COMPARATIVE STUDIES ON CITRIC ACID PRODUCTION FROM CHEESE WHY BY SUBMERGED AND IMMOBILIZED ASPERGILLUS NIGER

Abstract

Citric acid production from cheese whey using submerged culture and immobilized cell of Aspergillus niger was
investigated. In this work, effect of substrate (lactose) and product (citric acid) concentrations, medium pH, sesame
oil on production of citric acid was evaluated. In addition, the cell dry weight was measured during the fermentation
process. For submerged culture of A. niger, maximum citric acid concentration of 4.45 g/l was obtained at pH value
of 4, lactose concentration of 50 g/l, and 0.1% (v/v) sesame oil for incubation of 6 days. For incubation of 5 days, in
immobilized cell operation at optimal pH value of 3 and lactose concentration of 70 g/l, maximum citric acid
concentration of 8.4 g/l was achieved. Immobilized cells of A. niger had a significant impact on improvement of
citric acid production and increased the yield up to 62.6%. The immobilized cells had about 3 folds increase in citric
acid productivities in comparison with free cells of A. niger. The productivity of citric acid in immobilized cell
system was 4 times greater than the free cells.