Skim milk membranes

Janolino, V. G. and Swaisgood, H. E. 1984. Isolation, solubilization, fractionation by electrofocusing, and immobilization of skim milk membranes. J. Dairy Sci. 67, 1161-1168. 

The distribution and fatty acid composition of phospholipids in skim milk are similar to those in the MFGM. This has led to the suggestion that these membrane-associated constituents originate from a common cellular source and that the skim milk membranes, which contain much of the skim milk phospholipid pool, may be shed MFGM (for review, see Keenan and Dylewski, 1995). This assumption remains to be tested critically. 

Membrane Sep r tion. The separation of components ofhquid milk products can be accompHshed with semipermeable membranes by either ultrafiltration (qv) or hyperfiltration, also called reverse osmosis (qv) (30). With ultrafiltration (UF) the membrane selectively prevents the passage of large molecules such as protein. In reverse osmosis (RO) different small, low molecular weight molecules are separated. Both procedures require that pressure be maintained and that the energy needed is a cost item. The materials from which the membranes are made are similar for both processes and include cellulose acetate, poly(vinyl chloride), poly(vinyHdene diduoride), nylon, and polyamide (see AFembrane technology). Membranes are commonly used for the concentration of whey and milk for cheesemaking (31). For example, membranes with 100 and 200 p.m are used to obtain a 4 1 reduction of skimmed milk. 

Ultrafiltration. Membranes are used that are capable of selectively passing large molecules (>500 daltons). Pressures of 0.1—1.4 MPa (<200 psi) are exerted over the solution to overcome the osmotic pressure, while providing an adequate dow through the membrane for use. Ultrafiltration (qv) has been particulady successhil for the separation of whey from cheese. It separates protein from lactose and mineral salts, protein being the concentrate. Ultrafiltration is also used to obtain a protein-rich concentrate of skimmed milk from which cheese is made. The whey protein obtained by ultrafiltration is 50—80% protein which can be spray dried. 

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. 

After preincubation of the membrane with TBST containing 5% skim milk for 60 min, the membrane was incubated with 1 4,000 anti-HaloTag rabbit IgG antibody (Promega) in TBST containing 1% skim milk for 60 min. 

Depending on the preparative method used, the membrane may or may not contain skim-milk proteins (i.e. caseins and whey proteins) if the membrane has been damaged prior to isolation, it may contain considerable amounts of these proteins. The membrane contains unique proteins which do not occur in the skim-milk phase. Many of the proteins are glycoproteins and contain a considerable amount of carbohydrate (hexose, 2.8-4.15% hexosamine, 2.5-4.2% and sialic acid, 1.3—1.8%). 

Kitchen, B. J. 1974, A comparison of the properties of membranes isolated from bovine skim milk and cream. Biochim. Biophys. Acta 356, 257-269. 

Plantz, P. E. and Patton, S. 1973. Plasma membrane fragments in bovine and caprine skim milks. Biochem. Biophys. Acta 291, 51-60. 

Wooding, F.B.P. 1974. Milk fat globule membrane material in skim milk. J. Dairy Res. 41, 331-337. 

Milk containing fat globules with a natural fat globule membrane can be activated, deactivated, and reactivated by proper changes in temperature. However, some loss of activity will occur upon repeated activation (Wang and Randolph 1978). The phenomenon of temperature activation is found only when the fat globules have their natural layer of adsorbed materials. Neither homogenized milk, nor emulsions of tributyrin, nor butter oil emulsified in skim milk can be activated in this manner. 

Various other investigators have isolated PAS-0 or fragments of this glycoprotein from either milk lipid globule membranes (Fischer et al. 1984) or human skim milk (Ormerod et al 1983). The preparation of Ormerod et al., called "epithelial membrane antigen," was hetero-disperse and appears to consist of proteolytic cleaved peptides of the... 

Anderson, M., Brooker, B. E., Andrews, A. T. and Alichanidis, E. 1975. Membrane material in bovine skim-milk from udder quarters infused with endotoxin and pathogenic organisms. J Dairy Res. 42, 401-417. 

Demineralization of UF whey retentate as compared to UF whey permeate is generally slowed down by salt and/or proteins that build up onto and in the membranes (Perez et al., 1994). Finally, in the case of skim milk the aim of the ED process is not only to reduce the overall ash content, but also to increase the calcium/phosphate ratio to about 0.77 in skim milk powder used in infant formula (Batchelder, 1987), this goal being much easily achievable by replacing the conventional membranes with selective ones (Andres et al., 1995). 

Andres, L.J., Riera, F.A., and Alvarez, R. 1995. Skimmed milk demineralization by electrodialysis Conventional versus selective membranes. J. Food Eng. 26, 57-66. 

Bazinet, L., Ippersiel, D., Montpetit, D., Mahdavi, B., Amiot, J, and Lamarche, F. 2000a. Effect of membrane permselectivity on the fouling of cationic membranes during skim milk electroacidification. J. Membr. Sci. 174, 97-110. 

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