1. Laboratory for Chemical Surface Science, Department of Chemistry, Physical Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden, and Institute for Surface Chemistry, Box 5607, S-114 86 Stockholm, Sweden, Department of Food Technology, University of Lund, Box 124, S-221 00 Lund, Sweden, and Department of Bioresource Engineering, Oregon State University, Gilmore Hall 116, Corvallis, Oregon 97331-3906