Effect of pH and stirring rate on itaconate production by Aspergillus terreus

The production of itaconic acid from glucose-based media by Aspergillus ter reus NRRL 1960 was found to be controlled by stirring rate and pH. When the phosphorous (P) level in the production medium was reduced to less than 10 mg 1(-1), the fungal mycelium exhausted its primary growth and started to excrete itaconic acid, while it continued its secondary growth at the expen se of ammoniacal nitrogen. The fermentation exhibited a mixed-growth-associ ated product formation kinetics, the non-growth associated production term (m(I)) being practically zero only when the pH was left free to change from 3.4 down to 1.85. On the contrary, when the pH was kept reducing up to a c onstant value by automatic addition of KOH 4 mol 1(-1), the itaconate yield coefficient on the initial glucose supplied (Y-I/So) and m(I) and were 0.5 3 g g(-1) and 0.028 h(-1) at pH 2.4 and 320 rev min(-1) and 0.5 g g(-1) and 0.036 h(-1) at pH 2.8 and 400 rev min(-1), respectively. Although the diff erences between m(I) and Y-I/So were statistically insignificant at the 95% confidence level, the net difference in the corresponding yield coefficien ts for itaconic acid on mycelial biomass resulted in a maximum itaconate pr oduction rate of 0.41 g 1(-1) h (-1) at pH 2.8 and 400 rev min (-1), thus s howing that this operating condition is no doubt optimal for the process un der study. (C) 2000 Elsevier Science B.V. All rights reserved.