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

ABSTRACT

Biofuels 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.

KEYWORDS:

• Hemicelluloses
• co-fermentation
• engineered yeast
• bioethanol
• bioeconomics

Acknowledgements

Authors are obliged to Department of Biotechnology, Government of India, for sponsoring the project entitled “Production of lignocellulosic fuels: from lab to pilot scale” [grant number BT/PR15280/AGR/26/255/2011], Council for Scientific and Industrial Research [grant number 20-06/2010 (i) EU-IV] and Ministry of New and Renewable Energy [grant number 10/14/2010-P & C], Government of India for financial support and Indian Institute of Technology, Kharagpur, for infrastructural support based on which the present review article was able to take shape.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Department of Biotechnology, Ministry of Science and Technology (IN) [grant number BT/PR15280/AGR/26/255/2011]; Council for Scientific and Industrial Research, India [grant number 20-06/2010 (i) EU-IV]; Ministry of New and Renewable Energy India [grant number 10/14/2010-P & C].