Is it possible to screen for milk or whey protein adulteration with melamine, urea and ammonium sulphate, combining Kjeldahl and classical spectrophotometric methods?

• Published in: Food chemistry Vol. 141; no. 4; pp. 3649 - 3655
• Main Authors: Finete, Virgínia de Lourdes Mendes, Gouvêa, Marcos Martins, Marques, Flávia Ferreira de Carvalho, Netto, Annibal Duarte Pereira
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.12.2013; Elsevier
• Subjects: adulterated products; Ammonium Sulfate; Ammonium Sulfate - analysis; Ammonium sulphate; analysis; Animals; Biological and medical sciences; Cattle; chemistry; Chemistry Techniques, Analytical; Chemistry Techniques, Analytical - methods; Food Contamination; Food Contamination - analysis; Food toxicology; Kjeldahl method; Medical sciences; Melamine; methods; Milk; Milk - chemistry; Milk adulteration; Milk protein; Milk Proteins; Milk Proteins - analysis; protein content; Protein determination; sampling; screening; Spectrophotometry; Spectrophotometry - methods; Toxicology; Triazines; Triazines - analysis; UHT milk; Urea; Urea - analysis; urea ammonium sulfate; whey; whey protein; Whey Proteins; whole milk; Urea; Milk protein; Milk adulteration; Protein determination; Ammonium sulphate; Melamine; Assay; Ammonium; Ureas; Adulteration; Quantitative analysis; Milk
• ISSN: 0308-8146; 1873-7072; 1873-7072
• DOI: 10.1016/j.foodchem.2013.06.046

•Milk adulteration by nitrogen-rich compounds is an important issue.•Standard (Kjeldahl) methods fail to identify adulteration by nitrogen compounds.•Classical spectrophotometric methods for protein are not sensitive to these compounds.•A combination of methods is able to recognize nitrogen addition to milk.•These methods can be used in combination to screen for milk adulteration. 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.