Mechanical and thermal characteristics of amaranth starch isolated by acid wet-milling procedure

Abstract

Effects of soaking conditions during acid wet-milling of amaranth grain on mechanical and thermal properties of amaranth starch were investigated. A factorial design based on temperature (40-60 °C) and SO2 concentration (0.1-1.0 g/L) was used. Dynamic oscillatory tests involved heating and cooling cycles (25-90 °C) with tempering at 90 °C followed by a frequency sweep (0.1-20 Hz) at constant temperature. Thermal properties of starch suspensions were based on DSC tests. Viscoelastic modulus and thermal properties were affected by both factors, being significant the interaction effect. Maximum values of viscoelastic modulus at the end of heating and cooling steps were determined for samples corresponding to soaking conditions of 50 °C and 1.0 g/L SO2. Based on Ross-Murphy index from frequency sweep analysis it was found that paste behavior occurs at 60 °C and 0.1 g/L, while at 47.4 °C and 0.72 g/L starch suspension gave a strong gel. Onset (61.7 °C) and peak (66.2 °C) temperatures showed a minimum at 50 °C and 1.0 g/L. As SO2 concentration decreased, the end of gelatinization took place at lower temperature. Maximum gelatinization enthalpy (12.7 J/g) was found at 40 °C and 0.1 g/L SO2.