Evaluation of the colouring strength of saffron spice by UV—Vis spectrometry

The influence of various steps of the extract preparation procedure on the absorbance readings used for the commercial evaluation of the colouring strength of saffron is described. The study was prompted by the diversity of extraction protocols found in the literature. Extraction period, stage of the extract filtration, filter type and extraction solvents influenced the size and the repeatability of the absorbance measurements. Long extraction periods (24 h) caused loss of the colouring strength. Filtration through narrow pore filters yielded extracts with higher colouring strength. The latter was significantly increased when the extract was filtered prior to final dilution. Alcoholic extracts presented higher colouring strength when compared to aqueous extracts. Derivative spectroscopy was applied to clarify the maxima wavelengths of the extracts. The ‘peak to peak’ method was used to evaluate the major absorbances in the region 400–500 nm of the second derivative spectrum.