The kinetics of water uptake by amaranth grain soaked in plain water, SO2 aqueous solution (0.01% and 0.02%, w/v) and SO2 solution (0.02%, w/v) with variable concentrations of lactic acid (0.0025% and 0.0050%, v/v), covering a temperature range from 30 °C to 60 °C was investigated. The resulting kinetics data were correlated by means of Peleg’s equation. The Peleg model predicted adequately the hydration kinetics of amaranth grain till saturation moisture content using short-time data at the given conditions. The Peleg rate constant k1 and Peleg constant capacity k2 were affected by temperature and soaking conditions. The constant k1 decreased from 50.8 to 21.3 for increasing temperature from 30 to 60 °C, while for k2 the decreased was from 1.87 to 1.17 when soaking in plain water. Amaranth soaking in SO2 aqueous solution gave lower k1 than those for plain water, indicating acceleration in the absorption rate. The effect on k2 was less marked, being the moisture saturation capacities of the grain in plain water and SO2 solution almost coincident. The increase of SO2 concentration did not have practical effects on both constants k1 and k2.

Absorption rates for lactic acid concentration were significantly higher than those soaked only in SO2 solutions (the constant k1 was less in lactic acid solutions than in SO2 solutions); the values of k2 and consequently the saturation moisture contents were not practically affected by the presence of lactic acid in the soaking media.

Andrea Calzetta Resioa, Roberto J. Aguerreb and Constantino Suareza