Swelling kinetics of waxy maize and maize starches at high temperatures and heating rates

Abstract

For product and process development of starch-thickened products, it is essential to obtain data representative of the process conditions. Kinetics of granule swelling was followed when applying thermomechanical treatments in a lab simulator coupled to a rheometer. This lab simulator enables to follow the apparent viscosity development of starch dispersions for temperature profiles, heating and cooling rates as well as shear rates in the range of those encountered in industrial processes (pasteurisation/sterilisation in heat exchangers). Owing to sampling of the starch dispersions at different stages of the thermomechanical treatment (heating up to 120 °C and at a heating rate of 1 °C s −1), the evolution of the granule size distribution of modified waxy maize, native waxy maize and native maize starch was obtained and compared to the apparent viscosity development. As expected, native starches were much more affected by the process than modified waxy maize starch, which maintained its granular structure. Kinetics of granule swelling is generally described as following a first-order kinetics except for the early stages of gelatinisation for which multi-order kinetics apply. However, most studies were done under isothermal conditions or at heating rates much lower that the one used in this work. In our case, for a hydrothermal treatment at high heating rates, it was found that granule swelling was best described by second-order kinetics.