Contents lists available at ScienceDirect Biochemical Engineering Journal journal homepage: www.elsevier.com/locate/bej Regular article Integrated enzymatic pretreatment and hydrolysis of apple pomace in a bubble column bioreactor Saverio Niglio a , Alessandra Procentese b , Maria Elena Russo b, ⁎ , Alessandra Piscitelli c,d , Antonio Marzocchella a a Dipartimento di Ingegneria Chimica dei Materiali e della Produzione Industriale, Università degli Studi di Napoli Federico II, P.le V. Tecchio 80, 80125 Napoli, Italy b Istituto di Ricerche sulla Combustione - Consiglio Nazionale delle Ricerche, P.le V. Tecchio 80, 80125 Napoli, Italy c Dipartimento di Scienze Chimiche, Università degli Studi di Napoli Federico II, Complesso Universitario di Monte Sant’Angelo, Via Cinthia, 80126 Napoli, Italy d Biopox srl, Via Salita Arenella 9, 80129 Napoli, Italy HIGHLIGHTS • Bubble column was successfully adopted for enzymatic saccharification of biomass. • Sequential enzymatic delignification and hydrolysis processes were optimized in bubble column. • Lignin modification by laccases affects final sugar yield more than lignin removal. ARTICLE INFO Keywords: Biorefinery Biomass hydrolysis Bubble column Laccase Lignin ABSTRACT Waste biomass from agro-food industry can be exploited to produce several products according to the sugar- based biorefinery concept. The success of the biomass exploitation stems from the equilibrium among several issues regarding the process costs, the environmental impact, and the energy efficiency. The present work is focused on the use of apple pomace as possible renewable feedstock for the production of biofuels and of bio- commodities. The aim of the present work was the optimization of the enzymatic pretreatment and hydrolysis of apple pomace in a bubble column bioreactor by using a recombinant laccase as biocatalyst for the delignification step and commercial cellulases for the hydrolysis step. Both the enzymatic processes were investigated to select the optimal operating conditions for the maximization of sugar yields. Optimal conditions for the sequential enzymatic delignification and hydrolysis process in the bubble column were: 15%w/v biomass concentration; 60 nL/h air flow rate, 30 U/g biomass laccase activity; 20 FPU/g cellulose cellulase activity. Moreover, the selected operating conditions were applied to a long term test of the sequential pretreatment/hydrolysis in the bubble column that resulted in a maximum sugar yield of 0.34 g sugars /g raw biomass and 0.61 g sugars /g sugars in the pretreated biomass from the raw apple pomace. Result discussion highlighted advantages and drawback of pneumatic mixing and sequential pretreatment/hydrolysis strategy applied to enzymatic delignification and cellulose hydrolysis. 1. Introduction Second generation biofuels and bio-commodities (e.g. bio-plastics) can be produced according to biorefinery processes applied to lig- nocellulosic residue/wastes used as feedstock. The industrial success of sugar-based biorefinery depends on several issues. These issues include the optimization of biomass pretreatment and hydrolysis to provide cellulose/hemicellulose conversion, high sugar concentration in the solution to be delivered to the fermentation step, low content of fer- mentation inhibitors and energetic cost saving. The use of residue/ waste biomass (e.g. agricultural residues and industrial agro-food wastes) asks for re-thinking the pretreatment process typically opti- mized for the delignification of dedicated crops and wood biomass used as feedstock for the production of first-generation biofuels [1]. The wide spectrum of waste biomass composition provides numerous feedstocks characterized by low (12–25%) lignin content, potential candidates for the development of mild/low energy consuming pre- treatment. Moreover, a further advantage of mild pretreatment is the low production of fermentation inhibitors compounds [2]. A potential biorefinery feedstock from agro-food industry is the https://doi.org/10.1016/j.bej.2019.107306 Received 1 April 2019; Received in revised form 27 June 2019; Accepted 16 July 2019 ⁎ Corresponding author. E-mail address: m.russo@irc.cnr.it (M.E. Russo). Biochemical Engineering Journal 150 (2019) 107306 Available online 17 July 2019 1369-703X/ © 2019 Published by Elsevier B.V. T