Synthesis of .beta.-ionone in an aldehyde/xanthine oxidase/.beta.-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 O 2 .- alone is not active on BC. BI formation in this case is not observed