Influence of the esterification method on the quantification of olive oil fatty acids

To analyze fatty acids by gas chromatography, it is necessary to apply esterification procedures to convert fatty acids into more volatile compounds, such as fatty acid methyl esters (FAME). Esterification methods are usually subdivided into two categories: acidic catalysis and basic catalysis. Due to the possibility of obtaining different concentrations of fatty acids for the same sample as a function of the esterification method used, the efficiency of eight different esterification methods that involve acidic and basic catalysis in the quantitative determination of FAME in olive oil was verified. The selected methods were described by Metcalfe, 1966 (MET); Bannon, 1982 (BAN); Joseph and Ackman, 1992 (JAC); Hartman and Lago, 1973 (HLA); Jham, 1982 (JHA); ISO 5509, 1978 (ISO); Bannon, 1982 (BBA) and Schuchardt and Lopes, 1988 (SLO). The results showed the efficiency of the esterification methods for the main saturated fatty acids that were present in the olive oil analyzed. The most efficient methods for the esterification of unsaturated fatty acids in the oils analyzed were JAC, ISO, and BBA. Nevertheless, the reagent BF3 in methanol, used in the JAC method, is extremely toxic. Thus, when the oil to be analyzed has low acidity, the basic catalysis methods ISO and BBA can be used instead, since they use inexpensive reagents of low toxicity. The results obtained showed that the choice of a method for the analysis of fatty acids also depends on the composition of the oil to be studied.