HS-SPME gas chromatographic characterization of volatile compounds in milk tainted with off-flavour

Milk samples, collected from nine healthy mid-lactation Holstein cows, were analysed organoleptically by two sensory panels, and chromatographically using mass spectrometry/flame ionization (MSD/FID) and olfactometric detectors. The sensory panels found that the samples collected after the cows were forage-starved for approximately 12 h were of good flavour quality, whereas at least 89% of the samples collected after they were fed baled grass silage were tainted with off-flavour characterized as "feed". The corresponding MSD/FID chromatograms revealed that 30 min post-feeding samples had significantly (p<0.05) higher concentrations of ethanol, propane-2-one, dimethyl sulphide, butane-2-one, hexanal, heptanal and octane-2,3-dione, whereas 3 h post-feeding samples showed higher concentrations of four of these compounds (propane-2-one, dimethyl sulphide, butane-2-one and hexanal). Olfactometric analysis performed on five milk samples (four off-flavoured and one of good flavour quality) revealed approximately 75 aroma-active compounds. Nearly all these compounds were common to all the analysed milk extracts (both off-flavoured and good quality samples), suggesting that off-flavour originated from the concentration differences of a common set of compounds rather than from the absence or presence of specific compounds..