Impact of Microwave Treatment on Protein and Starch Characteristics of Black Wheat and Whole Wheat (T. aestivum L.) Flour

This study investigated the structural and functional responses of whole wheat flour (WWF) and black wheat flour (BWF) to microwave (MW) dielectric heating. MW exposure impaired gluten network stability in WWF, whereas BWF exhibited limited cohesive gluten formation, acting as an elasticity-attenuating component. FTIR and XRD analyses demonstrated significant increases in relative starch crystallinity after 220 s of MW exposure, due to Vh-type complexation. AFM confirmed pronounced increases in surface roughness (BWF: Sa +39%, Sq +41%; WWF: Sa +42%, Sq +30%). Protein secondary structure deconvolution confirmed thermal denaturation rather than beneficial ordering: native β-sheets decreased (WWF: 37.04% to 32.68%; BWF: 37.97% to 31.49%), while β-turns increased (WWF: 22.32% to 30.14%). Water contact angle measurements showed reduced surface hydrophobicity (−19.20% in WWF, −22.70% in BWF). Thiol-disulfide (-SH/-SS) determinations highlighted different molecular mechanisms: WWF underwent intensive disulfide cross-linking (+419.6%), whereas BWF preserved free thiols (+75.5%) due to protective phenolic–protein complexation. Granular thermal damage increased in vitro enzymatic amylolysis, significantly elevating the amount of rapidly digestible starch (RDS) and estimated glycemic index (eGI). Overall, MW processing preferentially remodeled protein networks in WWF while predominantly altering starch matrix morphology in BWF, providing key insights into the dielectric thermal processing of conventional and pigmented wheat flours.