Optimizing two green-like biomass pretreatments for maximum bioethanol production using banana pseudostem by effectively enhancing cellulose depolymerization and accessibility

Abstract

The banana is an important fruit crop that generates enormous quantities of lignocellulose-rich pseudostem residues that can be converted into biofuels and biochemicals. By performing response surface methodological modeling, optimized green liquor (GL) and liquid hot water (LHW) pretreatments of representative banana samples were studied. Using banana (BP-1) pseudostem residues rich in directly fermentable soluble sugars (27% hexoses and 2.7% pentoses via dry matter) and easily digestible xyloglucans, we measured nearly complete enzymatic saccharification with a hexose yield of 99% (% cellulose) from the most optimal GL pretreatment under relatively mild conditions. Notably, both optimal LHW (20 min, 110 °C) and GL (26.74% TTA, 105 °C, 26 min) pretreatments led to the highest bioethanol yields achieved thus far, at 27% and 31% (% dry matter), respectively, subjective to yeast fermentation with all hexose sources obtained in the BP-1 sample. Furthermore, we determined that optimal LHW and GL pretreatments extracted lignin by 25% and 40%, and reduced the cellulose crystalline index by 35% and 44% and polymerization degree by 34% and 36%, respectively, with distinctively altered lignin and hemicellulose features. Cellulose accessibility was increased 2–3 fold for remarkably enhanced enzymatic saccharification of biomass. Hence, we propose a mechanism model to elucidate why banana lignocellulose underwent complete biomass enzymatic saccharification under mild green-like pretreatments, providing an applicable strategy that can be used to produce large quantities of bioethanol from banana lignocellulose residues and beyond.