Biotechnological Production of Odor-Active Methyl-Branched Aldehydes by a Novel α-Dioxygenase from Crocosphaera subtropica

Abstract

As a result of their pleasant odor qualities and low odor thresholds, iso- and anteiso-fatty aldehydes represent promising candidates for applications in flavoring preparations. A novel cyanobacterial α-dioxygenase from Crocosphaera subtropica was heterologously expressed in Escherichia coli and applied for the biotechnological production of C₁₂-C₁₅ branched-chain fatty aldehydes. The enzyme has a sequence identity of less than 40% to well-investigated α-dioxygenase from rice. Contrary to the latter, it efficiently transformed short-chained fatty acids. The kinetic parameters of α-dioxygenase toward unbranched and iso-branched-chain substrates were studied by means of an oxygen-depletion assay. The transformation products (C₁₂-C₁₅ iso- and anteiso-aldehydes) were extensively characterized, including their sensory properties. The aldehydes exhibited green-soapy, sweety odors with partial citrus-like, metallic, peppery, and savory-tallowy nuances. Moreover, the two C₁₄ isomers showed particularly low odor threshold values of 0.2 and 0.3 ng/L in air as determined by means of gas chromatography-olfactometry.

Keywords: Crocosphaera subtropica (former Cyanothece sp. ATCC 51142); flavoring substances; methyl-branched aldehydes; odor threshold; α-dioxygenase.