1. NIZO food research, P.O. Box 20, 6710 BA Ede, The Netherlands, Department of Dairy and Food Science, The Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark, and Van't Hoff Laboratory, Debeye Research Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands