| Summary: | 碩士 === 大同大學 === 生物工程研究所 === 93 === The formation of mycelial clumps in conventional cultures of Rhizopus oryzae resulted mainly from the depletion of nitrogen source in the cultural medium. Based on this behavior, L(+)-lactic acid production could be enhanced in the submerged culture using mycelial flocs induced by replenishing ammonium-nitrogen in the cultural medium, thereby the formation of mycelial clumps or pellets which often occurred in conventional cultures of R. oryzae was prevented. When the fermentation was performed in a 5-L stirred tank bioreactor with the pH being controlled in the range of 4.3 – 4.5 by adding calcium carbonate slurry, and small amounts of ammonium sulfate was added at 8-h intervals to sustain ammonium level of the culture in the range of 0.3 – 0.5 g/L, lactic acid production was optimized. The lactic acid concentration produced was 105 g/L, with the yield of 0.88 and the productivity of 2.63 g/L-h, using 120 g/L of glucose as substrate. Without replenish of ammonium-nitrogen, mycelial clumps attached everywhere in the bioreactor and lactic acid production dramatically declined. This article demonstrates a simple way to obtain mycelial flocs of R. oryzae thereby an optimized lactic acid production can be achieved.
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