Fungi-Mediated Biotransformation of the Isomeric Forms of the Apocarotenoids Ionone, Damascone and Theaspirane

Abstract

In this work, we describe a study on the biotransformation of seven natural occurring apocarotenoids by means of eleven selected fungal species. The substrates, namely ionone (α-, β- and γ-isomers), 3,4-dehydroionone, damascone (α- and β-isomers) and theaspirane are relevant flavour and fragrances components. We found that most of the investigated biotransformation reactions afforded oxidized products such as hydroxy- keto- or epoxy-derivatives. On the contrary, the reduction of the keto groups or the reduction of the double bond functional groups were observed only for few substrates, where the reduced products are however formed in minor amount. When starting apocarotenoids are isomers of the same chemical compound (e.g., ionone isomers) their biotransformation can give products very different from each other, depending both on the starting substrate and on the fungal species used. Since the majority of the starting apocarotenoids are often available in natural form and the described products are natural compounds, identified in flavours or fragrances, our biotransformation procedures can be regarded as prospective processes for the preparation of high value olfactory active compounds.

Keywords: apocarotenoids; biotransformation; damascone; flavours; fungi; ionone; oxidation; theaspirane.

Figure 1

The formation of apocarotenoids through degradation of carotenoids and the seven C₁₃ apocarotenoids (compounds 1–7) selected as substrates for the fungal biotransformation investigated in the present study.

Figure 2

Compounds obtained through biotransformation of α-, β- and γ-ionone by means of the fungal strains employed in the present study. Reagents and conditions: (a) fungal strain, malt extract medium (MEM), aerobic conditions, 140 rpm, 20 or 25 °C, 8–20 days; (b) Ac₂O/pyridine (Py), 4-dimethylaminopyridine (DMAP) catalyst, room temperature (rt), 6 h.

Figure 3

Compounds obtained through biotransformation of 3,4-dehydro-β-ionone and theaspirane by means of the fungal strains employed in the present study. Reagents and conditions: (a) fungal strain, MEM, aerobic conditions, 140 rpm, 20 or 25 °C, 14–20 days; (b) Ac₂O/Py, DMAP catalyst, rt, 6 h.

Figure 4

Compounds obtained through biotransformation of α- and β-damascone by means of the fungal strains employed in the present study. Reagents and conditions: (a) fungal strain, MEM, aerobic conditions, 140 rpm, 20–25 °C, 14–20 days; (b) Ac₂O/Py, DMAP catalyst, rt, 6 h.