Biocatalytic synthesis of natural dihydrocoumarin by microbial reduction of coumarin

Dihydrocouinarin is a natural product of great relevance (or the flavour industry. In this work, we describe a study on the biotransformation of the toxic compound coumarin into natural dihydrocoumarin, recognized as safe for food aromatization. To this end, we screened a variety of yeasts and filamentous fungi, isolated from different sources, in order to evaluate their ability to reduce selectively the conjugated double bond of coumarin. Moreover, since coumarin induces cytotoxicity and therefore inhibits cell growth as well as the cell metabolic activity, we tested out different substrate concentrations. All strains were able to convert the substrate, although showing very different conversion rates and different sensitivity to the coumarin concentration. In particular, the yeasts Torulaspaa delbruedcii, Klui/veromifces marxianus and the fungus Peniallium amtembati displayed the higher activity and selectivity in the substrate transformation. Among the latter strains, KIUlfVeiomvee$ marxiaiUS presented the best resistance to substrate toxicity, allowing the biotransformation process even with coumarin concentration up to 1.8 g/L.