Method for measuring content of protein in protein polyacrylonitrile fiber
Through the combination of elemental analysis method and amino acid analysis method, the protein content in protein polyacrylonitrile fibers is accurately measured, which solves the problem of measurement deviation caused by insufficient hydrolysis and modified proteins in traditional methods, and achieves a highly accurate protein content determination.
Patent Information
- Application Number
- CN202510224227.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-27
- Publication Date
- 2025-04-25
AI Technical Summary
It is difficult to accurately determine the protein content in protein polyacrylonitrile fibers in the prior art. Traditional methods have problems with insufficient sample hydrolysis and deviation in the determination results caused by modified proteins.
The nitrogen content of protein, polyacrylonitrile fiber and protein polyacrylonitrile fiber were determined by elemental analysis method, and the protein content was calculated by amino acid analysis method to avoid the determination deviation caused by insufficient hydrolysis and modified protein.
The accurate determination of protein content in protein polyacrylonitrile fibers is achieved, the reliability and accuracy of the measurement results are improved, and the deviation problem in traditional methods is solved.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of polymer composite materials and fiber materials, and in particular to a method for determining the protein content in protein polyacrylonitrile fibers. Background Art
[0002] Protein polyacrylonitrile fiber is made by directly mixing various proteins such as milk protein, collagen, corn protein, rice protein with polyacrylonitrile fiber for grafting reaction, or by modifying these proteins and mixing them with polyacrylonitrile to make spinning solution, and then processing them by wet spinning process. Taking collagen as an example, it has a triple helix structure with active hydroxyl, amino and carboxyl groups on the surface, and exhibits good moisture absorption and vapor permeability when used in fibers. Because it contains a large amount of animal protein amino acids, collagen polyacrylonitrile fiber not only has good skin affinity, but also effectively improves the antistatic property of polyacrylonitrile fiber, while also preserving the strength, warmth retention and resilience of polyacrylonitrile fiber. Protein polyacrylonitrile fiber products are currently a hot research topic, and market demand is increasing rapidly.
[0003] In the process of protein and polyacrylonitrile wet spinning, protein will be lost to a certain extent because it needs to go through the dissolution bath, coagulation bath, high temperature heating, washing and other treatment processes. How to accurately determine the protein content in protein polyacrylonitrile fiber has always been a bottleneck problem that troubles R&D personnel, and there is no publicly reported solution. The textile industry standard "FZ / T50018-2013 Test Method for Protein Content of Protein Viscose Fiber" Method A directly uses the Kjeldahl nitrogen determination method, using sulfuric acid to digest the sample to convert the nitrogen in the protein into ammonium salt, and then distilling it. The total nitrogen content is determined by titration, and then multiplied by the protein coefficient to calculate the protein content. Although the Kjeldahl nitrogen determination method can determine the nitrogen content in protein polyacrylonitrile fiber, it is found in actual application that the protein polyacrylonitrile fiber is not completely digested in sulfuric acid, resulting in a low nitrogen content determination. In addition, the textile industry standard "FZ / T 52021-2012 Milk Protein Modified Polyacrylonitrile Short Fiber" stipulates the total amino acid content in this type of fiber, and the determination method of the total amino acid content is implemented in accordance with the provisions of the national standard GB / T 5009.124. However, in actual application, it was found that due to the chemical bonding between collagen and polyacrylonitrile molecules after modification or the coating of collagen by polyacrylonitrile molecules, protein polyacrylonitrile fibers are difficult to be completely hydrolyzed by hydrochloric acid (6 mol / L) at the specified temperature and time in the standard method (GB / T 5009.124), which ultimately leads to inaccurate measured protein content and large errors.
[0004] Elemental analysis is an analytical method used to determine the type and content of elements in a substance to be tested. This method has been widely used in the fields of chemistry, materials science, environmental monitoring and food testing. The principle of elemental analysis is as follows: Under high temperature conditions, the sample to be tested undergoes oxidation combustion and reduction reactions under the combined action of oxygen and a composite catalyst, and each component in the sample to be tested is converted into gaseous substances (such as CO2, H2O, N2 and SO2). These gaseous substances enter the separation and detection unit under the promotion of the carrier gas; the separation and detection unit is based on the principle of chromatography, and uses a gas chromatography column to load gaseous substances such as CO2, H2O, N2, SO2 into the chromatographic column. Since different components flow out of the chromatographic column at different times (i.e., different retention times), each component will be separated in the order of N, C, H, and S; the separated single-component gas is analyzed and measured by a thermal conductivity detector. Since the thermal conductivity coefficients of different components of gas in the thermal conductivity detector are different, the instrument produces different readings for different components, and the purpose of quantitative analysis is achieved by comparing with the standard sample (detection limit 0.0016mg).
[0005] In summary, the elemental analysis method has many advantages such as high sensitivity, accurate and reliable results, good selectivity, wide application range and simple operation. It makes up for the shortcomings and deficiencies of the above-mentioned current determination methods and is expected to solve the problem of the inability to accurately determine the protein content in protein polyacrylonitrile fibers. Summary of the invention
[0006] The main purpose of the present invention is to solve the above problems existing in the prior art, and to provide a new method for determining the protein content in protein polyacrylonitrile fiber. The method uses elemental analysis to respectively determine the protein, polyacrylonitrile fiber and the nitrogen content of protein polyacrylonitrile fiber, and then the protein content of protein polyacrylonitrile fiber can be conveniently and quickly calculated according to the formula. The method has many advantages such as simple method, easy implementation, accurate and reliable results, etc. To achieve the above purpose, the technical scheme adopted by the present invention is as follows:
[0007] A method for determining the protein content in protein polyacrylonitrile fiber comprises: using elemental analysis to respectively determine the content of protein, polyacrylonitrile fiber, and nitrogen in the protein polyacrylonitrile fiber, wherein the protein and polyacrylonitrile fiber are two raw materials for preparing the protein polyacrylonitrile fiber; and calculating the protein content of the protein polyacrylonitrile fiber using the determined nitrogen content.
[0008] Furthermore, the protein includes plant protein extracted from plants, casein extracted from milk, collagen extracted from animal bones or skins, and modified proteins obtained by modifying the aforementioned proteins.
[0009] Furthermore, the protein is divided into two categories, one is modified protein introduced with a nitrogen-containing modifier through modification, recorded as nitrogen-modified protein; the other is other proteins except nitrogen-modified protein, including unmodified protein and other element modified protein, recorded as non-nitrogen-modified protein.
[0010] Furthermore, the specific process of the elemental analysis method is as follows: first, the elemental analyzer is calibrated, then the sample to be tested is dried to constant weight, and then the dried sample to be tested is added to the elemental analyzer to determine its nitrogen content.
[0011] Furthermore, the carrier gases used in the elemental analysis method are high-purity helium and high-purity oxygen, and the flow ratio between the two is 6-8:1; the combustion tube temperature of the elemental analyzer is 1000-1200°C, the reduction tube temperature is 800-900°C, and the oxygen passing time is 80-100s.
[0012] Furthermore, for the protein polyacrylonitrile fiber made from non-nitrogen modified protein as raw material, the nitrogen content N2 of the non-nitrogen modified protein, the nitrogen content N0 of the polyacrylonitrile fiber, and the nitrogen content N3 of the protein polyacrylonitrile fiber were measured by elemental analysis, and the protein content A1 in the protein polyacrylonitrile fiber was calculated according to the following formula:
[0013]
[0014] Among them, 6.25 is the coefficient of nitrogen content converted to protein.
[0015] Furthermore, for the protein polyacrylonitrile fiber made from nitrogen-modified protein as raw material, the nitrogen content N2 of the nitrogen-modified protein, the nitrogen content N0 of the polyacrylonitrile fiber, and the nitrogen content N3 of the protein polyacrylonitrile fiber are first measured by elemental analysis, and then the total amount of various amino acids in the nitrogen-modified protein is determined by amino acid analysis and calculated as the protein content P of the nitrogen-modified protein. Finally, the protein content A2 of the protein polyacrylonitrile fiber is calculated according to the following formula:
[0016]
[0017] Furthermore, the specific process of the amino acid analysis method is as follows: under a protective atmosphere, the nitrogen-modified protein and the hydrochloric acid solution are evenly mixed and then heated for hydrolysis. After the hydrolysis, the mixture is cooled, filtered, and washed. The filtrate and the washing liquid are combined and repeatedly concentrated and dried. The obtained solid is dissolved with an acidic buffer solution and the amino acid content thereof is determined using an amino acid analyzer.
[0018] Furthermore, the protective atmosphere is specifically nitrogen. After the nitrogen-modified protein is mixed with the hydrochloric acid solution, it is first evacuated and then filled with nitrogen. The evacuation and nitrogen filling are repeated multiple times to obtain a nitrogen atmosphere. The hydrolysis temperature of the mixture is 100-120°C, the concentration and drying method is specifically heating and reduced pressure drying, and the acidic buffer is specifically a sodium citrate buffer solution.
[0019] Furthermore, the amino acids whose contents need to be measured include at least aspartic acid, threonine, serine, glutamic acid, glycine, alanine, cystine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, histidine, lysine, arginine, and proline. For collagen, the content of hydroxyproline also needs to be measured.
[0020] The new method provided by the present invention does not require hydrolysis of the protein polyacrylonitrile fiber during the determination process, which completely solves the problem of low determination results caused by insufficient and incomplete sample hydrolysis in traditional determination methods. In addition, the new method uses elemental analysis combined with amino acid analysis to further eliminate the problem of high determination results caused by nitrogen-containing compound-modified proteins.
[0021] Compared with the existing determination methods, the method of the present invention has the following advantages:
[0022] (1) Creatively introduce elemental analysis into the determination of protein content of protein polyacrylonitrile fiber, which completely solves the problem of inaccurate results caused by insufficient dissolution of protein polyacrylonitrile fiber in traditional amino acid analysis or Kjeldahl nitrogen determination method. Practice shows that the results measured by the method of the present invention are more accurate and reliable;
[0023] (2) In order to solve the problem that the introduction of nitrogen in the protein modification process in the new determination method leads to high results, the present invention combines elemental analysis with traditional amino acid analysis to ensure the accuracy and reliability of the determination results;
[0024] (3) The determination method of the present invention also has the advantages of simple operation, easy implementation, wide application range, accurate and reliable results, etc. It can be used for large-scale testing and quickly obtain results, which not only improves the test efficiency but also reduces the test cost. DETAILED DESCRIPTION
[0025] In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, the following is a further detailed description in conjunction with specific embodiments.
[0026] It should be emphasized that these embodiments are only preferred implementations of the present invention and do not constitute any limitation to the present invention. Any simple improvements made without departing from the spirit of the present invention should fall within the protection scope of the present invention.
[0027] The present invention uses elemental analysis to respectively determine the nitrogen content of two raw materials (protein and polyacrylonitrile fiber) required for preparing protein polyacrylonitrile fiber and the protein polyacrylonitrile fiber itself, and then calculates the protein content of the protein polyacrylonitrile fiber based on the nitrogen content of the protein polyacrylonitrile fiber. The specific process is as follows:
[0028] Step a: The proteins used to prepare protein polyacrylonitrile fiber include plant protein extracted from plants, casein extracted from milk, collagen extracted from animal bones or skin, and modified proteins obtained by modifying the above proteins. If a nitrogen-containing modifier is used, it is called nitrogen-modified protein, and the remaining modified proteins and unmodified proteins are collectively referred to as non-nitrogen-modified proteins. The nitrogen content determination methods of these two types of proteins are different, as follows:
[0029] For non-nitrogen modified proteins, the nitrogen content N2 is directly determined by elemental analysis. First, weigh 3-7 groups of sulfonamide standard samples weighing 2-5 mg, and use them to calibrate the elemental analyzer. Then weigh 2-5 groups of non-nitrogen modified protein samples weighing 2-5 mg (dried to constant weight in advance), and use the calibrated elemental analyzer to determine the nitrogen content of these parallel samples. The test conditions are: high-purity helium flow rate 200-300mL / min, high-purity oxygen flow rate 30-50mL / min, combustion tube temperature 1000-1200℃, reduction tube temperature 800-900℃, oxygen passage time 80-120s.
[0030] For nitrogen-modified protein, firstly, the nitrogen content N2 is determined by elemental analysis according to the above method, and then the amino acid content is determined by amino acid analysis, and then the total amount of each type of amino acid is calculated as the protein content P of nitrogen-modified protein. In this process, the process of determining the amino acid content of nitrogen-modified protein by amino acid analysis is as follows: the hydrochloric acid solution is mixed with the nitrogen-modified protein and heated to hydrolyze it, and then the different types of amino acids are separated by the ion exchange chromatograph in the amino acid analyzer, and further the color reaction of ninhydrin and amino acid is performed, and the absorbance of the sample at 570nm and 440nm is detected by a visible light detector to determine the amino acid content in the hydrolyzate. For collagen, the content of hydroxyproline needs to be additionally determined.
[0031] Step b: Referring to the method for determining the nitrogen content of non-nitrogen modified protein, the nitrogen content (N0) of the raw material polyacrylonitrile is determined by elemental analysis.
[0032] Step c: Referring to the method for determining the nitrogen content of non-nitrogen modified protein, the nitrogen content (N3) of the protein polyacrylonitrile fiber is determined by elemental analysis.
[0033] Step d: Calculate the protein content A1 of the protein polyacrylonitrile fiber made from non-nitrogen modified protein according to the above formula, and calculate the protein content A2 of the protein polyacrylonitrile fiber made from nitrogen modified protein according to the above another formula.
[0034] Example 1
[0035] The protein polyacrylonitrile fiber prepared by wet mixing of sheepskin collagen (powdered solid) and polyacrylonitrile was used as the test object, wherein the sheepskin collagen raw material was not modified.
[0036] First, 6 groups of 3.0 mg sulfonamide standard samples were weighed to calibrate the elemental analyzer. Three samples to be tested, including sheepskin collagen (powdered solid), polyacrylonitrile, and protein polyacrylonitrile fiber, were dried to constant weight in advance, and then 4.0 mg of each sample to be tested were weighed for nitrogen element analysis, with 3 parallel samples set up in each group. The test conditions were: high-purity helium flow rate of 250 mL / min, high-purity oxygen flow rate of 36 mL / min, combustion tube temperature of 1150°C, reduction tube temperature of 850°C, and oxygen passing time of 90 s.
[0037] The test results are as follows: the nitrogen content N2 of sheepskin collagen (powdered solid) is 14.09%, the nitrogen content N0 of polyacrylonitrile is 23.71%, the nitrogen content N3 of protein polyacrylonitrile fiber is 23.25%, and the protein content A1 of the protein polyacrylonitrile fiber is 4.21% calculated according to the formula.
[0038] Example 2
[0039] The protein polyacrylonitrile fiber prepared by wet mixing of isocyanate-modified bovine collagen (powdered solid) and polyacrylonitrile was used as the test object.
[0040] First, referring to the method in Example 1, the nitrogen content of isocyanate-modified sheepskin collagen (powdered solid), polyacrylonitrile, and protein polyacrylonitrile fiber was measured respectively. Among them, the nitrogen content N2 of modified cowhide collagen (powdered solid) was 16.48%, the nitrogen content N0 of polyacrylonitrile was 23.71%, and the nitrogen content N3 of protein polyacrylonitrile fiber was 22.66%.
[0041] Then, the amino acid content of the isocyanate-modified bovine collagen (powdered solid) was determined according to the following amino acid analysis method and calculated as the total protein content P:
[0042] Accurately weigh 0.01795g of isocyanate-modified cowhide collagen sample and put it into a hydrolysis tube. Add 10mL of 6mol / L hydrochloric acid to the hydrolysis tube, and then add 3 drops of phenol. Freeze the hydrolysis tube for 5 minutes and connect it to the vacuum pump's exhaust pipe. First evacuate (close to 0Pa) and then fill it with nitrogen. Repeat the evacuation-nitrogen filling at least 3 times, and finally seal the hydrolysis tube under nitrogen filling. Transfer the sealed hydrolysis tube to an electric blast thermostat or hydrolysis furnace, hydrolyze at 110℃±1℃ for 22h, take out the hydrolysis tube and cool it, filter the filtrate and let it flow into a 50mL volumetric flask, rinse the filter residue with a small amount of water, and the water washing liquid also flows into the volumetric flask.
[0043] The volumetric flask was made up to the mark with water and then shaken to mix well. 1.0 mL of the solution was taken and transferred to a 15 mL test tube. The solution in the test tube was dried under reduced pressure using a test tube concentrator or a parallel evaporator at 50°C. The dried residue was dissolved in water and dried under reduced pressure again until it was evaporated to dryness. 2.0 mL of pH=2.2 sodium citrate buffer solution was added to the dried test tube to completely dissolve the solid residue. After shaking and mixing, the solution was taken to pass through a 0.22 μm filter membrane, and the filtrate was transferred to a sample injection bottle for determination of the content of 18 amino acids.
[0044] The same volume of amino acid standard working solution and the test solution obtained by membrane filtration were injected into the amino acid analyzer (wavelength 570nm and 440nm) respectively, and the concentrations of 17 amino acids in the test solution were calculated by peak area using the external standard method. The hydroxyproline content was determined according to the method in GB / T9695.23-2008. The test results of the amino acid content of isocyanate-modified bovine collagen are as follows:
[0045] Table 1 Amino acid content of isocyanate-modified cowhide collagen described in Example 2
[0046] Serial number Amino Acid Type Molecular formula Amino acid weight percentage (%) 1 Aspartic acid <![CDATA[C4H7NO4]]> 5.00 2 Threonine <![CDATA[C4H9NO3]]> 1.03 3 Serine <![CDATA[C3H7NO3]]> 2.18 4 Glutamate <![CDATA[C5H9NO4]]> 9.17 5 Glycine <![CDATA[C2H5NO2]]> 20.00 6 Alanine <![CDATA[C3H7NO2]]> 7.12 7 Cystine <![CDATA[C6H 12 N2O4S2]]> 0.53 8 Valine <![CDATA[C5H 11 NO2]]> 2.12 9 Methionine <![CDATA[C5H 11 O2NS]]> 0.18 10 Isoleucine <![CDATA[C6H 13 NO2]]> 0.94 11 Leucine <![CDATA[C6H 13 NO2]]> 2.05 12 Tyrosine <h2 style=";text-align:left;direction:ltr"><![CDATA[C9H <h2 style=";text-align:left;direction:ltr"> 11 <h2 style=";text-align:left;direction:ltr"> NO3]]><h2 style=";text-align:left;direction:ltr"> 0.28 13 Phenylalanine <![CDATA[C9H 11 NO2]]> 1.99 14 Histidine <![CDATA[C6H9N3O2]]> 0.27 15 Lysine <h2 style=";text-align:left;direction:ltr"><![CDATA[C6H <h2 style=";text-align:left;direction:ltr"> 14 <h2 style=";text-align:left;direction:ltr"> N2O2<h2 style=";text-align:left;direction:ltr"> 2.92 16 Arginine <![CDATA[C6H 14 N4O2]]> 7.84 17 Proline <![CDATA[C5H9NO2]]> 13.83 18 Hydroxyproline <![CDATA[C5H9NO3]]> 6.14 total 83.59
[0047] It can be seen from Table 1 that the protein content of the converted isocyanate-modified bovine collagen (powdered solid) is 83.59% (P value in formula A2). Combined with the above-measured nitrogen content results of N0, N2, and N3, the protein content A2 of the protein polyacrylonitrile fiber is calculated to be 12.14%.
[0048] Example 3
[0049] Protein polyacrylonitrile fibers prepared by wet mixing of zein (powdered solid) and polyacrylonitrile were used as test objects, wherein the zein raw material was not modified.
[0050] Referring to the method in Example 1, the nitrogen content of zein (powdered solid), polyacrylonitrile, and protein polyacrylonitrile fiber was measured respectively. The nitrogen content N2 of zein (powdered solid) was 14.83%, the nitrogen content N0 of polyacrylonitrile was 23.70%, and the nitrogen content N3 of protein polyacrylonitrile fiber was 23.18%. The protein content A1 of the protein polyacrylonitrile fiber was calculated to be 5.43% according to the formula.
[0051] Example 4
[0052] The protein polyacrylonitrile fiber prepared by wet mixing of rice protein (powdered solid) and polyacrylonitrile was used as the test object, wherein the rice protein raw material was not modified.
[0053] With reference to the method among the embodiment 1, the nitrogen content of rice protein (powdery solid), polyacrylonitrile, protein polyacrylonitrile fiber has been measured respectively.Wherein the nitrogen content N2 of rice protein (powdery solid) is 15.03%, the nitrogen content N0 of polyacrylonitrile is 23.70%, the nitrogen content N3 of protein polyacrylonitrile fiber is 23.11%, and the protein content A1 that obtains this protein polyacrylonitrile fiber according to formula calculation is 6.39%.
[0054] Comparative Example 1
[0055] The test object of Comparative Example 1 is the same as that of Example 1, which is protein polyacrylonitrile fiber prepared by wet mixing and spinning sheepskin collagen (powdered solid) and polyacrylonitrile. 0.4095g of the protein polyacrylonitrile fiber sample was weighed, and then the amino acid content of the sample was determined according to the amino acid analysis method in Example 2. The results are as follows:
[0056] Table 2 Amino acid content of the protein polyacrylonitrile fiber described in Comparative Example 1
[0057] Serial number Amino Acid Type Amino acid weight percentage (%) 1 Aspartic acid 0.205 2 Threonine 0.0461 3 Serine 0.0805 4 Glutamate 0.385 5 Glycine 0.716 6 Alanine 0.242 7 Cystine 0.0753 8 Valine 0.142 9 Methionine 0.0662 10 Isoleucine 0.0848 11 Leucine 0.111 12 Tyrosine 0.052 13 Phenylalanine 0.073 14 Histidine 0.0434 15 Lysine 0.156 16 Arginine 0.0861 17 Proline 0.0497 18 Hydroxyproline 0.5011 total 3.1152
[0058] Analysis shows that for the same protein polyacrylonitrile fiber sample, the protein content measured in Example 1 is 4.21%, while the protein content measured in Comparative Example 1 is 3.12%, which is significantly lower than that in Example 1. This is because the protein polyacrylonitrile fiber in Comparative Example 1 is not completely hydrolyzed, and the direct use of the amino acid analysis method results in a low measurement result. From the measurement principle, the method of Example 1 is more accurate and reliable.
[0059] Comparative Example 2
[0060] The test object of Comparative Example 2 is the same as that of Example 2, which is protein polyacrylonitrile fiber prepared by wet mixing spinning of isocyanate-modified cowhide collagen (powdered solid) and polyacrylonitrile. 0.1780 g of the protein polyacrylonitrile fiber sample was weighed, and then the amino acid content of the sample was determined according to the amino acid analysis method in Example 2. The results are as follows:
[0061] Table 3 Amino acid content of the protein polyacrylonitrile fiber described in Comparative Example 2
[0062]
[0063] For the same protein polyacrylonitrile fiber sample, the protein content (12.14%) measured in Example 2 is higher than the protein content (8.43%) measured in Comparative Example 2, mainly because the protein polyacrylonitrile fiber in Comparative Example 2 was not completely hydrolyzed, and the direct use of amino acid analysis affected the measurement results.
[0064] Comparative Example 3
[0065] The test objects of Comparative Example 3 are the same as those of Example 2, which are protein polyacrylonitrile fibers prepared by wet-mixing isocyanate-modified cowhide collagen (powdered solid) and polyacrylonitrile.
[0066] Referring to the method in Example 1, the nitrogen content of isocyanate-modified bovine collagen (powdered solid), polyacrylonitrile, and protein polyacrylonitrile fiber dried to constant weight was directly measured. The nitrogen content N2 of the modified bovine collagen (powdered solid) was 16.48%, the nitrogen content N0 of polyacrylonitrile was 23.71%, and the nitrogen content N3 of the protein polyacrylonitrile fiber was 22.66%.
[0067] The protein content A1 of the protein polyacrylonitrile fiber calculated according to the formula is 14.96%. This result is higher than the result (12.14%) measured in Example 2, mainly because the cowhide collagen introduces nitrogen-containing isocyanate during the modification process, and this part of nitrogen is also counted as protein, resulting in a higher result.
[0068] Comparative Example 4
[0069] The test objects of Comparative Example 4 are the same as those of Example 1, which are protein polyacrylonitrile fibers prepared by wet mixing of sheepskin collagen (powdered solid) and polyacrylonitrile. Referring to the FZ / T50018-2013 standard, the nitrogen content N2 of sheepskin collagen (powdered solid) was 14.05%, the nitrogen content N0 of polyacrylonitrile was 22.82%, and the nitrogen content N3 of protein polyacrylonitrile fiber was 22.22% by Kjeldahl nitrogen determination method.
[0070] The protein content of the protein polyacrylonitrile fiber calculated according to the formula is 6.01%. This result is higher than the result (4.21%) measured in Example 1, mainly because the nitrogen content test results of the polyacrylonitrile fiber and the protein polyacrylonitrile fiber are low due to incomplete hydrolysis, which makes the final result higher when calculating the protein content.
Claims
1. A method for determining the protein content in protein polyacrylonitrile fiber, characterized in that The method comprises: using elemental analysis method to respectively determine the nitrogen content of protein polyacrylonitrile fiber and its preparation raw material protein and polyacrylonitrile fiber, and calculating the protein content of the protein polyacrylonitrile fiber accordingly.
2. The method according to claim 1, characterized in that: The protein is divided into two categories: nitrogen-modified protein and non-nitrogen-modified protein, wherein the nitrogen-modified protein is specifically a modified protein into which a nitrogen-containing modifier is introduced through modification, and the non-nitrogen-modified protein is other proteins except nitrogen-modified protein, including unmodified protein and other element-modified protein.
3. The method according to claim 1, characterized in that: The protein includes plant protein extracted from plants or modified products thereof, casein extracted from milk sources or modified products thereof, collagen extracted from animal bones or skins or modified products thereof.
4. The method according to claim 1, characterized in that: The specific process of the elemental analysis method is as follows: first, the elemental analyzer is calibrated, then the sample to be tested is dried to constant weight, and then the dried sample to be tested is added to the elemental analyzer to determine its nitrogen content.
5. The method according to claim 4, characterized in that: The carrier gases used in the elemental analysis method are high-purity helium and high-purity oxygen, and the flow ratio between the two is 6-8:1; the combustion tube temperature of the elemental analyzer is 1000-1200°C, the reduction tube temperature is 800-900°C, and the oxygen passing time is 80-100s.
6. The method according to claim 2, characterized in that: For the protein polyacrylonitrile fiber made from non-nitrogen modified protein as raw material, the nitrogen content N2 of the non-nitrogen modified protein, the nitrogen content N0 of the polyacrylonitrile fiber, and the nitrogen content N3 of the protein polyacrylonitrile fiber were measured by elemental analysis, and the protein content A1 in the protein polyacrylonitrile fiber was calculated according to the following formula:
7. The method according to claim 2, characterized in that: For the protein polyacrylonitrile fiber made from nitrogen-modified protein as raw material, the nitrogen content N2 of the nitrogen-modified protein, the nitrogen content N0 of the polyacrylonitrile fiber, and the nitrogen content N3 of the protein polyacrylonitrile fiber were first measured by elemental analysis, and then the total amount of various amino acids in the nitrogen-modified protein was determined by amino acid analysis and calculated as the protein content P of the nitrogen-modified protein. Finally, the protein content A2 of the protein polyacrylonitrile fiber was calculated according to the following formula:
8. The method according to claim 7, characterized in that: The specific process of the amino acid analysis method is as follows: under a protective atmosphere, the nitrogen-modified protein and the hydrochloric acid solution are evenly mixed and then heated for hydrolysis. After the hydrolysis, the mixture is cooled, filtered, and washed. The filtrate and the washing liquid are combined and repeatedly concentrated and dried. The obtained solid is dissolved in an acidic buffer solution and its amino acid content is determined using an amino acid analyzer.
9. The method according to claim 8, characterized in that: The protective atmosphere is specifically nitrogen. After the nitrogen-modified protein is mixed with the hydrochloric acid solution, it is first evacuated and then filled with nitrogen. The evacuation and nitrogen filling are repeated multiple times to obtain a nitrogen atmosphere. The hydrolysis temperature of the mixture is 100-120°C, the concentration and drying method is specifically heating and reduced pressure drying, and the acidic buffer is specifically a sodium citrate buffer solution.
10. The method according to claim 7, characterized in that: The amino acids whose content needs to be measured include at least aspartic acid, threonine, serine, glutamic acid, glycine, alanine, cystine, valine, methionine, isoleucine, leucine, tyrosine, phenylalanine, histidine, lysine, arginine, proline, and for collagen, also hydroxyproline.