Method for determining urea content in dairy product based on magnetoelectric coupling field

Abstract

The invention discloses a method for determining the content of urea in a dairy product based on a magnetoelectric coupling field. The method comprises the following steps: respectively mixing a series of urea standard solutions with different concentrations with a diacetylmonoxime solution and an antipyrine sulfuric acid solution by adopting a standard curve method, reacting in a magnetoelectric coupling field, and then detecting absorbance values of a series of obtained urea standard solutions to be detected at 460 nm, establishing a standard curve of the urea concentration and the absorbance value; and pretreating a dairy product to be detected to obtain a supernatant, mixing the supernatant with a diacetylmonooxime solution and an antipyrine sulfuric acid solution, carrying out a reaction in the magnetoelectric coupling field, detecting the absorbance value of the obtained dairy product solution to be detected at 460 nm, and comparing the absorbance value with the standard curve, so that quantitative detection of urea in the dairy product to be detected is realized. The urea content determination method provided by the invention is simple in operation process and has excellent accuracy and sensitivity.

Description

Technical Field

[0001] The invention belongs to the technical field of urea detection, and in particular relates to a method for measuring the urea content in dairy products based on a magnetoelectric coupling field. Background Art

[0002] Milk is a common dairy product in daily life, and is widely loved by consumers for its rich nutrition and mellow taste. Urea is one of the components of milk, but the content is very small. During production, the nutritional status and health status of dairy cows can be monitored in real time by measuring the urea content. Illegal addition of urea in dairy products will increase the detected protein content, but it has potential harm to human health. Testing the urea content can prevent milk adulteration.

[0003] At present, the main detection methods for urea in milk include chemical method, chromatography, colorimetry, etc. Among them, the current national standard method is the post-distillation titration method (GB / T 2441.1-2008), which has good accuracy, but the analysis process is cumbersome, the heating digestion takes a long time, and it is easy to have operational errors; the chromatography method has good separation effect and high sensitivity, but the sample pretreatment is complicated and the equipment cost is high; the colorimetric method is easy to operate and low in cost, but the selectivity and sensitivity are low. Based on this, researchers have also proposed some innovative methods, such as the use of electrical sensors for determination in patent CN202310301739.5, and the use of enzyme coupling method to prepare urea test kits for determination in patent CN202211336926.9. Although these methods simplify the operation process, there is still a lot of room for optimization in the precision and accuracy of the detection. Summary of the invention

[0004] The main purpose of the present invention is to provide a method for measuring the urea content in dairy products based on magnetoelectric coupling field, so as to overcome the shortcomings of the prior art.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: The embodiment of the present invention provides a method for measuring the urea content in dairy products based on a magnetoelectric coupling field, which comprises: A standard curve method is adopted, a series of urea standard solutions of different concentrations are mixed with diacetyl monoxime solution and antipyrine sulfuric acid solution respectively and reacted in a magnetoelectric coupling field, and then the absorbance values ​​of a series of obtained urea standard solutions to be tested at 460 nm are detected, so as to establish a standard curve of urea concentration Y and absorbance value A, wherein Y=105.2A+C, and C is -8.5~25; the magnetoelectric coupling field includes a high-frequency oscillating electric field and a static magnetic field; Also, the dairy product to be tested is pretreated to obtain a supernatant, which is then mixed with a diacetyl monoxime solution and an antipyrine sulfuric acid solution and reacted in a magnetoelectric coupling field, and then the absorbance value of the obtained dairy product solution to be tested at 460 nm is detected and compared with the standard curve, thereby achieving quantitative detection of urea in the dairy product to be tested.

[0006] Compared with the prior art, the beneficial effects of the present invention are as follows: the method for determining the urea content provided by the present invention has a simple operating procedure, and according to the different magnetoelectric properties of urea and its detection reagent, the response orientation under the magnetoelectric coupling field promotes a rapid and effective reaction between the components, shortens the reaction time and the detection time, and realizes the detection of the urea content in dairy products, while having good repeatability, accuracy and sensitivity. DETAILED DESCRIPTION

[0007] In view of the defects of the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0008] Specifically, as one aspect of the technical solution of the present invention, a method for determining the urea content in dairy products based on a magnetic electric field comprises: A standard curve method is adopted, a series of urea standard solutions of different concentrations are mixed with diacetyl monoxime solution and antipyrine sulfuric acid solution respectively and reacted in a magnetoelectric coupling field, and then the absorbance values ​​of a series of obtained urea standard solutions to be tested at 460 nm are detected, so as to establish a standard curve of urea concentration Y and absorbance value A, wherein Y=105.2A+C, and C is -8.5~25; the magnetoelectric coupling field includes a high-frequency oscillating electric field and a static magnetic field; Also, the dairy product to be tested is pretreated to obtain a supernatant, which is then mixed with a diacetyl monoxime solution and an antipyrine sulfuric acid solution and reacted in a magnetoelectric coupling field, and then the absorbance value of the obtained dairy product solution to be tested at 460 nm is detected and compared with the standard curve, thereby achieving quantitative detection of urea in the dairy product to be tested.

[0009] The magneto-electric coupling field strengths set in the present invention are different, and the corresponding detection ranges are different.

[0010] In some preferred embodiments, the electric field frequency of the high-frequency oscillating electric field is 100-150 kHz, the electric field strength is 3-8 V / cm, and the power is 2-5 W; the magnetic field strength of the static magnetic field is 5-10 mT.

[0011] In some preferred embodiments, the reaction endpoint temperature in the magnetoelectric coupling field is 85-95° C., and the residence time is 3-5 min.

[0012] In some preferred embodiments, the method specifically comprises: Using the standard curve method, a series of urea standard solutions with different concentrations are mixed with diacetyl monoxime solution and antipyrine sulfuric acid solution respectively and reacted in a magnetoelectric coupling field to obtain a series of mixed standard solutions to be tested; And, using distilled water as a reference, an ultraviolet spectrophotometer was used to detect the absorbance values ​​of a series of 3 mL of the mixed standard solution to be tested at 460 nm, so as to establish a standard curve of urea concentration Y and absorbance value A.

[0013] Furthermore, the concentration of the urea standard solution is 0-100.0 mg / L.

[0014] Furthermore, the concentration of the diacetyl monoxime solution is 1.5-2.5 g / mL.

[0015] Furthermore, the concentration of antipyrine in the antipyrine sulfuric acid solution is 1.5-2.5 g / mL, and the concentration of sulfuric acid is 60 wt%-70 wt%.

[0016] Furthermore, the volume ratio of the diacetyl monoxime solution to the urea standard solution is 1:1 to 10:1.

[0017] Furthermore, the volume ratio of the antipyrine sulfuric acid solution to the urea standard solution is 1:1 to 20:1.

[0018] In some preferred embodiments, the method specifically comprises: Firstly, the dairy product to be tested is diluted, and then the diluted sample to be tested is treated by at least salting-out method or isoelectric precipitation method, and then centrifuged to obtain a supernatant; The supernatant is mixed with a diacetyl monoxime solution and an antipyrine sulfuric acid solution and reacted in a magnetoelectric coupling field to obtain a mixed sample solution to be tested; And, using distilled water as a reference, an ultraviolet spectrophotometer is used to detect the absorbance value of 3 mL of the mixed sample solution to be tested at 460 nm, and compared with the standard curve, so as to achieve quantitative detection of urea in the sample to be tested.

[0019] Furthermore, the dilution factor of the dairy product to be tested is 5 to 10 times.

[0020] Furthermore, the concentration of the diacetyl monoxime solution is 1.5-2.5 g / mL.

[0021] Furthermore, the concentration of antipyrine in the antipyrine sulfuric acid solution is 1.5-2.5 g / mL, and the concentration of sulfuric acid is 60 wt%-70 wt%.

[0022] Furthermore, the volume ratio of the diacetyl monoxime solution to the supernatant is 1:1 to 10:1.

[0023] Furthermore, the volume ratio of the antipyrine sulfuric acid solution to the supernatant is 1:1 to 20:1.

[0024] In some preferred embodiments, the detection range of the method for determining the urea content in dairy products is 200.0~450.0 mg / L.

[0025] In some preferred embodiments, the dairy product to be tested includes any one of fresh milk, pure milk, modified milk, and nutritionally fortified milk.

[0026] In some more specific embodiments, the method for determining the urea content in dairy products based on the magnetoelectric coupling field comprises: S1. Take fresh milk and dilute it with distilled water. Use salting out method or isoelectric precipitation method to precipitate protein. Centrifuge and separate. Keep the supernatant for inspection.

[0027] S2, uniformly mixing the supernatant with the diacetyl monoxime solution and the antipyrine sulfuric acid solution to obtain a mixed solution.

[0028] S3. After the mixed solution is fully reacted in a magnetoelectric coupling field, a test solution is obtained. The absorbance value A of the test solution is measured at 460 nm with distilled water as a reference. The magnetoelectric coupling field includes a high-frequency oscillating electric field and a static magnetic field.

[0029] S4. Take a series of 3 mL urea standard solutions of different concentrations and test them according to the methods described in S1-S3 to determine the relationship between the urea content Y and the sample absorbance value A at the corresponding concentration. The standard curve formula is Y=105.2A+C, and the value of C is -8.5~25. Calculate the urea content in the milk to be tested. The detection range is 200.0~450.0 mg / L.

[0030] Preferably, the dilution multiple of the milk is 5 to 10 times.

[0031] Preferably, the concentration of the diacetyl monoxime solution is 1.5-2.5 g / mL, and the amount of the diacetyl monoxime solution added is 1-10 times the volume of the S1 supernatant.

[0032] Preferably, the concentration of antipyrine in the antipyrine sulfuric acid solution is 1.5-2.5 g / mL, the concentration of sulfuric acid is 60 wt%-70 wt%, and the amount of antipyrine sulfuric acid solution added is 1-20 times the volume of the S1 supernatant.

[0033] Preferably, the electric field frequency of the high-frequency oscillating electric field is 100-150 kHz, the electric field strength is 3-8 V / cm, and the power is 2-5 W; the magnetic field strength of the static magnetic field is 5-10 mT.

[0034] Preferably, the reaction temperature of the mixed solution is 85-95° C., the heating method is a water bath, and the reaction time is 3-5 min.

[0035] Preferably, the milk includes but is not limited to fresh milk, pure milk, nutritionally fortified milk and the like.

[0036] In the present invention, urea is the final product of protein and amino acid metabolism in mammals, and is an organic nitrogen compound. Urea molecules contain unpaired electrons and have antimagnetism, while the chemical reagents, acids, bases, salts and their compounds to be detected have extremely low differential relative magnetic permeability. In addition, different substances have different dielectric properties and respond to orientation under an electric field. Under an external magnetoelectric coupling environment, different substances move in a directional manner and spin polarize, and the probability of interaction increases, which promotes faster and more effective reactions of each component, shortens the reaction time, and realizes the detection of samples with different urea contents.

[0037] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments. This embodiment is implemented on the premise of the technical solution of the invention, and provides a detailed implementation method and a specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0038] Unless otherwise specified, the experimental materials used in the following examples can be purchased from conventional biochemical reagent companies.

[0039] Example 1 A method for determining urea content in fresh milk comprises the following steps: S1. Take 10 mL of fresh milk, add distilled water to make up to 100 mL, mix well, centrifuge, and keep the supernatant for inspection.

[0040] S2. Take 2 mL of the supernatant and put it in a test tube. Add 2 mL of 1.5 g / mL diacetyl monoxime solution and 2 mL of 2.0 g / mL antipyrine sulfuric acid solution (sulfuric acid concentration 65 wt%) into the test tube and shake well.

[0041] S3. Place the mixed solution in a magnetoelectric coupling field, the electric field frequency of the high-frequency oscillating electric field is 100 kHz, the electric field strength is 3 V / cm, the power is 2 W, the static magnetic field strength is 5 mT, and react in an 85°C water bath for 3 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0042] Take 3 mL of standard solution with urea content of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, and test it according to the method described in S2~S3 to obtain the standard urea content Y, which is related to the sample absorbance value A at the corresponding concentration by Y=105.2A-4.8.

[0043] According to steps S1 to S3, the fresh milk with unknown urea content is measured to obtain the corresponding absorbance value A, and then the urea content Y0 is calculated according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0044] Fresh milk produced by 8 different manufacturers was tested by the method of this embodiment and the method of GB / T 2441.1-2008, and the test results are shown in Table 1.

[0045] Table 1 Detection results of urea content in fresh milk from different manufacturers using the method in Example 1 and the national standard method

[0046] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0047] The average detection time using the detection method of this embodiment is 8 minutes; in comparison, the average detection time using the method of GB / T2441.1-2008 is 30 minutes, which is much longer than the detection method of this embodiment, and there is no significant difference in the detection results of the two, the relative deviation is always less than ±2%, and the detection results are highly accurate.

[0048] Example 2 A method for determining urea content in pure milk comprises the following steps: S1. Same as method S1 in Example 1.

[0049] S2. Same as method S2 in Example 1.

[0050] S3. Place the mixed solution in a magneto-electric coupling field, the electric field frequency of the high-frequency oscillating electric field is 120 kHz, the electric field strength is 5 V / cm, the power is 3 W, the static magnetic field strength is 8 mT, and react in a 90°C water bath for 3.5 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0051] Take standard solutions with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, respectively, take 3 mL of the standard solution and perform detection according to the methods described in S2~S3, and obtain the relationship Y=105.2A+0.5 between the standard urea content Y and the sample absorbance value A at the corresponding concentration.

[0052] Determine the pure milk with unknown urea content according to steps S1 to S3 to obtain the corresponding absorbance value A, and then calculate the urea content Y0 according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0053] The method of this embodiment and the GB / T 2441.1-2008 method were used to measure and test pure milk produced by 8 different manufacturers. The test results are shown in Table 2.

[0054] Table 2 Test results of urea content in pure milk from different manufacturers using the method in Example 2 and the national standard method

[0055] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0056] The average detection time using the detection method of this embodiment is 8.5 min; in comparison, the average detection time using the method of GB / T2441.1-2008 is 30 min, which is much longer than the detection method of this embodiment, and there is no significant difference in the detection results of the two, the relative deviation is always less than ±2%, and the detection results are highly accurate.

[0057] Example 3 A method for determining urea content in fresh milk comprises the following steps: S1 is the same as method S1 in Example 1.

[0058] S2. Take 2 mL of the supernatant and put it in a test tube. Add 4 mL of 1.5 g / mL diacetyl monoxime solution and 8 mL of 1.5 g / mL antipyrine sulfuric acid solution (sulfuric acid concentration 60 wt%) into the test tube and shake well.

[0059] S3. Place the mixed solution in a magneto-electric coupling field, the electric field frequency of the high-frequency oscillating electric field is 150 kHz, the electric field strength is 8 V / cm, the power is 5 W, the static magnetic field strength is 10 mT, and react in a 95°C water bath for 5 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0060] Take 3 mL of standard solution with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, respectively, and test it according to the methods described in S2~S3 to determine the urea content Y, which is related to the absorbance value A of the sample at the corresponding concentration by Y=105.2A-7.5.

[0061] According to steps S1 to S3, the fresh milk with unknown urea content is measured to obtain the corresponding absorbance value A, and then the urea content Y0 is calculated according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0062] The method of this embodiment and the GB / T 2441.1-2008 method were used to measure and test fresh milk produced by 8 different manufacturers. The test results are shown in Table 3.

[0063] Table 3 Test results of urea content in fresh milk from different manufacturers using the method in Example 3 and the national standard method

[0064] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0065] The average detection time using the detection method of this embodiment is 10 min; in comparison, the average detection time using the method of GB / T2441.1-2008 is 30 min, which is much longer than the detection method of this embodiment, and there is no significant difference in the detection results of the two, the relative deviation is always less than ±2%, and the detection results are highly accurate.

[0066] Example 4 A method for determining urea content in pure milk comprises the following steps: S1. Take 10 mL of pure milk, add distilled water to make up to 50 mL, mix well, centrifuge, and keep the supernatant for inspection.

[0067] S2. Take 2 mL of the supernatant and put it in a test tube. Add 6 mL of 1.5 g / mL diacetyl monoxime solution and 4 mL of 2.5 g / mL antipyrine sulfuric acid solution (sulfuric acid concentration 70 wt%) into the test tube and shake well.

[0068] S3. Place the mixed solution in a magneto-electric coupling field, the electric field frequency of the high-frequency oscillating electric field is 150 kHz, the electric field strength is 8 V / cm, the power is 5 W, the static magnetic field strength is 10 mT, and react in a 90°C water bath for 4 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0069] Take 3 mL of standard solution with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, respectively, and test it according to the methods described in S2~S3 to determine the urea content Y, which is related to the absorbance value A of the sample at the corresponding concentration by Y=105.2A+2.4.

[0070] Determine the pure milk with unknown urea content according to steps S1 to S3 to obtain the corresponding absorbance value A, and then calculate the urea content Y0 according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=5Y0.

[0071] The method of this embodiment and the GB / T 2441.1-2008 method were used to measure and test pure milk produced by 8 different manufacturers. The test results are shown in Table 4.

[0072] Table 4 Detection results of urea content in pure milk from different manufacturers using the method of Example 4 and the national standard method

[0073] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0074] The average detection time of the detection method of this embodiment is 9 minutes; in comparison, the average detection time of the method of GB / T2441.1-2008 is 30 minutes, which is much longer than the detection method of this embodiment, and there is no significant difference in the detection results of the two, and the relative deviation is always less than ±2%, and the accuracy of the detection results is high. In addition, compared with Example 2, the magnetoelectric coupling strength of this embodiment is increased, the detection range is increased, and the sample dilution concentration is reduced.

[0075] Example 5 A method for determining the urea content in a modulated milk comprises the following steps: S1. Take 10 mL of the prepared milk, add distilled water to make up to 50 mL, mix well, centrifuge, and keep the supernatant for inspection.

[0076] S2. Take 5 mL of the supernatant and put it in a test tube. Add 10 mL of 2.0 g / mL diacetyl monoxime solution and 20 mL of 2.0 g / mL antipyrine sulfuric acid solution (sulfuric acid concentration 60 wt%) into the test tube and shake well.

[0077] S3. Place the mixed solution in a magneto-electric coupling field, the electric field frequency of the high-frequency oscillating electric field is 140 kHz, the electric field strength is 6 V / cm, the power is 4 W, the static magnetic field strength is 5 mT, and react in a 90°C water bath for 5 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0078] Take 3 mL of standard solution with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, respectively, and test it according to the methods described in S2~S3 to determine the urea content Y, which is related to the absorbance value A of the sample at the corresponding concentration by Y=105.2A+25.

[0079] According to steps S1 to S3, the modulated milk with unknown urea content is measured to obtain the corresponding absorbance value A, and then the urea content Y0 is calculated according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=5Y0.

[0080] The method of this embodiment and the method of GB / T 2441.1-2008 were used to measure and test 8 kinds of modulated milk produced by different manufacturers. The test results are shown in Table 5.

[0081] Table 5 Test results of urea content in formula milk from different manufacturers by the method of Example 5 and the national standard method

[0082] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0083] The average detection time using the detection method of this embodiment is 10 min; in comparison, the average detection time using the method of GB / T2441.1-2008 is 30 min, which is much longer than the detection method of this embodiment, and there is no significant difference in the detection results of the two, the relative deviation is always less than ±2%, and the detection results are highly accurate.

[0084] Comparative Example 1 A method for determining urea content in fresh milk comprises the following steps: S1. Same as S1 in Example 1.

[0085] S2. Same as S2 in Example 1.

[0086] S3. Place the mixed solution in a magneto-electric coupling field, the electric field frequency of the high-frequency oscillating electric field is 60 kHz, the electric field strength is 2 V / cm, the power is 1 W, the static magnetic field strength is 3 mT, and react in an 85°C water bath for 3 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0087] Take 3 mL of standard solution with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, respectively, and test it according to the methods described in S2~S3 to determine the urea content Y, which is related to the absorbance value A of the sample at the corresponding concentration by Y=98.2A+8.9.

[0088] According to steps S1 to S3, the fresh milk with unknown urea content is measured to obtain the corresponding absorbance value A, and then the urea content Y0 is calculated according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0089] Fresh milk produced by 8 different manufacturers was tested by the method of this comparative example and the GB / T 2441.1-2008 method. The test results are shown in Table 6.

[0090] Table 6 Test results of urea content in fresh milk from different manufacturers using comparative example 1 and national standard method

[0091] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0092] The average detection time using the detection method of this embodiment is 8 minutes; in comparison, the average detection time using the method of GB / T2441.1-2008 is 30 minutes, which is much longer than the detection method of this embodiment. However, the magneto-electric coupling field strength of Comparative Example 1 is relatively small, and the interaction effect on material components such as urea is weakened, resulting in an increase in the relative error of its detection result, and the relative deviation fluctuates in the range of -4% to 3%.

[0093] Comparative Example 2 A method for determining urea content in fresh milk comprises the following steps: S1. Same as S1 in Example 1.

[0094] S2. Same as S2 in Example 1.

[0095] S3. Place the mixed solution in a magneto-electric coupling field, the electric field frequency of the high-frequency oscillating electric field is 200 kHz, the electric field strength is 10 V / cm, the power is 7 W, the static magnetic field strength is 20 mT, and react in an 85°C water bath for 3 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0096] Take 3 mL of standard solution with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, respectively, and test it according to the methods described in S2~S3 to determine the urea content Y, which is related to the absorbance value A of the sample at the corresponding concentration by Y=102.6A+21.

[0097] According to steps S1 to S3, the fresh milk with unknown urea content is measured to obtain the corresponding absorbance value A, and then the urea content Y0 is calculated according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0098] Fresh milk produced by 8 different manufacturers was tested by the method of this comparative example and the GB / T 2441.1-2008 method. The test results are shown in Table 7.

[0099] Table 7 Test results of urea content in fresh milk from different manufacturers using comparative example 2 and national standard method

[0100] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0101] The average detection time using the comparative example detection method is 8 minutes; in comparison, the average detection time using the GB / T2441.1-2008 method is 30 minutes, which is much longer than the detection method of the comparative example. However, the magneto-electric coupling field intensity of comparative example 2 is relatively large, which may lead to aggravated spin polarization of some reaction substances, inhibit the interaction between different substances, and increase the relative error of the detection result, with the relative deviation fluctuating in the range of -4% to 3%.

[0102] Comparative Example 3 A method for determining urea content in fresh milk comprises the following steps: S1. Same as S1 in Example 1.

[0103] S2. Same as S2 in Example 1.

[0104] S3. Place the mixed solution in a magneto-electric coupling field, the electric field frequency of the high-frequency oscillating electric field is 200 kHz, the electric field strength is 10 V / cm, the power is 5 W, the static magnetic field strength is 15 mT, and react in an 85°C water bath for 3 min to obtain the test solution. Take 3 mL of the test solution in a quartz cuvette with a 1 cm optical path, use distilled water as a reference, and measure the absorbance value A of the test solution at 460 nm.

[0105] Take 3 mL of standard solution with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, respectively, and test it according to the methods described in S2~S3 to determine the urea content Y, which is related to the absorbance value A of the sample at the corresponding concentration by Y=69.8A-3.6.

[0106] According to steps S1 to S3, the fresh milk with unknown urea content is measured to obtain the corresponding absorbance value A, and then the urea content Y0 is calculated according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0107] Fresh milk produced by 8 different manufacturers was tested by the method of this comparative example and the GB / T 2441.1-2008 method, and the test results are shown in Table 8.

[0108] Table 8 Test results of urea content in fresh milk from different manufacturers using comparative example 3 and national standard method

[0109] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0110] The average detection time of the comparative example detection method is 9 minutes; in comparison, the average detection time of the method using GB / T2441.1-2008 is 30 minutes, which is much longer than the detection method of the comparative example. However, the increase in the magneto-electric coupling field intensity of comparative example 3 may lead to the intensification of the spin polarization of a small number of reaction substances and the weakening of the reaction between different substances, resulting in an increase in the relative error of the detection result, and the relative deviation fluctuates in the range of -4% to 3%.

[0111] Comparative Example 4 A method for determining urea content in pure milk comprises the following steps: S1. Same as S1 in Example 2.

[0112] S2. Same as S2 in Example 2.

[0113] S3. The method is the same as in Example 4, except that a high-frequency oscillating electric field is used instead of a magnetoelectric coupling field. The mixed solution is placed in a high-frequency oscillating electric field with an electric field frequency of 120 kHz, an electric field strength of 5 V / cm, and a power of 3 W. After reacting in a 90°C water bath for 3.5 min, a test solution is obtained. 3 mL of the test solution is placed in a quartz cuvette with a 1 cm optical path, and the absorbance value A of the test solution is measured at 460 nm using distilled water as a reference.

[0114] For standard solutions with urea contents of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, take 3 mL of the standard solution and perform detection according to the methods described in S2~S3 to obtain the standard urea content Y, which is related to the sample absorbance value A at the corresponding concentration by Y=112.9A+2.7.

[0115] Determine the pure milk with unknown urea content according to steps S1 to S3 to obtain the corresponding absorbance value A, and then calculate the urea content Y0 according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0116] The method of this embodiment and the GB / T 2441.1-2008 method were used to measure and test pure milk produced by 8 different manufacturers. The test results are shown in Table 9.

[0117] Table 9 Test results of urea content in pure milk from different manufacturers using comparative example 4 and national standard method

[0118] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0119] The average detection time of the comparative example detection method is 8 min; in comparison, the average detection time of the method using GB / T2441.1-2008 is 30 min, which is much longer than the detection method of the comparative example. However, comparative example 4 only uses a high-frequency oscillating electric field, which may cause ionization and degradation of a small number of reaction substances and weaken the reaction between different substances, resulting in an increase in the relative error of the detection result, and the relative deviation fluctuates in the range of -4% to 3%.

[0120] Comparative Example 5 A method for determining urea content in pure milk comprises the following steps: S1. Same as S1 in Example 2.

[0121] S2. Same as S2 in Example 2.

[0122] S3. The method is the same as in Example 4, except that a static magnetic field is used instead of a magnetoelectric coupling field. The mixed solution is placed in a static magnetic field with an intensity of 8 mT, and reacted in a water bath at 90°C for 3.5 min to obtain a test solution. 3 mL of the test solution is placed in a quartz cuvette with a light path of 1 cm, and the absorbance value A of the test solution is measured at 460 nm using distilled water as a reference.

[0123] Take 3 mL of standard solution with urea content of 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg / L, and test it according to the method described in S2~S3 to obtain the standard urea content Y, which is related to the sample absorbance value A at the corresponding concentration by Y=109.5A-5.2.

[0124] Determine the pure milk with unknown urea content according to steps S1 to S3 to obtain the corresponding absorbance value A, and then calculate the urea content Y0 according to the above relationship. The total urea content Y1=Y0*dilution factor, that is, Y1=10Y0.

[0125] The method of this embodiment and the GB / T 2441.1-2008 method were used to measure and test pure milk produced by 8 different manufacturers. The test results are shown in Table 10.

[0126] Table 10 Test results of urea content in pure milk from different manufacturers using comparative example 5 and national standard method

[0127] Note: The data in the above table are the average values ​​of the test results obtained after testing multiple groups of samples.

[0128] The average detection time using the comparative example detection method is 8 min; in comparison, the average detection time using the GB / T2441.1-2008 method is 30 min, which is much longer than the detection method of the comparative example. However, comparative example 5 only uses a static magnetic field, which may cause a small number of reaction substances to be spin polarized, their tendency to weaken, and the reaction between different substances to weaken, resulting in an increase in the relative error of its detection result, and a relative deviation fluctuation in the range of -4% to 4%.

[0129] In addition, the inventors of this case also referred to the aforementioned embodiments and conducted experiments with other raw materials, process operations, and process conditions described in this specification, and obtained relatively ideal results.

[0130] It should be understood that the technical solution of the present invention is not limited to the above-mentioned specific implementation cases. Any technical deformation made according to the technical solution of the present invention without departing from the scope of protection of the purpose of the present invention and the claims shall fall within the protection scope of the present invention.

Claims

1. A method for determining the urea content in dairy products based on magnetoelectric coupling field, characterized in that: include: A standard curve method is adopted, a series of urea standard solutions of different concentrations are mixed with diacetyl monoxime solution and antipyrine sulfuric acid solution respectively and reacted in a magnetoelectric coupling field, and then the absorbance values ​​of a series of obtained urea standard solutions to be tested at 460 nm are detected, so as to establish a standard curve of urea concentration Y and absorbance value A, wherein Y=105.2A+C, and C is -8.5~25; the magnetoelectric coupling field includes a high-frequency oscillating electric field and a static magnetic field; Also, the dairy product to be tested is pretreated to obtain a supernatant, which is then mixed with a diacetyl monoxime solution and an antipyrine sulfuric acid solution and reacted in a magnetoelectric coupling field, and then the absorbance value of the obtained dairy product solution to be tested at 460 nm is detected and compared with the standard curve, thereby achieving quantitative detection of urea in the dairy product to be tested.

2. The method according to claim 1, characterized in that: The electric field frequency of the high-frequency oscillating electric field is 100-150 kHz, the electric field strength is 3-8 V / cm, and the power is 2-5 W; the magnetic field strength of the static magnetic field is 5-10 mT.

3. The method according to claim 1, characterized in that: The reaction end point temperature in the magnetoelectric coupling field is 85-95° C., and the residence time is 3-5 min.

4. The method according to claim 1, characterized in that Specifically include: Using the standard curve method, a series of urea standard solutions with different concentrations are mixed with diacetyl monoxime solution and antipyrine sulfuric acid solution respectively and reacted in a magnetoelectric coupling field to obtain a series of mixed standard solutions to be tested; And, using distilled water as a reference, an ultraviolet spectrophotometer was used to detect the absorbance values ​​of a series of 3 mL of the mixed standard solution to be tested at 460 nm, so as to establish a standard curve of urea concentration Y and absorbance value A.

5. The method according to claim 4, characterized in that: The concentration of the urea standard solution is 0-100.0 mg / L; and / or, the concentration of the diacetyl monoxime solution is 1.5-2.5 g / mL; and / or, the concentration of antipyrine in the antipyrine sulfuric acid solution is 1.5-2.5 g / mL, and the concentration of sulfuric acid is 60 wt%-70 wt%; And / or, the volume ratio of the diacetyl monoxime solution to the urea standard solution is 1:1-10:1; and / or, the volume ratio of the antipyrine sulfuric acid solution to the urea standard solution is 1:1-20:

1.

6. The method according to claim 1, characterized in that Specifically include: Firstly, the dairy product to be tested is diluted, and then the diluted sample to be tested is treated by at least salting-out method or isoelectric precipitation method, and then centrifuged to obtain a supernatant; The supernatant is mixed with a diacetyl monoxime solution and an antipyrine sulfuric acid solution and reacted in a magnetoelectric coupling field to obtain a mixed sample solution to be tested; And, using distilled water as a reference, an ultraviolet spectrophotometer is used to detect the absorbance value of 3 mL of the mixed sample solution to be tested at 460 nm, and compared with the standard curve, thereby achieving quantitative detection of urea in the sample to be tested.

7. The method according to claim 6, characterized in that: The dilution multiple of the dairy product to be tested is 5 to 10 times; and / or, the concentration of the diacetyl monoxime solution is 1.5-2.5 g / mL; and / or, the concentration of antipyrine in the antipyrine sulfuric acid solution is 1.5-2.5 g / mL, and the concentration of sulfuric acid is 60 wt%-70 wt%.

8. The method according to claim 6, characterized in that: The volume ratio of the diacetyl monoxime solution to the supernatant is 1:1 to 10:1; and / or the volume ratio of the antipyrine sulfuric acid solution to the supernatant is 1:1 to 20:

1.

9. The method according to claim 1, characterized in that: The detection range of the method for determining the urea content in dairy products is 200.0~450.0 mg / L.

10. The method according to claim 1, characterized in that: The dairy product to be tested includes any one of fresh milk, pure milk, formulated milk, and nutritionally fortified milk.

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