Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy


Chemical and Biochemical Engineering


Bassi, Amarjeet


Increasing concern about the negative impacts of the excessive use of synthetic polymers on the environment and human health has fueled the quest for environmental benign and safe alternatives. Biopolymers have the capacity to replace synthetic polymers in many applications, as they are both benign and biodegradable. This research is focused on the production of biopolymers from the yeast-like fungus, Aureobasidium pullulans. The pullulan biopolymer produced by this fungus has high potential in many biotechnological applications.

During this study twelve strains of A. pullulans were screened for pullulan production. Tetra detection Gel permeation chromatography (TD-GPC) system was used for pullulan molecular characterization to determine molecular weight (MW), intrinsic viscosity (IV) and hydrodynamic radius (Rh). The molecular weight of the produced pullulans varied widely from 46 kDa to 9.7 MDa. These results could be used as guideline for production of pullulans with certain molecular weight range.

In order for the pullulan to compete with petroleum based synthetic plastics, the production cost has to be reduced. To address this challenge, the metabolic pathway for melanin, the main by-product during pullulan production, was blocked by ascorbic acid. This novel approach would reduce the down steam processing steps for pullulan purification which in turn would reduce the overall production cost.

Liquid digestate, the second major biogas product, was used for as a sole medium for pullulan production without any pre-treatment and this is the first time to produce biopolymer using liquid digestate. Digestate is a low value stream, which has heavy load of suspended solids, nutrients and lignocellulosic materials, is mainly used as fertilizer. Five selected strains of A. pullulans were able to utilize the digestate as a sole media without the addition of any other nutrients. The pullulan chemical structure was confirmed by FT-IR and characterized by TD- GPC system.

Finally, A. pullulans strains were investigated as biocontrol agents against plant pathogenic fungi. The abilities of five strains of A. pullulans have been tested and evaluated as effective antagonistic agents against seven different phytopathogens. Most of the tested A. pullulans strains were good candidates as biocontrol agents.

Summary for Lay Audience

There is an urgent need to find suitable alternatives to replace the petroleum based synthetic plastics with environmental benign biobased plastics. The excessive use of plastic is causing severe environmental issues such as plastic wastes, and microplastics, in the marine habitats such as rivers, lakes and oceans.

Cost of production is the main challenge preventing the widespread applications of biodegradable bioplastics. Pullulan, which is produced by the black yeast fungus Aureobasidium pullulans, is a unique biopolymer with huge potential applications in many industries. The main goal of this study is to reduce the production cost of the pullulan biopolymers by using low value waste streams as fermentation media. Digestate, the second main product of biogas production was successfully use as a fermentation media for pullulan production. In addition, decrease the cost of pullulan purification by eliminating the melanin byproduct through chemical treatment by ascorbic acid during the fermentation process. This was, less steps will be required to purify pullulan which would significantly reduce the production cost.

On the other hand, the application of the fungus A. pullulans strains as a biocontrol agent against plant pathogenic fungi was investigated. The results confirmed the potential application of this fungus as a bio fungicide again seven plan pathogens.

Available for download on Tuesday, December 31, 2030