Theses and dissertations (Applied Sciences)
Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/6
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Item A mucor circinelloides-based integrated biorefinery(2024-09) Zininga, Johnson Tungamirai; Permaul, Kugen; Singh, SurenABSTRACT The utilization of agro-based waste residue is a prominent example for establishing a circular bioeconomy. When agro-based waste is used to replace commercial growth media in microbial fermentation processes, it becomes expedient that the implementation of the biorefinery concept becomes integrated as the microbial biomass and their metabolites will add to the product spectrum. This study demonstrates an integrated approach towards valorization of sugarcane bagasse and microbial biomass comprising of Mucor circinelloides ZSKP. A maximum reducing sugar recovery of 80.67 g/l was achieved after combining lignocellulosic pretreatment with saccharification. A low temperature, glycerol and ammonium phosphate pretreatment method was established, where glycerol pretreatment conditions were reduced to 150°C and almost a third of the initial duration. This strategy will potentially result in lower energy consumption costs, decreased release of inhibitors and lower water consumption. The ammonium phosphate-containing hydrolysate yielded 12.89 g/l of fungal biomass after fermentation to add to 20.8 g lignin from the delignification step. Sequential fermentations were performed by addition of Saccharomyces cerevisiae as a co-culture to produce biomass and ethanol. The initial aerobic M. circinelloides fermentation was followed by mixed culture anaerobic fermentation. Fermentation of M. circinelloides (3 days aerobic growth) and S. cerevisiae (5 days of anaerobic growth) generated a balanced biomass yield of 17.9 g/l and ethanol yield of 18.69 g/l. Ethanol production demonstrated effective utilization of bagasse hydrolysate and offered the possibility of concurrent production with biodiesel in this biorefinery. The mixed biomass gave a lipid yield of (3.72 g/l) and a chitosan yield of (1.84 g/l), The lignin infused glycerol plasticized chitosan biocomposite plastic had a 100% improvement in thermogravimetric properties with almost 50% more energy needed to increase the temperature of the material when compared to glycerol-only-plasticized biocomposite. The deproteination step in chitosan extraction was modified and replaced with a protein recovery step, with protein yield being improved to a maximum of 187.89 mg/g. The amino acid composition of the protein showed that it has a relatively high content of lysine making it suitable as an animal feed supplement. This study presents strategies to address feasibility concerns for production of fungal chitosan, biodiesel and bioethanol from lignocellulosic waste and realizing the goal of a circular bioeconomy.Item Evaluation of chitosan–coated magnetic nanoparticle-immobilized thermostable hemicellulases for enhanced saccharification and production of bioethanol(2022-09) Mdlaka, Sibongile Patience; Singh, Suren; Puri, Adarsh KumarEnhancing the efficiency of saccharification of pentose and hexose sugars present in lignocellulosic biomass is a major bottleneck for industrial bioethanol production. This problem can be addressed by a concerted effort combining nanotechnology, enzymology and fermentation technology. Functionalized chitosan-coated magnetic nanoparticles (CCMNPs) were prepared and used for co-immobilization of purified xylan hydrolysing xylanase and xylosidase from the thermophilic fungus Thermomyces lanuginosus SSBP for the release of xylose. Stability studies revealed that immobilized enzymes were more stable than free enzymes over a wide range of pH (4.0 – 7.0) and temperature (40 – 90 °C) for xylanase and 30 – 80 °C for xylosidase. The optimum activity of the co-immobilized enzymes shifted slightly as compared to the free enzymes, with coimmobilized xylanase and xylosidase showing optimum activity at pH 6.5 and 6.0, respectively. The study showed sustained production of xylose as the major fermentable sugar under repeated batch and fed-batch saccharification of lignocellulosic biomass. Statistical optimization of saccharification of 1% xylan using response surface methodology indicated the enhanced release of xylose at 50 °C, pH 7.0 and enzyme dose of 60 U/mL xylanase and 30 U/mL xylosidase. Finally, liberated xylose was fermented with Scheffersomyces stipitis to yield bioethanol.Item Utilization of shrimp waste for the recovery of valuable bioactive compounds(2018) Dlamini, Nosihle; Permaul, KugenShrimp waste is a major by-product of crustacean processing and represents an interesting source of bioactive molecules. In addition, its use increases the sustainability of processing fishery products. The present study reports a process developed for recovering bioactive molecules from shrimp waste through the use of chemical methods. The samples of shrimp were confirmed to be from the species Haliporoides triarthrus. The recovery of chitin was 30% of the processing waste and 30-60% chitosan (CH) from chitin. CH was characterized by FTIR analysis and exhibited a degree of deacetylation (DDA) of 72%. From the demineralization extract, CaCO3 was extracted and confirmed by FTIR. Based on a kinetic study of acid hydrolysis, it was demonstrated that chitin can be quantitatively hydrolysed into glucosamine (GlN), N-acetyl glucosamine (GlcNAc) and their respective oligomers with 32% hydrochloric acid at 60oC and qualitatively from CH with 32% hydrochloric acid at 80oC. The oligomer mixed fractions were desalted by activated charcoal extraction and the components of each fraction were analysed by TLC and HPLC. Chitooligosaccharides (COS) and N-acetly chitooligosaccharides (NAcCOS) with degrees of polymerization (DP) ranging from 2 to 6 were obtained from CH and chitin, respectively. The antimicrobial activities of chitosan, COS and NAcCOS were investigated against five gram-negative bacteria and five gram-positive bacteria. Chitosan exhibited stronger bacteriostatic effects against gram- positive bacteria than gram-negative bacteria in the presence of 1% chitosan. The oligomers showed no bacteriostatic or bactericidal effects on all tested bacteria. A total 30.74± 0.078 µg.g-1 astaxanthin was extracted with 90% acetone from the species; Haliporoides triarthrus and TLC analysis indicated that the species contained both astaxanthin and its esters. Chitosan films were obtained by solution casting of blends of chitosan with glycerol, polyethylene glycol 200 (PEG-200) and polyethylene glycol 600 (PEG-600) as plasticizers. Films were characterized by FTIR, XRD diffraction, TGA, and SEM analysis. The tensile strength and elongation at break properties of the films were also evaluated. CH films and CH/GLY blended films were translucent in appearance and the CH/PEG 200 and CH/PEG 600 films were opaque. The CH films yielded mechanically resistant films without the use of a plasticizer. These data point to the feasibility of an integrated process for isolating highly bioactive molecules, such as oligosaccharides, with a broad spectrum of applications from shrimp processing waste.