Whey proteins 3-lactoglobulin

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... 

Study of heat denaturation of major whey proteins ((3-lactoglobulin or a-lactalbumin) either in separated purified forms, or in forms present in fresh industrial whey or in recomposed mixture respecting whey proportions has been recently carried out (Bertrand-Harb et al., 2002), indicating significant differences in their denaturation depending on pH,... 

RP-HPLC can be used to determine the extent of degradation of native whey proteins ( 3-lactoglobulin and a-lactalbumin) by enzymes and to study their kinetics of degradation by monitoring both the disappearance of a-lactalbumin and p-lactoglobuhn and the appearance of peptide products. " It can also be used to evaluate whether the chromatographic profile obtained is affected by... 

Whey protein Lactoglobulin, lactoalbumin Soluble under acid conditions. Emulsifying or foaming... 

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). 

In the case of cold-induced aggregation and gelation, two different types of gel microstructure, namely filamentous and particulate (Figure 2.1), have been obtained by adding different concentrations of a ferrous salt to solutions of pre-denatured p-lactoglobulin (the major whey protein). This substantial difference in microstructure turns out to have a major impact on the iron delivery, due to the different sensitivities of the structures to the relevant environmental conditions, such as pH and the presence of digestive enzymes. In particular, the filamentous gel micro-... 

Caseins are highly disordered proteins having rather limited secondary structure. This is mainly due to the unusually high proline content, which is fairly uniformly distributed along the polypeptide chain. This feature leads to an open extended structure of the casein molecules which differentiates them from the globular whey proteins like a-lactalbumin and (3-lactoglobulin. The caseins have been described as rheomorphic ... 

In contrast, the whey proteins are relatively small globular proteins. a-Lactalbumin represents about 20 % of the protein content of bovine whey (3.5 % of total bovine milk protein), and it is the principal protein in human milk (Brew and Grobler, 1992). Nanotube assembly has been discovered in some solutions containing a hydrolysed derivative of this protein. And it appears that the a-lactalbumin nanotube is unique in the sense that it is the only artificial nanotube that has so far been made from a food protein (Graveland-Bikker et al., 2004 Graveland-Bikker and de Kruif, 2006). As for p-lactoglobulin, it has the capacity under certain specific conditions to form nano-fibres in aqueous media (as can various other globular food proteins, such as ovalbumin, soy proteins, and bovine serum albumin) (van der Linden, 2006 Nicolai, 2007). 

We turn now to the other major whey protein, p-lactoglobulin. This is an acidic globular protein (p/= 5.1) with a molar mass of 18.4 kDa and a radius of about 2 nm (Aymard et al., 1999). The protein can form long semi-flexible fibrils when heated in solution at around or above its dena-turation temperature (60-80 °C) at pH = 2 and low ionic strength (Durand et al., 2002 Veerman et al., 2002, 2003a,b). (An example of the... 

Bikker, J.F., Anema, S.G., Li, Y., Hill, J.P. (2000). Rheological properties of acid gels prepared front heated milk fortified with whey protein mixtures containing the A, B and C variants of p-lactoglobulin. International Dairy Journal, 10, 723-732. 

Proteins of egg white denature more rapidly than those of whey protein concentrate (13, 34). However, isolated p-lactoglobulin from the whey concentrate was more susceptible to surface denaturation than egg white ovalbumin. These data suggest that whey contains substances that protect the proteins from surface denaturation and may account for the lower stability of whey protein concentrate foams than those of egg white protein. A balance between the disaggregation effect of select pH values and the tendency toward greater aggregation of proteins at higher heating temperatures were correlated closely with maximum foam stability (13, 15). 

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... 

Fluid milk contains approximately 3.5% protein (USDA, CFEI 1976). Casein, found only in milk, comprises about 82% of the total milk protein, and whey proteins, principally /3-lactoglobulin and a-lactalbumin, constitute the remaining 18% (Lampert 1975 Jonas et al. 1976). Casein, because of its excellent nutritional value, is used routinely as a reference protein to evaluate the quality of protein in other foods (Jonas et al. 1976 Hambraeus 1982). 

It has been reported that as2-casein forms disulfide bridges when heated with /3-lactoglobulin and can interfere with the ability of K-casein to bind to /3-lactoglobulin (Kinsella 1984 Kudo 1980B). Farah (1979) noted that the total amount of whey protein attached to casein increases as heat treatment is intensified, but that the ratio of whey proteins attached remains constant. 

McKenzie, H. A. 1971. Whey proteins and minor proteins (3-Lactoglobulins. In Milk Proteins Chemistry and Molecular Biology, Vol. 2. H.A. McKenzie (Editor). Academic Press, New York, pp. 257-330. 

A good example of its use applied to a protein associated with food chemistry is that of P-lactoglobulin. Ikeuchi et al. (2001) used ANS as a probe to follow P-lactoglobulin de-naturation under high pressure and its subsequent renaturation on release of pressure (Fig. B3.6.11). The denaturation was shown to be completely reversible at pH 2 but not at neutral pH, explaining why whey protein isolates subjected to high pressures form a gel at pH 7 but not at acid pH. 

Whey proteins /8-Lactoglobulin 8-17 18,205-18,363 5.35-5.49 Globular protein, containing one cysteine and two cystine residues Formation of dimers in pH range 5.2-7.5 octamerization may occur at pH 3.5-5.2... 

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.)...

GO Regester, GW Smithers. Seasonal changes in the /3-lactoglobulin, a-lactalbumin, glycomacro-peptide, and casein content of whey protein concentration. J Dairy Sci 74 796-802, 1991. 

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