Cold generation of smoke flavour by the first phenolic acid decarboxylase from a filamentous ascomycete – Isaria farinosa

A decarboxylase (IfPAD) from the ascomycete Isaria farinosa converted ferulic acid to 4-vinylguaiacol (4-VG), a volatile which imparts the distinct “smoke flavor” of pyrolized wood. The activity was enhanced by adding (E)-ferulic acid to the culture medium and peaked with 3.6 U g−1 mycelium (1 μmol 4-VG min−1). The coding sequence of 543 bp was translated into a 25 kDa protein with a homology of 91 % to putative phenolic acid decarboxylases of its teleomorph, Cordyceps militaris, and Beauveria bassiana, the anamorph of Cordyceps bassiana. Cold shock expression in Escherichia coli yielded 411 U g−1 wet mass. Substrate conversion required a hydroxyl substituent para to a trans-unsaturated C3-side chain of the aromatic ring. Km and kcat/Km values were determined to 0.3 mM and 78.4 mM−1s−1 for p-coumaric acid and 1.9 mM and 45.1 mM−1s−1 for (E)-ferulic acid, respectively. The native enzyme and its recombinant counterpart showed pH-optima at pH 6.0 and pH 5.5, and low temperature optima of 19 °C and 14 °C, respectively. IfPAD produced 4-VG from destarched wheat bran and sugar beet fiber, confirming activity on complex plant biomass. This is the first report on the biochemical characterization of a phenolic acid decarboxylase from a filamentous ascomycete. [Display omitted] •First biochemical characterization of a phenolic acid decarboxylase from filamentous Ascomycota.•Enzyme sequence showed homology only to hypothesized phenolic acid decarboxylases.•Recombinant enzyme was expressed with the cold shock system in E. coli.•Wildtype and recombinant enzyme exhibited temperature optima below 20 °C.•The enzyme produced 4-vinylguaiacol from destarched wheat bran and sugar beet fibre.