Hydration kinetics of amaranth grain

Abstract

The kinetics of water uptake by amaranth grain soaked in plain water, SO 2 aqueous solution (0.01% and 0.02%, w/v) and SO 2 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 k 1 and Peleg constant capacity k 2 were affected by temperature and soaking conditions. The constant k 1 decreased from 50.8 to 21.3 for increasing temperature from 30 to 60 °C, while for k 2 the decreased was from 1.87 to 1.17 when soaking in plain water. Amaranth soaking in SO 2 aqueous solution gave lower k 1 than those for plain water, indicating acceleration in the absorption rate. The effect on k 2 was less marked, being the moisture saturation capacities of the grain in plain water and SO 2 solution almost coincident. The increase of SO 2 concentration did not have practical effects on both constants k 1 and k 2. Absorption rates for lactic acid concentration were significantly higher than those soaked only in SO 2 solutions (the constant k 1 was less in lactic acid solutions than in SO 2 solutions); the values of k 2 and consequently the saturation moisture contents were not practically affected by the presence of lactic acid in the soaking media.