SEPARATION AND IDENTIFICATION OF CIS TRANS CAROTENOID ISOMERS

To have a better assessment of major carotenoids, there is a need to systematically elucidate cis isomers of these polyenes. The combination of separation (Vydac and Zorbax C18 columns), spectral ratios (D(B)/D(II) and D(II)/D(III)), and spectral characteristics was used to help identify cis/trans isomers. The less lipophilic carotenoids are better separated by the Zorbax column and the more lipophilic carotenes by the Vydac column. The optimized isocratic mobile-phase composition for both columns was CH3CN:CH3OH:CH2Cl2 (80:18:2). One to four cis isomers were differentiated from their corresponding trans isomers in four acyclic (phytoene, phytofluene, zeta-carotene, and lycopene) and three cyclic (gamma-carotene, beta-carotene, and lutein) carotenoids. The D(B)/D(II) ratios were used to predict conjugated double bonds between 9 and 11 and the D(II)/D(III) ratios for conjugated double bonds between 3 and 7.