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

BACKGROUND: The aim of our work was to compare two methods, both based on direct transmethylation with different reagents, BF(3)/MeOH (boron trifluoride in methanol) or HCl/MeOH (hydrochloride acid in methanol), in acid catalysis, without prior extraction, to find the fast, non-expensive but enough precise method for 9 principal fatty acids (lauric, myristic, palmitic, stearic, oleic, linoleic, linolenic, arahidic and behenic acids) analysis in vegetal matrix with low fat content (forage from grassland), for nutrition and agrochemical studies. RESULTS: 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 BF(3)/MeOH than HCl/MeOH, because of the better accuracy and repeatability of this method. Method that uses BF(3)/MeOH reagent produces small amounts of interfering compounds than the method using HCl/MeOH reagent, results reflected by the better statistical parameters. CONCLUSION: The fast and non-expensive BF(3)/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.