Four minor protein components were detected in whey from Romagnola
cows' milk by polyacrylamide gel isoelectric focusing and two dimensional
gel
electrophoresis. Individual protein spots were transferred by electroblotting
on to a
polyvinylidene difluoride membrane and isolated by cutting out the relevant
area.
After in situ trypsinolysis, a portion of the digest was analysed
directly by
matrix-assisted laser desorption ionization–time of flight mass spectrometry.
The mass
profile allowed us to establish a correlation between β-lactoglobulins
A and B and the
four minor whey protein components. They were identified as C-terminally
truncated
β-lactoglobulin A and B variants with missing N-terminal peptides,
beyond residues
in the range 100–123 and 136–147 respectively. Two of the minor
components were
related to β-lactoglobulin A and two to β-lactoglobulin B.