Fig. 8

Extended-batch fermentation of U. cynodontis ITA Max pH grown with thick juice as sole carbon source with limiting ammonium chloride concentration (4 g/L NH4Cl). (A) Course of the oxygen and carbon dioxide transfer rates and respiratory quotient. The black arrow indicates the start of the nitrogen limitation. The horizontal green dotted-dashed line indicates an RQ = 1. (B) Sugar (sucrose, glucose, fructose) and product concentrations (itaconic acid, cell dry weight) and filling volume. For the batch phase, 200 g/L sucrose from thick juice were initially added to the medium. During the feed phase (between the vertical solid lines) 200 g of additional sucrose in form of thick juice were added into the fermentation vessel. Vertical dotted lines show the addition of antifoam. In addition, antifoam was added at the end of the feed phase. Cultivation was performed in a 2 L Sartorius BIOSTAT^® stirred tank reactor (Sartorius AG, Göttingen, Germany) with an initial filling volume of 1 L at 30 °C. Dissolved oxygen tension was kept > 30% by increasing the stirring frequency from 800 to 1200 rpm. pH was kept constant at 6.5 by addition of 1 M HCl and 5 M NaOH. Absolute aeration rate, pH, dissolved oxygen tension and stirring frequency are shown in Figure S4. RQ values are only shown for OTR values > 5 mmol/L/h. Samples were taken regularly and analyzed via HPLC. Concentrations are shown as mean values of three replicates, and standard deviation as shaded area. Due to high reproducibility of the measurements, the standard deviation might not be visible for every data point. For clarity, only every tenth data point is shown for the online data