Abstract
Many countries have their biofuel policy programs in place as part of their overall strategy to achieve sustainable development. Among biofuels, bioethanol as a promising alternative to gasoline is of substantial interest. However, there is limited availability of a sufficient quantity of bioethanol to meet demands due to bottlenecks in the present technologies to convert non-edible feedstocks, including lignocelluloses. This review article presents and critically discusses the recent advances in the pretreatment of lignocellulosic biomass, with a focus on the use of green solvents, including ionic liquids and deep eutectic solvents, followed by enzymatic saccharification using auxiliary proteins for the efficient saccharification of pretreated biomass. Different techniques used in strain improvement strategies to develop hyper-producing deregulated lignocellulolytic strains are also compared and discussed. The advanced techniques employed for fermentation of mixed sugars contained in lignocellulosic hydrolysates for maximizing bioethanol production are summarized with an emphasis on pathway and transporters engineering for xylose assimilation. Further, the integration of different steps is suggested and discussed for efficient biomass utilization and improved ethanol yields and productivity.
Highlights
The ever-increasing demands for energy due to rapid increase of global population, industrialization, and geopolitical factors have called for the search for alternative and carbon neutral sources of energy (Souza et al, 2017; Chandel et al, 2020)
While the oxidative pathway is used as a defensive mechanism against oxidative stress and to generate NADPH, which is a major precursor for biomass formation, and is a driving element of xylose reductase (XR) (Karhumaa et al, 2007; Kwak and Jin, 2017)
The results revealed that Hxt7 had a higher xylose consumption ability compared to the other transporters; the substrate affinity was 200 folds higher for glucose as compared to xylose in the medium containing glucose/xylose mixture making xylose the second choice even in the presence of low concentrations of glucose
Summary
The ever-increasing demands for energy due to rapid increase of global population, industrialization, and geopolitical factors have called for the search for alternative and carbon neutral sources of energy (Souza et al, 2017; Chandel et al, 2020). The widespread application of conventional energy resources has contributed to serious challenges, including global warming and climate change by releasing greenhouse gases (GHGs) like carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and chlorofluorocarbons (Kiran et al, 2014) These adverse impacts have overshadowed the previous justifications used, including burgeoning petroleum prices, finite nature of fossil fuels, and have encourage the government and non-government agencies to find environmentally friendly, renewable, and sustainable energy resources for transportation, heating, and electricity generation (Nikolić et al, 2016). The aim of the present article is to review and critically discuss the advanced approaches used for the pretreatment of LCB, enzymatic saccharification, development of modified microbial strains to improve bioethanol yield, and different action mechanisms for bioethanol production using wild and genetically-modified strains It provides a summary of various integration approaches used for fermentative production of bioethanol.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
