Analysis of the fruity off-flavor in milk using headspace concentration capillary column gas chromatography

Ethyl butyrate and ethyl hexanoate, compounds considered to be primarily responsible for the fruity off-flavor in milk, were measured by using an automated headspace concentration system coupled to a capillary column gas chromatograph. Sampling conditions were optimized for recovery of the esters in whole milk. Concentrations as low as 0.001 ppm could be detected and quantified. The coefficients of variation for ethyl butyrate and ethyl hexanoate at this concentration were 61.7% and 53.2% while relative errors were 55.6% and 23.5%, respectively. Sensory analysis determined a fruity flavor threshold of 0.01 ppm (0.005 ppm of ethyl butyrate and 0.005 ppm of ethyl hexanoate) in whole milk. At this level, the headspace concentration system quantified these esters with 29.9-36.4% relative error and 25.3-30.7% coefficient of variation. Commercial milks judged to be fruity by sensory analysis were found to contain ethyl butyrate and ethyl hexanoate concentrations of 0.026-0.152 and 0.20-0.268 ppm, respectively.