SPHINGOMYELIN FROM MILK - CHARACTERIZATION OF LIQUID-CRYSTALLINE, LIPOSOME AND EMULSION PROPERTIES

The properties of sphingomyelin obtained from bovine milk were investi gated. In particular, the properties of liposomes and emulsions prepar ed from the spingomyelin, as well as the liquid crystalline behavior, were investigated and compared to those of related phosphatidylcholine systems. Like sphingomyelins from other sources, sphingomyelin from m ilk contains a large fraction of long and saturated acyl groups, which results in a high gel to liquid crystal transition temperature (T-c 3 5-82 degrees C, depending on the lipid concentration). At high sphingo myelin concentrations, a lamellar phase forms above T-c, while a swoll en gel phase is obtained below T-c. The gel phase swells to about 20 w t% water, whereas the swelling continues to about 40 wt% water above T -c. The limiting areas per molecule are 51 and 68 Angstrom A(2) below and above T-c, respectively. Sphingomyelin from milk forms liposomes r eadily in the presence of cholesterol. The liposomes formed have a dia meter of about 100 mm and are stable, even at 0.1M NaCl or HCl. Materi als entrapped in the liposomes are released rather slowly (typically 4 0% over 5 h). A comparison shows that the sphingomyelin liposomes beha ve similarly to those formed by phosphatidylcholine systems. Furthermo re, sphingomyelin from milk forms stable oil-in-water emulsions with s oybean oil. The size of the emulsion droplets obtained was about 200 n m. Both the size of the emulsion droplets and its dependence on electr olyte addition correlate closely with those of emulsions formed by the corresponding phosphatidylcholine system. Therefore, it is possible t o use sphingomyelin as an alternative for saturated phosphatidylcholin es, which may be advantageous for oral and dermal pharmaceutical appli cations, as well as in cosmetics.