Structural comparisons of pyrodextrins during thermal degradation process: The role of hydrochloric acid.

Hydrochloric acid (HCl) is widely used to prepare pyrodextrins, especially the water-soluble pyrodextrin. In this study, the structural difference between pyrodextrins as affected by HCl is compared by characterizing the molecular size, chain-length distributions (CLDs), crystallinity, and solubility. It is found that: 1) dry heating of starch granules without HCl mainly degrades long-amylose chains while slightly affects amylopectin branches; 2) the presence of HCl during dry heating decreases the degree of polymerization (DP) range of amylose chains upon degradation from DP ~ 833-1267 to DP ~ 206-432, suggesting that the presence of HCl accelerates the breakdown of long-amylose chains; 3) both pyroconversion processes have slight effects on A-(DP ~ 6-12) and B- chains (DP ~ 12-24), which might explain the retained granular and crystalline structure during the process. This study could improve the understanding of the role of HCl in affecting the structure and property during pyroconversion of native starch.