Modulation of starch ordering by cold storage and microwave reheating alters starch digestibility and glycemic...

Cooked white rice was stored under cold-storage conditions representative of household practice, including refrigeration at 4 °C for 1-7 days or freezing at -18 °C for 3-21 days, with or without a selected microwave reheating (700 W, 90 s), to determine how storage and reheating modulate starch ordering, in vitro digestibility fractions, and murine glycemic response. Refrigeration induced more pronounced structural reorganization than freezing, increasing relative crystallinity from 12.1% in freshly cooked rice (CR) to 17.2% after 7 d and FT-IR absorbance ratio (R_1047/1022) from 0.686 to 0.774, with detectable retrogradation enthalpy of 4.2 J/g. These changes reduced rapidly digestible starch (RDS) from 80.8% to 65.0%, increased slowly digestible starch (SDS) from 18.9% to 30.3% and resistant starch (RS) from 0.4% to 4.7%, and lowered murine glycemic response index (mGRI) from 86.0 to 74.0. Frozen storage produced less pronounced changes; after 21 d, relative crystallinity and R_1047/1022 were 13.9% and 0.716, respectively, while RDS, RS, and mGRI were 73.7%, 2.8%, and 80.8, respectively. Under the selected microwave reheating condition, the storage-induced changes were partially reversed. In the 7-d refrigerated sample, reheating decreased relative crystallinity from 17.2% to 14.5%, while increasing RDS from 65.0% to 75.9% and mGRI from 74.0 to 78.3; however, these values did not return to those of CR. Correlation analysis showed that both short-range order (R_1047/1022) and long-range crystallinity were comparably and strongly associated with RDS, RS, and mGRI, indicating that starch ordering at both scales was closely linked to starch digestibility and glycemic response in cold-stored, microwave-reheated cooked rice.