Cereals contain lipids
that fulfill important physiological
roles
and are associated with stress in the plant. However, many of the
specific biological roles of lipids are yet unknown. Comprehensive
analysis of these polar lipid categories in whole grain wheat and
oat, cereals highly relevant also in nutrition, was performed. Hydrophilic
interaction liquid chromatography (HILIC) and reversed-phase high-performance
liquid chromatography (RP-HPLC) coupled with high-resolution mass
spectrometry using electrospray ionization in both positive and negative
ionization mode was used. Exploiting the different separation mechanisms,
HILIC was used as a screening method for straightforward lipid class
assignment and enabled differentiation of isomeric lipid classes,
like phosphatidylethanolamine and lyso-N-acylphosphatidylethanolamine,
while RP-HPLC facilitated separation of constitutional isomers. In
combination with data-dependent MS/MS experiments, 67 lipid species
belonging to nine polar lipid classes could be identified. Furthermore,
with both ionization modes, fatty acyl chains directly connected to
the lipid headgroups could be assigned. This work focused on the four
lipid classes N-acylphosphatidylethanolamines, acyl-monogalactosyldiacylglycerols,
digalactosyldiacylglycerols, and monogalactosyldiacylglycerols as
they were less studied in detail in the past. Applying the complementary
approach, the relative lipid species compositions in these lipid classes
was investigated in detail.