Microbial Characterization of Distillers Wet Grains: Results and Challenges

Authors: Lehman, R - Michael

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/16/2009
Publication Date: 6/22/2009
Citation: Lehman, R.M. 2009. Microbial Characterization of Distillers Wet Grains: Results and Challenges. American Phytopathological Society North Central Division Meeting, Ames IA, June 21-23, 2009.

Interpretive Summary:

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 have characterized the microbiology of distillers wet grains (DWG) over a nine-day period following their production at an industrial fuel ethanol plant. This freshly-produced DWG had a pH of about 4.4, a moisture content of about 53.5% (wet weight basis), and 4 x 105 total yeast cells/dry g, of which about 0.1% were viable. Total bacteria cells were initially below detection limits (ca. 106 cells/dry g) and then were estimated to be ~ 5 x 107 cells/dry g during the first four days following production. Culturable aerobic heterotrophic organisms (fungi plus bacteria) ranged between 104 and 105 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. After nine days, total viable bacteria and yeasts/molds topped 108 CFU/dry g and LAB approached 106 CFU/dry g. Community phospholipid fatty acid analysis (PLFA) yielded limited data, but 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. Significant challenges are encountered when applying culture-independent analyses (DNA-based, PLFA, total protein, and direct observation techniques) to characterize the microbiology of wet distillers grains.