Fat Globule Membrane MFGM

About one-third of the phospholipids in freshly drawn milk are located in the milk serum as small lipoprotein particles, sometimes referred to as milk microsomes. Their proportion in milk serum can be increased in processed milk as a result of disruption of the MFGM and release of membrane phospholipids into the aqueous phase (Mulder and Walstra, 1974 McPherson and Kitchen, 1983). Modification of the MFGM by processing treatments that may alter the distribution of pro-oxidants and antioxidants can markedly affect the stability of milk (McPherson and Kitchen, 1983). 

Xanthine oxidoreductase, a metalloprotein abundant in the MFGM, may also be partially responsible for the susceptibility of the membrane to lipid oxidation (Allen and Humphries, 1977 Aurand et al., 1977 Bruder et al., 1982 Bouzas et al., 1985). Allen and Humphries (1977) prepared two protein fractions from MFGM and found that oxidative activity resided almost entirely in the first fraction, devoid of phospholipids, but richer in Xanthine oxidoreductase. They proposed that the metalloprotein, and not 

The mechanism(s) by which Xanthine oxidoreductase exerts its prooxidant effect(s) is not fully understood. Hydrogen peroxide, resulting from oxidation of a suitable substrate by Xanthine oxidoreductase, could oxidize milk lipids. However, normal milk contains little or no substrate for the enzyme. A possible mechanism involving interaction between native and denatured Xanthine oxidoreductase in MFGM and lactoperoxidase or copper in milk serum has been proposed (Hill, 1979 Allen and Wreiden, 1982b). 

1 mg/kg Cu2+ was not inhibited by superoxide dismutase and catalase. When formate (an OH scavenger) was added to the milk, lipid oxidation was inhibited, suggesting that OH was the active pro-oxidant. Hill (1979) postulated that two major systems in milk catalyze lipid oxidation  

O in the membrane lipids in association with bound Cu2+ could make these reactions of some significance in lipid oxidation. 

---

Milk fat globule membrane (MFGM) emulsion was shown to enhance the absorption of epidermal growth factor (EGF) from the intestine, especially to intestinal lymph. The oral bioavailability of propanolol was shown to increase when administered in oleic acid and other lipid media. It is thought that the oleic acid forms an ion-pair with the drag and the entire complex is incorporated into chylomicrons. A further factor in the absorption enhancing effects may be that oleic acid per se stimulates chylomicron production. 

Phospholipids account for only 0.8% of milk lipids. However, they play a major role in milk due to their amphiphilic properties. About 65% of them are found in the milk fat globule membrane (MFGM), whereas the rest remain in the aqueous phase. Phosphatidyl choline, phosphatidyl etha-nolamine and sphingomyelin are the major phospholipids of milk, which together comprise about 90% of the total. Sterols are also a minor component, comprising about 0.3% of the fat cholesterol, being the principal sterol, accounts for over 95% of the total sterols. 

The concentration of phospholipids in the milk fat ranges from 0.5 to 1.0% of the total (Patton and Jensen, 1976 Table 1.1). About 60 to 65% of these phospholipids are associated with the intact milk fat globule membrane (MFGM). The remaining 35 to 40% are found in the aqueous phase associated with protein/membrane fragment material in solution, rather than still attached to the MFGM (Huang and Kuksis, 1967 Patton and Keenan, 1971). 

Engel Cl al. have attempted to enclose insulin in a W/O/W emulsion to improve intestinal absorption (63). These data are in agreement with those presented by Malsuzawa et al. who stated that W/O/W multiple emulsions stabilized by gelatin can improve ileal and colonic absorption of insulin (64). Recent studies have shown that the oral or intestinal absorption of vitamin A. vitamin D). and insulin was improved by administering them as milk fat globule membrane (MFGM) emulsions compared with the administration of simple solution or emulsions using synthetic emulsifiers (65). 

---