Whey proteins Immunoglobulins

Casein can be precipitated from solution by any of several salts. Addition of (NH4)2S04 to milk to a concentration of 260 g 1 1 causes complete precipitation of the casein together with some whey proteins (immunoglobulins, Ig). MgS04 may also be used. Saturation of milk with NaCl at 37°C precipitates the casein and Igs while the major whey proteins remain soluble, provided they are undenatured. This characteristic is the basis of a commercial test used for the heat classification of milk powders which contain variable levels of denatured whey proteins. 

Particularly labile milk proteins are the whey protein immunoglobulins, serum albumin, p-lactoglobuHn and a-lactalbumin. During milk pasteurisation ° at a temperature of 72-74 °C (20-40 s), about 50-90% of whey proteins are denatured and most... 

Chemical reactions Polymerization of casein and whey proteins are due to some kind of chemical reactions. The different proteins as found in the supernatant of milk after precipitation at pH 4.6 are collectively called whey proteins. These globular proteins are more water soluble than caseins and are subject to heat dena-turation. Denaturation increases their water-binding capacity. The principal fractions are P-lactoglobulin, a-lactalbumin, bovine serum albumin (BSA), and immunoglobulins (Ig). 

One of the important developments in dairy technology in recent years has been the fractionation of milk into its principal constituents, e.g. lactose, milk fat fractions and milk protein products (caseins, caseinates, whey protein concentrates, whey protein isolates, mainly for use as functional proteins but more recently as nutraceuticals , i.e. proteins for specific physiological and/or nutritional functions, e.g. lactotransferrin, immunoglobulins). 

Casein is synthesized in the mammary gland and is found nowhere else in nature. Some of the whey proteins (/Mactoglobulin and a-lactalbumin) are also synthesized in the mammary gland, while others (e.g. bovine serum albumin and the immunoglobulins) are derived from the blood. 

The lactoglobulin fraction consists mainly of immunoglobulins (Ig), especially IgGj, with lesser amounts of IgG2, IgA and IgM (section 4.10). The lactalbumin fraction of bovine milk contains three main proteins, / -lactoglobulin (j8-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... 

Figure 9.14 The denaturation of the total ( ) and individual whey proteins in milk, heated at various temperatures for 30 min /l-lactoglobulin ( ), a-lactalbumin (O). proteose peptone ( ), immunoglobulins (A), and serum albumin ( ) (from Webb and Johnson, 1965).

The proteins of milk fall into several classes of polypeptide chains. These have been delineated most completely in bovine milk, and a system of nonmenclature has been developed for them (Chapter 3 Eigel et al. 1984). One group, called caseins, consists of four kinds of polypeptides asr, as2-. and 3-, and k- with some genetic variants, post translational modifications, and products of proteolysis. Almost all of the caseins are associated with calcium and phosphate in micelles 20-300 fim in diameter (see Chapter 9). The other milk proteins, called whey proteins, are a diverse group including /3-lactoglobulin, a-lactalbumin, blood serum albumin, and immunoglobulins (Chapter 3). Almost all... 

Electrophoretic Methods. Little use has been made of electrophoretic techniques for the fractionation of the whey proteins. Column isoelectric focusing has been used to fractionate further the crude immunoglobulin fraction obtained by Smith s procedure (Josephson et al. 1972). Two major peaks, a shoulder, and two minor peaks were obtained, but no attempt was made to identify the components in the peaks. 

Fig. 1 Ion-exchange chromatography of whey proteins on a Mono Q column using different buffer systems (A) a 100-/rl sample of total whey protein dissolved in 0.05 M sodium acetate buffer, pH 6.3, was injected into the column and eluted with a 0.05-0.7 M sodium acetate linear ionic-strength gradient for (B) and (C) the sample was dissolved in 0.02 M Tris-HCl, pH 7 (B) or pH 8 (C), and a 0-0.35 M NaCl linear gradient was applied. Key 1 immunoglobulins, 2 a-lactalbumin, 3 bovine serum albumin, 4 /3-lac-toglobulin B, 5 /3-lactoglobulin A. (From Ref. 37.)...

Whey proteins contain several major allergens, such as P-lg and a-la, and minor constituents, e.g., lactoferin, bovine serum albumin (BSA), and immunoglobulins. In this fraction, proteolytic fragments of casein and fat globule membrane proteins can occur during analysis. 

Li-Chan, E., Kwan, L., and Nakai, S. (1990). Isolation of immunoglobulins by competitive displacement of cheese whey proteins during metal chelate interaction chromatography. J. Diary Sci. 73, 2075-2086. 

Whey proteins are consisted of ]S-lactoglobulin, a-lactalbumin, proteose peptone, serum albumin, immunoglobulins and lactoferrin. In contrast with caseins, they are... 

Contrary to other whey proteins, a Fe " ion is present in lactoferrin molecule [3]. Similarly to immunoglobulins, it has the antimicrobial character [46]. Whey is appropriate for extraction of lactoferrin and cation-exchange chromatography is proposed for its purihcation. Heat treatment at pH 4.0 does not denature the protein therefore, this pH is suitable for its pasteurization. Recently, some beneficial aspects of lactoferrin on human s health have been regarded. Its exceptional properties such as antiinfective, anticancer, antioxidant and antimicrobial activities enhance its utility in pharmaceutical and food industries. Remarkably, lower pH values (2-3) enhance its antibacterial activity. The results of clinical studies about positive effects of lactoferrin on human and animals health have been published [49]. 

Milk proteins soluble proteins present in milk, consisting of caseins and whey proteins. The chief caseins are a, p and K-casein. The most important whey proteins are p-Iactoglobulin, a-lactalbumin and lactoferrin. In addition, milk contains several enzyme proteins, e.g. lactoperoxidase, xanthine oxidase and immunoglobulins. IgG, IgA and IgM. These immunoglobulins are absorbed directly and without cleavage by the intestine of the infant, and provide it with passive immtmity against those pathogens to which the mother is immune. 

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