Continuous production of citric acid by immobilized whole cells of Aspergillus niger.

Abstract

A process of continuous citric acid production from sugarcane molasses by fermentation with immobilized whole cells of A. niger KCU 520 is described. Both calcium alginate beads and polyacrylamide gel (PAG) slab entrapment methods were used for immobilization of cells. The optimum fermentation conditions for citric acid fermentation by immobilized cells were sugars, 10%; pH, 4.0; inoculum size, 20%, and temperature, 32-35°C. With calcium-alginate and PAG-immobilized cells, an overall citric acid production rate of 8.5g and 12.0g/l/day (9.3% and 12% sugar conversion to citric acid per day), respectively was achieved in a single-stage bioreactor. When the PAG-immobilized cells were used in a two-stage bioreactor, approximately 20.0g citric acid/l/day (20% sugar conversion to citric acid per day) was produced and the PAG-immobilized cells were continuously used for at least 20 days without any significant loss of productivity.