Carbonyl Pattern of Sunlight-Exposed Milk

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Abstract
A comparative micro-analysis ~as made of the carbonyl compounds in con- trol and sunlight-exposed milk. Alk-2-enals (C6-C~o) were detectable in the exposed milk and absent from the control milk. Significantly higher levels of butanone and pentanone were observed in the exposed than in the control milk. Exposure caused a significant decrease in the formaldehyde content of the milk. Methional could not be detected in the exposed milk. The previously indicated role of methional in sunlight milk flavor may be mediated by its conversion to other flavorful sulfur compounds. Exposure of milk to light is generally be- lieved to produce flavor defects due to trace oxidative degradation of lipids aald proteins. Much evidence to support this belief has been obtained in many laboratories during the past 35 yr from studies of the effects of environ- mental factors on nfilk and model systems (16, 18). However, the identities of the flavor com- pounds produced from this type of milk deg- radation are unknown. Sulfur compounds have been suspected of being involved in the flavor resulting from protein degradation (6, 11, 12), and Patton (11) has suggested that a single sulfur aldehyde, methional, might be an im- portant component of sunlight-milk flavor. By analogy to our knowledge of the products of lipid autoxidation (17), one would expect car- bonyl compounds to be involved in the flavor resulting from milk lipid degradation. The present work was undertaken to test experi- mentally the suggestion that carbonyl com- pounds may be formed in sunlight-exposed milk. EXPERIMENTAL PROCEDURE