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 of Life, Utrechtseweg 48, 3704 HE Zeist, The Netherlands