The interaction of sweet potato amylose/amylopectin and KCl during drying

• Attraction of amylose/amylopectin to KCl leads to presence of snowflake crystals.
• The Cl− of KCl is attracted by hydrogen of hydroxyl in sweet potato starch.
• The K+ of KCl is attracted by oxygen of hydroxyl in sweet potato starch.
• KCl is entrapped by sweet potato starch in crystallization progress during drying.
• Amylose promotes the growth of KCl crystals, while amylopectin inhibit it.

Sweet potato amylose and amylopectin were isolated from retrograded sweet potato starch. During isolation, the retrograded starches were resolved in 4.0 M KOH and then 4.0 M HCl was added to adjust the pH of the solutions to neutral, therefore KCl was formed in starch solutions. Long or short crystals of KCl grew on sweet potato amylose solution or amylopectin solution in the drying process. The results of IR, NMR, XRD, DSC and SEM of corresponding samples suggest that the attraction of amylose or amylopectin to KCl leads to the formation of snowflake crystals. The shape of KCl crystals growing in starch solutions acts more like biological macromolecular crystals than that of inorganic salt. Amylose promotes the growth of KCl crystals, while amylopectin inhibits it. The different up and down field of C-6 signals in NMR indicates the different link pattern of starch with KCl salt. In the course of crystallization, sweet potato starch grows into B-type crystal, with the characteristic strongest peak located at 17°. KCl is entrapped by starch in the crystallization progress during starch drying. The findings in the paper provide an insight into the interaction between starch and salts.

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