Abstract
Citric acid is an edible acid with the current global demand of 1.7x10(6) tons/annum. It is required to improve the industrial production of citric acid to satisfy the exponentially growing demands, using low-cost and renewable sources. Hydrol is a byproduct of starch industry which contains approximately 70% fermentable sugars and can be exploited to produce citric acid. Here, the hydrol was subjected to fermentation in 23-L and 150-L fermenter to produce citric acid. Medium containing reducing sugar (S-0= 80-180 gL(-1)) from hydrol was used as the basal fermentation medium using a derepressed mutant derivative of MUNAR 120 Aspergillus niger. Different process variables for the accumulation of citric acid were optimised. At optimum substrate concentration (150 gL(-1)) citric acid titer of 130 gL(-1), the product yield of 0.86 gg(-1), the maximum volumetric productivity of 3.45 gL(-1)h(-1), and specific productivity of 2.47 gg(-1)h(-1) were achieved. In 23-L fermenter studies, 90-100% sugars were consumed at temperatures ranging from 22-38(degrees)C. Where, in a 150-L pilot-scale fermenter 80% of the theoretical yield was achieved. The experimental data and kinetic parameters have shown that the mutation has a dramatic impact on the metabolic activities. Enzymes inactivation phenomena implied a little increase in entropy during the activated state and suggested an improved protection conferred by mutant cell system. Overall metabolic activity of the mutant was significantly improved when compared to its wild-type parent.