Continuous butanol fermentation and feed starch retrogradation: butanol fermentation sustainability using Clostridium beijerinckii BA101

Use of starch solution as feed for butanol bioconversion processes employing Clostridium beijerinckii BA101 may have added economic advantage over the use of glucose. 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 volume (3 L) was replaced every 72 h. The continuous reactor fed with cornstarch solution (feed temperature 19 °C) produced approximately 6.0 g L−1 total ABE. Increasing the feed storage temperature to 37 °C improved ABE production to 7.2 g L−1 suggesting that retrogradation was occurring more rapidly at 19 °C. In both these cases the fermentation drifted toward acid production after approximately 260 h, consistent with the retrogradation of starch overtime. The use of soluble starch, which is less prone to retrogradation, resulted in the production of 9.9 g L−1 ABE at 37 °C feed storage temperature, as compared to 7.2 g L−1 ABE when cornstarch was used. It should be noted that gelatinized starch retrogradation takes place after sterilization and prior to use of the feed medium, and does not occur during long-term storage of the raw corn material in the months leading up to processing. The degree of hydrolysis of gelatinized starch decreased from 68.8 to 56.2% in 3 days when stored at 37 °C. Soluble starch which does not retrograde demonstrated no change in the degree of hydrolysis.