Production of simple sugars from olive grove pruning using acid pretreatment and enzymatic hydrolysis
¹Polytechnic University of Castelo Branco, Faculty of Agriculture, Department of Natural Resources and Sustainable Development, Quinta da Sra. de Miércoles, apartado 119, PT6001-909 Castelo Branco, Portugal
²QRural - Qualidade De Vida No Mundo Rural, Av. Pedro Álvares Cabral, n.º12, PT6000-084 Castelo Branco, Portugal
³UTAD - University of Trás-os-Montes and Alto Douro, Quinta de Prados, PT5000-801 Vila Real, Portugal
⁴CITAB - Centre for the Research and Technology of Agro-Environmental and Biological Sciences. UTAD, Quinta de Prados, PT5000-801 Vila Real, Portugal
⁵UBI - University Beira Interior. Convento de Sto. António, PT6201-001 Covilhã, Portugal
⁶CICS-UBI - Health Sciences Research Centre, University Beira Interior,
Av. Infante D. Henrique, PT6200-506 Covilhã, Portugal
*Correspondence: npedro@ipcb.pt; lnova@ipcb.pt
Abstract:
The purpose of this paper was to optimize the production of simple sugars from olive grove pruning (OGP) using acid pretreatment and enzymatic hydrolysis. This study was based on a model composition corresponding to a 34 orthogonal factorial design and employed the response surface methodology (RSM) to optimize the pretreatment and hydrolysis conditions, aiming to attain maximum glucose, xylose and arabinose extraction from cellulose and hemicellulose of biomass. The pretreatment operating conditions considered for optimization, were temperature (60–180 °C), residence time (30–120 min) and sulphuric acid concentration (0.5–5% w w-1). Enzymatic hydrolysis experiments on solid fraction pretreated with diluted acid were performed at a solid concentration of 5% (w v-1, based on dry weight), using 50 mM citrate buffer pH 4.8 with BSA at a concentration of 60 mg g-1 dry biomass. The reaction mixture was incubated at 50 °C for 174 h on an orbital shaker at 150 rpm. Three commercial enzyme preparations (cellulase complex, b-glucosidase and xylanase) were used in enzymatic saccharification. Total carbohydrate content of the initial biomass was 51.25% (in dry mass), of which glucose was the major constituent with 33.59%. Contents of lignin and extractable found in biomass were 24.96% and 15.84%, respectively. In this work, it was possible to extract 93.1% of the sugars present in the olive grove pruning, with pretreatments carried out for 102 min at 156 °C with a sulfuric acid load of 4.09% (w w-1), followed by enzymatic hydrolysis performed for 174 h, with an enzyme loading of 18 PFU, 36 p-NPGU and 36 IU per gram of substrate.
Key words:
acid hydrolysis, enzymatic hydrolysis, olive pruning, pretreatment, RSM, sugars