Effects of particle size distribution, compositional and color properties of ground corn on quality of distillers dried grains with solubles (DDGS)

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 not established this relationship. In this study, six ground corn samples and their resulting DDGS were analyzed for particle size distribution (PSD), using a series of six selected US standard sieves: Nos. 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.