The production of citric acid from carob pod extract by cell recycle o
f Aspergillus niger at different pHs was investigated. Best results in
terms of citric acid concentration, productivity, yield and sugar uti
lization were obtained with a substrate pH of 5.0. The citric acid con
centration (85.5 g/l) and the productivity (4 g/ld) remained constant
up to the second and third cycles, respectively.