Application of capillary electrophoresis to the characterization of processed cheeses

Capillary electrophoresis using a hydrophilically coated capillary and a low pH buffer containing urea has been used to characterize processed cheeses. Different electrophoretic patterns were obtained depending on the ingredients used in the blend such as acid casein, rennet casein, sodium and calcium caseinates and skim milk powder. Isoelectric casein, and sodium and calcium caseinates were shown to contain intact non-glycosylated kappa-casein (kappa-CN), while rennet casein contained only trace amounts of kappa-CN and mainly para-kappa-CN. Therefore, the addition of casein or caseinate to processed cheeses has been detected by analysing the intact non-glycosylated kappa-CN. Quantitation of intact non-glycosylated kappa-CN in processed cheeses of known and unknown composition was carried out using a regression curve from standard mixtures of 150-550 g isoelectric casein/kg total rennet casein. This capillary electrophoresis method successfully confirmed the addition of isoelectric casein or caseinate to processed cheeses of known composition. The quantitative determination range was 0.605-3.688 mg kappa-CN/ml. This method cannot be used for measuring additions of rennet casein or any caseinates that have been exposed to chymosin.