Submitted to: Cereal Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/30/2005
Publication Date: 3/1/2006
Citation: Doehlert, D.C., McMullen, M.S., Jannink, J.L. 2006. Oat grain/groat size ratios: a physical basis for test weight. Cereal Chemistry. 83(1):114-118. Interpretive Summary: The value of oats to a farmer is largely determined by their test weight. This is the bushel weight and gives an estimation of the density of the grain. Yet, very little is known of the physical characteristics of oats associated with high test weight. We hypothesized that a larger sized groat relative to the whole oat might generate higher test weight oats, because the groat is the most dense structure in the oat. We tested this idea by measuring oat kernel size and oat groat size by digital image analysis, where a digital photograph is taken of oat kernels and their groats, and their size is analyzed by a computer. We found that test weight was highly correlated with the groat:oat size ratio in eight cultivars of oats grown at four locations over two years. Because the whole oat kernel size was nearly twice that of the groat, it would appear that there may be some empty space within the hulls of an oat kernel, which would certainly detract from test weight. We suggest that thin, tight fitting hulls will contribute to higher test weight in oats.
Technical Abstract: Market value of oat grain is largely determined by its test weight or bulk density, yet little is known of the physical basis for test weight in oats. We have hypothesized that a larger sized groat relative to the whole oat would generate higher test weight oats, because the groat is the densest structure in the oat. We tested this by measuring oat kernel size and oat groat size by digital image analysis for ten genotypes grown in eight environments. We also measured other physical characteristics of the oats and groats, including mean kernel and groat mass, test weight, and groat percentage. We found that the groat: oat size ratio was highly correlated with test weight. Because the oat kernel image area was nearly twice that of the groat, we suggest that there are significant amounts of empty space within the oat hull, which detracts from test weight. We also found that oat groat size distributions, like oat kernels, fit a bimodal distribution better than a normal distribution. The two subpopulations of kernel size appear derived from the primary and secondary kernels of the two-kernel oat spikelet. Kernel size analyses of the two subpopulations indicate that the secondary kernels have greater groat/oat size ratios, and thus are suggested to have greater test weight.