Effect of membrane pore size on quality of ultrafiltered apple juice

Fresh apple juice was processed using an ultrafiltration (UF) unit, with polysulphone membranes of 10 000 and 50 000 daltons pore size. Trans-membrane pressures of 103, 120.5, 138 and 155 kPa were studied. Recovery percentages of 0, 25, 50 and 75 were tested for the smaller pore membrane, as well as 0, 10, 20, 30, 40, 50 and 60 for the larger pore membrane. The responses to these factors were evaluated for the quality attributes pH, acid content, soluble solids and colour. In general terms, pH, acid content, and soluble solids did not change but presented less variability for the smaller pore membrane treatment. Relative colour changes were observed for both membranes, with an evident browning trend, which was more detectable for the larger pore membrane treatment.