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pH and cations influence permeability of marsh grapefruit pectinesterase on polysulfone ultrafiltration membrane

Snir, R., Koehler, P.E., Sims, K.A., Wicker, L.
Journal of agricultural and food chemistry 1995 v.43 no.5 pp. 1157-1162
grapefruits, citrus pulp, ultrafiltration, pectinesterase, permeability, pH, sodium, sodium chloride, calcium chloride, inorganic ions, calcium, extracts
Marsh grapefruit pulp extract was filtered through a 30 000 molecular weight cutoff hollow fiber polysulfone ultrafiltration (UF) membrane in a crossflow mode. At pH values of 3.8 and no added salt, pectinesterase (PE) was retained by the membrane. Permeability increased with increasing pH and/or cation concentration. Flux was not increased at higher pH and/or cation concentration. Divalent cations were more effective 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 retained 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.