An experimental study of the swelling behavior of starch granules under heat treatment

Current models for predicting the transformation state of starch suspensions define the swelling degree in terms of the mean diameter of granules, with no information regarding the observed diversity of size and swelling onset. This article analyzes the thermal history of 143 granules as obtained from images captured during hot-stage normal light microscopy of droplets of a modified waxy maize starch suspension. The evolution of 0.5 mL samples was studied under heat treatment from 50 to 90 ◦C at rate of 5 ◦C/min. No relationship was found between initial granule diameter and swelling onset temperature. Changes in the starch swelling state were relatively weak below 60 ◦C and above 80 ◦C. Simultaneous occurrence of uncooked starch and swollen granules was observed at intermediate temperatures