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Isolation of Milk Phospholipids and Determination of Their Polyunsaturated Fatty Acids¹

Department of Dairy Industry, University of California, Davis

ABSTRACT

Several methods were compared for recovery and purification of mixtures of phospholipids from dried buttermilk. Samples were analyzed for phosphorus, nitrogen, and unsaturated fatty acids. Evidence was obtained that phospholipids purified by repeated acetone precipitation are not representative of the original milk phospholipids. An improved procedure was developed to extract the lipids from buttermilk with ethanol, ether, and chloroform. Most of the phospholipids were separated from the other lipids by precipitation with acetone. Acetone-soluble phospholipids were recovered by chromatography with silicic acid columns. The two fractions were combined and nonlipid contaminants were removed by washing. In an alternative procedure, the lipids were extracted from buttermilk with methanol and chloroform before the foregoing method was used to isolate the phospholipids.

The amounts of unsaturated fatty acids were estimated from spectrophotometric data and iodine values. A representative sample of milk phospholipids (3.72% phosphorus, 2.23% nitrogen, iodine value 53.8) contained 26.3% monocne, 1.5% conjugated diene, and 5.8, 2.4, 1.3, and 1.5% nonconjugated diene, triene, tetraene, and pentaene acids, respectively. Percentages of each of these acids in the total fatty acids (with corresponding percentages for milk fat from the same source given in parentheses) were: 39.8 (32.1), 2.3 (1.4), 8.8 (1.6), 3.6 (0.9), 2.0 (0.3), and 2.2 (0.2), respectively. The phospholipids contained 41.3% saturated fatty acids and the milk fat 63.5%. These data show that there was a selective concentration of nonconjugated polyunsaturated acids in milk phospholipids.

¹ A preliminary report on this research was presented at the 53rd Annual Meeting of the American Dairy Science Association, Raleigh, N. C., June, 1958. Some of the data in the published abstract are incorrect. The correct data are in this paper.