On the role of the internal chain length distribution of amylopectins during retrogradation: Double helix lateral aggregation and slow digestibility.

A structure-digestion model is proposed to explain the formation of α-amylase-slowly digestible structures during amylopectin retrogradation. Maize and potato (normal and waxy) and banana starch (normal and purified amylopectin through alcohol precipitation), were analyzed for amylose ratio and size (HPSEC) and amylopectin unit- and internal-chain length distribution (HPAEC). Banana amylopectin (BA), like waxy potato (WP), exhibited a larger number of B3-chains, fewer BS- and Bfp-chains and lower S:L and BS:BL ratios than maize, categorizing BA structurally as type-4. WP exhibited a significantly greater tendency to form double helices (DSC and 13C-NMR) than BA, which was attributed to its higher internal chain length (ICL) and fewer DP6-12-chains. However, retrograded BA was remarkably more resistant to digestion than WP. Lower number of phosphorylated B-chains, more S- and Bfp-chains and shorter ICL, were suggested to result in α-amylase-slowly digestible structures through further lateral packing of double helices (suggested by thermo-rheology) in type-4 amylopectins.