Different effects of pectin and κ-carrageenan on the multiscale structures and in vitro digestibility of extruded rice starch

This study compared the different effects of pectin (PE) and κ-carrageenan (CG) on the multilevel structures (i.e. granule, crystallites, helices, fractals, and short-range order) and in vitro digestibility of extruded rice starch (MERS). The addition of either PE or CG altered the multiscale structures, increased the resistant component (RC) content, and reduced predicted glycemic index (pGI), with CG being more effective especially at a low content. CG led to the growth of molecular aggregates (α), single-helices, and V-type crystals (X_V). PE resulted in higher contents of double-helices and A + B-type crystals (X_A+B) and enhanced the short-range order (R_1045/1022) and particle compactness. Pearson correlation analysis indicates that, for MERS/PE, the slowly-digestible component (SDC) and RC contents were influenced by different factors in the sequence of total crystallinity (X_Total) > X_A+B > X_V > single-helix content > α > R_1045/1022 > double-helix content. For MERS/CG, the RC content was affected by X_Total > single-helix content > X_V.