Exposure to acids is thought to produce ion-pairs, which can
then dissociate to form a carotenoid carbocation. This process
can be seen in Eq. 3
Optical spectra of carotenoid carbocations have been reported
for beta-carotene, 8′-apo-caroten-8′-al, and canthaxanthin
when exposed to trifluoroacetic acid in benzene, CH2Cl2,
and acetonitrile solution (Konovalov and Kispert, 1999). He
and Kispert (2001) showed that canthaxanthin and 8′-apo-betacaroten-
8′-al incorporated into sol-gels could be degraded by
sulfuric acid (pH 3-3.5).