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Milk Lipase System. II. Comparison of Solvent Extraction and Churning Methods for Obtaining Fat from Milk for Free Fatty Acid Measurement.¹

Maryland Agricultural Experiment Station, College Park

ABSTRACT

A method for the removal of fat from milk products which involves the use of ethanol, ethyl ether and Skellysolve F was developed.

The application of this solvent extraction method to rancid milk yielded fat averaging 30 per cent higher in acidity than fat obtained by churning and resulted in better recovery of the fat. The solvent method is adapted particularly to the removal of fat from homogenized products of low fat content, thereby eliminating the loss of water-soluble fatty acids through separation. Moreover, the addition of lactic acid and/or formalin to cream had little effect upon the acidity of the fat resulting from solvent extraction, but increased appreciably the acidity of that obtained by the churning process.

The solvent method was superior to the churning method for recovery of pure fatty acids from cream, particularly the lower acids, butyric and caproic. This is emphasized by the fact that many samples of fat which were solvent-extracted from milk exhibited a rancid flavor, whereas churned fat from the same source did not. However, even with the solvent method, butyric acid recovery was low as determined by titration.

Improved recovery of butyric acid added to cream resulted when the temperature and pressure of solvent removal from fat was lowered from 100° C. and 500 mm. mercury to 60° C. and 20 mm. mercury. However, when rancid cream was extracted, these modifications proved to be of questionable value so far as fat titration values were concerned, due to the small amounts of volatile, water-soluble fatty acids present.

Chemical analysis failed to show any appreciable differences, other than in acid degree, between solvent-extracted and churned fat, whether the fat was from normal or rancid milk. Also, analysis of the ethanolic soluble and insoluble fractions of solvent-extracted fat failed to indicate definitely selective hydrolysis by milk lipase.

The data presented in this study indicate the need for re-evaluation of results from lipase studies which are based upon the titration of fat obtained by churning methods.

¹ Scientific paper no. A224. Contribution no. 2149 of the Maryland Agricultural Experiment Station (Dairy Department).

² Present address: Dairy Technology Dept., Ohio State University Columbus.