Physicochemical properties of jet milled wheat flours and doughs

Abstract

The aim of this study was to evaluate the physicochemical properties of white wheat flour pulverized by jet mill and the rheological behavior of the resultant doughs. A commercial coarse (control) wheat flour with d50 < 75 μm (CON) was micronized by jet-mill under two different feed rates, resulting in fine and ultrafine flour preparations with d50 < 21 μm (JM1) and d50 < 12 μm (JM2), respectively; d50 value was reduced with decreasing feed rate. The levels of damaged starch (5.3–11.5% as is) and water soluble arabinoxylans (0.4–0.5% d.b.) increased (p < 0.05) with reduction of flour particle size, while no changes in apparent peak molecular weight, determined by HPSEC–RI, and primary structure of the AXs (e.g. degree of branching) estimated by 1H NMR, were noted upon flour jet-milling. Starch gelatinization properties and dough rheological behavior of CON, JM1, JM2 flours and a mixture (CON:JM1 1:1), covering a particle size range applicable to actual breadmaking processes, were studied. Calorimetry of aqueous flour dispersions (flour:water 30:70 w/w) showed a decrease in starch gelatinization enthalpy of the flours containing jet mill fractions compared to control flour. For the jet mill flours, the creep-recovery test of doughs (flour:water 56:44) revealed an increase (p < 0.05) in resistance to deformation, elasticity and zero shear rate viscosity. Additionally, Texture Profile Analysis (TPA) and compression - stress relaxation testing after lubricated squeezing flow (LSF) revealed that with decreasing flour particle size, the doughs become harder with higher consistency, more sticky and gummy and exhibit longer half relaxation time, lower relaxation rate and higher elongational viscosity.