CHO source could be starch, starch hydrolysate, cane juice, glucose, sucrose or molasses sucrose was the most favourable carbon source followed by glucose, fructose and galactose.
Nitrogen source : ammonium salts are preferred, e.g. urea, ammonium sulfate, ammonium chlorite, peptone, malt extract, etc.
Mineral : zinc, manganese, iron, copper and magnesium affect citric acid production. Potassium dihydrogen phosphate has been reported to be the most suitable phosphorous source.
Growth of A. niger on high concentrations of sugars and low concentrations of Fe3+ and Mn2+ gives high yield of citric acid