Carotenoid isomer test

It has been suggested (Koyama et al. 1990, Kuki et al. 1995) that cis carotenoid isomers, and specifically the l5-cis isomer, exists in the RC to enhance the ability of the carotenoid to dissipate triplet energy via cis-to-trans isomerization. Bautista et al. (1998) tested this mechanism using locked-15,15"-cw-spheroidene. By a comparison of the behavior of the locked-15,15"-c/x-spheroidene with the unlocked spheroidene incorporated into RCs, and also comparing these samples with wild type RCs, it was possible to determine whether cis-to-trans isomeri-... 

Reversed-phase liquid chromatography shape-recognition processes are distinctly limited to describe the enhanced separation of geometric isomers or structurally related compounds that result primarily from the differences between molecular shapes rather than from additional interactions within the stationary-phase and/or silica support. For example, residual silanol activity of the base silica on nonend-capped polymeric Cis phases was found to enhance the separation of the polar carotenoids lutein and zeaxanthin [29]. In contrast, the separations of both the nonpolar carotenoid probes (a- and P-carotene and lycopene) and the SRM 869 column test mixture on endcapped and nonendcapped polymeric Cig phases exhibited no appreciable difference in retention. The nonpolar probes are subject to shape-selective interactions with the alkyl component of the stationary-phase (irrespective of endcapping), whereas the polar carotenoids containing hydroxyl moieties are subject to an additional level of retentive interactions via H-bonding with the surface silanols. Therefore, a direct comparison between the retention behavior of nonpolar and polar carotenoid solutes of similar shape and size that vary by the addition of polar substituents (e.g., dl-trans P-carotene vs. dll-trans P-cryptoxanthin) may not always be appropriate in the context of shape selectivity. 

CO2 density on extraction of all-ira 5-lycopene from tomatoes and found the greatest yield at the highest density (0.90 g/mL) tested. However, while SFE is a relatively mild extraction technique, it is still necessary to consider the effect of extraction conditions on carotenoid stability to minimize the formation of isomer artifacts (Spanos et ah, 1993). 

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