Pectinesterase and pectin complexes inhibit ion exchange membrane separation

Ion exchange membrane disks (FMC Co., Pine Brook, NJ) equilibrated at pH 5.0, 6.0, 7.2, and 8.0 were tested for separation of pectinesterase (PE) extracted from Marsh grapefruit (MGF) pulp. Anionic exchange disks (QUAT, DEAE, and PEI) bound less PE and protein than cationic exchange disks (SP and CM). Less than 20% of PE was bound to SP membrane at pH 6.0, 7.2, and 8.0. Law PE binding ability in the ion-exchange system may be attributed to the presence of PE-pectin complexes, which act as a competitor with the inorganic ions of the membranes. Water washing the pulp prior to PE extraction lowered the pectin content by 86%, but did not substantially improve PE binding to SP membrane.