1. Inst. of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
2. Corresponding author. Phone: 0044 (0)1603 255012. Fax: 0044 (0)1603 507723. E-mail: klaus.wellner@bbsrc.ac.uk.
3. School of Chemical Sciences, Univ. of East Anglia, Norwich, NR4 7TJ, UK.