Regarding the Natureof the Blue Pigment in Arilsof Ravenala Madagascariensis Sonn.(Strelitziaceae)

Ravenala madagascariensis, the Traveler’s tree, is native to Madagascar but has adapted globally and is utilized for medical and cosmetic purposes. Focusing on the brightly blue colored arils of the plant’s seeds, this study aimed to examine their morphological and physicochemical properties and to shed light upon the previously undescribed structure of the pigment. Plant arils were examined by energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). Centesimal analyses indicated a lipid-rich composition (81.45%), carbohydrates (7.03%), moisture (3.71%), ash (0.78%), and proteins/peptides (7.1%). Analysis of the fatty acid methyl esters obtained from the lipid fraction by GC–MS indicated a composition of 41% palmitic, 14% stearic, 34% oleic and 7% linoleic acids. A battery of qualitative tests employing hexane, ethanol, and 10% aqueous sodium dodecyl sulfate (SDS) extracts of R. madagascariensis arils for the presence the following secondary metabolites was performed: alkaloids, triterpenes and phytosteroids, coumarins, phenolics, flavonoids, anthroquiones, saponins and tannins. Results for all classes were negative or, in one case, inconclusive. Factorial optimization of extraction conditions for isolation of the pigment was performed indicating 10% aqueous SDS at pH = 5 to be the most efficient to remove the pigment from the arils, while spectrophotometer scans indicated absorption peaks at 400 and 620 nm. Thin layer chromatography (TLC) of a 6 M HCl digest of the arils tested positive for amino acids when developed with ninhydrin. SDS-PAGE electrophoresis revealed a 14 kDa protein profile and the peptide fractions obtained after partial degradation with trypsin were analyzed by (UHPLC/MS/MS), lending important structural information that strongly suggests the presence of a phytocyanin (Blue Copper Protein). Analysis of our data and by comparison to the NCBI BLAST data bank indicated a phytocyanin domain-containing protein, responsible for the blue coloration of Ravenala arils due to copper coordination with the protein.