A desired partition of proteins
in such systems can be obtained by manipulating a variety of
system parameters [15,16]. The polymer–salt–water systems
have the advantage of low cost and low viscosity compared
to polymer–polymer–water systems. The most frequently used
among the former systems has been the polyethylene glycol
(PEG)–phosphate [13,17], however other salts with multivalent
anions have also been used [18]. Use of PEG–phosphate system
has earlier been reported for separation and purification of papain
from papaya latex [19]. The study showed that the separation of
papain was negatively affected by the presence of chymopapain,
however the use of PEG modified with Procion Blue enhanced
the partition of papain to the PEG rich upper phase.