1. Agrotechnological Research Institute (ATO-DLO), P.O. Box 17, NL-6700 AA Wageningen, The Netherlands, Department of the Science of Food of Animal Origin, Section Food Chemistry, Faculty of Veterinary Medicine, University Utrecht, P.O. Box 80175, NL-3508 TD Utrecht, The Netherlands, and Institute for Pharmacy, Department of Pharmacy, Freie Universität Berlin, Königin-Luise-Strasse 2+4, D-14195 Berlin, Germany