Geometrical-isomer-resolved spectroscopic characterization and in vitro functional screening of lycopene precursors: Repositioning lycopene biosynthetic intermediates as potential functional compounds.

Orange tomatoes deficient in carotenoid isomerase accumulate lycopene precursors primarily as Z-configured isomers that are difficult to separate and purify, limiting their systematic physicochemical and biological characterization. Here, we used optimized normal-phase HPLC to isolate >95% pure (15Z)-phytoene (PT), (15Z,9'Z)-phytofluene (PTF), (9Z,9'Z)-ζ-carotene (ζ-CAR), (9Z,7'Z,9'Z)-neurosporene (NEU), and (7Z,9Z,7'Z,9'Z)-lycopene (LYC), and confirmed their structures by NMR. These purified isomers were evaluated, with (all-E)-LYC and a thermally generated Z-isomer-enriched LYC (T-(Z)-LYC), for UV-Vis properties, antioxidant capacity, and enzyme inhibition related to reactive oxygen species (ROS) generation, skin quality, and blood pressure. UV-Vis analyses showed strong UV shielding by (15Z)-PT, (15Z,9'Z)-PTF, and T-(Z)-LYC. Singlet oxygen quenching increased with conjugation length of carotenoids, whereas hydroxyl and DPPH radical scavenging were highest for (9Z,7'Z,9'Z)-NEU and T-(Z)-LYC. Enzyme assays showed carotenoid- and isomer-dependent potency, e.g., (15Z)-PT strongly inhibited tyrosinase and elastase, and (7Z,9Z,7'Z,9'Z)-LYC strongly inhibited ROS-generating oxidases. These data support the industrial utilization of underexplored lycopene precursors.