PROCESS OPTIMIZATION OF CITRIC ACID PRODUCTION FROM ASPERGILLUS NIGER USING FUZZY LOGIC DESIGN

摘要

The inherent non-linearity of citric acid fermentation from Aspergillus niger renders its control difficult, so there is a need tofine-tune the bioreactor performance for maximum production of citric acid in batch culture. For this, fuzzy logic is becoming apopular tool to handle non-linearity of a batch process. The present manuscript deals with fuzzy logic control of citric acid accretionby A. niger in a stirred tank reactor using blackstrap sugarcane molasses as a basal fermentation medium. The customary batcheswere termed as ‘control’ while those under fuzzy logic were ‘experimental’. The performance of fuzzy logic control of stirred tankreactor was found to be very encouraging for enhanced production of citric acid. The comparison of kinetic parameters showedimproved citrate synthase ability of experimental culture (Yp/x = 7.042 g/g). When the culture grown on 150 g/l carbohydrates wasmonitored for Qp, Qs and Yp/s, there was significant enhancement in these variables over the control. Specific productivity of culture(qp = 0.070 g/g cells/h) was several fold increased. The enthalpy (ΔHD = 70.5 kJ/mol) and entropy of activation (ΔS = -144 J/mol/K)of enzyme for citric acid biosynthesis, free energies for transition state formation and substrate binding for sucrose hydrolysis ofexperimental were substantially improved.