Análise das macromoléculas e origem do pigmento azul dos arilos de Ravenala madagascariensis (Strelitziaceae)

Abstract

The Strelitziaceae is a family of monocotyledons belonging to the order Zingiberales which contains three genera: Strelitzia with five species in meridional África, Ravenala with a single specie in Madagascar and Phenakospermum with a single specie in the Northern regions of South America. Ravenala madagascariensis produces a fibrous aril with a waxy texture and blue coloration, which, contrary to the majority of plant tissues, does not lose its color after cell death. What is interesting from a chemical point of view is: I) the rarity of blue pigments in the plant kingdom and II) its stability is greater than other common classes of naturally occurring plant pigments such as carotenoids, betalains and chlorophyls which make it an attractive candidate as a pigment for use in food and cosmetics. The current work describes attempts to isolate, purify, analyze and characterize naturally occurring macromolecules present in the non-polar and polar fractions of the seed arils of R. madagascariensis. In the non-polar fraction, which comprises approximately 70% of the arils, the prescence of triacylglycerides was confirmed by 1H NMR and infrared spectroscopies. The identities and relative proportions of the fatty acids present were determined by GC-MS, calculation of their Kováts indices and by comparison to authenic reference standards after conversion to their methyl esters by transesterification. The four principal compounds encountered were: palmitic (C16:0, 41%), stearic (C18:0, 14%), oleic (C18:1 ω9cis, 34%) and linoleic (C18:2 ω6, 7%) acids. Analysis of the polar fraction of the arils suggests the presence of a chromophore related to the phycobilins, a class of tetrapyrrole pigments, due to absorptions at 680 and 620nm in the UV-Vis of the HOAc and SDS extracts respectively, and a positive result to the Ehrlich test. Examination of the infrared and Raman spectra indicate the presence of a protein, due to absorptions characteristic of amide I, II and III bands in the infrared, while the absence of absorptions in the region between 500 and 200cm-1 in the Raman spectra would indicate the absence of a metal coordinated to the chromophore.. The protein profile obtained by gel electrophoresis strongly suggests the presence of a protein with a mass of aproximately 48KDa, which possesses a chromophore responsible for the blue color observed in the arils of R. madagascariensis. Analysis by RP-HPLC at various wavelengths of the SDS extracts suggest that the chromophore is held in place by intermolecular interactions as opposed to covalent bonding.