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

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Abstract
Protein contents ranging from 0.46-0.86 g. per 100 g. of fat, and lipid P contents ranging from 8.9-16.3 mg. per 100 g. of fat were found in 19 samples of cream that had been washed 6 times with dist. water. The protein content was relatively constant in washed creams from any given group of cows; it was lower in Jersey than in Holstein creams. The protein/phospholipid ratio varied from 1.8 to 2.4 in 15 samples of washed cream and was 2.7 in a 16th sample. Protein and lipid P contents and ratios of washed creams appeared to be independent of variations in fat composition produced by changes in feed. The protein and lipid P contents of 10 samples of washed cream, exhibiting only minor variations in average fat globule size, were respectively, 34-49 and 0.57-0.86 [gamma] per 100 cm2 of fat surface. The contents of "membrane" constituents per unit wt. of fat and even per unit of fat surface were correlated significantly with specific fat surface in 19 samples of washed cream prepd. to exhibit a considerable range in average fat globule size. Butters churned from 11 samples of washed cream had protein/phospholipid ratios of 1-2. The corresponding buttermilks had ratios of 2.4-3.8. Butters from washed cream retained protein at a rather constant level of 0.21-0.3 g. per 100 g. of fat or of protein in the washed creams from which they were churned. They did not retain a constant level of phospholipid. These findings imply that churning involves an "erosion" of protein from the fat globules to a constant critical level. Furthermore, a disruption of the original lipoprotein complex occurs in such a manner that the butter contains much more phospholipid per unit of protein than does the buttermilk.