Synergistic heat-moisture-ultrasound modification enhances starch-glutelin interactions: A pathway to tailored physicochemical properties and reduced digestibility in purple rice blends

While physical modifications like heat-moisture treatment (HMT) and ultrasound (UT) improve starch functionality, the role of glutelin—the major rice protein—in modulating starch behavior during such treatments remains unexplored. This study investigates the synergistic effects of HMT-UT co-modification on purple rice starch–glutelin (PRS-G) blends to elucidate structural, thermal, and digestibility changes. PRS-G mixtures (0–20 % glutelin) were subjected to HMT (110 °C, 30 % moisture) followed by UT (600 W, 30 min). SEM revealed fragmented lamellar structures with irregular pores, while rheological analyses demonstrated maximal gel strength at 5 % glutelin. DSC and XRD indicated that HMT-UT increased gelatinization temperatures (ΔT up to 8.2 °C) and short-range molecular order, particularly in HUPRS-10 %G (purple rice starch subjected to HMT-UT with 10 % glutelin), due to enhanced starch-glutelin crosslinking. FTIR confirmed hydrogen bonding between starch hydroxyl groups and glutelin residues, forming compact aggregates. In-vitro digestibility showed that HMT-UT reduced rapidly digestible starch (RDS) by 21.5 % and increased resistant starch (RS) by 172 % in HUPRS-10 %G, outperforming physically mixed PRS-G systems. Kinetic modeling revealed dual-phase digestion inhibition, with glutelin acting as a steric barrier to enzymatic hydrolysis. This work establishes that HMT-UT co-modification promotes starch-protein interactions via structural denaturation and binding-site exposure, yielding thermally stable, slow-digesting starch-protein matrices.