Fe Bioavailability Research Articles

The Potential of Encapsulated Iron Compounds in Food Fortification: A Review

Iron (Fe) encapsulation has the potential to help overcome several major challenges in Fe fortification of foods. It may decrease unwanted sensory changes in fortified products and reduce interactions of Fe with food components that lower Fe bioavailability. However, the effect of encapsulation per se on Fe bioavailability is a concern. Rat studies comparing encapsulated ferrous sulfate, ferric ammonium citrate, and ferrous fumarate to non-encapsulated compounds indicate that a ratio of capsule:substrate of > or = 60:40 may decrease the relative bioavailability (RBV) of the Fe by approximately 20%. At a ratio of capsule:substrate of < or = 50:50, the RBV of encapsulated ferrous sulfate appears to be similar to ferrous sulfate. Even minor changes in capsule composition may influence Fe bioavailability. Encapsulated ferrous fumarate given with ascorbic acid as a complementary food supplement and encapsulated ferrous sulfate fortified into salt have been shown to be efficacious in anemic children. For salt fortification, further refinements in Fe capsule design are needed to increase resistance to moisture and abrasion, while maintaining bioavailability. Studies evaluating the potential efficacy of encapsulated Fe in staple cereals (wheat and maize flours) are needed. A potential barrier to use of encapsulated forms of Fe in staple food fortification is the relatively low melting point of the capsules, which may cause unwanted sensory changes during food preparation. Research and development efforts to improve the quality of coatings and their resistance to high temperatures are ongoing. Process costs for encapsulation can be high, and unless they can be reduced, may limit applications. Further research is needed to determine which encapsulation technologies are most effective in ensuring iron bioavailability from encapsulated compounds.

Iron nutrition in the UK: getting the balance right

Fe homeostasis is considered in the context of the UK diet, using information on Fe intake and status from the National Diet and Nutrition Surveys. The importance of assessing Fe availability rather than total Fe intake is discussed. Dietary and host-related factors that determine Fe bioavailability (Fe utilised for Hb production) are reviewed using information from single-meal studies. When adaptive responses are taken into consideration, foods associated with higher Fe status include meat (haem-Fe and the 'meat factor') and fruits and fruit juice (vitamin C). Foods that may have a negative impact include dairy products (Ca), high-fibre foods (phytate) and tea and coffee (polyphenols), but the effects are more apparent in groups with marginal Fe deficiency, such as women of childbearing age. Analysis of dietary intake data on a meal-by-meal basis is needed to predict the influence of changing dietary patterns on Fe nutrition in the UK. Current information suggests that in the UK Fe deficiency is a greater problem than Fe overload.

The respiratory inhibitor antimycin A specifically binds Fe(III) ions and mediates utilization of iron by the halotolerant alga Dunaliella salina (Chlorophyta).

It is demonstrated that Antimycin A (AA), a respiratory inhibitor produced by Streptomyces bacteria, forms lipophylic complexes with Fe(III) ions. Spectroscopic titration indicates that Fe(III) ions interact with 2AA molecules. At growth-limiting Fe concentrations, AA mediates Fe uptake and promotes growth and chlorophyll synthesis better than other Fe chelators in the halotolerant alga Dunaliella salina. It is proposed that AA enhances Fe bioavailability in hypersaline solutions by formation of lipophylic Fe-AA complexes which are taken-up and utilized by the algae. The results suggest that the respiratory inhibitor AA can affect Fe metabolism in microorganisms.

Genotypic Differences in Concentration and Bioavailability of Kernel‐Iron in Tropical Maize Varieties Grown Under Field Conditions#

Iron deficiency is estimated to affect over one‐half the world population. Improving the nutritional quality of staple food crops through breeding for high bioavailable iron represents a sustainable and cost effective approach to alleviating iron malnutrition. Forty‐nine late maturing tropical elite maize varieties were grown in a lattice design with two replications in three locations representing three agroecologies in West and Central Africa to identify varieties with high levels of kernel‐Fe. Bioavailable iron was assessed for some varieties selected for high Fe concentration in kernel and improved agronomic traits using an in vitro digestion/Caco‐2 cell model. Significant differences in kernel‐Fe and ‐zinc concentration were observed among varieties (P < 0.001). Kernel‐Fe levels ranged from 16.8 to 24.4 mg kg−1, while kernel‐Zn levels ranged from 16.5 to 24.6 mg kg−1. Environment did not have a significant effect on kernel‐iron and ‐zinc levels, but genotype by environment (G × E) interaction was highly significant. The genetic component accounted for 12% of the total variation in kernel‐Fe and 29% for kernel‐Zn levels. Kernel‐Fe was positively correlated with kernel‐Zn (R 2 = 0.51, P < 0.0001). Significant differences in iron bioavailability were detected among selected Fe‐rich varieties grown at one location. Mean bioavailable Fe ranged between 30% below to 88% above the reference control variety. The results indicate that genetic differences exist in kernel‐Fe and ‐Zn concentrations and Fe bioavailability. These differences may be useful in biofortification intervention programs, but additional research is needed to determine the efficacy of iron‐rich maize varieties in alleviating iron deficiency in humans. #This research was supported by USDA-ARS/USAID and IITA.

Iron body status of rats chronically exposed to cadmium and ethanol.

The present study was performed to assess the effect of simultaneous long-term exposure to cadmium (Cd) and ethanol on iron (Fe) status of male Wistar rats. The animals received drinking water containing 50 mg of Cd/l and/or 10% (w/v) ethanol for 12 weeks. Fe and Cd concentrations in serum (blood), certain tissues, urine and feces were determined by atomic absorption spectrometry. The total pool of Fe was calculated as a sum of its content in liver, spleen, kidneys, heart and brain. Fe bioavailability was evaluated based on its apparent absorption. The daily Cd intake ranged from 3.17 to 4.28 mg/kg (Cd group) and from 2.41 to 3.17 mg/kg (Cd + ethanol group); ethanol consumption ranged from 47.5 to 86.9 g/kg/24 h (ethanol group) and from 47.3 to 63.4 g/kg/24 h (Cd + ethanol group). Exposure to Cd or/and ethanol caused serious disturbances in Fe metabolism, as indicated by Fe body depletion. Both substances, applied alone and in combination, reduced the apparent Fe absorption and decreased its total pool in certain organs, and urinary excretion. However, the Cd- and ethanol-induced changes in the tissue Fe concentrations were different. Cd exposure decreased the concentration of Fe in serum, liver, spleen and femur, whereas ethanol decreased it in the spleen. In rats co-exposed to Cd and ethanol, decreased serum, spleen and brain Fe concentrations were all observed. The changes in Fe status in rats co-exposed to Cd and ethanol can be explained by the independent action of the two substances, leading to a decrease in Fe bioavailability, or by their interactions, which involves a modifying effect of ethanol on Cd turnover. The results allow the conclusion that ethanol may increase Cd accumulation, making the organism more susceptible to Fe depletion. Alcoholics thus may be at increased risk of disorders in Fe body status.

PHYSIOLOGICAL CHARACTERIZATION OF A SYNECHOCOCCUS SP. (CYANOPHYCEAE) STRAIN PCC 7942 IRON‐DEPENDENT BIOREPORTER FOR FRESHWATER ENVIRONMENTS1

The complex chemical speciation of Fe in aquatic systems and the uncertainties associated with biological assimilation of Fe species make it difficult to assess the bioavailability of Fe to phytoplankton in relation to total dissolved Fe concentrations in natural waters. We developed a cyanobacterial Fe‐responsive bioreporter constructed in Synechococcus sp. strain PCC 7942 by fusing the Fe‐responsive isiAB promoter to Vibrio harveyi luxAB reporter genes. A comprehensive physiological characterization of the bioreporter has been made in defined Fraquil medium at free ferric ion concentrations ranging from pFe 21.6 to pFe 19.5. Whereas growth and physiological parameters are largely constrained over this range of Fe bioavailability, the bioreporter elicits a luminescent signal that varies in response to Fe deficiency. A dose‐response characterization of bioreporter luminescence made over this range of Fe3+ bioavailability demonstrates a sigmoidal response with a dynamic linear range extending between pFe 21.1 and pFe 20.6. The applicability of using this Fe bioreporter to assess Fe availability in the natural environment has been tested using water samples from Lake Huron (Laurentian Great Lakes). Parallel assessment of dissolved Fe and bioreporter response from these samples reinforces the idea that measures of dissolved Fe should not be considered alone when assessing Fe availability to phytoplankton communities.

Iron bioavailability and weight gains to iron-deficient rats fed a commonly consumed tunisian meal ‘bean seeds ragout’ with or without beef and with green or black tea decoction

The Fe bioavailability and the weight gains were evaluated in rats fed a commonly consumed Tunisian meal ‘bean seeds ragout’ (BSR), with or without beef and with black or green tea decoction. The Fe bioavailability was evaluated in Fe-deficient rats by the hemoglobin repletion method and the Fe stored in the liver. The addition of beef to the BSR significantly increased the Fe bioavailability from this meal by 147% and the reserve of Fe stored in the liver by 77% (P < 0.001). In contrast, both black and green tea decoctions caused a significant decrease of the Fe bioavailability from BSR meal (−19.6 ± 4.9% and −14.9 ± 4.1%, respectively). The reserve of Fe stored in the liver was significantly lower in the BSR, the black and the green tea groups than in the positive control group (FeSO 4). The weight gains were significantly lower in the black and the green tea groups (3.9 ± 5.7 g, 13 ± 1.9 g, respectively) than in the BSR group (24.9 ± 6 g). The addition of beef to BSR meal counteracted the inhibitory effect of the kidney bean and considerably improved the Fe bioavailability and the Fe stored in the liver of rats. The green tea decoction, which constitutes an important source of antioxidant factors, had the same inhibitory effect as the black tea decoction on the Fe bioavailability from BSR meal. In addition, both black and green teas significantly reduced the weight gains, where the black tea decoction has the most effect.

Effects of Fe(III) chemical speciation on dissimilatory Fe(III) reduction by Shewanella putrefaciens.

Shewanella putrefaciens, a heterotrophic member of the gamma-proteobacteria is capable of respiring anaerobically on Fe(III) as the sole terminal electron acceptor (TEA). Recent genetic and biochemical studies have indicated that anaerobic Fe(III) respiration by S. putrefaciens requires outer-membrane targeted secretion of respiration-linked Fe(III) reductases. Thus, the availability of Fe(III) to S. putrefaciens may be governed by equilibrium chemical speciation both in the solution phase and at the bacterial cell-aqueous or cell-mineral interface. In the present study, effects of Fe(III) speciation on rates of bacterial Fe(III) reduction have been systematically examined by cultivating S. putrefaciens anaerobically on a suite of Fe(III)-organic complexes as the sole TEA. The suite of Fe(III)-organic complexes spans the range of stability constants normally encountered in natural water systems and includes Fe(III) complexed to citrate, 5-sulfosalicylate, NTA, salicylate, tiron, and EDTA. Rates of bacterial Fe(III) reduction in the presence of dissolved chelating agents correlate with the thermodynamic stability constants of the Fe(III)-organic complexes, implying that chemical speciation governs Fe(III) bioavailability. Equilibrium Fe(III) sorption experiments measured the reversible coordination of Fe(III) with S. putrefaciens as a function of cell/Fe(III) concentration, time, and activity of competing chelating agents. Results show that S. putrefaciens readily sorbs dissolved Fe(III) but that adsorption is restricted by the presence of strong Fe(III)-chelating agents. Our results indicate that dissimilatory Fe(III) reduction by S. putrefaciens is controlled by equilibrium competition for Fe(III) between dissolved organic ligands and strongly sorbing functional groups on the cell surface.

Bioavailability of natural colloid‐bound iron to marine plankton: Influences of colloidal size and aging

Iron (Fe) is mostly complexed with the organic ligands or colloids that are very abundant in natural seawater. In this study, natural colloids were isolated by ultrafiltration and radiolabeled with 59Fe. The biological uptake of radiolabeled colloid‐bound Fe of different sizes (1–10 kDa and 10 kDa‐0.2 μ) and ages (1 and 15 d) by diatoms (Thalassiosira pseudonana) and copepods (Acartia spinicauda) was then determined. The uptake of radiolabeled colloid‐bound Fe was compared with the uptake of low molecular weight (LMW) complexed Fe (&lt;1 kDa) or that of EDTA‐Fe (at a ratio of 1 : 2 for Fe :EDTA). Our study demonstrates that the colloid‐bound Fe of different sizes and ages was bioavailable to the diatoms. The uptake of colloidal bound Fe was, however, 6–31 times lower than the uptake of LMW Fe, suggesting that colloidal binding reduced Fe bioavailability to diatoms. Fe bound with small colloids (1–10 kDa) was taken up at a higher rate than Fe bound with large colloids (10 kDa‐0.2 μ) at typical colloidal organic carbon concentrations. The uptake of colloid‐bound Fe was also much higher when the Fe had been bound with the colloids for 1 d rather than for 15 d. Differences in the colloidal organic carbon concentration did not appreciably affect the uptake of colloid‐bound Fe by the diatoms. Similarly, copepods accumulated colloid‐bound Fe at a much higher rate when the Fe was associated with small colloids rather than with large colloids. Direct ingestion of colloidal particles by the copepods appeared to be negligible. In both diatoms and copepods, Fe uptake may involve its dissociation from the colloids before being accumulated by the organisms. The study therefore demonstrates that colloid‐bound Fe is less available for marine phytoplankton and that colloidal size and thus the colloidal speciation may be critical in controlling colloid‐bound Fe uptake by aquatic organisms.

Investigation of the mechanisms affecting Cu and Fe bioavailability from legumes: role of seed protein and antinutritional (nonprotein) factors.

Chemical composition and content in polyphenols, phytic acid, and dietary fiber of whole cooked common bean (Phaseolus vulgaris L.) and faba bean (Vicia faba L.) and of soluble and insoluble fractions separated from them were determined. Simultaneous determination of Cu, Fe, and protein bioavailability in the small intestine of rat was carried out in single-dose, short-term (1 h) experiments. After cooking, about 80% of seed components (on a weight basis) of either legume was recovered in the precipitate (insoluble fraction) after extraction with water. Protein, lipid, starch, dietary fiber, and polyphenols underwent the most severe insolubilization, together with more than 70% of total Cu and Fe. Cu, Fe, and protein bioavailability showed a similar trend (i.e., the lower the protein, the lower the Cu and Fe availability). Availability of proteins, Cu, and Fe in the insoluble fractions were the lowest, but Cu bioavailability was higher than that of Fe in all fractions. The results provide evidence that the heat-induced insolubilization process adversely affects not only protein but also Cu and Fe bioavailability from legumes and that polyphenols are likely to be a major inhibitor on absorption.

Meat enhances nonheme iron absorption in pigs

Human subjects absorb heme iron (Fe) more efficiently than nonheme Fe under most conditions. Meat enhances nonheme Fe absorption from most diets. It is not known whether these effects also occur in the pig, a promising model for human Fe absorption studies. The objective of this study was to compare Fe bioavailability from diets containing nonheme Fe (NHI), nonheme Fe with meat (NHI/M) and heme Fe (HI) in the weanling pig. Iron bioavailability was measured by hemoglobin (Hb) repletion assay. Diets were formulated to contain 150 mg Fe/kg diet. Nonheme Fe was supplied as ferric citrate and heme Fe as dried animal red blood cells. Pigs were made anemic by reducing the standard Fe injection at birth to 30 mg and feeding a low Fe transition diet post-weaning until age 41 days. At 41 days of age, pigs were assigned to 3 groups of 8 animals such that mean Hb concentration and body weight of each group were nearly equal. Groups were randomly assigned to 1 of 3 repletion diets. After 7 days feeding, Hb repletion efficiency (HRE) was 21.8% in pigs fed the NHI/M diet compared to 11.2% and 9.1% in pigs fed the NHI or HI diets, respectively. The results presented here demonstrate that, in Fe-deficient weanling pigs, meat increases nonheme Fe bioavailability from corn-based diets while heme Fe, supplied by dried animal red blood cells, is no more bioavailable than Fe from ferric citrate. The results of this study provide further evidence of the validity of the pig model for studying food Fe bioavailability.

The effect of calcium on iron absorption

The experimental and epidemiological evidence demonstrating that Ca inhibits Fe absorption was reviewed, with the objectives of estimating the potential impact of variations in Ca intake on dietary Fe bioavailability and of providing some guidelines for predicting the effects on Fe status of recent recommendations for higher dietary Ca intake. In animal models Ca salts reduced both haem- and non-haem-Fe absorption, the effect being dependent on the amount of Ca administered rather than the Ca:Fe molar ratio; dairy products had a variable effect; factors other than Ca may have been important. In single-meal human absorption studies, both haem- and non-haem-Fe absorption was inhibited by Ca supplements and by dairy products, the effect depending on the simultaneous presence of Ca and Fe in the lumen of the upper small intestine and also occurring when Ca and Fe were given in the fasting state. The quantitative effect, although dose dependent, was modified by the form in which Ca was administered and by other dietary constituents (such as phosphate, phytate and ascorbic acid) known to affect Fe bioavailability. The mechanism by which Ca influences Fe absorption has not been elucidated. The effects of factors that modulate Fe bioavailability are known to be exaggerated in single-meal studies, and measurements based on several meals are more likely to reflect the true nutritional impact. The results of most multiple-meal human studies suggest that Ca supplementation will have only a small effect on Fe absorption unless habitual Ca consumption is very low. Outcome analyses showed that Ca supplements had no effect on Fe status in infants fed Fe-fortified formula, lactating women, adolescent girls and adult men and women. However it should be noted that the subjects studied had adequate intakes of bioavailable Fe and, except in one study, had relatively high habitual Ca intakes. Although cross-sectional analyses in Europe have shown a significant inverse correlation between Ca intake (derived primarily from dairy foods) and Fe stores, the quantitative effect was relatively small. The general conclusion is that dietary Ca supplements are unlikely to have a biologically significant impact on Fe balance in Western societies unless Ca consumption is habitually very low; however, increased consumption of dairy products may have a small negative effect that could be functionally important in pregnancy if Fe supplements are not taken. It is uncertain whether the inverse relationship between consumption of dairy products and Fe status is due entirely to increased Ca intake; substitution of milk proteins for meat may also have negative effects on Fe balance.

Erythrocyte incorporation of iron by infants: iron bioavailability from a low-iron infant formula and an evaluation of the usefulness of correcting erythrocyte incorporation values, using a reference dose or plasma ferritin concentrations

Bioavailability of iron (Fe) from a low-Fe infant formula was determined by erythrocyte incorporation of 58Fe 14 d after administration in ten healthy, non-Fe-deficient infants. Two feeding protocols were compared, with each infant acting as his/her own control. At 140 and 154 d of age, infants were fed 1000 g of 58Fe-labelled formula (1.44 mg total Fe/1000 g) as six feeds over 24 h (Protocol A) or as two feeds/day on three consecutive days (Protocol B). A water solution with 57Fe and ascorbic acid was given separately as a reference dose in both study protocols. Erythrocyte incorporation of 58Fe and 57Fe was determined by thermal ionisation mass spectrometry. Geometric mean 58Fe incorporation was 7.6% (range 3.3-13.5%) with Protocol A as compared to 10.6% (range 6.7-18.6%) with Protocol B (P = 0.05); paired t test. Inter-individual variability of 58Fe was not reduced by correcting for the incorporation of 57Fe from the reference dose, or by correcting for plasma ferritin concentration. Fractional erythrocyte incorporation of Fe from low-Fe infant formula was in the same range as our earlier published data on erythrocyte incorporation of Fe from human milk extrinsically labelled with 58Fe (Davidsson et al. 1994a). The methodological evaluations included in this study clearly indicate the importance of using standardised study protocols when evaluating Fe bioavailability in infants. Corrections of erythrocyte incorporation data based on plasma ferritin or erythrocyte incorporation of Fe from a reference dose were not found to be useful.

Genetic Selection for Enhanced Bioavailable Levels of Iron in Bean (Phaseolus vulgaris L.) Seeds

The bioavailability of Fe from 24 select genotypes of bean (Phaseolus vulgaris L.) seeds containing a range of concentrations of Fe, myo-inositol pentaphosphate plus phytic acid (IP5+IP6), and tannins was studied using a rat model. Bean accessions, selected from field trials for their variations in Fe, phytate, and tannin seed concentrations, were grown in a greenhouse in nutrient solutions radiolabeled with (59)Fe. Mature seeds were autoclaved and lyophilized. Test meals (containing 1 g of dried bean, 0.5 g of sucrose, and 1 g of basal Fe-deficient diet) were fed to marginally Fe-depleted weanling rats over a 3-h period; rats were radioassayed in a gamma-spectrometer immediately after feeding and daily thereafter for the next 10 d. Radioiron retention data were used to calculate percent Fe absorption (i.e., Fe bioavailability) from the meals. Seed Fe concentrations ranged from 52 to 157 microg g(-)(1) dry weight. There was a tendency to also select for higher Zn concentrations in the beans when selecting for high Fe concentrations. The Fe bioavailability to rats from test meals depended on the genotype and varied from 53% to 76% of the total Fe. Bean genotypes with higher seed Fe concentrations resulted in increased amounts of bioavailable Fe to rats. There was no significant correlation between the Fe concentration in different bean genotypes and Fe bioavailability to rats attributable to variations in IP5+IP6 or tannins, even though these antinutrients varied widely (i.e., from 19.6 to 29.2 micromol of IP5+IP6 g(-)(1) and from 0.35 to 2.65 mg of tannins g(-)(1)) in the test meals. Other unknown seed factors (i.e., antinutrients or promoter substances) may be contributing factors affecting Fe bioavailability from bean seeds.

Erratum: An investigation into iron-stimulated phytoplankton productivity in epipelagic Lake Erie during thermal stratification using trace metal clean techniques

We tested the hypothesis that phytoplankton productivity in pelagic Lake Erie is limited by low Fe bioavailability during the period of thermal stratification. Iron enrichment (20 and 200 nM Fe) of...

An investigation into iron-stimulated phytoplankton productivity in epipelagic Lake Erie during thermal stratification using trace metal clean techniques

We tested the hypothesis that phytoplankton productivity in pelagic Lake Erie is limited by low Fe bioavailability during the period of thermal stratification. Iron enrichment (20 and 200 nM Fe) of water sampled from the eastern basin surface water (5 m depth) in July 1996 revealed a dramatic 180 and 30% increase in the standing crop of the picoplankton (0.2-2 µm) and nanoplankton (2-20 µm) size fractions, respectively. Light-saturated rates of photosynthesis for picoplankton increased 2.8 times that of the controls within 24 h. In contrast, simultaneous P and Fe enrichment experiments carried out in July 1997 and August 1998 with water samples from three pelagic stations revealed that P enrichment alone stimulated phytoplankton growth, although at several stations, phytoplankton yield was greater in combined P- and Fe-amended experiments relative to P-enriched treatments. Periodogram analysis of meteorological buoy wave height data and heat budgets calculated from thermal profiles in the eastern basin revealed important interyear differences in precruise conditioning of the epilimnion. Low-frequency, turbulent mixing events that characterized the 30-day precruise period in the years 1997 and 1998 relative to 1996 may have prevented Fe-stressed conditions in the phytoplankton community studied in 1997 and 1998.

Mechanisms of absorption of caseinophosphopeptide bound iron

Binding iron (Fe) to the 1-25 caseinophosphopeptide obtained from enzyme hydrolysis of β casein (β CPP) improves Fe bioavailability in the rat. To assess the mechanisms involved in its absorption, a perfused, vascularized duodenal rat loop model was used in controls and in Fe-deficient (bleeding of 25% blood volume) rats. Inhibitors of oxidative phosphorylation [2-4 dinitrophenol (DNP)] and/or of endocytosis [phenylarsine oxide (PAO)] were added to the perfusion solution containing 50 μM Fe as β CPP bound Fe (Fe-β CPP) or gluconate (Fe Gluc). Fe-β CPP enhanced Fe uptake, reduced mucosal storage, and improved net absorption both in controls and in deficient animals. DNP reduced uptake, mucosal storage, and net absorption by the same percentage in Fe-β CPP and Fe Gluc perfused rats in both control and Fe-deficient animals. PAO decreased uptake, mucosal storage, and net absorption of Fe-β CPP but not of Fe Gluc. At the end of the experiment Fe serum levels were increased only in Fe Gluc animals. These results confirm the improved bioavailability of β CPP bound Fe. They suggest that at least part of its absorption can occur by a different pathway than usual Fe salts. Fe-β CPP can be taken up by endocytosis and absorbed bound to amino acids or peptides.

Phytase improves iron bioavailability for hemoglobin synthesis in young pigs.

Dietary phytase supplementation improves bioavailabilities of phytate-bound minerals such as P, Ca, and Zn to pigs, but its effect on Fe utilization is not clear. The efficacy of phytase in releasing phytate-bound Fe and P from soybean meal in vitro and in improving dietary Fe bioavailability for hemoglobin repletion in young, anemic pigs was examined. In Exp. 1, soybean meal was incubated at 37 degrees C for 4 h with either 0, 400, 800, or 1,200 units (U) of phytase/kg, and the released Fe and P concentrations were determined. In Exp. 2, 12 anemic, 21-d-old pigs were fed either a strict vegetarian, high-phytate (1.34%) basal diet alone, or the diet supplemented with 50 mg Fe/kg diet (ferrous sulfate) or phytase at 1,200 U/kg diet (Natuphos, BASF, Mt. Olive, NJ) for 4 wk. In Exp. 3, 20 anemic, 28-d-old pigs were fed either a basal diet with a moderately high phytate concentration (1.18%) and some animal protein or the diet supplemented with 70 mg Fe/kg diet, or with one of two types of phytase (Natuphos or a new phytase developed in our laboratory, 1,200 U/kg diet) for 5 wk. In Exp. 2 and 3, diets supplemented with phytase contained no inorganic P. In Exp. 1, free P concentrations in the supernatant increased in a phytase dose-dependent fashion (P<.05), whereas free Fe concentrations only increased at the dose of 1,200 U/kg (P<.10). In Exp. 2 and 3, dietary phytase increased hemoglobin concentrations and packed cell volumes over the unsupplemented group; these two measures, including growth performance, were not significantly different than those obtained with dietary supplemental Fe. In conclusion, both sources of phytase effectively degraded phytate in corn-soy diets and subsequently released phytate-bound Fe from the diets for hemoglobin repletion in young, anemic pigs.

Iron binding by tannic acid: Effects of selected ligands

Foods with high tannin content inhibit Fe absorption from meals. Presumably, tannins form complexes with Fe in the intestinal lumen reducing Fe bioavailability. Our objective was to assess the influence of various ligands on Fe binding by tannic acid in vitro. Different mixing sequences were employed to determine whether the ligands could prevent Fe from binding to the tannin or could remove Fe already bound. Solutions of Fe +3 (FeC 3 in 0.1 n HCl), ligand (ethylenediamine-tetraacetic acid (EDTA), ascorbic acid, nitrilotriacetic acid (NTA) or citric acid) and tannic acid (200 μg ml −1) in pH 4.4 acetate buffer were combined to obtain a final ligand:Fe molar ratio of 1:1 (89 μ m). Three mixing sequences were followed: sequence I (Fe and ligand combined and added to tannin); sequence II (tannin and ligand combined and added to Fe); and sequence III (Fe and tannin combined and added to ligand). Fe-tannin binding was assessed by measuring absorbance at 560 nm (visible absorbance maximum) at 15 s intervals for 5 min. An Fe-tannin mixture without ligand served as the control. With EDTA, sequence I resulted in no binding. In sequence II and III, there was some binding initially, but it decreased with time. With ascorbic acid, sequence I resulted in no binding. In sequence II and III, initial binding was slightly lower than the control. Binding did not change with time. With NTA, initial binding varied with the sequence, but converged with time to a value slightly lower than the control. Citric acid did not affect binding regardless of addition sequence. These findings suggest that ligands with high affinity for Fe (e.g. EDTA) can prevent Fe from binding tannin and can remove Fe already bound. Ligands with lower affinity (e.g. citric acid) have little effect. The implications are that EDTA, ascorbic acid and NTA may affect Fe bioavailability from meals containing tannins.

Bioavailability of iron in cottonseed meal, ferric sulfate, and two ferrous sulfate by-products of the galvanizing industry

Iron depletion-repletion assays were carried out with young chicks to establish Fe bioavailability values for Fe2(SO4)3.7H2O (22.7% Fe), Fe-ZnSO4.H2O (20.2% Fe, 13.0% Zn), Zn-FeSO4.H2O (20.2% Zn, 14.2% Fe), and cottonseed meal (200 mg Fe/kg). Standard hemoglobin response curves were established using feed-grade FeSO4.H2O (28.8% Fe) or reagent-grade FeSO4.7H2O (20.1% Fe) as standards such that relative bioavailability (RBV) could be assessed for the experimental sources of Fe. Weight gain, hemoglobin, and hematocrit responded linearly (P < 0.05) to Fe supplementation in all assays. Using hemoglobin as the response criterion, slope-ratio calculations established Fe RBV values of 126% for Fe-ZnSO4.H2O and 93% for Zn-FeSO4.H2O. The 126% value for Fe-ZnSO4.H2O was greater (P < 0.05) than the FeSO4.H2O standard (100%), but the 93% value for Zn-FeSO4.H2O was not different (P > 0.10) from the standard. However, evaluation of all criteria of response (hemoglobin, hematocrit, weight gain) suggested that neither Fe-ZnSO4.H2O nor Zn-FeSO4.H2O had different Fe RBV values than FeSO4.H2O. Standard-curve calculations were used for assessment of Fe RBV in Fe2(SO4)3.7H2O and cottonseed meal, as only a single level of Fe addition was studied for each of these products. Iron RBV in Fe2(SO4)3.7H2O was estimated to be 37%, whereas Fe RBV in cottonseed meal was found to be 56%. Both of these values were lower (P < 0.05) than the FeSO4 standard. The data suggest that the two new products, representing combinations of FeSO4.H2O and ZnSO4.H2O by-products of the galvanizing industry, are excellent sources of bioavailable Fe, whereas ferric sulfate and cottonseed meal are relatively poor sources of usable Fe.