The Research Of Detection Methods For The True Protein And Urea With Ammonium Nitrogen In Milk

The requirement amounts for diary product are increasing, but there is an obvious lack of the raw milk which the origin for it. In this case, some badmen mix external substances into it for the interest of themselves. The phenomenon fastens on milk protein, and its reasons contain lack of determination methods for it and localization of detection methods for adulteration.In the face of above-mentioned complexion, we research the detection methods and systems for milk true protein (TP) and urea nitrogen together with ammonium nitrogen separately. The TP's determination employ the Micro-Lowry method that set up by experimentation, and for urea nitrogen with ammonium nitrogen are used Urease-Berthelot method. In the study, we researched the major issues relating to each reaction system that was in the process of establishing, and evaluate the systems based on methodology.The result showed that two reaction systems are accuracy, efficiency and sensitive, not only detect the total amount of TP and urea nitrogen with ammonium nitrogen, but distinguish urea nitrogen from ammonium nitrogen. The principal characteristics of every system are following.In the auto-analyze system, the Micro-Lowry reaction's result is accurate, and no marked difference with Kjeldahl method (when no inorganic nitrogen and organic nonprotein nitrogen substances in sample). The linear is well when the protein concentration in the range of 10～100μg/mL in reaction solution, and it's least detection limit is 5μg. The sample can direct determination by dilution 500 times. The milk protein can accurate quantitation while its concentration in the range of 0.5～ 5.0g/100g. The method's reproducibility is well between distinct sample and assay time. Sodium azide, sodium bicarbonate, sodium sulphate, urea, ammonium sulphate, hydroxylamine hydrochloride, thiourea, nitrite, sucrose and sodium chloride in milk don't influence result. Potassium dichromate increase reaction result in the concentration above 10mg/mL.The recovery rate are high (>96%) and data are exact, when the Urease-Berthelot method used for determination outside urea nitrogen and ammonium nitrogen in milk. The linear is well when the nitrogen concentration in the range of 1～40μg N in reaction solution, and it's least detection limit is 0.09μg N. The urea nitrogen and ammonium nitrogen in milk can can accurate quantitation while its concentration in the range of 0.5～400mg/100g (correspond with urea 1.073mg/100g～0.858g/100g or ammonium sulfate 2.36mg/100g～1.888g/100g, equivalent to nitrogen concentration in protein quantity 3.125 mg/100g～2.5g/100g), because of sample dilution to 1～50 time after by urease hydrolysis. The reproducibility is well among different sample, assay time and operator. Sodium azide, sodium bicarbonate, sodium sulphate, sucrose, glucose and sodium chloride in milk don't influence result. Potassium dichromate (>10mg/mL), hydrogen peroxide (>0.6%), copper sulfate (>10mg/mL),hydroxylamine hydrochloride (>10mg/mL), thiourea(>50mg/mL) and nitrite(>10mg/mL) decrease reaction result in the above concentration.