Citric acid production: Surface culture versus submerged culture

Abstract

Surface and submerged fermentation methods were used to produce citric acid byAspergillus niger using chemically defined media or cane molasses. Fermentation process parameters were optimized in pilot scale tower and tray fermenters. Fermentation was running from 10 - 20 days with pH controlled at 3 - 6.5. Citric acid concentrations varied from 60 - 100 g/L depending on the strain used, the substrate, the fermentation system and the general conditions under which fermentation took place (initial sugar concentration, aeration rate, inoculum size, pH and temperature). Some essential criteria such as lower process sensitivity to short interruptions or breakdowns in aeration, expenses for equipment, consumption of electrical energy and higher yield and productivity, showed that surface fermentation is superior to submerged fermentation. However, the yield and productivity obtained in submerged fermentation using indigenous strains of fungi is not yet high enough for commercial production. Key words: Citric acid, surface, submerged indigenous strains, yield, productivity.