Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 24, 2009
Publication Date: May 21, 2009
Citation: Liu. K.S. 2009. Effects of particle size distribution, compositional and color properties of ground corn on quality of distillers dried grains with solubles (DDGS). BioResource Technology. 100: 4433-4440. Interpretive Summary: Increase in the demand of ethanol as a fuel additive and a decrease in dependency on fossil fuels have resulted in a dramatic increase in the amount of corn used for ethanol production. A major process for making ethanol from corn is dry-grind method, by which, the first step is to grind corn into powder whereas the last step is to recover a co-product, distillers dried grains with solubles (DDGS). One major factor affecting quality of DDGS and thus economics of ethanol production is its variation in chemical and physical properties. Oftentimes, corn processors believe that ground corn and DDGS are interrelated in certain quality parameters. Yet, previous research, although rather limited, has shown no scientific basis for it. In order to gain better insights about relationships between ground corn and DDGS, this study was conducted by first measuring particle size distribution (PSD) of ground corn and the resulting DDGS samples from 6 different processing plants, analyzing proximate composition and surface color of these samples and their sieved fractions, and comparing these attributes symmetrically not only in whole fractions but also in sieve sized fractions. Results show that in terms of geometric mean diameter (dgw) of particles of the whole fraction and mass frequency of individual particle size classes, the relationship between ground corn and DDGS varied, but in term of PSD, the two correlated very well (r = 0.807). There also were some positive correlations in contents of protein and non-starch carbohydrate and in L value between corn and DDGS, but variations in nutrients and color attributes were larger in DDGS than in corn. Raw material, processing method and addition of yeasts are among major factors considered for causing large variations in these attributes. These observations disagree with previous reports and provide scientific basis to partially support the common belief expressed by processors regarding relationships between corn and DDGS. The study provides better understanding of the physical and chemical changes of corn during ethanol production, which may lead to strategies for improving end product quality.
Technical Abstract: Oftentimes, corn processors believe that ground corn (raw material) and distillers dried grains with solubles (DDGS) are interrelated in certain quality parameters. Yet, previous studies, although rather limited, have shown no scientific basis for it. In this study, six ground corn samples and their resulting DDGS were analyzed for particle size distribution (PSD), 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 contents of moisture, protein, oil, ash and starch, and surface color. Total carbohydrate (CHO) and total non-starch CHO were also calculated. Results show that the geometric mean diameter (dgw) of particles varied with individual corn and DDGS samples, and that dgw of DDGS was larger than that of corn (0.696 vs. 0.479 mm, average values), indicating that during conversion of corn to DDGS, certain particles became enlarged. For dgw and mass frequency of individual particle size classes, the relationship between ground corn and DDGS varied, but PSD of the whole sample was well correlated between them (r = 0.807). Upon conversion from corn to DDGS, on an average, protein was concentrated 3.59 times; oil, 3.40 times; ash, 3.32 times; and total non-starch CHO, 2.89 times. There were some positive correlations in contents of protein and non-starch CHO and in L value between corn and DDGS. Yet, variations in nutrients and color attributes were larger in DDGS than in corn. For either corn or DDGS, these variations were larger in sieved fractions than in the whole fraction. Raw material, processing method and addition of yeasts are among major factors considered for causing larger variations in these attributes among DDGS. The study partially supports the common belief by processors that quality attributes of corn affect those of DDGS.