5-Lactoglobulin

It was recognized 60 years ago that whey prepared by any of the above methods contained two well-defined groups of proteins which could be fractionated by saturated MgS04 or half saturated (NH4)2S04 the precipitate (roughly 20% of total N) was referred to as lactoglobulin and the soluble protein as lactalbumin. 

The lactoglobulin fraction consists mainly of immunoglobulins (Ig), especially IgGj, with lesser amounts of IgGj, IgA and IgM (section 4.10). The lactalbumin fraction of bovine milk contains three main proteins, p-lactoglobulin (jS-lg), a-lactalbumin (a-la) and blood serum albumin (BSA), which represent approximately 50, 20 and 10% of total whey protein, respectively, and trace amounts of several other proteins, notably lactotrans-ferrin, serotransferrin and several enzymes. The whey proteins of sheep, goat 

Since the 1930s, several methods have been developed for the isolation of homogeneous whey proteins, which have been crystallized (McKenzie, 1970, 1971). Today, homogeneous whey proteins are usually prepared by ion-exchange chromatography on DEAE cellulose. 

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Fig. 42. LS plots for 0-lactoglobulin A (concentration c2) dissolved in water/2-chloroethanol mixtures of compositions (% voL/vol. of 2-chloroethanol) indicated in (a). Plots (a) and (b) correspond to constant molality m3 and constant chemical potential JU3 respectively of the organic solvent135 The primary data points have been omitted for clarity...

Figures 42 illustrate forcibly how a variety of apparent molecular weights (M ) of 0-lactoglobulin A is obtained from LS plots in aqueous 2-choroethanol mixtures of various composition when the molality of the alcohol is kept constant135. If the chemical potential of the alcohol is maintained constant, a common intercept yielding the correct molecular weight, M2, is obtained for all the solvent mixtures135. ...

Grosclaude, F., Mahe, M.-F., Mercier, J.-C., Bonnemarie, J. and Tessier, J. H. 1976A. Polymorphism of the milk proteins of Nepalese bovines. I. The Yak and biochemical characterization of two new variants 0-lactoglobulin D (Yaki and usi-casein E. Ann. Genet. Sel. Anim. 8, 461-479 (French). 

Mild heat treatments (up to 60 °C) mainly affect hydrophobic bonding within and between proteins. Such effects are important in those milk proteins which have large hydrophobicities, such as 0-casein and 0-lactoglobulin (de Wit and Klarenbeek 1984 Payens and Vreeman 1982). 

Elfagm, A. A. and Wheelock, J. V. 1978A. Heat interaction between a-lactalbumin, 0-lactoglobulin and casein in bovine milk. J. Dairy Res. 61, 159-163. 

Smits, P. and Brouwershaven, J. 1980. Heat-induced association of 0-lactoglobulin and casein micelles. J. Dairy Res. 47, 313-325. 

Proteins. Crystalline lysozyme, bovine serum albumin, ribonucle-ase, and pepsin were obtained from the Armour Laboratories and crystalline 0-lactoglobulin was prepared from skimmed milk. a-Lactalbu-min was obtained from W. G. Gordon of this laboratory. Crystalline ovalbumin and human serum albumin were obtained from Nutritional Biochemical Corp. and purified pigskin gelatin from the Eastman Kodak Co. 

Other proteins similarly studied are bovine serum albumin 5, 6, 36, 65, 67) and ovalbumin 65) actin 61) fumarase 43) a-chymotrypsin 44) lysozyme 59, 64) arachin 5) 0-lactoglobulin and /c-casein 45) 7-globulin 56) ribonuclease 24, 35, 68) glutamic dehydrogenase (7) soybean trypsin inhibitor 15, 57) and pepsinogen 14, 21, 58). 

Despite the relatively low level of )0-lactoglobulin in the whole milk (2.5% based on dry weight of milk solids) the protein in the deposits contained almost 50% of the solids dry weight. A large proportion of the mineral deposit is calcium phosphate. Caseins in deposits were reported as 18% [Tissier et al 1984]. 

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