182 Chapter 8
In the pH range 4 to 5, β - lactoglobulin is
insoluble in aqueous solutions with low salt
concentration. During extensive demineral-
ization of whey, as achieved by ion exchange,
conditions may lead to a loss of protein solu-
bility (de Wit 1981 ). Protein solubility is rel-
evant in the formulation of whey - containing
beverages and is affected by pH, protein con-
centration, and concentrations of salts and
other ingredients such as sugars. In general,
sugars may protect proteins against the loss of
solubility by heat treatment. The least heat -
sensitive pH range of the whey proteins lies
between 2.5 and 3.5. Whereas the susceptibil-
ity of whey proteins to denaturation is largely
determined by the pH of the solution, the
extent of protein aggregation depends on
the presence of calcium salts (de Wit 1981 ).
Heating is universally applied during the
industrial processing of foods. The increase
in heat sensitivity of proteins in the presence
of calcium is believed to be due to the forma-
tion of ionic intermolecular cross links that
increase the proximity of the molecules. With
α - lactalbumin, however, calcium is used in
the formation of intramolecular ionic bonds
that tend to make the molecule resistant to
thermal unfolding (Kilara 2008 ).
β - Lactoglobulin contains two disulfi de
bonds and one sulfhydryl group. It is through
thiol/disulfi de interchanges that protein
aggregation is initiated. It is also through
heat - induced sulfhydryl and disulfi de inter-
actions of α - lactalbumin with β - lactoglobulin
that the heat sensitivity of α - lactalbumin is
increased (de Wit 1981 ).
β - Lactoglobulin is not present in human
milk. Treatments to reduce the allergenicity
of bovine milk generally involve the hydro-
lysis of β - lactoglobulin.Processing Techniques
In the processing of whey streams one objec-
tive is to reduce the water content of the
product stream to recover dairy solids and
preserve them for further use in formulatedherds usually produce milk for only 8 to 9
months during a typical milking season.
Seasonal changes in the milk composition
result from variation in the nutritional
intake of the milking herd. During the last
three months of lactation, the α - lactalbumin
content of whey declines and the contents
of β - lactoglobulin and glycomacropeptide
contents are maximized (Regester and
Smithers 1991 ).Chemistry of Whey Proteins
The whey proteins found in whey streams
include globular proteins ( β - lactoglobulin,
α - lactalbumin, and bovine serum albumin),
immunoglobulins (Ig - G, Ig - A, and Ig - M),
some minor proteins (lactoperoxidase, lacto-
ferrin, and lysosyme), and polypeptides
(proteose - peptone 3, and proteose - peptone 5)
and glycomacropeptides (present in rennet
casein or cheese whey only) (Swaisgood
1996 ). The functional properties of whey
ingredients are defi ned by the physico -
chemical properties of the whey proteins that
contribute to the desired characteristics in
food products (Mangino 1984 ). The confor-
mation and functional properties of whey
proteins are interrelated and governed by
changes in the globular folded structure of
the molecule (de Wit 1989 ). In order to
understand the behavior of whey proteins in
food systems, knowledge of both the physico -
chemical properties of individual proteins
and the effects of environmental factors
(process history, product composition,
thermal treatment, etc.) is required (Regester
et al. 1992 , De la Fuente et al. 2002a ). In addi-
tion to physico - chemical properties, various
proteins present in whey have important bio-
logical properties (Harper 2000, 2001 ).
β - lactoglobulin comprises more than 50%
of the whey proteins in bovine milk. Because
of its prevalence in bovine milk, the proper-
ties of β - lactoglobulin determine the proper-
ties of whey protein concentrates (Abd
El - Salam et al. 2009 ).