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 Churning

Previous papers in this series (11,12, 14,18,19) have shown that at least part of the stability of the emulsion of fat in milk may be attributed to an adsorption "membrane" so tenaciously held at the fat surface as to resist removal by a process of repeated dilution and separation.This "membrane" was found to contain a protein (12), not identifiable with the other proteins of milk (14, 19), and a mixture of phospholipides (12).A highmelting phosphorus-free glyceride was found in "membrane" preparations ( 12), but its relation to the other components was not established.Rimpila and Palmer (14) found considerable variation in the percentages of protein and phospholipide in the "membrane" from various samples of natural cream, although for any one sample, the amounts and proportions of these adsorbed materials remained relatively constant from the fourth through at least the tenth washing.Palmer and Wiese (12) observed that when washed cream is churned, the adsorbed materials become divided between the buttermilk and the butter.Their data did not permit a statement as to the quantitative division of these materials upon churning washed creams.However, the experiments of Sandelin (15) on creams consisting of butterfat emulsified in soap or lecithin sols, showed that the stabilizing material is divided in such a way upon churning that it is more concentrated in the butter than in the buttermilk.That a similar division may occur on churning washed cream is indicated by the observation Of Powell (see Palmer ( 10)) that butter serum from washed cream is a more effective depressant of interracial tension than is the free buttermilk from washed cream.These results may be interpreted as indicating a higher ratio of phospholipide to protein in the butter serum, particularly in view of the contention of Ma~mistova (8) that the capillary activity of the fat globule "membrane" depends on its phospholipide content.The work reported in the present paper was undertaken to determine