F. Chavarri et al., DETERMINATION OF FREE FATTY-ACIDS IN CHEESE - COMPARISON OF 2 ANALYTICAL METHODS, Journal of Dairy Research, 64(3), 1997, pp. 445-452
Two methods were compared for the determination of free fatty acids (F
FA) from acetic to long-chain acids in samples with a large excess of
triacylglycerols (TG) (1:200, w/w), such as cheese and other dairy pro
ducts. In method 1, after fat extraction, FFA were separated from TG b
y aminopropyl-bonded phase chromatography, injecting the fraction cont
aining 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 FPA and TG; in different proportions mere 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 c
omposition of the standard mixtures analysed by method 1 closely refle
cted that of the original mixture and gave 90-100% recovery of FFA, re
gardless of their chain length and the ratio of FFA:TG (1:1 or 1:200,
w/w). The composition of samples with a FFA:TG ratio of 1:200 (w/v) wa
s severely distorted (as compared with the original composition of the
sample) when analysed by method 2. Varying recoveries of FFA were als
o 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 PPA represent a minor fraction o
f the TG.