Article pubs.acs.org/JAFC
Iron Contamination during In-Field Milling of Millet and Sorghum Christèle Icard-Vernière,*,† Fatoumata Hama,§ Jean-Pierre Guyot,† Christian Picq,† Bréhima Diawara,§ and Claire Mouquet-Rivier† †
IRD, UMR 204 “Prévention des Malnutritions et des Pathologies associées” (Nutripass), IRD/Université Montpellier 2/Université Montpellier 1, B.P. 64501, 34394 Montpellier Cedex 5, France § IRSAT, Département Technologie Alimentaire, 03 BP 7047, Ouagadougou 03, Burkina Faso ABSTRACT: Nutritionally, contaminant iron in foods may lead to overestimation of the satisfaction of iron requirement while iron deficiencies remain a widespread health problem. Iron contamination was measured in millet and sorghum grains after decortication and in-field milling using different equipments in Burkina Faso. Total iron content did not change significantly after decortication, probably due to a balance between losses resulting from the removal of iron-rich peripheral parts and contamination. Total iron contents increased significantly after mechanical milling irrespective of whether iron or corundum grindstones were used. Contamination was highly variable, ranging from 3 to 6 mg iron/100 g DM, and was mainly due to wear of the milling equipment. After in vitro digestion of traditional cereal dishes prepared with iron-contaminated or uncontaminated flours, the contaminant iron was found mainly in the insoluble fraction. Only in sorghum was a small proportion (4%) bioaccessible, showing that contaminant iron has poor nutritional interest. KEYWORDS: contamination, decortication, milling, bioavailability, phytate/iron molar ratio, Burkina Faso
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INTRODUCTION Iron and zinc deficiencies are the most prevalent micronutrient deficiencies worldwide, especially in developing countries.1 The diet found in these countries is mostly plant-based and then contains mainly nonheme iron, the absorption of which is greatly decreased by dietary factors and by the presence of chelating agents such as phytate or certain phenolic compounds.2 These compounds also influence the absorption of other divalent cations such as zinc.3 The bioavailability of iron and zinc is thus lower in plant-based diets than in diets that include foods from both plant and animal sources. Food processing is known to influence both mineral content and bioavailability.4 Grain decortication is often part of postharvest processing of cereals in both northern and southern countries. In previous studies, it was shown that during traditional manual or mechanical decortication of millet, iron losses were about 50% and zinc losses ranged from 35 to 46%.5,6 Mineral losses from sorghum were of the same order of magnitude, whereas phytates and other chelating agents were only partially removed.5 Analogous results were obtained with rice, with losses reaching almost two-thirds of iron content depending on the whitening technology practices.7 Other unit operations such as sieving, fermentation, or cooking can lead to iron losses or increases due to contamination.8 As reported in a literature review,9 in developing countries, contaminant iron, also called extrinsic iron, may represent several times the iron content in the staple foods or dishes. This extrinsic iron may originate from food contamination by soil or dust, from iron leaching from iron or steel pots into food during storage and cooking, or from equipment during food processing. As shown in an experimental study in the United States,10 70% of the iron in plant samples could originate from soil particulate inclusion by the plant tissues during growth and can be considered as contaminant iron. Despite careful washing © 2013 American Chemical Society
of plants or grains during the preparation of most dishes, extrinsic iron is still present in the foods finally consumed. Extrinsic iron may thus considerably increase iron intake. Contaminant iron on the surface of cereals and pulses purchased in a market in India was estimated to comprise between 13 and 47% of total iron.11 Iron contents up to 20 times higher were found in endogenous Ethiopian teff than in other cereals such as maize and barley and were attributed to soil contamination linked to the traditional method of threshing.12 A non-negligible part of extrinsic iron in foods can also come from cookware: the iron content of most foods cooked in stainless steel utensils can be higher than that of the same foods cooked in glassware.13 Similarly, other authors14 measured from 1.5- to 2-fold more iron in Ethiopian foods cooked in iron pots than in the same foods cooked in aluminum or clay pots. In another study, a significant increase of from 2 to 7 mg/100 g was measured in iron content in the flour after milling, and it was estimated that 1, the threshold value under which the intestinal iron absorption from cerealbased food is improved.2 Iron bioaccessibility in millet and sorghum was measured in “as-eaten” foods, that is, in samples of tô, in this case prepared with the previously mentioned flours (Table 3). In the following text, these samples are referred to as “ironcontaminated tô ” and “less-contaminated tô ”. In ironcontaminated tô prepared from millet, the content and the percentage of dialyzable iron were very low, showing poor bioaccessibility. The percentage of dialyzable iron did not exceed 2.4%. Expressed as a percentage, the dialyzable iron fractions were lower in iron-contaminated tô than in the lesscontaminated tô. This shows very low bioaccessibility of the contaminant iron, lower than that of the intrinsic iron. However, whereas in millet the dialyzable iron content did not differ with the level of contamination, in sorghum, the dialyzable iron content was significantly higher in the ironcontaminated tô than in the less-contaminated tô. This suggests that a small part of contaminant iron could be available for absorption. The soluble ND iron fractions represent the proportion of total iron that is potentially absorbable, but is most probably bound in macromolecular complexes. It can be assumed that this soluble iron could be released and dialyzed if fewer chelating factors were present in the tô or if the tô were eaten simultaneously with food containing some absorption enhancers such as ascorbic acid. In both millet and sorghum tô, these soluble ND fractions did not significantly differ with the level of contamination, which ranged from 21 to 27%. 10382
dx.doi.org/10.1021/jf402612k | J. Agric. Food Chem. 2013, 61, 10377−10383
Journal of Agricultural and Food Chemistry
Article
status and growth of young children: a randomized trial. J.-Lancet 1999, 353, 712−716. (15) Hallberg, L.; Bjö rn-Rasmussen, E. Measurement of iron absorption from meals contaminated with iron. Am. J. Clin. Nutr. 1981, 34, 2808−2815. (16) Hallberg, L.; Björn-Rasmussen, E.; Rossander, L.; Suwanik, R. Iron absorption from Southeast Asian diets. II. Role of various factors that might explain low absorption. Am. J. Clin. Nutr. 1977, 30, 539− 548. (17) Derman, D. P.; Bothwell, T. H.; Torrance, J. D.; MacPhail, A. P.; Bezwoda, W. R.; Charlton, R. W.; Mayet, F. G. Iron absorption from ferritin and ferric hydroxyde. Scand. J. Haematol. 1982, 29, 18−24. (18) Geerligs, P. D. P.; Brabin, B. J.; Omari, A. A. A. Food prepared in iron cooking pots as an intervention for reducing iron deficiency anemia in developing countries: a systematic review. J. Hum. Nutr. Diet. 2003, 16, 275−281. (19) Greffeuille, V.; Mouquet-Rivier, C.; Icard-Vernière, C.; Ouattara, L.; Hounhouigan, J.; Kayodé, A. P.; Amoussa, W.; Hama, F. Traditional recipes of millet-, sorghum- and maize-based dishes and related sauces frequently consumed by young children in Burkina Faso and Benin; http://www.instapa.org/instapa, 2010. (20) Lestienne, I.; Icard-Vernière, C.; Mouquet, C.; Picq, C.; Trèche, S. Effects of soaking whole cereal and legume seeds on iron, zinc and phytate contents. Food Chem. 2005, 89, 421−425. (21) Lestienne, I.; Buisson, M.; Lullien-Pellerin, V.; Picq, C.; Trèche, S. Losses of nutrients and antinutritional factors during abrasive decortication of two pearl millet cultivars (Pennisetum glaucum). Food Chem. 2007, 100, 1316−1323. (22) Miller, D.; Schricker, B.; Rasmussen, R.; Van Campen, D. An in vitro method for estimation of iron availability from meals. Am. J. Clin. Nutr. 1981, 34, 2248−2256. (23) Wolfgor, R.; Drago, S. R.; Rodriguez, V.; Pellegrino, N. R.; Valencia, M. E. In vitro measurement of available iron in fortified foods. Food Res. Int. 2002, 35, 85−90. (24) Lamand, M. Les oligoéléments dans la biosphère. In Les Oligoéléments en Médecine et Biologie; Tec et Doc Lavoisier: Paris, France, 1991; 653 pp. (25) FAO. http://www.fao.org/ag/agp/AGPC/doc/Counprof/ BurkinaFaso/BurkinaFfrench.htm, 2001. (26) Proulx, A. K.; Reddy, M. B. Fermentation and lactic acid addition enhance iron bioavailability of maize. J. Agric. Food Chem. 2007, 55, 2749−2754.
fortification to meet iron requirements. Meanwhile, with the aim of increasing the quantity of iron absorbed from this type of iron-contaminated cereal-based foods, it is recommended to eat simultaneously vegetable sauces rich in ascorbic acid or including small pieces of animal foods that are able to enhance iron absorption.
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AUTHOR INFORMATION
Corresponding Author
*(C.I.-V.) E-mail:
[email protected]. Phone: +33 4 67 41 62 80. Fax: +33 4 67 41 61 57. Funding
This research was conducted within the framework of the INSTAPA Project, funded by the European Union’s Seventh Framework Programme (Fp7/2007-2013) under Grant Agreement 211484. Notes
The authors declare no competing financial interest.
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ABBREVIATIONS USED IP6, inositol-6-phosphate or phytate; DM, dry matter REFERENCES
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