HPAC Pretreatment Facilitates Enzymatic Hydrolysis of Softwood

Abstract

Background: Woody plants with high glucose content are alternative bioresources for the production of biofuels and biochemicals. Various pretreatment methods may be used to reduce the effects of retardation factors such as lignin interference and cellulose structural recalcitrance on the degradation of the lignocellulose material of woody plants. Results: Here, a hydrogen peroxide-acetic acid (HPAC) pretreatment was used to reduce the lignin content of several types of woody plants, and the effect of the cellulose structural recalcitrance on the enzymatic hydrolysis was analyzed. The cellulose structural recalcitrance and the degradation patterns of the wood fibers in the xylem tissues of Quercus acutissima (hardwood) resulted in greater retardation in the enzymatic saccharification than those in the tracheids of Pinus densiflora (softwood). In addition to the HPAC pretreatment, application of supplementary enzymes (7.5 FPU cellulose for 24 hours) further increased the hydrolysis rate of P. densiflora from 61.42% to 91.94% whereas the same effect was not observed for Q. acutissima. Also, it was observed that endoxylanase synergism significantly affects the hydrolysis of P. densiflora. However, this synergistic effect was lower for other supplementary enzymes. The maximum concentration of the reducing sugars produced from 10% softwood was 89.17 g L-1 in 36 hours of hydrolysis with 15 FPU cellulase and other supplementary enzymes. Approximately 80 mg mL-1 of reducing sugars was produced with the addition of 7.5 FPU cellulase and other supplementary enzymes after 36hours, achieving rapid saccharification. Conclusion: HPAC pretreatment thus removed the interference of lignin, reduced structural recalcitrance of cellulose in the P. densiflora, and thereby enabled rapid saccharification of the woody plants including a high concentration of insoluble substrates with only low amounts of cellulase. HPAC pretreatment may thus be a viable as an alternative for the cost-efficient production of biofuels or biochemicals from softwood plant tissues.