Comparison of methods for evaluating citric acid production ability by Aspergillus niger

Two laboratory methods for evaluating citric acid production ability by Aspergillus niger were tested with twenty selected strains from various sources. The classical evaluation method using Petri dish with agar medium and pH indicator did not show good correlation with citric acid production by surface and submerged methods. Better correlation was observed when a horizontal tube method was compared with surface (r = 0.550) and submerged (r = 0.352) methods of citric acid production in synthetic medium. These results indicated that the tube method was superior to the Petri dish method for evaluation of the citric acid production potential of Aspergillus niger.