Field Anjalie, Field Jeffrey
Department of Pharmacology, and Center of Excellence in Environmental Toxicology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
Food Chem. 2010 Aug 1;121(3):912-917. doi: 10.1016/j.foodchem.2010.01.018.
In the fall of 2007 pet food contaminated with melamine and cyanuric acid caused kidney stones in thousands of animals. In the summer of 2008, a more serious outbreak of adulterated dairy food caused the deaths of six infants and sickened about 290,000 children in China. In all cases, melamine was likely added to inflate the apparent protein content of the foods. To determine if we could measure protein without interference from melamine and cyanuric acid we tested these compounds in the Bradford and Ninhydrin assays, two common dye-based assays for protein, as well as by ammonia release, the most common assay used in the food industry. Neither compound was detected in the Ninhydrin and Bradford assays at concentrations of >100 μg/ml. The ammonia assay detected melamine but was inconclusive with respect to cyanuric acid. To develop an accurate test for food that would not detect either chemical as a protein, assays were run on cat food and reconstituted milk powder. The Bradford assay readily measured the protein content of each food, and importantly, the addition of melamine or cyanuric acid to reconstituted milk did not affect the readings. The protein concentrations obtained for reconstituted milk powder were as expected, but those for the cat food were 10 to 30-fold lower, due to its low solubility. We conclude that dye-binding assays can be employed to detect protein in food without interference from melamine and cyanuric acid, thus reducing the incentive to use them as additives.
2007年秋季，受三聚氰胺和氰尿酸污染的宠物食品致使数千只动物患上肾结石。2008年夏季，一起更为严重的掺假乳制品事件导致中国6名婴儿死亡，约29万名儿童患病。在所有这些案例中，三聚氰胺很可能是被添加进去以虚增食品的表观蛋白质含量。为了确定我们能否在不受三聚氰胺和氰尿酸干扰的情况下测定蛋白质，我们在考马斯亮蓝法和茚三酮法这两种常见的基于染料的蛋白质测定方法中对这些化合物进行了测试，同时也通过氨释放法进行了测试，氨释放法是食品行业最常用的测定方法。在茚三酮法和考马斯亮蓝法中，当浓度>100μg/ml时均未检测到这两种化合物。氨测定法检测到了三聚氰胺，但对氰尿酸的检测结果尚无定论。为了开发一种不会将这两种化学物质误检测为蛋白质的食品精确检测方法，我们对猫粮和复原奶粉进行了测定。考马斯亮蓝法能够轻松测定每种食品中的蛋白质含量，重要的是，向复原奶中添加三聚氰胺或氰尿酸并不会影响读数。复原奶粉所测得的蛋白质浓度与预期相符，但猫粮的蛋白质浓度由于其低溶解度而低了10至30倍。我们得出结论，染料结合测定法可用于检测食品中的蛋白质而不受三聚氰胺和氰尿酸的干扰，从而减少将它们用作添加剂的动机。
