Ultrastructural Observations on the Milk Fat Globule Envelope of Cow's Milk

To further elucidate the complex fine structure of the milk fat globule envelope, fresh cream and isolated fat globule membrane material were examined electron microscopically by three different but complementary preparation techniques: Thin sectioning, negative staining, and freeze-etching.After thin sectioning most of the fat globules were surrounded only by a simple limiting membrane to which casein mieelles may be adsorbed.A higher percentage of fat globules still enveloped by a unit membrane was found after freeze-etching, indicating that physical stabilization by rapid freezing is preferable to chemical fixation.Vesicle formation of isolated fat globule membrane material depends upon the purity of the membrane fractions.Based on these morphological observations a structural model of the milk fat globule envelope which may serve as a working hypothesis for further more detailed studies is proposed.