Hazelnut: Explorations towards the biocatalytic synthesis of its aroma precursor.

Biocatalysis has gained significant industrial interest due to its controlled stereoselectivity and use of mild process conditions. Here we propose a biosynthetic route for the synthesis of filbertone (5-methyl-2-hepten-4-one, 1), which is the principal flavour compound of hazelnut. The enantiomeric purity of the industrially synthesized compound is defined, contrary to the natural aroma, which varies according to the source of the nut extraction conditions and treatments. The novel synthetic pathway for a hazelnut aroma precursor proposed here consists of a multi-enzyme cascade, which starts from the two amino acids D-Ile and L-Thr that are individually converted by enzyme catalysts, i.e., D-amino acid oxidase and threonine deaminase, followed by C-C ligation of the obtained products allowing a potentially sustainable production of the natural aroma. The most critical step is C-C ligation that uses two carbonyl compounds as starting material. This step is catalysed by a regioselective transketolase (TK) that originates from Geobacillus stearothermophilus. Our approach holds promise for an industrial production of natural hazelnut aroma precursor, addressing the growing demand in the aroma industry for synthesis methods that sustain the regulatory claims for natural compounds.