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.