Impact of Iron Salt Addition on the Viscoelastic Properties of Rice Flours

Authors

• Aldrin P. Bonto, De La Salle University
• Joanne Jerenice Añonuevo, National Cheng Kung University College of Medicine
• Guiller Sarmenta, De La Salle University
• Kathrina Lois Taaca, University of the Philippines Diliman, College of Engineering
• Mitch Irene Kate Oyales, University of the Philippines Diliman, College of Engineering
• John Paul Maulion, University of the Philippines Diliman, College of Engineering
• Glenn Vincent Ong, International Rice Research Institute
• Nese Sreenivasulu, International Rice Research Institute
• Guiller Sarmenta, Department of Chemistry and Biochemistry, College of Allied Sciences, De La Salle Medical and Health Sciences Institute

Publication Date

6-2026

Document Type

Article

Publication Title

Food Biophysics

Abstract

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. At the same time, spectroscopic (FTIR and Raman) and microscopic and elemental mapping were done through FESEM. 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 rice, highlighting the amylose-dependent modulation of viscoelastic properties induced by NaFeEDTA. Spectroscopic and microstructural analyses supported these findings: FTIR revealed the emergence of carboxylate-associated bands (~ 1620 and ~ 1590 cm⁻¹) indicative of NaFeEDTA–starch interactions, at the same time, Raman spectroscopy confirmed fortificant incorporation without altering the starch backbone. SEM-EDX observations further showed that NaFeEDTA was physically dispersed within the gelatinized matrix without inducing major morphological changes. 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. These findings further indicate that localized coordination interactions between the iron–EDTA complex and starch hydroxyl groups govern the observed rheological changes rather than large-scale structural modification. 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.

APA Citation

Bonto, A.P., Añonuevo, J.J., Sarmenta, G. et al. (2026). Impact of Iron Salt Addition on the Viscoelastic Properties of Rice Flours. Food Biophysics, 21(50). https://doi.org/10.1007/s11483-026-10143-7