• KSBB Journal
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• v.14 no.6
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• pp.672-676
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• 1999

Encapsulated Aspergillus niger was prepared in order to inspect the effect of oxygen supply on the production of citric acid. A. niger cells which had been immobilized in the calcium alginate capsule grew and mycellia penetrated through the capsule membrane after two days of cultivation and covered over all of the capsule after eight days. The mycellia became loose when the nitrogen source was sufficient of oxygen was deficient. The larger amount of encapsulated cells were put into a given growth medium, the smaller quantity of citric acid was produced. The increase of volumetric oxygen transfer coefficient from 1.8 $hr^-$ to 2.55 $hr^-$ in the flask culture accelerated cell growth rate but did not influence the production of citric acid. The high oxygen supply rate($k_La:\;150\;hr^-$) in the concentric air lift reactor hastened the growth of cells and hindered the production of the citric acid. The reduction of nitrogen source level in the growth medium in the concentric air lift reactor increased citric acid production by 40 percent of that of flask cultivation and the culture period was shortened by 3 days. The variation of the geometry of the concentric air lift reactor did not influence the growth rate of encapsulated cells and production rate of citric acid.

• KSBB Journal
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• v.10 no.1
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• pp.78-88
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• 1995

The encapsulatpd A. niger grew up inside the capsule and mycelia penetrated through the pore of the capsule membrane. The mycelia on the capsule wall became loose when the carbon source and oxygen were deficient in the medium. On the contrary, the production rate increased and mycelia made a lump tightly when the carbon source and oxygen were sufficient. Namely, number of proper capsule of unit volume in the medium was existed. The phenomenon which was swelled of capsule membrane in cultivation could prevented by adding CaCl2 into the medium. According to the time adding CaCl2 into the medium, the production rate of citric acid was influenced. In case of adding CaCl2 into the medium at 7th day cultivation, the production yield of citric acid was increased about 40 percent higher than that of adding CaCl2 initially. The production yield of citric acid using encapsulated A. niger of flask culture was influenced with oxygen supply. The production yield of citric acid ($\Delta$p/$\Delta$s) of the flask culture was increased 3.88 time by using T-flask instead of parafilm sealed flask. Therefore, the productivity and consumption rate concerning production which was taken carbon source were increased when oxygen supply was sufficient. The production of citric acid using encapsulated A. niger was increased average 30 percent higher than that of bead in between 6th and 13th day cultivation.