Insights into milled rice quality formation via moisture migration and dynamic histological structure visualization

Moisture migration and starch gelatinization significantly influence the cooking quality of rice with different milling degrees (MD). Therefore, it is necessary to clarify the effects of MD on rice by examining the relationship between these factors. This study investigated changes in kernel morphology, starch phase, aleurone layer, and autofluorescence structure, together with moisture diffusion kinetics, migration pathways, and dynamic structural evolution. During cooking, rice exhibited a softer texture with increasing MD. Diffusion kinetic analysis showed that Deff increased from 6.49 × 10^-9 m²/s to 9.93 × 10-9 m²/s, whereas K₁ decreased from 0.1223%^-1 to 0.0032%^-1, indicating that milling disrupted the surface layer and created additional pathways for water penetration. Water gradually shifted toward the weakly bound state (T₂₂), with the proportion of T₂₂ increasing from 81.51% to 97.14% as MD increased. Rice with higher MDs contained more water in the belly region during the first 10 min of cooking, whereas no major differences were observed after 15 min, except for MD0. The aleurone layer gradually disintegrated, and the internal starch granules transformed into a continuous phase, forming a dense honeycomb-like network, with these changes occurring more rapidly as MD increased. The OH vibrations of starch in high-MD rice exhibited greater sensitivity, whereas those in low-MD rice were less responsive. Overall, milling weakened the barrier effect of the aleurone layer, promoting moisture migration and the formation of a continuous starch phase, thereby reducing rice hardness. This study provides a visual understanding of the dynamic evolution of rice quality formation and offers valuable insights into the development of high-quality rice.