Quantitative Determination of Short-Chain Free Fatty Acids in Milk Using Solid-Phase Microextraction and Gas Chromatography

The objective was to establish a rapid, precise, and accurate methodology for the quantification of short-chain free fatty acids (FFA) (C4−C12) in milk by solid-phase microextraction and gas chromatography. Sampling conditions such as fiber type, pH, salt addition, temperature, volume, and time were investigated. FFA extraction consisted of placing 40 mL of milk containing 28% NaCl at pH 1.5 in a sealed vial and equilibrating for 30 min at 70 °C. A polyacrylate fiber was exposed to the sample headspace for 60 min and desorbed for 5 min into the gas chromatograph. Calibration curves for FFA followed linear relationships with highly significant (p < 0.001) correlation coefficients (R 2 = 0.99). Coefficients of variation of less than 7.7% for FFA concentrations indicated that the technique was reproducible. The limits of quantification for C4−C10 were in the low parts per million level, which were below the concentration range found in fresh pasteurized milk (0.48−2.52 ppm) or rancid milk (4.73−32.31 ppm). Keywords: Solid-phase microextraction−gas chromatography; short-chain free fatty acids; milk; rancid flavor