Milk fat globules

In milk fat, cholesterol is associated with Hpoproteins in the milk fat globule. It is also a component of animal membranes and controls rigidity and permeabihty of the membranes. Cholesterol has interesting surface properties and can occur in Hquid crystalline forms. Plants contain sterols such as P-sitosterol [83-46-5] (4b) or stigmasterol [83-48-7] (4c). Their functions in plant metaboHsm are not yet well understood. Analysis of sterols has proven useful for detection of adulteration of edible fats (9). 

Fluorescent probes are divided in two categories, i.e., intrinsic and extrinsic probes. Tryptophan is the most widely used intrinsic probe. The absorption spectrum, centered at 280 nm, displays two overlapping absorbance transitions. In contrast, the fluorescence emission spectrum is broad and is characterized by a large Stokes shift, which varies with the polarity of the environment. The fluorescence emission peak is at about 350 nm in water but the peak shifts to about 315 nm in nonpolar media, such as within the hydrophobic core of folded proteins. Vitamin A, located in milk fat globules, may be used as an intrinsic probe to follow, for example, the changes of triglyceride physical state as a function of temperature [20]. Extrinsic probes are used to characterize molecular events when intrinsic fluorophores are absent or are so numerous that the interpretation of the data becomes ambiguous. Extrinsic probes may also be used to obtain additional or complementary information from a specific macromolecular domain or from an oil water interface. 

These assumptions were confirmed by the electrophoresis study of the washed creams. Electrophoresis of purified fat globules is a convenient method to characterize and quantify proteins adsorbed at the oil-water interface [35]. Electrophoretic data indicate that no casein, nor whey proteins, were adsorbed at the surface of raw-milk fat globule. Upon homogenization, caseins adsorbed preferentially at the lipid-water interface. In this case, bound a-lactalbumin accounted for 16% of the total interfacial proteins. Heat treatment also induced the interaction of proteins with the fat globules. The amount of bound proteins (per mg of lipids) for heated raw milk was half that for homogenized milk. 

Skimming fresh whole milk allowed us to obtain milk fat globules with natural membranes that were blended at a concentration of 35 g/L with hydrated skim milk powder (35g/L). This reconstituted milk was coded CREAM. 

TABLE 1 Average Diameter of the Natural Milk Fat Globules and Emulsified Milk Fat Droplets Stabilized by Different Fat-Water Interfaces in Reconstituted Milks... 

Reconstituted milks with natural milk fat globules (CREAM) or emulsified milk fat droplets stabilized by jS-casein (BCAS), /i-lactoglobulin 5g/L (BLG5), skim milk proteins (MP). 

Epithelial Membrane Antigen (EMA)/Milk Fat Globule Protein (MEG)... 

Lactadherin is a glycoprotein produced by mammary epithelial cells during lactation and associated with the milk fat globule membrane (Newburg et ah, 1998). Its concentration in milk peaks at 0.139 mg/ml immediately postpartum and declines thereafter (reviewed by Kvistgaard et ah, 2004). It has been reported to bind to human Rotavirus,... 

Peterson, J. A., Patton, S., and Hamosh, M. (1998). Glycoproteins of the human milk fat globule in the protection of the breast-fed infant against infections. Biol. Neonate 74, 143-162. 

Schroten, H., Hanisch, F. G., Plogmann, R., Hacker, J., Uhlenbruck, G., Nobis-Bosch, R., and Wahn, V. (1992). Inhibition of adhesion of S-fimbriated Escherichia coli to buccal epithelial cells by human milk fat globule membrane components A novel aspect of the protective function of mucins in the nonimmunoglobulin fraction. Infect. Immun. 60,2893-2899. 

King, N. "The Milk Fat Globule Membrane", Comm. Agr. Bur., Farnham Royal, Bucks, England, 1955. 

Table 3.9 Gross composition of the milk fat globule membrane...

Table 3.10 Composition of bovine milk fat globule membranes...

Table 3.12 Enzymatic activities detected in bovine milk fat globule membrane preparations...

Figure 3.18 Schematic representation of a trilaminar cell membrane which is derived from the apical membrane of the mammary cell and forms the outer layer of the milk fat globule membrane following expression from the mammary cell, but which is more or less extensively lost on ageing. 1, phospholipid/glycolipid 2, protein 3, glycoprotein.

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