1. Wageningen Center for Food Sciences (WCFS), P.O. Box 557, 6700 AN, Wageningen, The Netherlands, Food Physics Laboratory, Department of Agrotechnology and Food Sciences, Wageningen University, P.O. Box 8129, 6700 EV, Wageningen, The Netherlands, and NIZO food research, P.O. Box 20, 6710 BA, Ede, The Netherlands