HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS OF THE PIGMENTS OF BLOOD-RED PRICKLY PEAR (OPUNTIA-FICUS-INDICA)

A method for the extraction, separation and evaluation of betalaines, the pigments of bood-red Opuntia ficus indica grown in Sicily, was studied. Tests with different solvent systems showed that extraction of the pigments with water-ethanol was the most complete. For the preparative separation of the betalaines, reversed-phase low-pressure column chromatography on an octadecylsilica bonded phase (RP-18) was the most suitable. Using phosphate buffer (pH 5)-methanol (85:15) the major yellow and red-violet pigments were sharply separated and recovered in good purity. Elution with the same mixture in the ratio 70:30 separated three minor yellow and red-violet components. The amounts of the yellow pigment were evaluated spectrophotometrically at 475 nm and of the red-violet pigment at 538 nm. For the evaluation of the purity of the recovered pigments, a reversed-phase high-performance liquid chromatographic method was applied using a LiChrosorb Select B column eluted with 0.1 M phosphate buffer (pH 5)-methanol (85:15), with spectrophotometric detection at 538 nm for the red pigments and 475 nm for the yellow pigment. The yellow pigment obtained was pure indicaxanthin, whereas in the red-violet pigments betanin and isobetanin were identified with another not yet characterized betalainic glucoside.