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United States Department of Agriculture

Agricultural Research Service

Title: Groat Proportion in Oats as Measured by Different Methods: Analysis of Oats Resistant to Dehulling and Sources of Error in Mechanical Dehulling

item Doehlert, Douglas
item Mcmullen, M
item Riveland, N

Submitted to: Canadian Journal of Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2010
Publication Date: 7/1/2010
Citation: Doehlert, D.C., Mcmullen, M.S., Riveland, N.R. 2010. Groat Proportion in Oats as Measured by Different Methods: Analysis of Oats Resistant to Dehulling and Sources of Error in Mechanical Dehulling. Canadian Journal of Plant Science. 90: 391-397

Interpretive Summary: The oat grain consists of the meaty groat, which is used for human consumption, and the hull, which is removed in the dehulling process and discarded. The groat proportion is the percentage of the kernel which is groat and determines the economic value of the oat grain. Our studies here show that groat proportion values determined by mechanical procedures are lower than values obtained by hand dehulling, Mechanical dehull involves a mechanical stress upon the grain, which breaks the hulls from the groats. The hulls are removed by aspiration. Not all oat grains are dehulled by any mechanical procedure, so we considered that some properties of the oats resistant to dehulling might affect the observed difference in groat proportion. We also considered that aspiration might remove pieces of groat along with the hulls. We concluded that it was the aspiration that caused the differences in the observed values of groat proportion, but found some interesting properties of oats resistant to dehulling. They have lower groat proportion than most other kernels and pack particularly poorly. These seem to have altered external structure, associated with increased hull mass and external structure that inhibits efficient packing. We don’t understand exactly what this structure is, but the reduction of such kernels could increase the value of oats.

Technical Abstract: Groat proportion is the groat yield from an oat dehulling process. We have consistently found hand dehulling generates higher groat proportion values than those determined by mechanical means, using either impact or compressed air dehullers. In this study, we have investigated possible sources of this error. During hand dehulling, all groats and hulls are accounted for, so there is little opportunity for error. Mechanical dehullers apply a mechanical stress that beaks the hull from the groat, then hulls are removed by aspiration. Not all kernels are dehulled during any mechanical dehulling, and groats may be lost by aspiration. We have examined oats resistant to dehulling. Although these are smaller, have lower bulk density, and lower packing efficiency than the original kernel sample, as long as their mass is subtracted from the starting mass, they do not seem to introduce an error into groat proportion determination. Therefore, according to the principle of the conservation of mass, groats must be lost during the aspiration process. During impact dehulling, we find a significant decrease in measured groat proportion with increased rotor speed. This is consistent with the concept that faster rotor speeds break more groats which are more easily removed by aspiration.

Last Modified: 09/18/2017
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