Occurrence of Astaxanthin in the Flower Petals of Adonis annua L.

Abstract

WHEN the dried petals of Adonis annua L. (Ranunculaceæ) (pheasant's eye) are extracted with light petroleum or methanol comparatively large quantities of a deep orange-red carotenoid are obtained. This pigment had an absorption spectrum (in light petroleum, n-hexane, carbon disulphate and pyridine) very similar to that of astaxanthin¹; as the pigment is epiphasic in the 90 per cent aqueous methanol/light petroleum partition test, it would appear to be esterified astaxanthin². The nature of the pigment was confirmed by saponifying the extract. This hydrolyses the esters and converts the liberated astaxanthin into astacin³ which when the reaction mixture is shaken with ether to extract the unsaponifiable material, collects at the interface as a flocculent orange-red mass. No other known carotenoid behaves in this manner; they are all extractable from a saponification mixture with ether. The flocculent red mass was washed free of alkali and dissolved in dilute hydrochloric acid; as is the case with authentic astacin, the pigment was now extracted from the aqueous phase by ether. The pigment was then purified by chromatography on sugar. Further confirmation of the identification of our pigment with astacin came from various comparisons with authentic astacin (from lobsters); (1) the absorption spectra of the two pigments measured in a number of solvents were identical in position and shape; (2) on co-chromatography on icing sugar using light petroleum containing 2 per cent (v/v) acetone the mixture of the two pigments moved slowly down the column but there was no resolution into two bands; (3) treatment of both pigments with lithium aluminium hydride produces identical pigments (probably 3,4,3′,4′-tetrahydroxy-β-carotene) with absorption spectra indistinguishable from that of β-carotene.