Effects of Pearling, Grinding Conditions, and Roller Mill Flow on the Yield and Composition of Milled Products from Hull-less Barley

Two hull-less barley cultivars, one with waxy starch and the other with high-amylose starch, were roller-milled unpearled and after 15% pearling. Flows of varying length, with diverse roll settings and roll surfaces were used to determine effects on the yield, composition, and properties of milled products. Similar trends were noted for the two cultivars. When using a short flow comprising four break passages and a sizing passage, power consumption during grinding was reduced by 10% when roll flute orientation was changed from dull-to-dull (DID) to sharp-to-sharp (S/S). Flute orientation had minimal effects on the yield and brightness of flour, but SS grinding gave a higher yield of a fiber-rich fraction (FRF). FRF yield and composition are of particular interest because FRF has potential as a functional food ingredient due to elevated levels of beta-glucans (BC) and arabinoxylans (AX). When using smooth frosted rolls (SM) for the sizing passage, power consumption increased by several times over using fluted sizing rolls with little advantage for either yield or BC content of FRF. FRF starch damage increased when smooth sizing rolls were used, and water swelling, a measure of water hydration capacity, also increased. Setting break and sizing rolls sharp-to-sharp significantly lowered the mean particle size of the FRF fraction, accompanied by moderate declines in FRF BC and AX contents. FRF yield decreased <= 50% when milling flow was lengthened to three sizing passages with intermediate impact passages, with only a moderate accompanying increase in FRF fiber content, regardless of roll conditions. Pearling 15% before milling reduced the yield of FRF by approximate to 30% while moderately reducing flour yield. Flour brightness was improved by pearling. When barley was pearled, FRF contained higher amounts of BG, but lower amounts of AX, phenolics, ash, and protein.