Citric Acid Production from Nontreated Beet Molasses by a Novel Aspergillus niger Strain: Effects of pH, Sugar and Ingredients

Abstract

Effects of factors on the citric acid production from non-treated beet molasses were studied in Aspergillus niger OE55. Maximum amount of citric acid (19.13 and 34.62 g/L) was achieved when the initial pH of fermentation medium was 6.0 from 200 g/L and 150 sugar respectively. Citric acid production and biomass formation continuously increased during fermentation period in the media initially containing 200 g/L sugar. Remaining sugar (from 3.20 to 6.03 g/L) was higher at the end of fermentation in the media initially containing 160 g/L sugar than 200 g/L sugar. Yield of citric acid after 4 days of fermentation were ranged from 0.16 to 0.28 g/g from 160 g/L sugar. The high phosphorus and nitrogen levels stimulated biomass formation and reduced citric acid production. The optimum incubation for maximal citric acid production varies both with the sugar concentration in non-treated molasses and fermentation conditions for the novel A. niger strain. pH of fermentation media cannot have reduced below 4.72 and 3.35 in the media containing 200 and 160 g/L sugar, respectively, during fermentation, therefore citric acid production was not increased over 19.96 and 34.58 g/L respectively. This would be due to the formation of nitrogenous and polysaccharide compounds from molasses. Strain development in the citric acid production from wild strains depends mainly on the fermentation conditions.