Acid modification of wheat, potato, and pea starch applying gentle conditions—impacts on starch properties

Abstract

Acid‐thinned wheat, potato, and pea starch products were systematically prepared applying gentle conditions with variation of acid type (HCl and H2SO4), acid concentration (0.36 and 0.72 N in a 40% (w/w) suspension) as well as hydrolysis time (4 and 24 h). Starch granule properties as well as molecular and rheological characteristics in the solution state were analyzed and the impact of all parameters varied was found to be immense. Carbohydrate solubilization of wheat and potato starch was significantly higher compared to pea starch. Noteworthy progress in solubilization was found when hydrolyzed with HCl, and with increasing acid concentration and increasing hydrolysis time by trend. The hydrolysis affected the reduction of the hot paste viscosity most dominant in the first period of treatment (0–4 h), however, size exclusion chromatography‐multi angle laser light scattering (SEC‐MALS) analysis revealed a more prominent molecular degradation during the second period (4–24 h). This observation led to the interpretation that the molecular degradation in the initial phase results particularly in “debranching” of the high molar mass amylopectin fraction and lower hot paste viscosity. Continued hydrolysis with significant reduction of the molecular size, however, had reduced impact on further lowering of viscosity. SEM micrographs displayed intact pea starch granules with unchanged surface after hydrolysis, whereas wheat and potato starch granules were visibly affected with damage not evenly distributed but a variation over the granule population. Granular wheat and potato starch exhibited significantly enhanced particle size after short period modification measured in water. However, this was found eliminated at extended hydrolysis time. Reasons were hydrolysis induced molecular rearrangement resulting in better crystalline packing on the amorphous/crystalline threshold reducing the ability to swell, and the progress in granular erosion. That was in line with changed swelling characteristics determined using DSC. The study gave evidence for strong impact of acid hydrolysis on functional properties like water binding.