1. Department of Analytical Chemistry, Chemistry Faculty, University of Barcelona, Martí i Franquès, 1-11, E-08028 Barcelona, Spain, National Cancer Center Research Institute, 1-1 Tsukiji 5-chome, Chuo-ku, Tokyo 104-0045, Japan, and Department of Food Technology, Engineering and Nutrition, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden