Abstract
As part of a program aiming at the selection of yeast strains which might be of interest as sources of natural flavours and fragrances, the bioreduction of (4R)-(−)-carvone and (1R)-(−)-myrtenal by whole-cells of non-conventional yeasts (NCYs) belonging to the genera Candida, Cryptococcus, Debaryomyces, Hanseniaspora, Kazachstania, Kluyveromyces, Lindnera, Nakaseomyces, Vanderwaltozyma and Wickerhamomyces was studied. Volatiles produced were sampled by means of headspace solid-phase microextraction (SPME) and the compounds were analysed and identified by gas chromatography–mass spectroscopy (GC-MS). Yields (expressed as % of biotransformation) varied in dependence of the strain. The reduction of both (4R)-(−)-carvone and (1R)-(−)-myrtenal were catalyzed by some ene-reductases (ERs) and/or carbonyl reductases (CRs), which determined the formation of (1R,4R)-dihydrocarvone and (1R)-myrtenol respectively, as main flavouring products. The potential of NCYs as novel whole-cell biocatalysts for selective biotransformation of electron-poor alkenes for producing flavours and fragrances of industrial interest is discussed.
Highlights
Biocatalysis represents an effective and sometimes preferable alternative to the standard synthesis of fine and/or optically active chemicals [1,2,3,4,5,6,7]
The ER-catalysed reduction was followed by the subsequent reduction of the carbonyl group of both dihydrocarvone isomers, catalyzed by carbonyl reductases (CRs), which determined the formation of a mixture of four dihydrocarveols 3a–d (Scheme 1)
non-conventional yeasts (NCYs) used in this study showed good aptitudes to biotransform
Summary
Biocatalysis represents an effective and sometimes preferable alternative to the standard synthesis of fine and/or optically active chemicals [1,2,3,4,5,6,7]. From an industrial point of view, carvone and related compounds are important flavours and fragrances of industrial interest [33] Due their high volatility, dihydrocarvones are potent inhibitors of bacteria and filamentous fungi, as well as prospective insect repellents [34], and have been used as chiral starting compounds in the synthesis of natural products (e.g., striatenic acid, pechueloic acid) [35,36,37], antimalarial drugs [38] and valuable chiral synthons [39,40]. As a part of a program aiming at the selection of yeast strains as novel sources of natural flavouring molecules, the production of flavours and fragrances via bioreduction of (4R)-(−)-carvone and (1R)-(−)-myrtenal by whole-cells of non-conventional yeasts (NCYs), belonging to the genera. Cryptococcus, Debaryomyces, Hanseniaspora, Kazachstania, Kluyveromyces, Lindnera, Nakaseomyces, Vanderwaltozyma, and Wickerhamomyces was studied
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