To study the milk proteome, milk is usually separated into three
protein fractions: caseins, serum, and milk fat globule membrane
(MFGM) [5,6]. As a start, the whole milk is separated in cream
and skim milk. The cream contains the milk fat, which is present in
globules. These globules consist of a triglyceride core surrounded
by the MFGM, derived from the apical membrane of the milkproducing
epithelial cells [7]. The protein component of the
MFGM (about 1–4% of total milk protein) can be isolated from
the cream. The skim milk can be centrifuged to obtain a casein
pellet and a supernatant containing the serum proteins. The
MFGM and serum protein fractions, which contain the low abundance
proteins from milk, can then be used for proteomic
analyses.