174 Chapter 7
high for micellar casein at pH 6 and 8. Rennet
casein displayed the lowest emulsifying
capacity and did not foam under the condi-
tions tested.
Sodium caseinates are extensively used as
emulsifi ers owing to the random structure
and non - uniform distribution of hydrophobic
and hydrophilic residues of the caseins. In
emulsions, the protein load of sodium casein-
ate needed to stabilize oil - water interfaces
is very low (1.4 to 3.7 mg/m^2 ), but depends
on the physico - chemical conditions such
as salt and sodium caseinate concentration
(Srinivasan et al. 1996 ). However, although
sodium caseinate is considered to be a good
emulsifi er, an excess in an emulsion formula-
tion can lead to destabilization by depletion
fl occulation (Dickinson 2006 ). Calcium
caseinates are also known to be good emulsi-
fi ers, although due to the aggregated state of
the proteins, their surface load is higher than
that of sodium caseinate, particularly when
high protein concentration is used (Srinivasan
et al. 1999 ).Heat Stability
Heat stability is the ability of milk to with-
stand coagulation at high temperatures.
Because heat treatment is an essential unit
operation, heat stability is a desirable prop-
erty for milk protein ingredients used in
many applications.
Micellar casein is reported to display
greater heat stability than acid casein or
rennet casein (Barbano 2004 ). Heat stability
was further increased at pH less than or equal
to 6.6 at low - and high - ionic strength using
re - micellized casein (Mounsey et al. 2005a ).
Heat stability was also markedly improved at
pH above 6.8 following incubation with
transglutaminase (Mounsey et al. 2005a ).
Caseinates are more stable to heat than
milk. However, extensive heating of casein-
ate solution can result in polymerization of
the caseins as well as degradation of the pro-Milk protein concentrates have applica-
tions in cheese making as the micellar casein
participates in gel network formation. When
milk protein concentrates with high protein
content (e.g., MPC 70 to 85) are used, added
calcium is required to form rennet gels (Kuo
and Harper 2003 ). A major use of milk protein
concentrates is in the standardization of cheese
milk as an alternative to skim milk powder.
One of the advantages of using milk protein
concentrate powders for standardization of
cheese milk is that it has lower lactose content
than skim milk powder, resulting in cheese
with reduced residual lactose. Modifi cation
of the cheese making procedure may be
required to enhance fl avor development and
ripening of the cheese (Rehman et al. 2003 ).
Surface - Active Properties
The open and fl exible structure of the caseins,
combined with their amphiphilicity, imparts
excellent surface - active properties (e.g.,
foaming, emulsifying) to the caseins (Fox
and Kelly 2004 ). Euston and Hirst (2000)
compared the emulsifying properties of com-
mercial milk protein products. When the
caseins in products were in a non - aggregated
state (i.e., in sodium caseinate), they had
higher emulsifying capacity than those in an
aggregated/micellar state (i.e., in skim milk
powder or milk protein concentrate).
The surface - active properties of acid pre-
cipitated and subsequently neutralized casein,
rennet casein, and native micellar casein
were compared, with the infl uences of pH
and salt concentration taken into account
(Roman and Sgarbieri 2006 ). Compared to
micellar casein, emulsifying capacity was
higher for acid casein at pH 4 and 7. Emulsion
stability was high for acid casein at pH 4 and
for micellar casein at pH 7. Foaming capacity
was higher for micellar casein compared to
acid casein at pH 4, but higher for acid casein
at pH 6 and 8. Foam stability was low for
micellar casein and acid casein at pH 4, but