Gross Structure of the Fat Globule Membrane of Cow's Milk

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Abstract
Washed cream was stirred at 25[degree]C and centrifuged to separate the cream and aqueous layers. Water was added each time as the process was repeated until the cream phase inverted. The butter was melted and the aqueous portion isolated. All aqueous portions were centrifuged at 50,000 G for 90 min at 4*C. Supernatants were adjusted to pH 4.9 and the aggregated lipoproteins isolated. The outer layer of the membrane desorbed from the cream accounted for 54.4% of the membrane. It consisted of reddish-brown pellets high in protein, low in lipid, and fluffy-white supernatant aggregates low in protein and high in lipid. The inner layer accounted for 44.6% of the total membrane. Three lipoprotein aggregates were separated by centrifugation. A greenish-white pellet was high in protein and low in lipid. The supernatant aggregates were low in protein and high in lipid. An interfacial portion was high in protein and low in lipid. Phospholipids in all fractions consisted of lecithin, phosphatidyl ethanolamine, and sphingomyelin. Phospholipids were high in 16:0, 18:0, 18:1, 18:2, and long-chain saturated acids, whereas the neutral lipids were high in 14:0, 16:0, 18:0, and 18:1 acids. Slip points of the neutral lipids in all fractions varied from 30 C to 47 C.