Impact of polishing duration on milling quality, surface microstructure, and grain uniformity in rice

This study investigated the effects of polishing duration (15-120 s) in a laboratory abrasive rice polisher on milling quality, grain characteristics, and kernel surface microstructure. The results revealed that the degree of polishing (DOP) increased significantly from 2.38% (15 s) to 15.29% (120 s), which was accompanied by a higher broken content (from 6.35% to 18.45%) and a reduced head rice yield (from 93.6% to 80.3%). The complete removal of bran streaks required a DOP >13.05%, but this threshold also coincided with over-milling and yield loss. Scanning electron microscopy (SEM) images revealed the progressive abrasion of the protuberances and bran layers, with uniform polishing achieved only after 90 s. These findings clearly indicate the trade-off between bran removal and grain integrity, underscoring the need to optimize the polishing time for balanced quality, yield, and sustainability in rice processing. Therefore, this study highlights how optimizing rice polishing through abrasive milling can reduce grain breakage, increase head rice yield, and improve grain uniformity, thereby minimizing postharvest losses. By balancing whiteness, transparency, and surface structure, this research supports more efficient use of harvested rice, promoting food security and sustainability in grain processing.