Milk serum proteins

Davies, D. T. 1974. The quantitative partition of the albumin fraction of milk serum proteins by gel chromatography. J. Dairy Res. 41, 217-228. 

Kannan, A. and Jenness, R. 1961. Relation of milk serum proteins and milk salts to the effects of heat treatment on rennet clotting. J. Dairy Sci. 44, 808- 822. 

In unhomogenized dairy cream the natural phospholipids contribute to the whipping properties of the cream. However, after homogenization the particle size of the fat globules decreases, and the total fat surface area increases. This means that the interfacial concentration of polar lipids decreases because milk serum proteins adsorb at the newly formed interfaces, and the whipping properties are lost. Consequently, additional polar lipids or emulsifiers are needed to obtain good whipping properties in most industrially manufactured products. 

Sharma, R., Dalgleish, D.G. 1994. Effects of heat treatments on the incorporation of milk serum proteins into the fat globule membrane of homogenised milk. J. Dairy Res. 61, 375-384. 

Sharma, S.K., Dalgleish, D.G. 1993. Interactions between milk serum proteins and synthetic fat globule membrane during heating of homogenized whole milk. J. Agric. Food Chem. 41, 1407-1412. 

Korycka-Dahl, M., Richardson, T. 1979. Photogeneration of superoxide anion upon illumination of bovine milk serum proteins with fluorescent light in the presence of riboflavin. J. Dairy Sci. 62, 183-188. 

Alexander, M., and Dalgleish, D.G. (2005). Interactions between denatured milk serum proteins and easein micelles studied by diffusing wave spectroscopy. Langmuir. 21, 11380... 

Needs, H.C., and A. Huitson, The Contribution of Milk Serum Proteins to the Development of Whipped Cream Structure, Ibid 10 353-360 (1991). 

Damianou, K., Kiosseoglou, V. (2006). Stability of emulsions containing a whey protein concentrate obtained from milk serum through carboxymethylcellulose complexation. Food Hydrocolloids, 20, 793-799. 

Initially, it was believed that milk contained only one type of protein but about 100 years ago it was shown that the proteins in milk could be fractionated into two well-defined groups. On acidification to pH 4.6 (the isoelectric pH) at around 30°C, about 80% of the total protein in bovine milk precipitates out of solution this fraction is now called casein. The protein which remains soluble under these conditions is referred to as whey or serum protein or non-casein nitrogen. The pioneering work in this area was done by the German scientist, Hammarsten, and consequently isoelectric (acid) casein is sometimes referred to as casein nach Hammarsten. 

About 20% of the total protein of bovine milk belongs to a group of proteins generally referred to as whey or serum proteins or non-casein nitrogen. Acid and rennet wheys also contain casein-derived peptides both contain proteose-peptones, produced by plasmin, mainly from /J-casein, and the latter also contains (glyco)macropeptides produced by rennets from K-casein. These peptides are excluded from the present discussion. 

The serum-protein binding ability, which varies between animals and is also influenced by the disease state of the animal, will also determine the free diffusible concentration. This, in turn, will have an effect on the elimination of drug residues as well as on their penetration in eggs or milk. This effect will be more pronounced for drugs with a higher tendency for protein binding such as sulfonamides, doxycycline, and cloxacillin (47). 

Babajimopoulos, M. and Mikolajcik, E. M. 1977. Quantification of selected serum proteins of milk by immunological procedures. J. Dairy Sci. 60, 721-725. 

A copper-binding protein, ceruloplasmin, which is a blood serum protein, has been demonstrated in milk by immunodiffusion techniques (Hanson et al. 1967 Poulik and Weiss 1975). It may be the enzyme ferroxidase (EC 1.16.3.1). 

Clegg, R. A. 1980. Activation of milk lipase by serum proteins Possible role in the occurrence of lipolysis in raw bovine milk. J. Dairy Res. 47, 61-70. 

Fractionation of milk and titration of the fractions have been of considerable value. Rice and Markley (1924) made an attempt to assign contributions of the various milk components to titratable acidity. One scheme utilizes oxalate to precipitate calcium and rennet to remove the calcium caseinate phosphate micelles (Horst 1947 Ling 1936 Pyne and Ryan 1950). As formulated by Ling, the scheme involves titrations of milk, oxalated milk, rennet whey, and oxalated rennet whey to the phenolphthalein endpoint. From such titrations, Ling calculated that the caseinate contributed about 0.8 mEq of the total titer of 2.2 mEq/100 ml (0.19% lactic acid) in certain milks that he analyzed. These data are consistent with calculations based on the concentrations of phosphate and proteins present (Walstra and Jenness 1984). The casein, serum proteins, colloidal inorganic phosphorus, and dissolved inorganic phosphorus were accounted for by van der Have et al (1979) in their equation relating the titratable acidity of individual cow s milks to the composition. The casein and phosphates account for the major part of the titratable acidity of fresh milk. 

Clarification by removal of casein with such agents as calcium chloride, acetic acid, cooper sulfate, or rennin has often been employed to obtain a serum more suitable for refractometric measurements. Obviously the composition, and hence the refractive index, of such sera will depend on the method of preparation. Furthermore, some of the serum proteins may be precipitated with the casein by some of the agents used, particularly if the milk has been heated. Refractive index measurements of such sera are not generally considered as satisfactory as freezing point measurements for detection of added water (David and MacDonald 1953 Munchberg and Narbutas 1937 Schuler 1938 Tell-mann 1933 Vleeschauwer and Waeyenberge 1941). Menefee and Overman (1939) reported a close relation between total solids in evaporated and condensed products and the refractive index of serum prepared therefrom by the copper sulfate method. Of course, a different proportionality constant would hold for each type of product. 

Munchberg, F. and Narbutas, J. 1937. Contribution to the refractometric investigation of protein-free milk serum. Milchwiss. Forsch. 19, 114-121. 

Porter, R. M. 1965. Fluorometric determination of protein in whole milk, skim milk and milk serum. J. Dairy Sci. 48, 99-100. 

Major proteins of globule and serum membranes are immunochemi-cally identical (Nielsen and Bjerrum 1977), and electrophoretic profiles of the proteins from either membrane are similar (Kitchen 1974). The major quantitative difference is the presence of higher amounts of a protein of Mr 85,000 in serum membrane fractions. In summary, the information suggests that milk serum membranes are related, but not identical, to milk lipid globule and plasma membranes. 

About 20% of milk protein is soluble in the aqueous phase of milk. These serum proteins are primarily a mixture of /3-lactoglobulin, a-lactalbumin, bovine serum albumin, and immunoglobulins. Each of these globular proteins has a unique set of characteristics as a result of its amino acid sequence (Swaisgood 1982). As a group, they are more heat sensitive and less calcium sensitive than caseins (Kinsella 1984). Some of these characteristics (Table 11.1) cause large differences in susceptibility to denaturation (de Wit and Klarenbeek 1984). 

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