Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/14/2010
Publication Date: 1/5/2011
Publication URL: http://handle.nal.usda.gov/10113/55460
Citation: Liu, K., Han, J. 2011. Changes in mineral concentrations and phosphorus profile during dry-grind process of corn into ethanol. Bioresource Technology. 102:3110-3118. Interpretive Summary: A major process for making fuel ethanol from grains (mainly corn) is the dry-grind method, in which all kernel components are processed through several sequential steps, including grinding, cooking, liquefaction, scarification, fermentation, distillation, and co-product recovery. Dried distillers grains with solubles (DDGS) are the major co-product available for marketing. Production of DDGS has increased significantly in recent years, as the number of dry-grind ethanol production facilities increases. High concentrations and high variation of minerals impact the value and end use of DDGS as animal feed. High concentration can lead to not only nutritional disorders but also excessive minerals in wastes, while high variation in mineral contents makes accurate diet formulation difficult because assumed concentrations could be different from actual concentrations. Of greatest concern is high phosphorus (P) concentration (0.5-1.0%) in DDGS. Its inclusion in animal diets caused high excretion in wastes. The chemical forms of P in DDGS also affect its bioavailability and thus the amount excreted in wastes. The present study was conducted to determine concentrations of minerals as well as levels of different types of P in all possible streams of the dry-grind process, from corn to DDGS, and also variation among ethanol plants. Study results showed that compared with ground corn, all minerals increased in concentrations in down stream products, but the extent of the increase varied greatly with individual streams and minerals. Fermentation brought about most dramatic changes due to starch depletion, but other steps, such as slurring/cooking of ground corn, centrifuging whole stillage, and evaporation of thin stillage into solubles, also caused changes in mineral composition. Compared with other ingredients, Na, S and Ca, had much higher increases in DDGS, presumably due to exogenous addition during the process. Among different types of co-products, thin stillage (not distillers solubles) had the highest concentrations of all minerals while distillers grains had the lowest. Furthermore, the present study is the first to document changes in all four types of P during the entire dry-grind process from corn, including phytate P, inorganic P, total P, and rest P. The rest P is not considered in previous literature on biomasses. It is also the first to show that during fermentation, % phytate P in total P decreased significantly, while % inorganic P increased, suggesting phytate degradation by yeast phytase. Information gained in this study can help us better understand the reasons for nutrient variation and develop strategies to modify individual processing steps for maximum balance of nutrients in DDGS.
Technical Abstract: For determining variation in mineral composition and phosphorus (P) profile among streams of dry-grind ethanol production, samples of ground corn, intermediate streams, and distillers dried grains with solubles (DDGS) were obtained from 3 commercial plants. Most attributes (dry matter concentrations) increased significantly from corn to cooked slurry but fermentation caused most significant increase in all attributes. During centrifugation, more minerals went into thin stillage than wet grains, making minerals most concentrated in the former. Mineral increase in DDGS over corn was about 3 fold, except for Na, S and Ca, which had much higher fold of increase, presumably due to exogenous addition. During fermentation, phytate P and inorganic P had 2.54 and 10.37 fold of increase over corn, respectively, while relative to total P, % phytate P decreased and % inorganic P increased significantly. These observations suggest that phytate underwent some degradation, presumably due to activity of yeast phytase.