Microbial production of 4-hydroxybenzylidene acetone, the direct precursor of raspberry ketone.

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. 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. 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. Raspberry ketone or frambinone represents a total market value of between euro6 million and euro10 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.