The Fragility of Glassy Corn Starches

Abstract

The fragility m of starches derived from corn and waxy corn, dried at various temperatures are computed with different water contents and heating rates (1,3,5,7,10, and 15 K/min) using Differential Scanning Calorimetry (DSC) data. Three theoretical approaches namely, Augis & Bennett, Lasocka and Vogel-Fulcher-Tammanni (VFT) are utilized to fit the DSC gelatinization transition temperature, TgT data to calculate the fragility m. The fragility m at a 7 K/min heating rate, with water contents from 30 to 90% at drying temperature 20 °C for corn starch is in the range 41 to 68, whereas at drying temperature of 100 °C for the same corn starch remains constant around 42. The waxy corn starch having water contents 50 to 90% and at drying temperatures 70 °C and 90 °C, the fragility m is unstable. On the whole, fragility m is in between 39 and 63 and according to the Angell’s criterion (16<m<100) the corn starches are intermediately strong glasses.