Identification of Lycopene Stereoisomers in Tomato Extracts Employing LC-NMR

4 IDENTIFICATION OF LYCOPENE STEREOISOMERS IN TOMATO EXTRACTS EMPLOYING LC-NMR 

The lycopene stereoisomers were identified by using a Bruker AMX 600 spectrometer and, as a control unit, a Bruker peak sampling unit (BPSU 12). In general, the assignments of the Z/Z-isomers are available, adapted from the Karplus equation, by taking the differences of the coupling constants into consideration. 

Human serum contains a variety of carotenes and xanthophylls. These carotenoids are solely ingested from nutritional sources, for instance lycopene is 

Therefore, a mild and quick extraction technique is necessary to exclude the preparation of artifacts. The carotenoid stereoisomers can be quantitatively analysed, employing MSPD extraction, from plant material, as well as from serum samples, using on-line SPE without any isomerisation or oxidation of the carotenoids. The extraction step is coupled to the separation and identification steps. Here, LC-NMR hyphenation, employing C30 stationary phases, is suitable for unambiguous distinction between all of these stereoisomers. 

We were able to identify five geometrical isomers of lycopene in tomato peel extracts (all-E1, 9-Z, 13-Z, 9,13-ZZ and 9,13 -ZZ lycopenes) by recording LC-NMR spectra. In human serum, we have identified three of these isomers (all-E, 9-Z and 13-Z lycopenes). In comparison to the nutritional source (tomato), the two identified lycopene Z-isomers are enriched in the human serum sample, which indicates a specific role of these geometrical isomers within human organisms. 

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