J Nutr. 2002 Apr;132(4 Suppl):806S-12S.
Fortification: overcoming technical and practical barriers.
Hurrell RF.
Laboratory of Human Nutrition, Institute of Food Science ETHZ, Rüschlikon, Switzerland.
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The main barriers to successful iron fortification are the following: 1) finding an iron compound that is adequately absorbed but causes no sensory changes to the food vehicle; and 2) overcoming the inhibitory effect on iron absorption of dietary components such as phytic acid, phenolic compounds and calcium. These barriers have been successfully overcome with some food vehicles but not with others. Iron-fortified fish sauce, soy sauce, curry powder, sugar, dried milk, infant formula and cereal based complementary foods have been demonstrated to improve iron status in targeted populations. The reasons for this success include the use of soluble iron such as ferrous sulfate, the addition of ascorbic acid as an absorption enhancer or the use of NaFeEDTA to overcome the negative effect of phytic acid. In contrast, at the present time, it is not possible to guarantee a similar successful fortification of cereal flours or salt. There is considerable doubt that the elemental iron powders currently used to fortify cereal flours are adequately absorbed, and there is an urgent need to investigate their potential for improving iron status. Better absorbed alternative compounds for cereal fortification include encapsulated ferrous sulfate and NaFeEDTA, which, unlike ferrous sulfate, do not provoke fat oxidation of cereals during storage. Encapsulated compounds also offer a possibility to fortify low grade salt without causing off-colors or iodine loss. Finally, a new and useful additional approach to ensuring adequate iron absorption from cereal based complementary foods is the complete degradation of phytic acid with added phytases or by activating native cereal phytases.

From the full text article:

Iron is the most difficult mineral to add to foods and ensure adequate absorption (1 ). The main problem is that the water-soluble iron compounds, which are the most bioavailable, often lead to the development of unacceptable color and flavor changes in the food vehicle. When water-soluble compounds are added to cereal flours, for example, they often cause rancidity, and in low-grade salt, they rapidly lead to color formation. Insoluble compounds, such as elemental iron powders, on the other hand, do not cause sensory changes but may be so poorly absorbed as to be of little or no nutritional benefit.

The selection of the iron compound, however, is only part of the problem. The other major difficulty to ensuring adequate absorption is the presence of iron absorption inhibitors in the fortification vehicle itself, or in the accompanying diet. The main inhibitory compound is phytic acid (myo-inositol 6-phosphate) (2 ), which is widely present in cereal grains and legume seeds (3 ). Phytic acid binds iron strongly in the gastrointestinal tract and can decrease the absorption of even the most bioavailable iron compounds to very low levels (4 ).

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These barriers can be overcome, and iron-fortified foods that have demonstrated an improved iron status in the target population include infant formula (5 ), infant cereal (6 ,7 ), sugar (8 ) and fish sauce (9 ). It is noteworthy that all of these foods were consumed with an enhancer of iron absorption (ascorbic acid or EDTA) added to overcome absorption inhibitors. Currently, however, there is little direct evidence that iron fortification of major staple foods, such as wheat flour or corn flour, is a useful strategy to combat iron deficiency. This is due mainly to the common use of poorly bioavailable iron compounds and the high level of phytic acid in cereal foods. With salt, despite much progress in fortification (10 ), there are still major problems of color formation and iodine loss when iron is added to the low-grade iodized salt most frequently consumed by the poorer population groups in developing countries.

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The advantage of ferrous bisglycinate [Ferrochel] over EDTA is that it is more "natural." It is, however, more expensive, it promotes fat oxidation in stored cereals (58 ) and it promotes off-colors in a similar way to other soluble iron compounds. Another major disadvantage, however, is that it is a patented compound (Albion Laboratories, Clearfield, UT), marketed very aggressively, and it has been extremely difficult to obtain an independent verification of its claimed protective effect against phytic acid because the compound tested is always provided by the company. There are also contradictory reports in the literature with respect to its bioavailability. Fox et al. (59 ) reported that infants fed vegetable purée or whole grain cereal absorbed iron to a similar extent from ferrous bisglycinate and ferrous sulfate. In contrast, iron absorption was 4-fold better from ferrous bisglycinate fortified whole corn porridge (60 ) and about 2-fold better from breakfast meals based on corn flour or wheat flour (61 ) than from the equivalent foods with ferrous sulfate.

Bovell-Benjamin et al. (60 ) argued that the results of Fox et al. (59 ) could be explained because ascorbic acid was used to maintain isotopically labeled ferrous sulfate in the ferrous state. The amount added, however, was only 0.83 mg ascorbic acid/mg iron, which is much lower than the 6:1 weight ratio required for a useful increase in absorption as discussed earlier. It is doubtful therefore whether this amount of ascorbate would result in a measurable increase in iron absorption. Ferrous bisglycinate is nevertheless a well absorbed iron compound, which may in the future be confirmed as being protected against phytic acid. Its high cost, however, and tendency to provoke unwanted sensory changes make it an unsuitable choice for many food vehicles. It does appear to be a useful compound in liquid milk (62 ) and other milk products.

Categories: 2002, Iron, Iron absorption, Cereals, Phytates, Vitamin C