Rapeseed (Brassica napus) oils differing in cultivar, sites of growth,
and harvest year were characterized by fatty acid concentrations and
carbon, hydrogen, and oxygen stable isotope analyses of bulk oils
(delta(13)C(bulk), delta(2)H(bulk), delta(18)O(bulk) values) and
individual fatty acids (delta(13)C(FA)). The delta(13)C(bulk),
delta(2)H(bulk), and delta(18)O(bulk) values were determined by
continuous flow combustion and high-temperature conversion elemental
analyzer isotope ratio mass spectrometry (EA/IRMS, TC-EA/IRMS). The
delta(13)C(FA) values were determined using gas
chromatography-combustion isotope ratio mass spectrometry (GC/C/IRMS).
For comparison, other C(3) vegetable oils rich in linolenic acid (flax
and false flax oils) and rich in linoleic acid (poppy, sunflower, and
safflower oils) were submitted to the same chemical and isotopic
analyses. The bulk and molecular delta(13)C values were typical for C(3)
plants. The delta(13)C value of palmitic acid (delta(13)C(16:0)) and n-3
alpha-linolenic acid (delta(13)C(18:3n-3)) differed (p < 0.001) between
rape, flax, and poppy oils. Also within species, significant differences
of delta(13)C(FA) were observed (p < 0.01). The hydrogen and oxygen
isotope compositions of rape oil differed between cultivars (p < 0.05).
Major differences in the individual delta(13)C(FA) values were found. A
plant-specific carbon isotope fractionation occurs during the
biosynthesis of the fatty acids and particularly during desaturation of
C(18) acids in rape and flax. Bulk oil and specific fatty acid stable
isotope analysis might be useful in tracing dietary lipids differing in
their origin.