Thermal Isomerization of All-trans-Lutein in a Benzene Solution

Abstract

  Four major cis-lutein isomers could be identified after thermal isomerization of all-trans-lutein in a benzene solution system; namely, 13′-, 13-, 9′- and 9-cis-luteins. Using both all-trans-lutein and a mixture of these purified cis-luteins as starting materials, the quantitative changes determined by HPLC response show that this thermal isomerization was a reversible reaction. The equilibrium constants (k_C) of 13′- and 13-cis-luteins were higher than those of 9′-, and 9-cis-luteins, suggesting that the amount formed of the former isomers was higher than that of the latter.