Effect of parboiling conditions on zinc and iron retention in biofortified and non‐biofortified milled rice

Abstract

BACKGROUND Zinc‐biofortified rice could contribute to zinc intake in deficient populations, but processing it into parboiled rice could affect this potential benefit. Zinc and iron true retention (TR) in milled rice produced under conditions resembling household and commercial parboiled methods was evaluated. Zinc and iron TR in milled rice obtained from biofortified and non‐biofortified rice subjected to different soaking temperatures during parboiling was also evaluated. RESULTS Conditions resembling commercial parboiling methods resulted in 52.2–59.7% zinc TR and 55.4–79.1% iron TR, whereas those used for household parboiling resulted in 70.7–79.6% zinc TR and 78.2–119.8% iron TR. Zinc TR in milled (8–16% bran removal) biofortified and non‐biofortified parboiled rice was 50.6–66.8% when soaking rough rice at 20 °C and 29.9–56.0% when soaking rough rice at 65 °C; both had lower zinc TR than non‐parboiled rice (58.0–80.6%). Iron TR was generally similar between milled non‐parboiled and parboiled rice (26.2–67.6%) and between parboiled biofortified and non‐biofortified milled rice. CONCLUSION Parboiling conditions used to obtain milled rice targeted for own household consumption resulted in higher zinc and iron TR compared to parboiling conditions used for milled rice targeted for markets. More zinc from the inner endosperm moved towards the outer layers at high soaking temperature, resulting in lower zinc TR for milled parboiled rice soaked in hotter water. Parboiled rice soaked at temperatures used in households could provide more zinc to diets compared to rice soaked in hotter water commonly used in large rice mills, especially when rice is extensively milled. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Rural Bangladeshi consumers’ (un)willingness to pay for low‐milled rice: Implications for zinc biofortification

“…Parboiled rice is also preferred in Bangladesh due to its longevity (less spoilage), digestibility, and reduced stickiness (Jaim & Hossain, 2012). While zinc is contained in the endosperm of the grain and, therefore, is mostly protected during milling, this is not the case if paddy rice is first parboiled (Taleon et al., 2022). During parboiling, zinc moves from the endosperm towards the kernel bran, making it more vulnerable to removal during milling (Taleon et al., 2020).…”

“…In a recent study conducted in Bangladesh, zinc concentration was measured for parboiled rice at the low‐milling level of 8% (to remove most of the pericarp and germ), and the highest milling level of 16% which produces white rice. The analysis showed that the low‐milled grain had up to 77% more zinc than the highly milled grain and when combining the zinc content increase through biofortification and low‐milling, biofortified low‐milled rice had up to 156% higher zinc content than non‐biofortified high‐milled rice (Taleon et al., 2022). In addition to zinc loss, other vitamin and micronutrients are also lost during a high degree of milling (Muthayya et al., 2014).…”