Research On Ultrasound-aided Enzymatic Hydrolysis Of Bamboo And Its Mechanism

Degumming is an important processing method to extract the fiber from bamboo. The tightness of bamboo internal structure and the complex of composition would influence the efficiency of enzyme degumming. In our work ultrasound was used to pretreat bamboo prior to enzyme degumming with the purpose to destroy the tightness and complex internal structure of bamboo to improve the degumming efficiency. Meanwhile, the mechanism of ultrasonic processing lignocellulose biomass was discussed.Firstly, the parameters for ultrasonic processing has been determined by univariate analysis with cellulase as model enzyme. Then the optimal ultrasonic processing parameters were determined by orthogonal experiment. The results indicated that the optimal ultrasonic processing was conducted as a pretreatment for cellulase hydrolysis of bamboo at the frequency of 25 KHz for 10 min with the bath ratio of 1:20, the power of 650 W, the pulse period of 3/4. The reducing sugar yield increased 5.47μg/m L, the percentage improved 58.37% under this condition than the original bamboo powders. The optimal ultrasonic pretreatment was launched at the frequency of 25 KHz for 10 min with the bath ratio of 1:20, the power of 700 W, and the pulse period of 3/4 for xylanase hydrolysis of bamboo. The reducing sugar yield increased 0.5μg/m L, the percentage improved 8.50% under this condition than the original bamboo powders. The optimal ultrasonic pretreatment was carried out at the frequency of 25 KHz for 10 min with the bath ratio of 1:20, the power of 650 W, and the pulse period of 3/4 for combined cellulase-xylanase hydrolysis of bamboo powders. The reducing sugar yield increased 6.84μg/m L, the percentage improved 23.34% under this condition than the original bamboo powders. Experimental results revealed that cellulase and xylanase showed synergistic effect on the hydrolysis of bamboo. The ultrasonic parameters setting different when different enzyme involved in the hydrolysis of bamboo due to the specificity of the enzyme towards the substrate.The relative mechanism for ultrasound treating has been discussed. The surface morphological structure of bamboo was changed with ultrasound pretreatment. The crystallinity degree decreased by 13.58% and the water retention value increased by 33.38%. However, no obvious chemical group disappeared or new group generated were observed in the bamboo pretreated by ultrasound. The result from ultraviolet-spectrophotometer showed the watersoluble lignin substance presented in the liquid medium from ultrasonic pretreatment. Analysis from fourier transform infrared spectra indicated there were many specific groups related with cellulose, hemicellulose and lignin existing in the liquid medium. The result of Ion Chromatography showed that galactose and glucose were available in the liquid medium. The increase of enzymatic hydrolysis efficiency by ultrasonic pretreatment were explained from the analysis of substrate and the liquid medium. Ultrasonic pretreatment destroyed the complex and dense structure formed by cellulose, hemicellulose and lignin. Part of the substance were separated from the main body of bamboo. Therefore, more active sites and space were accessible for enzymatic hydrolysis. In this case, the efficiency of enzymatic hydrolysis of bamboo has been greatly increased after ultrasound pretreatment.