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

摘要

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 H-1 NMR (800 MHz) aromatic chemical shifts of the mixture were fully assigned by overlaying them with the characterized H-1 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 H-1 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 degrees C and the powdered material at 180 degrees C. From integration of high-resolution H-1 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.