, which can improve the structural stability of the modified ceramic membrane. In addition, the additive liquid of specific polyvinyl alcohol can improve the adhesion of the ceramic membrane matrix and graphene oxide, thereby also being able to improve the structural stability of the modified ceramic membrane. But considering the agglomeration effect of graphene oxide, its addition amount should not be too much, and excessive agglomerated graphene oxide loads on the ceramic membrane surface may block ceramic pores, affecting the filtering effect.

[0051] The preparation method of seaweed iodized salt comprises the following steps: dissolving seaweed iodine crystals in water and stirring evenly, adding ammonium ferric citrate and continuing stirring, adding baking soda to adjust the pH of the solution to 7-9, adding the solution to iodine-free salt, stirring evenly, and drying to obtain the seaweed iodized salt.

[0052] Preferably, the solid-liquid ratio of the seaweed iodine to water is 1 g: 100-150 mL.

[0053] Preferably, the added amount of the ammonium ferric citrate does not exceed 0.0025% of the total mass of the iodine-free salt and the seaweed iodine crystals.

[0054] Preferably, the pH of the baking soda solution is adjusted to 8-9.

[0055] The inventors discovered that, during the preparation of seaweed iodine salt, by mixing seaweed iodine crystals and ammonium ferric citrate by weight and then adjusting the pH to a specific value, the stability of the seaweed iodine salt can be enhanced while also ensuring the anti-caking effect of the ammonium ferric citrate. This is likely because under specific pH conditions, the trivalent iron in the ammonium ferric citrate does not generate ferric hydroxide, and inorganic iodine, trivalent iron, and oxygen do not undergo oxidation and reduction, leading to the precipitation of elemental iodine. This greatly ensures the stability of the system and enhances the stability of inorganic iodine, while the ammonium ferric citrate can still exert its anti-caking effect. Other properties of the seaweed iodine salt are not affected, resulting in excellent stability.

[0056] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0057] 1. The present invention provides a seaweed iodized salt, which has a high organic iodine content, good inorganic iodine stability, and a low heavy metal content, meets national edible salt requirements, and has good edible value.

[0058] 2. The present invention uses specific enzymes and buffers to treat seaweed materials under ultrasonic conditions, which can increase the iodine content in seaweed iodine crystals.

[0059] 3. The present invention can improve the iodine separation efficiency by selecting a specific anion separation column, thereby increasing the iodine content in the seaweed iodine crystals.

[0060] 4. The present invention can further improve the collection rate of organic iodine by selecting a specific eluent, thereby increasing the iodine amino acid content in seaweed iodized salt.

[0061] 5. The present invention can increase the elution amount of organic iodine by selecting a specific mobile phase concentration and pH.

[0062] 6. The present invention constructs a new graphene oxide film on the surface of the ceramic membrane, which can improve the stability of the modified ceramic membrane while also increasing the adsorption capacity of heavy metals in the eluent, thereby improving the purity of the prepared seaweed iodine crystals and making their heavy metal content lower than the national standard. DETAILED DESCRIPTION

[0063] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0064] The raw materials used in the present invention are all commercially available, specifically:

[0065] Trypsin with an enzyme activity of approximately 20,000 U / g was purchased from Hunan Yunbang Pharmaceutical Co., Ltd.

[0066] The enzyme activity of the composite protease was about 50,000 U / g and was purchased from Shandong Aicai Biotechnology Co., Ltd.

[0067] The bonded phase of the anion separation column is quaternary ammonium, the particle size is 5 μm, the theoretical plate number of one column is ≥10,000, and it was purchased from Lisennok Scientific Instruments (Shanghai) Co., Ltd., Shodex ICS I-504E.

[0068] The separation pore size of the ceramic membrane is 0.45 μm, the material is Al2O3-ZrO2, and it was purchased from Beijing Taopusen Membrane Application Engineering Technology Co., Ltd.

[0069] The polyvinyl alcohol has a degree of alcoholysis of ≥99% and an ash content of ≤0.5%. The viscosity of the polyvinyl alcohol prepared into a 4 wt % aqueous solution is 15-25 CP and is purchased from Kuraray Polyvinyl Alcohol 80-18 of Japan.

[0070] The average thickness of single-layer graphene oxide is 0.5-1.2 nm, and the diameter is 4-7 μm; the average thickness of multi-layer graphene oxide is 1-3 nm, the diameter is 4-7 μm, and the number of layers is 2-5; all are purchased from Zhejiang Zhiti Nano Micro New Materials Co., Ltd.

[0071] Example 1

[0072] This embodiment provides a seaweed iodized salt, the raw materials for its preparation are, by weight: 120 parts of iodine-free salt, 0.3 parts of seaweed iodine crystals, and an appropriate amount of ammonium ferric citrate.

[0073] The preparation method of seaweed iodine crystals comprises the following steps:

[0074] S1. Rinse the seaweed material with deionized water three times, dry it at 60°C, and grind it through a 40-mesh sieve to obtain seaweed powder;

[0075] S2, mixing the seaweed powder with the buffer solution, stirring evenly, adjusting the pH to 8, adding the enzyme, ultrasonicating, centrifuging, and vacuum filtering to obtain a filtrate, repeating the above operation with the residue, combining the filtrates, and concentrating the filtrates under reduced pressure to dryness to obtain a crude seaweed extract;

[0076] S3. Dissolve the crude seaweed extract in water, pass it through an anion separation column at a flow rate of 3 BV / h, and elute it stepwise with the mobile phase for 60 minutes. Collect the eluate, let it stand for 25 hours, and then filter it with a ceramic membrane. Collect the filtrate, concentrate it under reduced pressure and dry it to obtain seaweed iodine crystals.

[0077] The seaweed material is kelp.

[0078] The solid-to-liquid ratio of the seaweed powder to the buffer solution is 1 g:20 mL.

[0079] The buffer solution is NaH2PO4 solution.

[0080] The concentration of NaH2PO4 in the buffer solution is 0.15 mol / L.

[0081] The added amount of the enzyme is 0.4% of the mass of the seaweed powder.

[0082] The enzymes are trypsin and complex protease.

[0083] The mass ratio of the trypsin to the composite protease is 3:1.

[0084] The specific conditions of the ultrasonic treatment are: ultrasonic power of 120W, ultrasonic time of 10h, and ultrasonic temperature of 50°C.

[0085] The solid-to-liquid ratio of the seaweed crude extract and water is 1 g:15 mL.

[0086] The mobile phase is (NH4)2CO3 / NaOH solution.

[0087] The concentration of (NH4)2CO3 in the mobile phase is 0.015 mol / L.

[0088] The pH of the mobile phase is 9.

[0089] The specific steps of the stepwise elution are: the flow rate of the mobile phase is 0.8 mL / min before 25 minutes, and the flow rate is 1.2 mL / min thereafter.

[0090] The transmembrane pressure difference during the filtration in step S3 is 0.1 MPa.

[0091] The preparation method of the modified ceramic membrane comprises the following steps:

[0092] B1. Hydrolyze the silane coupling agent in an 80 wt% ethanol aqueous solution and heat it to 60°C. Immerse the ceramic membrane in the solution for 3 hours, rinse with deionized water, and dry at 110°C for 4 hours to obtain a silane coupling agent-modified ceramic membrane.

[0093] B2. Polyvinyl alcohol is prepared into a polyvinyl alcohol aqueous solution with a mass concentration of 1%, and graphene oxide is added thereto and evenly dispersed to obtain a mixed solution. The silane coupling agent-modified ceramic membrane is completely immersed in the mixed solution using a vacuum migration method. After vacuum treatment for 25 minutes, the membrane is taken out and heat-treated at 150° C. for 2 hours to obtain the obtained product.

[0094] The volume ratio of the silane coupling agent to the ethanol aqueous solution is 1:40.

[0095] The silane coupling agents are 3-aminopropyltrimethoxysilane and gamma-mercaptopropyltrimethoxysilane.

[0096] The mass ratio of the 3-aminopropyltrimethoxysilane to the γ-mercaptopropyltrimethoxysilane is 1:6.

[0097] The graphene oxide is single-layer graphene oxide and multi-layer graphene oxide.

[0098] The weight ratio of the single-layer graphene oxide to the multi-layer graphene oxide is 1:1.

[0099] The solid-to-liquid ratio of the graphene oxide to the polyvinyl alcohol aqueous solution is 1 g:20 mL.

[0100] The preparation method of seaweed iodized salt comprises the following steps: dissolving seaweed iodine crystals in water and stirring evenly, adding ammonium ferric citrate and continuing stirring, adding baking soda to adjust the pH of the solution to 8.5, adding the solution to iodine-free salt, stirring evenly, and drying to obtain the seaweed iodized salt.

[0101] The solid-liquid ratio of the seaweed iodine to water is 1 g:120 mL.

[0102] The added amount of the ammonium ferric citrate is 0.002% of the total mass of the iodine-free salt and the seaweed iodine crystals.

[0103] Example 2

[0104] The difference between this embodiment and embodiment 1 is that the mass ratio of trypsin to compound protease is 4:1.

[0105] Example 3

[0106] The difference between this embodiment and embodiment 1 is that the specific steps of the stepwise elution are: the flow rate of the mobile phase is 0.6 mL / min before 20 minutes, and the flow rate is 1.3 mL / min thereafter.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 1 is that the enzyme is trypsin.

[0109] Comparative Example 2

[0110] The difference between this comparative example and Example 1 is that the specific conditions of the ultrasonic treatment are: ultrasonic power of 120 W, ultrasonic time of 15 h, and ultrasonic temperature of 50°C.

[0111] Comparative Example 3

[0112] The difference between this comparative example and Example 1 is that the added amount of the enzyme is 1% of the seaweed powder.

[0113] Comparative Example 4

[0114] The difference between this comparative example and Example 1 is that the bonded phase of the anion separation column is quaternary ammonium, the particle size is 9 μm, the theoretical plate number of one chromatographic column is ≥5000, and it is purchased from Lisenok Scientific Instruments (Shanghai) Co., Ltd., Shodex ICS I-904E.

[0115] Comparative Example 5

[0116] The difference between this comparative example and Example 1 is: S3, take the crude seaweed extract and dissolve it in water, pass it through the anion separation column at a flow rate of 3BV / h, use the mobile phase to elute at a flow rate of 1.0mL / min for 60min, collect the eluate, let it stand for 25h, filter it with a ceramic membrane, collect the filtrate, concentrate it under reduced pressure and dry it, so as to obtain seaweed iodine crystals.

[0117] Comparative Example 6

[0118] The difference between this comparative example and Example 1 is that the separation pore size of the ceramic membrane is 0.9 μm, the material is Al2O3-ZrO2, and it is purchased from Beijing Taopusen Membrane Application Engineering Technology Co., Ltd.

[0119] Comparative Example 7

[0120] The difference between this comparative example and Example 1 is that the silane coupling agent is 3-aminopropyltrimethoxysilane

[0121] Comparative Example 8

[0122] The difference between this comparative example and Example 1 is that the graphene oxide is a single-layer graphene oxide.

[0123] Comparative Example 9

[0124] The difference between this comparative example and Example 1 is that the preparation method of the seaweed iodized salt comprises the following steps: dissolving seaweed iodine crystals in water and stirring evenly, adding ammonium ferric citrate, continuing stirring, adding baking soda to adjust the pH of the solution to 10, and then adding iodine-free salt, stirring evenly, and then drying and concentrating to obtain the seaweed iodized salt.

[0125] Performance Testing

[0126] The iodine and lead contents in seaweed iodine crystals were tested according to GB 1903.39-2018, "National Food Safety Standard for Food Nutrition Fortifiers: Seaweed Iodine." The percentage of organic iodine in the total iodine content in seaweed iodine crystals was determined using the method described in the paper "Study of Organic Iodine in Seaweed II: Forms and Contents" by Han Lijun et al. A thermal stability test was performed on seaweed iodized salt at 200°C for 1 hour. The iodine content was then measured after the test. Iodine loss rate = (initial iodine content - iodine content after thermal stability test) / initial iodine content × 100%. The results are shown in Table 1.

[0127] Table 1 Measurement results

[0128]

[0129] According to statistics, the iodine content and Pb content of the seaweed iodine crystals prepared in Examples 1 to 3 of the present invention meet national standards, and the proportion of organic iodine is high. The iodine loss rate of the prepared seaweed iodine salt is low and has excellent stability. Comparative Example 1 does not add composite protease, Comparative Example 2 has a long ultrasonic treatment time, Comparative Example 3 adds too much enzyme, Comparative Example 4 has anion separation column particle size that is too high and the number of theoretical plates is low, Comparative Example 5 does not perform step elution, Comparative Example 6 has a ceramic membrane separation pore size that is too high, Comparative Example 7 does not add γ-mercaptopropyltrimethoxysilane, Comparative Example 8 does not add multilayer graphene oxide, Comparative Example 9 has a seaweed iodine salt pH value that is too high, and the iodine content and organic iodine content of the prepared seaweed iodine crystals are both low, but the Pb content is too high, and the iodine loss rate of the prepared seaweed iodine salt at high temperature is too high. Therefore, the iodine content in the seaweed iodine crystals prepared using the raw materials and methods described in this application meets national requirements, has a high organic iodine content, and has good stability of inorganic iodine. At the same time, the heavy metal content is low, meeting national edible salt requirements, and has good edible value.

[0130] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A seaweed iodine salt, characterized in that: The raw materials for its preparation include, by weight, 100 to 150 parts of iodine-free salt, 0.1 to 0.5 parts of seaweed iodine crystals, and an appropriate amount of ammonium ferric citrate; The preparation method of seaweed iodine crystals comprises the following steps: S1. Rinse the seaweed material with deionized water 2-3 times, dry it at 50-70°C, and grind it through a 40-mesh sieve to obtain seaweed powder; S2. Mix the seaweed powder with the buffer solution, stir evenly, adjust the pH to 7-8, add the enzyme, ultrasonicate, centrifuge, and vacuum filter to obtain a filtrate. Repeat the above operation with the residue, combine the filtrates, and concentrate and dry the filtrates under reduced pressure to obtain a crude seaweed extract; the ultrasonication time is 8-12 h; S3. Dissolve the crude seaweed extract in water and pass it through an anion separation column at a flow rate of 2.5 to 3.5 BV / h. Elute with the mobile phase in steps for 40 to 70 minutes. Collect the eluate, let it stand for 20 to 30 hours, and then filter it with a modified ceramic membrane. Collect the filtrate, concentrate it under reduced pressure, and dry it to obtain seaweed iodine crystals. The enzyme is added in an amount of 0.2% to 0.5% of the seaweed powder; the enzymes are trypsin and compound protease; the mass ratio of trypsin to compound protease is (2 to 4):1; the enzyme activity of the trypsin is ≥15,000 U / g; the enzyme activity of the compound protease is ≥40,000 U / g; The amount of ammonium ferric citrate added does not exceed 0.0025% of the total mass of the non-iodized salt and the seaweed iodine crystals; The preparation method of the modified ceramic membrane comprises the following steps: B1. Hydrolyze the silane coupling agent in an 80 wt% ethanol aqueous solution and heat it to 55-65° C. Immerse the ceramic membrane in the solution for 2-4 hours, rinse with deionized water, and dry at 100-120° C. for 3-5 hours to obtain a silane coupling agent-modified ceramic membrane. B2. Prepare a polyvinyl alcohol aqueous solution with a mass concentration of 0.5% to 2%, add graphene oxide thereto and disperse evenly to obtain a mixed solution, completely immerse the silane coupling agent-modified ceramic membrane in the mixed solution by a vacuum migration method, vacuum treat for 20 to 30 minutes, then remove the membrane and heat treat at 100 to 200° C. for 1 to 3 hours to obtain the obtained product; The silane coupling agents are 3-aminopropyltrimethoxysilane and gamma-mercaptopropyltrimethoxysilane.

2. The seaweed iodine salt according to claim 1, wherein The buffer solution is a NaH2PO4 solution; the concentration of NaH2PO4 in the buffer solution is 0.1-0.2 mol / L.

3. The seaweed iodine salt according to claim 1, wherein The specific conditions of the ultrasonic treatment are: ultrasonic power of 100-150W, and ultrasonic temperature of 45-55°C.

4. The seaweed iodine salt according to claim 1, characterized in that The bonded phase of the anion separation column is quaternary ammonium, the particle size is 4 to 6 μm, and the theoretical plate number of a chromatographic column is ≥10,000.

5. The seaweed iodized salt according to claim 1, characterized in that The mobile phase is (NH4)2CO3 / NaOH solution; the concentration of (NH4)2CO3 in the mobile phase is 0.01-0.02 mol / L; and the pH of the mobile phase is 8-10.

6. The seaweed iodine salt according to claim 1, characterized in that The specific steps of the stepwise elution are: the flow rate of the mobile phase is 0.6-1.0 mL / min for the first 20-30 minutes, and the flow rate is 1.1-1.3 mL / min thereafter.

7. The seaweed iodized salt according to claim 1, characterized in that The separation pore size of the ceramic membrane is 0.4-0.5 μm, and the material is Al2O3-ZrO2.

8. A method for preparing seaweed iodized salt according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: dissolving seaweed iodine crystals in water and stirring evenly, adding ammonium ferric citrate and continuing stirring, adding baking soda to adjust the pH value of the solution to 7-9, adding the solution to iodine-free salt, stirring evenly and drying the solution to obtain seaweed iodine salt.

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