Clarification and sterilization of raw depectinized apple juice by ceramic ultrafiltration membranes

Raw depectinized apple juice was clarified and sterilized in a cross-flow pilot scale ultrafiltration system using ceramic tubular membranes (MEMBRALOx (R), Pall) with mean pore size of 100nm. The permeate flux significantly decreased with time until a steady-state was established. An increase in filtration pressure increased the permeate flux while there is an optimum pressure (about 0.85 bar) above which the increase of pressure does not increase the flux significantly. The higher the cross-flow velocity was, the higher was the transmembrane flux. When the operating temperature increased, the permeation rate increased subsequently. Analytical measurement showed that suspended solids and turbidity could almost be removed by the ceramic ultrafiltration membrane, but pH, acidity, sugar and soluble solid content of the juices showed no significant change. The bacteria challenge tests with Micrococcus flavus showed that the logarithm value of the bacteria reduction rate came up to above 9 in the cross-flow tubular ceramic system. When the permeate was collected in sterile bottles in a laminar flow shell and kept at 4 degrees C, 8 degrees C, 25 degrees C and 35 degrees C, for 28 days, the apple juice experienced minimal changes in physicochemical properties at lower temperatures of 4 degrees C, or 8 degrees C. (c) 2005 Society of Chemical Industry.