Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Research paper Enhanced ethanol production from Glycyrrhiza glabra residue by fungus Mucor hiemalis Sara Kooravand, Amir Goshadrou ⁎ , Mohammad Sadegh Hatamipour Department of Chemical Engineering, Faculty of Engineering, University of Isfahan, Isfahan 81746-73441, Iran ARTICLE INFO Keywords: Glycyrrhiza glabra residue Alkali pretreatment Characterization Enzymatic hydrolysis Bioethanol Mucor hiemalis ABSTRACT Glycyrrhiza glabra residue (GGR) contains 30.5% cellulose and 23.0% hemicellulose and can be considered as a promising low-cost and non-edible feedstock for production of ethanol. For the first time, GGR was subjected to inexpensive sodium hydroxide (SH) pretreatment to enhance fermentable sugars production through enzymatic hydrolysis and subsequent utilization by fungus Mucor hiemalis. The pretreatment was carried out at 5% (w/v) solid loading and different temperatures (0, 28 and 110 °C) with 2, 4, 6, 8 and 10% (w/v) SH solutions. When applying no pretreatment, the glucose and ethanol production yields through separated hydrolysis and fer- mentation of GGR were only 13.9% and 14.3%, respectively. However, a major improvement was achieved after alkali pretreatment of GGR and the maximum hydrolysis yield of 93.7% was observed when the substrate was pretreated with 4% SH solution at 28 °C for 24 h. Consequently, fermentation of the SH pretreated materials by M. hiemalis led to a maximum 5.9-fold increase in ethanol production yield (∼217 kg per ton of GGR), which was slightly higher than the ethanol yield through the yeast Saccharomyces cerevisiae (∼207 kg per ton of GGR). Semi-quantitative analyses of the substrate after pretreatment indicated that crystallinity reduction and ex- panded surface area were the main reasons for the observed improvements. In brief, the results revealed that SH pretreatment (4% w/v) at room temperature is an effective strategy to valorize GGR to ethanol through hy- drolysis and fermentation by fungus M. hiemalis. 1. Introduction Energy crisis, global warming and obligations for greenhouse gas emissions reduction are the main drivers of biofuels promotion by public authorities in industrialized countries (Creutzig et al., 2015; Gnansounou et al., 2009). Bioethanol is the most widespread renewable and eco-friendly transportation fuel with a worldwide production of ∼26 million gallons per year. However, the current fuel ethanol, which is almost entirely produced from edible sources, interferes with the food supply. Lignocellulosic materials are the most abundant bio-renewable resources with the worldwide production of ∼200 × 10 9 tons per year. The emerging alternative technology for ethanol production from lig- nocelluloses has become the focus in recent years (RFA, 2016; Zabed et al., 2016). The Licorice (Glycyrrhiza glabra), as one of the most widely assessed plant of economic importance, is harvested primarily for its rhizomes and roots. This of 70–200 cm-height plant and is able to grow wild or be cultivated in subtropical regions. This plant is a natural sweetener (50–170 times sweeter than sucrose) widely used in tobacco, food, confectionary and pharmaceutical industries. The root is composed of several bioactive compounds and water-soluble glycyrrhizin (∼16%), which are the main cause for its sweetness. In the traditional glycyr- rhizin extraction process with hot water, a considerable amount of lignocellulosic residue is often discarded or directly burnt in the field, leading to serious environmental problems (Fenwick et al., 1990; Gui et al., 2014; Mukhopadhyay and Panja, 2008). However, the Glycyr- rhiza glabra residue (GGR) can be consumed as a non-edible low-cost resource for ethanol production. To the best of our knowledge, there exists no previous study on assessing ethanol production from GGR. Lignocellulose matrix, which is mainly composed of cellulose, hemicellulose and lignin, has a recalcitrant structure to resist enzymatic hydrolysis and microbial attacks. There exist several physical, chemical, physicochemical and biological pretreatments to enhance the com- mercial production of bioethanol (Brienzo et al., 2016; Karimi and Taherzadeh, 2016a, 2016b; Ye et al., 2016). Among various techniques, sodium hydroxide (SH) pretreatment has received considerable atten- tion since it is a simple, safe, non-corrosive, cost-effective, eco-friendly and energy efficient technology. Moreover, the alkali process is run at low temperature and pressure in a simple reactor. Previous studies in- dicate that SH can remove lignin barrier, increase available surface area http://dx.doi.org/10.1016/j.indcrop.2017.07.030 Received 16 November 2016; Received in revised form 12 July 2017; Accepted 16 July 2017 ⁎ Corresponding author. E-mail address: a.goshadrou@eng.ui.ac.ir (A. Goshadrou). Industrial Crops & Products 108 (2017) 767–774 0926-6690/ © 2017 Elsevier B.V. All rights reserved. MARK