초록
<P>Batch fermentations by Clostridium thermobutyricum ATCC49875 at various pH values ranging from 5.9 to 6.8 were investigated. Based on the analysis of the experimental results, a two-stage pH-shift control strategy was proposed, with the aim of improving the efficiency of butyric acid production. At the first 24 h, pH was controlled at 6.8 to obtain the higher μx, and subsequently pH 6.2 was used to maintain high μp to enhance the production of butyric acid. Compared to control group (those of constant pH operations), a fermentation process by using this control strategy for butyric acid production had a significant improvement on the maximal butyric acid (24.60 g/l vs. 20.06 g/l) and glucose conversion efficiency (49.20% vs. 46.33%). Fed-batch fermentation by using pH-shift control strategy was also applied to produce butyric acid; and the maximal butyric acid yield and glucose conversion efficiency reached 28.75 g/l and 47.92%, respectively. These results showed that pH-shift fermentation could serve as an excellent alternative to conventional butyric acid fermentation.</P>