Internal structures and phase-transitions of starch granules during gelatinization

The internal structures of corn starch granules with different amylose/amylopectin contents were studied using different microscopic techniques. The gelatinization phase transitions of the various starches were investigated by hot-stage confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The influence of the amylose/amylopectin ratio on the internal structures and morphologies could be revealed by these techniques. Sharp growth ring structures could be clearly identified for high-amylopectin starches by CLSM and SEM following acid treatment. CLSM allowed the visualization of cross-sections of starch granules without the need for sectioning techniques that lead to destruction of the microstructure of sample, allowing exploration of the gelatinization mechanism. Three-dimensional images of starch granules during gelatinization could be constructed to further explore phase transition mechanisms. It was found that the granules of waxy maize and normal maize starch subsequently break through at their cavity and channels, when the granules became swollen during gelatinization, whilst the granules of G50 and G80 remain granular and break down to smaller pieces.