Volatile Carbonyl Compounds in Stored Dry Whole Milk

Abstract

Flavor constituents in the low temperature vacuum distillate of reconstituted dry whole milks were largely carbonyl in nature. The 2,4-dinitrophenylhydrazone derivatives identified by paper and column chromatography, ultraviolet studies, and melting points revealed qualitative differences in the milks studied. The following were conclusively or tentatively identified in the distillate from an average dry whole milk: C3 through C7, C9, C11 and C15 n-alk-2-ones; C1, C2 and C9 alkanals and cis- and trans-furfural. In contrast a badly deteriorated powder yielded: C3, C4, C9, C11 and C15 n-alk-2-ones; C1 through C3, C5 through C7, C9, C10 and C12 n-alkanals; benzaldehyde, 2 mono- and 2 di-unsaturated carbonyls. The poor powder could be distinguished from the average dry milk mainly by the large number and concentrations of aldehydes it contained. The relative amounts of individual carbonyls in 4 additional dry whole milks manufactured and stored under various conditions were determined. The results suggest that the complex problem of organoleptically characterizing stale and oxidized flavor deterioration in dry whole milk stems in part from the large numbers and variable quantitative relationships of the carbonyl compounds involved. The absence of methyl ketones in dry whole milk prepared with deodorized milk fat suggests a potential means of increasing the storage life of the product. Ketone formation appears to be an important deterioration mechanism in stored dairy products containing milk fat.