Microbial transformation carvone

Limonene (92) is the most widely distributed terpene in nature after a-pinene [68]. The (+)-isomer is present in Citrus peel oils at a concentration of over 90% a low concentration of the (-)-isomer is found in oils from the Mentha species and conifers [26]. The first data on the microbial transformation of limonene date back to the sixties. A soil Pseudomonad was isolated by enrichment culture technique on limonene as the sole source of carbon [69]. This Pseudomonad was also capable of growing on a-pinene, / -pinene, 1-p-menthene and p-cymene. The optimal level of limonene for growth was 0.3-0.6% (v/v) although no toxicity was observed at 2% levels. Fermentation of limonene by this bacterium in a mineral-salts medium resulted in the formation of a large number of neutral and acidic products. Dihydrocarvone, carvone, carveol, 8-p-menthene-1,2-cw-diol, 8-p-menthen-1 -ol-2-one, 8-p-menthene-1,2-trans-diol and 1 -p-menthene-6,9-diol were among the neutral products isolated and identified. The acidic compounds isolated and identified were perillic acid, /Msopropenyl pimelic acid, 2-hydroxy-8-p-menthen-7-oic acid and... 

Flavor of Microbial Transformation Products. The flavor of terpenoids produced by microbial transformation was evaluated. (-)-Carvone (1) is well known as a spearmint flavor component. Transformation products (4 - 7) of 1 had peppermint-like flavor although these are slightly different to each other in terms of the odor quality. The metabolites, bottrospicatols (10a and 10b) Streptomyces species did not have a characteristic flavor but quite different activities (Figure 8). (+)-Bottrospicatal (15) which was produced by the oxidative reaction of (+)-bottrospicatol (10a) with CrOa in pyridine had a weak spice-flavor (slightly black-pepper like). The ester derivatives (13 in Figure 7) had a weak medicinal flavor. The flavor of acetyl ester (13a) was the strongest of all. 

Noma, Y., S. Nonomura, H. Ueda, H. Sakai, and C. Tstusmi, 1974b. Microbial transformation of carvone. Proceedings of the 18th TEAC, pp. 20-23. 

The main products of limonene oxidation, carvone and carveol, cause a terpenic off-flavour in essential oils and juices. Valencene oxidation products, such as (-F)-nootkatone, cause a grapefruit-like off-flavour in orange juices. Large amounts of alcohol (-F)-o(-terpineol, which arises, for example, during storing of juices by acid catalysed hydration or microbial transformation of limonene, is also perceived as an off-flavour. 

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