Natural sources of colorants from Madagascar biodiversity

Madagascar is a world hotspot of biodiversity, with an endemism rate that reach up to 80%. Therefore, its flora represents a potential reservoir for bio-compounds, the development of which represents a scientific, an economic as well as an environmental challenge. Today, the harmfulness of petrochemical dyes to both human health and the environment is established. An alternative relies on the production of natural dyes trough green chemistry processes. Our research, based on indigenous empirical knowledge of dyers at Madagascar (in Indian Ocean), proposes as a first step to record all Malagasy dye plant species through an ethnobotanical survey and chemical screening of the coloration potential of some plant extracts. In a second step, the most interesting plant extracts (in aqueous ethanolic solution) were selected for a more indepth characterization of the color properties of the raw extracts. Several Malagasy plants species have been identified to have promising coloration potential as alternative sources of dyes or pigments. Two sources of natural yellow and two sources of natural red dyes will be discussed in this study. The plant biomass includes barks of Acridocarpus excelsus and Harungana madagascariensis, leaves of Tectona grandis and roots of Paracarphalea kirondron. The main chemical families identified in these four plant extracts are polyphenols, flavonoids, tannins, xanthonoids and quinonoids. Most of the pigments extracted from these five plants showed very good stability toward pH and high temperatures (up to 200 degrees C). Moreover, some plant extracts also showed high antioxidant and antimicrobial properties. Finally, an acute toxicity test performed using a zebrafish model showed that most of these extracts are less toxic than the usual artificial dyes. It should be noted that very little information has been found in the literature about the composition of roots of the endemic species P. kirondron. HPCL/DAD/MS analysis of the yellow colors extracted from P. kirondron showed a high concentration of different quinonoid pigments with potentially new structures (research in progress in laboratory). The diversity of dye plants from Madagascar is a promising source of natural dyes that can replace the artificial ones. However, the supply of a production chain for these dyes involves the respect for the rights of local actors and the implementation of actions to manage this biodiversity in a sustainable way.