Hydration kinetics of direct expanded tef flour breakfast cereals in water and milk

Hydration kinetics of tef flour breakfast cereals extruded at barrel temperatures of 110, 130, and 150 degrees C was investigated by hydrating them in water and whole milk at 25 degrees C (+/- 1 degrees C). The normalized Weibull model described the rehydration characteristics of the extrudates in water and milk adequately (R-2 = 0.98-0.99). Water absorption rate was significantly (P < 0.05) influenced by barrel temperature where extrudates processed at 150 degrees C barrel temperature exhibited high water absorption rate followed by those extruded at 130 and 100 degrees C, respectively. Hydration rate and equilibrium moisture content were higher for samples hydrated in water than those in milk. In view of the values of the shape parameter beta, the hydration process is predominantly controlled by diffusion (beta = 0.40-0.51) for samples extruded at 110 degrees C whereas external resistance to mass transfer dominated (beta = 0.60-0.73) those extruded using 150 and 130 degrees C. Extrudates processed at 130 and 150 degrees C exhibited better hydration characteristics. Thus, these temperature ranges could be used to produce extruded products from tef.