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Title:	Production of xylitol from oil palm fronds (OPF) hydrolysate by Kluyveromyces marxianus ATCC 36907
Authors:	Shareena Fairuz Abdul Manaf (P81197)
Supervisor:	Jamaliah Md Jahim, Prof. Dr.
Keywords:	Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia Oil palm fronds Xylitol Kluyveromyces marxianus
Issue Date:	17-Jun-2021
Description:	Polysaccharide content of 0.62 g/g on dry weight basis of oil palm frond (OPF) has a potential to become a feedstock for sustainable development of a biotechnological route for xylitol production. This research aimed to explore the dilute acid hydrolysis (DAH) on OPF and to acquire optimum utilization of fermentable sugars from pretreated OPF using Kluyveromyces marxianus ATCC 36907 for xylitol production by developing fermentation techniques and improving the strain performance. DAH is one of the effective methods to fractionate hemicellulose into xylose-rich liquor. Parameters of DAH conditions were optimized using one-factor-at-a-time (OFAT) method. The maximum amounts of sugars recovered were 22.1 g xylose and 8.9 g glucose per 100 g OPF with 5.6 g/L total inhibitors obtained from 4% (v/v) HNO3 at 130°C for 20 minutes. Physicochemical analysis using Scanning Electron Microscopy, Fourier Transformation Infrared Spectroscopy and X-ray Diffraction were used to determine the structural changes of the OPF upon DAH. Results indicated that DAH treatment able to improve sugar yield by altering the recalcitrant structure of the OPF. Fermentability test of non-detoxified OPF hydrolysate as carbon source by K. marxianus ATCC 36907 gave maximum yield of 0.31 g/g xylitol. Conditions of adsorption parameters (ratio of activated charcoal to hydrolysate, pH, adsorption temperature, and contact time) for detoxification of hydrolysate resulted from DAH were then experimentally optimized using response surface methodology (RSM) with the loss of monomeric sugars, hydrolysate volume reduction and inhibitors removal as the response variables. It was found that the low sugar loss of 10% and high furfural removal of 80% were achieved at pH 2.5 and 55.6°C by 5.3% (w/v) of activated carbon for 74 minutes while 87% of original volume of hydrolysate was retained upon detoxification. The pH control at 6.0 to 6.5 in bioreactor during fermentation further improved the reduction of the acetic acid inhibition in the hydrolysate and increased the xylitol yield up to 45%. The study on the effects of agitation speed of impeller, initial xylose concentration and aeration was conducted in in 3.6 L of bioreactor at 30°C for kinetics fermentative parameters analysis. The optimum xylitol yield (0.38 g/g) was attained at pH 6 and 300 rpm with initial sugar of 50 g/L. The highest production of xylitol achieved was 15.1 g/L with 0.21 g/L/h productivity rate under limited oxygen conditions. Sensitivity analysis depicted the maximum specific growth rates (μmax) and substrate consumption constant (KS) were the most influential model parameters for the xylitol production. The fermentation profiles were modelled using xylose as carbon source and the model fitted well with experimental data. Xylose utilization capability by K. marxianus ATCC 36907 was improved through evolutionary adaptation technique after underwent 25 successive batch culture in Yeast Extract-Peptone-Dextrose (YEPD) media containing 80 g/L of xylose incubated at 30°C. Enzymatic assays for xylose reductase (XR) activities revealed that the adapted strain increased two-fold compared to wild-type strain. The highest yield of xylitol was 0.46 g/g and produced 26.45 g/L xylitol at maximum productivity of 0.37 g/L/h showed 56% higher xylose utilization than the wild-type strain which was explained by enhanced XR activity of the adapted strain. This study has successfully demonstrated the bioconversion of OPF hydrolysate into xylitol. Those findings from this study could serves as a knowledge platform towards better understanding for biorefinery commercialization in creating a new resource-from-waste in biomass utilization for production of high-value product.,Ph.D.
Pages:	257
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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