Donkeys’ milk protein fraction investigated by electrophoretic methods and mass spectrometric analysis

Donkeys’ milk has attracted a growing interest in human nutrition, particularly in the dietotherapy ofpatients affected by cows’ milk protein allergy. In this paper, donkeys’ milk protein fractions wereanalysed by isoelectric focusing (IEF) and sodium dodecyl sulphate polyacrylamide gel electrophoresis(SDS-PAGE). Four different IEF patterns were observed out of 51 individual milk samples. Thirty-sixsamples presented a common pattern, used as a reference, whereas 15 were characterized by thepresence or absence of protein bands. A single sample, lacking two bands of the casein fraction, showedan apparent reduced amount of caseins, by SDS-PAGE as well as by chromatographic analysis.Mass spectrometry and high-performance liquid chromatography were used to characterize the IEFpatterns. Compared with the reference, one pattern lacked two as1-casein bands, another lacked twob-lactoglobulin II bands and one accounted for a different b-lactoglobulin II variant. No signals related toputative as2- and k-casein were observed.