Effect of Aeration and Agitation on Volumetric Oxygen Transfer in Pichia pastoris Culture System

The oxygen mass transfer coefficient (K_La) often serves to compare the efficiency of bioreactors and their mixing devices as well as being an important scale up factor. In submerged fermentation, four methods are available to estimate the overall oxygen mass transfer coefficient. Each method provides a distinct estimation of the value of K_La. Dynamic gassing out method was used to obtain a more probable value of K_La during the fermentation in 5L fermentor with Pichia pastoris. The aeration and agitation were varied to study the effect on K_La. Results showed that the K_La value increased with increase in agitation and aeration. While working in 5L fermentor with Pichia pastoris the maximum K_La value of 441.36 was obtained when the agitator speed 300 RPM and aeration 1.5 vvm was maintained. This shows that the volumetric oxygen transfer rate varies in variation with aeration and agitation and not based on organism used. The optimum conditions of agitation and aeration to achieve maximum K_La for a given microorganism depends on its shear sensitive nature.