Sonication of olive pomace to improve xylanases production by SSF

Abstract

Olive mill wastes are an important environmental problem in the areas where they are generated. Portugal is an important producer of olive oil in the world, thus it is interesting to find the most suitable valorization strategy to exploit their wastes which are generated in huge quantities in short periods of time. In this study, it was used the olive pomace as solid substrate to produce xylanases and cellulases by filamentous fungi. To improve the enzymes production ultrasounds pretreatment of olive pomace was evaluated. The results showed that the sonication led to a 3-fold increase of xylanase activity and a decrease of cellulase activity, indicating that ultrasounds treatment attacked the integrity of cell walls and increased the accessibility of hemicelluloses inducing the xylanases production by fungi. have been identified as hydrolyzers of cellulose and hemicellulose, however the filamentous fungi considered as strong cellulases and xylanases secreting strains, perform better using SSF (Ang et al., 2013). On an industrial scale, cellulases and xylanases are secreted mainly by Aspergillus and Trichoderma spp. (Kulkarni et al., 1999). The physical pre-treatments can increase size of pores and accessible surface area, and decrease degrees of polymerization of cellulose and crystallinity, which can be used to improve the biodegradability or enzymatic hydrolysis of these residues (Taherzadeh et al., 2008). Ultrasound pre-treatment causes a cavitation bubbles formation in the liquid phase (Tiehm et al., 2001), the bubbles grow and then violently collapse when they reach a critical size. Cavitational collapse produces turbulence, intense local heating and high pressure at the liquid-gas interface, high shearing phenomena in the liquid phase and formation of radicals (Atchley et al., 1988; Gonze et al., 1998). It was also proven that the degradation of excess sludge is more efficient when using low frequencies: mechanical effects facilitate particles solubilization (Tiehm et al., 2001). The aim of the present work was to prepare olive pomace for solid-state fermentation by A. niger using ultrasounds pretreatment to improve the accessibility of fungi to hemicellulose and cellulose. Thus, the ultrasounds pretreatment was optimized by full factorial experimental design (3) to maximize the production of xylanases and cellulases varying the time of ultrasounds treatment and the liquid and solid ratio. 2 MATERIALS AND METHODS