Paprika carotenoids:: Analysis, isolation, structure elucidation

Paprika, Capsicum annuum is one of the oldest, most important and widely used carotenoid food colorants. The composition of the carotenoid pigments produced by paprika has been investigated for a long time. The red carotenoids in paprika are mainly capsanthin, capsorubin, and capsanthin 5,6-epoxide, possessing a 3-hydroxy kappa-end group. At the same time, the fruits are also rich in yellow xanthophylls such as beta-cryptoxanthin zeaxanthin, and antheraxanthin, as well as beta-carotene. In the past fifteen years many other carotenoids with interesting structures, especially those with the 5-hydroxy-5,6-dihydro-3,6-epoxy-beta (oxabicyclo)-end group (cycloviolaxanthin, cucurbitaxanthin A and B, capsanthin 3,6-epoxide, cucurbitachromes), the 3,5,6-trihydroxy-5,6-dihydro-beta-end group (5,6-diepi-karpoxanthin, 6-epikarpoxanthin, 5,6-diepilatoxanthin, 5,6-diepicapsokarpoxanthin) and the 6-hydroxy-gamma-end group (nigroxanthin, prenigroxanthin), have been isolated and characterized. Capsanthone and capsanthone 3,6-epoxide, possessing a 3-oxo-kappa-end group, were also isolated from red paprika. This review gives a summary of the analyses of different kinds of paprika and the isolation and structure clarification of the above mentioned carotenoids, paying special attention to the stereochemistry of the 3,5,6-trihydroxy-5,6-dihydro-beta-end groups. The occurrence of these carotenoids in other natural sources is also demonstrated. The formation of these carotenoids in red paprika may be interrelated with the biosynthesis of carotenoids containing the kappa-end group. The biosynthesis of paprika carotenoids is discussed, focusing on the possible biosynthetic route in the red paprika, in comparison with that of yellow paprika.