Casein, Caseinates, and Milk Protein Concentrates 171cheese analogues (O ’ Sullivan and Mulvihill
2001 ). Insuffi cient hydration of rennet casein
can cause under - emulsifi cation of the oil
phase (i.e., large oil droplets are formed)
during manufacture of the cheese analogue
(Aimutis 1995 , Ennis
et al. 2000 ). Consequently, the cheese
analogue that is produced may exhibit
poor stretchability and free oil release on
heating. If excessive solubilization of the
casein occurs, then over - creaming or over -
emulsifi cation (i.e., very small oil droplets
are formed) can occur during manufacture of
the cheese analogue (Meyer 1973 ). In this
case, the cheese analogue exhibits poor melt-
ability and decreased fl ow characteristics
on heating (Savello et al. 1989 ), which are
undesirable in mozzarella cheese analogues
intended for pizza toppings, for example.
Micellar casein: Rehydration of spray -
dried micellar casein powders prepared by
membrane microfi ltration is slow when com-
pared, for example, to low - heat milk powder
(Schuck et al. 2007 ). This has been attributed
to low water transfer into the casein micelle
(Schuck et al. 2007 ). Rehydration of the
powder can be improved by adding citrate or
phosphate to the suspension prior to drying
or addition of NaCl during the rehydration
process (Schuck et al. 2002 ). In contrast,
addition of CaCl 2 has an adverse effect, pro-
ducing insoluble structures during spray
drying (Schuck et al. 2002 ).
Water absorption capacity, water solubil-
ity, and water - holding capacity are higher for
micellar casein than for rennet casein (Roman
and Sgarbieri 2006 ).
Caseinate: Although caseinates are cred-
ited with very good solubility, this strongly
depends on different conditions such as pH,
ionic strength, and temperature. For instance,
at pH from 5.6 to 6.2, the solubility of both
sodium caseinate and calcium caseinate is
improved when sodium phosphate is added
(Konstance and Strange 1991 ). Sodium
caseinate has the lowest solubility near its
pI (i.e., pH around 4.6) and the solubility oftards, aquatic feeds, ice cream, spreads, fi ll-
ings and creams (e.g., synthetic cream whip),
cream liquers, puddings, and fabricated
meats (Fox and Kelly 2004 ).
The functional properties of casein - based
ingredients are affected by various factors,
including changes in pH, method of prepara-
tion, ionic strength, and the nature of the salt
ion present in the preparation. Some of the
key physical properties of casein - based
powders are discussed below. It is the physi-
cal functional properties that often dictate
their suitability for an application. Specifi c
examples of their physical properties that
relate to their functionality as food ingredi-
ents are described.
Solubility/Hydration
The solubility and hydration of protein ingre-
dients is a pre - requisite for other physical
functional properties of milk proteins, with
insolubility or inadequate hydration compro-
mising functionality in many applications.
Casein: The hydration of rennet casein
relies on disruption of the calcium - mediated
protein - protein interactions to increase the
protein - aqueous solvent interactions (Aimutis
1995 , Caric and Kalab 1993 , Ennis and
Mulvihill 1997 ). The pH of the solution, and
concentration and type of sequestering salt
used to disperse the casein, infl uences the
extent of its hydration (Ennis et al. 2000 ,
Savello et al. 1989 ). Differences in protein
and mineral (ash and calcium) contents, as
a result of different heat conditions in the
pasteurization of skim milk prior to rennet
manufacture (Ennis and Mulvihill 1999 ,
O ’ Sullivan and Mulvihill 2001 ) and heat
treatment during rennet casein manufac-
ture, may also affect the hydration of rennet
casein (O ’ Sullivan et al. 2002a, 2002b ).
The extent and nature of casein hydration
are critical factors in determining its func-
tional performance. An example of the effect
of hydration on functionality is the use of
rennet casein during the manufacture of