Enhancing enzymatic hydrolysis of industrial hemp hurds (Cannabis sativa L.) by combination of soaking in dilute acid and steam pretreatment

The goal of this study was to develop an operational pretreatment for effective modifications of physico-chemical properties of industrial hemp hurds (IHH) to improve hemicelluloses solubilization and enzymatic hydrolysis extent of potentially fermentable sugars. The pretreatment consisted firstly in soaking in dilute H 2 SO 4 solution, at concentrations ranged from 0.4 to 5% (w/w) and secondly in thermomechanical treatment, termed as IV-HMT (Intensive Vacuum associated to Heat Moisture Treatment) that works at moderate saturated steam conditions (0.7 MPa for 30 min) corresponding to combined severity factor (CS) from-1.02 to 1.4. The pretreatment efficiency was investigated according to changes in chemical composition, microstructure of IHH ( A BET surface area, SEM, crystallinity by XRD, FTIR) and enzymatic hydrolysis yield. FTIR analysis showed that the structure linkages between lignin and carbohydrates were changed, as indicated by the reduction in peak bonds intensities ranged from 1510 to 1242 cm −1 and confirmed from chemical analysis by a maximum of 70.3% lignin removal. The specific surface area exhibited progressive increase with CS, reaching up 2.3 times that of raw IHH (0.9 m 2 /g). Due to extractives removal, crystallinity index (CI) increased from 15 (raw) to 25% for acid-free IV-HMT and then decreased in presence of H 2 SO 4 consequently to transition from crystalline to amorphous structure. Maximum xylose and glucose production were obtained at low acid concentration (0.6%) combined with IV-HMT, with overall reducing sugars of 96.3%. The maximum production of inhibitors was obtained for 2% H 2 SO 4 and corresponded to 0.022 g/L and 0.48 g/L for furfural and HMF respectively.