Bioconversion of hemicelluloses of lignocellulosic biomass to ethanol: an attempt to utilize pentose sugars

Abstract

ABSTRACTBiofuels are the imperative commodities influential in future bioeconomy that can be made sustainable by utilizing hemicelluloses which are the primary unutilized residues obtained from a lignocellulosic ethanol refinery. The abundant fraction in these hemicelluloses include pentoses (mainly xylose). The rationale behind the huge loss of hemicellulosic fraction is their heteropolymeric nature, low fermentability, lack of pentose specific transporters and enzyme cascades required for pentose fermentation by natural yeast strains. These lacunae lead to lower overall yield and productivity of ethanol thus rendering the entire process uneconomical. However, improvements in the conventional cellulose to ethanol know-how can trigger evolution towards bioeconomy. For industrial implementation of process technology, hemicellulosic stream should be integrated as a primary fraction along with celluloses for converting into ethanol. Thus, a novel hexose and pentose co-fermenting yeast strain is essential for a consolidated bioprocess aiming to achieve process economization. Considering a range of value added platform chemicals other than ethanol, such as xylitol, sorbitol, furfurals, hydroxyl methyl furfurals, ethylene glycol, glycolic acid, acetic acid, acetone, ethylene, and other residual biomass based products, such as biomanure, can render the biofuel production process more economical as multiple products may be obtained from the same biomass making the production process a comprehensive one. Therefore, the present review showcases the various technical impediments, breakthroughs, and bioeconomic aspects in the field of pentose to ethanol research which are instrumental in the future of the biofuel sector to address escalating oil prices and diminishing oil reserves.