Two methods were compared for the determination of free fatty acids
(FFA) from acetic to long-chain acids in samples with a large excess of
triacylglycerols (TG) (1[ratio ]200, w/w), such as cheese and other
dairy products. In
method 1, after fat extraction, FFA were separated from TG by aminopropyl-bonded
phase chromatography, injecting the fraction containing FFA directly into
the gas chromatograph. In method 2, extracted fat was treated with
tetramethylammonium hydroxide, the methyl ester derivatives being formed in the
injector. Cheese samples and standard mixtures of FFA and TG in different
proportions were analysed by both methods. The cheese sample contained 2·4
times more FFA when analysed by method 2 as compared with the result obtained with
method 1. The composition of the standard mixtures analysed by method 1 closely
reflected that of the original mixture and gave 90–100% recovery of FFA,
regardless
of their chain length and the ratio of FFA[ratio ]TG (1[ratio ]1 or 1[ratio ]200,
w/w). The composition
of samples with a FFA[ratio ]TG ratio of 1[ratio ]200 (w/v) was severely
distorted (as compared
with the original composition of the sample) when analysed by method 2. Varying
recoveries of FFA were also obtained, the largest differences being found for the
shorter-chain components. We conclude that the FFA fraction should be separated
from the TG fraction before derivatization and chromatographic analysis,
particularly for samples in which the FFA represent a minor fraction of the TG.
Determination of the Authenticity of Dairy Products on the Basis of Fatty Acids and Triacylglycerols Content using GC Analysis