Aims:  To investigate the enzymatic aldol reaction between acetone as a donor and 4‐hydroxybenzaldehyde as a receptor to generate 4‐(4‐hydroxyphenyl)‐but‐3‐ene‐2‐one or 4‐hydroxybenzylidene acetone, the direct precursor of 4‐(4‐hydroxyphenyl)‐butan‐2‐one or raspberry ketone, using different species of filamentous fungi and bacteria. Methods and Results:  Different classes of micro‐organisms were tested in a medium containing mainly acetone and 4‐hydoxybenzaldehyde. Of the micro‐organisms tested, only bacteria were able to synthesize significant amounts of 4‐hydroxybenzylidene acetone, ranging from 15 to 160 mg l−1 after 21 h of bioconversion, as a function of the bacteria tested. Conclusions:  The biological production of 4‐hydroxybenzylidene acetone has been described with bacteria possessing 2‐deoxyribose‐5‐phosphate aldolase (DERA, EC 4·1·2·4). This result suggests that DERA is involved in the catalytic aldolization of precursors for the production of 4‐hydroxybenzylidene acetone. Significance and Impact of the Study:  Raspberry ketone or frambinone represents a total market value of between €6 million and €10 million. The possibility of producing its direct precursor through a simple process using bacteria is of considerable interest to the flavour market and the food industry as a whole. This paper broadens the spectrum for the use of aldolase to achieve the biological synthesis of compounds of interest.

Cell structure modifications and beta-oxidation induction were monitored in two strains of Sporidiobolus, Sp. Ruinenii and Sp. pararoseus after cultivation on ricinoleic acid methyl ester. Ultrastructural observations of the yeast before and after cultivation on fatty acid esters did not reveal major modifications in Sp. ruinenii. Unexpectedly, in Sp. pararoseus a proliferation of the mitochondrion was observed. After induction, Sp. ruinenii principally exhibited an increase in the activities of acyl-CoA oxidase (ACO), hydroxyacyl-CoA deshydrogenase (HAD), thiolase and catalase. In contrast, Sp. pararoseus lacked ACO and catalase activities, but an increase in acyl-CoA deshydrogenase (ACDH) and enoyl-CoA hydratase (ECH) activity was observed. These data suggest that in Sp. ruinenii, beta-oxidation is preferentially localized in the microbody, whereas in Sp. pararoseus it might be localized in the mitochondria.

In order to study differences in gamma-decalactone production in yeast, four species of Sporidiobolus were cultivated with 5% of methyl ricinoleate as the lactone substrate. In vivo studies showed different time courses of intermediates of ricinoleic acid breakdown between the four species. In vitro studies of the beta-oxidation system were conducted with crude cell extracts of Sporidiobolus spp. and with ricinoleyl-CoA (RCoA) as substrate. The beta-oxidation was detected by measuring acyl-CoA oxidase, 3-hydroxyacyl-CoA dehydrogenase activities, and acetyl-CoA production. The time courses of the CoA esters resulting from RCoA breakdown by crude extract of Sporidiobolus spp. permit the proposal of different metabolic models in the yeast. These models explained the differences observed during in vivo studies.