EFFECT OF BARREL TEMPERATURE ON REHYDRATION KINETICS OF DIRECT-EXPANDED TEF FLOUR BREAKFAST CEREAL

摘要

The effect of barrel temperature (110, 130 and 150C) on the rehydration kinetics of tefflour extrudates was investigated. Rehydration was conducted in distilled water for 300-420 min using a constant-temperature water bath at 25C (±1C). Water absorption rate was high at the early stages (60-90 min) of hydration, decreased subsequently and finally approached an equilibrium. Three models, namely, Peleg's equation, first-order kinetic and normalized Weibull model, were fitted to the rehydration data. The three models described the rehydration characteristics adequately (R~2 = 0.95-0.99). The water absorption rate and equilibrium moisture content were found to be barrel temperature-dependent (P < 0.05). Extrudates processed at a barrel temperature of 150C exhibited a high water absorption rate, followed by those extruded at 130 and HOC, respectively. The equilibrium moisture content of extrudates processed at 150 and 130C was significantly (P < 0.05) higher than those extruded at HOC. In view of the values of the shape parameter β of the normalized Weibull model, the mechanism of water absorption appeared to be by diffusion for extrudates processed at 130C(β = 0.67), whereas in extrudates processed at 110 (β = 0.89) and 150C (β = 1.03), external resistance to mass transfer and relaxation phenomena, respectively, were found to be the water absorption mechanisms. In comparison, the normalized Weibull model described the rehydration characteristics relatively better, resulting in smaller RMSE value.