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Five cumulative pretreatments involving bleaching and/or steam explosion and/or alkaline extraction processes have been studied for polymeric hemicelluloses extraction from Okoumé sapwood. Morphological analysis of the cell wall of untreated and steam exploded wood was performed by optical and fluorescence microscopy after staining. Hemicelluloses extracts were characterized by HPEAC/PAD ion chromatography, steric exclusion chromatography (SEC), and high-performance liquid chromatography (HPLC). Near infrared spectroscopy, FTIR and HSQC - NMR spectroscopy analyses were also performed on the hemicelluloses extracts. Alkali extraction of bleached wood led to high yields (≈ 19%) of high molecular mass hemicelluloses (Mw ≈ 65 KDa) while neutral SE pretreatment allowed the recovery of highly acetylated polymers with a low degree of branching. A bleaching step prior to SE increased accessibility to hemicelluloses extraction but weakened the pulp and led to the removal of micro-particles of wood during the SE.