aTo utilize hemicelluloses from biomass as a feedstock to produce various value-added products, the soluble hemicelluloses must be isolated from the liquid phase with a high yield and purity. In this study, acacia wood was extracted by hydrothermal treatment, catalyzed by acetic acid at 170 °C for different lengths of time, and then precipitated after concentration and mixing with ethanol. Acetic acid led to faster hydrolysis of hemicelluloses, a process that was confirmed by a larger amount of total saccharides than the controlled results. A yield of more than 90% oligosaccharides was achieved in the hydrolysate with 1% (w/w) acetic acid. The maximum precipitate yield obtained was reduced, but a faster increase was observed in the first 30 min at 170 °C depending on the utilization of acetic acid. Analysis of 13 C nuclear magnetic resonance ( 13 C NMR) confirmed that the side chains, such as arabinose linked on the xylan chain, were severely broken down, and more dissolved hemicelluloses bonded with lignin (LCC) were present in the precipitates with 1% (w/w) acetic acid. Based on gel permeation chromatography (GPC), a molecular weight of not less than 1900 is suggested when ethanol is used to precipitate the oligosaccharides from hydrolysate. Keywords INTRODUCTIONThe chemical pulping industry is one of the largest manufacturers of lignocellulosic material, from which high strength and whiteness fibers are produced to make various grades of end-use papers. However, due to the increased capacity of the pulp and paper industry, the profitability of this industry is decreasing. Biorefining has been proposed to reshape the pulping industry by utilizing biomass resources more effectively and producing a variety of products (Vila et al. 2011;Liu et al. 2015). In kraft pulping, about 20% of biomass, mainly hemicelluloses, are dissolved in the black liquor along with lignin and then burned in the recovery cycle to produce energy for the process. However, the heating value of hemicelluloses is half that of lignin (13.6 MJ/kg) (Tunc and van Heiningen 2008). Therefore, instead of burning the hemicelluloses with black liquor, hemicellulose extraction prior to chemical pulping has been widely discussed as a practical approach in the implementation of a pulp mill-based biorefinery. There is great potential for the conversion of hemicelluloses derivatives into high-value added products such as fuels, films, health products, and polymers (Vila et al. 2011).Hydrothermal pretreatment (hot water treatment or autohydrolysis) is widely used to extract hemicelluloses from biomass for producing fermentable sugars and PEER-REVIEWED ARTICLE bioresources.com Shi et al. (2017). "Hemicelluloses from Acacia," BioResources 12(3), 6094-6108. 6095oligosaccharides (Ertas et al. 2014;Batalha et al. 2015;Cuevas et al. 2015). This method is a simple, low-cost, and attractive technology for extracting lignocelluloses in the kraft pulping (Deb et al. 2016), soda, soda-anthraquinone, and soda ethylenediamine processes for producing dissolving pulp (...