FAMEs were prepared according to the AOAC official method 948.22 (AOAC International, 1990b). For each sample, the process was prepared in duplicate.
The FAMEs were obtained from the lipid fractions after alkaline hydrolysis (NaOH/methanol 0.5 mol L−1), followed by methylation with boron trifluoride 14% in methanol (solvent reflux temperature). Samples were extracted with heptane and washed with saturated sodium chloride solution. 1 mL of the organic phase was purified though a micro column fitted with anhydrous sodium sulphate and then eluted with 2 mL of heptane. Finally the eluate was evaporated to dryness over N2 and reconstituted with 1 mL of dichloromethane for the chromatographic analysis.