Structural-functional modulation and macromolecular interactions in buckwheat protein films induced by heat, rutin,...

Thermal energy processing, enzymatic crosslinking by transglutaminase, and polyphenol-rutin interaction modulated the buckwheat protein (BWP) macromolecular structure and functional properties. In this study, film formation as a model system was investigated to evaluate structure-function relationships. Isoelectric-precipitated BWP was used for film production and conditioned at 50% relative humidity (RH) at 25 °C. Standard methods were used to evaluate water vapor permeability (WVP) and mechanical, microstructural, physical, and physicochemical properties. Formation of hydrophobic barriers through matrix reorganization, enzymatic crosslinking, and protein-phenolic interactions reduced WVP by 1.09%-43.92% and increased tensile strength (TS) (p < 0.05) in the treated films. The heated group showed the strongest effect on TS (57.88% increase, 7.23 MPa). The treated films' lightness (L*) and yellowness (b*) were improved, while thermal treatment notably reduced opacity. The 1% TGase film showed the highest time-dependent moisture-sorption uptake. The rutin and TGase BWP films' antioxidant potentials were enhanced by an increase of 9.17%-15.34% Trolox antioxidant equivalents. The ninhydrin assay indicated an optimum crosslinking at 1% TGase, with a reduction at higher concentrations indicating saturation. Structural integrity and compactness improved progressively in the heated, rutin, and TGase-treated BWP film. The 2% rutin and 1% TGase films showed the most cohesive and homogeneous matrices, correlating with reduced WVP and enhanced TS. FTIR analysis showed that heat, rutin, and TGase treatments altered hydrogen bonding and protein conformation, enhancing molecular stability and improving the biofunctional, mechanical, and barrier properties of BWP films for sustainable food packaging.