Effects of Ultrahigh Temperature Steam Injection Processing on Composition of Carbonyls in Milk Fat

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Raw whole milk was processed by a No-Bac Unitherm IV System (Cherry Burrell Corporation) modified to allow steam injection heating followed by vacuum cooling. Milk was processed at 140.5°C for 4.4s, vacuum cooled to 74°C, and indirectly cooled to approximately 4°C.Raw and ultrahigh temperature milk samples were centrifuged to obtain milk fat, which then was extracted with carbonyl-free hexane. After reaction of carbonyls with 2,4-dinitrophenylhydrazine, concentrations were estimated for total carbonyls, total monocarbonyls, and methyl ketones. Thin layer and gas chromatography identified individual monocarbonyl compounds as their dinitrophenylhydrazone derivatives.Ultrahigh temperature milk samples showed an average decrease in total carbonyls of 11.2% compared to raw milk.Monocarbonyl concentration showed an average overall decrease after processing.Analysis with gas-liquid and thin layer chromatography indicated relative qualitative and quantitative changes in methyl ketones and saturated aldehydes. Both raw and ultrahigh temperature samples contained acetone, 2-butanone, 2-pentanone, 2-hexanone, and in some cases 2-heptanone. Gas-liquid chromatography of raw samples indicated the saturated aldehydes with 1, 3, 4, 5, and 9 carbons as well as some longer chain aldehydes. Thin layer chromatography confirmed propanal, butanal, and longer chain aldehydes. Gas-liquid chromatography analysis of ultrahigh temperature samples indicated saturated aldehydes with 1 to 10 carbons as well as some longer chain aldehydes, and thin layer chromatography analysis confirmed propanal, butanal, nonanal, and some longer chain aldehydes. Acetaldehyde, hexanal, heptanal, octanal, and nonanal appeared to be heat-induced.