Improving the production of high molecular weight pullulan using a new radial reciprocating plate impeller

Yun Lin, Université D'Ottawa / University Of Ottawa, Université D'Ottawa / University Of Ottawa
2013
Pullulan is a natural biopolymer with many useful traits. It has been produced commercially through fermentation with Aureobasidium pullulans at a fairly stable level for decades. Yet, the use of pullulan has been largely limited to the food industry due to its relatively high price. This research project was carried out in order to improve the cost efficiency in the mass production of high molecular weight pullulan and hopefully render it more economically available for many of its potential
more » ... of its potential applications. One of the main challenges in its production is the mixing of viscous non-Newtonian broth that is formed gradually through fermentation. A new radial reciprocating plate impeller was designed based on the axial reciprocating plate impeller, which was shown to be efficient when dealing with highly viscous non-Newtonian media. The new design was focused on making the mechanism of the axial reciprocation more adaptable to existing industrial mixing devices. A prototype of this new impeller was built and tested to determine its power requirement and mass transfer characteristics in a laboratory scale bioreactor. Compared to a triple Rushton impeller and an axial reciprocating plate impeller, the new impeller proved to be efficient in different media with a wide range of rheological properties. Simulation using computational fluid dynamics also confirmed that mixing using this new impeller was more uniform compared to the triple Rushton impeller. Experimental designs were employed to optimize the mass production of high molecular weight pullulan using this new impeller. An exopolysaccharide productivity of 0.30 gL-1h-1 was obtained while maintaining the molecular weight of pullulan, which is indicated by the broth viscosity, at a high level. The findings of this study provide a new way to adequately mix viscous broth of aerobic fermentations. Also, this new radial reciprocating plate impeller should be easily adapted to large scale industrial bioreactors to achieve more uniform mixing in rheologically-evolving ferme [...]
doi:10.20381/ruor-13261 fatcat:cir4aj7ynjcolptusbtgitpgne