The Effect of Lipids on Citric Acid Production by an Aspergillus niger Mutant

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Abstract
A mutant strain, 72-44, of Aspergillus niger was selected after ultraviolet irradiation of the spores of A. niger strain 72-4. This mutant was capable of giving high yields of citric acid in shaken-flask fermentations. A study was made of the effect of various lipids on the yield of citric acid produced by A. niger strain 72-44. Fatty acids with less than 15 carbon atoms inhibited growth and no citric acid was produced. Natural oils with a high content of unsaturated fatty acids and oleic acid itself, when added at 2% (v/v) to suitable fermentation media, increased the yield of citric acid by about 20%. Lipids which improved the yield of citric acid had no effect on the dry weight of mycelium. The possible mode of action of effective lipids is discussed. It is suggested that unsaturated lipids act as alternative hydrogen acceptors to oxygen during the fermentation and thus improve the yield of citric acid.

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