PHYSICAL, CHEMICAL, and THERMAL CHARACTERIZATION of WHEAT FLOUR MILLING COPRODUCTS1,2

Abstract

ABSTRACTHard red winter (HRW) and hard red spring (HRS) wheat milling coproducts (bran, germ, shorts, and red dog) from three commercial flour mills and the Kansas State University pilot mill were evaluated for differences in physical, chemical, and thermal properties. the ranges of bulk density for bran, germ, and red dog determined at three moisture levels were 146.5 to 205.2 kgm−3, 269.2 to 400.6 kgm−3, and 298.9 to 398.1 kgm−3, respectively. the true density ranking order was: red dog >shorts = germ >bran, independently of the moisture level. Red dog had the smallest geometrical mean diameter with the highest variation (coefficient of variation of 23.8%). There was a significant (P < 0.05) difference among wheat blends and milling flows in the thickness of bran and germ at the same particle separation size. the image analysis study determined that the equivalent projected area diameter of bran at the same separation size was significantly (P < 0.05) larger than that of germ. the ratio between the equivalent projected area diameter and the particle thickness were within ranges of 15.7 to 37.6 for bran and 15.5 to 32.2 for germ particles. the chemical composition (ash, protein, lipids and fiber) ranges were determined for each coproduct. Ranges of thermal conductivity for bran, germ, shorts, and red dog were 0.049 to 0.074, 0.054 to 0.0907, 0.057 to 0.076, and 0.063 to 0.080 W(mK)−1, respectively. Specific heat of coproducts, measured with a differential scanning calorimeter, exhibited a wider range [1.08–1.94 kJ(kgK)−1] than that observed in whole wheat kernels and wheat flour. the variability observed among the samples was due to the different wheat sources and characteristic milling flows for the flour mills.