Method for the Quantitative Analysis of Volatile Free and Total Branched-Chain Fatty Acids in Cheese and Milk Fat

Volatile free fatty acids ( 12 ) in Parmesan cheese and milk fat were extracted with diethyl ether:hexane, adsorbed on neutral alumina, eluted from alumina with formic acid in diisopropyl ether, and separated from long-chain fatty acids by simultaneous distillation-extraction. Volatile branched-chain fatty acids in total lipid extracts were isolated similarly after alkaline hydrolysis. Butyl esters of isolated fatty acids were prepared, extracted into pentane, washed with methanol:water, and analyzed on a bonded polyethylene glycol (Supelcowax10) capillary column. Esters of fatty acids were identified by gas chromatographymass spectroscopy and were quantified by gas chromatography using 2-ethylnonanoic acid as an internal standard. In addition to the usual even carbon-numbered FFA, 2-methylbutanoic, 3-methylbutanoic, 2ethylbutanoic, pentanoic, 3-methylpentanoic, 4methylpentanoic. 2-ethylhexanoic, 4-methylhexanoic, heptanoic, a methylheptanoic, an ethylheptenoic, 4-ethylheptanoic (or 3-methyloctanoic), 4-methyloctanoic, a methyloctanoic, nonanoic, 4-methylnonanoic, 8-methylnonanoic, 2-ethyldecanoic, and 9-decenoic acids were identified and quantified. Substantial reservoirs of volatile branched-chain. odd carbon-numbered, and unsaturated fatty acids occur in cow's milk fat.