[show abstract][hide abstract] ABSTRACT: The gas–liquid mass transfer in 250 ml shake flasks has previously been sucessfully modelled on basis of Higbie’s penetration theory. The current contribution presents advances in understanding and modelling the gas–liquid mass transfer in shake flasks at waterlike liquid viscosity in flask sizes between 50 and 1000 ml. An experimental investigation of the maximum gas–liquid mass transfer capacity OTRmax using the sodium sulphite system was extended to relative filling volumes of 4–16%, shaking diameters of 1.25, 2.5, 5, 7, 10 cm and shaking frequencies of 50–500 rpm for the above flask sizes. Simultaneously, the previous model of the gas–liquid mass transfer was extended to a “two sub-reactor model” to account for different mechanisms of mass transfer in the liquid film on the flask wall and the bulk of the liquid rotating within the flask. The shake flask is for the first time considered to be a two-reactor system consisting of a stirred tank reactor (bulk liquid) and a film reactor (film on flask wall and base). The mass transfer into the film on the flask wall and base at “in-phase” operating conditions is described by Higbie’s penetration theory. Two different mass transfer theories were applied to successfully describe the mass transfer into the bulk liquid: a model by Kawase and Moo-Young and a model by Gnielinski. The agreement between the new modelling approach, which requires absolutely no fitting parameters and the experimental is within ±30%. The applicability of the models to a biological system was shown using a Pichia pastoris culture. This is particularly notable since geometrically non-similar liquid distributions in very different sizes of shaking flasks are covered. A comparable description of the gas–liquid mass transfer in bubble aerated reactors like stirred tanks is absolutely out of reach. A spatially- and time-resolved consideration of the mass transfer in the liquid film on the flask wall and base has shown that the validity of Higbie’s theory sensitively depends on the film thickness and contact time.
[show abstract][hide abstract] ABSTRACT: Screening cultures are usually non-monitored and non-controlled due to a lack of appropriate measuring techniques. A new device for online measurement of oxygen transfer rate (OTR) in shaking-flask cultures was used for monitoring the screening of Hansenula polymorpha. A shaking frequency of 300 rpm and a filling volume of 20 ml in 250-ml flasks ensured a sufficient oxygen transfer capacity of 0.032 mol (l h)(-1) and thus a respiration not limited by oxygen. Medium buffered with 0.01 mol phosphate l(-1) (pH 6.0) resulted in pH-inhibited respiration, whereas buffering with 0.12 mol phosphate l(-1) (pH 4.1) resulted in respiration that was not inhibited by pH. The ammonium demand was balanced by establishing fixed relations between oxygen, ammonium, and glycerol consumption with 0.245+/-0.015 mol ammonium per mol glycerol. Plate precultures with complex glucose medium reduced the specific growth rate coefficient to 0.18 h(-1) in subsequent cultures with minimal glycerol medium. The specific growth rate coefficient increased to 0.26 h(-1) when exponentially growing precultures with minimal glycerol medium were used for inoculation. Changes in biomass, glycerol, ammonium, and pH over time were simulated on the basis of oxygen consumption.
Journal of Industrial Microbiology and Biotechnology 11/2003; 30(10):613-22. · 2.32 Impact Factor