Structurally induced modulation of in vitro digestibility of amylopectin corn starch upon esterification with folic acid

The present study aims to identify how structural modifications of amylopectin corn starch on esterification with folic acid (FA) affects its in vitro digestion. Small angle X-ray scattering (SAXS) confirmed that at low FA esterification (5–10%), the mesophase order showed the absence of any super-structural order. However, a discotic stacking of SF forming columnar hexagonal phases and columnar helical phases (with strong optical anisotropy) was observed upon increasing FA esterification (20–40%). X-ray diffraction (XRD) evidenced the development of a V and B-type molecular packing order in SF with increased FA esterification from 20 to 40%, with a consequential increase in the percentage of slow digestible starch (SDS) and resistant starch (RS). The slower digestion phenomenon displayed a dual-phase behavior, with digestion rates k1 > k2, where k2 being ca. 0.3 of k1. Stacking over packing order appeared to be more influential in limiting the enzymatic action. A k-means clustering analysis of the total digested starch and Fourier transform infrared (FTIR) spectroscopy peak ratios (1000/1022) cm−1 indicated that 0.04 level FA substitution was crucial for slower hydrolysis of SF. This study provides structural insights for developing starch-folic acid ester derivatives that could form building-block copolymers for future development of oral drug/nutraceutical delivery vehicles with tailored starch digestion properties.