1. Wageningen Centre for Food Sciences (WCFS), P.O. Box 557, 6700 AN, Wageningen, The Netherlands, Wageningen University, Laboratory of Physical Chemistry & Colloid Science, P.O. Box 8038, 6700 EK Wageningen, The Netherlands, and TNO Nutrition and Food Research Institute, P.O. Box 360, 3700 AJ Zeist, The Netherlands