FACTORS CONTROLLING CITRIC ACID PRODUCTION BY SOME OF ASPERGILLUS NIGER STRAINS

Different strains of A. niger were used to examine their ability to produce citric acid and the results revealed that most of the nine tested strains were able to produce citric acid. A. niger CA2 was the highest producer strain during the fermentation on medium No. 2, while highest biomass weight was obtained during the growth of A. niger CA2 on medium No.1. But, highest value of consumption of sugars was found during the growth of A. niger NRRL 2270 on medium No.5. Highest value of conversion coefficient and the citric acid yield were obtained during the growth of A. niger CA2 on medium No. 2. Maximum production of citric acid was obtained after 8 days of fermentation and pH 5.5. At the same time, highest value of biomass, conversion coefficient and total sugars consumed were obtained at these conditions. At 15% sugars concentration, citric acid reached its maximum being 29.3 g/L. Maximum production (32.03 g/L) of citric acid was obtained with 2.0 g/L ammonium phosphate, also, give highest amount of biomass and citric acid yield. Highest value of citric acid concentration (32.88 g/L) and citric acid yield (21.92%) were obtained with 0.3 ml/L of phosphoric acid which was found as the best phosphorus source.