Submitted to: Canadian Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 2007
Publication Date: September 1, 2007
Citation: Lehman, R.M., Rosentrater, K.A. 2007. Microbial Development in Distillers Wet Grains Produced During Fuel Ethanol Production from Corn (Zea mays). Canadian Journal of Microbiology. 53:1046-1052. Interpretive Summary: No published information is available of the microbiology of distillers grains produced during fuel ethanol production. Distillers grains are used as livestock feed. Spoilage is a concern, as well as development of deleterious organisms. Conversely, probiotic organisms may colonize the distillers grains. We found numerous and viable microorganisms, fungi and bacteria, in freshly produced distillers grains, despite the harsh conditions of this industrial process. Over 4 days, distillers grains stored at the plant were microbiologically stable. At 9 days, spoilage was initiated. Organisms that may have probiotic potential were present and increased numbers during storage.
Technical Abstract: Distillers grains are co-produced with ethanol and carbon dioxide during the production of fuel ethanol from the dry milling and fermentation of corn grain, yet there is little basic microbiological information on these materials. We undertook a replicated field study of the microbiology of distillers wet grains (DWG) over a nine-day period following their production at an industrial fuel ethanol plant. Freshly-produced DWG had a pH of about 4.4, a moisture content of about 53.5% (wet weight basis), and 4 x 10E5 total yeast cells/dry g, of which about 0.1% were viable. Total bacteria cells were initially below detection limits (ca. 10E6 cells/dry g) and then were estimated to be ~ 5 x 10E7 cells/dry g during the first four days following production. Culturable aerobic heterotrophic organisms (fungi plus bacteria) ranged between 10E4 and 10E5 CFU/dry g during the initial four day period and lactic-acid bacteria (LAB) increased from 36 to 103 CFU/dry g over this same period. At nine days, total viable bacteria and yeasts/molds topped 10E8 CFU/dry g and LAB approached 10E6 CFU/dry g. Community phospholipid fatty acid analysis indicated a stable microbial community over the first four days of storage. Thirteen morphologically-distinct isolates were recovered of which ten were yeasts and molds from six different genera, two were strains of the lactic acid-producing Pediococcus pentosaceus, and only one was an aerobic heterotrophic bacteria, Micrococcus luteus. The microbiology of DWG is fundamental to assessment of spoilage, deleterious effects (e.g., toxins), or beneficial effects (e.g., probiotics) in its use as feed or in alternative applications.