1. Institute for Nutrition and Food Sciences, Food Microbiology and Hygiene, University of Bonn, Meckenheimer Allee 168, D-53115 Bonn, Germany, Institute of Physics, University of Bonn, Nussallee 12, D-53115 Bonn, Germany, The J. Bennett Johnston, Sr. Center for Advanced Microstructures and Devices (CAMD), Louisiana State University, 6980 Jefferson Highway, Baton Rouge, Louisiana 70806, and German Research Center for Food Chemistry, Lichtenbergstrasse 4, D-85748 Garching, Germany