Lehrstuhl für Lebensmittelchemie
Am Hubland, 97074 Würzburg
Other participating persons and organisations:
Research foci (and basic equipment-based research projects):
The interest is focused on the following research areas, i.e. (i) authenticity; (ii) biogenesis; (iii) flavour precursors; and (iv) biotransformations.
(i) Authenticity: The authenticity of 'natural' flavours is studied by enantiodifferentiation and stable isotope analysis. Our pioneering work done in the separation of enantiomers, in particular, by coupling achiral and chiral columns in multi-dimensional gas chromatography (MDGC) as well as its combination with mass spectrometry (MDGC-MS) was extended to coupled high resolution gas chromatography-isotope ratio mass spectrometry (HRGC-IRMS) for D/H-, 13C/12C-, 15N/14N- and 18O/16O- ratio determinations. Thus, high-sophisticated instrumental-analytical techniques are available to investigate the origin of a wide range of chiral and achiral substances.
(ii) Biogenesis: Investigations of biosynthetic and metabolic pathways of the secondary plant metabolism are performed by labeling experiments (2H, 3H, 13C, 14C and 18O). Particular attention is focused on the formation and metabolism of oxygenated lipid derivates. In addition, increasing interest is devoted to plant-microorganism interaction. Products are analyzed by means of radio-HPLC, radio-TLC, HRGC-MS, HPLC-MS/MS, HPLC-NMR and HRGC-IRMS techniques.
(iii) Flavour Precursors: The worldwide increasing industrial demand for 'natural' flavours requires the evaluation of novel research strategies to use the still unexploited potential of 'bound' flavour compounds of plant origin. By means of chemical-analytical, enzyme-technological and microbiological studies information is provided to create a fundament for the subsequent industrial use of technical enzymes to liberate attractive flavour compounds from plant tissues.
(i) Biotransformations: Bacterial and fungal biotransformations are used (i) to study selective biogenetic pathways of attractive flavour compounds and (ii) to use the high potential of bacteria and fungi for the selective production of chiral compounds, thus extending our activities in the bioorganic synthesis (cf. "Enzymes in Organic Chemistry") by alternative strategies.
(i) Authenticity studies:
By application of sophisticated techniques such as MDGC-MS and HRGC-IRM (in the combustion(C)- and the pyrolysis(P)-mode) we achieved the origin differentiation of the most important chiral flavour compounds as well as a high number of natural products such as benzaldehyde, linalool, citral, C6-aldehydes and alcohols, caffeine, etc.
(ii) Biogenesis: The biosynthetic pathway of (R)-octane-1,3-diol and 2,5-dimethyl-4-hydroxy-3(2H)-furanone was elucidated in apple and in strawberry fruits, respectively. Novel metabolites of these natural compounds were isolated and characterised. The isolation, cloning and heterologous expression of an O-methyltransferase involved in the biosynthesis of the important strawberry aroma compound 2,5-dimethyl-4-hydroxy-3(2H)-furanon was achieved for the first time in collaboration with the chair of plant physiology of the University of Würzburg
(iii) Flavour precursors: Numerous 'bound' flavor progenitors from plant tissues were chemically characterizied. In addition,
glycosidases were obtained from Aspergillus ssp. capable of releasing flavour compounds from their glycosylated precursors in an industrial scale. Especially one isoform showed optimal properties owing to its glucose tolerance and stability in a wide pH range.
(iv) Biotransformations: Various classes of substances were hydroxylated and sulfoxised by microorganisms. The products are hardly available by chemical methods.
Rewards and prizes:
Dr. W. Schwab
1999 Joseph-Schormüller-scholarship (Lebensmittelchemische Gesellschaft, subdivision of Gesellschaft Deutscher Chemiker)
1998 Research grant from Jubiläumsstiftung of the Universität of Würzburg
The instrumentation comprises among others HRGC, dynamic headspace-HRGC, HRGC-SCD, HRGC-MS, SPE-HRGC-MS, HRGC-IRMS, HPLC, HPLC-DAD, HPLC-ELSD, as well as HPLC-MS/MS and HPLC-NMR. For configurational studies MDGC, MDGC-MS and CD spectroscopy are well established. Quantifications are performed routinely by HRGC-MS and HPLC-MS/MS using preferably isotope dilution analysis.