Fractionation by ultrafiltration of an aqueous extract of chestnut obtained by pressurized hot water extraction

Abstract

Different types, ceramic and polyethersulfone, ultrafiltration membranes were evaluated to purify a wood extract obtained in pressurized hot water conditions. Tests were performed at transmembrane pressure (TMP) from 0.4 to 2.0 bars with membrane molecular weight cut-offs ranging from 5 kDa to 100 kDa. The results showed the permeate fluxes were lower than 15 L.h-1.m-², except for the 100 kDa organic membrane, with no influence of the feed flowrate. The retention of total phenolic compounds highly depends on the membrane cut-off but the retention rates of gallic and ellagic acid were not directly link to the cut-off. The retention rate of gallic acid is lower than 10%, when ellagic acid had retention ranging from 75 to 95 % for the membrane 5 kDa. It is suggested that other phenomena could be involved in solute retention, i.e. Donnan effect or solubility, that could explain so large differences.