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Structure and Synthesis of Milk Fat. X. Characterization of the Major Hydroxy Compounds in Milk Lipids¹

Lipids Laboratory, Divison of Food Science and Industry, The Pennsylvania State University, University Park 16802

ABSTRACT

Lipids of fresh raw bovine and caprine milks were extracted under mild conditions and immediately reacted with pyruvyl chloride 2,6-dinitrophenylhydrazone. The resulting derivatives were separated and isolated by column and thinlayer chomatography. Quantification was spectrophotometrically at 402 mµ. The l,2-diglyceride and hydroxytriglyceride fatty acids were characterized as their methyl esters utilizing gas-liquid chromatography. Concentrations in weight percent of the major classes of hydroxy compounds in the lipids of bovine herd milk were: 1,2-diglycerides 1.43 ± .ll, hydroxytriglycerides .61 ± .05, and sterols .35 ± .03. Lipids of individual caprine milks yielded similar values. Following lipolytic treatment of milks from individual animals, 1,2-diglycerides tripled, whereas h droxytriglycerides decreased slightly and sterols remained unchanged. During early lactation 1,2-diglycerides and hydroxytriglycerides increased slightly whereas sterols, composed primarily of cholesterol, decreased from a high of 1.1 to 1.2% to a normal of .3% in the bovine. Bovine mammary tissue lipids were characterized by much higher levels of sterols and slightly higher levels of 1,2-diglycerides when compared with milk lipids from the same tissue. Fatty acid composition of the 1,2-diglycerides lacked short chain fatty acids, namely butyric and caproic acids. Hydroxytriglycerides were composed of the nonnal complement of fatty acids, however fewer short chain acids were evident when compared with triglycerides from the same milk.

¹ Authorized for publication January 25, 1972 as Paper 4122 in Journal Series of the Pennsylvania Agricultural Experiment Station.

² Present address: Institut für Chemie, Bundesanstalt fiir Milchforschung, Kiel, Germany.