Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 4, 2007
Publication Date: April 4, 2007
Citation: Flores, R.A., Hicks, K.B., Wilson, J. 2007. Surface abrasion of hulled and hulless barley: Physical characterization of the milled fractions. Cereal Chemistry. 84(5):485-491. Interpretive Summary: Barley is a crop that is considered to have great potential for applications in fuel ethanol production and as a source of health promoting compounds, such as beta-glucans. We want to use new barley varieties in ethanol production and use the non-fermentable components (components of the kernels that can not be converted to fuel ethanol) in highly nutritious food products. To achieve the separation of the various barley components, two milling techniques where evaluated in this study, one called 'whitening' and another called 'scarification'. Both techniques abrade the kernel to remove the outermost layers of the kernel, which are called the 'pericarp' and 'hull'. The whitener uses the friction generated between kernels and the scarifier uses an abrasive surface. Three milling levels were tested with the whitener and three abrasive surfaces with the scarifier on four barley varieties, two hulled, Thoroughbred and Nomini, and two hulless (also spelled Hull-less), Doyce and Merlin. The best milling level to remove the hulls of the hulled barley with the whitener was found to be at setting #2; however, the whitener also breaks the kernels. The scarifier rounds up the kernels but does not fracture them. It was found that the best abrasive surface to remove the hulls from hulled barley with the scarifier was 36 grit. The yield of the milled fraction produced (the amount of the surface abraded off) with the whitener and scarifier determined the color of the fractions. This information is useful to determine the level of mass removal based on a simple color measurement, rather than a tedious chemical method. The results obtained in this study are useful for designing equipment and processes capable of removing particular layers of barley kernels for ethanol production or food ingredients.
Technical Abstract: Abrasion techniques were used to remove the hull and pericarp layers of grain kernels to obtain a smaller kernel, or kernel pieces that were enriched in endosperm. The objective of this study was to abrade and remove the outer layers of four barley varieties with two milling techniques, scarification and whitening. Both of these techniques produce a fraction enriched in hull and/or pericarp, potentially useful for value added food and feed applications and a fraction enriched in starchy endosperm, suitable for fuel ethanol production via yeast fermentation. Four barley samples, two hulled (Thoroughbred and Nomini) and two hulless (Doyce and Merlin), were scarified and whitened at 22 scarification times and three milling degrees (settings of 2, 4 and 6), respectively. Three different abrasive surfaces (36, 40 and 50 grit) were used in the scarifier to determine the material removal ratio for each barley variety. Material balances and color analysis were conducted for all of the fractions produced. Three fractions were produced with the whitener at each milling degree, they were: broken kernels, fine fractions greater than 323 um, and fine fractions less than 323 um. The milling degree of 2 seems to be the setting that releases most of the hull in the hulled barley with the whitener, however, only a small increase in the yield was observed between the milling degrees of 4 and 6. During the first 50 s of scarification, no major differences were observed in the amount of fine material produced by the different abrasive surfaces. However, after 50 s of scarification, rougher surfaces produced more fine material and consequently less coarse material. It was found that to induce faster hull removal, in hulled barley, lower grit (36 grit) abrasive surface produced better results. Color parameters L* and b* were good indicators of the fine and coarse fractions produced by abrasive methods because they indicate the kernel layer removed and were modeled as a function of the fraction of the material produced. The information obtained in this study is useful for designing equipment and processes capable of removing and recovering hull and pericarp layers of barley kernels and thereby producing smaller kernels or kernel pieces containing mainly endosperm tissue.