1. Chair of General Food Technology, Center of Food and Life Sciences, Technical University of Munich, Am Forum 2, 85350 Freising-Weihenstephan, Germany, Laboratorium für Stabil-Isotope, Isolab GmbH, Woelkestrasse 9, 85301 Schweitenkirchen, Germany, and Laboratorio di Analisi e Ricerche, Istituto Agrario di San Michele all'Adige, Via Edmondo Mach 1, 38010 San Michele all'Adige, Trento, Italy