The physical state of amorphous corn starch and its impact on crystallization

Crystallization of amorphous polymers is affected by their physical state and molecular mobility. In the present study, crystallization behaviour of amorphous corn starch was related to its physical state and glass transition. Amorphous corn starch was produced by freeze-drying a gelatinized 5% (w/w) starch suspension. State diagram and sorption properties were determined to characterize the material. Amorphous corn starch samples containing 60, 70, and 80% solids were stored at various temperatures that gave various temperature differences between storage temperature and glass transition temperature (T-T-g). The melting behaviour of crystallites formed was determined using differential scanning calorimetry. Crystallization in starch samples occurred with a rate that was dependent on storage temperature, water content, and T-T-g. In addition, the melting temperature and the extent of crystallization were affected by storage temperature, water content, and T-T-g. The data reported allow the prediction of crystallization in starch, as a physical state-dependent phenomenon and, therefore, stability of starch-containing products during storage. (C) 1997 Elsevier Science Ltd.