1. Contribution from the Centre for Advanced Food Studies (LMC), The Royal Veterinary and Agricultural University (KVL), Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark, Plant Biochemistry Laboratory, Department of Plant Biology and Center for Molecular Plant Physiology (PlaCe), The Royal Veterinary and Agricultural University (KVL), Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark, and Centre de Recherches sur les Macromolécules Végétales, CNRS, BP 53X, 38041 Grenoble cédex, France