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

Mechanisms of formation of aroma compounds in milk and milk products

“…Of course, aldol condensations may occur equally well with carbonyl compounds derived from lipids or carbohydrates, and an oily flavour defect in fresh butter made from factory-separated cream may be partly due to 2-alkyl-alk-2-enals such as 2-butyl-oct-2-enal (32). A major contributor to the gluey flavour of casein, and first identified in dry and sterile concentrated milks (59), is o-aminoacetophenone which has a Concord grape odour. Though its origin has not been definitely established, it probably comes from tryptophan or indoxyl:…”

Volatile compounds associated with the off-flavour in stored casein

“…After removal of acids the extract was still gluey, as was the reflux concentrate prepared by method C, which contained negligible quantities of acids, which were relatively non-volatile under these conditions. The flavour of the lower alkanoic acids is well-known as a sharp, bitter, rancid-fat taste with a threshold in water of the order of 5 ppm (Patton, 1964). These properties suggest that the acids have little relevance to gluey flavour although they are major components of the casein extract and several are present in amounts close to their flavour threshold values.…”

“…Only one of these components, o-aminoacetophenone, was examined organoleptically as Parks et al (1964) found that it was an important constituent in the flavour of stale skim-milk powder. In 1 % sodium caseinate solution, it had a threshold of 3-10 parts in 10 9 (i.e.…”

“…Nawar, Lombard, Dall, Ganguly & Whitney (1963) and Kurtz (1965) found evidence that the stale flavour in whole-milk powder had 2 elements-one volatile in vacuum distillation and the other non-volatile and tightly bound to the milk powder. Parks & Patton (1961) identified a range of volatile carbonyl compounds including n-alkanals (about 1 ppm), n-alkanones, furfural and benzaldehyde in stale whole-milk powder and Bassette & Keeney (1960) isolated a similar range of carbonyl compounds from stored skim-milk powder including alkanals at a level of 5 parts in 10 8 . Shtal 'berg & Kretovich (1953) found 50 ppm aldehydes in dried milk which exhibited a darker colour and an unpleasant gluey flavour.…”

“…These groups of workers all concluded that stale flavour was due largely to the increasing quantity of carbonyl compounds-particularly aldehydes-formed during storage of the milk powder. Parks, Schwartz & Keeney (1964) isolated a less volatile compound, o-aminoacetophenone, from skim-milk powder and showed that it was an important component of the stale flavour.…”