EVALUATION OF FLOUR PARTICLE-SIZE DISTRIBUTION BY LASER DIFFRACTION, SIEVE ANALYSIS AND NEAR-INFRARED REFLECTANCE SPECTROSCOPY

Laser diffraction and sieve analysis were used to measure flour partic le size distributions as per cent volume and per cent weight, respecti vely, among different wheat types and milling methods. Near-infrared ( NIR) reflectance spectroscopy was used to predict the per cent volume of flour particles within selected size ranges based on laser diffract ion reference values. According to laser diffraction analysis, 89-98% of the flour particles were distributed within the size ranges 10-41 m um and 41-300 mum, and 2-11% of the particles were distributed within the size range < 10 mum. Flour particle size distributions were differ ent (P<0.05) among the wheat types tested, except that hard red winter and hard white wheats were not different in flour particle size <10 m um, and hard red spring and hard white wheats were not different in fl our particle size within 10-41 mum and 41-300 mum. The milling method affected particle size distributions of hard wheat flours but not thos e of soft wheat flours. A high correlation (r=0.95) occurred between p er cent volume and per cent weight of hard wheat flour particles <45 m um, but the correlation decreased (r=0.77) when soft wheat flours were included in the comparison. Near-infrared calibration equations were developed by partial least-squares regression for predicting the per c ent volume of flour particles. The per cent volume of flour particles within the size ranges <10 mum, 10-41 mum and 41-300 mum were predicte d by NIR within +/- 2 standard errors for greater-than-or-equal-to 96% of the flours tested.