Most carotenoids are derived from a 40-carbon basal structure that includes a system of conjugated double bonds . The pattern of conjugated double bonds in the carotenoid backbone determines their light absorbing properties and antioxidant ability of carotenoids. In addition, the number of double bonds enable several cis or trans-configurations of a given carotenoid molecule. While the all-trans forms are predominant in nature generally, carotenoids tend to isomerize and form a mixture of mono- and poly-cis-isomers apart from the all-trans form .
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