Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Enhancement of Xylanase Activity in Xylooligosaccharide Production From Lignocellulosic Biomass(01. Izmir Institute of Technology, 2023) Büyükkileci, Ali Oğuz; Büyükkileci, Ali Oğuz; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyXylo-oligosaccharides (XOS) with prebiotic properties are obtained through xylan hydrolysis. Previously organosolv was found to be an effective pretreatment for XOS production from corncob. However, this process suffered from low XOS yields because of the limited hydrolysis of xylan in the pretreated biomass. This study was designed to test some approaches toward increasing the efficiency of xylanases on the organosolv-treated corncob. The two commercial enzymes (Shearzyme 500L and Veron 191S) used in this study showed a synergistic effect yielding higher XOS compared to single enzyme application. Partial removal of acetyl groups on the xylan in organosolv-treated corncobs enhanced XOS production significantly. The solid loading above 10% decreased XOS yield as it resulted in a highly viscous slurry that may have limited heat and mass transfer. Fed-batch addition of enzyme and biomass did not play a role in the improvement of hydrolysis. In sequential batch mode, the residual enzyme activity from the previous batch could release more XOS from the fresh biomass, though the yield was low. Addition of fresh enzymes to the previous hydrolysate together with biomass provided a more concentrated XOS solution (15.4 g/l) after the second batch. The addition of surfactants into the hydrolysis media to prevent enzyme binding to lignin did not improve XOS production. This study showed that organosolv could be considered an effective treatment for XOS production from corncob and the enzymatic hydrolysis could be improved by optimizing the conditions.Master Thesis Organosolv Treatment for Prebiotic Oligosaccharide Production From Agro-Food Waste(01. Izmir Institute of Technology, 2020) Büyükkileci, Ali Oğuz; Büyükkileci, Ali Oğuz; 03.08. Department of Food Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologyXylooligosaccharides (XOS), which are among the prebiotic carbohydrates, are produced by hydrolysis of xylan in the lignocellulosic agricultural and food wastes. Production processes, such as autohydrolysis and enzymatic hydrolysis following alkali extraction, have some limitations. In this study, it was aimed to develop a process that could overcome those limitations. Corn cob was used as the model biomass and it was pretreated with organosolv. The organosolv pretreatment conditions (solvent concentration, time, temperature, catalyst addition) were adjusted to maximize the lignin removal from the biomass while recovering xylan in the biomass. Delignification could be achieved with 40%-50% lignin removal, and around 85% of the xylan was retained in the biomass. The effect of the organosolv conditions on XOS formation was investigated by the hydrolysis of the pretreated biomass using three commercial xylanases. The organosolv and the enzymatic hydrolysis conditions influenced the XOS formation. The maximum XOS production was observed with the biomass pretreated at 150°C for 1 h with 70% ethanol and 0.1 M MgO. That biomass was enzymatically hydrolyzed at 70°C with 0.6 U/ml xylanase and 70% of the xylan was converted to XOS yielding a hydrolysate containing 9.5 g/l XOS. With the process developed in this study, the need for the application of concentrated alkaline and acidic solutions can be eliminated since the xylan extraction step is not needed. In addition to that, the formation of carbohydrate degradation products can be avoided due to the lower treatment temperatures compared to autohydrolysis. These can simplify the downstream processing following the production of XOS and minimize the environmentally harmful chemical wastes. In this process, a liquid stream rich in lignin and a solid stream rich in cellulose were released. Following a biorefinery concept, these streams can potentially be valorized together with the xylan, so that lignocellulosic wastes can have an added value. This study will be followed by related projects on XOS purification and determination of the prebiotic potential of XOS. In addition to that, the process developed will be tested on other lignocellulosic wastes.