Isomerization and increase in the antioxidant properties of lycopene from Momordica cochinchinensis (gac) by moderate heat treatment with UV-Vis spectra as a marker

Momordica cochinchinensis (gac) is a plant rich in lycopene. This pigment tends to solubilize in oil and get damaged during extraction. The impact of heating on cis-isomerization of oil-free lycopene in hexane was studied at 50 and 80 °C during 240 min with UV-Vis spectrometry, DAD-HPLC and TEAC test. The initial all-trans-form isomerized to the 13-cis isomer more rapidly at 80 °C. After this treatment, 16% of the lycopene compounds were in the 9-cis-form. This isomer triggered an increase in the antioxidant properties which was detectable from concentrations above 9% and resulted in a change from 2.4 to 3.7 μmol Trolox equivalent. It is thus possible to increase the bioactivity of lycopene samples by controlling heating. The evolution of ratios calculated from the global UV-Vis spectrum was representative of cis-isomerization and spectrometry can thus be a simple way to evaluate the state of isomerization of lycopene solutions.