1. Wageningen Centre for Food Sciences, Diedenweg 20, P.O. Box 557, 6700 AN Wageningen, The Netherlands, Laboratory for Food Chemistry, Wageningen University and Research Centre, Bomenweg 2, 6700 EV Wageningen, The Netherlands, and TNO Quality for Life, Utrechtseweg 48, 3704 HE Zeist, The Netherlands