Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2008
Publication Date: 4/29/2008
Citation: Liu, K.S. 2008. Particle Size Distribution of Distillers Dried Grains with Solubles (DDGS) and Relationships to Compositional and Color Properties. BioResource Technology 99:8421-8428
Interpretive Summary: Increase in demand of ethanol as a fuel additive and decrease in dependency on fossil fuels have led to a dramatic increase in the amount of corn used for ethanol production. A key co-product of the conversion process is distillers’ dried grains with solubles (DDGS). Factors that affect quality of DDGS directly impact the price and end use of DDGS, and thus the economics of ethanol production. DDGS is a mix of particulate materials. Surprisingly, there is limited information in literature on its particle size distribution (PSD). PSD, that is, the relative amounts of particles present, sorted according to size, has been widely used to describe many other powder materials, since it is an important quality parameter that helps in understanding physical and chemical properties of a particular powder materials. In this study, 11 DDGS samples were collected from 11 ethanol processing plants in the Midwest region, and measured for their particle size distributions by using series of U.S. standard sieves. The original DDGS samples and all sieve sized fractions were then measured for color and contents of moisture, protein, oil, ash, and starch. Total carbohydrate and total non-starch carbohydrate were also calculated. The objective was to investigate PSD of DDGS and its relationships to composition of various nutrients and surface color in the original and sieve sized fractions. Here is the summary of the significant findings of this study. First, particle size varied greatly within a DDGS sample and particle size distribution varied greatly among DDGS samples. Thus PSD is a characteristic of a particular DDGS. Second, chemical composition and color varied greatly among DDGS. In particular, this study was the first one to document that a few samples had unusually high amounts of residual starch, ranging from 11 to 17%, as compared with 5% of majority samples. The finding indicates that removal of fiber prior to fermentation may lead to incomplete conversion of starch to ethanol. Third, distributions of color and nutrients were mostly linked to PSD. However, the composition of the original DDGS had little effect on how particle size and other attributes were distributed. Therefore, it is highly feasible to fractionate DDGS by sieving to produce fractions enriched or reduced in certain attributes. Results of this study would be a vital addition to quality and baseline data of DDGS. They are essential for many aspects, including formulation of animal feed, digestibility and nutrient availability, design of equipment and processing facilities, optimization of unit operation, storage, material handling systems, assessment of potential or flexibility for a particular nutrient enrichment by sizing, and of end product quality. The study would also help improving quality and consistency of DDGS, which has become necessary for market expansion of the coproudct beyond cattle to swine, poultry, aquaculture, and other industries. It concluded with a high recommendation that PSD of DDGS be an important attribute for quality evaluation.
Technical Abstract: Eleven distillers’ dried grains with solubles (DDGS), processed from yellow corn, were collected from 11 ethanol processing plants in the Midwest area of America. Particle size distribution (PSD) of each sample was measured according to a standard ASAE procedure, using a series of six selected U.S. standard sieves: No. 8, 12, 18, 35, 60, and 100, and a pan. The original sample and sieve sized fractions were measured for surface color and contents of moisture, protein, oil, ash, and starch. Total carbohydrate (CHO) and total non-starch CHO were also calculated. Results show that there was a great variation in composition and color among DDGS from different plants. Surprisingly, a few DDGS samples contained unusually high amounts of residual starch (11.1-17.6%, dry matter basis), presumably resulting from a pretreatment to remove fiber. Particle size of DDGS varied greatly within a sample and PSD varied greatly among samples. With a mean value of 0.660 mm for the geometric mean diameter (dgw) of particles, the majority of DDGS had PSD of a bell-shaped unimode with a mode in the size class between 0.5-1.0 mm. Distribution of nutrients as well as color related much to the distribution of particle size but composition of the original DDGS had little effect on how particle size and nutrients were distributed. Protein, ash, and L value were negatively while ash and total CHO positively correlated with particle size. The above information would be a vital addition to quality and baseline data of DDGS. It is highly recommended that PSD of DDGS be an important attribute for quality evaluation.