REVIEW PAPER Influence of reactors, microbial carbohydrate uptake, and metabolic pathways on ethanol production from grass biomass: A review Sonali Mohapatra 1 | Suruchee Samparana Mishra 1 | Swagat Kumar Das 1 | Hrudayanath Thatoi 2 1 Department of Biotechnology, College of Engineering and Technology, Biju Pattnaik University of Technology, Bhubaneswar 751003, India 2 Department of Biotechnology, North Orissa University, Sriram Chandra vihar, Takatpur, Baripada 757003, India Correspondence Hrudayanath Thatoi, Department of Biotechnology, North Orissa University, Sriram Chandra vihar, Takatpur, Baripada 757003, India. Email: hnthatoi123@gmail.com Summary Grasses are considered to be potential lignocellulosic feedstock for renewable and sustainable biofuels such as bioethanol. However, the process involved, ie, pretreatment, enzymatic saccharification, and fermentation in conversion of these lignocellulosic biomass to bioethanol, remains expensive and at pres- ent is not affordable for industrial production. Thus, the present review assesses the influence of the recent technologies that can be employed for the bio‐refinery based pretreatment and enzymatic hydrolysis of grass biomass using advanced bioreactors. Since plant extracts have been seen to enhance the glucose uptake, an experiment was implemented to elucidate the role of plant extracts (bark extracts of Xylocarpus granatum) on glucose uptake capac- ity of microorganisms like Saccharomyces cerevisiae, Pichia sp., and Zymomonas mobilis and their subsequent ethanol production capability from glucose and xylose sugars. The results of these experiments indicated that sup- plementation of plant extracts promoted both glucose and xylose uptake in S. cerevisiae and Pichia sp. as compared with the control and Z. mobilis strain. Further, as Pichia sp. exhibited good uptake ability for both glucose and xylose, a model was proposed focusing on the gene silencing and operon concept in Pichia sp. for preferential pentose utilization during the fermentation of grass biomass to bioethanol. KEYWORDS bioreactor, glucose uptake, lignocellulose, metabolic pathway, pentose phosphate pathway 1 | INTRODUCTION The fossil fuels which are the major source of energy supply are depleting at a faster rate and simultaneously generate the threat of environmental concerns such as global warming. 1 To address these challenges, bioethanol from lignocellulosic biomass, which is a form of quasi‐ renewable transport biofuel, is capable of reduction up to 80% greenhouse gas (GHG) emissions as compared with conventional fossil fuels have been considered. 2 The escalating interest for production of sustainable bioethanol can be exemplified by the production of 21 812 million gallons in 2012; 23 429 million gallons in 2013; 24 570 million gallons in 2014; 25 682 million gallons in 2015; 31 093 million gallons in 2016; and 30 961 million gallons in 2017. 3 Although a trivial Received: 30 April 2018 Revised: 14 October 2018 Accepted: 14 October 2018 DOI: 10.1002/er.4294 Int J Energy Res. 2018;1–32. © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/er 1