Low heavy metal residual food-grade cuttlefish ink and preparation method thereof

Abstract

The present application relates to the technical field of marine food processing, and particularly relates to a food-grade cuttlefish ink with low heavy metal residue and a preparation method thereof. The method comprises the following steps: mixing cuttlefish ink and water, performing homogenization treatment to obtain pretreated ink; mixing the pretreated ink and phytic acid, performing a first chelation reaction to obtain an intermediate product; mixing the intermediate product and a chitosan-based material, performing a second chelation reaction to obtain a chelation reaction liquid; and performing solid-liquid separation on the chelation reaction liquid to obtain the food-grade cuttlefish ink with low heavy metal residue. Through the step-by-step cooperative process of phytic acid pre-chelation and chitosan-based material flocculation separation, combined with pH regulation and centrifugal separation, the method can simultaneously and efficiently remove multiple heavy metals such as cadmium, lead and copper, while well retaining melanin in the cuttlefish ink, and the whole process uses food-grade raw materials, which is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of marine food processing technology, and in particular to a food-grade squid ink with low heavy metal residue and its preparation method. Background Technology

[0002] Cuttlefish ink is a natural secretion from the ink sac of cephalopods (squid). Its main components are melanin, polysaccharides, proteins, and minerals. Due to its natural color and certain nutritional properties, cuttlefish ink is widely used as a natural coloring agent in foods such as cuttlefish noodles, cuttlefish sausages, and baked goods. In recent years, the market demand for cuttlefish ink in the field of natural pigments has continued to grow.

[0003] However, as marine cephalopods, squid have the physiological characteristic of accumulating metal elements from their surrounding environment, and their ink commonly contains multiple metal components such as cadmium, lead, and copper. In some near-shore sources, the residual levels of these metal components are relatively high, which has somewhat limited the application of squid ink products in the high-end food market and export trade.

[0004] Currently, there is relatively little research on processes that directly remove metal components from squid ink itself. In existing literature, the melanin in squid ink is mostly used as an adsorbent to remove metal ions from other food systems or water bodies. The technical approach is to use squid ink as a means of purifying an external matrix, rather than purifying the ink itself. In the few reports involving squid ink products, the removal methods mainly involve physical separation operations such as water washing combined with centrifugation.

[0005] The existing methods described above have significant limitations. First, regarding removal efficiency, water washing and centrifugation mainly rely on physical dispersion and solid-liquid separation, which can only remove some free or physically adsorbed metal components. For metal components in the ink that are tightly bound to the matrix such as proteins and melanin, the removal capacity is clearly insufficient, and the removal effect varies greatly for different types of metal components, making it difficult to achieve simultaneous and efficient removal of multiple components. Second, regarding product quality maintenance, while removing some metal components, the water washing operation also results in the loss of a large number of melanin particles with the aqueous phase, leading to a decrease in product yield and a significant reduction in coloring performance, directly affecting its commercial value as a natural pigment. Furthermore, squid ink itself is a high-viscosity, high-pigment-content colloidal system with fine pigment particles and a complex matrix composition. It is also prone to changes in properties under extreme acidic or alkaline conditions. Conventional processing techniques suitable for simple food matrices cannot be directly applied to this colloidal environment, lacking specific process parameters. Furthermore, existing solutions are mostly at the laboratory stage of exploration, lacking a systematic operation window and stable process route, and are insufficient in operability and scalability, making it difficult to meet the requirements of large-scale and continuous production of food-grade raw materials.

[0006] In summary, there is an urgent need for a food-grade processing method that can effectively reduce the residue of various metal components while retaining melanin and active ingredients, and is industrially feasible, taking advantage of the colloidal properties of squid ink. Summary of the Invention

[0007] The purpose of this invention is to address the problems existing in the prior art by providing a food-grade squid ink with low heavy metal residue and its preparation method. This method utilizes a stepwise synergistic process of phytic acid pre-chelation and chitosan-based material flocculation separation, combined with pH control and centrifugation, to achieve simultaneous and efficient removal of multiple heavy metals such as cadmium, lead, and copper, while effectively preserving the melanin in the squid ink. Furthermore, the entire process uses food-grade raw materials, making it suitable for industrial production.

[0008] To achieve the above objectives, the present invention provides a method for preparing food-grade squid ink with low heavy metal residue, comprising the following steps: S1. Mix squid ink and water, and homogenize to obtain pretreated ink; S2. Mix the pretreated ink and phytic acid to carry out the first chelation reaction to obtain an intermediate product; mix the intermediate product with chitosan-based material to carry out the second chelation reaction to obtain a chelation reaction solution; S3. Perform solid-liquid separation on the chelation reaction solution to obtain the food-grade squid ink with low heavy metal residue.

[0009] In some optional embodiments, in S1, the squid ink is fresh or thawed squid ink; the mass ratio of the squid ink to water is 1:(1-3); the homogenization treatment is performed at a pressure of 20-30 MPa, and repeated 1-2 times; the homogenization treatment breaks down melanin aggregates and releases encapsulated heavy metal ions. After the homogenization treatment, a step is further included to adjust the pH value using a 1-2% (w / w) acetic acid solution, so that the pH value of the pretreated ink is 4.5-7.0.

[0010] Wherein, when the chitosan-based material in S2 is chitosan, the pH value of the pretreated ink is 4.5-5.5; when the chitosan-based material in S2 is carboxymethyl chitosan, the pH value of the pretreated ink is 4.5-7.0, preferably 6.0-7.0.

[0011] In some optional embodiments, in S2, the amount of phytic acid added is 0.1-0.3 wt% of the dry weight of the pretreated ink.

[0012] In some optional embodiments, in S2, the chitosan-based material includes at least one of chitosan and carboxymethyl chitosan; the amount of chitosan-based material added is 0.5-2 wt% of the dry weight of the pretreated ink.

[0013] In some optional embodiments, when the chitosan-based material is chitosan, the chitosan is mixed with the intermediate product in the form of chitosan colloid; the method for preparing the chitosan colloid includes: mixing chitosan and acetic acid solution under stirring, and stirring continuously for 30-60 minutes until completely dissolved to obtain chitosan colloid; when the chitosan-based material is carboxymethyl chitosan, the carboxymethyl chitosan is directly mixed with the intermediate product.

[0014] In some optional embodiments, the chitosan has a degree of deacetylation of 85-95% and a molecular weight of 100-500 kDa; the acetic acid solution has a mass fraction of 1-2%; and the chitosan colloid has a mass fraction of 0.5-1%.

[0015] In some optional embodiments, in S2, the temperature of the first chelation reaction is 25-35°C, the stirring speed is 300-500 r / min, and the time is 10-20 min; the temperature of the second chelation reaction is 25-35°C, the stirring speed is 300-500 r / min, and the time is 30-60 min. In the first chelation reaction, phytic acid utilizes its multidentate chelating properties to simultaneously chelate cadmium, lead, and copper heavy metals in both free and weakly bound states in the system; in the second chelation reaction, chitosan-based materials utilize their cationic flocculation effect to capture negatively charged phytic acid-heavy metal complexes, forming large-particle flocs.

[0016] In some optional embodiments, in step S3, the solid-liquid separation is performed by centrifugation; the centrifugal force is 3000-4000g, and the time is 10-15 minutes; during centrifugation, the heavy metal chelate flocs, due to their larger density and particle size, settle to the bottom, while the melanin particles, due to their smaller particle size, are mostly retained in the supernatant, achieving selective separation, and the upper black clear liquid is collected. After centrifugation, the step further includes adjusting the pH value using an 8-12% sodium bicarbonate solution to make the pH value of the low-heavy-metal-residue food-grade squid ink 6.0-7.0.

[0017] In some optional embodiments, S1 further includes an enzymatic hydrolysis step of the mixed solution before homogenization; the enzymatic hydrolysis is performed at a pH of 7.0-8.0, a temperature of 40-45°C, and a time of 20-30 min; specifically, the enzymatic hydrolysis process includes: adjusting the pH of the mixed solution to 7.0-8.0 using a sodium bicarbonate solution with a mass fraction of 8-12%, adding an alkaline protease at 0.1-0.3 wt% of the dry weight of squid ink, and hydrolyzing at 40-45°C for 20-30 min to break only the peptide bonds at the heavy metal binding sites without destroying the overall structure of melanin; then heating to 75-85°C to inactivate the enzyme for 5-15 min, and finally cooling naturally to room temperature.

[0018] The present invention also provides a food-grade squid ink with low heavy metal residue, which is prepared according to the preparation method of the food-grade squid ink with low heavy metal residue.

[0019] In some optional embodiments, the food-grade squid ink with low heavy metal residue has a cadmium content ≤0.5 mg / kg, a lead content ≤0.8 mg / kg, and a copper content ≤5.0 mg / kg.

[0020] This invention targets the inherent characteristics of the high-viscosity melanin colloidal system in squid ink. Through a stepwise chelation-centrifugation process design, it precisely controls the electrostatic interaction and chelation competition relationship. The mechanism of action is as follows: (1) Selective regulatory mechanism of electrostatic interaction between melanin and chitosan Cuttlefish ink melanin is composed of eumelanin nanoparticles with a surface rich in acidic functional groups such as carboxyl and phenolic hydroxyl groups. Its isoelectric point is approximately pH 2.0-3.0, and it carries a negative surface charge in environments with pH > 3. Under neutral conditions, its Zeta potential is approximately -20 to -25 mV, and it is stable in a colloidal state. Ordinary chitosan has an amino pKa of approximately 6.2-6.5 and becomes positively charged under weakly acidic conditions through protonation. If chitosan is directly added in high doses to the ink system, the two will aggregate on a large scale through electrostatic neutralization, causing the melanin to settle along with the flocs, resulting in a significant loss of coloring power. Therefore, current technologies make it difficult to directly apply chitosan to the purification of melanin systems.

[0021] This invention achieves selective separation through the following four-fold design, thereby controlling melanin loss to a low level: (a) A stepwise addition method is adopted, in which phytic acid is added first, followed by chitosan-based material. Small molecule phytic acid has a fast diffusion rate and preferentially combines with heavy metal ions in the system to form a phytic acid-heavy metal anion complex with a high charge density; the positively charged segments in the subsequently added chitosan-based material will preferentially combine with the phytic acid-heavy metal anion complex with a higher charge density to form flocs, rather than preferentially adsorbing melanin nanoparticles with larger particle size and lower surface charge density.

[0022] (b) The amount of chitosan-based material added is 0.5-2 wt% of the dry weight of the pretreated ink, which is far lower than the proportion of melanin in the system and is insufficient to trigger large-scale electrostatic aggregation of melanin.

[0023] (c) For chitosan, the pH of the pretreated ink is controlled within the range of 4.5-5.5. This pH window has a dual function: on the one hand, it ensures the appropriate protonation of the chitosan amino groups, enabling it to exert effective cationic flocculation; on the other hand, it avoids excessive positive charge due to excessive pH, which could lead to excessive adsorption of melanin, while also keeping it away from the isoelectric point of melanin, ensuring that the melanin nanoparticles maintain a stable negatively charged colloidal state throughout the reaction process, making them less prone to self-aggregation. For carboxymethyl chitosan, the pH of the pretreated ink is controlled within the range of 4.5-7.0. It has natural water solubility and can stably exert chelating flocculation under weakly acidic to neutral conditions. Under near-neutral conditions, the negative charge on the melanin surface is stronger, the colloidal stability is higher, the pigment co-precipitation loss is less, and the product color purity is better.

[0024] (d) The chelated flocs formed by phytic acid-heavy metal-chitosan-based materials are micron-sized large particles with high density and easy sedimentation; melanin consists of nano-sized particles of 100-200 nm with strong colloidal stability. Centrifugation with a force of 3000-4000 g can completely settle the heavy metal chelated flocs, while most of the melanin remains in the supernatant, achieving efficient separation of the two.

[0025] (2) Competitive breaking mechanism of heavy metal chelation in complex matrices The total proportion of proteins, polypeptides, and free amino acids in the dry matter of squid ink can reach about 30%. The amino, carboxyl, and thiol groups in its molecules can form coordination bonds with heavy metal ions, causing heavy metals to exist in three forms: free, weakly bound, and tightly bound. Among these, the bound heavy metals account for a relatively high proportion. Conventional chelation processes can only remove free heavy metals, are significantly affected by matrix competition, and generally have a total removal rate of less than 70%. Furthermore, they are difficult to simultaneously remove multiple heavy metals such as cadmium, lead, and copper.

[0026] This invention systematically solves the matrix competition problem through the synergistic effect of "enzymatic decomposition-strong chelation and replacement-flocculation and trapping," achieving simultaneous removal of multiple heavy metals. (a) Phytic acid is inositol hexaphosphate, which is a multidentate strong chelating agent. Its conditional chelation stability constant for divalent heavy metal ions such as cadmium, lead, and copper ions can reach 10. 7 -10 12 The order of magnitude; while the coordination stability constants of amino acids, small molecule peptides, and heavy metal ions are only 10. 2 -10 5 The difference is several orders of magnitude. Phytic acid can simultaneously remove various heavy metal ions that are weakly bound to proteins and peptides through a competitive substitution effect, forming a more stable phytic acid-heavy metal complex, thereby breaking through the constraints of matrix binding.

[0027] (b) For tightly bound heavy metals embedded in the melanin protein backbone that cannot be directly replaced by phytic acid, the present invention uses low-dose alkaline protease to controllably hydrolyze the protein, breaking only the peptide bonds exposed on the protein surface, releasing the bound heavy metals without damaging the overall structure and coloring properties of the melanin particles, and converting the bound heavy metals into a chelateable state.

[0028] (c) Positively charged chitosan-based materials can neutralize and cross-link flocculate negatively charged phytic acid-heavy metal complexes to form large-particle flocs, which can be efficiently removed by centrifugation, thus avoiding the rebinding of chelated heavy metal ions with matrix proteins.

[0029] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention utilizes the stepwise chelating synergistic effect of phytic acid and chitosan-based materials. Phytic acid, as a strong multidentate chelating agent, can effectively replace various heavy metal ions such as cadmium, lead, and copper that are weakly bound to matrix proteins, forming a stable phytic acid-heavy metal complex. The chitosan-based material further captures this complex through cationic flocculation, forming large-particle flocs, which can be removed by centrifugation. The synergistic effect of both ensures the simultaneous and efficient removal of multiple heavy metals. In addition, this invention can also add a mild enzymatic pretreatment step according to the quality of the raw materials. Through controlled enzymatic hydrolysis with a low dose of alkaline protease, the bound heavy metals tightly wrapped by the melanin backbone are released and converted into a chelateable state, thereby further improving the removal effect. This process has good adaptability to raw materials with different levels of pollution.

[0030] (2) This invention utilizes a step-by-step addition sequence of "phytic acid first, then chitosan-based material" to preferentially bind with heavy metal ions to form a high-charge-density anionic complex, competitively consuming the positive charge of the chitosan-based material. Combined with low-dose addition of chitosan-based material and precise pH window control, this effectively prevents large-scale electrostatic aggregation of the chitosan-based material and negatively charged melanin nanoparticles. Simultaneously, based on the significant particle size difference between the chelated flocs (micrometer-sized) and melanin particles (nanometer-sized), selective separation can be achieved through centrifugation, allowing the heavy metal chelated flocs to completely settle while the vast majority of the melanin particles remain in the supernatant. Through these multiple design steps, the product maintains excellent coloring performance while removing heavy metals.

[0031] (3) All raw materials used in this invention, such as phytic acid, chitosan-based materials, acetic acid, and sodium bicarbonate, are food-grade and contain no toxic or harmful substances. The process conditions are mild, requiring no high temperature or high pressure or special equipment; conventional food processing equipment is sufficient. The operation is simple, the processing cost is controllable, and it is suitable for large-scale industrial continuous production. Furthermore, the process allows for flexible selection of whether to add an enzymatic pretreatment step based on the degree of heavy metal contamination in the raw materials, demonstrating good process adaptability and operational flexibility. Detailed Implementation

[0032] The following embodiments are provided to better understand the present invention and are not limited to the described embodiments. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0033] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0034] In the following embodiments and comparative examples of the present invention, the squid ink is fresh squid ink with a dry matter content of 12%, an original cadmium content of 2.3 mg / kg, a lead content of 1.5 mg / kg, and a copper content of 12.6 mg / kg.

[0035] Example 1 This embodiment provides a method for preparing food-grade squid ink with low heavy metal residue, including the following steps: Take 1000g of squid ink and dilute it with 1000g of pure water. Homogenize it once at 25MPa. Adjust the pH to 5.0 with a 1% acetic acid solution to obtain pretreated ink.

[0036] Under stirring, 1.2g of food-grade chitosan with a degree of deacetylation of 90% and a molecular weight of 300kDa was slowly added to a 1% acetic acid solution and stirred for 40 minutes until completely dissolved to obtain chitosan colloid with a chitosan mass fraction of 1%.

[0037] Food-grade phytic acid was added to the pretreated ink at a rate of 0.2 wt% of the dry weight of the pretreated ink. The mixture was stirred and chelated at 30°C and 400 rpm for 15 min to obtain an intermediate product. Subsequently, chitosan colloid was slowly added dropwise at a rate of 1 wt% of the dry weight of the pretreated ink (based on chitosan content). The mixture was stirred and chelated at 30°C and 400 rpm for 45 min to obtain a chelated reaction solution.

[0038] The chelation reaction solution was transferred into a centrifuge and centrifuged at 3500g for 12 minutes. After centrifugation, the upper black clear liquid was collected and the pH was adjusted to 6.5 using a 10% sodium bicarbonate solution to obtain food-grade squid ink with low heavy metal residue.

[0039] Example 2 This embodiment provides a method for preparing food-grade squid ink with low heavy metal residue. The only difference from Example 1 is that an enzymatic hydrolysis step is added before homogenization. Specifically, 1000g of fresh squid ink is taken and diluted with 1000g of pure water. The pH is adjusted to 7.5 using a 10% sodium bicarbonate solution. Food-grade alkaline protease (0.2wt% of the dry weight of the squid ink) is added, and the mixture is enzymatically hydrolyzed at 42°C for 25min. Then, the temperature is raised to 80°C to inactivate the enzyme for 10min, and the mixture is allowed to cool naturally to room temperature. Subsequently, the mixture is homogenized once at 25MPa. The pH is adjusted to 5.0 using a 1% acetic acid solution to obtain pretreated ink.

[0040] The remaining steps and conditions are exactly the same as in Example 1.

[0041] Example 3 This embodiment provides a method for preparing food-grade squid ink with low heavy metal residue, which differs from Example 1 only in that: (1) Adjust the pH value to 6.0 with acetic acid solution with a mass fraction of 1% to obtain pretreated ink.

[0042] (2) Replace the chitosan colloid with carboxymethyl chitosan (the amount of carboxymethyl chitosan added is 1 wt% of the dry weight of the pretreated ink).

[0043] The remaining steps and conditions are exactly the same as in Example 1.

[0044] Comparative Example 1 This comparative example provides a method for preparing cuttlefish ink, which differs from Example 1 only in that the stirring and chelation reaction time after adding phytic acid is adjusted to 60 min, and the step of adding chitosan colloid for chelation reaction is omitted.

[0045] The remaining steps and conditions are exactly the same as in Example 1.

[0046] Comparative Example 2 This comparative example provides a method for preparing cuttlefish ink, which differs from Example 1 only in that the step of adding phytic acid for chelation reaction is omitted, and the stirring chelation reaction time after adding chitosan colloid is adjusted to 60 min.

[0047] The remaining steps and conditions are exactly the same as in Example 1.

[0048] Comparative Example 3 This comparative example provides a method for preparing cuttlefish ink, which uses a water washing and centrifugation process, specifically including the following steps: Take 1000g of squid ink, add an equal volume of water, stir and soak for 2 hours. Then centrifuge at 3500g for 15 minutes, discard the supernatant and collect the precipitate. Add water to the obtained precipitate to redissolve it, so that the dry matter content in the redissolved system is 8.5%.

[0049] Experimental Example The cadmium, lead, and copper contents in the products obtained in Examples 1-3 and Comparative Examples 1-3 were tested, and the removal rate of each heavy metal was calculated: Removal rate (%) = (Heavy metal content in raw material - Heavy metal content in product) / Heavy metal content in raw material × 100%. Simultaneously, the melanin retention rate was calculated by measuring the absorbance of the product at a wavelength of 420 nm using ultraviolet-visible spectrophotometry: Melanin retention rate (%) = Absorbance of product / Absorbance of raw material × 100%. The test results are recorded in Table 1.

[0050] Table 1 Test Results

[0051] The test results above show that Examples 1-3 of this invention, through the stepwise chelation synergistic effect of phytic acid and chitosan-based materials, achieved removal rates of over 84% for cadmium, lead, and copper, which is far superior to Comparative Example 1 (using phytic acid alone) and Comparative Example 2 (using chitosan-based materials alone), and also significantly superior to Comparative Example 3 (using a water washing and centrifugation process). This indicates a synergistic effect between phytic acid and chitosan-based materials, and the stepwise addition method of phytic acid followed by chitosan-based materials can effectively overcome the problem of poor removal efficiency of single chelating agents or single flocculants.

[0052] Regarding melanin retention, Comparative Example 1, which used only phytic acid without adding chitosan-based materials, achieved a melanin retention rate as high as 96.8%, but its heavy metal removal effect was poor. Comparative Example 2, which used chitosan-based materials alone, saw its melanin retention rate drop to 85.7%, indicating that using chitosan-based materials alone causes a certain degree of melanin loss. Comparative Example 3, using a water washing and centrifugation process, had a melanin retention rate of only 68.3%, severely impairing the product's coloring performance. In contrast, Examples 1-3 of this invention all achieved melanin retention rates exceeding 90%, with Example 3, using carboxymethyl chitosan, achieving a melanin retention rate as high as 93.5%. This demonstrates that this invention, through its stepwise addition of phytic acid followed by chitosan-based materials, low-dose chitosan-based material addition, and narrow pH window control, effectively protects melanin while efficiently removing heavy metals.

[0053] Furthermore, in Example 2, after enzymatic pretreatment, the heavy metal removal rate was further increased to over 90%, while the melanin retention rate remained above 90%. This indicates that mild enzymatic hydrolysis can effectively release heavy metals tightly bound to the melanin protein backbone, converting them into a state that can be chelated by phytic acid, and that the hydrolysis conditions do not damage the overall structure of the melanin particles.

[0054] Therefore, this invention effectively overcomes the shortcomings of low heavy metal removal efficiency and large melanin loss in the prior art by using the stepwise chelation synergistic effect of phytic acid and chitosan-based materials, combined with the process design of narrow pH window control, low dosage and centrifugal selective separation, and achieves simultaneous and efficient removal of multiple heavy metals and high retention of melanin.

[0055] Finally, it should be noted that the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing food-grade squid ink with low heavy metal residue, characterized in that, Includes the following steps: S1. Mix squid ink and water, and homogenize to obtain pretreated ink; S2. Mix the pretreated ink and phytic acid to carry out the first chelation reaction to obtain an intermediate product; mix the intermediate product with chitosan-based material to carry out the second chelation reaction to obtain a chelation reaction solution; S3. Perform solid-liquid separation on the chelation reaction solution to obtain the food-grade squid ink with low heavy metal residue.

2. The method for preparing food-grade squid ink with low heavy metal residue according to claim 1, characterized in that, In S1, the mass ratio of squid ink to water is 1:(1-3); the homogenization treatment pressure is 20-30 MPa, and the number of times is 1-2; after the homogenization treatment, a step of adjusting the pH value is also included, and the pH value of the pretreated ink is 4.5-7.

0.

3. The method for preparing food-grade squid ink with low heavy metal residue according to claim 1, characterized in that, In S2, the amount of phytic acid added is 0.1-0.3 wt% of the dry weight of the pretreated ink.

4. The method for preparing food-grade squid ink with low heavy metal residue according to claim 1, characterized in that, In S2, the chitosan-based material includes at least one of chitosan and carboxymethyl chitosan; the amount of chitosan-based material added is 0.5-2 wt% of the dry weight of the pretreated ink.

5. The method for preparing food-grade squid ink with low heavy metal residue according to claim 4, characterized in that, When the chitosan-based material is chitosan, the chitosan is mixed with the intermediate product in the form of chitosan colloid; the preparation method of the chitosan colloid includes: mixing chitosan and acetic acid solution to obtain chitosan colloid; when the chitosan-based material is carboxymethyl chitosan, the carboxymethyl chitosan is directly mixed with the intermediate product.

6. The method for preparing food-grade squid ink with low heavy metal residue according to claim 5, characterized in that, The chitosan has a degree of deacetylation of 85-95% and a molecular weight of 100-500 kDa; the acetic acid solution has a mass fraction of 1-2%; and the chitosan colloid has a mass fraction of 0.5-1%.

7. The method for preparing food-grade squid ink with low heavy metal residue according to claim 1, characterized in that, In S2, the temperature of the first chelation reaction is 25-35℃ and the time is 10-20 min; the temperature of the second chelation reaction is 25-35℃ and the time is 30-60 min.

8. The method for preparing food-grade squid ink with low heavy metal residue according to claim 1, characterized in that, In S3, the solid-liquid separation method is centrifugation; the centrifugal force is 3000-4000g and the time is 10-15min; after centrifugation, a step of adjusting the pH value is also included, and the pH value of the food-grade squid ink with low heavy metal residue is 6.0-7.

0.

9. The method for preparing food-grade squid ink with low heavy metal residue according to claim 1, characterized in that, In step S1, before homogenization, the mixture is further subjected to an enzymatic hydrolysis step; the enzymatic hydrolysis is performed at a pH of 7.0-8.0, a temperature of 40-45℃, and a time of 20-30 minutes.

10. A food-grade squid ink with low heavy metal residue, characterized in that, The food-grade squid ink with low heavy metal residue is prepared according to any one of claims 1-9.

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