Weakening the integrity of waxy starch granules by selective degradation of amorphous matrices using gaseous hydrogen...

Waxy corn starch with 6-12 % moisture was degraded by gaseous hydrogen chloride (HCl_(g)) then characterized chromatographically and microscopically to investigate the relationship between moisture-resulting changes in unit chain properties of starch and its susceptibility to swelling. Starches with the highest degradation extents at different moisture content had recoveries of 76-83 % (w/w) and the weight-average degrees of polymerization of 66-93 anhydroglucose unit. Additionally, the HCl_(g)-degraded starches were still of birefringent granules but with internal cavity. When increasing the swelling temperature from 25 to 40 °C, some granules showed enlarged internal cavity, and some were fragmented. Change in granule morphology, accompanied by leaching of constituting polymers, was particularly evident for starch with preferential degradation of B₁ chains over B₂₊ chains as the moisture content decreased from 9 % to 6 %. These findings not only manifest the impact of changes in B₂₊ and B₁ chains on the swelling characteristic of HCl_(g)-degraded granules, but also demonstrate an approach for weakening the integrity of granules by selective degradation of amorphous matrices using HCl_(g).