Lipid Globules Retain Globule Membrane Material After Homogenization

The composition of lipid globules collected by centrifugal flotation after homogenization was compared with globules from unprocessed milk. Lipid globules from homogenized milk contained more protein but less total lipid, phospholipid, and cholesterol than globules from equal volumes of unprocessed milk. Homogenization did not alter distribution of individual phospholipids in globules and skim milk. Homogenization induced redistribution of the membrane-associated enzymes 5'-nucleotidase and acid phosphatase between lipid globules and skim milk whereas distribution of phosphodiesterase largely was unaffected. Homogenization altered morphology of membrane surrounding lipid globules. Numerous casein micelles appeared to be associated with membrane-like material on surfaces of homogenized milk lipid globules. Membrane-associated coat material was less intensely stained, and some unit membrane was obscured or lost. Xanthine oxidase and butyrophilin, major milk lipid globule membrane-associated polypeptides, remained associated with lipid globules from homogenized milk. Results suggested that homogenization induced some loss of membrane material from the floating lipid globule fraction but that a large proportion of the original membrane material remained on lipid globule surfaces.