PHOTOISOMERIZATION OF BETA-CAROTENE BY PHOTOSENSITIZATION WITH CHLOROPHYLL DERIVATIVES AS SENSITIZERS

The ability of chlorophyll compounds, naturally present in extracts of green vegetables, to sensitize the photoisomerization of all-trans-beta-carotene was investigated. Eight individual chlorophyll derivatives were evaluated for their ability to induce the photoisomerization of all-trans-beta-carotene. All of the derivatives were found to act as sensitizers in the photoisomerization of all-trans-beta-carotene. Additionally, all-trans-beta-carotene added to vegetable extracts was photoisomerized. The final isomer distribution was similar to the equilibrium mixtures found using individual sensitizers. Isomerization reactions induced by chlorophyll may explain the presence of high percentages of cis isomers measured in photosynthetic tissues. Given the susceptibility of carotenoids to isomerize in the presence of chlorophyll derivatives, extra measures should be taken to avoid any exposure to light when handling extracts of plant tissue containing small quantities of chlorophyll. The results of these findings question whether the cis isomers in foods and biological tissues are naturally present or formed artifactually.