Production of citric acid using immobilized conidia of Aspergillus niger |
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Authors: | Emine Bayraktar Ülkü Mehmetoglu |
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Institution: | (1) Chemical Engineering Department, Science Faculty, Ankara University, 06100 Tandogan, Ankara, Turkey |
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Abstract: | Conidia of Aspergillus niger were immobilized in calcium alginate gel for the production of citric acid. First, the type of the preactivation medium,
together with the preactivation period, was investigated. It was found that A. niger requires a 2-d preactivation period at a 0.05 g/L NH4NO3 concentration. Second, preactivated cells were used to determine the effects of nitrogen concentration and the flow rate
of oxygen and air on the production of citric acid. Maximum citric acid production was attained with medium containing 0.01
g/L of NH4NO3. The rate of citric acid production in the nitrogenous medium was 33% higher when oxygen was used instead of air during the
production phase. This corresponds to an increase of 85% when compared to production when neither oxygen nor air was fed into
the system. In the nonnitrogenous medium citric acid concentration remained similar regardless of the use of air or oxygen.
However, in the nonnitrogenous production medium, citric acid production was not influenced considerably when oxygen was used
instead of air. The advantage of using immobilized cells is that production is achieved easily in the continuous system. Therefore,
citric acid production was also tested using a packed-bed bioreactor, and an increase in productivity by a factor of 22 was
achieved compared to the batch system. |
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Keywords: | Aspergillus niger citric acid immobilization Ca alginate particles packed-bed bioreactor |
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