Analysis of simultaneous water absorption and water–starch reaction during soaking of amaranth grain

• Published in: Journal of food engineering 2005-05, Vol.68 (2), p.265-270
• Main Authors: Calzetta Resio, Andrea N., Aguerre, Roberto J., Suarez, Constantino
• Format: Article
• Language: English
• Subjects: absorption; Activation energy; Amaranth grain; amaranth starch; Amaranthus cruentus; Biological and medical sciences; diffusion; diffusivity; Food engineering; Food industries; Fundamental and applied biological sciences. Psychology; Gelatinization; General aspects; Moisture diffusivity; reaction kinetics; soaking; Starch and starchy product industries; temperature; water
• ISSN: 0260-8774; 1873-5770
• DOI: 10.1016/j.jfoodeng.2004.05.043

The soaking process of a grain amaranth variety ( Amaranthus cruentus) was investigated in water between 30 and 90 °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 m 2 s −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 °C. The calculated values were E D = 31.0 kJ mol −1 and E k = 24.5 kJ mol −1 below 64 °C and E D = 53.6 kJ mol −1 and E k = 136.5 kJ mol −1 above 64 °C. These results suggest that at least, for the soaking temperatures above 64 °C, the absorption process is controlled by water–starch reactivity.