Thermal Stability and Isomerization of Lycopene in Tomato Oleoresins from Different Varieties

ABSTRACT: Lycopene, a tomato carotenoid, has been associated with the inhibition of certain chronic diseases including prostate cancer. Tomato oleoresin is a lipid-rich material resulting from successive solvent extraction of the tomato fruit. Thermal stability and isomerization of lycopene in oleoresins prepared from 3 different tomato varieties, Roma, High Lycopene, and Tangerine, and tomato peel waste, were studied at 25 °C, 50 °C, 75 °C, and 100 °C in the dark. Thermally degraded lycopene compounds and isomers of lycopene were analyzed by a combination of C₃₀ reversed-phase high-performance liquid chromatograph with a photodiode array detector, UV-visible spectrometer, or mass spectrometer. Effects of antioxidants on lycopene were also studied at 50 °C. As the storage temperature increased from 25 °C to 100 °C, the degradation of total lycopene in oleoresin from all samples increased significantly ( P <0.05). Lycopene at 25 °C and 50 °C may degrade mainly through oxidation without isomerization. Isomerization of lycopene in tomato oleoresins increased at 75 °C and 100 °C. Tetra- cis lycopene in Tangerine tomato varieties followed different degradation and isomerization pathways compared with all -trans lycopene in other tomato varieties. Addition of α-tocopherol or butylated hydroxytoluene slowed the rate of degradation of lycopene in oleoresin.