Proteome Mapping of Human Skim Milk Proteins in Term and Preterm Milk

The abundant proteins in human milk have been well characterized
and are known to provide nutritional, protective, and developmental
advantages to both term and preterm infants. However, relatively little
is known about the expression of the low abundance proteins that are
present in human milk because of the technical difficulties associated
with their detection. We used a combination of electrophoretic techniques,
ProteoMiner treatment, and two-dimensional liquid chromatography to
examine the proteome of human skim milk expressed between 7 and 28
days postpartum by healthy term mothers and identified 415 in a pooled
milk sample. Of these, 261 were found in human skim milk for the first
time, greatly expanding our understanding of the human skim milk proteome.
The majority of the proteins identified were involved in either the
immune response (24%) or in cellular (28%) or protein (16%) metabolism.
We also used iTRAQ analysis to examine the effects of premature delivery
on milk protein composition. Differences in protein expression between
pooled milk from mothers delivering at term (38–41 weeks gestation)
and preterm (28–32 weeks gestation) were investigated, with
55 proteins found to be differentially expressed with at least 90%
confidence. Twenty-eight proteins were present at higher levels in
preterm milk, and 27 were present at higher levels in term milk.