Incorporating ions during thermal processing tailors the microstructure and practical features of rice...

Understanding the interplay among salt ions, anthocyanin and starch within food matrices under thermal conditions is important for the development of starch-based foods with demanded quality attributes. However, how salt ions presence influences the microstructure and properties of starch/anthocyanin binary system remains largely unclear. Herein, indica rice starch (IRS) and rice anthocyanin (RA) were used to construct an IRS-RA binary system, with thermal treatment under different concentrations of Na⁺ (10-40 mM) and types of salt ions (Na⁺ and Ca²⁺). The incorporation of salt ions induced the formation of a porous gel matrix, and destroyed the hydrogen bond between starch and anthocyanin through electrostatic interactions, reducing the storage modulus and radius of gyration of the binary system, and increasing the relative crystallinity (from 1.08 % to 1.51 % (20 mM Na⁺) and 1.69 % (20 mM Ca⁺)) of the IRS-RA binary system at 90 °C. Also, the DPPH radical scavenging ability of the binary system at 90 °C was enhanced upon incorporating salt ions (0.93 for Na⁺ condition and 0.94 for Ca²⁺ condition at 20 mM ion concentration). It is noteworthy that Ca²⁺ inclusion had more significant effects than the case for Na⁺ presence, presumably due to the increased charge density.