Dissolution of waxy maize pyrodextrin granules in mixtures of glycerol and water, separating loss of crystallinity from loss of birefringence

Abstract

Pyrodextrins were prepared by heating waxy maize starch for 4 h at pH 3 & 150 °C, pH 3 & 170 °C, and pH 2 & 150 °C. Those pyrodextrins were soluble in water at 25 °C, but insoluble in glycerol. The objectives of this study were to investigate dissolution of the pyrodextrins in glycerol/water mixtures, and to determine how crystallinity and birefringence of the pyrodextrins were affected by swelling. Pyrodextrins prepared at pH 3 & 170 °C and pH 2 & 150 °C either dissolved or swelled little in glycerol/water mixtures at 25 °C. In contrast, the pyrodextrin prepared at pH 3 & 150 °C, which showed the least depolymerization, swelled in 40% glycerol to increase granule diameter ~80%. Despite that significant swelling, those swollen granules still displayed a Maltese cross pattern but were amorphous, demonstrating the separation of loss of crystallinity from loss of birefringence.