Rearranged supramolecular structure of resistant starch with polymorphic microcrystals prepared in high-solid enzymatic system

Abstract

Resistant starch (RS) is widely used as a new type of dietary fiber, but it is still a limitation of controllable formation of microstructure and polymeric architecture for preparing single-component RS (pure-phase). In this study, RS was prepared using maize starch with two ratios of amylose to amylopectin (RAA1:1 and RAA1:2) and four pullulanase concentrations (5, 15, 25, 35 U/g) in a high-solid dynamic reaction environment of bio-extrusion. Based on the long- and short-range orders reflected by the glycosidic bonds (13C NMR), chain-length distributions (SEC/FACE), single-/double-helices (FTIR), lamellas (SAXS) and crystalline pattern (XRD), the rearranged supramolecular structure of starch and their relationships with physicochemical properties (DSC and RVA) was illuminated. There were two morphologies of RS were created: 1) disordered fusion-like structure displayed by RAA1:1-P15 and RAA1:2-P35, which had the high contents of RS (54.95 and 54.19%) and short amylopectin (DP ≤ 24) (70.52% and 60.20%). The short (A chains) and extremely short (DP < 6) amylopectin could contribute to form submicro-crystallite with B1 chains in the extruded matrix at a low moisture level; 2) thinner, scalier and layered-like structure displayed by RAA1:2-P15 that was the transition state from thick layered strips of large granules. Its SDS content was high (33.61%) and owned the larger rearranged dLorentz (16.97 nm). Overall, the entangled regime of amylose and amylopectin in the modifications of starch with different structural units or micro-domains in this study will provide a new idea and reference to explore the preparation of novel RS.