Identification of O-Aminoacetophenone as a Flavour Compound in Stale Dry Milk

Abstract

IN our efforts to improve the keeping quality of dry milk products, attention has been directed towards isolating and identifying flavour compounds present in stale products. This communication deals with the isolation of a compound with a ‘grape-like’ flavour, identified as o-aminoacetophenone. Preliminary work on the solvent extraction of stale non-fat dry milk indicated that a strong flavour fraction characterized as potato-like or cocoa-like could be extracted with hexane. The odour was materially altered by adding a strong acid but could be regenerated by adding alkali. Crude concentrates were prepared by hydrochloric acid extraction of hexane extracts of stale dry milk powder. The alkali-liberated flavour fraction was back extracted in small volumes of hexane which were then gas chromatographed on an ‘Apiezon L’ column. A flavour fraction, ‘grape-like’ in character, was detected with the nose at the tail pipe of the instrument. The odour emergence coincided with a characteristic peak on the recorder. This flavour material was collected in a cold trap attached to the outlet of the column and was shown to contain nitrogen by the method of Feigl and Amaral¹. The material collected from numerous successive chromatograms was analysed in a mass spectrometer. The results indicated that the sample was ‘Apiezon’ grease contaminated with a small amount of a compound with a parent peak at mass 135. Infra-red analysis indicated the possible presence of carbonyl oxygen and aromatic structure. The observations were consistent with aminoaceto-phenone. Examination of the authentic isomers revealed that o-aminoacetophenone had an odour identical with the natural fraction collected from the gas chromatograph. Further evidence supporting the identity of the isolated compound as o-aminoacetophenone is presented.