|Mcmullen, Michael - NORTH DAKOTA STATE UNIV.|
Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 15, 2008
Publication Date: September 1, 2008
Citation: Doehlert, D.C., Mcmullen, M.S. 2008. Oat Grain Density and the Physical Basis of Test Weight. Cereal Chemistry. 85 (5): 654-659. Interpretive Summary: Test weight of grain is the bulk density or the weight of grain that fits into a specified container volume. High test weight grain is in general more highly valued than lower test weight grain. In spite of its importance in determining value, little is known of the physical characteristics of oats that affect test weight. In this study, we assume that test weight is determined by the average density of individual oat grains and the amount of empty space between the grains, which we call the packing efficiency. We have measured the density of oat kernels from their displacement of sand, in an application of Archimedes Principle. We determined the density of oat kernels to be about 1.00 g/cm3. With this, we calculated that about 54% of a container is occupied by oat kernels, while the remainder is the empty space between the grains. We determined that larger grains packed less efficiently than smaller grains. We dehulled the oat grains and measured the densities of the oat groats and hulls. Oat groats had densities of about 1.29 g/cm3 and hulls had about half that density. Because of this, oats with higher proportions of the grain weight as groat usually have higher test weights. By examining a number of different samples we have concluded that at least 80% of the observed variation in test weight among samples is from variation in grain density and no more than 20% of the variation is from differences in packing efficiency.
Technical Abstract: Test weight or bulk density of oats (Avena sativa L.) has a major influence on the monetary value of oat grain. Test weight can be attributed to grain density and packing efficiency. We have measured oat grain volume and density by a sand displacement method and thus derived the packing factor for six oat cultivars grown in three environments. Grain envelope volumes ranged from 31 to 38 mm3 and were highly correlated with grain mass. Grain densities ranged from 0.96 to 1.03 g/cm3. Packing efficiency ranged from 53 to 55%. Both values exhibited genotypic and environmental variation. Regression analysis suggested that 78% of the variation in test weight could be attributed to grain density. Size fractionation of grain by sieving and size analysis by digital image analysis indicated that smaller grains within an oat sample packed more efficiently than larger grains and larger grains in a sample were less dense than the smaller grains. Analysis of oat grain components indicated groat densities were about 1.29 g/cm3 and hull densities were about 0.69 g/cm3, with very little genotypic variation in these traits. However, the sum of groat and hull volumes was consistently less than that of whole grains, suggesting the presence of empty space within the hulls. The difference in densities between groat and hull provide a physical basis for the recognized relationship between groat percentage and test weight.