Rajendran, K., Department of Biological and Ecological Engineering, Oregon State University, Corvallis, OR, United States, MaREI Research Centre, Environmental Research Institute, University College Cork, Cork, Ireland; Drielak, E., Department of Molecular Biosciences and Bioengineering, University of Hawai’i at Mānoa, Honolulu, HI, United States; Sudarshan Varma, V., Agricultural Research Organization, Institute of Soil, Water and Environmental Sciences, Newe Ya’ar Research Center, Newe Yaar, Israel; Muthusamy, S., Downstream Processing Laboratory, Department of Biotechnology, Kumaraguru College of Technology, Coimbatore, India; Kumar, G., Center for Materials Cycles and Waste Management Research, National Institute for Environmental Studies, Tsukuba, Japan

Lignocellulosic biomass is the most abundant renewable energy bioresources available today. Due to its recalcitrant structure, lignocellulosic feedstocks cannot be directly converted into fermentable sugars. Thus, an additional step known as the pretreatment is needed for efficient enzyme hydrolysis for the release of sugars. Various pretreatment technologies have been developed and examined for different biomass feedstocks. One of the major concerns of pretreatments is the degradation of sugars and formation of inhibitors during pretreatment. The inhibitor formation affects in the following steps after pretreatments such as enzymatic hydrolysis and fermentation for the release of different bioenergy products. The sugar degradation and formation of inhibitors depend on the types and conditions of pretreatment and types of biomass. This review covers the structure of lignocellulose, followed by the factors affecting pretreatment and challenges of pretreatment. This review further discusses diverse types of pretreatment technologies and different applications of pretreatment for producing biogas, biohydrogen, ethanol, and butanol. © 2017, Springer-Verlag Berlin Heidelberg.