title: Mousy off-flavor of wine: precursors and biosynthesis of the causative N-heterocycles 2-ethyltetrahydropyridine, 2-acetyltetrahydropyridine, and 2-acetyl-1-pyrroline by Lactobacillus hilgardii DSM 20176.
abstract: The N-heterocyclic bases, 2-ethyltetrahydropyridine (1), 2-acetyl-1-pyrroline (2), and 2-acetyltetrahydropyridine (3) are associated with the occurrence of mousy off-flavor in wine. The biosynthesis of these N-heterocycles by the wine lactic acid bacterium, Lactobacillus hilgardii DSM 20176, was studied by high-cell-density incubation in combination with a minimal chemically defined N-heterocycle assay medium. The key components of the defined N-heterocycle assay medium included D-fructose, ethanol, L-lysine, L-ornithine, and mineral salts. N-heterocycle formation was quantitatively determined by gas chromatography-mass spectrometry. The formation of 2 and 3 required the concomitant availability of a fermentable carbohydrate (D-fructose), ethanol, and iron (Fe(2+)). In addition, L-ornithine stimulated the formation of 2 and repressed 3 formation, whereas L-lysine stimulated the formation of 3 and repressed 2 formation. Incorporation of d(6)-ethanol into the acetyl side chain of 2 and 3, and of d(4)-acetaldehyde into the acetyl side chain of 3, confirmed that ethanol and acetaldehyde could serve as major side chain precursors. A pathway for the formation of 2 and 3 by heterofermentative lactic acid bacteria is proposed involving the interaction of accumulated C-2 intermediates from the heterolactic pathway and N-heterocyclic intermediates derived from the metabolism of L-ornithine and L-lysine.
authors.affiliation: The Australian Wine Research Institute, P.O. Box 197, Glen Osmond, SA, 5064, Australia. Peter.Costello@awri.com.au
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Costello
authors.forename: Paul A
authors.initials: PA
authors.lastname: Henschke
mesh_terms: D000079:Acetaldehyde / Q000032:analysis / Q000378:metabolism; D000215:Acylation; D002413:Cations, Divalent; D003903:Deuterium; D000431:Ethanol / Q000032:analysis / Q000378:metabolism; D005632:Fructose / Q000032:analysis / Q000378:metabolism; D006571:Heterocyclic Compounds / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D007778:Lactobacillus / Q000378:metabolism*; D008239:Lysine / Q000032:analysis / Q000378:metabolism; D008670:Metals; D009952:Ornithine / Q000032:analysis / Q000378:metabolism; D011725:Pyridines / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D011758:Pyrroles / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D013649:Taste; D014920:Wine / Q000032:analysis*
chemical_list: D002413:Cations, Divalent; D006571:Heterocyclic Compounds; D008670:Metals; D011725:Pyridines; D011758:Pyrroles; D005632:Fructose; D000431:Ethanol; D003903:Deuterium; D009952:Ornithine; D000079:Acetaldehyde; D008239:Lysine