How does the current protein detect and add melamine and other substances to milk powder?

How does the current protein detect and add melamine and other substances to milk powder?

At present, there are three main measurement methods: Kjeldahl, Dumas, infrared.
The Kjeldahl method is now commonly used for protein detection in the food industry, measuring the total nitrogen content of a sample, and then calculating the protein content based on nitrogen content, which is the current standard method.
The Kjeldahl method was started in 1883. This method is not a very ideal detection method. However, it is still used because there is no alternative method to replace it. This method is time consuming and takes several hours to make a sample, and the chemical reagents used are also very dangerous and need to be heated to 400 degrees with sulfuric acid.
The Dumars method is considered to be a method of significant progress and has achieved some success. In essence, it burns the sample, measures the nitrogen released, and calculates the protein content. Because you are burning this sample, you have to deal with all the combustibles in this instrument. This can cause a preservation problem, and it cannot measure liquid samples and large sample volumes. The larger the sample size, the more problems will occur, which forces people to have to detect fewer samples than they want to detect in order to operate the instrument correctly.
Another method is the infrared method, which is a surface measurement method. However, the instruments of the infrared detection method need to be calibrated frequently, and the calibration requires a large number of calibration reagents. In addition, it requires a large amount of cleaning agents and is susceptible to other components of the sample. Therefore, when measuring protein, people only take it as The way to think about it. None of the above methods of measurement are direct methods for measuring true proteins. Both the Kjeldahl method and the Dumas method measure the total nitrogen content and, depending on the total nitrogen content, are converted to protein content by conversion. Practice has proven that it has caused many problems. Because nitrogen-containing compounds other than proteins are similarly digested during the Kjeldahl process, resulting in high protein values, we collectively refer to these compounds as non-protein nitrogen. Melamine is such a substance. The current method of detecting protein content does not identify these illegal additives. When you use these methods to measure adulterated foods, these methods cannot tell you that there is no protein, but the nitrogen content is very high.

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