Submitted to: Cereal Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/8/2001
Publication Date: 11/1/2001
Citation: Doehlert, D.C., McMullen, M.S. 2001. Optimizing conditions for experimental oat dehulling. Cereal Chemistry. 78:675-679. Interpretive Summary: The groat percentage is the proportion of the whole oat kernel that is not hull. Higher quality oats have higher groat proportions. This study investigated the best and most accurate ways to determine groat percentage. One of the most accurate ways to determine groat percentage is by hand dehulling. Unfortunately, this is also the most tedious and time consuming methods. Several mechanical methods are also available, including the compressed air dehuller and the impact dehuller. Both of these exert a physical stress upon the oat which loosens it from its hull. The hulls are removed from the free groats by aspiration. The strength of the aspiration is critical to the accuracy of the whole process. Inadequate aspiration results in hulls remaining in with the groats, whereas excessive aspiration results in removal of groats as well as hulls. The mechanical stress applied to the kernels controls the extent of dehulling that can occur and excessive force will result in excessive groat breakage. Grain moisture also affects dehulling efficiency and groat breakage. Drier groats will break more, but may also be more readily dehulled.
Technical Abstract: The determination of groat percentage of experimental oat breeding lines requires the dehulling of oats. Here, we report the results of our efforts to optimize dehulling conditions so that the most accurate and reliable result can be obtained. Hand dehulling is always reliable and accurate, however, it is the most time consuming and tedious of the methods studied. Two mechanical methods of oat dehulling; compressed air dehulling and impact dehulling, also frequently provided reliable results, however, results were strongly influenced by dehulling conditions. Optimal dehulling conditions represented compromises between unfavorable extremes. Correct aspiration strength was critical to accurate groat percentage determination. We have found that a secondary aspiration is highly desirable after compressed air dehulling to remove hulls remaining with the groats after dehulling. Also, increased mechanical stress upon oats as exerted either by the number of passes through the impact dehuller, or by the air pressure in the compressed air dehuller, resulted in higher dehulling efficiency, but increased groat breakage as well. Increased grain moisture resulted in decreased dehulling efficiency of oats from 7.5 to 15% moisture, but resulted in increased dehulling efficiency from 15 to 30% moisture. In contrast, groat breakage with impact dehulling decreased with increasing moisture, from 7.5 to 30% moisture. A new equation for groat percentage calculation has also been introduced, where the mass of undehulled oats remaining after dehulling is subtracted from the mass of the original oat sample, so that the poor dehulling efficiency does not influence the groat percentage.