Thermally-induced geometrical isomerisation of lycopene and its potential influence on functional activity

About 90–98% of native lycopene exists in the all-E form, but 79–88% of the lycopene found in the human body are Z-isomeric forms. Thermally-induced geometrical isomerisation of lycopene occurred within 24 h of refluxing in ethyl acetate and the proportion of Z-isomers increased from 5.8% to 49.9%. Accordingly, the concentration of lycopene required to double quinone reductase (QR) activity in Hepa 1c1c7 cells decreased from >100 to ∼22 μg/mL following thermo-isomerisation, while cell viability was retained at >87% at levels up to 50 μg/mL. The inhibition of nitric oxide (NO) production in activated RAW 264.7 macrophages was 50% at ∼100 μg/mL thermo-isomerised lycopene and increased to >80% when the concentration in the medium was increased to 500 μg/mL. No significant inhibition of NO evolution by macrophages occurred with native (∼94% all-E) lycopene. Both QR induction and NO inhibition bioassays revealed that the structural changes evoked by thermo-isomerisation were accompanied by enhanced biological functionality.