Molar absorptivity (ε) and spectral characteristics of cyanidin-based anthocyanins from red cabbage

Red cabbage extract contains mono and di-acylated cyanidin (Cy) anthocyanins and is often used as food colorants. Our objectives were to determine the molar absorptivity (epsilon) of different red cabbage Cy-derivatives and to evaluate their spectral behaviors in acidified methanol (MeOH) and buffers pH 1-9. Major red cabbage anthocyanins were isolated using a semi-preparatory HPLC, dried and weighed. Pigments were dissolved in MeOH and diluted with either MeOH (0.1% HCl) or buffers to obtain final concentrations between 5 x 10 (5) and 1 x 10 (3) mol/L. Spectra were recorded and epsilon calculated using Lambert-Beer's law. The epsilon in acidified MeOH and buffer pH 1 ranged between similar to 16,000-30,000 and similar to 13,000-26,000 L/mol cm, respectively. Most pigments showed higher epsilon in pH 8 than pH 2, and lowest epsilon between pH 4 and 6. There were bathochromic shifts (81-105 nm) from pH 1 to 8 and hypsochromic shifts from pH 8 to 9 (2-19 nm). Anthocyanins molecular structures and the media were important variables which greatly influenced their epsilon and spectral behaviors. (C) 2015 Elsevier Ltd. All rights reserved.