Enhancing the enzymatic digestibility of bamboo residues by biphasic phenoxyethanol-acid pretreatment

The high content of lignin in bamboo is considered as the major obstacle for its biorefining. In this work, a green, lignin-selective, and recyclable solvent of phenoxyethanol was coupled with acid solution to deconstruct recalcitrant structure of bamboo residues (BR) to boost its enzymatic digestibility. Results showed phenoxyethanol has excellent lignin-removal ability from 29.4% to 91.6% when phenoxyethanol:acid ratios increased from 0:1 to 4:1 at 120 °C. 82.5%–87.8% of cellulose was preserved in pretreated BR. The enzymatic digestibility of BR significantly improved from 20.0% to 91.3% when it was pretreated under optimized conditions. With lower enzyme dosages (10 FPU/g) and 5 recycled using of pretreatment liquor, pretreated BR still showed a good enzymatic digestibility of 67.4%–93.7% and 67.1–76.8%, respectively. Examination of physicochemical changes revealed that improvements to accessibility, reduction of crystallite size, decrease of surface lignin and hydrophobicity for pretreated BR showed positive correlations (R2 > 0.7) with their enzymatic digestibility.