Whey-based Ingredients 185the whey proteins is altered by the effects of
high and low pHs. These changes include
unfolding, which is usually reversible, and
the interaction of sulfhydryl groups and
disulfi de bonds, which is irreversible. Both
can affect the effi ciency of protein recovery
because the unfolded or denatured protein
can bind covalently and irreversibly to the
ion exchanger. This can cause a decrease in
the processing effi ciency. Therefore, extreme
pHs should be avoided (Howell et al. 1990 ).
The separation of proteins by ion exchange
chromatography occurs in four steps (Figure
8.6 ):- Adsorption. The whey stream is pH
adjusted, diluted, and mixed or passed
through the tank fi lled with ion exchanger.
Only the proteins charged appropriately
are adsorbed. - Washing. The tank is washed with
enough water to displace any non -
adsorbed components of the whey solu-
tion still in the tank. - Elution. A salt, acid, or basic solution is
used to displace the proteins and con-
comitantly regenerate the ion exchanger. - Washing. The tank is washed with enough
water to remove all the protein solution.
After the ion exchange treatment, the
protein solution is often very dilute (3% to
5%) and contains a large quantity of salts.
Ultrafi ltration is recommended before evapo-
ration and drying, both to increase the con-
centration of the stream and to reduce the
amount of minerals.
Etzel (1995) reviewed the existing
methods for isolating proteins from whey
However, a ceramic membrane system costs
three to 10 times more than a spiral - wound,
polymeric membrane system. That said, it is
only recently that polymeric membranes
capable of defatting whey with similar selec-
tivity to ceramic membranes have been suc-
cessfully developed.
The biggest issue in processing whey with
microfi ltration membranes is the balance
between throughput — through greater per-
meability of the valuable components such as
whey proteins — and membrane pore block-
ing. To control the membrane fouling and
reduce the potential for membrane pore
blocking, microfi ltration is run at increased
cross - fl ow velocities. The transmembrane
pressure in ceramic membranes is kept
uniform along the length of the module via
co - current permeate fl ow or manufacture of
membranes with a controlled gradient of
resistance against permeation. The process
operates under pressures below 1.5 bar.
Pre - treatment of the feed to microfi ltra-
tion, for example, via heat treatment and pH
adjustment, is also recommended to stabilize
fat and protein aggregates (Merin and Daufi n
1990 ), thus enhancing the separation ability
of the process.
Ion Exchange (Protein Isolation
and Fractionation)
Ion exchange chromatography is used to
produce high purity whey proteins. The sepa-
ration is based on the electric charge of the
proteins, which is a function of the number
and nature of the ionizable groups on the
polypeptide chains. The separation by ion
exchange chromatography is based on the
fact that at a pH lower than the isolectric
point (Table 8.2 ), proteins have a net positive
charge and can be adsorbed on cationic ion
exchangers, whereas, at a pH higher than the
isoelectric point, they have a negative charge
and can be adsorbed on anionic ion exchang-
ers (Kaczmarek 1980 ).
In choosing conditions for adsorption, it
should be noted that the tertiary structure of
Table 8.2. Isoelectric point of whey proteins.
Protein Isoelectric
point (pH)
β - Lactoglobulin 5.2 – 5.5
α - Lactalbumin 4.2 – 4.8
Bovine serum albumin 4.7 – 5.1
Immunoglobulins 5.5 – 8.3
Proteose - peptones 3.3 – 3.7
Adapted from Swaisgood (1996) , Kilara (2008)