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Volatile Carbonyl Compounds in Stored Dry Whole Milk ¹

Department of Dairy Science, The Pennsylvania Agricultural Experiment Station, University Park

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, two mono- and two diunsaturated 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 four 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 deteriorative mechanism in stored dairy products containing milk fat.

¹ Authorized for publication as Paper No. 2467 on June 24, 1960, in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² Present address: Dairy Products Laboratory, Eastern Utilization Research and Development Division, USDA, Washington 25, D. C.