Food Product Design: Ingredient Insight - March 2005 - Pumping Iron

March 2005

Pumping Iron

By R. J. FosterContributing Editor

Iron is one of the most-important compounds in our bodies. Primarily functioning in oxygen transport, it's also essential in numerous biochemical pathways and as part of hundreds of proteins and enzymes.

Yet according to the World Health Organization (WHO), iron deficiency is one of the world's primary nutritional disorders. While Americans' iron intake meets the average person's needs, several segments of our population -- including pregnant women, infants, growing children, teenage girls and even athletes trying to improve performance -- need increased iron in their diets. The recommended daily allowance (RDA) for iron ranges from 8 to 18 mg per day, depending on gender and age. Men and women need about 18 mg per day.

In our bodies, iron is present in two major forms. Functional heme iron comes mainly from the hemoglobin present in meat, poultry and fish, and is found in our own hemoglobin and enzymes. Transport and storage falls on nonheme iron, obtained from plants, dairy products, meat and iron salts added to foods. The enzyme heme-oxygenase releases the iron from hemoglobin, resulting in very efficient absorption of ingested heme iron, about 25%. Inorganic iron must be in the ferrous, Fe2+ form for absorption, which reduces the overall absorption of these compounds to 5% to 10%.  

Easy come, easy go When considering iron fortification, developers must carefully analyze the application and balance form with function. What seems like the obvious choice is not always correct, as Ram Chaudhari, senior vice president of research and development, Fortitech Inc., Schenectady, NY, illustrates: "Ferrous sulfate is the most soluble and bioavailable form of iron there is. It is also the most problematic."  

Oxidation during normal storage of iron-fortified items converts ferrous iron, Fe2+ to the ferric form Fe3+. Ferric complexes can cause the formation of off-colors and precipitates, limiting the use of these compounds in lightly colored foods and beverages. Ferrous sulfate added to infant cereals can cause gray or green color formation, blue if bananas are included. Salt fortified with water-soluble compounds, such as ferrous sulfate, can turn yellow or brown.    

Flavor limitations are also a concern, especially in otherwise neutral-tasting items with a pH greater than 4.5. Water-soluble iron can impart a metallic taste or, through catalysis of oxidation reactions, accelerate the onset of rancidity, creating off-flavors and reducing shelf life. More-acidic conditions reduce the occurrences of these adverse reactions and can mask metallic notes with sourness.   

Ferrous gluconate and ferrous lactate are water-soluble compounds that exhibit similar bioavailability as ferrous sulfate, with additional benefits. "Ferrous lactate and ferrous gluconate are iron sources that are soluble enough to reach generally applied fortification levels, with the added benefit that the lactate and gluconate sequester the iron," notes Sharon Rokosh, senior market development specialist, PURAC America, Inc. Keeping the iron from reacting with its environment limits adverse color and oxidative reactions. She adds that these products have found worldwide acceptance as a fortificant in infant formula, yogurt and fruit juices, and as a color fixative in black olives.  

Using products such as these in conjunction with a ferrous sulfate brings interesting options to developers. "Blending forms like gluconate or lactate with the sulfate form can give improved stability without sacrificing the nutritional and economical benefits you have with the sulfate," says Chaudhari.

Some compounds are insoluble in water, but soluble under acidic conditions. They can provide similar absorption as the water-soluble products as they dissolve in the stomach, only more slowly than their water-soluble counterparts. Not without potential problems, ferrous fumarate and ferrous citrate can both cause off-colors in foods, like chocolate milk, for example, although the extent of discoloration will be less than with ferrous sulfate.  

Forms insoluble in water rely on dissolution in the stomach for absorption. While this is not normally a concern for healthy adults, studies have shown reduced absorption in children and individuals whose gastric-acid secretion might be lacking due to infection or other nutrient deficiency.    

Tough as iron Iron compounds that are poorly soluble in water and acid exhibit excellent stability. Because these products never completely dissolve, they exhibit much lower and more-variable bioavailability. This category includes the "elemental iron" or "reduced-iron" powders, terms that actually refer to five types of compounds distinguished by their preparation: electrolytic, H-reduced, CO-reduced, atomized and carbonyl. Low cost and very low occurrence of adverse reactions makes these compounds some of the most prevalently used worldwide. Their performance is difficult to predict, though, as bioavailability hinges on solubility in gastric juice, which can vary with meal composition. Furthermore, solubility under given gastric conditions depends on particle characteristics, like size, shape, porosity, etc.    

Elemental iron's dark-gray color and insoluble nature can limit its use in lightly colored foods. A commonly used fortificant in breakfast cereals, elemental iron can be observed as gray flecks, or slough off when milk is applied. The displaced iron collects in the milk -- an aesthetic negative, yet a delightful justification for cereal bowl milk-slurpers of all ages. Reducing the size of the particles reduces the visibility of the iron particles, along with improving bioavailability. Another option for enriching pale products is ferric orthophosphate, also referred to as "white iron." It's often the iron fortificant of choice for rice applications.  

Iron protection program Water-soluble and acid-soluble iron compounds can be microencapsulated with hydrogenated oils, maltodextrins or ethyl cellulose to provide some protection from unwanted interactions. Typically these coatings are heat labile, melting within the range of 50?C to 70?C (122?F to 158?F). While this would exclude their use in some types of applications, like a pasteurized beverage, the encapsulated material could be an excellent choice for enriching a powdered beverage, keeping the iron from interacting with the components of the powder during storage.    

While encapsulation protects foods from added iron, certain compounds hinder absorption of iron from fortified items. Phytic acid, present in cereal and legume-based foods; phenolic compounds from sorghum and chocolate-based products; and certain milk and soy proteins are all potent inhibitors of iron absorption.  

Addition of ascorbic acid is one of the most-common approaches to enhancing iron absorption. It's been shown to dramatically improve absorption of iron -- native and added -- that dissolves in the stomach. Reducing ferric iron to the ferrous state maintains solubility and subsequent absorption even as pH rises beyond the stomach. In general, an ascorbic-acid-to-iron ratio of 2:1 will improve absorption in milk products and those with low phytate levels. Products high in phytates or phenolics will require ratios upward of 4:1. And ascorbic acid's sensitivity to heat and oxidative degradation can result in significant losses through processing and storage.  

Preformed iron complexes provide improved availability of otherwise poorly absorbed iron. Chelates are one such complex, in which a metal atom and an organic molecule, or ligand, are bonded together. Ethylene diamine tetraacetic acid (EDTA) is a hexadentate chelate that has the ability to bind with almost every metal in the periodic table.

Chaudhari suggests that EDTA chelation provides an excellent source of iron that will not participate in the discoloration reactions seen with other sources of similar bioavailability. In the stomach and intestinal   tract, chelation protects the iron from the aforementioned inhibitors and can bind unprotected iron, forming       insoluble, nonabsorbable complexes. Sodium iron EDTA (NaFeEDTA)     has been shown to be two to three times more absorbable than ferrous sulfate in the presence of phytic acid, making it especially useful in flour-base items.

Another innovative approach to improving the absorption of iron combines particle-size reduction and advanced coating materials. Bill Driessen, technical sales manager, Taiyo International Inc., Minnea- polis, describes the approach as "a micronized and microencapsulated ferric pyrophosphate, originally developed to address the difficult challenges of fortifying beverage products." With particle sizes averaging 0.3 mm, and a protective coating that allows the iron to reach the lower intestine, it yields a bioavailability rivaling that of ferrous sulfate without adversely affecting appearance or taste. "We've seen great success in dairy beverages, yogurt smoothies, fruit juices and sport drinks," he continues, "as well as applications not previously considered, such as bread dough, rice, processed cheese, sausages and sweets."  

Fortification with iron is far more complicated than it initially sounds. Chaudhari concludes: "Optimization of a plan for iron enrichment begins with understanding the food product and the desired label claims, reviewing the processing parameters, and then determining the best source or sources of iron to use, as well as antioxidants or enhancers that should be added."

R. J. Foster has more than a decade of experience in research & development and technical service in the food industry. He is a freelance writer specializing in technical communications, and can be reached at [email protected].

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