Casein, Caseinates, and Milk Protein Concentrates 1737.0, but reaches a maximum value at about
pH 9.5 (Carr et al. 2002 ).
Solutions of caseinate form gels on acidi-
fi cation (Braga et al. 2006 ) due to the forma-
tion of a protein network. An example of the
microstructure of acid - induced gelation of
sodium caseinate is shown in Figure 7.4 ,
where a protein network (appears in white)
is formed. Recently, reversible cold gelation,
induced by salt addition and refrigeration, of
sodium caseinate solution was also reported
(Carr and Munro 2004 ). Gelation can also be
achieved, for example, via cross linking the
protein by addition of transglutaminase
(Dickinson and Yamamoto 1996 ).
Milk protein concentrates: Milk protein
concentrate dispersions have lower viscosity
than sodium caseinate and calcium caseinate
dispersions at an equivalent protein concen-
tration (Zwijgers 1992 ). This is related in part
to caseins having a higher capacity to bind
water than whey proteins. Micellar casein
holds approximately 3.3 g water/g casein and
undenatured whey protein holds approxi-
mately 0.4 g water/g protein (Walstra and
Jenness 1984 ).2000 ). It increases the protein content of
cheese milk, thereby improving the quality of
cheese and increasing the capacity of a cheese
plant (Kelly et al. 2000 ). Garem et al. (2000)
described the production of a micellar casein
milk powder using a combination of micro-
fi ltration and ultrafi ltration with improved
cheese yielding capacity. Mozzarella cheese
yield was 7.3% higher in comparison to
control cheese prepared from fresh milk. A
three - stage microfi ltration process that
removes 95% of the whey proteins from skim
milk prior to cheese making has also been
developed with the potential for continuous
production of cottage cheese without acid
whey production (Nelson and Barbano 2005 ).
Caseinate: As a consequence of their
hydration and protein - protein interactions,
solutions of caseinates exhibit very high vis-
cosity. The viscosity increases rapidly
(usually exponentially for sodium caseinate)
with concentration. However, the viscosity
of calcium caseinate is much lower than
that of sodium caseinate as it exists in
water as a colloidal dispersion (Southward
1985 ). Caseinate solutions exhibit Newtonian
behavior at low protein concentrations and
a pseudoplastic behavior at high concentra-
tions, and are thixotropic at high shear rates.
The viscosity of caseinate solutions
also increases with salt concentration and
decreases with temperature. Carr et al. (2002)
reported that the addition of monovalent
cations (K^ +^ , Na^ +^ , and NH 4 +^ ) exponentially
increased the viscosity of sodium caseinate
solutions due to the competition of the salt
for water, resulting in an effective increase in
protein concentration. However, divalent
cations (Ca^ +^ , Mg^ +^ , and Zn^ +^ ) increased the
viscosity of sodium caseinate solution to a
maximum, and then decreased it, due to
protein aggregation. The viscosity of sodium
caseinate also strongly depends on pH, with
a minimum at pH 7.0 and higher viscosity
at low pH (2.5 to 3.5) than at neutral pH
(Mulvihill 1992 ). The viscosity is not mark-
edly affected by the pH in the range of 6.5 to
Figure 7.4. Confocal micrograph of 5% sodium
caseinate gel induced by the addition of 2% glucono -
δ - lactone at 30 ° C for 3 hours. Bar scale represents
50 μ m; inset 5 μ m.