Oxygen uptake and transfer rates were studied in recombinant Pichia pastoris cultivation carried out in a stirred tank bioreactor.The oxygen uptake rate was determined by the macrokinetic model proposed earlier.Based on pseudo-steady state mass transfer balance

an oxygen transfer model was established.Volumetric oxygen transfer coefficient kLa was estimated as a function of aeration rate and power input per unit volume.Oxygen uptake rate obtained from the macrokinetic model matched well with the oxygen transfer rate estimated by the mass balance model during the whole cultivation.The application of the oxygen transfer model for on-line biomass estimation was also presented.