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Supplement: Nutrient Composition for Fortified Complementary Foods

Zinc and Copper: Proposed Fortification Levels and Recommended Zinc Compounds¹

School of Natural Sciences, University of Queretaro, Mexico

²To whom correspondence should be addressed. E-mail: jlrosado{at}avantel.net.mx.

	ABSTRACT

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 
Micronutrient fortification of foods is now a highly relevant tool worldwide for overcoming micronutrient deficiency. Recent data show that subclinical zinc deficiency is widespread; in Mexico a national survey showed that 25% of children less than age 11 y had plasma zinc concentrations below 10.0 µmol/L (65 µg/dL). Copper deficiency in populations is unknown but copper supplementation is recommended to accompany zinc supplementation. Of the foods available for fortification, staple cereals are very good candidates for reducing micronutrient deficiencies. Because of its higher stability and lower cost, we recommend fortification of cereal flours with zinc oxide, which is absorbed as well as the less stable and more expensive forms of zinc. Depending on the amount of the food that is expected to be eaten, zinc fortification of staple foods could be 20–50 mg/kg of flour. For copper fortification the safer compound is copper gluconate. Copper sulfate is significantly less expensive, but an evaluation of potential physicochemical reactions that affect the final food product is recommended. The suggested amount of copper added to staple foods is 1.2–3.0 mg/kg of flour. For food supplements designed as part of supplementation programs to reduce micronutrient deficiency in children less than age 3 y, a dose of the final product (usually 40–50 g) should contain 4–5 mg of zinc and 0.2–0.4 mg of copper depending on the habitual diet, magnitude of deficiencies and period of supplementation.

KEY WORDS: • zinc • copper • food fortification • staple foods • mineral bioavailability

The magnitude of marginal zinc deficiency in developing countries is unknown, but the results of many studies, most of which have been conducted within the past few years, attest to widespread zinc deficiency in children in different regions of the world. The clinical signs of marginal zinc deficiency are depressed immunity, impaired taste and smell, onset of night blindness, impairment of memory and decreased spermatogenesis (1,2). Functional consequences of marginal zinc deficiency have also been documented in populations in developing countries. Zinc supplementation in children is associated with substantial reduction in the duration and severity of diarrhea and pneumonia in developing countries (3,4). Although supported by only a few studies, there are some suggestions that zinc supplementation might also improve the neuropsychologic performance of children with marginal zinc deficiency (5).

The incidence of zinc deficiency in Mexican children is high. Table 1 shows the percentage of children with serum zinc concentrations < 10.0 µmol/L (65 µg/dL). Children are divided by age and by rural and urban population (6); 25% of all children between ages 0 and 11 y were deficient. Rural areas had a higher incidence of zinc deficiency (40%) than did urban areas (18%).

The average per capita intake of corn in Mexico is 120 kg/y, which is the highest per capita intake in the world. The corn tortilla is the staple food eaten by most of the population in significant amounts, which makes it a good vehicle for micronutrient addition. Corn tortillas are prepared from corn flour. A formula recently developed for corn flour fortification contains zinc and other micronutrients (8).

	Nutrient fortification of complementary foods

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 
The addition of minerals to foods began in South America in 1833 when Boussinggault, a French chemist, recommended the addition of iodine to salt as a public measure to prevent goiter. The addition of iodine to salt has been one of the most successful uses of food fortification in several countries. The number of foods fortified with minerals and other nutrients is continuously increasing.

Food fortification is generally carried out to restore nutrients that are lost during harvesting, refinement, storage, cooking or processing of foods. This process is known as nutrient restoration of foods and is applied to many foods, such as cereals, for which many countries have regulatory laws. Food fortification may also be a strategy for increasing the intake of some nutrients that are known to be deficient in specific population groups, and thus fortification contributes to reducing the incidence of nutrient deficiencies, especially of vitamins and minerals. Recommendations in this paper are given for the addition of zinc and copper to food to reduce micronutrient deficiencies.

	Evaluation of vehicles for nutrient addition

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 
Zinc and copper can be added to many foods including milk, cereals, flours, fruit juices, sugar and water. When the objective of food fortification is to increase the intake of specific nutrients that are known to be deficient in a population, the selection of an adequate vehicle is crucial for program success. The following characteristics should be met when choosing a vehicle for such purposes (9): 1) Food chosen as a vehicle should be ingested by the target population in sufficient quantities and with a small variability in the amount ingested. 2) The fortified food should be stable and physicochemical properties such as appearance, texture and flavor should not change when the nutrient is added. 3) The added nutrient should be relatively bioavailable and well tolerated. 4) Fortification of the food should not significantly increase its price. 5) Fortification should be carried out with available ingredients and technology and preferably at low cost.

	Zinc fortification of foods

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 
Successful fortification of a food depends on the fortificant acting in a relatively benign manner in the food. Unfortunately, this level of chemical inertness is often associated with insolubility and relatively poor bioavailability. Minerals are chemically reactive substances, not the inert compounds they are often thought to be. This reactivity becomes particularly apparent in a food in the presence of moisture, when reactions may occur with free radicals, other food components and oxygen. Any of these reactions could result in undesirable changes in color, flavor and appearance or could affect nutrient stability. Potential changes in physicochemical and functional properties as well as changes in nutrient content during the required shelf life of fortified foods need to be evaluated before any firm recommendation in dose and source of minerals is made.

In the United States, minerals used for fortification of foods are classified by the Food and Drug Administration as generally recognized as safe (GRAS). GRAS classification may be based on scientific procedures that use the same quantity and quality of evidence required to obtain approval for a food additive or the substance may have demonstrated evidence through its use in food (11). There are currently five zinc compounds listed as GRAS that may be used in fortifying foods: zinc sulfate, zinc chloride, zinc gluconate, zinc oxide and zinc stearate (11). Of these compounds, zinc oxide is by far the most commonly used. Data compiled by the National Academy of Sciences on the amount of zinc compounds used by food manufacturers in the United States are shown in Table 2(12,13). Zinc oxide is the compound most commonly used and its consumption has increased significantly.

	Bioavailability of added compounds

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

To make judgments about bioavailability and functionality so that the most adequate compound may be chosen, it is important to understand the major physicochemical properties that affect bioavailability and how they may be influenced by food environment, processing and storage. These properties have been discussed by Clydesdale (10) and include solubility, charge density, reduction potential and pH, complex formation and the effect of processing.

Solubility.

Even though it is believed that minerals must be soluble in the intestine to be absorbed, not all soluble minerals are absorbed. Because solubility depends on the type and strength of the chemical bonds, all chemical reactions occurring in the food environment must be understood for mineral solubility and bioavailability to be understood.

Charge density.

Charge density is important to cell permeability because the rate at which a molecule diffuses across the lipid bilayer of the cell membrane depends on its size and degree of polarity. Small nonpolar molecules readily dissolve in the lipid bilayer and therefore diffuse across it.

Reduction potential and pH.

The transition metals including zinc and copper exist in solution as hydrates rather than ions. As pH is raised, the hydrates lose protons and form the less soluble or insoluble hydroxides. This means that acidic foods may be the logical choice for fortification with minerals.

Complex formation.

Solubility may be due to the inherent chemical nature of the mineral, its immediate environment and the presence of food components that will bond with the mineral to form a complex or chelate. Enhancers and inhibitors act as mineral-binding agents, and it is merely the nature of the bond that they form and the solubility of their complex that determine their role as either an enhancer or an inhibitor.

Effect of processing.

Processing of food may influence mineral bioavailability depending on its effect on any of the factors previously discussed.

	Absorption of zinc compounds added to corn flour

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 
Even though zinc oxide is the zinc compound that has been most widely used for zinc fortification of foods (Table 2), some authors have suggested that this compound should be avoided because of its lower solubility (14,15). As stated previously, solubility is only one important factor that affects bioavailability. The use of zinc oxide has some advantages over the use of other zinc compounds because it is more stable and does not significantly change the food to which it is added. Zinc oxide is also much less expensive than other zinc compounds (Table 3). Zinc sulfate is the second most used source of zinc and is more soluble than zinc oxide. Its stability depends on the food matrix to which it is added. To compare the absorption of zinc oxide with zinc sulfate, we conducted a study in 10 women using stable isotopes of zinc in corn tortilla (unpublished observations). A summary of the fractional absorption results are shown in Table 4; the fractional absorption of zinc oxide added to corn tortillas was similar to that of zinc sulfate.

	Mineral interactions: zinc, copper and iron

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

Another concern is that many zinc-fortified foods also contain added iron. Whittaker (11) reviewed studies testing the effect of iron on zinc absorption and found that in many studies iron decreased zinc absorption when added to water, but only one study showed a negative effect of iron on zinc absorption when added to foods. Sandstrom et al. (19) showed a negative effect when iron was added in a 25:1 ratio with zinc. Corn flour in Mexico is being fortified with zinc (20 mg/kg) and iron (30 mg/kg). To evaluate the potential negative effect of iron on zinc absorption, we carried out a study using stables isotopes of zinc (unpublished observations). Fractional absorption of zinc in 10 women consuming tortillas fortified with zinc to which different amounts of iron were added showed no effect of iron fortification (Table 5).

	Copper fortification of foods

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

	Amount of nutrient considered for fortification

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 
Amounts of fortificant to be added should be carefully evaluated, especially for minerals that may be hazardous to humans at some level of intake. The decision should be based on knowledge of the total amount of the fortified food that could be eaten and the amounts of the mineral in other foods that are eaten. The intake of some foods is highly variable in a population; this is the case for tortillas in Mexico. When variability of intake is high, it is preferable to be conservative in the amounts of mineral that are added to foods to avoid the risk of excessive intakes in a proportion of the population that regularly eats the fortified food in higher amounts. Table 6 shows recommended intakes and Tolerable Upper Intake Levels for zinc and copper suggested by the Dietary Reference Intakes of the U.S. National Academy of Sciences (20). Other countries where the intake of zinc and iron is associated with foods and diets with lower bioavailability may have their own recommendations for intake of these nutrients. These values could be used to help decide how much copper and zinc should be added to a specific food, an amount that will ultimately depend on the food vehicle and the purpose of food fortification.

	Conclusions and recommendations

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 
Because of its higher stability and lower cost, we recommend fortification of cereal flours with zinc oxide, which has been demonstrated to have the same absorption as the less stable and more expensive forms of zinc. Depending on the amount of the food that is expected to be eaten, zinc fortification of staple foods could be done in an amount equivalent to 20–50 mg/kg of flour. For copper fortification, copper gluconate is the safer compound. Because it is significantly less expensive, copper sulfate could be used, but an evaluation of potential physicochemical reactions that affect the final food product is recommended. The amount of copper suggested for staple foods is 1.2–3.0 mg/kg of flour. For food supplements designed as part of supplementation programs to reduce micronutrient deficiencies in small children, one dose of the final product (usually 50 g), should contain 4–5 mg of zinc and 0.2–0.4 mg of copper depending on the habitual diet, magnitude of deficiencies and period of supplementation.

	FOOTNOTES

 
¹ Presented as part of the technical consultation "Nutrient Composition for Fortified Complementary Foods" held at the Pan American Health Organization, Washington, D.C., October 4–5, 2001. This conference was sponsored by the Pan American Health Organization and the World Health Organization. Guest editors for the supplement publication were Chessa K. Lutter, Pan American Health Organization, Washington, D.C.; Kathryn G. Dewey, University of California, Davis; and Jorge L. Rosado, School of Natural Sciences, University of Queretaro, Mexico.

	LITERATURE CITED

TOP ABSTRACT Nutrient fortification of... Evaluation of vehicles for... Zinc fortification of foods Bioavailability of added... Absorption of zinc compounds... Mineral interactions: zinc,... Copper fortification of foods Amount of nutrient considered... Conclusions and recommendations LITERATURE CITED

 

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