Production of hemicellulose oligomers from softwood chips using autohydrolysis followed by an enzymatic post-hydrolysis

In the context of value added valorization of hemicelluloses (HCs), their soft extraction by autohydrolysis (AH) of softwood (SW) chips has been optimized via the temperature/time parameters (170°C/2 h, 170°C/1 h and 150°C/1 h). Two enzyme mixtures containing mainly a glucanase and a mannanase were used to decrease the degree of polymerization (DP) of the extracted HCs. Hydrolysates containing HCs were analyzed in terms of monomers and oligomers, molecular weight distribution (MWD) and chemical composition. The MW was strongly dependent on AH conditions: most of the water-soluble HCs with 1800 Da MW were obtained at 150°C/1 h. The parameters 170°C/2 h gave rise to MWs<1800 Da. Enzymatic hydrolysis (EH) reduced efficiently the DP of HCs, and the glucosidase was more efficient than the mannanase, but the former also hydrolyzed more oligomers into their monomeric components.