Effects of ozone and oxygen on the degradation of carotenoids in an aqueous model system

The effects of ozone and oxygen on the degradation of carotenoids in an aqueous model system were studied. All-trans beta -carotene, 9-cis beta -carotene, beta -cryptoxanthin, and lycopene were adsorbed onto a C-18 solid phase and exposed to a continuous flow of water saturated with oxygen or ozone at 30 degreesC. Carotenoids were analyzed using HPLC with a C-30 column and a photodiode array detector. Approximately 90% of all-trans beta -carotene, 9-cis beta -carotene, and beta -cryptoxanthin were lost after exposure to ozone for 7 h. A similar loss of lycopene occurred in only 1 h. When exposed to oxygen, all carotenoids, except beta -cryptoxanthin, degraded at lower rates. The degradation of all the carotenoids followed zero-order reaction kinetics with the following relative rates: lycopene > beta -cryptoxanthin > all-trans beta -carotene > 9-cis beta -carotene. The major degradation products of-carotene were tentatively identified on the basis of their elution on the HPLC column, UV-Vis spectra, and electrospray LC-MS. Predominant isomers of beta -carotene were 13-cis, 9-cis, and a di-cis isomer. Products resulting from cleavage of the molecule were beta -apo-13-carotenone and beta -apo-14'-carotenal, whereas epoxidation yielded beta -carotene 5,8-epoxide and beta -carotene 5,8-endoperoxide.