Comparative researches on two direct transmethylation without prior extraction methods for fatty acids analysis in vegetal matrix with low fat content

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The fast and non-expensive BF3/methanol method was applied with good accuracy and sensitivity for the determination of free or combined fatty acids (saturated and unsaturated) in forage matrix with low fat content from grassland. Also, the final extract obtained by this method, poorer in interfering compounds, is safer to protect the injector and column from contamination with heavy or non-volatile compounds formed by transmethylation reactions.

Comparatively, between the average values obtained for all analysed fatty acids by the two methods based on direct transmethylation without prior extraction no significantly difference was identified (p > 0.05). The results of fatty acids for the same forage sample were more closely to their average value, being more homogenous for BF3/MeOH than HCl/MeOH, because of the better accuracy and repeatability of this method. Method that uses BF3/MeOH reagent produces small amounts of interfering compounds than the method using HCl/MeOH reagent, results reflected by the better statistical parameters.