Optimization of low-temperature energy-efficient pretreatment for enhanced saccharification and fermentation of Conocarpus erectus leaves to produce ethanol using Saccharomyces cerevisiae

Abstract

Leaves of Conocarpus erectus are potential feedstock for bioethanol production due to their lower lignin and higher cellulosic content and are among one of the least explored biomass sources. The present study reported a low-temperature (90 °C) energy-efficient pretreatment method for the release of fermentable sugars from C. erectus leaves and its conversion into bioethanol by using industrial and lab yeast strains. Optimization of process parameters was performed by monitoring glucose utilization and ethanol production. The maximum glucose concentration of 12 g L−1 and 19.75 g L−1 were obtained after the low-temperature (90 °C) pretreatment and enzymatic saccharification, respectively. The optimum enzymatic assay conditions were with 10% biomass and enzyme loading of 30 FPU/g cellulose, resulting in the release of ~ 20 g L−1 of glucose from pretreated biomass which is equivalent to the glucose concentration in standard growth media. Hydrolysate fermentation by S. cerevisiae strains SPSC01, ER, YB2625, and 6525 exhibited highest ethanol yields of 0.47 g g−1 and 0.46 g g−1 which is the highest ever reported for C. erectus even under acetic acid stress, where a fermentation efficiency of 92.3% was achieved. The present study may lead to establishing low-cost, energy-efficient biological conversion of C. erectus to ethanol.