“…This shows that tube shaking conditions are relevant for cell culture performance, especially at high cell density, and that they can induce a change in cell metabolism when fresh medium is not fed often enough. Although we have not investigated the effect of the tested culture conditions on product quality, it has been reported, that damage to proteins in solution by shear and the related phenomena exerted on proteins at the moving gas-liquid interface may result in protein unfolding, dissociation of subunits, or increased aggregation, thus leading to protein inactivation (and/or increased immunogenicity of protein drug products) (Ghadge et al, 2003;Klockner and Buchs, 2012;Thomas and Geer, 2011). Therefore, it is possible that the adjustment in the shaking angle and speed also altered the mechanical shear of the fluid inside the shake tubes, resulting in an increased product yield as determined by enzyme's activity (Fig.…”