Quantification of FFAs

The most widely used method for quantifying FFAs is gas chromatography (GC), which has attained widespread favor due to its versatility, high sensitivity and relatively low cost. GC complexed with a flame ionization detector is used routinely to quantify FFAs, either directly or derivatized as fatty acid methyl esters (FAME). GC with mass spectroscopic detection has become the favored technique for quantification of volatile compounds derived from lipids (esters, lactones, ketones, alcohols and acids). 

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GC combined with mass spectroscopic (MS) detection provides very accurate identification and quantification of FFAs. Pinho et al. (2003) monitored changes in the FFA content during the ripening of ewe cheese. Sampling was done by headspace solid-phase microextraction (SPME). An excellent correlation was observed between the initial concentration of the sample and the amount absorbed on the SPME fiber. SPME sampling was done at 65 °C with a fiber coated with 85-p.m polyacrylate film. After equilibration at 65 °C for 40 min, the fiber was exposed to the sample headspace for 20 min and inserted into the GC port. Despite its accuracy, the GC-MS method is not widely used, presumably because of its cost and complexity. 

Quantification of FFAs in dairy products, especially in cheese, is particularly important due to the impact of some FFAs on flavor. However, FFAs act as precursors of a wide range of flavor compounds (e.g., methyl ketones, lactones, esters and aldehydes), (Singh et al, 2003). The extent of lipolysis in cheese varies widely between varieties (Table 19.2). Typically, those cheeses with more than 3000 mg/kg have a characteristic lipolytic aroma/flavor and lipolysis plays an important role in their ripening. A major difficulty in quantifying FFAs in cheese is the distribution of FFAs of different chain length within the cheese matrix. SCFFA (C4 o—C8 0) partition mainly into the aqueous phase, whereas medium (Cio q—C14 0) and longer... 

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