224 DAIRY CHEMISTRY AND BIOCHEMISTRY
properties and applications have been thoroughly described (e.g. Marshall,
1982; Morr, 1989; de Wit, 1989a, b).
The presence of even a low level of lipids impairs the functionality of
WPCs and reduces flux rates during UF processing. Both problems are
minimized by clarifying the whey prior to UF, e.g. by adding CaC1, to whey
(to 1.2gI-'), adjusting the pH to 7.3 and heating to 50°C; the flocculent
calcium phospholipoprotein complexes formed are allowed to settle and the
clear supernatant siphoned off, or removed by centrifugation or microfiltra-
tion.
Whey proteins complex with, and are precipitated by, several polyionic
compounds which may be used to prepare WPCs (see Marshall, 1982). The
most effective of these are polyphosphates which can be removed from the
resolubilized protein by precipitation with Ca2 +, electrodialysis, ion-ex-
change or gel filtration. Polyphosphate-precipitated WPCs are commercial-
ly available.
The use of ion-exchange resins (Figure 4.41) offers an effective method for
the preparation of high-quality whey protein products, referred to as whey
protein isolates (WPI), containing 90-95% protein (see Marshall, 1982;
Mulvihill, 1992). Although the functional properties of WPI are superior to
those of WPCs on an equiprotein basis (due to lower levels of lipids, lactose
and salts), their production is rather limited, due to higher production costs.
Fractionation of whey proteins. Techniques for the isolation of individual
whey proteins on a laboratory scale by salting-out, ion-exchange
chromatography and/or crystallization have been available for about
40 years. Owing to the unique functional, physiological or other biological
properties of many of the whey proteins, there is an economic incentive for
their isolation on an industrial scale. For example, p-lg, the principal whey
protein in bovine milk, produces better thermoset gels than a-la. However,
human milk does not contain p-lg, which is the most allergenic of the bovine
milk proteins for the human infant; therefore, a-la would appear to be a
more appropriate protein for the preparation of infant formulae than total
whey protein.
A number of methods have been developed for the separation of x-la and
B-lg (Figure 4.42). Probably the most commercially feasible of these exploits
the low heat stability of calcium-free x-la to precipitate it from whey, leaving
p-lg, BSA and Ig in solution. x-La loses its calcium on acidification to about
pH 5.0, aggregates on heating to about 55°C and can be recovered by
centrifugation, filtration or microfiltration.
a-La and B-lg are insoluble in pure water at their isoelectric points
(around pH 5); p-lg requires a higher ionic strength for solubility than a-la,
a characteristic which may be exploited to fractionate a-la and p-lg. When
UF-concentrated whey is acidified to pH 4.65 and demineralized by elec-