Biological Systems Engineering


First Advisor

Mark R. Wilkins

Date of this Version

Summer 8-2022


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Agricultural and Biological Systems Engineering, Under the Supervision of Professor Mark R. Wilkins. Lincoln, Nebraska: August 2022

Copyright © 2022 Twissa Mitra


Poly(3-hydroxybutyrate) (PHB) is one of the most broadly studied members of the polyhydroxyalkanoates (PHA) family. It is a fully biodegradable thermoplastic produced by microbial fermentation having properties similar to polypropylene. PHB has a market price that is three times higher than the cost of synthetic plastics. Substrate cost makes up 50 to 60 % of that cost; hence, researchers have been exploring various cheap natural resources with high carbohydrate content to be used as a substrate for PHB production.

In this study, corn fiber, a lignocellulosic biomass has been studied as an option for a substrate to produce PHB. This is a leftover product of dry milling to produce corn ethanol. Paraburkholderia sacchari, a hexose, and pentose-consuming bacterium is used for the production of PHB. P. sacchari is a gram-negative bacterium isolated from the soil of a sugar-cane plantation in Brazil to identify a strain that can integrate into a biorefinery to successfully produce PHB.

To successfully execute the production of PHB from corn fiber hydrolysate, various factors were studied concerning their effect on PHB yield. Chapter 1 explores the previous studies and the possibility of using corn fiber as a substrate for PHB production using P. sacchari. In chapter 2, two different pretreatment methods, three different pH control strategies for enzymatic hydrolysis, and the effect of using pH control during fermentation in a shake flask were studied. It was observed that the best PHB yield of 0.31 g/g was obtained by using liquid hot water pretreatment, 50mM acetate buffer at pH 5 as pH control in enzymatic hydrolysis, and 50 mM phosphate buffer at pH 6.8 as pH control during fermentation. In an effort to increase the existing PHB yield from corn fiber hydrolysate, the effect of protein extraction of corn fiber and the inoculation method of P. sacchari was studied in chapter 3. The highest PHB yield of 0.53 g/g was obtained. Chapter 4 concluded the findings and understanding of this research study along with recommendations for future experiments.

Advisor: Mark R Wilkins