1. Scientific Collaborator F.N.R.S., Statistics and Computer Sciences Department, University of Agronomical Sciences, Avenue de la Faculté 8, 5030 Gembloux, Belgium, Quality and Safety Department, Nestlé Research Centre, Vers-chez-les-Blanc, P.O. Box 44 1026 Lausanne, Switzerland, and Quality of Agricultural Product Department, Walloon Agricultural Research Centre (CRA-W), Chaussée de Namur no. 24, 5030 Gembloux, Belgium