The fatty acid composition of each sample was determined by
gas chromatography (GC). The methyl esters of fatty acids were extracted
with hexane and analysed using a Perkin–Elmer Sigma 3D
chromatograph with FID detector and automatic injection system
(García-Olmo et al., 2002). Although, these 52 fat samples were
not analysed in duplicate, to evaluate the repeatability of the GC
method, the statistic SEL (standard error of the reference method)
were calculated using a similar set of 20 fat samples analysed in
duplicate applying the following formula