Comparison of various pretreatment strategies and their effect on chemistry and structure of sugar beet pulp

Pretreatment is deemed as a key step to destroy biomass recalcitrance and improve enzyme accessibility to cellulose during the second generation bioethanol production. A series of pretreatments were applied to treat sugar beet pulp (SBP) to uncover their impact on chemical and structural changes, and enzymatic digestibility. The results showed that all the four pretreatments had effects on the physical structure and chemical compositions of SBP. When being subjected to aqueous ammonia pretreatment, SBP exhibited high cellulose content due to the degradation of neutral detergent soluble fraction and other amorphous components. FTIR analysis showed that aqueous ammonia pretreatment could cleave ester linkages between carbohydrates and lignin, and modify the phenolic hydroxyl in lignin, yet without obvious delignification. In addition, the aqueous ammonia pretreatment led to cell wall dislocation and lignin redistribution, and enhanced enzymatic hydrolysis. The results obtained here indicated that biomass recalcitrance was destroyed by morphological and chemical alternation. The reducing sugar yield of SBP pretreated by AA could reach 487.8 mg/g, which was 2.73 times higher than that of the control. Consequently, AA might be more suitable to pretreatment for SBP, compared to the other pretreatments.