Determination of molecular weights of caprine milk proteins by matrix-assisted laser desorption/ionization mass spectrometry

Molecular weights (MW) of major proteins in milk of 3 Korean dairy goat breeds were determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, after treatment of milk samples with the reduction buffer used in capillary electrophoresis. The MW of caprine milk proteins were compared with those of Holstein milk counterparts using commercial bovine milk protein standards. The MW of alpha-lactalbumin, beta-lactoglobulin, and alpha- and beta-casein standards were 14,197 +/- 3.4, 18,326 +/- 26.3, 23,591 +/- 13.0, and 23,967 +/- 12.8 m/z, respectively, whereas those of Holstein milk treated with the reduction buffer were 14,199 +/- 8.3, 18,397 +/- 25.9, 23,614 +/- 64.8, and 23,984 +/- 75.6 m/z, respectively. The respective MW of a-lactalbumin in Saanen, Toggenberg, and Alpine milk were 14,194 +/- 27.2, 14,266 +/- 105.9, and 14,241 +/- 13.2 m/z, which were not different from those of the bovine milk. The respective MW of beta- lactoglobulin in corresponding caprine milk were 18,840 +/- 31.5, 18,856 +/- 26.3, and 18,857 +/- 21.3 m/z, which were higher than those in the bovine milk. The MW of beta-casein in corresponding caprine milk were 23,860 +/- 27.2, 23,886 +/- 12.3, and 23,901 +/- 8.4 m/z, which were lower than those in the bovine milk. The results indicated that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry could be used for rapid determination of MW of Korean caprine milk proteins without protein separation steps.