172 Chapter 7
Viscosity and Gelation
The ability of proteins to build viscosity and
to gel enables them to be used in a variety of
applications. Functional tests that examine
the properties of the proteins are sometimes
used to screen protein - based ingredients for
specifi c applications (Ennis and Mulvihill
1999 ).
Casein: The most important application
of casein - based products is in cheese making
and cheese analogues (processed cheese), in
which the casein ’ s ability to form gel net-
works is used. Rennet casein is the primary
protein source used in mozzarella cheese
analogues due to its desired sensory attri-
butes (pale color, bland fl avor) and superior
functionality (fi rmness, stretchability, shred-
dability, emulsifi cation and melt) over alter-
nate protein sources (Aimutis 1995 , Ennis
and Mulvihill 1997 ).
Acid casein has been shown to display
useful properties in baked goods. For
example, an aggregated acid casein - based
ingredient fortifi ed with calcium has the
potential to replace the highly functional
covalent (disulfi de) bonds in wheat dough
to produce gluten - free breads and cakes
(Stathopoulos and O ’ Kennedy 2008 ). The
aggregated casein samples (30 mg Ca/g
sample) were more elastic than gluten, but
their behavior on heating above 40 ° C (104 ° F)
produced materials that were weaker and
more viscous. Hence, further improvements
are required to improve its heat stability.
Micellar casein: Micellar casein displays
excellent rennet - coagulation properties. A
3% miceller casein suspension reduced coag-
ulation time by 53% compared to that of raw
milk, and increased gel fi rmness at 30 minutes
by more than 50% (Pierre et al. 1992 ). Re -
micellized casein produced stronger rennet
gels but had poorer acid gelation properties
than native micellar casein (Mounsey et al.
2005b ).
Micellar casein is particularly well suited
for cheese making (Saboya and Mauboissodium caseinate increases dramatically as
the pH is increased from 6.5 to 8.0 (Jahaniaval
et al. 2000 ). Bastier et al. (1993) compared
the solubility of several commercial casein-
ates at pH 7.0. They reported that solubility
of calcium caseinate was not signifi cantly
different from that of sodium caseinate, but
was signifi cantly lower than that of potas-
sium caseinate.
Milk protein concentrates: The solubil-
ity of milk protein concentrate powders
(MPC powders) is low compared to that of
skim milk powders. The solubility of the
powders deteriorates on storage, particularly
at elevated temperatures. A survey of com-
mercially available MPC powders with 82%
to 86% protein showed that there was wide
variability in the solubility of these powders,
although the cause of the variation was not
investigated in that study (de Castro - Morel
and Harper 2002 ).
The nature of the insoluble material has
been examined. McKenna (2000) found that
the insoluble material obtained on dispersion
of MPC85 that had been stored for six months
at 20 ° C (68 ° F) was mainly fused casein
micelles. Havea (2006) demonstrated that the
material was primarily α - and β - caseins that
were associated by weak non - covalent
protein - protein interactions.
Studies on the rehydration of MPC 85
suggest two processes control the dissolution
of the powders, namely the disruption of
agglomerated particles into primary powder
particles and the release of material from the
particle into water (Mimouni et al. 2009 ).
The addition of monovalent salts is claimed
to improve the solubility of the milk protein
concentrate and milk protein isolate powders
(Carr et al. 2002 ). However, simply increas-
ing the temperature of the water increases the
dissolution rate of milk protein concentrate
powders. MPC powders should be dispersed
in water at temperatures of 40 ° C to 60 ° C
(104 ° F to 140 ° F) with a high energy dissolu-
tion unit (e.g., Venturi) for optimum solubil-
ity (Zwijgers 1992 ).