Submitted to: Society of Industrial Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/14/2003
Publication Date: 8/14/2003
Citation: EZEJI, T.C., BURROWS, M., QURESHI, N., BLASCHEK, H.P. CONTINUOUS BUTANOL FERMENTATION AND FEED STARCH RETROGRADATION: BUTANOL FERMENTATION SUSTAINABILITY USING CLOSTRIDIUM BEIJERINCKII. SOCIETY OF INDUSTRIAL MICROBIOLOGY ANNUAL MEETING. 2003. ABSTRACT P. 65. Interpretive Summary:
Technical Abstract: Use of solubilized starch as feed for a butanol bioconversion process employing Clostridium beijerinckii may be economically advantageous over the use of glucose solution. C. beijerinckii can hydrolyze and utilize starch for butanol production. For this reason, butanol (also called acetone-butanol-ethanol, ABE, or solvents) was produced from 30 g L**-1 starch solution in a continuous process. The bioreactor was fed at a dilution rate of 0.02 h**-1, and starch solution was replaced every 72 h. The continuous reactor, fed with corn starch 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 faster at 19 deg C. In both these cases, fermentation drifted toward acid production after approximately 260 h, further indicating strong evidence for starch retrogradation. The use of a soluble starch, which is less prone to retrogradation, resulted in the production of 9.9 g L**-1 ABE at 37 deg C feed temperature as opposed to 7.2 g L**-1 with corn starch (which is more prone to retrogradation). It should be noted that gelatinized starch becomes retrograded over time. The degree of hydrolysis of gelatinized corn starch decreased from 66% (fresh) to 54% in 3 days when stored at 37 deg C. Soluble starch, which is not retrograded, 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 major role in the premature termination of the continuous fermentation process since maintenance of culture metabolism depends on the availability of simple sugars (hydrolysis products) in the bioreactor.