Amino lactoglobulin

Casein. Milk contains proteins and essential amino acids lacking in many other foods. Casein is the principal protein in the skimmed milk (nonfat) portion of milk (3—4% of the weight). After it is removed from the Hquid portion of milk, whey remains. Whey can be denatured by heat treatment of 85°C for 15 minutes. Various protein fractions are identified as a-, P-, and y-casein, and 5-lactoglobulin and blood—semm albumin, each having specific characteristics for various uses. Table 21 gives the concentration and composition of milk proteins. 

The caseins are often considered to be rather hydrophobic molecules. However, consideration of the amino acid composition indicates that they are not particularly so in fact, some are more hydrophilic than the whey protein, /3-lactoglobulin (Table 4.2). However, the caseins do have high... 

Preaux, G., Braunitzer, G., Schrank, B. and Stangl, A. 1979. The amino acid sequence of goat d-lactoglobulin. Hoppe-Seyler s Z. Physiol. Chem. 360S, 1595-1604 (German). 

Townend, R., Herscovits, T. T. and Timasheff, S. N. 1969. The state of amino acid residues in /3-lactoglobulin. Arch. Biochem. Biophys. 129, 567-580. 

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). 

Titration curve of /3-lactoglobulin. At very low values of pH (<2) all ionizable groups are protonated. At a pH of about 7.2 (indicated by horizontal bar) 51 groups (mostly the glutamic and aspartic amino acids and some of the histidines) have lost their protons. At pH 12 most of the remaining ionizable groups (mostly lysine and arginine amino acids and some histidines) have lost their protons as well. 

Chevalier el al,163 glycated /j-lactoglobulin (0.217 mM) with equimolar amounts of ribose, arabinose, galactose, glucose, rhamnose, or lactose at 60 °C in 0.1 M phosphate buffer (pH 6.5) for 72 h, strictly anaerobically, the average number of amino groups modified being 11.0, 8.8, 6.7, 6.6, 6.5, and 5.5, respectively. 

Bertrand-Harb, C., Charrier, B., Dalgalarrondo, M., Chobert, J.-M., and Haertle, T. 1990. Condensation of glycosidic and aromatic structures on amino groups of (3-lactoglobulin B via reductive alkylation. Solubility and emulsifying properties of the protein derivatives. Lait 71, 205-215. 

Studies on bovine whey proteins. IV. Amino acid analyses of crystalline / -lactoglobulins and lactalbumin by quantitative paper chromatography. Arch. Biochem. Biophys., 55, 315 (1955). With K. W. Weiss. 

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