Off-Flavor Compounds in Spray-Dried Skim Milk Powder

Off-flavor of a spray-dried skim milk powder has been investigated. Commercially processed spraydried skim milk was homogenized with water, and the volatiles were isolated by simultaneous steam distillation-extraction under reduced pressure using diethyl ether as a solvent. The odor concentrate was analyzed by gas chromatography and gas chromatograph-mass spectrometry. To elucidate the compounds contributing to the off-flavor, the concentrate was fractionated by silica gel TLC. A slightly polar fraction with cowhouse-like odor, which was similar to the odor attribute of off-flavor, was further fractionated by a preparative GC. Tetradecanal, having a content about 10 times higher in the offflavored skim milk than in a normal one, was responsible for a sickening and aldehydic odor. β-Ionone and benzothiazole were 76 and 37 times higher in the off-flavored skim milk, respectively, and the former imparted a fragment and haylike odor and the latter a sulfuric and quinoline-like odor.