Isolation of Geometrical Isomers of Lycopene Using Liquid-Solid Chromatography LI Wei, SUN Xinhu, XIAO Gang, DING Xiaolin (School of Food Science, Southern Yangtze University, Wuxi 214036, China)
Abstract: A normal phase high performance liquid chromatographic method, using three columns in series, was used to separate the geometrical isomers of lycopene. The results showed a better performance for isomer separation than reversed-phase high performance liquid chromatography (RP-HPLC). Five samples were measured, includ ing tomato,tomato paste, tomato oleoresin and other two products of lycopene. The identities of all-trans lycopene peaks were assigned based on retention time and absorbance spectra obtained by the photodiode array detectorby comparing with standard. The isomers were identified by their absorbance spectra and DB/DⅡ ratios, the value of the absorbance at the cis-peak(362 nm) divided by the absorbance at the maximum wavelength. All-translycopene was quantified by determining peak areas in the HPLC chromatograms calibrated against known amounts of all-trans standard. The contents of cis-isomers were calculated using all-trans standard for the cis-isomer standards are unavailable. All-trans lycopene was the predominant geometrical isomer in all the samples, whose contents varied from 96.38% of fresh tomato to 37.65% of 0.1% tomato oleoresin. The results indicate that during the processing of tomatos and extraction of lycopene, all-trans lycopene underwent isomerization, which increased the portions of cis-isomers. Key words: liquid-solid chromatography; lycopene; geometrical isomer
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