Comparison of three methods to determine the whey protein to total protein ratio in milk

Three methods for quantification of the ratio of whey protein in total protein [capillary electrophoresis (CE), sodium dodecyl sulfate capillary electrophoresis (SDS-CE), and UV fourth derivative absorption spectroscopy (UV-4th Der.)] were applied to raw (n = 21), pasteurized (n = 5) and UHT (n = 18) milk samples. All methods effectively measured the whey protein to total protein ratio independently of the heat treatment applied to the milk. Mean values obtained by CE, SDS-CE and UV-4th Der. were respectively, 17.1, 18.5, and 17.2% for raw milks, 16.6, 17.7, and 18.8% for pasteurized milks, and 16.8, 17.0, and 17.2% for UHT milks. (Key words: whey protein to total milk protein ratio, capillary electrophoresis, sodium dodecyl sulfate capillary electrophoresis, fourth derivative ultraviolet spectroscopy)