1. Department of Biochemical Engineering, University College London, Torrington Place, London WC1E 7JE, U.K.
2. Research Specialties, Sigma-Aldrich Chemie GmbH, Industriestrasse 25, Buchs CH-9471, Switzerland
3. Center for BioProcess Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark, DK-2800 Lyngby, Denmark