Comparison of the morphological, crystalline, and thermal properties of different crystalline types of starches after acid hydrolysis

A-type maize starch, B-type Fritillaria ussurensis, and C-type Rhizoma dioscorea starches were hydrolyzed (32 days) with 2.2 N HCl. Regardless of the crystallinity level, starch with predominant B-crystalline type was less susceptible to acid degradation than A-type and C-type starches, and initial rates of hydrolysis in B-type was lower than others. The SEM and XRD results revealed that different types of starch displayed different hydrolysis mechanisms. The acid corrosion started from the exterior surface of A-type and B-type starches followed by the core of granules. However, the hydrogen ions primarily attacked the interior of the C-type R. dioscorea starch granules and then the exterior. FT-IR results confirmed that the amorphous regions in the starch granules were hydrolysed first. After 8-32 days of hydrolysis, the acid-modified C-type starch showed typical A-type characteristics upon analysis of the XRD pattern. The average particle size of hydrolytic starch decreased with increasing hydrolysis time. The thermal results revealed that the hydrolytic starch showed lower Delta H than the native starch, while displaying higher peak width (T(c) - T(o)) value.