CITRIC ACID FERMENTATION OF HYDROLYSED RAW STARCH BY ASPERGILLUS NIGER IIB-A6 IN STATIONARY CULTURE

S. Anwar, S. Ali, A. A. Sardar

Abstract


In the present investigation, better citric acid production (23.87±2.75g/l) was obtained with sweet potato starch hydrolysate at an initial sugar concentration of 200 g/l by Aspergillus niger IIB-A6. The product formation kinetic parameters viz., Qp (0.1 g/l/h) and qp (0.02 g/g/h) were higher for sweet potato when compared to maize starch hydrolysate. Incubation period (264h), initial H (3.0), volume of fermentation medium (50 ml/250 ml Erlenmeyer flask) and inoculum size (2.0 %) were also optimized. The optimal citric acid production was obtained when methanol (1.5 %, v/v) as a stimulant was added into the medium 24 h after the inoculation. Different metal complexing agents such as ethylenediamine tetra aceticacid (EDTA) and potassium ferrocyanide were used to reduce heavy metal ions during the fermentation process. The maximum amount of citric acid (45.90±4.20g/l) was achieved when 200 ppm of K4Fe (CN)6 was added into the medium just before inoculation under hot conditions. EDTA however, showed insignificant results.


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