ARS | Publication request: Contamination issues in continuous fermentation for ethanol production

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 19, 2011
Publication Date: October 19, 2011
Citation: Khullar, E., Kent, A.D., Leathers, T.D., Bischoff, K.M., Rausch, K.D., Tumbleson, M.E., Singh, V. 2011. Contamination issues in continuous fermentation for ethanol production [abstract]. Cereal Foods World. 56:A48.

Technical Abstract: Continuous fermentation processes are employed by corn wet milling plants all over world to convert starch to ethanol. Contaminations by bacterial microorganisms like Lactobacillus and wild yeasts like Brettanomyces are common and result in lower ethanol yields. Contaminants compete with inoculated yeast for nutrients and produce inhibitory end products, leading to stuck fermentations and expensive down times required for cleaning unit operations. Low ethanol yields and poor yeast viabilities in continuous fermentations for ethanol production were investigated. For hydrolysate preparation, starch liquefaction and saccharification steps at a commercial ethanol facility were reproduced in laboratory. Fermentations with hydrolysates prepared in laboratory were compared with plant hydrolysate for final ethanol concentrations and total yeast counts. Fermentation controls were prepared using hydrolysates (plant and laboratory), but were not inoculated with yeast. Hydrolysates prepared in laboratory resulted in higher final ethanol concentrations (15.8% v/v) than plant hydrolysate (13.4% v/v). Controls resulted in ethanol production from both laboratory (12.2% v/v) and plant hydrolysates (13.7% v/v), indicating the presence of a contaminating microorganism. Upon further experimentation, involving yeast colony counts on cycloheximide and virginiamycin plates, we confirmed the presence of a contaminant. DNA sequencing and fingerprinting studies conducted also were indicative of a number of dissimilar communities in samples obtained from fermenters, coolers, saccharification tanks and thin stillage.