Pullulan fermentation using a prototype rotational reciprocating plate impeller.

Area of Science:

• Biotechnology
• Biochemical Engineering
• Microbial Fermentation

Background:

• Fermentation broth viscosity significantly impacts microbial production processes.
• Optimizing bioreactor conditions is crucial for maximizing yield and product quality.
• Pullulan, a high molecular weight exopolysaccharide (EPS), has diverse industrial applications.

Purpose of the Study:

• To evaluate a novel rotational reciprocating plate impeller for improved mixing in viscous fermentation broth.
• To optimize fermentation parameters for enhanced pullulan production by Aureobasidium pullulans.
• To maximize both exopolysaccharide (EPS) concentration and broth viscosity for high molecular weight pullulan.

Main Methods:

• Utilized experimental designs, including uniform and custom designs, to investigate influencing factors.
• Tested a rotational reciprocating plate impeller prototype in a 22-L bioreactor.
• Optimized pH and agitation speed as key parameters for pullulan yield and molecular weight.

Main Results:

• Achieved 29.0 g/L EPS production under initial optimized conditions.
• Identified an optimal operating zone yielding 23.3 g/L EPS at 78 h with high molecular weight.
• Attained an EPS productivity of 0.30 g/L/h and a broth viscosity of 0.38 Pa·s at a shear rate of 10 s⁻¹.

Conclusions:

• The rotational reciprocating plate impeller effectively improves mixing for viscous fermentation broths.
• Optimized fermentation conditions significantly enhance the production of high molecular weight pullulan.
• The study provides a framework for maximizing EPS production and controlling broth rheology in bioreactors.