Lipids and Metals in Fat Globule Membrane Fractions

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Abstract
Fat globule membrane material (FGMM) was isolated from buttermilk of churned washed cream. Unfractionated FGMM was obtained by isoelectric precipitation of buttermilk solids. Fractionated FGMM obtained by differential centrifugation of buttermilk yielded 3 pellets, and isoelectric precipitation of the remaining supernatant solids yielded a fourth pellet. Two minor fractions were obtained by lyophilization of the final supernatants from the isoelectric precipitation steps. Analyses of the centrifugal fractions indicated 2 basic categories: a high density reddish-brown fraction high in protein and low in lipid and a low density cream-colored fraction low in protein and high in lipid. Lipid of the high density fraction was higher in phospholipid and greater in total unsaturation and polyunsaturation than the low density fractions. There were no qualitative differences, but there were quantitative differences among the various fractions. Iron was high in the high density fractions, while Cu was more evenly distributed. Highest ratios of metal to fatty acid indicate one Cu and one Fe ion/24 and 21 poly-unsaturated fatty acid molecules, respectively.