Impact of iron salt addition on the viscoelastic properties of rice flours

Iron addition to rice is widely promoted to address iron-deficiency anemia, yet its effects on the rheological behavior of rice flour remain poorly understood. This study investigated the impact of iron salt (sodium iron EDTA) on the viscoelastic properties of rice flours with varying amylose content, specifically waxy IR65, low-amylose IR24, and high-amylose IR36. Dynamic oscillatory rheology, including temperature ramp, frequency sweep, and stress sweep tests, was employed to evaluate gel formation, elasticity, and deformation behavior. During gelatinization, high-amylose IR36 exhibited significantly stronger gel formation, with a maximum storage modulus (G′max) of 11,420 ± 270 Pa, compared with IR24 (9,376 ± 122 Pa) and IR65 (338 ± 29 Pa). Frequency sweep measurements showed that elasticity increased with amylose content, with G′ at 10 rad s⁻¹ reaching 16.90 ± 0.96 Pa for IR36. The addition of iron (2.5–10%, w/w) further modulated viscoelasticity in an amylose-dependent manner, enhancing gel elasticity and consistency in high-amylose rice while reducing elastic strength in waxy and low-amylose systems. Stress sweep tests revealed that iron addition did not alter the intrinsic deformation behavior of the starch gels, with IR36 and IR24 exhibiting Type III weak-strain overshoot and IR65 exhibiting Type I strain-thinning behavior. Overall, the results demonstrate that iron–starch interactions selectively reinforce amylose-rich networks while weakening amylopectin-dominant gels, providing critical insights for optimizing the formulation and processing of iron-fortified rice-based food products.