Analysis of simultaneous water absorption and water-starch reaction during soaking of amaranth grain
2005
Resio, A.N.C. | Aguerre, R.J. | Suarez, C.
The soaking process of a grain amaranth variety (Amaranthus cruentus) was investigated in water between 30 and 90 degrees C. A mathematical model describing simultaneous unsteady water diffusion and first-order irreversible water-starch reaction is proposed to simulate soaking process of grains. The observed water absorption curves are used to estimate the effective diffusivities (D(ef)) and reaction rate (k). The values of D(ef) and k were between 10(-12) and 10(-11) m2s(-1) and 10(-5) and 10(-3) s(-1), respectively. The dependence on temperature of D(ef) and k was evaluated through an Arrhenius type equation with two distinct activation energies for diffusion (E(D)) and reaction (E(k)) below and above 64 degrees C. The calculated values were E(D) = 31.0 kJ mol(-1) and E(k) = 24.5 kJ mol(-1) below 64 degrees C and E(D) = 53.6 kJ mol(-1) and E(k) = 136.5 kJ mol(-1) above 64 degrees C. These results suggest that at least, for the soaking temperatures above 64 degrees C, the absorption process is controlled by water-starch reactivity.
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