Effect of Gamma Irradiation on the Hydrolysis of Lignocellulosic Materials using Cellulase derived from Aspergillus niger

摘要

The effect of high-dose irradiation as a pretreatment method on two common lignocellulosic materials; softwood (Triplochiton scleroxylon) and hardwood (Khaya senegalensis) were investigated by assessing the potential of cellulase enzyme derived from Aspergillus niger to hydrolyse the materials. The wood samples were exposed to gamma-ray ranging from 10kGy to 100kGy emitted from ~(60)Co (cobalt-60 AECL), at a dose rate of 0.6 Gray per second. Each irradiated sample was soaked in 1% (w/v) sodium hydroxide solution at a ratio of 1:10 (substrate:solution) for 2h at room temperature after which they were washed free of the chemical and autoclaved at 120 deg C (15 psig steam) for 1 h. Hydrolysis of the sawdust samples with cellulase was conducted by suspending specified part of the dried sample in a 250 ml flask with 0.05 M citrate buffer (pH 5) for 1 h in an incubator at 45 deg C before adding the cellulase enzyme produced above in an amount corresponding to 10 ml enzyme solution per 1 g of dry sample.The results obtained showed that the irradiation strongly affected the materials, causing the enzymatic hydrolysis to increase by more than 2 fold. Maximum digestibility occurred in softwood at 70kGy dosage of irradiation, while in hardwood it was at 90kGy dosage. It was also observed that, at the same dosage levels (p <= 0.05), hardwood was hydrolysed significantly better compared to the softwood. In conclusion, A. niger have been shown to be a good source of cellulase and in addition, irradiated woodshave been demonstrated to be good candidates for cellulose biomass conversion into useful products; however, hardwood (Khaya senegalenesis) is more suitable for this process compared with softwood {Triplochiton scleroxylon) since it yielded more reducing sugars.