Impact of molecular and crystalline structures on in vitro digestibility of waxy rice starches

Abstract

The in vitro digestibility, molecular structure and crystalline structure of waxy rice starches isolated from six Korean cultivars (Shinsun, Dongjin, Baekok, Whasun, Chungbaek, and Bosuk) were investigated. The molecular weight (Mw) of waxy rice starches ranged from 1.1×108g/mol to 2.2×108g/mol. Chungbaek waxy rice starch had the highest average chain length (24.3) and proportion (20.7%) of long branch chains (DP≥37), and the lowest proportion (19.0%) of short branch chains (DP 6–12) among the tested six waxy rice starches. The relative crystallinity and intensity ratio of 1047/1022 ranged from 38.9% to 41.1% and from 0.691 to 0.707, respectively. Chungbaek had the highest gelatinization temperature and enthalpy. Chungbaek had the highest pasting temperature (70.7°C), setback (324cP) and final viscosity (943cP), whereas Baekok showed the highest peak viscosity (1576cP) and breakdown (1031cP). Chungbaek had lower rapidly digestible starch (RDS) content and expected glycemic index (eGI), and higher resistant starch (RS) content, whereas Whasun exhibited higher RDS content and eGI. The slowly digestible starch (SDS) content of Shinsun (38.3%) and Bokok (32.0%) was significantly higher than that of other cultivars (11.3–22.0%).