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

•Molar absorptivity (ε) of all major anthocyanins from red cabbage was determined.•ε of the anthocyanins ranged from ∼13,000–30,000 L/mol cm in different solvents.•ε and λmax were generally higher in acidified MeOH than in buffer pH 1.•High ε were found in pH 1–2, decreased in pH 3–6, and increasing again from pH 7 to 8.•Position and number of acylating groups were critical factors that affected the ε.

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 (ε) 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 × 10−5 and 1 × 10−3 mol/L. Spectra were recorded and ε calculated using Lambert–Beer’s law. The ε in acidified MeOH and buffer pH 1 ranged between ~16,000–30,000 and ~13,000–26,000 L/mol cm, respectively. Most pigments showed higher ε in pH 8 than pH 2, and lowest ε 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 ε and spectral behaviors.