Clasificación o Escalas de la Enfermedad

Addition of ascorbic acid

Ascorbic acid is the most commonly added com- pound for the enhancement of iron absorption from iron fortified foods. It is routinely added to

infant formulas and commercial infant cereals, to iron fortified chocolate drink powders and a va- riety of dietetic products. It enhances the absorp- tion of fortification iron (with the exception of the chelates) and intrinsic food iron in a dose depend- ent way (81). The enhancing effect has been attributed to its reducing and chelating properties during the digestion of the food (82). The addition of ascorbic acid overcomes the negative effects of all major inhibitors of iron absorption, including phytate, polyphenols (83), calcium and casein from milk products (84), and can increase iron absorption two to threefold, although recent stud- ies indicate that insoluble iron compounds such as elemental iron and ferric pyrophosphate are less enhanced by ascorbic acid than ferrous sulfate (43, 59). A 2:1 molar ratio of ascorbic acid to iron is recommended for low phytate products and powdered milk, and a 4:1 ratio is recommended for high phytate products (85).

The use of ascorbic acid as an enhancing agent is limited by its instability in aqueous solutions, during storage of powdered foods, and during prolonged heat processing or cooking. Adequate packaging to exclude oxygen can help preserve ascorbic acid during storage, however, almost all will be destroyed during heat treatments such as baking or during preparation for consumption if extensive cooking is required (e.g. non precooked cereal based complementary foods). A possible solution is the use of ascorbyl palmitate, a syn- thetic ester composed of palmitic acid and ascor- bic acid. This compound is thermostable and its reductive and vitamin properties are reported to be maintained during baking (86). When baked with ferrous sulfate into bread, it increased iron absorption in women from 10.5% to 14.6% at a 2:1 molar ratio, and to 20.2% at a 4:1 molar ratio (87).

Addition of erythorbic acid

Erythorbic acid is a stereoisomer of ascorbic acid which appears to have a better enhancing effect on iron absorption but to be more sensitive to oxi- dation (88). It has strong reducing properties and

89 Bioavailability of iron compounds for food fortification

is a common additive in processed foods (89), but has limited antiscorbutic activity in guinea pigs (90). Its antiscorbutic activity in humans has not been investigated. When added to a ferrous sul- fate fortified cereal porridge, iron absorption by women increased from 4.1% to 10.8% at a 2:1 molar ratio, and to 18.8% at a 4:1 molar ratio (91). The addition of ascorbic acid to the same meal at a 4:1 molar ratio increased iron absorption from 4.1% to 11.7%. Although erythorbic acid was 1.6 fold more potent as an enhancer of iron absorp- tion than ascorbic acid (P<0.0002) in this study, its lack of antiscorbutic activity and sensitivity to oxidation may limit its usefulness in iron fortifi- cation programs.

Addition of other organic acids

With the possible exception of fruit drinks, the addi- tion of other organic acids does not appear to be an option, as the large quantities of organic acids which are required to enhance iron absorption will cause unacceptable flavor changes in most vehicles (92). Although citric, lactic, tartaric and malic acids do enhance iron absorption and are commonly used food additives, they effectively enhance iron absorption only at molar ratios in excess of 100:1. One gram or more of citric, malic or tartaric acid was necessary to increase iron absorption by two to threefold, from 3 mg ferrous sulfate iron added to a rice meal (93).

Addition of EDTA complexes

Na₂EDTA and CaNa₂EDTA are permitted food additives and could be used as enhancers of forti- fication iron absorption. Na₂EDTA has been demonstrated to substantially increase iron absorption in human subjects from a ferrous sul- fate fortified rice meal (79) and from a ferrous sulfate fortified wheat-soy infant cereal (38) even at molar ratios below 1:1. However, unlike with NaFeEDTA, the mixture of ferrous sulfate and Na₂EDTA promoted fat oxidation reactions in stored wheat flour (71). Unfortunately, Na₂EDTA

does not appear to increase the absorption of the more insoluble iron compounds that cause fewer organoleptic problems. Na₂EDTA at a 1:1 molar ratio did not increase iron absorption in adoles- cent girls consuming ferrous fumarate fortified tortillas (94), or by adults consuming either a fer- rous fumarate or a ferric pyrophosphate fortified cereal porridge (38, 40), or an elemental iron for- tified breakfast cereal (95).

Phytic acid degradation

Phytic acid in cereal and legume based foods is a potent inhibitor of iron absorption from iron forti- fication compounds and from native food iron (96). It can, however, be degraded in an aqueous environment by the addition of exogenous phy- tases or by the activation of native phytases in the cereal grains under controlled pH and tempera- ture conditions (97). To obtain a meaningful increase in iron absorption, it is necessary to achieve near complete degradation of phytate from meals containing few or no enhancers of iron absorption (98, 99) although, when enhan- cers of iron absorption are present in a meal, even a 50% phytate reduction can considerably improve iron absorption (100).

Low cost cereal and legume based comple- mentary foods would be appropriate foods for dephytinization, as it is usually not possible to add ascorbic acid to these products without expensive packaging. In single meal studies, complete dephytinization of cereal porridges with added phytase under controlled temperature and pH conditions increased fractional iron absorp- tion from two to twelvefold (101). In such por- ridges, with no enhancers of iron absorption, it has been recommended that the phytate to iron molar ratio should be reduced to <1:1 and, if pos- sible, to <0.4:1 (85). When commercial phytases are not available, native cereal phytases can be activated by a similar wet processing methodol- ogy. Egli et al. (102) screened 26 cereals, pseudo- cereals, legumes and oilseeds for phytase activity.

Legumes and oilseeds had low phytase activity, as did sorghum, maize and rice. Rye, triticale, wheat, buckwheat and barley had the highest phytase levels and whole wheat, whole rye and buckwheat were considered useful sources of phytase for dephytinizing complementary foods. When 10% whole wheat or rye was added to a cereal and legume based complementary food mixture, phy- tate could be degraded completely after one to two hours of wet processing (103). While sophis- ticated industrial processing methods may be too expensive and complicated for developing coun- tries, phytate degradation by traditional fermenta- tion processes (104) or germination processes (105) would seem to be a possibility. In industrialized countries, it is probably simpler and less expensive to add ascorbic acid than to degrade phytate.

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