Membranous Material of Bovine Milk Fat Globules. I. Comparison of Membranous Fractions Released by Deoxycholate and by Churning^*

Abstract

20,w, of ca. 13 S. Similar lipoproteins were isolated, but in smaller amounts, from untreated buttermilk, a source of membranous material used widely by previous investigators. However, DOC released water-soluble lipoproteins from buttermilk in amounts comparable to those released from intact fat globules. These findings led to the view that the membrane surrounding the milk fat globule consists of two types of lipid-protein complexes, approximately equal in amount, and distinguishable on the basis of their solubility in water.The water-soluble lipoproteins are considered to be adsorbed on a water-insoluble matrix, composed of lipids and proteins, bordering the triglyceride core of the fat globule. layer in turn is surrounded by proteins attached to these hydrophilic groups.Another concept of the structure of the milk fat globule was advanced by Morton (1954), who observed, with the aid of an electron microscope, small particles adhering to both intact and collapsed globules. Morton suggested that "the fat globule in milk is surrounded by a continuous protein membrane onto which microsomal particles may be adsorbed." He termed these particles "milk microsomes."According to Morton's concept of the membrane, it seems possible that the adhering particles could be released without disrupting the remaining portion of the membrane. This paper describes a preparative procedure effective in releasing lipoprotein particles from intact fat globules and reports some chemical and physical properties of the released lipoproteins. The results obtained by this new approach are compared with data obtained from fractions prepared by the churning technique, widely employed in past studies of the membrane of the milk fat globule. Preliminary ConsiderationsThe apparent composition of the membranous material of the milk fat globule varies with the method of preparation. Much of the present knowledge of the membrane has been derived from studies made on buttermilk prepared as follows. The milk is centrifuged first in a cream separator to concentrate the fat globules in the cream. The cream is washed to remove milk plasma constituents that are not an integral part of the S. HAYASHI AND L. M. SMITH

Technical difficulties and future challenges in isolating membrane material from milk fat globules in industrial settings – A critical review

“…They also found that cream washing with salt solutions caused more coalescence of fat globules, and thus, a higher amount of MFGM proteins was obtained with deionised water. Silva et al, 1980;Evans & Pillinger, 1973;Fong et al, 2007;Kanno & Kim, 1990;Le et al, 2009;Mather, 1978;Nielsen & Bjerrum, 1977;Rombaut et al, 2006;Shimizu et al, 1978;Swope & Brunner, 19684 Dowben et al, 1967Erickson et al, 1964;Fink & Kessler, 1985;Hayashi & Smith, 1965;Kanno et al, 1975 Kanno et al, 1975;Kanno & Kim, 1990;Lamothe et al, 2008;Le et al, 2009;Newman & Harrison, 1973;Swope & Brunner, 1968;Yamauchi et al, 1978 Skim milk ultrafiltrate Britten et al, 2008;Fink & Kessler, 1985 Simulated milk ultrafiltrate Le et al, 2009;Morin et al, 2007a 1.5 g KCl L À1 Le et al, 2009;Rombaut et al, 2006 0 Anderson & Cheeseman, 1971;Erickson et al, 1964;Hayashi & Smith, 1965 Phosphate buffer, pH 6.8 Nielsen & Bjerrum, 1977 50 mM phosphate, 0.15 M NaCl, pH 6.8 Le et al, 2009 10 mM TriseHCl, pH 7.5 Mather, 1978 10 mM Tris, 0.14 M NaCl, pH 7.5 Da Silva et al, 1980…”

The milk-fat globule membrane

“…This is the converse of triglyceride :phospholipid ratios observed in fractions of MFGM prepared by other methods (13,46,67,175). Deoxycholate treatment of washed cream releases about 50 % of the membrane, apparently without disrupting the fat globule (io, 13,67).…”

“…Walstra (183) pointed out that the triglyceride content of deoxycholate (DOC) soluble MFGM is less than its phospholipid content (67). This is the converse of triglyceride :phospholipid ratios observed in fractions of MFGM prepared by other methods (13,46,67,175).…”

“…Early studies (46,66,67,70) revealed that MFGM components can be solubilized using a variety of different methods and the resulting lipoprotein constituents are found to be heterogenous in lipid and protein content. Hayashi & Smith (67) proposed that these lipoproteins exist within a 2-layered membrane where an insoluble lipoprotein layer borders the triglyceride core and provides a structural matrix on to which soluble lipoproteins are adsorbed.…”

“…There has been no systematic investigation of breed effects on overall MFGM composition, although values for MFGM composition in the literature include different breeds (43,67,78,136,174,175, for example). There are indications from electrophoretic studies (40) that differences in the proportions of some minor proteins, particularly in the higher mol.…”