| Summary: | 碩士 === 大同大學 === 生物工程學系(所) === 94 === Pellet-form Rhizopus arrhizus was cultured in a stirred tank bioreactor for enhanced L-lactic acid production using glucose as substrate and an ammoniacal solution as neutralizing agent. Ammonium hydroxide may cause damage to fungal cells in terms of “chemical burn”, leading to a poor production of lactic acid. It was found when ammonium bicarbonate was added to the ammonia water or urea was added to the culture medium, the toxicity of ammonium hydroxide decreased and lactic acid production was enhanced. The fermentation was carried out at pH 5.0 with the addition of 1 g L–1 urea in the culture medium, using an ammoniacal solution as neutralizing agent, which was 2% (w/v) ammonium bicarbonate in 10% (w/v) ammonia water. The batch fermentation completed in 48 h. The final concentration of lactic acid was 98 g L–1 with a yield of 82%. However, the final concentrations of lactic acid obtained in the first four cycles of repeated batch fermentation were 98, 95, 88 and 82 g L–1, with fermentation times being 48, 48, 52 and 54 h, respectively.
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