1. University of Helsinki, Department of Food and Environmental Science, PO Box 66, FIN-00014 University of Helsinki, Finland.
2. VTT Technical Research Centre of Finland, PO Box 1000, FIN-02044 VTT, Finland.
3. Corresponding author. Phone: +358919158242. Fax: +358919158460. E-mail: jussi.loponen@helsinki.fi