| Instant powders, which require only reconstitution in liquid for use in products such as beverages, can be produced by extrusion cooking. Powders with good instant properties should disperse easily, without lumps. Instant cereal and soy powders are often difficult to disperse because of swelling and fine grinding, respectively. In this study, extrusion was done using a twin-screw extruder and varying the dough moisture content, barrel temperature, and screw speed. The extrudates were then milled to produce powders with different particle size ranges. The specific mechanical energy (SME), water absorption index (WAI), water solubility index (WSI), viscosity, ease of dispersibility, and stability to sedimentation were measured. The WAI and suspension viscosity of instant wheat powders were negatively correlated with the SME, and decreased with particle size. The WSI of wheat powders increased with the SME. The WAI and WSI of instant soy powders were not strongly influenced by the extrusion conditions used, Wheat powders with larger particle sizes were easily dispersed, however below 93 μm, dispersibility was inversely correlated with the SME. The addition of lecithin improved dispersibility. Soy powders displayed poor dispersibility when the particle size was reduced to approximately 15 μm. Stability to sedimentation was greater as particle size decreased for both wheat and soy powders. |
