Flow Properties of Low-Moisturized Starch Melts at an Elevated Temperature

The flow properties of starch melts (potato and corn starches) at the moisture content of 16, 20, 25, 30 and 35% (dry basis) were characterized using a capillary tube viscometer. By use of measured flow rates (Q, m^a s^-1), and pressure drops of capillary tube (ΔP_c, MPa) and orifice (ΔP_o, MPa), the relationships between the flow rate and the pressure drop in the capillary tube (ΔP_d, MPa) were obtained. The flow curves of both starch melts showed good linearly on logarithmic scales. These starch melts, however, gave a yield stress, especially at low moisture content. Then both flow curves satisfied an equation by Herschel-Bulkley power-law model after exchanging the flow rate and the pressure drop to apparent shear rate (γ̇_a, S^-1) and shear stress (τ_w, MPa), respectively. The flow properties were good representative by Herschel-Bulkley power-law model and these curves varied with the moisture content. The flow properties between potato and corn starch melts were different even though they were same moisture content, especially that was reflected in the consistency index.