Valorization of biodiversity and ethnobotanical, phytochemical and toxicological studies of dye plants of Madagascar: applications in the field of natural dyes.

Summary The current consumer trend for healthier and more environmentally friendly consumer products is pushing manufacturers to find natural alternatives. The synthetic dye industry, which is among the most polluting on the planet, is directly concerned. Madagascar's biodiversity, linked to a tradition of using plants to dye natural fibers, represents a renewable source of plant pigments, previously untapped. The substances extracted from these plants could give rise to natural dyes that can be used in industry, provided that the main scientific obstacles linked to the lack of knowledge about these plants are removed. Three complementary approaches were carried out during this work. A first ethnobotanical approach consisted in screening the biodiversity of dye plants in Madagascar. Thus 128 species, including 34 endemic, were identified and described. A second phytochemical approach allowed to develop the extraction of dyes by an eco-responsible process with ecological solvents and to characterize the physicochemical and technological properties of the extracts obtained. The results in terms of coloring power, stability (pH and temperature effect) and antioxidant and antimicrobial properties of the pigments (anthocyanins, proanthocyanidins) extracted from a few selected plant species, including Acridocarpus excelsus and Woodfordia fruticosa, underline their potential as natural bioactive colorants. The HPLC-DAD-CAD-MS chromatographic analysis of pigments extracted from Paracarphalea kirondron revealed for the first time secondary metabolites responsible for dyeing and biological properties. Finally, the third toxicological approach, carried out from the zebrafish model and the albino mice animal model, allowed to characterize the biological activity and toxicity profiles of these plant extracts. These initial results open up directly applicable prospects for the industrial valorization of these biological resources and Malagasy know-how, which may represent the natural alternative solutions sought. However, accompanying measures will have to be put in place to ensure a sustainable exploitation of this biodiversity.