Bioconversion Of Rice Husk To Polyhydroxybutyrate Via Pretreatment And Enzymatic Hydrolysis
| dc.contributor.author | Heng, King Sern | |
| dc.date.accessioned | 2017-01-12T07:22:09Z | |
| dc.date.available | 2017-01-12T07:22:09Z | |
| dc.date.issued | 2016-08 | |
| dc.description.abstract | Rice is one of the largest sources of food worldwide. In Malaysia, average paddy production is more than 2 million tonnes annually. From the yield of harvested paddy, approximately 20% of it consists of the husks, which are typically disposed. Rice husks (RH) consist mainly of lignocellulose, which can be converted to substrates for fermentation. This study was conducted to evaluate the potential of RH as a carbon source for the production of polyhydroxyalkanoate (PHA), a bioplastic produced by many types of bacteria. To overcome the recalcitrant nature of this biomass, physicochemical pretreatments were performed on the rice husks under different conditions and their efficiencies were compared in terms of sugar yield upon enzymatic hydrolysis. Based on all the pretreatment methods tested, the use of potassium hydroxide (KOH) combined with high temperature and pressure, was found to be most effective in increasing the enzymatic digestibility of the material, resulting in 70% sugar yield per total carbohydrate content. The sugar yield was increased to 87% when enzyme and substrate loading were optimized for enzymatic hydrolysis using two commercial enzymes, Celluclast 1.5L and Novozyme 188. Characterization of the enzymatic hydrolysate revealed that glucose was present in the highest proportion, which was approximately 80%, followed by 15% xylose and 5% arabinose. The hydrolysate also contained total phenolics of approximately 3.7 mg gallic acid equivalent (GAE)/g of pretreated substrate. The hydrolysate was then fed to two bacterial strains, Burkholderia cepacia USM (JCM 15050) and Cupriavidus necator NSDG-GG, a genetically engineered strain of Cupriavidus necator H16, to assess their growth and PHA production on this carbon source. The pH of the hydrolysate was adjusted to pH 7.0 and 6.8 for the culture of B. cepacia USM and C. necator NSDG-GG respectively. C. necator NSDG-GG exhibited higher cell dry weight (CDW) and PHA content when cultivated on synthetic medium containing pure glucose, which was 10.4 g/L and 70 wt%. However, B. cepacia USM was able to utilize the RH hydrolysate more efficiently, with a maximum CDW of 4.9 g/L and 40 wt% PHA at shake-flask scale. It was also found that B. cepacia USM had a preference for glucose compared to xylose when the sugars were present in a mixture. When cultivated in a 5-L fermentor, the CDW and PHA content of B. cepacia USM increased to 7.8 g/L and 50 wt%, respectively. The decrease in total phenolics in the hydrolysate at the end of fermentation suggested that B. cepacia USM was able to metabolize phenolic compounds. This study has proven that RH can be converted to PHA through optimized alkali pretreatment, enzymatic hydrolysis, and biosynthesis by B. cepacia USM. | en_US |
| dc.identifier.uri | http://hdl.handle.net/123456789/3425 | |
| dc.subject | To evaluate the potential of rice husk as a carbon source | en_US |
| dc.subject | for the production of polyhydroxyalkanoate | en_US |
| dc.title | Bioconversion Of Rice Husk To Polyhydroxybutyrate Via Pretreatment And Enzymatic Hydrolysis | en_US |
| dc.type | Thesis | en_US |
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