Submitted to: Journal of Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2004
Publication Date: 1/3/2005
Citation: Ezeji, T.C., Qureshi, N., Blaschek, H.P. 2005. Continuous butanol fermentation and feed starch retrogradation: butanol fermentation sustainability using Clostridium beijerinckii BA101. Journal of Biotechnology. 115:179-187. Interpretive Summary: Butanol is a superior liquid fuel to ethanol and can be produced from agricultural crops such as corn. Utilization of corn for butanol production would enhance economics of U.S. farmers. Currently, 2.6 billion pounds of butanol are produced from petrochemical sources in the U.S. Clostridium beijerinckii BA101 can convert cornstarch into butanol efficiently. Use of cornstarch rather than glucose would add economic advantage to the process of butanol production using microbial culture. It was found that cornstarch solution fed to the bioreactor at 19 deg C produced less butanol than fed at 37 deg C. The reason behind this was that starch solution stored at 19 deg C was not hydrolyzed efficiently as compared to starch solution stored at 37 deg C by the culture. This phenomenon of starch not being hydrolyzed efficiently at lower temperature than at 37 deg C is called retrogradation. Starch retrogradation affects butanol production efficiency. These studies detail production of butanol from cornstarch and how retrogradation affects the culture. This investigation would benefit the fermentation industry and the farmers.
Technical Abstract: During these investigations, starch retrogradation was studied in butanol fermentation. Use of starch solution as feed for butanol bioconversion processes employing Clostridium beijerinckii BA101 may have added economic advantage over the use of glucose. C. beijerinckii BA101 can hydrolyze and utilize starch for butanol production. Acetone butanol ethanol (ABE) was produced from 30 g L**-1 starch solution using a continuous process. The bioreactor was fed at a dilution rate of 0.02 h**-1, and starch solution/feed was replaced every 72 h. The continuous reactor fed with cornstarch solution (feed temperature 19 deg C) produced approximately 6.0 g L**-1 total ABE. Increasing the feed temperature to 37 deg C improved ABE production to 7.2 g L**-1, suggesting that retrogradation was occurring more rapidly at 19 deg C. In both these cases, the fermentation drifted toward acid production after approximately 260 h, consistent with retrogradation of starch. It should be noted that gelatinized starch is retrograded over time. The degree of hydrolysis of gelatinized starch decreased from 68.8% to 56.2% in 3 days when stored at 37 deg C. Soluble starch, which does not retrograde, demonstrated no change in the degree of hydrolysis. It is concluded that retrogradation, which may lower the susceptibility of gelatinized starch to enzymatic hydrolysis, plays a role in the premature termination of the continuous fermentation process since the maintenance of culture metabolism depends on the availability of simple sugars (hydrolysis products) being available in the bioreactor.