Method for removing heavy metals in fish gelatin

Abstract

The invention relates to a method for removing heavy metals in fish gelatin, which comprises the following steps: uniformly mixing fish gelatin with a natural eutectic solvent, heating, centrifuging, washing, precipitating and drying in vacuum to obtain the fish gelatin without heavy metals, a hydrogen bond donor of the natural deep-eutectic solvent is any one of glycerol and ethylene glycol, and a hydrogen bond acceptor of the natural deep-eutectic solvent is any one of L-proline and L-arginine. Compared with the traditional acid eluent, the fish gelatin treated by the natural deep-eutectic solvent keeps good appearance, color and texture, and the retention rate of the content of the nutrient substance collagen in the fish gelatin is high. According to the method, the non-toxic natural eutectic solvent and the water are used as the eluent and the solvent to remove the heavy metals in the fish gelatin, meanwhile, ultrahigh pressure can be used in cooperation with the natural eutectic solvent to remove the heavy metals in the fish gelatin, and the process is simple, efficient, safe and green. In the three eluents, the viscosity of EgPro is small, operation is convenient, the effect of removing heavy metal is good, and the influence on the content of collagen is small.

Description

Technical Field

[0001] The invention relates to the field of food processing, in particular to a method for removing heavy metals from isinglass, and specifically to application of a natural low eutectic solvent and synergistic ultrahigh pressure in green removal of heavy metals from isinglass. Background Art

[0002] Fish maw, also known as fish belly, fish bladder, and fish maw, is made from the fish's maw (the organ that fish use to regulate buoyancy in water) by dehydration. Its main component is collagen, which is rich in various vitamins and trace elements such as calcium, zinc, iron, and selenium. Its protein content is as high as 84.2%, and its fat content is only 0.2%. It is an ideal high-protein, low-fat food, a raw material for human protein supplementation, and a food that is easily absorbed and utilized by the human body. Fish maw is known as the "marine ginseng" and is as famous as bird's nest and shark fin, and is listed as one of the eight delicacies. In my country, eating fish maw has a long history. In the Tang Dynasty, fish maw became a tribute. In recent years, my country's fish maw industry has continued to develop. In 2020, the domestic fish maw production was 7,495 tons, a year-on-year increase of 0.97%. It is estimated that by 2025, the scale of my country's fish maw market will reach 5.432 billion yuan.

[0003] However, with the rapid development of industry and agriculture, heavy metal pollution in the marine environment has become increasingly serious in recent years. Arsenic, cadmium, mercury, lead, chromium and copper in polluted seawater are absorbed by marine organisms through natural migration. Arsenic and chromium are easily enriched in marine organisms such as fish, resulting in excessive heavy metals in fish maw. Arsenic is highly cumulative and toxic. The main symptoms of arsenic poisoning include skin pigmentation, skin keratinization, skin cancer and other skin diseases, as well as damage to the nervous system, cardiovascular system, liver and kidneys. More seriously, arsenic is also considered a carcinogen that can increase the risk of many cancers. After chromium, especially hexavalent chromium, is ingested into the human body, it is easy to accumulate in organs such as the liver and kidneys, and may spread throughout the body through the blood system. Long-term intake or exposure to hexavalent chromium may lead to a variety of health problems, including skin damage, respiratory diseases, digestive system problems, and even cancer. Therefore, long-term intake of seafood such as fish maw may lead to the accumulation of arsenic and chromium in the human body, seriously endangering human health. Therefore, how to reduce the residue of heavy metals in seafood such as fish maw before sales has become a top priority.

[0004] There are two main measures to prevent seafood pollution. One is to start from the external environment and repair the marine environment polluted by heavy metals; the other is to start from the heavy metal polluted products themselves and control the content of heavy metals in seafood through processing technology. The restoration of the marine environment is a slow process, which requires continuous strengthening of the treatment of industrial wastes. It is difficult to solve the existing problem of heavy metal pollution in seafood in a timely manner. Therefore, at present, the main method is to remove heavy metals from seafood to control the content of heavy metals in seafood. The main methods include chemical precipitation method, chemical complexation method, etc.

[0005] Among them, chemical precipitation is the most widely used method for heavy metal removal in industry. This method is simple, easy to operate, economical and effective. It uses chemical reagents to react with heavy metal elements to produce water-insoluble precipitates. At the same time, the pH of the solution is adjusted to control the reaction to achieve the purpose of heavy metal removal. The chemical reagents commonly used in chemical precipitation are mainly lime (Ca(OH) 2 ), caustic soda (NaOH), sodium sulfide (Na 2 S) and sodium hydrosulfide (NaHS) and other hydroxides and sulfides, for example, the prior art discloses a rapid preparation method of fish collagen peptide chelated calcium, which uses a chemical precipitation method to remove heavy metals in fish scales and fish skin, including the following steps: placing tilapia collagen peptide clear solution in a reactor, adding a mixture weight 0.1% papain and bromelain combination (1:1), adding a saturated calcium hydroxide solution to adjust the pH value to 6.5, the reaction temperature is 55 ° C, the reaction time is 1.5 hours, and high-speed centrifugation to obtain tilapia collagen peptide chelated calcium clear solution. This method mainly utilizes the characteristics that the sulfates and hydroxides of heavy metals (such as arsenic, cadmium, mercury, lead and chromium) are not soluble in water to remove heavy metals, but these chemical precipitations are mainly colloidal, and when removing the heavy metals of fish glue samples, these colloidal precipitations are difficult to be completely separated from the fish glue samples, resulting in poor heavy metal removal effect, and the pH of different heavy metal precipitations is different. In the process of removing heavy metals by adjusting the pH, while reducing the concentration of one heavy metal element, it may cause another heavy metal element concentration to increase. At the same time, the lime (Ca(OH) 2 ) and caustic soda (NaOH) are not food additives, which limits the application of chemical precipitation method in actual production. In addition, it is found in the research process of the present invention that the chemical reagents used in the chemical precipitation method affect the edible quality of fish glue, resulting in a decrease in the nutritional value and economic benefits of fish glue. Based on this, it is urgent to develop a green and efficient method for removing heavy metal arsenic and chromium from heavy metal contaminated fish glue. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a green and efficient method for removing heavy metals arsenic and chromium from heavy metal-contaminated fish glue. This method will also have a good application prospect in removing heavy metals such as arsenic and chromium from other seafood.

[0007] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0008] A method for removing heavy metals from fish glue comprises the following steps:

[0009] The fish glue and the natural low eutectic solvent are mixed evenly, heated, centrifuged, washed and precipitated, and vacuum dried to obtain the fish glue with heavy metals removed;

[0010] The hydrogen bond donor of the natural deep eutectic solvent is any one of glycerol and ethylene glycol, and the hydrogen bond acceptor is any one of L-proline and L-arginine.

[0011] Compared with the prior art, the present invention applies natural deep eutectic solvents (NADESs) to the removal of heavy metals from fish glue for the first time, and finds that a variety of NADESs have a good heavy metal removal effect on fish glue samples, and can remove a variety of heavy metals on the surface and inside of the sample, and the post-processing method is simple, and has little effect on the food quality of fish glue. Among them, NADES prepared from ethylene glycol and L-proline has a high removal rate for arsenic and chromium, and has little effect on the texture of fish glue and the content of collagen, and can effectively remove heavy metals while minimizing the reduction of the edible quality of fish glue, and has the best comprehensive effect on the removal of heavy metals in fish glue. In addition, the method provided by the present invention uses non-toxic natural deep eutectic solvents and water as eluents and solvents to remove heavy metals in fish glue, and has the advantages of simple process, low cost, high efficiency, safe components and green.

[0012] Furthermore, the natural low eutectic solvent is a solvent formed by heating a hydrogen bond donor and a hydrogen bond acceptor to form a eutectic at a molar ratio of 3-4.5:1 at 60° C. and cooling the resulting mixture.

[0013] Furthermore, the heavy metals include arsenic and / or chromium.

[0014] Furthermore, the heating of the mixture of fish glue and natural deep eutectic solvent includes heating the mixture at 60° C. for 1 hour, during which the mixture is ultrasonically subjected to 35-45° C. for 2 minutes every 15 minutes.

[0015] Furthermore, the heated mixture is subjected to ultrahigh pressure treatment and then centrifuged.

[0016] Furthermore, the ultra-high pressure treatment condition is 200-400 MPa for 10 min.

[0017] Further, the fish glue is mixed with the natural deep eutectic solvent at a solid-liquid ratio of 1:10-1:25.

[0018] Furthermore, the hydrogen bond donor of the natural low eutectic solvent is ethylene glycol, the hydrogen bond acceptor is L-proline, and the molar ratio is 3:1.

[0019] Furthermore, the solid-liquid ratio is 1:20.

[0020] Furthermore, deionized water is added to the natural deep eutectic solvent until the water content of the natural deep eutectic solvent is 0-10%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1The effect of eluent type on the chromium removal rate in isinglass.

[0022] Figure 2 The effect of eluent types on the loss rate of collagen in fish glue.

[0023] Figure 3 This is the appearance of fish glue samples before treatment with different types of eluents, where 1-7 represent GlyPro, GlyArg, EgPro, HCl, oxalic acid, citric acid, and NaOH treatments, respectively.

[0024] Figure 4 This is the appearance of fish glue samples after being treated with different types of eluents, where 1-7 represent GlyPro, GlyArg, EgPro, HCl, oxalic acid, citric acid, and NaOH treatments, respectively.

[0025] Figure 5 is the viscosity of EgPro eluent with different water contents.

[0026] Figure 6 The effect of EgPro water content on the removal rate of heavy metals in fish glue.

[0027] Figure 7 The effect of the solid-liquid ratio of isinglass to EgPro on the removal rate of heavy metals in isinglass.

[0028] Figure 8 The effect of ultrahigh pressure and its synergy EgPro on chromium removal efficiency.

[0029] Fig. 9 The effect of ultrahigh pressure and its synergy EgPro on arsenic removal efficiency. DETAILED DESCRIPTION

[0030] In order to solve the problems of low heavy metal removal rate, difficulty in removing multiple heavy metals at the same time, the reagents used in the existing chemical precipitation method for removing heavy metals from seafood, and the troublesome post-processing, affecting product quality and being unfriendly to the environment, the present invention aims to establish a green and efficient method for removing heavy metals from fish maw and improve the quality of fish maw.

[0031] Natural deep eutectic solvents (NADESs) are two-component or three-component mixtures composed of a certain molar ratio of hydrogen bond acceptors (such as quaternary ammonium salts) and hydrogen bond donors (such as polyols, carboxylic acids, amides and other compounds) through hydrogen bond interactions. Since its freezing point is lower than the melting point of all the pure substances of the components, it is called a deep eutectic solvent. The solvent is inexpensive, non-volatile, safe in components, and biodegradable. It is a green solvent that can also be used to remove heavy metals in the soil. At present, there is no research on the use of NADESs to remove heavy metals in fish glue in China. Based on this, the present invention explores the removal effect of natural deep eutectic solvents on heavy metals in fish glue and the influence of fish glue quality. It is found that the effect of natural deep eutectic solvents on the quality of fish glue is significantly lower than that of organic reagents in chemical precipitation methods, and has a good heavy metal removal effect.

[0032] The study found that the adsorption of heavy metals by natural deep eutectic solvents is mainly chemical adsorption, and changes in chemical bonds and electronic displacements occur between the adsorbent and the adsorbate. Through the adsorption kinetic model, it is inferred that NADESs provide a large number of adsorption sites in the first stage to complex with heavy metals complexed on the surface of organic matter, and gradually enter the sample for adsorption in the second stage. The entire adsorption stage shows rapid adsorption first, until the active sites on the adsorbent surface decrease, the adsorption rate slows down, and saturation is reached. Therefore, limited by the number of active sites on the adsorbent surface, natural deep eutectic solvents have the problem of long time consumption in the later stage of heavy metal adsorption but no significant increase in adsorption amount. If you want to further improve the removal rate of heavy metals in fish glue, you can choose to increase the amount of natural deep eutectic solvents, but the increase in the amount will significantly increase the cost of heavy metal removal in fish glue, and the increase in the amount will have limited improvement in efficiency.

[0033] Based on this, the present invention intends to combine natural low eutectic solvents with other heavy metal removal methods to further improve the heavy metal removal rate in fish glue, while reducing the impact of heavy metal removal on the quality of fish glue.

[0034] High pressure processing (HPP) can use high pressure conditions to accelerate solvent penetration and extract target compounds from solid samples. Due to isostatic pressure and rapid pressure increase, HPP has the potential to allow the extract (water or solvent) to quickly, effectively and evenly penetrate into the solid and extract the target components. Compared with traditional extraction methods, the mass transfer rate under HPP conditions can be increased by 2-4 times, and the dissolution equilibrium can be reached in a short time. HPP technology can also increase the dissociation degree of the extract. Under the action of HPP, the pH of neutral or weakly acidic solutions is reduced by 1.5-2 units. The lower pH of the liquid environment can provide more H +HPP technology competes with heavy metal ions to bind to organic matter as Lewis base, so it has the potential to replace heavy metal ions, bind to the anionic groups of the extract and be eluted. In addition, HPP has no effect on covalent bonds, but affects non-covalent bonds related to macromolecules, that is, it affects the binding of heavy metals to macromolecules in food, so HPP technology can promote the release of heavy metal ions into the extract. However, there is currently no report on the removal of heavy metals in fish glue by HPP in China, so the present invention explores the effect of removing residual heavy metals in fish glue by HPP.

[0035] Based on the above research, the present invention further explores the effect of HPP in synergizing NADESs in removing heavy metals, aiming to improve the removal rate and efficiency of heavy metal removal from fish glue, and reduce the impact of the heavy metal removal process on the quality of fish glue. In the process of HPP in synergizing NADESs in removing heavy metals, NADESs is a weakly acidic solvent (pH about 5-7), which, as a Lewis acid, preferentially interacts with the electron donor in fish glue, and pulls out heavy metal cations through NADESs anions; on this basis, applying HPP accelerates the uniform penetration of NADESs solvent into fish glue, while accelerating the dissociation rate of the extract, thereby further improving the removal effect of heavy metals in fish glue.

[0036] In summary, the present invention aims to establish a method for removing heavy metals from fish glue using NADESs and HPP technology, providing a green and efficient removal technology, which is expected to fill the current domestic research gap. Based on this, the present invention provides a method for removing heavy metals from fish glue, comprising the following steps:

[0037] The fish glue and the natural low eutectic solvent are mixed evenly, heated, centrifuged, the precipitate is washed and vacuum dried to obtain the fish glue with heavy metals removed.

[0038] Based on the above method, the present invention screened the hydrogen bond donors and hydrogen bond acceptors of the natural low eutectic solvent, and found that the natural low eutectic solvent synthesized by glycerol or ethylene glycol as the hydrogen bond donor and L-arginine or L-proline as the hydrogen bond acceptor has a good removal effect on the heavy metals remaining in fish glue.

[0039] Furthermore, the present invention studies the effects of the composition, water content and addition amount of the natural low eutectic solvent on the heavy metal removal rate of isinglass when the isinglass sample is treated with the solvent alone.

[0040] Then, the effect of pressure on the removal rate of heavy metals in isinglass when it was treated with ultrahigh pressure alone was studied, and the optimal treatment conditions were further used to treat the heated isinglass and natural low eutectic solvent mixture with ultrahigh pressure and then centrifuged.

[0041] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0043] The reagents used in the following examples, unless otherwise specified, are all commercially available; the methods used in the following examples, unless otherwise specified, are all achievable by conventional methods.

[0044] Example 1

[0045] Referring to Table 1, glycerol is selected as a hydrogen bond donor and L-proline is selected as a hydrogen bond acceptor to prepare a natural low eutectic solvent GlyPro, which specifically includes the following steps:

[0046] Glycerol and L-proline are mixed in a molar ratio of 3:1, placed in a constant temperature magnetic stirrer for stirring, and the temperature is set to 60°C to heat the mixture for eutectic melting until the mixture forms a uniform and stable solvent. The solvent is cooled to room temperature and then placed in a desiccator until constant weight is reached, thereby obtaining the natural low eutectic solvent GlyPro.

[0047] Example 2

[0048] Referring to Table 1, glycerol is selected as a hydrogen bond donor and L-arginine is selected as a hydrogen bond acceptor to prepare a natural low eutectic solvent GlyArg, which specifically includes the following steps:

[0049] Glycerol and L-arginine are mixed in a molar ratio of 4.5:1, the mixture is placed in a constant temperature magnetic stirrer for stirring, and the temperature is set to 60° C. to heat the mixture for eutectic melting until the mixture forms a uniform and stable solvent, the solvent is cooled to room temperature, and then placed in a desiccator until constant weight is reached, and then deionized water is added to make the water content of the solvent 10%, thereby obtaining a natural low eutectic solvent GlyArg.

[0050] Table 1 Preparation of NADESs solvents

[0051]

[0052] Example 3

[0053] Referring to Table 1, ethylene glycol is selected as a hydrogen bond donor and L-proline is selected as a hydrogen bond acceptor to prepare a natural deep eutectic solvent EgPro, which specifically includes the following steps:

[0054] Glycerol and L-proline are mixed in a molar ratio of 3:1, placed in a constant temperature magnetic stirrer for stirring, and the temperature is set to 60°C to heat the mixture for eutectic melting until the mixture forms a uniform and stable solvent. The solvent is cooled to room temperature and then placed in a desiccator until constant weight is reached to obtain the natural low eutectic solvent EgPro.

[0055] Example 4

[0056] (1) This embodiment uses a natural deep eutectic solvent to remove heavy metals from fish glue, including the following steps:

[0057] S11. Soak the fish glue sample in deionized water, cut it into pieces of about 2×2 cm, and then mix the fish glue sample with the natural low eutectic solvents (GlyPro, GlyArg and EgPro) prepared in Examples 1-3 at a ratio of 1:10 (w / w), and vortex to mix them evenly.

[0058] S12. Place the uniformly mixed mixture in a 60°C water bath and heat it at a constant temperature for 1 hour. During the heating period, ultrasonicate the mixture at 40±1°C for 2 minutes every 15 minutes, and then return the ultrasonicated mixture to the water bath for further heating.

[0059] S13, centrifuging the mixture at 8000 rpm for 10 min, discarding the supernatant, adding 10 times the volume of deionized water to wash the precipitate, and then centrifuging at 8000 rpm for 10 min to obtain a precipitate, i.e., the treated fish glue sample.

[0060] S14. Freeze-dry the treated fish glue sample for 48 hours, seal it and store it in a dry environment at 4°C.

[0061] Among them, the fish glue samples were treated with an equal volume of deionized water instead of the natural deep eutectic solvent as the control group, and each treatment was repeated 3 times.

[0062] (2) Referring to the first method of GB5009.268-2016: the chromium and arsenic contents in the fish glue samples were determined by inductively coupled plasma mass spectrometry (ICP-MS), and the effects of different solvents on the removal rates of chromium and arsenic in fish glue were calculated.

[0063] See also Figure 1The removal rates of heavy metal chromium in fish glue by GlyArg, GlyPro, EgPro and water control group were 58.79%, 57.93%, 63.35% and 22.79%, respectively. Compared with the water phase, the removal rates of chromium by the three natural low eutectic solvents were significantly improved (p < 0.05), and the removal effect was good.

[0064] See also Figure 2 The removal rates of heavy metal arsenic in fish glue by GlyArg, GlyPro, EgPro and the water control group were 48.36%, 55.80%, 53.31% and 18.56%, respectively. Compared with the water phase, the removal rates of arsenic by the three natural low eutectic solvents were significantly improved (p < 0.05), among which GlyPro achieved the effect of completely removing arsenic (below the detection limit of 0.002 mg / kg).

[0065] In summary, the natural low eutectic solvents prepared in Examples 1-3 have a good removal effect on heavy metals in fish glue, among which EgPro has a good comprehensive effect on the removal of multiple heavy metals in fish glue.

[0066] Comparative Example 1

[0067] This comparative example uses a traditional eluent to remove heavy metals from fish glue, specifically comprising the following steps:

[0068] The fish glue sample was first soaked in deionized water and cut into pieces of about 2×2cm. Then the fish glue sample was mixed with HCl solution (pH about 3), 10% oxalic acid, 10% citric acid, and NaOH solution (pH about 9) at a fixed ratio of 1:10 (w / w), and vortexed to mix evenly. The mixed mixture was placed in a 60℃ water bath and heated at a constant temperature and continuously shaken at 100rpm for 1h. During the heating period, the mixture was ultrasonicated at 40±1℃ for 2min every 15min, and then the ultrasonicated mixture was returned to the water bath for further heating. The mixture was centrifuged at 8000rpm for 10min, the supernatant was discarded, and 10 times the volume of deionized water was added to wash the precipitate several times, and then centrifuged at 8000rpm for 10min to obtain the precipitate, which was the treated fish glue sample. Each treatment group had 6 samples, and parallel controls were set up for subsequent tests.

[0069] The fish glue samples treated with different NADESs obtained in step S13 of Example 4 and the fish glue samples treated with different reagents in this comparative example were tested for fish glue quality. The testing method and results are as follows:

[0070] (1) Isinglass color detection:

[0071] The color of fish glue is one of the important indicators for evaluating the quality of fish glue. In this method, a colorimeter was used to measure the fish glue after all groups were treated. Black and white calibration was performed before the experiment. The reflection mode was selected. The water treatment group was used as the control. Each group of samples was paralleled three times, and the average value was taken to calculate the total color difference and whiteness of the fish glue.

[0072] The total color difference (ΔE) refers to the difference between the color of the treated group samples and the color average of the control group samples. The calculation formula is: ΔE = [(ΔL * ) 2 +(Δa * ) 2 +(Δb * ) 2 ] 1 / 2 , where ΔL * , Δa * and Δb * The difference between samples in the treatment group and the control group is * 、a * 、b * The difference between the average values ​​of .

[0073] Whiteness (WI) usually refers to the brightness and purity of the sample surface color. In the food industry, it can be used to evaluate the purity and quality of food raw materials. The calculation formula is: WI = 100-[(100-L * ) 2 +(a * ) 2 +(b * ) 2 ] 1 / 2 , where L* is the brightness, ranging from 0 to 100, with 0 being black and 100 being white; a* is the redness, representing the value from red (100) to green (-80), * When it is a negative number, the color tends to be green. The smaller the value, the darker the green. * When it is a positive value, the color tends to be red. The larger the value, the more obvious the red. When it is close to 0, the color is neutral, neither red nor green. b* represents the value from yellow (100) to blue (-80). * A positive value indicates that the color tends to be yellow. The larger the value, the more obvious the yellow is.

[0074] See also Figure 3 and Figure 4, the fish glue before treatment is naturally light yellow, with uniform color and no obvious spots or impurities. The color of the fish glue after treatment is quite different. The fish glue treated with NADES is slightly darker, especially the GlyPro group is yellowish brown. The reason may be that glycerol, one of the components of the GlyPro reagent, is decomposed during the heating preparation process or turns yellow after being oxidized by air, and the colored substances still remain on the fish glue after elution. After hydrochloric acid treatment, the color of the fish glue becomes lighter, similar to the color of foaming hair bleaching. The surface of the fish glue treated with oxalic acid, citric acid and NaOH solution is wrinkled, and the epidermis is separated from the internal white meat. The citric acid and NaOH solution groups have more serious apparent damage, which may be that the reagent reacts with the fish glue protein component, causing the fish glue to melt. The three NADES treatment groups can better retain the delicate texture formed by the fiber structure on the surface of the original fish glue, while the surface texture of the fish glue treated with hydroxy acid, strong acid and strong alkali is almost destroyed, which is quite different from the original fish glue morphology.

[0075] Refer to Table 2, which shows the total color difference and whiteness of fish glue after being treated with different types of eluents. * The value was 74.34, and the brightness of the gelatin in all eluent treatment groups was L * The value decreased significantly and the sample color became darker. * The values ​​ranged from -2.35 to 4.46, with a relatively small range, indicating that the red-green color of the fish glue only changed slightly. The color of the fish glue in each eluent treatment group was a neutral color with a slight yellow tint. Compared with the control group, b * The values ​​decrease, the yellow becomes lighter, and Figure 4 The appearance of fish glue after being treated with the eluent is confirmed by the fact that the fish glue treated with HCl and citric acid solutions is white in color. Similarly, the whiteness WI values ​​of these two groups are greater than that of the control group (60.65). ΔE reflects the change in color. The smaller the ΔE, the closer the color is to the control group. The ΔE value results show that acid and alkali eluents have little effect on the color of fish glue, with ΔE values ​​between 7.20-17.03. The three NADESs eluents have a greater effect on the surface color of fish glue, with ΔE values ​​of 17.93-21.95. The reason may be that during the removal of heavy metals by the NADESs reagent, the heat treatment causes the glycerol to undergo an oxidation reaction with oxygen in the air, causing the color to turn yellow. But from Figure 4 It can be seen that there is no significant visual difference in the overall slight yellow tint of the isinglass samples.

[0076] Table 2 Effect of different eluents on the color of fish glue

[0077]

[0078]

[0079] Among them, L* value is brightness, which varies in the range of 0-100, a * Represents the range of colors from green to red, a * When it is a negative number, the color tends to be green. The smaller the value, the darker the green. * When the value is positive, the color tends to be red. The larger the value, the more obvious the red is.

[0080] (2) Texture testing:

[0081] Fish glue (2cm×2cm) treated with different eluents was tested for hardness, adhesion, elasticity, chewiness, and adhesiveness using a Brookfield CT3 texture analyzer TA11 / 1000 flat-bottom cylindrical probe. The test type was set to TPA texture analysis mode, with a test speed of 1mm / s, a return speed of 1mm / s, two cycles, a 2s interval between two compressions, a trigger point load of 5.0g, a test target value of 3mm, a waiting time of 0s, and each group of experiments was repeated 8 times. The average value was taken after removing the outliers.

[0082] The water content, fat, collagen content, and muscle fiber diameter of fish glue are all factors that affect the texture characteristics. The texture parameters obtained by simulating the mechanical process of chewing food with teeth are important indicators for measuring the edible quality of fish glue. Chewability refers to the measure of the energy required to chew food. Refer to Table 3. The chewability values ​​and adhesiveness of fish glue samples in all experimental groups have roughly the same trend. The fish glue treated with NADESs retains the hardness, viscosity, elasticity, and adhesiveness of the original samples to a large extent. Among them, the fish glue in the EgPro treatment group is closer to the control group in terms of hardness, cohesion, and elasticity. However, acid-base eluents cause the texture characteristics of fish glue to deviate more significantly from the control group, and the hardness, viscosity, viscosity, elasticity, adhesiveness, and chewiness are greatly reduced. The work required for chewing is relatively small, and the texture of fish glue is soft. The reason may be that acid-base eluents cause fish glue to lose more collagen and lose good elasticity and toughness. Therefore, NADESs treatment helps to maintain the edible quality of fish glue.

[0083] Table 3 Effects of different eluents on the texture of fish gelatin

[0084]

[0085] (3) Collagen loss rate:

[0086] The fish gelatin treated with different eluents was freeze-dried to remove moisture, 0.1 g of the sample was weighed and digested in 2 ml of hydrochloric acid solution (6M) until there was no black block, the pH was adjusted to 6-8 and the volume was fixed to 5 ml, diluted, and the reaction solution was added to react and the absorbance was measured at 560 nm. The hydroxyproline (HYP) content detection kit was used to determine the hydroxyproline content, which was multiplied by a coefficient of 11.1 to convert it into the collagen content, and the loss rate was calculated by obtaining the difference in collagen content in fish gelatin before and after treatment with different types of eluents.

[0087] Refer to Table 4, which shows the changes in collagen content after fish glue was treated with different eluents. All treatment groups showed a decrease in collagen content. The reason may be that the heat and ultrasonic treatment accelerated the dissolution of collagen during the removal of heavy metals, and the proteins that provided binding sites for heavy metals were eluted together. Among them, the collagen content of fish glue treated with three NADESs was higher overall. Compared with the control group, the loss rate of collagen was in the range of 11.76%-55.94%, and the order of loss rate was GlyPro>GlyArg>EgPro. The loss rates of GlyPro and GlyArg groups were 4.76 and 3.44 times that of EgPro group, respectively. The reason may be that the viscosity of glycerol in the components of these two groups of reagents is greater than that of ethylene glycol, and more collagen will be attached during the elution process, resulting in serious loss. Acid eluents and NaOH solutions have a greater impact on the collagen content in fish glue. The reason may be that both acids and alkalis hydrolyze collagen, and the alkaline and acidic groups on the collagen molecular chain react with acids or alkalis, causing the protein molecules to be destroyed or even lose their activity.

[0088] Table 4 Effect of different eluents on the collagen content in fish glue

[0089]

[0090] In summary, compared with traditional eluents, NADESs treatment has the least damage to the appearance, color, and texture of fish glue, and can also better retain the content of collagen, a nutrient component in fish glue. Therefore, the NADESs provided by the present invention have the potential to be used to remove heavy metals from fish glue. Among the three NADESs, EgPro has less effect on the texture and collagen of fish glue, and has a good removal effect on a variety of heavy metals. It is the best natural low eutectic solvent, so EgPro was selected as the subsequent research object.

[0091] Example 5 Effect of water content on heavy metal removal by NADESs

[0092] Based on the heavy metal removal effect and collagen loss rate, EgPro was selected for research to examine the effect of water content on the removal of heavy metals by NADESs:

[0093] S10. Dilute the NADESs with deionized water to a water content of 10%, 20%, 30%, 40%, and 50%, respectively.

[0094] S11. Mix the fish gelatin sample and NADESs with different water contents at a solid-liquid ratio of 1:20.

[0095] S12, heating the uniformly mixed mixture at 60°C for 1 h. During this period, ultrasonically subjecting the mixture to 40±1°C for 2 min every 15 min until the heating is completed.

[0096] S13, centrifuging the mixture at 8000 rpm for 10 min, discarding the supernatant, adding an equal volume of deionized water to wash the precipitate, and then centrifuging at 8000 rpm for 10 min to obtain a precipitate, i.e., the treated fish glue sample.

[0097] S14. Wash the treated fish glue sample three times with deionized water, freeze-dry it and store it in a dry environment at 4°C.

[0098] The contents of chromium and arsenic in isinglass samples before and after treatment were determined, and the effects of NADESs with different water contents on the removal rates of chromium and arsenic in isinglass were calculated.

[0099] See also Figure 5-6 When the water content of EgPro is 10%, it has the best effect on the removal of heavy metals in fish glue, and its removal rates of chromium and arsenic are 71.32% and 67.40% respectively. In addition, the viscosity of EgPro with a water content of 0% is significantly greater than that of EgPro with a water content of 10%-50%, and when the water content of EgPro is 10%, its effect on removing fish glue is slightly lower than that of EgPro with a water content of 0%, but the use of DES is reduced, thereby significantly reducing costs.

[0100] Example 6 Effect of solid-liquid ratio on heavy metal removal by NADESs

[0101] According to the heavy metal removal effect and collagen loss rate, EgPro with a water content of 10% was selected to continue the study and investigate the effect of solid-liquid ratio on the removal of heavy metals by NADESs:

[0102] S11. Mix the fish glue sample and NADESs evenly at a solid-liquid ratio of 1:10, 1:15, 1:20, and 1:25 respectively.

[0103] S12, heating the uniformly mixed mixture at 60°C for 1 h. During this period, ultrasonically subjecting the mixture to 40±1°C for 2 min every 15 min until the heating is completed.

[0104] S13, centrifuging the mixture at 8000 rpm for 10 min, discarding the supernatant, adding an equal volume of deionized water to wash the precipitate, and then centrifuging at 8000 rpm for 10 min to obtain a precipitate, i.e., the treated fish glue sample.

[0105] S14. Wash the treated fish glue sample three times with deionized water, freeze-dry it and store it in a dry environment at 4°C.

[0106] The contents of chromium and arsenic in isinglass samples before and after treatment were determined, and the effects of NADESs with different solid-liquid ratios on the removal rates of chromium and arsenic in isinglass were calculated.

[0107] See also Figure 7 When the solid-liquid ratio was 1:20, EgPro achieved the best effect in removing heavy metals from fish glue, with the chromium removal rate reaching 71.32% and the arsenic removal rate reaching 67.40%.

[0108] Example 7

[0109] This embodiment uses ultra-high pressure (HHP) to remove heavy metals from fish glue. All HHP treatments are carried out in a 5L HP food processing device (CQC-2L-600 full liquid phase ultra-high pressure food sterilizer, Beijing Suyuan Zhongtian Technology Co., Ltd.), which specifically includes the following steps:

[0110] S21. Weigh 4 g of fish glue sample and place it in a polyester (PET) vacuum bag, add deionized water at a solid-liquid ratio of 1:10 (w / w) to mix, and seal the vacuum bag.

[0111] S22. Using water as the pressure transmission fluid, the pressure vessel equipment is kept stable at ambient temperature (25°C), and the pressure values ​​are set at 200, 300, and 400 MPa to treat the fish glue samples respectively, and the duration is 10 minutes.

[0112] S23. The treated fish glue sample was centrifuged at 8000 rpm for 10 min, the precipitate was taken, the precipitate was washed three times with deionized water, the precipitate was freeze-dried for 48 h, sealed and stored in a dry environment at 4°C.

[0113] Among them, the fish maw samples were treated with normal pressure instead of ultra-high pressure as the control group, and each treatment was repeated 3 times.

[0114] The contents of chromium and arsenic in isinglass samples before and after treatment were determined, and the removal rates of chromium and arsenic in isinglass treated with ultrahigh pressure were calculated.

[0115] See also Figure 8-9The removal effect of ultra-high pressure treatment on arsenic first increases and then decreases with the increase of pressure value, and the removal rate is 48.68-55.12%. The treatment effect of ultra-high pressure on chromium shows an increasing trend with the increase of pressure, and the removal rate reaches 55.73% at 400MPa.

[0116] Example 8

[0117] In this embodiment, NADESs were used in conjunction with ultra-high pressure (HHP) to remove heavy metals from fish glue. All HHP treatments were carried out in a 5L high-pressure food processing device, specifically including the following steps:

[0118] S31. Mix the fish glue sample with the EgPro prepared in Example 3 at a ratio of 1:20 (w / w), and vortex to mix them evenly.

[0119] S32. Place the uniformly mixed mixture in a 60°C water bath and heat it at a constant temperature for 1 hour. During the heating period, ultrasonicate the mixture at 40±1°C for 2 minutes every 15 minutes, and then return the ultrasonicated mixture to the water bath for further heating.

[0120] S33. Add the fish glue sample and NADESs into a vacuum bag, seal it, and treat it at an ultra-high pressure of 200 MPa for 10 min.

[0121] S34. The treated fish glue sample was centrifuged at 8000 rpm for 10 min, the precipitate was taken, the precipitate was washed three times with deionized water, the precipitate was freeze-dried for 48 h, sealed and stored in a dry environment at 4°C.

[0122] Among them, the fish maw samples treated with water of equal volume were used as the control group, and each treatment was repeated 3 times.

[0123] The contents of chromium and arsenic in isinglass samples before and after treatment were determined, and the removal rates of chromium and arsenic in isinglass treated with ultrahigh pressure and NADESs were calculated.

[0124] See also Figure 8-9 , based on a pressure of 200MPa, using EgPro eluent instead of deionized water, the removal rates of chromium and arsenic in fish glue were 77.46% and 79.20%, respectively, which increased by 49.88% and 57.24%, respectively.

[0125] In summary, compared with the prior art, the method for removing heavy metals from fish glue provided by the present invention has the following advantages:

[0126] (1) The NADESs prepared by the present invention have the advantages of low solvent price, low volatility, safe components, and biodegradability. The present invention is the first to apply NADESs to the removal of heavy metals from fish maw, and it is found that it has excellent heavy metal removal effect, while being able to better maintain the edible quality of fish maw, so that the processed fish maw has higher nutritional value and economic benefits.

[0127] (2) The NADESs prepared by the present invention have a good heavy metal removal effect on fish glue samples, and can remove a variety of heavy metals on the surface and inside of the samples, and the post-treatment method is simple. In addition, EgPro has little effect on the texture and collagen content of fish glue, and can effectively remove heavy metals while minimizing the reduction of the edible quality of fish glue. It has the best comprehensive effect on the removal of heavy metals in fish glue.

[0128] (3) The present invention applies ultrahigh pressure technology to the removal of heavy metals from fish glue for the first time, and improves the extraction efficiency of heavy metals in fish glue by static pressure and rapid pressure increase. In addition, the present invention uses ultrahigh pressure to cooperate with NADESs to treat fish glue samples for the first time. Ultrahigh pressure accelerates the uniform penetration of NADESs solvent into fish glue, and at the same time accelerates the dissociation rate of the extract, overcoming the problem of low efficiency in the late adsorption stage when NADESs was used to treat fish glue, thereby further improving the removal effect and removal efficiency of heavy metals in fish glue.

[0129] (4) The method for removing heavy metals from fish maw provided by the present invention has the advantages of being green, efficient, having little pollution to the environment, and being low in cost, which helps to maintain the edible quality of fish maw. In addition, the method will also have good application prospects in removing heavy metals from other seafood.

[0130] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0131] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for removing heavy metals from fish glue, characterized in that: The steps include: The fish glue and the natural low eutectic solvent are mixed evenly, heated, centrifuged, washed and precipitated, and vacuum dried to obtain the fish glue with heavy metals removed; The hydrogen bond donor of the natural deep eutectic solvent is any one of glycerol and ethylene glycol, and the hydrogen bond acceptor is any one of L-proline and L-arginine.

2. The method according to claim 1, characterized in that: The natural low eutectic solvent is a solvent formed by heating a hydrogen bond donor and a hydrogen bond acceptor at a molar ratio of 3-4.5:1 to form a eutectic solvent at 60° C. and cooling the solvent.

3. The method according to claim 2, characterized in that: The heavy metals include arsenic and / or chromium.

4. The method according to claim 2, characterized in that: The heating of the mixture of fish glue and natural deep eutectic solvent comprises heating the mixture at 60° C. for 1 hour, during which the mixture is ultrasonically subjected to 35-45° C. for 2 minutes every 15 minutes.

5. The method according to claim 4, characterized in that: The heated mixture was subjected to ultrahigh pressure treatment and then centrifuged.

6. The method according to claim 5, characterized in that: The ultra-high pressure treatment condition is 200-400 MPa for 10 min.

7. The method according to claim 6, characterized in that: The fish glue and the natural deep eutectic solvent are mixed at a solid-to-liquid ratio of 1:10-1:

25.

8. The method according to claim 2, characterized in that: The hydrogen bond donor of the natural deep eutectic solvent is ethylene glycol, the hydrogen bond acceptor is L-proline, and the molar ratio is 3:

1.

9. The method according to claim 8, characterized in that: The solid-to-liquid ratio is 1:

20.

10. The method according to any one of claims 1 to 9, characterized in that: Deionized water is added to the natural deep eutectic solvent until the water content of the natural deep eutectic solvent is 0-10%.

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