| Summary: | 碩士 === 朝陽科技大學 === 應用化學系碩士班 === 98 === Using C. acetobutylicum ATCC 824, the fermentation was accomplished anaerobically in a 5L fermentor, in which we mainly investigated the use of ORP (oxidation-reduction potential) response as the key monitoring indicator. By manipulating the timing for cell transfer, the lag phase of this culture was shortened to be 6 h, as compared with 12 h in our preliminary experiments using serum bottles. In experiments, it was likely that cell growth was inhibited under the acid environment of the fermentation at pH 4.
Without controlling the initial value of pH (pHi), the ORP response was minimized at -530 mV in the fermentation when the cells reached the log phase of cell growth; meanwhile, gas production was also initiated. After that, ORP was increased and stabilized higher at -380 mV. It was found that cell growth was positively proportional to the value of d(ORP)/dt. For example, the value of d(ORP)/dt was calculated to be 0 when a stationary growth phase was achieved. This finding implied that energy supplements through electron transport system (ETS) was largely reduced after the log phase of cell growth, since ETS was considered to be uni-directional.
Furthermore, in the experiments of controlling a different pHi (4, 6 or 8) cell growth was somehow inhibited and sugar utilization was also decreased. In such operations, the fermentation pH was close to 4 after a 12 h of the elapsed time, where a stable response of ORP was observed after this timing. Together with the results of no pHi control, we concluded that cell growth, pH change, or production shift of liquid metabolites mutually interacted with the ORP response in the fermentation.
Key words: Clostridium acetobutylicum, anaerobic fermentation, oxidizing reducing potential.
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