Effect of size reduction methods on raw and microwave-parboiled white sorghum and their physico-chemical, functional, rheological, and structural characteristics

Abstract

There is a growing trend to ameliorate local flour sources to substitute wheat flour. Sorghum grain's nutritional profile is comparable to that of wheat but it is gluten-free and can be consumed by celiac patients. They can be used to provide much-needed healthy alternatives to the grain industry. Hammer, burr, and ball mills were utilized for polished raw and parboiled sorghum flour production to study the effect of various milling techniques on sorghum flour properties. The physico-chemical, functional, rheological, and structural attributes of the different milled white sorghum flours were analyzed. The highest recovery of sorghum flour was from the ball mill 97.46 ± 0.48% and 97.43 ± 0.26% for raw and microwave parboiled sorghum flour, respectively. The particle size of the flour samples produced by the hammer mill have lower geometric mean diameters (raw - 64.26 ± 1.26 μm, and microwave parboiled - 108.93 ± 1.92 μm) than those obtained using other mills. Considering that, particle size is a major determinant of quality. While porosity increased, bulk and true density decreased at higher particle. There is a less significant difference in proximate composition among the samples. The crystallinity value of raw samples follows the order ball mill (BA) (34.08%) > burr mill (BU) (31.54) > hammer mill (HM) (28.96%), and microwave parboiled samples follow the order parboiled ball mill (PBA) (13.58%) > parboiled burr (PBU) (12.86%) > parboiled hammer (PHM) (11.25%). The thermal, and pasting characteristics of the polished raw and microwave-parboiled white sorghum flours were considerably influenced by the type of mills.