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Journal of Dairy Science Vol. 37 No. 4 390-398
© 1954 by American Dairy Science Association ®
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The Unsaturated Fatty Acids of Milk Fat1 II. Conjugated and Nonconjugated Constituents

L. M. Smith and E. L. Jack

Department of Dairy Industry, University of California, Davis

ABSTRACT

Ultraviolet absorption curves for milk fats before and after alkali isomerization showed the presence of conjugated and nonconjugated polyethenoid constituents. The amounts of these polyunsaturated fatty acids in representative California milk fats were estimated by spectrophotometry and compared with other published data.

Methyl esters of the polyethenoid fatty acids were concentrated by combinations of vacuum distillation, preferential urea complex formation, and low temperature crystallization procedures. The latter technique was superior to the urea complex method for the concentration of polyethenoid esters by removal of saturated and monoethenoid components. Although individual conjugated and nonconjugated polyunsaturated constituents were not isolated in a pure state from a mixture of C18–20 methyl esters by fractional distillation in vacuum, appreciable fractionation was achieved. The results showed that the milk fat contained small amounts of conjugated and nonconjugated dienoic, trienoic, and tetraenoic fatty acids with carbon chain lengths of 18 or longer. Spectrophotometric evidence also indicated the presence of a nonconjugated pentaenoic constituent.

FOOTNOTES

1 The data in this paper are taken from a thesis presented by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy, University of Califomia.






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Copyright © 1954 by the American Dairy Science Association ®.