Abstract: The thermal degradation kinetics of lycopene and color in red grapefruit was investigated. The results indicated that the degradation of lycopene and color followed the first-order kinetics. The relationship between lycopene content and color during thermal processing at selected temperatures could be expressed by the same equation: C/C0 = 1.770 7 (a*/a0*) + 0.801 2. The relationship between purified lycopene content and color at 70, 80 and 90 ℃ could be described by the following equations: C/C0 = 1.856(a*/a0*) ? 0.841 5, C/C0 = 1.714 (a*/a0*) ? 0.711 8, and C/C0 = 1.492 1 (a*/a0*) ? 0.467 2, respectively. The thermal degradation pathway of lycopene as determined by high performance liquid chromatography coupled with photodiode array detection (HPLC-PAD) included the transformation of all-trans-lycopene into mono-cis-isomer and further into di-cis-isomer during heating, which could be transformed into mono-cis-isomer or degraded, resulting in a decrease in the content of total lycopene.

Key words: red grapefruit, lycopene, color, thermal degradation kinetics, degradation mechanism