Effect of different mills on the physical and flow properties of selected black bean flour particle size fractions

Background and Objectives Particle size and shape can influence inherent flour properties and eventually the quality of the finished food product. The objective of this study was to determine the effect of mill type on the physical and flow properties of selected particle size fractions of black bean flour. Findings Particle shape differed with mill type and particle size. Disc mill and stone mill produced flour particles with lower circularity and greater elongation than did hammer mill, cyclone mill, and centrifugal mill. Greater particle elongation with a stone mill and disc mill is attributed to compression/shear size-reduction forces applied to the particles trapped between the rotating/nonrotating stones or discs. Particle circularity increased with an increased particle size, which was reflected by a strong positive correlation between circularity and particle size (r = .93, n = 5) while elongation value was negatively correlated with average minimum particle size (r = -.90, n = 5). Particle circularity had a negative correlation of r = -.93, n = 30; r = -.81, n = 30; r approximate to -.95, n = 30; r = -.94, n = 30 with L*, angle of repose, angle of slide, and compact bulk density, respectively. Conclusions Mill type and particle size interaction significantly affected the physical and flow properties of selected particle size fractions of black bean flour. The results indicate that the large black bean particles were more circular and compact and less convex and elongated compared with small particles. Significance and Novelty These findings indicate that mill type affects not only particle size but also particle shape, both of which can affect the flow and functional processing properties of black bean flour.