Contents lists available at ScienceDirect Industrial Crops & Products journal homepage: www.elsevier.com/locate/indcrop Production of bioethanol from pumpkin peel wastes: Comparison between response surface methodology (RSM) and artificial neural networks (ANN) Moncef Chouaibi a,b, *, Khaled Ben Daoued b , Khouloud Riguane b , Tarek Rouissi c , Giovanna Ferrari a a Department of Chemical and Food Engineering, University of Salerno, Via Ponte Don Melillo, 84084, SA, Italy b High School of Food Industries, 58, Alain Savary street, Elkhadra city, 1003, Tunisia c Centre Technologique des Résidus Industriels 433, boulevard du Collège, Rouyn-Noranda, Québec, J9X 0E1, Canada ARTICLE INFO Keywords: Pumpkin peel wastes Bioethanol Response surface methodology Artificial neural networks Kinetic modeling ABSTRACT Pumpkin peel wastes are an unutilized source of starch, whose bioethanol production has not been reported by any research work so far. Such bioethanol is believed to show the potential uses of these wastes. Therefore, the present work was conducted to optimize the reducing sugar concentration and bioethanol production from pumpkin peel wastes using two modeling approaches (artificial neural networks and response surface metho- dology). Actually, a central composite rotatable design was used to optimize bioethanol production to obtain maximum reducing sugar and bioethanol concentrations. ANN proved to be superior to RSM in terms of its estimation and prediction capabilities. Therefore, the optimum conditions were obtained based on predicted ANN-model as follows. Concerning the hydrolysis process, hydrolysis time was 120 min, loading substrate was 17.5 g/L, α-amylase concentration was 7.5 U/g and amyloglucosidase concentration was 56.40 U/mL. As for the fermentation process, the optimal conditions were: fermentation temperature 45 °C, pH 5.06, shaking speed 188.5 rpm, and yeast concentration of 1.95 g/L. Under these conditions, the experimental concentration values of reducing sugar and bioethanol were 50.60 and 84.36 g/L, respectively, which are in good agreement with those predicted by the ANN-model (84.27 and 50.69 g/L, respectively). Besides, the results revealed that sub- strate loading and fermentation temperature were the most significant factors affecting the reducing sugar and bioethanol concentration, respectively (p < 0.01). Subsequently, the kinetics of yeast growth and bioethanol formation under the optimized conditions were estimated using the Monod, logistic and modified Gompertz models, respectively. Subsequently, the pumpkin peel wastes would offer an energy-saving alternative for fuel- ethanol production. 1. Introduction Bioethanol is the main biofuel that is the subject of impressive in- dustrial development today. Its production worldwide in 2010 reached 100 billion liters per year (Vohra et al., 2014). According to statistics from the Renewable Fuels Association (RFA), the two largest producers of bioethanol, namely the United States and Brazil, reached a produc- tion of 51 billion liters (48 %) and 29 billion liters (27 %), respectively in 2011 (Renewable Fuels Association, 2011). It should be noted that the African continent produces only 0.2 % of bioethanol versus 5.2 % in Europe (Renewable Fuels Association, 2011). Given the current eco- nomic conditions and the ever-increasing price of oil, bioethanol, pro- duced from plant biomass, has been increasingly attractive, experien- cing a renewed interest in the past fifteen years (Vohra et al., 2014; Sebayang et al., 2017a,b; Chohan et al., 2019). Hence, the substrates likely to be used for the production of ethanol are very varied, and the choice depends on the sugar composition, cost and profitability of the process (Lin and Tanaka, 2006). Usually, it is produced from renewable agricultural products like corn, sugar, sorghum, potatoes and molasses, to cite but a few (Khawla et al., 2014; Vohra et al., 2014; Sebayang et al., 2017a,b; Sewsynker-Sukai and Kana, 2018). Renewable energies constitute a set of solutions since they reduce dependence on petroleum and pollution of our environment (Thangavelu et al., 2016). Interestingly, ethanol is a compound for a wide variety of uses ranging from chemistry to food industries. The current market growth is mainly around the use of ethanol as a fuel (Thangavelu et al., 2016). Remarkably, ethanol has the advantage of being a renewable fuel on a human timescale rather than on a https://doi.org/10.1016/j.indcrop.2020.112822 Received 28 April 2020; Received in revised form 19 July 2020; Accepted 20 July 2020 ⁎ Corresponding author at: Department of Chemical and Food Engineering, University of Salerno, Via Ponte Don Melillo, 84084, SA, Italy. E-mail address: moncef.chouaibi@yahoo.com.au (M. Chouaibi). Industrial Crops & Products 155 (2020) 112822 0926-6690/ © 2020 Elsevier B.V. All rights reserved. T