Determination of free fatty acids in cheese: comparison of two analytical methods

Abstract

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.

Seasonal variation of the free fatty acids contents of Spanish ovine milk cheeses protected by a designation of origin: A comparative study

“…The comparison of the results obtained by different authors for the absolute amounts of FFAs in cheese should be made with caution, since the use of different methods may lead to different values. It has been proved by Cha´varri et al (1997) that classical methylation of FFAs before the separation of the triglyceride fraction can lead to an overestimation of the FFA concentrations, and very especially that of butanoic acid. In the three cheese varieties of our study, the major FFAs were palmitic (C16:0) and oleic (C18:1) acids, coinciding with the literature (Na´jera et al, 1993;Poveda et al, 2000).…”

Hygienic quality, lipolysis and sensory properties of Spanish Protected Designation of Origin ewe’s milk cheeses manufactured with lamb rennet paste

“…Free fatty acids (FFA) were extracted and analysed underivatised by gas chromatography with a flame ionisation detector, as described by Chavarri et al [27]. Quantification was done with n-pentanoic, n-nonanoic and n-heptadecanoic acids (Sigma-Aldrich, Alcobendas, Spain) as internal standards added to cheese samples at the time of extraction (100 µL of 1 mg·mL -1 solution of each fatty acid in n-heptane).…”

Determination of lipase activity in cheese using trivalerin as substrate

“…To determine the amount of free valeric acid produced, the FFA were extracted immediately following the method of de Jong and Badings (1990), as described by Cha´varri et al (1997). Briefly, to the reaction vessel, 100 mL of an internal standard solution (1.0 mg mL À1 heptanoic acid in heptane:diethyl ether, 1:1 by volume), 0.3 mL 2.5 M H 2 SO 4 , 0.3 mL absolute ethanol (99%) and 3.0 g anhydrous Na 2 SO 4 were added.…”