Comparative study on starch and protein secondary structures in brown, red, and black rice influenced by microwave...

This study compares the effects of microwave treatment (up to 220 s) on the starch and protein structures in brown, red, and black rice flours with 12 % initial moisture, representing typical low-moisture conditions. FTIR and XRD analyses revealed increased starch crystallinity, with brown rice showing the highest increase (9.71 %), followed by red (9.15 %) and black rice (4.40 %). A-type crystallinity rose in all rice types, while V-type decreased, suggesting disruption of amylose-lipid complexes. AFM and SEM confirmed partial starch granule disruption and reorganization into more compact structures. Protein analysis showed decreased β-sheet content, increased α-helix and β-turn structures, reduced hydrophobicity (by 10.06 %-51.65 %), and increased disulfide bonds, particularly in black rice (82.96 %), indicating enhanced molecular stability. These changes suggest potential improvements in texture, thermal stability, and possibly a reduced glycemic response, warranting further investigation of functional and digestibility properties.