Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.
The effect of shear forces on suspended cells is one of the most complex problems in the scale-up of cell cultures. In the present paper, recent advances in the understanding of power consumption during agitation of Erlenmeyer flasks in rotary shakers are applied to direct comparison of the effects of shear forces on suspension cultures of Rubia tinctorum cells in a standard bioreactor and in shake flask cultures. The criterion selected as indicative of the shear stress acting on the cells was the critical eddy length, l, following Kolmogoroff's theory of isotropic turbulence. Standard flasks and four-baffled shake flasks were used. The effect of shear stress and light irradiation on cell viability, biomass, and anthraquinones (AQs) production was evaluated. The biomass concentration and AQs production obtained using baffled shake flasks agitated at 360 rpm were similar to that achieved previously in R. tinctorum suspension cultures growing in a stirred tank bioreactor operating at 450 rpm. It can be concluded that this down-scaled and simple flask culture system is a suitable and valid small scale instrument to study intracellular mechanisms of shear stress-induced AQs production in R. tinctorum suspension cultures, including intracellular phenomena, and can be eventually extended to other systems.