Liquid films on shake flask walls explain increasing maximum oxygen transfer capacities with elevating viscosity

Abstract

In biotechnological screening and production, oxygen supply is a crucial parameter. Even though oxygen transfer is well documented for viscous cultivations in stirred tanks, little is known about the gas/liquid oxygen transfer in shake flask cultures that become increasingly viscous during cultivation. Especially the oxygen transfer into the liquid film, adhering on the shake flask wall, has not yet been described for such cultivations. In this study, the oxygen transfer of chemical and microbial model experiments was measured and the suitability of the widely applied film theory of Higbie was studied. With numerical simulations of Fick's law of diffusion, it was demonstrated that Higbie's film theory does not apply for cultivations which occur at viscosities up to 10 mPa s. For the first time, it was experimentally shown that the maximum oxygen transfer capacity OTRmax increases in shake flasks when viscosity is increased from 1 to 10 mPa s, leading to an improved oxygen supply for microorganisms. Additionally, the OTRmax does not significantly undermatch the OTRmax at waterlike viscosities, even at elevated viscosities of up to 80 mPa s. In this range, a shake flask is a somehow self-regulating system with respect to oxygen supply. This is in contrary to stirred tanks, where the oxygen supply is steadily reduced to only 5% at 80 mPa s. Since, the liquid film formation at shake flask walls inherently promotes the oxygen supply at moderate and at elevated viscosities, these results have significant implications for scale-up.

The Effects of Nutrient Concentration, Addition of Thickeners, and Agitation Speed on Liquid Fermentation of Steinernema feltiae

“…Previous liquid culture studies showed that increasing medium viscosity increased dissolved oxygen levels (Giese et al, 2013;Mascarin et al, 2015). Giese et al (2013) demonstrated that high-viscosity media tend to adhere to the flask wall, thus increasing oxygen transfer by increasing the surface area of the medium. In our case, it may be that agar's role in integration of the oil phase into the liquid medium may also have improved oxygen transfer by increasing exposure of the medium to air.…”

Shaken flasks by resonant acoustic mixing in the biosynthesis of alginate by Azotobacter vinelandii with non‐Newtonian rheological characteristics

“…Figure (c) shows a simulation of the apparent viscosity performance estimated from n and k values, assuming a shear stress value of 300 s ‐1 . The γ value of 300 s ‐1 used in this work for the η estimations was previously found to be the mean shear rate at the usual operating conditions in orbital shake flasks . The highest apparent viscosity of 15.47 ± 6.93 mPa.s was achieved by the cultures grown at 20 g , whereas at 5, 10, and 15 g , values of 3.03 ± 0.18, 5.22 ± 0.42, and 1.26 ± 0.03 mPa.s were obtained, respectively.…”

“…As shown previously, RAM is able to achieve higher k L a values;, therefore, higher OTR max are expected than those typically observed in orbital shake flasks. The maximum OTR for the RAMbio system has not been measured yet, but an approximate estimation can be made by using the k L a values from a previous experimental model and by assuming 0.21 mmol L ‐1 (culture medium) as the oxygen concentration at the water–air interface . This estimation gives us maximum OTR values between 11.0 and 49.7 mmol L −1 h −1 for the 500 mL flasks used with 100 mL of culture medium at shaking frequencies between 5 and 20 g.…”

“…Figure (a) shows the increase in the apparent viscosity as a function of commercial sodium alginate concentration estimated at a constant shear rate of 300 s ‐1 from the n and k values. The γ value of 300 s ‐1 used in this work for the η estimations was previously found to be the mean shear rate at the usual operating conditions in orbital shake flasks , . In order to have a deeper analysis of non‐Newtonian fluids, the typical shear rates in resonant acoustic mixed flasks should be determined.…”

Produção do fungo entomopatogênico Metarhizium rileyi (Farlow) por fermentação líquida e sólida

“…Sua disponibilidade é dependente da transferência de oxigênio do ambiente para o líquido, a qual é incrementada com o uso de Erlenmeyer baffled cell culture flasks, altas velocidades de agitação, baixo volume de cultura no frasco (50 mL) e maior viscosidade do meio 2015b). Maiores concentrações de carbono atuam justamente sobre a viscosidade do meio, tornando-o mais viscoso, e um meio com tal característica tende a aderir mais facilmente à parede do frasco, aumentando a transferência de oxigênio para o meio pelo incremente da superfície de contato (GIESE et al, 2013). Em um sistema de retro-alimentação positiva, o crescimento de blastosporos, em detrimento de hifas, melhora a transferência de oxigênio em culturas de fungos (PETER et al, 2004;ISSALY et al, 2005;JACKSON, 2012).…”