Iron-nitrogen co-doped biochar and application thereof in degradation of aflatoxin in edible oil

Abstract

The invention discloses construction of iron-nitrogen co-doped charcoal and application of the iron-nitrogen co-doped charcoal to degradation of aflatoxin in edible oil, and belongs to the technical field of food harmful pollutant control. The iron-nitrogen co-doped biochar is prepared by fully mixing straw powder and an iron-nitrogen dopant solution, then drying, grinding and calcining, a small amount of sodium hydrogen sulfite or sodium sulfite and FeNBC are added in an edible oil washing procedure, and due to the fact that doped elements of the FeNBC adjust a local electronic structure, the iron-nitrogen co-doped biochar can be used for preparing the iron-nitrogen co-doped biochar. Sodium sulfite and sodium hydrogen sulfite can be effectively activated to form active substances, so that effective degradation of AFB1 is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of food harmful pollutant control / new environmentally friendly material preparation, and specifically relates to an iron-nitrogen co-doped biochar and its application in degrading aflatoxin in edible oil. Background Art

[0005] Since AFB1 has good thermal and chemical stability and cannot be decomposed during the cooking process, a series of physical, chemical and biological methods have been developed to remove AFB1 from edible oil. Physical methods mainly include adsorption and radiation methods. The adsorption process can only enrich AFB1 in the adsorbent (Ref: CN110951540A). After adsorption saturation, it is often impossible to recycle. Improper treatment of used adsorbents will cause secondary pollution. Radiation methods usually use ultraviolet rays or other rays to destroy the structure of AFB1 (Ref: CN108123022A), but this will also lead to the destruction of nutrients in edible oil. Chemical methods usually use chemical substances such as acids, alkalis, and oxidants to decompose AFB1, but the use of a large number of chemical reagents will bring potential safety issues and environmental pollution. Biological adsorption and enzyme-catalyzed decomposition can also remove AFB1 (Ref: CN106399122A), but biosafety issues and harsh reaction conditions make it difficult to apply in practice. Obviously, the existing methods are not sufficient to simply and effectively eliminate the risks posed by AFB1 contamination in edible oils, so it is necessary to develop safe, efficient and environmentally friendly methods to remove AFB1 from edible oils. Summary of the invention

[0006] In view of the shortcomings of the prior art, the first object of the present invention is to provide a new environmentally friendly material for degrading aflatoxin in edible oil and a preparation method thereof, so as to remove AFB1 in edible oil in a simple, effective and safe manner, thereby eliminating the risks of AFB1 contamination in edible oil.

[0007] In order to achieve the above objectives, the present invention firstly prepares iron and nitrogen co-doped biochar (FeNBC) by a simple one-pot method. FeNBC can effectively activate sodium sulfite and sodium bisulfite (food additives allowed in the national standard) to form active substances due to the regulation of the local electronic structure by its doping elements, thereby achieving effective degradation of AFB1.

[0008] Specifically, the first object of the present invention is achieved as follows: an iron-nitrogen co-doped biochar is prepared by fully mixing straw powder and an iron-nitrogen dopant solution, drying, grinding and calcining the mixture, wherein the mass ratio of the straw powder to the iron source and the nitrogen source in the iron-nitrogen dopant is 1:(0.05-0.25):(0.5-2).

[0009] Further preferably, in the iron-nitrogen co-doped biochar as described above, the iron source is selected from at least one of the following: ferric nitrate or its hydrate (such as Fe(NO3)3·9H2O), ferric chloride or its hydrate (such as FeCl3·6H2O); the nitrogen source is urea, dicyandiamide or melamine; and the straw is selected from at least one of the following: rape straw, corn straw, and rice straw.

[0010] A method for preparing the iron-nitrogen co-doped biochar as described above, the method comprising the following steps:

[0011] (1) crushing the straw and sieving it to obtain 50-200 mesh straw powder for later use;

[0012] (2) dissolving an iron source and a nitrogen source in water to obtain an iron-nitrogen dopant aqueous solution for later use;

[0013] (3) fully mixing the straw powder and the iron-nitrogen doping agent aqueous solution, and drying them in an oven to remove moisture;

[0014] (4) grinding the dried mixture into powder, placing it in a muffle furnace for oxygen-free calcination at a temperature of 500-700° C. for a calcination time of 1-4 hours;

[0015] (5) After cooling, the black powdery calcined product is taken out, which is the iron-nitrogen co-doped biochar.

[0016] Further preferably, in the method for preparing iron-nitrogen co-doped biochar as described above, the drying temperature in step (3) is 60-120°C, and the drying time is 4-12 hours; and the heating rate in step (4) is 2-5°C / min.

[0017] Secondly, the second object of the present invention is to provide an AFB1 remover composition in edible oil, wherein the composition comprises the above-mentioned iron-nitrogen co-doped biochar and an activator, and the activator is sodium bisulfite and / or sodium sulfite.

[0018] Further preferably, in the AFB1 remover composition in edible oil as described above, the mass ratio of the iron-nitrogen co-doped biochar to the activator is 1:(0.1-1).

[0019] In addition, the third object of the present invention is to provide the use of the above-mentioned AFB1 remover composition in degrading aflatoxin in edible oil.

[0020] In view of the fact that water washing is an important procedure in edible oil processing, the present invention also proposes combining sulfate oxidation technology with the edible oil water washing procedure, adding a small amount of sodium bisulfite (or sodium sulfite) and FeNBC to the edible oil water washing procedure, and FeNBC activates sodium bisulfite to form an active substance to oxidatively decompose AFB1. This reaction only occurs in the water phase. As AFB1 in the water phase is consumed, AFB1 in the oil phase migrates to the water phase, and finally the AFB1 in the oil phase is removed.

[0021] Therefore, the fourth object of the present invention is a method for degrading AFB1 in edible oil, which removes AFB1 in edible oil through sulfate advanced oxidation technology, and specifically comprises the following steps: mixing AFB1-contaminated edible oil and water in a volume ratio of 1:(0.5-2), adding the above-mentioned iron-nitrogen co-doped biochar and activator, and stirring for 0-60 minutes, wherein the amount of the iron-nitrogen co-doped biochar added is 50-500 mg / L, the amount of the activator added is 0.5-2 mmol / L, and the activator is sodium bisulfite and / or sodium sulfite.

[0022] Further preferably, in the method for degrading AFB1 in edible oil as described above, the iron-nitrogen co-doped biochar and the activator can be added simultaneously or successively. Preferably, the iron-nitrogen co-doped biochar is added first and then the activator is added. The specific operation method is: first add the iron-nitrogen co-doped biochar, stir for 0-60 minutes, then add the activator, and stir for 0-120 minutes.

[0023] Compared with the prior art, the novel environmentally friendly material for degrading aflatoxin in edible oil and the preparation method thereof provided by the present invention have the following advantages and progress:

[0024] (1) The present invention prepares an iron-nitrogen co-doped biochar FeNBC by a one-pot method, which has few preparation steps, simple and easy operation, and is easy for large-scale industrial production.

[0025] (2) Co-doping of iron and nitrogen elements is achieved in biochar. The iron atoms in FeNBC act as electron acceptors and the N atoms act as atomic donors. Through the electron push-pull effect between Fe-N atoms, catalytic sites that can activate the activator are formed to generate active substances that can oxidatively decompose AFB1. Therefore, the present invention uses activated carbon in combination with sodium bisulfite to degrade AFB1 instead of simply adsorbing AFB1.

[0026] (3) A small amount of sodium bisulfite (or sodium sulfite) and FeNBC are added during the edible oil washing process. FeNBC activates sodium bisulfite to form an active substance to oxidize and decompose AFB1. Since the raw materials for generating the active substance (sodium bisulfite or sodium sulfite) are only soluble in the water phase but not in the oil phase, the oxidation process only occurs in the water phase. As AFB1 in the water phase is consumed, AFB1 in the oil phase migrates to the water phase, and finally AFB1 in the oil phase is removed.

[0027] (4) The AFB1 remover provided by the present invention can be directly combined with the edible oil washing process without adding additional detoxification processes, and the negative impact of this process on the quality of edible oil is negligible. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : Schematic diagram of the process for synthesizing iron-nitrogen co-doped biochar.

[0029] Figure 2 : Comparison of the appearance of corn oil before and after treatment; (left) before treatment, (right) after treatment. DETAILED DESCRIPTION

[0030] The following are specific embodiments of the present invention, which describe in detail the technical solutions and technical effects of the present invention. If no specific technical operations or conditions are specified in the embodiments, the operations are performed according to the conventional techniques or conditions described in the literature in the art; if no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased normally.

[0031] Example 1: Preparation of iron-nitrogen co-doped biochar

[0032] (1) Crush the dried rape straw and pass it through a 50-mesh sieve for later use.

[0033] (2) Dissolve 1.25 g of FeCl3·6H2O and 10 g of urea in 20 mL of water to prepare an iron-nitrogen dopant aqueous solution for later use.

[0034] (3) Take 10 g of rape straw powder, add it to the iron-nitrogen doping agent aqueous solution prepared in the previous step, and mix thoroughly to obtain a mixture.

[0035] (4) The mixture obtained in the previous step was placed in an oven to dry to remove moisture. The drying temperature was 80° C. and the drying time was 12 hours.

[0036] (5) The dried mixture is ground into powder and placed in a crucible with a lid to create an oxygen-deficient environment.

[0037] (6) The crucible was placed in a muffle furnace and heated from room temperature to a set temperature at a heating rate of 3°C / min. The set temperature was 550°C. After reaching the set temperature, it was kept at this temperature for a certain period of time and naturally cooled to room temperature. The holding time was 2 hours.

[0038] (7) The cooled crucible is taken out, and the obtained black powder is iron-nitrogen co-doped biochar (FeNBC).

[0039] Example 2: Degradation of AFB1 in edible oil

[0040] 50 ml of corn oil contaminated with AFB1 (the content of AFB1 in corn oil is 100 ug / L) and 50 ml of pure water were mixed, and the iron-nitrogen co-doped biochar prepared in Example 1 was added (the amount added was 200 mg / L relative to the volume of the oil-water mixture), and the mixture was stirred for 30 minutes (stirring speed was 600 rpm) to achieve the distribution equilibrium and adsorption equilibrium of AFB1 in the oil phase and the water phase. Then 5.2 mg of sodium bisulfite was added to the mixture (since sodium bisulfite is only soluble in water but not in oil, it is equivalent to a concentration of 1 mmol / L in the aqueous solution), the timing was started and the mixture was continued to be stirred, and samples were taken at regular intervals, and the aflatoxin content in the edible oil was detected according to the method of GB / T5009.23-2003.

[0041] Comparative Example 1: Degradation of AFB1 in edible oil

[0042] No FeNBC was added, only NaHSO3 was added, and other operating methods and parameters were the same as those in Example 2.

[0043] Comparative Example 2: Degradation of AFB1 in edible oil

[0044] No NaHSO3 was added, only FeNBC was added, and other operating methods and parameters were the same as those in Example 2.

[0045] Comparative Example 3: Degradation of AFB1 in edible oil

[0046] No NaHSO 3 and FeNBC were added (i.e., only a mixture of contaminated edible oil and water was used), and other operating methods and parameters were the same as those in Example 2.

[0047] Table 1: Removal rate of edible oil AFB1 under different operations (unit: %)

[0048] Time (min) Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 0 0 0 0 0 10 65.7 11.8 14.9 13.2 20 89.9 12.6 15.2 13.5 40 94.6 12.9 15.1 13.3 60 96.6 12.8 15.5 13.9 90 97.2 13.1 15.3 13.6 120 97.3 12.6 15.2 13.7

[0049] It can be seen from the experimental results in Table 1 that by simple water washing, that is, the distribution balance of AFB1 in the oil phase and the water phase, only about 13% of AFB1 can be removed (Comparative Example 3); when only the activator NaHSO3 is added, the removal rate of AFB1 does not change significantly, indicating that the activator alone cannot remove AFB1 (Comparative Example 1). When only FeNBC is added, the removal rate of AFB1 is slightly increased to 15-16%, indicating that the effect of FeNBC in removing AFB1 by adsorption is very limited (Comparative Example 2). In Example 2, FeNBC and the activator NaHSO3 are added at the same time, and the content of AFB1 in the edible oil decreases rapidly, indicating that FeNBC can effectively activate the activator through catalysis, generate a large amount of active substances, and oxidize and decompose AFB1.

[0050] As a comparison, the inventors also synthesized common biochar (BC), iron-doped biochar (FeBC) and nitrogen-doped biochar (NBC). The synthesis method is similar to that of FeNBC.

[0051] Comparative Example 4: FeBC was synthesized by adding only an iron source without adding a nitrogen source and using other synthesis steps similar to those of FeNBC.

[0052] Comparative Example 5: Only nitrogen source was added without adding iron source, and other synthesis steps were similar to FeNBC to synthesize NBC.

[0053] Comparative Example 6: BC was synthesized without adding iron source and nitrogen source and other synthesis steps were similar to FeNBC.

[0054] Table 2: Removal rate of AFB1 in edible oil by NaHSO3 activated by different biochars (unit: %)

[0055] Time (min) Example 2 Comparative Example 4 Comparative Example 5 Comparative Example 6 0 0 0 0 0 10 65.7 53.8 56.3 45.8 20 89.9 72.5 69.4 64.2 40 94.6 82.2 76.7 68.2 60 96.6 83.6 80.2 70.4 90 97.2 84.1 80.1 70.1 120 97.3 83.7 80.1 70.6

[0056] Note: The experimental conditions are consistent with those in Example 2.

[0057] It can be seen from the experimental results in Table 2 that FeNBC has the highest removal rate of AFB1 in edible oil by activating NaHSO3, which is better than single-doped biochar or original biochar, proving that the FeNBC synthesized by this method has good activation ability for NaHSO3 and can form a large amount of ROS to remove AFB1 in edible oil.

[0058] Example 3: Test on the effect of FeNBC activated bisulfite technology on edible oil quality

[0059] 50mL edible oil (Golden Arowana corn oil) was uniformly mixed with 50mL 1mmol / L NaHSO3 solution by stirring, and the stirring speed was 600 rpm, followed by the addition of 20mg FeNBC. The timing was started and the mixture was stirred continuously, and the reaction lasted for 120 minutes. After the reaction was completed, the catalyst was removed by centrifugation and the oil phase was collected. The acid value was determined by GB 5009.229-2016, the peroxide value was determined by GB 5009.227-2016, the iodine value was determined by GB / T5532-2022, and the color change of the oil was also measured by a colorimeter.

[0060] Table 3

[0061]

[0062] By comparing the appearance and other quality parameters of the edible oil before and after the treatment, it can be found that the appearance of the edible oil has changed slightly before and after the treatment, the acid value and iodine value have not changed, and the peroxide value has increased slightly, but it still meets the national standard for high-quality corn oil (less than 5.0mmol / kg). It can be seen that the FeNBC activated bisulfite technology proposed in the present invention not only degrades AFB1 residues during the edible oil washing process, but also the process only occurs in the water phase, which can avoid the negative impact of the oxidation process on the quality of the edible oil.

Claims

1. An iron-nitrogen co-doped biochar, which is prepared by fully mixing straw powder and an iron-nitrogen doping agent solution, followed by drying, grinding and calcining, wherein the mass ratio of the straw powder to the iron source and the nitrogen source in the iron-nitrogen doping agent is 1:(0.05-0.25):(0.5-2).

2. The iron-nitrogen co-doped biochar according to claim 1, characterized in that: The iron source is selected from at least one of the following: ferric nitrate or its hydrate, ferric chloride or its hydrate; the nitrogen source is urea, dicyandiamide or melamine.

3. The iron-nitrogen co-doped biochar according to claim 1, characterized in that: The straw is selected from at least one of the following: rape straw, corn straw, and rice straw.

4. A method for preparing iron-nitrogen co-doped biochar according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: (1) crushing the straw and sieving it to obtain 50-200 mesh straw powder for later use; (2) dissolving an iron source and a nitrogen source in water to obtain an iron-nitrogen dopant aqueous solution for later use; (3) fully mixing the straw powder and the iron-nitrogen doping agent aqueous solution, and drying them in an oven to remove moisture; (4) grinding the dried mixture into powder, placing it in a muffle furnace for oxygen-free calcination at a temperature of 500-700° C. for a calcination time of 1-4 hours; (5) After cooling, the black powdery calcined product is taken out, which is the iron-nitrogen co-doped biochar.

5. The method for preparing iron-nitrogen co-doped biochar according to claim 4, characterized in that: In step (3), the drying temperature is 60-120° C. and the drying time is 4-12 hours; in step (4), the heating rate is 2-5° C. / min.

6. A composition for removing AFB1 in edible oil, characterized in that: The composition comprises the iron-nitrogen co-doped biochar according to claim 1 and an activator, wherein the activator is sodium bisulfite and / or sodium sulfite.

7. The composition for removing AFB1 in edible oil according to claim 1, characterized in that: The mass ratio of the iron-nitrogen co-doped biochar to the activator is 1:(0.1-1).

8. Use of the AFB1 remover composition according to claim 6 or 7 in degrading aflatoxin in edible oil.

9. A method for degrading AFB1 in edible oil, characterized in that: The method comprises the following steps: mixing AFB1-contaminated edible oil and water in a volume ratio of 1:(0.5-2), adding the iron-nitrogen co-doped biochar and an activator according to any one of claims 1-3, and stirring for 0-60 minutes, wherein the amount of the iron-nitrogen co-doped biochar added is 50-500 mg / L, the amount of the activator added is 0.5-2 mmol / L, and the activator is sodium bisulfite or / and sodium sulfite.

10. The method for degrading AFB1 in edible oil according to claim 9, characterized in that: The operation mode of adding the iron-nitrogen co-doped biochar and the activator is: first add the iron-nitrogen co-doped biochar, stir for 0-60 minutes, then add the activator, and stir for 0-120 minutes.

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