Dust-borne iron plays an important role in modulating climate. Iron is a necessary micronutrient, crucial to growth of phytoplankton that fix atmospheric carbon dioxide into organic carbon. Bioavailable iron is relatively scarce in the oxygenated ocean due to the low solubility of oxidized iron, and it limits primary production in many ocean regions. Increased dust-borne iron reaching iron-limited regions is associated with lower atmospheric carbon dioxide, due to more complete utilization of new nitrogen (the biological pump). Since iron solubility in the ocean is low, most iron is in the solid phase, including particles and colloids from dust and insoluble iron oxyhydroxide minerals that precipitate when there is high dissolved iron not chelated by organic ligands. The chemical form (speciation) of iron greatly impacts its solubility, yet the mechanisms of solid-phase iron utilization by diatoms and the impact of solid-phase iron speciation on dust-borne iron bioavailability are not well known. Glacial activity has been associated with highly soluble minerals, but the impact of glacial activity on bioavailable iron supply has not previously been quantified. In this dissertation, I investigate the role of solid-phase dust-borne iron speciation on its bioavailability to iron-efficient diatoms, and its possible role in modulating climate through the efficiency of the biological pump in the Southern Ocean. In Chapter 1, I show that primary iron(II) silicates mobilized from bedrock through glacial physical weathering are more bioavailable than chemical weathering products such as iron(III)-rich iron oxyhydroxides and secondary clay minerals. In Chapter 2, I show that diatoms use solid-phase iron more efficiently when surface contact between the cell and particle is allowed, suggesting a mechanism of solid-phase iron utilization in addition to bulk solubility. In Chapter 3, I show that glacial activity increases the relative bioavailability of dust-borne iron reaching the Southern Ocean, by increasing the iron(II) silicate content. Finally, in Chapter 4, I present evidence that suggests physical weathering of iron(II)-rich bedrock controls the speciation and bioavailability of particulate iron across the globe. Thus, it is important to consider global and temporal changes in dust-borne iron speciation and the proximity of dust and phytoplankton cells when modeling carbon dioxide drawdown by iron fertilization of phytoplankton. It is also important to consider the relative importance of physical versus chemical weathering to understand iron fertilization on all timescales, and the relative importance of biotic and abiotic carbon dioxide drawdown.

The effect of iron absorption on subsequent hemoglobin regeneration was investigated by repletion and subsequent analysis of an anemic weanling rat model. Primary assay procedure in these studies was the Regeneration Efficiency method. As repletion or curative assay techniques form the central body of investigative research in iron utilization, the first subject of inquiry was the effect of repletion interval and degree of depletion upon the animals as monitored by physical indicators such as blood volume, growth and hematinic response. Percent blood volume is a particularly useful figure in the calculation of the amount of hemoglobin iron but was found to be relatively constant in a preliminary experiment. Accordingly, the effects of growth and anemia on hemoglobin response and blood volume were examined in 122 weanling male rats which had been depleted for seven days by low iron diet and phlebotomy, then repleted by feeding iron rich diet (47.1 ppm) for zero, five, 10 and 15 days. Percent blood volume proved to be rather constant at 7.5 in these pre-pubescent animals. The most severely depleted animals appeared to regenerate hemoglobin initially rather than replenish tissue iron. Regeneration Efficiency and AOAC assay methods were compared in a study involving the relative potency of two iron salts, ferrous sulfate and ferric orthophosphate, and three commercial cereal sources containing electrolytically reduced, hydrogen reduced or ferric orthophosphate supplements. These two assays utilized 202 albino male weanling rats. The superior availability of ferrous sulfate was evident in both regeneration efficiency and AOAC assays, as was the relative similarity of the dietary iron sources, yet the commercial sources in general provided more available iron in comparison to the reference ferrous sulfate than expected, possibly due to the influence of dietary components and processing variables. Bioavailability based on dietary iron concentration response correlated highly (r = 0.94) between animal groups analyzed using the Regeneration Efficiency and AOAC methods. Stress may have been a factor in animals assayed by the AOAC technique which used a 28 day depletion interval followed by a two week repletion. The Regeneration Efficiency method, which utilizes shorter depletion and repletion intervals also offered sufficient amounts of dietary iron for normal growth. The calculation of iron bioavailability also is dependent on such pertinent variables as dietary intake amount, body weight gain and percent blood volume.

Field pea (Pisum sativum L.) seeds have high nutritional value but also contain phytate which can inhibit the absorption and utilization of nutrients. Phytate is the main storage form of phosphorus in the seeds but chelates Fe, Zn and some other micronutrients and is not well digested by monogastrics. Peas with pigmented seed coats contain polyphenols which also have anti-nutritional properties. To increase the nutritional value of field pea seeds, two low phytate lines (1-150-81 and 1-2347-144) containing higher inorganic phosphorus concentration (IN-P) and lower phytate-phosphorus concentration (PA-P) than the normal phytate varieties were developed from CDC Bronco in previous research. The objectives of this research were 1) to determine the effect of genotype and environment on iron bioavailability in a set of five pea varieties differing in phytate concentration and iron concentration using in vitro digestion/Caco-2 cell culture bioassay; 2) to determine the effect of seed coats on iron bioavailability by testing whole seeds compared to dehulled seeds in varieties differing in seed coat pigmentation using in vitro digestion/Caco-2 cell culture bioassay; 3) to determine the inheritance of iron bioavailability in field pea by evaluating recombinant inbred lines differing in phytate concentration using in vitro digestion/Caco-2 cell culture bioassay; 4) to determine the effects of pea with the low phytate trait on body weight and hemoglobin concentration of chickens. Iron concentration (FECON) did not differ significantly between normal and low phytate varieties. Iron bioavailability (FEBIO) of the two low-phytate lines was 1.4 to 1.9 times higher than that of the three normal phytate varieties, and growing environment also had a significant effect on FEBIO. Peas with pigmented seed coats contained 7 times lower FEBIO than peas with non-pigmented seed coat. The removal of the seed coat increased the FEBIO in peas with pigmented seed coat 5 to 6 times. From previous research on PR-15 recombinant inbred lines (RILs) which were developed from a cross between low phytate line 1-2347-144 and a normal phytate variety CDC Meadow, it was found that PA-P was controlled by a single gene. FEBIO, in this study, was also found to follow a bimodal frequency distribution, characteristic of single gene control, and it was highly correlated with PA-P in the PR-15 lines. In vivo studies were used to evaluate iron absorption of chickens fed with low and normal phytate pea diets. The diets containing the low-phytate pea lines had no significant effect on chicken body weight and hemoglobin level, compared with the diets containing normal phytate pea varieties. An unexpected high FECON was discovered in the diets that was traced to the ingredients of limestone and dicalcium-phosphate which likely affected the experimental results.

Master of Science / Department of Food, Nutrition, Dietetics, and Health / Brian L. Lindshield / Fortified-blended foods (FBFs), grain-legume porridges (most commonly corn and soy), are frequently used for food aid purposes. Sorghum and cowpea have been suggested as alternative FBF commodities because they are drought-tolerant, grown locally in food aid receiving countries, and are not genetically modified. The objective of this thesis was to determine the protein quality and iron bioavailability of newly formulated, extruded FBFs in broiler chickens, which have been suggested as a good model for assessing iron bioavailability. Five FBFs were formulated to contain whey or soy protein to compare protein quality, sugar, oil, and an improved micronutrient premix. These included three white sorghum-cowpea FBFs; two were extruded with either whey protein concentrate (WSC) or soy protein isolate (WSC+SPI) added, one was non-extruded (N-WSC). Two others were white sorghum-soy (WSS) and corn-soy (CSB14) FBFs. Two additional white-sorghum cowpea FBFs were reformulated and “over-processed” to contain no sugar, less whey (O-WSC) or soy protein (O-WSC+SPI), and less oil, thus producing a less expensive FBF. Two studies were performed using prepared (Prep) or dry (Dry) FBFs, along with the United States Agency for International Development (USAID) corn and soy blend FBF, CSB+, fed to chickens for 3 and 2 weeks, respectively; food intake, body weights, hemoglobin, and hepatic iron were assessed. In the Prep study, new FBFs significantly increased caloric and protein efficiency compared to CSB+, despite similar food intake and body weight gain. In the Dry study, CSB+ significantly decreased food intake and caloric efficiency, with the exception of O-WSC+SPI, and nonsignificantly reduced body weight gain and protein efficiency compared to new FBFs. CSB+ significantly reduced hepatic iron content compared to all FBFs in the Dry study, and was nonsignificantly decreased compared to new FBFs in the Prep study. In conclusion, sorghum and cowpea FBFs performed similarly to corn and soy FBFs, suggesting these commodities are suitable replacements for corn and soy. Soy protein isolate (WSC+SPI) was an effective alternative to whey protein concentrate (WSC), suggesting SPI can be a less expensive protein supplement in FBFs. Surprisingly, non-extruded sorghum and cowpea (N-WSC) was equally efficacious to extruded WSC. However, N-WSC did not meet viscosity requirements and is not precooked, which limits its viability as an FBF. O-WSC+SPI resulted in poorer outcomes compared to other FBFs, which suggests the protein quality of cowpea may be inferior and the inclusion of whey protein is needed in this formulation, as O-WSC with whey performed similarly to other FBFs. Overall, new FBFs, with the exception of O-WSC+SPI, resulted in improved food efficiency and hepatic iron outcomes compared to CSB+, suggesting they are of higher nutritional quality. However, further research is needed to refine and identify the best FBF formulations.

Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2007.

Background: The high prevalence of iron deficiency and anaemia among South African children highlights the need for iron fortification, especially with a highly bioavailable iron compound. Fortification of staple foods is an adequate strategy to provide additional iron to populations at risk. In South Africa it is mandatory to fortify maize meal and wheat flour with iron, as well as other micronutrients. Elemental iron, specifically electrolytic iron, is currently the preferred choice but other compounds that might be more effective in alleviating iron deficiency are under consideration. Objectives: The objective of this study was to provide information about the bioavailability of ferrous fumarate and NaFeEDTA from maize meal porridge in young children, which would assist in selecting a bioavailable alternative to electrolytic iron in the South African National Food Fortification Programme, Methods: A randomized parallel study design was used, with each of the 2 groups further randomised to receive either one of two test regimens in a crossover design in which each child acted as his/her own control. Iron bioavailability was measured with a stable-isotope technique based on erythrocyte incorporation 15 days after intake. Results: The mean absorption of iron from NaFeEDTA and ferrous fumarate from the maize porridge meal was 11.5% and 9.29% respectively. NaFeEDTA and ferrous fumarate are both sufficiently bioavailable from a maize based meal rich in phytates. Conclusion: Both NaFeEDTA and ferrous fumarate would provide a physiologically important amount of iron should they replace electrolytic iron as fortificant in maize flour fortification. The final choice between ferrous fumarate and NaFeEDTA as when it comes to finding the alternative iron fortificant will depend on factors such as technical compatibility, bioavailability, relative cost and organoleptic characteristics. / Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2007

Background: The high prevalence of iron deficiency and anaemia among South African children highlights the need for iron fortification, especially with a highly bioavailable iron compound. Fortification of staple foods is an adequate strategy to provide additional iron to populations at risk. In South Africa it is mandatory to fortify maize meal and wheat flour with iron, as well as other micronutrients. Elemental iron, specifically electrolytic iron, is currently the preferred choice but other compounds that might be more effective in alleviating iron deficiency are under consideration. Objectives: The objective of this study was to provide information about the bioavailability of ferrous fumarate and NaFeEDTA from maize meal porridge in young children, which would assist in selecting a bioavailable alternative to electrolytic iron in the South African National Food Fortification Programme, Methods: A randomized parallel study design was used, with each of the 2 groups further randomised to receive either one of two test regimens in a crossover design in which each child acted as his/her own control. Iron bioavailability was measured with a stable-isotope technique based on erythrocyte incorporation 15 days after intake. Results: The mean absorption of iron from NaFeEDTA and ferrous fumarate from the maize porridge meal was 11.5% and 9.29% respectively. NaFeEDTA and ferrous fumarate are both sufficiently bioavailable from a maize based meal rich in phytates. Conclusion: Both NaFeEDTA and ferrous fumarate would provide a physiologically important amount of iron should they replace electrolytic iron as fortificant in maize flour fortification. The final choice between ferrous fumarate and NaFeEDTA as when it comes to finding the alternative iron fortificant will depend on factors such as technical compatibility, bioavailability, relative cost and organoleptic characteristics. / Thesis (Ph.D. (Nutrition))--North-West University, Potchefstroom Campus, 2007

Anaemia, which is caused by iron deficiency, is a global nutritional disorder of utmost concern. It has been assumed that meat, which contains haem as well as non-haem iron, enhances non-haem iron absorption due to the presence of the “meat factor”. In the experiment reported here, 24 semi-anaemic, 3-week-old piglets were utilised as human nutrition models to assess the effects of dietary lactoferrin, meat and LSF (Low Molecular Weight Sarcoplasmic Fraction) on iron bioavailability during a 4-week feeding period. The parameters that were used as measurements of iron bioavailability were changes in haematological indices, haemoglobin iron repletion efficiency, intestinal morphology and mineral balances. Non-significant (p > 0.05) dietary effects were observed for growth performance and for all the haematological and some histological parameters (small intestine villi height, crypt depth and mucosal thickness). Haemoglobin iron repletion efficiency was highest for the control group and was not significantly different between the other 3 diets. The superiority of the control diet in this respect was not consistent with previous trials and can not be explained. Results suggested that increased retention of calcium, magnesium, phosphorous and manganese tended to inhibit iron absorption. However, the LSF and meat diets significantly (p = 0.003) increased the number of goblet cells/100 µm suggesting that mucin secretion was favoured by these two diets. Additionally, all immunological parameters were significantly (p < 0.05) improved by the LSF diet. As such, the LSF diet can be a potential immunobooster feed ingredient for weanling piglets. Overall, the level of LSF in the LSF diet was insufficient to exert a desirable enhancement of iron bioavailability and betterment of 3 iron status of the semi-anaemic piglets relative to the control group. However, the diet containing LSF was as effective as the meat diet with respect to these characteristics.