Chemical composition of African mahogany ( K. ivorensis A. Chev ) extractive and tannin structures of the bark by MALDI-TOF
Résumé
The total phenolic and the condensed tannins content of the bark, the sapwood and the heartwood of Khaya ivorensis (K. ivorensis) from the natural forest of Gabon was investigated by Folin-Ciocalteu, vanillic assay and acid/butanol methods All these methods showed that the bark, the sapwood and the heartwood of K. ivorensis did not display a significant difference (p > 0.05) regarding their phenolic content and their condensed tannins content as well. The acetone/water extracted tannins from the bark were characterized by Matrix Assisted Laser Desorption/Ionization time of flight (MALDI-TOF) mass spectrometry and by Fourier Transform InfraRed spectroscopy (FTIR). The presence of fisetinidin, gallocatechin, and trihydroxyflavan monomers was observed for the first time. Flavonoid oligomers linked to sugars were found within K. ivorensis condensed tannins. An heptamer formed by mixed fisetinidin, trihydroxyflavan, three dihydroxyflavans, and a carbohydrate dimer including mannose was also identified for the first time in the bark of K. ivorensis. That mahogany hardwood species did not exhibit any antifungal activity against the white rot fungus Coriolus versicolor. However, bark powder decreased the radial fungus growth.