Synthesis of β‐Ionone in an Aldehyde/Xanthine Oxidase/β‐Carotene System Involving Free Radical Formation

The enzymic cooxidation of β‐carotene (BC) by xanthine oxidase (XO) in aqueous solutions leads to β‐ionone (BI) and derivatives: epoxy‐β‐ionone (EPBI), dihydroactinidiolide, β‐cyclocitral, pseudoionone, etc. We demonstrate, in this article, that this is due to free radical (R⋅) formation during the first hour of stirring and the use of aldehydes as substrate. The bleaching of BC does not occur when the common substrate of XO, xanthine, is used; this proves that the superoxide anion O2⋅‐ alone is not active on BC. BI formation in this case is not observed.