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Substances Adsorbed on the Fat Globules in Cream and their Relation to Churning. V. Composition of the "Membrane" and Distribution of the Adsorbed Substances in Churning¹

University of Minnesota, St. Paul, Minnesota

ABSTRACT

Protein contents ranging from 0.46–0.86 grams per 100 grams of fat, and lipide phosphorus contents ranging from 8.9–16.3 milligrams per 100 grams of fat were found in 19 samples of cream washed six times with distilled water. The protein content was relatively constant in washed creams from any given group of cows; it was lower in those from Jerseys than in those from Holsteins. The protein/phospholipide ratio varied from 1.8 to 2.4 in 15 samples of washed cream and was 2.7 in a sixteenth.

Protein and phospholipide contents and ratios of washed creams appeared to be independent of variations in fat composition produced by changes in feed.

The protein and lipide phosphorus contents of 10 samples of washed cream, exhibiting only minor variations in average fat globule size, were respectively 34.0-49.0 and 0.57–0.86 micrograms per 100 square centimeters of fat surface.

Contents of "membrane" constituents per unit weight of fat and even per unit of fat surface were correlated significantly with the specific fat surface in 19 samples of washed cream prepared to exhibit a considerable range in average fat globule size.

Butters from 11 samples of washed cream had protein/phospholipide ratios of 1.0–2.0. The corresponding buttermilks had ratios of 2.4–3.8. This verified the rather qualitative results of a preliminary investigation.

Butters from washed cream retained protein at a rather constant level of 0.21–0.30 grams per 100 grams of fat irrespective of the concentration of fat or of protein in the washed creams from which they were churned. They did not retain a constant level of phospholipide.

The significance of these findings in relation to a theoretical concept of orientation of protein and phospholipide in the "membrane" is discussed.

¹ Paper No. 2220, Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul, Minnesota. The data presented herein are taken from a thesis submitted by Eobeit Jenness to the Graduate School of the University of Minnesota, June 1944, in partial fulfillment of the requirements of the degree of Doctor of Philosophy.

² Deceased March 8, 1944.