Escola Politécnica de Saúde Joaquim Venâncio, Fundação Oswaldo Cruz, Av. Brasil, 4365, Manguinhos, CEP 21040-900, Rio de Janeiro, RJ, Brazil.
Food Chem. 2013 Dec 15;141(4):3649-55. doi: 10.1016/j.foodchem.2013.06.046. Epub 2013 Jun 20.
The Kjeldahl method and four classic spectrophotometric methods (Biuret, Lowry, Bradford and Markwell) were applied to evaluate the protein content of samples of UHT whole milk deliberately adulterated with melamine, ammonium sulphate or urea, which can be used to defraud milk protein and whey contents. Compared with the Kjeldahl method, the response of the spectrophotometric methods was unaffected by the addition of the nitrogen compounds to milk or whey. The methods of Bradford and Markwell were most robust and did not exhibit interference subject to composition. However, the simultaneous interpretation of results obtained using these methods with those obtained using the Kjeldahl method indicated the addition of nitrogen-rich compounds to milk and/or whey. Therefore, this work suggests a combination of results of Kjeldahl and spectrophotometric methods should be used to screen for milk adulteration by these compounds.
凯氏定氮法和四种经典的分光光度法（双缩脲法、Lowry 法、Bradford 法和 Markwell 法）被应用于评估超高温全脂牛奶样品中的蛋白质含量，这些样品被故意掺入三聚氰胺、硫酸铵或尿素等物质，以欺诈牛奶蛋白和乳清含量。与凯氏定氮法相比，分光光度法的响应不受向牛奶或乳清中添加氮化合物的影响。Bradford 法和 Markwell 法最为稳健，不受成分干扰。然而，同时解释使用这些方法和凯氏定氮法获得的结果表明，向牛奶和/或乳清中添加了富含氮的化合物。因此，这项工作建议使用凯氏定氮法和分光光度法的结果组合来筛选这些化合物对牛奶的掺假。
