R. Snir et al., PH AND CATIONS INFLUENCE PERMEABILITY OF MARSH GRAPEFRUIT PECTINESTERASE ON POLYSULFONE ULTRAFILTRATION MEMBRANE, Journal of agricultural and food chemistry, 43(5), 1995, pp. 1157-1162
Marsh grapefruit pulp extract was filtered through a 30 000 molecular
weight cutoff hollow fiber polysulfone ultrafiltration (UF) membrane i
n a crossflow mode. At pH values of 3.8 and no added salt, pectinester
ase (PE) was retained by the membrane. Permeability increased with inc
reasing pH and/or cation concentration. Flux was not increased at high
er pH and/or cation concentration. Divalent cations were more effectiv
e than monovalent cations at stimulating activity and permeability of
PE. Maximum PE permeability was obtained at pH 8.0 and 0.15 M NaCl, pH
6.0 and 0.15 M NaCl, pH 3.8 and 0.4 M NaCl, or pH 3.8 and 0.1 M CaCl2
. The results suggest that PE is bound to soluble pectin and is retain
ed by UF membranes. Adding cations or raising the pH releases PE from
the electrostatic binding to pectin and enables the enzyme to permeate
UF membranes.