As ammonium sulfate is commonly used for separation
of cysteine proteases, a two-phase system composed
of PEG–ammonium sulfate was evaluated for partitioning of
papain. According to the phase diagram of PEG–(NH4)2SO4
system by Salabat [25], the system comprising 12% (w/w) PEG
6000–15% (w/w) (NH4)2SO4 provides two separated phases.
These were the maximum concentrations of the phase components
that could be used for purification of papain from papaya
latex. The system containing more than 12% (w/w)PEGresulted
in a highly viscous mixture, whereas the system consisting of
more than 15% ammonium sulfate provoked the precipitation of
protein from the latex.