Iron and zinc and other mineral bioaccessibility improvement in African cereal-based porridges by food-to-food fortification

Abstract

Essential mineral deficiencies, notably iron and zinc are prevalent in Africa, especially among children and women of childbearing age, often resulting from monotonous cereal-based diets low in bioavailable minerals. This study investigated the effects of food-to-food fortification of African-type wholegrain pearl millet and maize porridges with locally available plant foodstuffs rich in minerals (moringa leaves and hibiscus calyxes) and their bioavailability enhancers, organic acids (baobab fruit) and β-carotene (carrot and mango), at 5–15 g/100 g porridge (dry basis), on iron, zinc and other mineral bioaccessibilities, as measured by dialysability assay. Notwithstanding baobab’s high tannin and polyphenol contents, its fortification of pearl millet and maize porridges generally increased both the percentage and amount of bioaccessible iron. Baobab was nearly as effective as citric and ascorbic acid inclusion and was more effective than just ascorbic acid inclusion, known enhancers of iron absorption. Hence, the positive effect of baobab was probably due it being high in citric and ascorbic acids. This positive effect was greatly enhanced (approximately 2-fold) when maize porridge was additionally conventionally fortified with iron as FeSO4. Baobab’s organic acids probably enhanced the solubility of the iron in the porridges, thereby alleviating its chelation by phytate and phenolics. The baobab’s ascorbic acid probably enhanced the solubility of the porridges’ iron (Fe3+) primarily by reducing it to the soluble Fe2+ form. However, zinc bioaccessibility was generally not improved by baobab fortification alone, probably due to baobab’s high polyphenol content. Moringa fortification of the porridges generally substantially decreased percentage and amount of bioaccessible iron and zinc. This was probably due to its high calcium and phytate contents, which would likely reduce iron and zinc solubility by forming insoluble calcium-phytate-iron/zinc complexes. Carrot plus mango fortification of maize porridge moderately increased iron and zinc bioaccessibility, in terms of percentage and amount when in combination with baobab. The high β-carotene content of carrot and mango probably contributed to this enhancement. Beta-carotene can enhance mineral bioavailability by forming soluble complexes with them. Food-to-food fortification with combinations of carrot, mango, papaya, baobab, hibiscus calyxes and small proportion of moringa (2.5 g/100 g porridge) or together with a commercial micronutrient premix (iron, zinc and vitamin A) generally increased mineral bioaccessibility in extrusion-cooked fortified-pearl millet-based porridges, both in term of percentage and amount by up to 22-fold for iron and 4-fold for zinc. However, the extruded products were notably high in iron, resulting from contamination during processing. The enhancement in iron and zinc bioaccessibility was probably primarily because the organic acids and β-carotene in the food fortificants improved the solubility of the contaminating iron plus the iron and zinc in the porridges. Percentage calcium bioaccessibility was generally decreased by the food fortificants, probably because of their high contents of phenolics. However, percentage magnesium bioaccessibility were generally moderately increased with baobab and/or carrot plus mango fortification of the porridges. Only moringa decreased the percentage magnesium bioaccessibility, presumably due to its high contents of calcium and phenolics. Amounts of bioaccessible calcium and magnesium were generally substantially increased by the plant food fortificants with moringa fortified-cereal porridges being by far the highest in bioaccessible calcium and magnesium. This is because moringa is very high in calcium and high in magnesium. Thus, a hybrid food-based strategy, such as food-to-food fortification of wholegrain cereal foods with baobab fruit, mango and carrot in combination with conventional iron and zinc fortification may be a viable strategy to improve bioavailable iron and zinc in the diets of at-risk populations in tropical Africa and also substantially increase their intake of provitamin A.