Influence of proteolysis of milk on the whey protein to total protein ratio as determined by capillary electrophoresis.

Capillary electrophoresis (CE) was used to determine the whey protein to total protein ratio in raw and UHT milk samples with different degrees of proteolysis caused by storage. In raw milks, the analysis of samples taken at regular times demonstrated the influence of proteolysis in the whey protein to total protein determination, which was overestimated after 4 d of storage. In UHT milks, the overestimation of the whey protein to total protein ratio took place after 30 or 60 d of storage. However, the ratios alphaS1-CN/beta-CN and alphas1-CN/kappa-CN permitted detection of the samples of raw or UHT milk with degraded proteins. The distorted capillary electrophoretic pattern obtained for UHT milks made necessary an integration of the electropherograms in a "valley-to-valley" way. Results for raw milk samples were identical when "valley-to-valley" was compared to standard integration techniques. This CE method could be considered an alternative method to derivative spectroscopy for the determination of the whey protein to total protein of milk and could be used to detect samples with proteolysis.