1. Institute of Plant Analysis, Federal Centre for Breeding Research on Cultivated Plants (BAZ), Neuer Weg 22-23, D-06484 Quedlinburg, Germany, Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland, and Department of Food Science, Danish Institute of Agricultural Sciences, Research Centre Aarslev, Kirstinebjergvej 10, DK-5792 Aarslev, Denmark