1. Institut für Ionenphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria, Department of Food Science, Food Technology and Nutrition, University College Cork, Western Road, Cork, Ireland, Istituto Agrario di S. Michele a/A, Via E. Mach, 2 38010 S. Michele, Italy, and Department of Plasmaphysics, University of Bratislava, SK-84248 Bratislava, Slovak Republic