Method for reducing trace heavy metal mercury in rice protein

Abstract

The invention relates to the technical field of rice protein processing, in particular to a method for reducing trace heavy metal mercury in rice protein, which comprises the following steps: alkali swelling is combined with wet high-pressure flash explosion pretreatment; performing low-temperature plasma treatment; performing thermal desorption treatment; and preparing a rice protein finished product. The alkali swelling and high-pressure steam flash explosion pretreatment process is combined with the low-temperature plasma treatment process, the effect of destroying the bonding force of heavy metal and protein can be achieved, the treatment process is not subjected to strong acid or high-temperature treatment, the requirement for equipment is low, the rice protein performance is well kept, and the method is suitable for large-scale production. The heavy metal content of the final finished product rice protein meets the national standard requirement, and meanwhile, the product performance is relatively good.

Description

Technical Field

[0001] The invention relates to the technical field of rice protein processing, in particular to a process method for reducing trace heavy metal mercury in rice protein while retaining the high-quality performance of the rice protein, specifically to a method for reducing trace heavy metal mercury in rice protein. Background Art

[0002] Heavy metal pollution in food is usually at trace levels. How to extract trace heavy metals from complex food systems, especially the need to destroy the protein structure that is tightly bound to the heavy metals to release the heavy metals from the system, and then separate the heavy metals from the protein, usually requires harsh conditions that damage the performance of high-quality products in the protein system. Most heavy metal removal processes require the use of strong acids, which will have a destructive effect on the protein structure under strong acidic conditions, and the strong acidic conditions also have high requirements for production equipment; or high-temperature treatment is used to achieve thermal desorption of mercury metal, but high-temperature treatment will inevitably have an adverse effect on the properties of the protein.

[0003] Rice protein has many excellent properties that other plant proteins do not have, and has broad application and development prospects. For rice protein products, the national standard requires that the total mercury (in terms of Hg) content be ≤ 0.02 mg / kg, which is a trace level. Rice protein contains proteins (peptides) that have affinity for metal ions - metallothioneins composed of cysteine, glutamic acid and glycine in different proportions. Metallothioneins are easily induced by metals, hormones and cytokines, and combine with As and Hg in cells to form complexes, which are not easy to extract and remove from samples.

[0004] Since the mercury in rice protein exists in the form of complexed organic mercury, mercury ions and methylmercury ions can form stable complexes with various organic ligands (such as cysteine ​​containing sulfur ligands, other amino acids, and ligands containing -OH or -COOH) and exist in the protein system. The toxicity of mercury is also greater than that of inorganic mercury. The vast majority of organic mercury in rice protein is methylmercury with a lower boiling point (mainly in the form of methylmercury-L-cysteine).

[0005] In the prior art, the removal of heavy metal mercury in rice protein products is usually carried out by strong acid and / or high temperature treatment. Although this can make the heavy metal content of rice protein meet the national standards, it will have many irreversible adverse effects on the excellent properties of rice protein. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a process for reducing trace amounts of heavy metal mercury in rice protein while retaining the high-quality properties of the rice protein.

[0007] The technical solution adopted by the present invention to solve the above technical problems is:

[0008] A method for reducing trace amounts of heavy metal mercury in rice protein comprises the following steps:

[0009] (S1) Alkaline swelling combined with wet high pressure flash explosion pretreatment

[0010] After the rice protein initial feed liquid is subjected to an alkali swelling reaction, the fully hydrated rice protein feed liquid is subjected to a wet method high pressure flash explosion treatment to obtain a pretreated rice protein feed liquid;

[0011] (S2) Low temperature plasma treatment

[0012] The pretreated rice protein liquid is placed in a low-temperature plasma reactor for low-temperature plasma treatment to free the heavy metal methylmercury from the rice protein system;

[0013] (S3) Thermal Desorption Treatment

[0014] The material after the process in step (S2) is subjected to thermal desorption treatment, so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution;

[0015] (S4) Preparation of rice protein finished product

[0016] The rice protein material after heavy metal removal is homogenized and then spray-dried to obtain rice protein with reduced heavy metal mercury.

[0017] Furthermore, in step (S1), the rice protein initial feed liquid is a protein feed liquid obtained by adding water to rice protein with excessive heavy metals and slurrying, and the mass concentration is 10-15%.

[0018] Furthermore, in step (S1), in the alkaline swelling reaction, the type of alkali used is one of NaOH, NaHCO3, and Na2CO3, the reaction pH is controlled at 8.0-9.5, the temperature is 50-70°C, and the swelling reaction time is 1-4h.

[0019] Furthermore, in step (S1), the wet high-pressure flash explosion treatment process is to load the material after the swelling reaction into a steam flash explosion reaction vessel, introduce steam to a pressure of 1-3 MPa and maintain it for 10-30 seconds.

[0020] Further, in step (S2), the low-temperature plasma treatment process is as follows: the pretreated rice protein liquid is placed in a dielectric barrier type low-temperature plasma reaction device, the built-in working gas is air, and the low-temperature plasma treatment voltage is controlled to be 60-100 kV during the reaction, and the time is 5-10 min.

[0021] Furthermore, the thermal desorption treatment process described in step (S3) is: the rice protein material treated with low-temperature plasma is heated at a temperature of 70-80° C. for a reaction time of about 2-5 hours, and a gas recovery device is used to recover gas.

[0022] Further, in step (S4), the rice protein finished product preparation process is as follows: the rice protein material after heavy metal removal is adjusted to a neutral pH, subjected to a homogenization treatment with a homogenization pressure of 30-60 MPa, and then spray-dried to prepare the rice protein finished product.

[0023] For the removal process of heavy metal mercury in rice protein, most of them require the use of strong acid. Under strong acidic conditions, the structure of rice protein will be destroyed, and strong acidic conditions also have high requirements for production equipment. Therefore, the difficulty of the heavy metal removal process in rice protein lies in the need to extract and separate the trace heavy metal elements bound in rice protein by non-strong acidic means. At the same time, it is also necessary to maintain the performance, taste and nutritional value of rice protein itself as much as possible.

[0024] The present invention adopts alkali swelling combined with high-pressure steam flash explosion pretreatment process to destroy the tertiary structure of rice protein, so that the rice protein is fully hydrated and has a relatively high specific surface area and a loose structure; combined with the low-temperature plasma high-energy reaction process, the sulfhydryl bonding between methylmercury and rice protein is destroyed to achieve the purpose of releasing trace heavy metals; finally, the protein and heavy metals are separated by heating desorption. After the process is processed, the rice protein can maintain good processing performance, and the total mercury content of heavy metals meets the national standard requirements.

[0025] Among them, the rice protein pretreatment process: first, it needs to be treated with alkali solution heat swelling to fully hydrate the rice protein. Simultaneously combined with high-pressure steam flash explosion treatment, the protein liquid is treated with short-term saturated steam pressure maintenance, and then the valve is quickly opened to spray out the materials in the reactor together with the high-pressure steam, and the compressed high-pressure steam is released instantly. The internal structure of the material, especially the tertiary structure of the protein, will be destroyed under the action of steam pressure. After the above process, the protein material has a higher surface area and a loose structure.

[0026] In the process of low-temperature plasma treatment of protein in step (S2), low-temperature plasma treatment is carried out by a dielectric barrier discharge device; the etching effect during the low-temperature plasma treatment process can cause the rice protein structure to unfold, and the active particles produced can also oxidize the amino acid groups of the protein, causing the protein secondary structure to change, and finally play the effect of changing the solubility of the protein. In the process, the rice protein system is subjected to the action of a high-energy electric field, and the sulfhydryl group bound to heavy metals in the protein is fully opened by the above-mentioned treatment, the binding bond between the protein and organic mercury is destroyed, and the methylmercury in the complex state is released from the protein system, and in the subsequent heating desorption treatment process, mercury can be effectively freed to become a gaseous state, and separated from the protein.

[0027] Subsequently, the sample is subjected to heating and desorption treatment, and the waste gas containing heavy metal pollutants is recovered and treated. During the heating and desorption treatment, the system is maintained above the boiling point of mercury, and a certain pressure difference is added to separate the gas from the liquid protein; adsorption and analysis is a dynamic equilibrium process, and the early pretreatment process is the prerequisite for realizing the analysis of mercury; the rice protein material is heated for a certain period of time at a temperature that does not affect the protein performance, and then the toxic mercury vapor is recovered and adsorbed in combination with a gas recovery device. Finally, the rice protein sample after the heavy metal is removed is subjected to the neutralization, homogenization, and spray drying process to prepare a rice protein sample with good performance and qualified heavy metal total mercury index.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The present application combines the alkali swelling and high-pressure steam flash explosion pretreatment processes with the low-temperature plasma treatment process, which can achieve the effect of destroying the bonding force between heavy metals and proteins. The treatment process does not undergo strong acid or high-temperature treatment, has low requirements for equipment, and maintains good performance of rice protein. The heavy metal content of the final finished rice protein meets the national standard requirements and has good product performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an electron micrograph of rice protein used as raw material for the experiment;

[0031] Figure 2 This is an electron microscope image of the corresponding finished product after the experimental raw materials were processed by Example 3. DETAILED DESCRIPTION

[0032] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0033] Embodiment 1: a method for reducing trace amounts of heavy metal mercury in rice protein, comprising the following steps:

[0034] (S1) alkaline swelling combined with wet high-pressure flash explosion pretreatment: after the alkaline swelling reaction, the rice protein feed liquid after the first feed liquid of rice protein is subjected to wet high-pressure flash explosion treatment to obtain the pretreated rice protein feed liquid; the first feed liquid of the rice protein is the protein feed liquid obtained by adding water to the rice protein with excessive heavy metals and mixing the resulting liquid, and the mass concentration is 15%; in the described alkaline swelling reaction, the alkali type used is NaOH, the reaction pH is controlled at 8.0, the temperature is 50 ℃, and the swelling reaction time is 1h; the described wet high-pressure flash explosion treatment process is, the material after the swelling reaction is loaded into a steam flash explosion reaction vessel, steam is introduced to a pressure of 1MPa and maintained for 10s;

[0035] (S2) low temperature plasma treatment: the rice protein feed liquid after pretreatment is placed in a low temperature plasma reactor for low temperature plasma treatment, so that the heavy metal methylmercury is freed from the rice protein system; the described low temperature plasma treatment process is: the rice protein feed liquid after pretreatment is placed in a dielectric barrier type low temperature plasma reaction device, the built-in working gas is air, and the low temperature plasma treatment voltage is controlled to be 60kV during reaction, and the time is 5min; the dielectric barrier discharge can work in a high pressure and a very wide frequency range, and the design form of the electrode structure is diverse; between the two discharge electrodes, the working gas is filled, and one or both electrodes are covered with an insulating medium, and when a sufficiently high AC voltage is applied between the two electrodes, the working gas between the electrodes will be broken down and discharge is generated, that is, a dielectric barrier discharge is generated. A relatively typical dielectric barrier discharge plasma generating device includes a ceramic tube (Al2O3) containing a stainless steel mesh, and the ceramic tube is close to a copper belt; the stainless steel tube and the copper belt are connected to a 10kVp-p, 10kHz power supply, and the intermediate working gas is air, and the air flow rate is 4L / min;

[0036] (S3) thermal desorption treatment: thermal desorption treatment is performed on the material after the treatment in step (S2), so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; the thermal desorption treatment process is specifically: the rice protein material treated with low-temperature plasma is heated at a temperature of 70° C. for a reaction time of about 2 hours, and a gas recovery device is used to recover gas;

[0037] (S4) rice protein finished product preparation: the rice protein material after removing the heavy metal is homogenized, and then spray-dried to obtain the rice protein that reduces the heavy metal mercury; the described rice protein finished product preparation process is: it is neutral that the rice protein material after removing the heavy metal is adjusted to pH, through homogenization, the homogenization pressure is 40MPa, and then adopts spray-drying to be prepared as the rice protein finished product.

[0038] Embodiment 2: a method for reducing trace heavy metal mercury in rice protein, it comprises the following steps:

[0039] (S1) alkaline swelling combined with wet high-pressure flash explosion pretreatment: after the alkaline swelling reaction, the rice protein feed liquid after the first feed liquid of rice protein is subjected to wet high-pressure flash explosion treatment to obtain the pretreated rice protein feed liquid; the first feed liquid of the rice protein is the protein feed liquid obtained by adding water to the rice protein with excessive heavy metals and mixing the resulting liquid, and the mass concentration is 15%; in the described alkaline swelling reaction, the alkali type used is NaOH, the reaction pH is controlled at 9.5, the temperature is 70 ℃, and the swelling reaction time is 4h; the described wet high-pressure flash explosion treatment process is, the material after the swelling reaction is loaded into a steam flash explosion reaction vessel, steam is passed into the pressure 3MPa and maintained for 30s;

[0040] (S2) low temperature plasma treatment: the pre-treated rice protein feed liquid is placed in a low temperature plasma reactor and treated with low temperature plasma to free the heavy metal methylmercury from the rice protein system; the low temperature plasma treatment process is as follows: the pre-treated rice protein feed liquid is placed in a dielectric barrier type low temperature plasma reaction device, the built-in working gas is air, and the low temperature plasma treatment voltage is controlled to be 100 kV during the reaction, and the time is 10 min;

[0041] (S3) thermal desorption treatment: thermal desorption treatment is performed on the material after the treatment in step (S2), so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; the thermal desorption treatment process is specifically: the rice protein material treated with low-temperature plasma is heated at a temperature of 80° C. for a reaction time of about 5 hours, and a gas recovery device is used to recover gas;

[0042] (S4) rice protein finished product preparation: the rice protein material after removing the heavy metal is homogenized, and then spray-dried to obtain the rice protein that reduces the heavy metal mercury; the described rice protein finished product preparation process is: it is neutral that the rice protein material after removing the heavy metal is adjusted to pH, through homogenization, the homogenization pressure is 40MPa, and then adopts spray-drying to be prepared as the rice protein finished product.

[0043] Embodiment 3: A method for reducing trace amounts of heavy metal mercury in rice protein, comprising the following steps:

[0044] (S1) alkaline swelling combined with wet high-pressure flash explosion pretreatment: after the alkaline swelling reaction, the rice protein feed liquid after the first feed liquid of rice protein is subjected to wet high-pressure flash explosion treatment to obtain the pretreated rice protein feed liquid; the first feed liquid of the rice protein is the protein feed liquid obtained by adding water to the rice protein with excessive heavy metals and mixing the resulting liquid, and the mass concentration is 10%; in the described alkaline swelling reaction, the alkali type used is NaOH, the reaction pH is controlled at 9.0, the temperature is 60 ℃, and the swelling reaction time is 2h; the described wet high-pressure flash explosion treatment process is, the material after the swelling reaction is loaded into a steam flash explosion reaction vessel, steam is passed into the pressure 2MPa and maintained for 20s;

[0045] (S2) low temperature plasma treatment: the pre-treated rice protein feed liquid is placed in a low temperature plasma reactor for low temperature plasma treatment to free the heavy metal methylmercury from the rice protein system; the low temperature plasma treatment process is: the pre-treated rice protein feed liquid is placed in a dielectric barrier type low temperature plasma reaction device, the built-in working gas is air, and the low temperature plasma treatment voltage is controlled to be 80kV during the reaction, and the time is 8min;

[0046] (S3) thermal desorption treatment: thermal desorption treatment is performed on the material after the treatment in step (S2), so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; the thermal desorption treatment process is specifically: the rice protein material treated with low-temperature plasma is heated at a temperature of 75° C. for a reaction time of about 3 hours, and a gas recovery device is used to recover gas;

[0047] (S4) rice protein finished product preparation: the rice protein material after removing the heavy metal is homogenized, and then spray-dried to obtain the rice protein that reduces the heavy metal mercury; the described rice protein finished product preparation process is: it is neutral that the rice protein material after removing the heavy metal is adjusted to pH, through homogenization, the homogenization pressure is 40MPa, and then adopts spray-drying to be prepared as the rice protein finished product.

[0048] Comparative Example 1: A method for reducing trace amounts of heavy metal mercury in rice protein, comprising the following steps:

[0049] (S1) preparation of the first feed liquid of rice protein: the first feed liquid of described rice protein is the protein feed liquid that the rice protein with excessive heavy metal adds water and sizing mixing gained, and mass concentration is 10%;

[0050] (S2) low temperature plasma treatment: the first feed liquid of rice protein is placed in a low temperature plasma reactor and is treated with low temperature plasma to free the heavy metal methylmercury from the rice protein system; the low temperature plasma treatment process is as follows: the first feed liquid of rice protein is placed in a dielectric barrier type low temperature plasma reaction device, the built-in working gas is air, and the low temperature plasma treatment voltage is controlled to be 80kV during the reaction, and the time is 8min;

[0051] (S3) thermal desorption treatment: thermal desorption treatment is performed on the material after the treatment in step (S2), so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; the thermal desorption treatment process is specifically: the rice protein material treated with low-temperature plasma is heated at a temperature of 75° C. for a reaction time of about 3 hours, and a gas recovery device is used to recover gas;

[0052] (S4) rice protein finished product preparation: the rice protein material after removing the heavy metal is homogenized, and then spray-dried to obtain the rice protein that reduces the heavy metal mercury; the described rice protein finished product preparation process is: it is neutral that the rice protein material after removing the heavy metal is adjusted to pH, through homogenization, the homogenization pressure is 40MPa, and then adopts spray-drying to be prepared as the rice protein finished product.

[0053] Comparative Example 2: A method for reducing trace amounts of heavy metal mercury in rice protein, comprising the following steps:

[0054] (S1) wet high pressure flash explosion pretreatment: the first feed liquid of rice protein is carried out wet high pressure flash explosion treatment to obtain the pretreated rice protein feed liquid; the first feed liquid of the rice protein is the protein feed liquid obtained by adding water to the rice protein with excessive heavy metals and mixing the resulting liquid, and the mass concentration is 10%; the wet high pressure flash explosion treatment process is to load the material after the swelling reaction into a steam flash explosion reaction vessel, pass steam to a pressure of 2MPa and keep for 20s;

[0055] (S2) low temperature plasma treatment: the pre-treated rice protein feed liquid is placed in a low temperature plasma reactor for low temperature plasma treatment to free the heavy metal methylmercury from the rice protein system; the low temperature plasma treatment process is: the pre-treated rice protein feed liquid is placed in a dielectric barrier type low temperature plasma reaction device, the built-in working gas is air, and the low temperature plasma treatment voltage is controlled to be 80kV during the reaction, and the time is 8min;

[0056] (S3) thermal desorption treatment: thermal desorption treatment is performed on the material after the treatment in step (S2), so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; the thermal desorption treatment process is specifically: the rice protein material treated with low-temperature plasma is heated at a temperature of 75° C. for a reaction time of about 3 hours, and a gas recovery device is used to recover gas;

[0057] (S4) rice protein finished product preparation: the rice protein material after removing the heavy metal is homogenized, and then spray-dried to obtain the rice protein that reduces the heavy metal mercury; the described rice protein finished product preparation process is: it is neutral that the rice protein material after removing the heavy metal is adjusted to pH, through homogenization, the homogenization pressure is 40MPa, and then adopts spray-drying to be prepared as the rice protein finished product.

[0058] Comparative Example 3: A method for reducing trace amounts of heavy metal mercury in rice protein, comprising the following steps:

[0059] (S1) alkaline swelling pretreatment: the first feed liquid of rice protein is subjected to alkaline swelling reaction to obtain pretreated rice protein feed liquid; the first feed liquid of described rice protein is the protein feed liquid obtained by adding water to the rice protein with excessive heavy metals and mixing the size, and the mass concentration is 10%; in the described alkaline swelling reaction, the alkali type used is NaOH, the reaction pH is controlled at 9.0, the temperature is 60 ℃, and the swelling reaction time is 2h;

[0060] (S2) low temperature plasma treatment: the pre-treated rice protein feed liquid is placed in a low temperature plasma reactor for low temperature plasma treatment to free the heavy metal methylmercury from the rice protein system; the low temperature plasma treatment process is: the pre-treated rice protein feed liquid is placed in a dielectric barrier type low temperature plasma reaction device, the built-in working gas is air, and the low temperature plasma treatment voltage is controlled to be 80kV during the reaction, and the time is 8min;

[0061] (S3) thermal desorption treatment: thermal desorption treatment is performed on the material after the treatment in step (S2), so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; the thermal desorption treatment process is specifically: the rice protein material treated with low-temperature plasma is heated at a temperature of 75° C. for a reaction time of about 3 hours, and a gas recovery device is used to recover gas;

[0062] (S4) rice protein finished product preparation: the rice protein material after removing the heavy metal is homogenized, and then spray-dried to obtain the rice protein that reduces the heavy metal mercury; the described rice protein finished product preparation process is: it is neutral that the rice protein material after removing the heavy metal is adjusted to pH, through homogenization, the homogenization pressure is 40MPa, and then adopts spray-drying to be prepared as the rice protein finished product.

[0063] Comparative Example 4: A method for reducing trace amounts of heavy metal mercury in rice protein, comprising the following steps:

[0064] (S1) alkaline swelling combined with wet high-pressure flash explosion pretreatment: after the alkaline swelling reaction, the rice protein feed liquid after the first feed liquid of rice protein is subjected to wet high-pressure flash explosion treatment to obtain the pretreated rice protein feed liquid; the first feed liquid of the rice protein is the protein feed liquid obtained by adding water to the rice protein with excessive heavy metals and mixing the resulting liquid, and the mass concentration is 10%; in the described alkaline swelling reaction, the alkali type used is NaOH, the reaction pH is controlled at 9.0, the temperature is 60 ℃, and the swelling reaction time is 2h; the described wet high-pressure flash explosion treatment process is, the material after the swelling reaction is loaded into a steam flash explosion reaction vessel, steam is passed into the pressure 2MPa and maintained for 20s;

[0065] (S2) thermal desorption treatment: thermal desorption treatment is performed on the material after the treatment in step (S1), so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; the thermal desorption treatment process is specifically: the pretreated rice protein material is heated at a temperature of 75° C. for a reaction time of about 3 hours, and a gas recovery device is used to recover gas;

[0066] (S3) Preparation of rice protein finished product: The rice protein material after the thermal desorption process is homogenized and then spray-dried to obtain rice protein with reduced heavy metal mercury; the rice protein finished product preparation process is as follows: the rice protein material after the thermal desorption process is adjusted to a neutral pH, homogenized at a homogenization pressure of 40MPa, and then spray-dried to be prepared as the rice protein finished product.

[0067] Comparative Example 5: A method for reducing trace amounts of heavy metal mercury in rice protein, comprising the following steps:

[0068] (S1) alkaline swelling combined with wet high-pressure flash explosion pretreatment: after the alkaline swelling reaction, the rice protein feed liquid after the first feed liquid of rice protein is subjected to wet high-pressure flash explosion treatment to obtain the pretreated rice protein feed liquid; the first feed liquid of the rice protein is the protein feed liquid obtained by adding water to the rice protein with excessive heavy metals and mixing the resulting liquid, and the mass concentration is 10%; in the described alkaline swelling reaction, the alkali type used is NaOH, the reaction pH is controlled at 9.0, the temperature is 60 ℃, and the swelling reaction time is 2h; the described wet high-pressure flash explosion treatment process is, the material after the swelling reaction is loaded into a steam flash explosion reaction vessel, steam is passed into the pressure 2MPa and maintained for 20s;

[0069] (S2) low temperature plasma treatment: the pre-treated rice protein feed liquid is placed in a low temperature plasma reactor for low temperature plasma treatment to free the heavy metal methylmercury from the rice protein system; the low temperature plasma treatment process is: the pre-treated rice protein feed liquid is placed in a dielectric barrier type low temperature plasma reaction device, the built-in working gas is air, and the low temperature plasma treatment voltage is controlled to be 80kV during the reaction, and the time is 8min;

[0070] (S3) Preparation of rice protein finished product: The material after the step (S2) is treated with homogenization, and then spray-dried to obtain rice protein with reduced heavy metal mercury; the rice protein finished product preparation process is as follows: the material after the step (S2) is treated with pH adjustment to be neutral, and then treated with homogenization at a homogenization pressure of 40MPa, and then spray-dried to be prepared as the rice protein finished product.

[0071] The raw materials adopted in Examples 1-3 and Comparative Examples 1-5 are all the same raw material rice protein.

[0072] The tertiary structure of rice protein maintains the spatial structure of protein. The tertiary structure mainly includes various interactions (including hydrophobic interaction, electrostatic interaction and van der Waals force) and hydrogen bonds between different groups. The change of protein hydrophobicity plays a very important role in the tertiary structure of rice protein. Hydrophobic interaction is a non-covalent interaction between ligands, which is an important force to maintain the tertiary structure stability, conformation and functional properties of protein. Under different pH, temperature and ionic strength, the number of hydrophobic groups on the protein surface determines its dissolution behavior. Alkali swelling combined with steam flash explosion treatment, that is, the change of rice protein tertiary structure before and after pretreatment can be reflected by the following table:

[0073] <![CDATA[Surface hydrophobicity H0]]> Protein raw materials 260.97 After step S1 of Example 1 1356.78 After step S1 of Example 2 1203.46 After step S1 of Example 3 1938.25

[0074] Compared with rice protein raw materials, the surface hydrophobicity of the protein increases after alkaline swelling and steam explosion treatment. The surface hydrophobicity of the protein is characterized by testing the change in fluorescence intensity. The higher the value, the more hydrophobic groups are exposed on the surface of the protein, indicating that after alkaline swelling and steam explosion treatment, the tertiary structure of the protein is opened and the hydrophobic groups inside the protein are exposed, which can improve the effectiveness of the next process treatment.

[0075] Regarding the changes in the secondary structure before and after low-temperature plasma treatment: After the initial alkaline swelling treatment and steam flash explosion treatment, the secondary structure of rice protein also changed to a certain extent. After the low-temperature plasma treatment, the protein surface was easily etched. At the same time, the oxidation of active oxygen and active nitrogen generated in the low-temperature plasma generator had a certain effect on the rearrangement of the secondary structure of rice protein. The numerical results showed that the α-helix of the protein increased, the β-fold decreased, and the β-turn increased.

[0076] The increase in the content of α-helix structure forms more stable interfaces and multilayer interfaces on the surface of rice protein, which is beneficial to the non-covalent intramolecular interactions and the mutual binding with water molecules, and has a positive effect on improving the hydration properties of rice protein.

[0077] The β-fold structure in rice protein or its complex is usually stabilized by the hydrogen bonds in the protein arranged in a parallel or antiparallel manner. The reduction of the β-fold content indicates a reduction in the orderliness of the rice protein structure and the folding of the rice protein is inhibited. The β-turn structure usually appears on the protein surface where it is convenient to hydrogen bond with the solvent. The electron micrograph of the rice protein of the experimental raw material and the electron micrograph of the corresponding finished product after the experimental raw material was treated with Example 3 are shown in FIG. Figure 1 and Figure 2 shown.

[0078] α-helix β-sheet β-turn Irregular curl Protein raw materials 0 15.3 34.4 50.8 After step S1 of Example 1 14.2 15.0 29.3 41.7 After step S1 of Example 2 13.8 15.0 26.6 42.9 After step S1 of Example 3 15.3 14.8 30.6 39.6 After step S2 of Example 1 19.7 12.4 29.5 38.4 After step S2 of Example 2 20.4 11.3 31.6 36.7 After step S2 of Example 3 20.6 11.5 31.1 37.2

[0079] The analysis of the processed samples is shown in the following table:

[0080]

[0081]

[0082] After the process of embodiments 1, 2 and 3, the basic physicochemical indexes of rice protein: protein content, fat content, ash content, and protein functional indexes: solubility, emulsification and foaming properties are as shown in the following table:

[0083]

[0084] It should be understood that the present invention is not limited to the forms disclosed herein, and modifications and variations made by those skilled in the art without departing from the spirit and scope of the present invention should be within the scope of protection of the appended claims of the present invention.

Claims

1. A method for reducing trace amounts of heavy metal mercury in rice protein, characterized in that: The following steps are involved: (S1) Alkaline swelling combined with wet high pressure flash explosion pretreatment After the rice protein initial feed liquid is subjected to an alkali swelling reaction, the fully hydrated rice protein feed liquid is subjected to a wet method high pressure flash explosion treatment to obtain a pretreated rice protein feed liquid; (S2) Low temperature plasma treatment The pretreated rice protein liquid is placed in a low-temperature plasma reactor for low-temperature plasma treatment to free the heavy metal methylmercury from the rice protein system; (S3) Thermal Desorption Treatment The material after the process in step (S2) is subjected to thermal desorption treatment, so that the heavy metal methylmercury in the rice protein undergoes phase change and is removed and separated from the rice protein solution; (S4) Preparation of rice protein finished product The rice protein material after heavy metal removal is homogenized and then spray-dried to obtain rice protein with reduced heavy metal mercury.

2. The method for eliminating trace amounts of heavy metal mercury in rice protein according to claim 1, wherein: In step (S1), the rice protein initial feed liquid is a protein feed liquid obtained by adding water to rice protein with excessive heavy metals and slurry mixing, and the mass concentration is 10-15%.

3. the method for subtracting trace heavy metal mercury in rice protein according to claim 2, is characterized in that: In step (S1), in the alkaline swelling reaction, the type of alkali used is one of NaOH, NaHCO3, and Na2CO3, the reaction pH is controlled at 8.0-9.5, the temperature is 50-70°C, and the swelling reaction time is 1-4h.

4. the method for subtracting trace heavy metal mercury in rice protein according to claim 2, is characterized in that: In step (S1), the wet high-pressure flash explosion treatment process is to load the material after the swelling reaction into a steam flash explosion reaction vessel, introduce steam to a pressure of 1-3 MPa and maintain it for 10-30 seconds.

5. The method for eliminating trace heavy metal mercury in rice protein according to claim 1, wherein: In step (S2), the low-temperature plasma treatment process is as follows: the pretreated rice protein liquid is placed in a dielectric barrier type low-temperature plasma reaction device, the built-in working gas is air, and the low-temperature plasma treatment voltage is controlled to be 60-100 kV during the reaction, and the time is 5-10 min.

6. The method for eliminating trace heavy metal mercury in rice protein according to claim 1, wherein: The thermal desorption process described in step (S3) is as follows: the rice protein material treated with low-temperature plasma is subjected to a heat treatment at a temperature of 70-80° C. for a reaction time of about 2-5 hours, and a gas recovery device is used to recover gas.

7. The method for eliminating trace amounts of heavy metal mercury in rice protein according to claim 1, wherein: In step (S4), the rice protein finished product preparation process is as follows: the rice protein material after heavy metal removal is adjusted to a neutral pH, homogenized at a homogenization pressure of 30-60 MPa, and then spray-dried to prepare the rice protein finished product.

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