Improved method for the determination of furosine in food by capillary electrophoresis

A previously described method for determination of furosine by capillary zone electrophoresis in food has been improved for greater accuracy and sensitivity. Acid-hydrolyzed samples are subjected to solid phase extraction; then they are dried and redissolved before injection. The electrophoresis separation is performed in a fused silica capillary tube (50 microns inside diameter) with an extended-path-length detection cell using a 3-(N-morpholino)-2-hydroxypropanesulfonic acid solution at pH 7.0 as run buffer. The in-laboratory repeatability was within +/- 7.1% at the 95% confidence level when the amount of furosine ranged between 8 and 250 mg per 100 g protein. The values of both repeatability and sensitivity fulfill the requirements stated in the EU and Italian regulations for furosine determination in pasteurized milk and Mozzarella cheese. The data obtained on 48 different food samples including heat-treated milk, cheeses, and durum wheat products were comparable with those obtained by an HPLC method and proved to be accurate for furosine values up to at least 400 mg per 100 g protein. The furosine values found in cultured fresh cheese samples suggest that the use of this furosine index holds promise for the characterization of this type of cheese.