Comparative Characterization of the Multiscale Structure, Physicochemical Properties, and In Vitro Digestibility of Starches from Selected Stress-Resistant Rice Varieties

Stress-resistant rice varieties are valuable for sustainable production and rice-based food development. Six rice varieties selected for salt alkali tolerance or low cadmium accumulation were characterized for starch composition, multiscale structure, physicochemical properties, rheological behavior, and in vitro digestibility. Rice flours contained 78.11% to 83.51% starch, 12.67% to 18.12% amylose, and 5.23% to 7.50% protein. All starches exhibited A-type crystallinity but showed varietal differences in granule morphology, particle size, molecular organization, thermal behavior, pasting properties, freeze–thaw stability, paste clarity, and rheological characteristics. Rapidly digestible starch ranged from 60.44% to 72.79%, slowly digestible starch ranged from 22.40% to 33.75%, and resistant starch ranged from 4.46% to 10.59%. Jingliangyou 3261 exhibited the highest resistant starch content, whereas Xinjiang aromatic rice combined the highest slowly digestible starch content with the lowest rapidly digestible starch content and the highest paste clarity. Ningjing 48 and Xinjiang aromatic rice also showed favorable freeze–thaw stability, highlighting distinct varietal profiles for targeted rice food applications. These findings provide preliminary information for further evaluation of these varieties under practical cooking and food-processing conditions.