Iron deficiency remains a global problem, and is especially high in populations that rely on polished rice as a staple food. Extrusion of rice flours provides an opportunity to use iron fortification, but the temperatures used and fortification approaches may influence iron availability. Scheuchzer and colleagues conducted a study to determine the impact of extrusion temperatures on iron solubility and bioavailability, and report the results in a paper published in the May 2022 issue of The Journal of Nutrition.
Iron fortified rice grains containing intrinsically labelled ferric pyrophosphate (57FePP) or ferrous sulfate (58FeSO4) were produced with or without citric acid (CA) and trisodium citrate (TSC). The flours were extruded at 40, 70, or 90°C and had a molar ratio of iron to CA/TSC of 1:0.3:5.5. Starch microstructure, color and in vitro iron solubility were determined. Using a standardized rice and vegetable meal, iron absorption was measured in young women.
Even though the 70 and 90°C extrusion temperatures increased retrograded starch, extrusion temperatures did not affect iron solubility or iron bioavailability. However, the fractional iron absorption from rice extruded with CA/TSC was more than twice the amount obtained when the rice did not contain CA/TSC. These observations led the authors to conclude that higher extrusion temperatures did not influence iron bioavailability, but that including CA/TSC with FePP led to a significant improvement in iron absorption.
In an editorial, Hennigar and Hamaker, describe the various reasons why it is easier to fortify wheat and corn products, including the fact that rice is primarily consumed as an intact grain, and it is sometimes cooked with excess water and after being washed. They conclude that CA/TSC should be used when fortifying rice with FePP, and that warmer extrusion temperatures are better for areas where rice is cooked with excess water and the water is discarded.
Pornpimol Scheuchzer, Michael B Zimmerman, Christophe Zeder, Antoni Sánchez-Ferrer, Diego Moretti, Higher Extrusion Temperature Induces Greater Formation of Less Digestible Type V and Retrograded Starch in Iron-Fortified Rice Grains But Does Not Affect Iron Bioavailability: Stable Isotope Studies in Young Women, The Journal of Nutrition, Volume 152, Issue 5, May 2022, Pages 1220–1227, https://doi.org/10.1093/jn/nxab435.
Stephen R Hennigar, Bruce R Hamaker, Optimizing Fortification of Rice with Micronutrients to Improve Public Health, The Journal of Nutrition, Volume 152, Issue 5, May 2022, Pages 1179–1180, https://doi.org/10.1093/jn/nxac023.
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Nancy Turner is a Professor of Nutrition at Michigan State University. Her research focus is on the role of diet on colon cancer and inflammatory bowel disease. She is the author of many papers on this topic, as well as the co-editor of a book, and co-author of a textbook.
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