Supramolecular structural changes of waxy and high-amylose cornstarches heated in abundant water

摘要

Being heated in abundant water, native waxy cornstarch displayed only one endotherm (G), while there were two endotherms (G and M2) for native Gelose 50 (G50) cornstarch. Waxy cornstarch granules could swell dramatically at around the T_0 of endotherm G, while G50 cornstarch granules presented a less significant increase in the volume near the T_0 of endotherm G. As the temperature increased up to 70 ℃, the scattering objects in both of the cornstarches became looser. Interestingly, when the temperature was 75 ℃ or higher, mass fractal structures at three scale levels emerged for waxy cornstarch, and a mass fractal structure at the higher scale level and a surface fractal structure at the lower scale level appeared for G50 cornstarch, suggesting the inhomogeneity at a nano-colloidal level and a nano-particle level respectively for the two starches. The scattering objects at the lower or intermediate scale level could form a mass fractal structure at the higher scale level with different compactness (D_(m1)). The average thickness of the semi-crystalline lamellae (d) of the both cornstarches changed slightly with an increase in the temperature and finally disappeared due to the multiple fractal structures. Additionally, the A-type crystalline structure of waxy cornstarch and the B-type crystalline structure of G50 cornstarch displayed a similar trend with the temperature regarding the anisotropy. For G50 cornstarch, the V-type crystalline structure required a higher temperature to complete its melting.