Institut für Lebensmittelchemie

Research Philosophy

Smells are surer than sounds or sights
to make your heart strings crack

Rudyard Kipling, 'Lichtenberg'

Aroma compounds (or, in American usage, volatile flavors) attract or repel human beings and affect our emotions and actions. A particular aroma may signal the quality of a food or of another item of the daily life, may create familiarity with persons and things, but may also exert numerous further bioactivities, from antioxidative to antimicrobial and medicinal. The high commercial value of plant parts carrying flavour has prompted seafaring nations like the early Phoenicians, Arabs, and later Dutch, Portuguese, Spanish and Venetians to equip ships and to explore new routes of trade; one of the unwanted side effects was the discovery of America.

Plants, however, are not the only source of flavours. The conversion of grape juice flavour to wine or sherry flavour, to give an example, must be traced back to the presence of microorganisms during processing. The scientific focus at the Institute of Food Chemistry is on those microbial pathways which are involved in flavour formation, conversion and degradation:

• Fungal cell cultures were applied to open new routes toward enantiopure terpene derivatives, were grown on lignocellulose materials to study degradation enzymes and products, and were equipped with vitality sensors.
   
  
• The fate of stable-isotope labeled substrates was studied to elucidate the biosynthesis of raspberry ketone, betuligenol, vanillin and methyl branched products from novalic acid (unpublished).
   
  
• Microbial and plant enzymes were isolated, characterised, immobilised and used to synthesise various acyloins and pyrazines derived thereof, cinnamic acid esters, and hex-2E-enal and related 'green' notes. A novel lipase for the cleavage of carotenoid esters and a process to isolate large quantities of fungal enzymes are also under investigation.
   
  
• For some enyzmes, such as the pyruvate decarboxylase from Zygosaccharomyces and the versatile peroxidase from Lepista the corresponding gene was isolated and compared to sequences from other sources.
   
  
• The research activities are rounded off by the recent development of an improved method for the recovery of flavours from lipids, synthesis and examination of selective porous adsorbents, and by extended studies on real time flavour release from solutions and emulsions using a computerised apparatus coupled with off-line trapping and thermodesorption as a mouth simulator.
   
  

The main advantages of enzyme catalysed flavour generation are high selectivitiy or specificity of reaction, high reaction rate even at low molar fractions, environmentally compatible and mild reaction conditions, and, if viable cells are used, the possibility to perform multi-step syntheses. This 'Technical Push' is amplified by a 'Business Pull' (Peter Cheetham), represented by the consumers´ demand for natural products, by the trace occurrence of many flavours in plants and the inherent imponderablilities of traditional field cultivation.

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