The growth of Aspergillus terreus and the production of itaconic acid in batch and continuous cultures. The influence of pH

Aspergillus terreus (NRRL 1960) was cultivated in batch and in continuous singlestage culture. The influence of pH on the growth of the organism, on the formation of itaconic acid and on the kinetics of fermentation was studied under phosphate limitation, both at controlled pH values and also when the pH was allowed to decrease in a natural way. In the pH range 1.7–3.5, the ratio of undissociated :half‐dissociated acid varied from 190:1 to 1.5:1. The amount of completely dissociated acid may be regarded as negligible. In batch systems operated without pH control, an initial pH of 3.1 proved to be the most effective. Product formation under such conditions started at a point where the exponential growth phase commenced and was described by a zero‐order equation. The maximum itaconic acid production rate was shifted behind maximum growth rate. The continuous single‐stage system was first order with respect to product formation. At pH > 3.1, a number of aberrant and pellet forms of the mould occurred, resulting in decreased acid production.