Effect of High-Speed Shaking on Oxygen Transfer in Shake Flasks

Abstract

Shake flasks are predominantly used in screening and the early stages of biotechnological process development. However, oxygen-demanding processes cannot easily be performed in shake flasks, since the maximum oxygen transfer capacity is usually smaller than in stirred reactors. Studies during the last decades suggest that the shaking frequency is one of the most crucial cultivation parameters to sustainably increase oxygen supply in orbitally shaken bioreactors. In this study — for the first time — a prototype of a self-balancing orbital shaker was used, which is capable to be operated at up to 750 rpm shaking frequency at 25 mm shaking diameter and 600 rpm at 50 mm. Kluyveromyces lactis cultivations were monitored with a modified TOM system to measure the maximum oxygen transfer capacities (OTR_max) and corresponding k_La values. A maximum k_La value of 650 h⁻¹ (OTR_max = 135 mmol/L/h) was reached at 10 mL filling volume in a 250 mL shake flask made of glass with a hydrophilic surface property. This is an increase of about 50%, compared to current commercial orbital shakers. The new high-speed orbital shaker provides new possibilities for screening applications and process development. High-speed shaking for enhanced oxygen supply is particularly beneficial at 25 mm shaking diameter, rather than at 50 mm, minimizing the impact of the elevated centrifugal force on the shaking system.