The potential for membrane distillation (MD) flux enhancement in apple juice concentration by removal of biopolymers has been investigated. Introduction of additional enzymatic deproteinization to conventional treatment with pectinase/amylase complexes and application UF as a clarification method provide an obtaining of clarified apple juice with minimal content of biopolymers. Such a pre-treatment enhances trans-membrane flux during concentration of clarified juice by MD. This has been attributed to a reduction in juice viscosity resulting in decrease of concentration and temperature polarisation. Lower initial viscosity is especially favourable for the treatment of highly viscous streams of concentrated juices. (C) 2003 Elsevier Ltd. All rights reserved.