Detection of adulteration of pasteurised milk with whey by determination of the casein-bound phosphorus and protein nitrogen content.

A new method to detect the adulteration of pasteurised milk with whey is described. The method is based on the determination of casein-bound phosphorus (Pcas) and the protein nitrogen content in milk. By using a mean Pcas content (0.85 g P/100 g casein), a Kjeldahl factor of 6.34 and protein N, the relative casein-N content (casein N/protein N x 100) can be estimated. Over a period of one year the variation in the phosphorus factor of dried skimmed milk samples amounted to 2.9%. In order to calculate the percentage of added whey, a standard curve has been prepared in which the relative casein content is plotted against the corresponding whey percentage. The results of 26 analyses on genuine pasteurised milk (Pcas = 21.7 mg/100 ml; casein N/protein N = 80.9%) and on 25 whey samples were used for the standard curve. In laboratory-made blends of pasteurised milk and cheese whey (5%, 10%, 20% and 30%), the estimated percentage of whey varied between -1.2% and +2.9% from the actual value. The analysis of nine samples from the Brazilian market showed that four samples were clearly adulterated with cheese whey. Sweet and/or acid whey addition will be detected by the proposed method.

Variacoes no teor de acido urico do leite de vaca. / Variations in the uric acid content of cow's milk

O teor de acido urico em 273 amostras de leite da ordenha da tarde de animais individuais (racas Schwarzbund e Fleckvieh) foi determinado enzimaticamente durante um ano. Mediante o metodo dos quadrados minimos foi determinado que o efeito da raca e do numero da lactacao no teor de acido urico do leite teve significancia estatistica (p<0,05), enquanto que o efeito sazonal (mes do ano) foi altamente significativo (p<0,001). O leite produzido nas primeiras semanas do periodo de lactacao contem maior teor de acido urico que o leite secretado por animais em estado de lactacao media ou avancada, entretanto a analise da variancia nao mostrou diferenca significativa (p>0,05) para a influencia do estagio da lactacao no teor de acido urico do leite