Enzymatic degradation of Elephant grass (Pennisetum purpureum) stems: Influence of the pith and bark in the total hydrolysis

•The inner pith of Elephant grass stalks is more easily degraded than the outer cortex.•Esterase supplementation increased deacetylation by reduced biomass solubilisation.•Enzymatic deacetylation of Elephant grass was improved by the addition of DMSO.•Low concentrations of DMSO can improve enzymatic removal of xylan and glucan.•Acetyl esterases removed acetic acid from lignin-enriched materials. The internal pith of a high energy plant, Elephant grass (EG), was more extensively degraded (>50% dry matter) compared to the outer cortex (31%) or the whole stem (35%) by an enzyme preparation from Humicola insolens, Ultraflo. Reducing sugars and acetic acid release from the pith was also higher compared to the cortex. Supplementation of Ultraflo with a type-C feruloyl esterase increased the level of deacetylation but also led to reduced solubilisation. The addition of 20% dimethyl sulfoxide (DMSO) as a co-solvent also reduced the solubility of EG by Ultraflo, although acetic acid release was increased, complimenting previous results found on model substrates. The presence of DMSO was also shown to have a protective effect on xylanase activity but not acetyl esterase activity in Ultraflo. Xylan in the biomass was preferentially solubilised by DMSO, while Ultraflo removed more glucose than xylose.