Objective evaluation of off-flavor in spray-dried skim milk powder

A determination method for off-flavor compounds in skim milk powder and the contribution of their contents to the organoleptic strength of the off-flavor have been investigated. Standard solutions of off-flavor compounds with various concentration were analyzed by single ion monitoring (SIM) method using gas chromatograph-mass spectrometer. Every plot of concentrations of off-flavor compounds vs ratios of their peak areas against that of internal standard gave straight line (r≥0.99) over a wide range. The odor concentrate isolated from commercially processed spray-dried skim milk obtained by simultaneous steam distillation-extraction under reduced pressure (SDE) was analyzed by present method. The reproducibilities (n = 5) of every peak of off-flavor compounds were 4.8-5.7% as a relative standard deviation. Contents of off-flavor compounds in various skim milk powders which differ from each other in manufacturing lot were compared. The mean contents of tetradecanal, β-ionone and benzothiazole were 20, 0.13 and 0.40 ppb for skim milk powders with normal flavor and 40, 0.62 and 0.80 ppb for those with off-flavor, respectively. As a result of sensory evaluation of the skim milk powders by triangle difference test, the off-flavor was perceived when tetradecanal and β-ionone increased beyond 27 and 0.35 ppb, respectively.