Main content area

Analysis of the Thermal Degradation of the Individual Anthocyanin Compounds of Black Carrot (Daucus carota L.): A New Approach Using High-Resolution Proton Nuclear Magnetic Resonance Spectroscopy

lliopoulou, Ioanna, Thaeron, Delphine, Baker, Ashley, Jones, Anita, Robertson, Neil
Journal of agricultural and food chemistry 2015 v.63 no.31 pp. 7066-7073
Daucus carota, anthocyanins, aqueous solutions, carrots, color, cooking, cyanidin, nuclear magnetic resonance spectroscopy, pH, reversed-phase high performance liquid chromatography, thermal analysis, thermal degradation
The black carrot dye is a mixture of cyanidin molecules, the nuclear magnetic resonance (NMR) spectrum of which shows a highly overlapped aromatic region. In this study, the 1H NMR (800 MHz) aromatic chemical shifts of the mixture were fully assigned by overlaying them with the characterized 1H NMR chemical shifts of the separated compounds. The latter were isolated using reverse-phase high-performance liquid chromatography (RP-HPLC), and their chemical shifts were identified using 1H and two-dimensional (2D) correlation spectroscopy (COSY) NMR spectroscopy. The stability of the black carrot mixture to heat exposure was investigated at pH 3.6, 6.8, and 8.0 by heat-treating aqueous solutions at 100 °C and the powdered material at 180 °C. From integration of high-resolution 1H NMR spectra, it was possible to follow the relative degradation of each compound, offering advantages over the commonly used ultraviolet/visible (UV/vis) and HPLC approaches. UV/vis spectroscopy and CIE color measurements were used to determine thermally induced color changes, under normal cooking conditions.