Comparison between novel and standard methods for analysis of free fatty acids in milk - Including relation to rancid flavour

A range of analytic methods for quantifying free fatty acids (FFAs) in milk were compared and further correlated to rancid flavour detected by sensory analysis. Proton transfer reaction-mass spectrometry (PTR-MS) and 1H nuclear magnetic resonance (NMR) spectrometry were introduced as novel methods for quantifying individual short chain FFAs. Gas chromatography-mass spectrometry (GC-MS) combined with in-solution derivatisation was used for quantifying all individual FFAs, and Bureau of dairy industries (BDI), acyl-CoA-synthetase-acyl-CoA oxidase (ACS-ACOD) assay, Fourier transform infrared spectroscopy were used to estimate the total FFA concentration in 28 milk samples. High correlations (r between 0.76 and 0.86) to rancid off-flavour were found for all analytical methods, and all the individual FFAs were quantitatively inter-correlated. Furthermore, a high correlation was found between PTR-MS and GC-MS quantification of hexanoic acid. For the BDI method, the sensory thresholds rancid off-flavour in farm bulk milk were 1.95 mmol 100 g−1 fat.