The Annatto Carotenoids and the Norbixin Absorption Coefficient

Abstract

Annatto seeds present cis-bixin as the major carotenoids, but the norbixin salt is the main pigment present in dyes obtained from the alkaline extraction process. For analyzing the norbixin, the absorptions are obtained in the two spectral peaks with higher intensity, but discrepanciesin the published extinction values have led to serious doubts. Taking into account the use of absorption coefficient for evaluating the norbixin concentration in annatto seeds and extracts, the present study evaluated the absorption coefficient in various solvents and the total uncertainty associated with this value was determined. The norbixin standard was prepared from annatto seeds, purified by column chromatography and the purity of norbixin was evaluated by HPLC-DAD. The absorption coefficients were determined for norbixin in different solvents and the uncertainty was evaluated. The 0.5% potassium hydroxide, the main solvent used for marketing the annatto seeds and extracts, showed the absorption coefficients of 2887 at 454nm and of 2546 at 483nm, and the estimation of expanded uncertainty (K=2) was ±86 and 85 g 100 mL-1, respectively.