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Milk protein is an important indicator of milk detection. As one of the material basis of life, proteins play a crucial role in catalyzing various reactions in the body of life, regulating metabolism, resisting invasion of foreign substances, and controlling genetic information. At present, the milk protein determination method is mainly the national standard Kjeldahl method, which is the most common method for determining the nitrogen content of organic compounds. It is a classical method for protein determination, ie, it is measured using a protein analyzer. Protein analyzer for a wide range of samples, accurate measurement results, good reproducibility, but the reagent consumption, long detection time, digestion of about 6 ~ 8 h, and after digestion of the sample to be constant volume, constant volume flask is not shaken, Crystallization is prone to take time and effort.
In order to improve the national standard detection method, the sample weight is large, the digestion time is long, the sample after digestion needs to be constant, and the operation steps are numerous. This paper optimizes the sample weight of the sample. The classical Kjeldahl method is called the liquid sample. The sample amount is 1 to 25 mL, because the uniformity of the milk sample is better, so this method optimizes the sample weight of the sample to 1.0 to 1.5 g. The sample weight of the sample was reduced from 10 g to 1.5 g, and other test conditions were unchanged. If the sampling is representative, changing the sample weight will have little effect on the test results.
Sample digestion time mainly includes oxidation time and boiling time. During the oxidation time, concentrated sulfuric acid converts the carbon in the organic sample to CO2 (in which case the solution is black), hydrogen is converted to H2O, and nitrogen is converted to ammonium. After the oxidation was completed, the solution became clear and entered the boiling time. After 30 minutes of boiling, all nitrogen in the sample was converted to ammonia, and the recovery of nitrogen was highest. After the sample is digested, 5-6 mL of concentrated sulfuric acid should remain in the digestive tube. If the sulfuric acid is consumed during digestion, nitrogen loss will result. During the digestion period, if the amount of sulfuric acid is small, the sample will crystallize. Therefore, the amount of sulfuric acid should be appropriate, and the amount of sulfuric acid depends on the amount of sample. The optimization of the amount of sulfuric acid in this method refers to the national standard method, the national standard method 10 g sample concentrated sulfuric acid The amount of 20 mL, that is 1 g of sulfuric acid consumption of the sample was 2 mL, the sample weight is now reduced to 1 ~ 1.5 g, sulfuric acid consumption should not exceed 3 mL, in order to ensure that the sample is concentrated after digestion The amount of sulfuric acid remains, so the amount of sulfuric acid is optimized to 8.5 mL.
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