SMELL & TASTE: Some rules for designing of odorants
For the design of a new odorant one needs first of all the most important knowledge about the existing odorants. Up to now about 10,000 volatile chemical compounds have been identified in natural isolates, foodstuffs and prepared food. The chemical structures of these compounds are well-known. Secondly it is useful to know the pathways along which the volatile products are formed, that is to say the biochemical formation in the natural products and the reactions, which occur during food preparation.
Aliphatic compounds
Biogenesis of aliphatic odorants: fatty acids (via acetylcoenzyme-A). Strecker degradation of aminoacids: Leucine, isoleucine, phenylalanine. During this degradation alcohols, aldehydes, acids and esters of the corresponding amino acids are formed.
Isoprenoid compounds
Biogenesis of isoprenoids: isopentenyl pyrophosphate (via acetylcoenzyme-A). Mono-, di, tri- and poly-cyclisation of geranyl- & farnesyl-pyrophosphates. Chemical reactions in nature (thin film, photochemical, high temparature, acidic medium: sclareol on labdanum plants)
Benzenoid compounds
Biochemical formation of benzenoid compounds. The oxidation of polysubstituted benzenoid compounds like anethol, (iso)eugenol, (iso)safrol and the formation of aldehydes, such as anisaldehyde, vanillin, heliotropin.
Nitrogen- and sulfur compounds
Amino acid reaction (aminotransfer) with sugars. Formation of sulfur compounds (hydrogensulfide and methylmercaptan addition to unsaturated natural odorants: cis-3-hexenol, 2,6-nonadienal, unsaturated ketones)
For the design of a new odorant we choose as functional group the unsaturated ketone, aliphatic, terpenoid or aromatic. One finds a whole range of different olfactive qualities.
Review of unsaturated ketones with their olfactive qualities
Chemical group Example Odourtype
linairy aliphatic octyl vinyl ketone kelp, algue
monocyclic carotenoïd irones floral (orris)
bicyclic alkenone hydropentamethylindanone herbal, floral, woody, musk
acyclic-monoterpenoid tagetones floral (tagetes)
monocyclic monoterpenoid (R) & (S)-carvone herbal (spearmint & caraway)
bicyclic monoterpenoid verbenone herbal (rosemary)
bicyclic sesquiterpenoid nootkatone citrusy (grapefruit)
aromatic (benzenoid) traseolide, tonalide musk
aryl (benzenoid- alkyl) raspberry ketone fruity (raspberry)
On the basis of this knowledge it is possible to design new natural odorants with the mono- (C-10) or a sesqui- (C-15) terpene-skeleton.