The ionisable iron in foods

The Early Years of 2,2'-Bipyridine-A Ligand in Its Own Lifetime

The first fifty years of the chemistry of 2,2′-bipyridine are reviewed from its first discovery in 1888 to the outbreak of the second global conflict in 1939. The coordination chemistry and analytical applications are described and placed in the context of the increasingly sophisticated methods of characterization which became available to the chemist in this time period. Many of the “simple” complexes of 2,2′-bipyridine reported in the early literature have been subsequently shown to have more complex structures.

The Iron, Copper and Manganese Content of the Human Brain

The observations recorded in this paper form part of an investigation into the mineral constituents of the central nervous system both in normal and pathological conditions.

The Iron Content of the Human Brain.—II

In a previous paper (1) the iron, copper and manganese content of the human brain were recorded, with special reference to the G.P.I. cortex, which in certain cases contained an excess of both total and “available” (i.e., non-hæmatin) iron.

A Study of English Diets by the Individual Method: Part I. Men

1. A study of the freely chosen diets of sixty-three men of the English middle class has been made by the “individual” method. All food was weighed for the period of a week, and the amounts of protein, animal protein, fat, carbohydrate, calories, calcium, total and available phosphorus and total and available iron in the individual diets have been calculated. Detailed and averaged results for the diets are given.

2. The average calorie intake was 3067 per day, but a very wide variation was observed (1772–4955 calories), and it is suggested that the adoption of 3000 calories as the requirement of an individual man may be most misleading.

3. There was a definite, but mathematically insignificant, decrease in calorie intake with increasing age. The individual variation at each age was so great, however, that no rules for the guidance of individuals as to their dietary requirements at different ages can possibly be formulated.

4. No significant correlation existed between calorie intake and body weight.

5. The proportion of calories derived from fat was higher than any figures previously recorded in this country. The proportion of calories derived from carbohydrate was correspondingly lower.

6. The total calcium, phosphorus and iron intakes were 0·87 g., 1·61 g. and 16·8 mg. per day respectively. 98 per cent, of the total phosphorus eaten was in an “available” form, while only 66 per cent, of the iron could be considered to be physiologically available.

7. A similar study has been carried out on six unemployed men, and the chemical composition of these diets is compared with that of employed, middle-class individuals.

Acknowledgments. The author wishes to thank Dr R. A. McCance for his enthusiastic encouragement and help, Miss M. Verdon-Roe for her assistance with the calculations, and all the subjects of the investigation for their willing co-operation. Part of the expense of this investigation were defrayed by a personal grant from the Medical Research Council.

IRON METABOLISM IN EXPERIMENTAL ANEMIA : "AVAILABILITY OF IRON"

In experimental anemia in dogs due to blood loss the term "available iron" as determined by the dipyridyl test has no physiological significance. Iron salts (100 per cent available by dipyridyl) given in optimum dose (560 mg. per 2 weeks) will cause a net production of 50 to 55 gm. hemoglobin above the control base line in anemic dogs. This means that an iron salt which is rated as 100 per cent available by the dipyridyl test is only 35 per cent physiologically available. The term "available iron (dipyridyl)" simmers down to iron not in the form of hematin compounds. The absorption of this "available iron" is conditioned by a great variety of factors, many unknown at this time. Iron is indeed an elusive sprite whose "availability" or comings and goings cannot be determined in dogs by dipyridyl—perhaps only in part by studies of absorption and excretion. Liver contains "available iron (dipyridyl)" but also organic factors influencing hemoglobin regeneration in anemia as liver ash contains only about 50 per cent the potency of the whole liver. One can readily dissociate the iron from other potent factors in various tissues. Fractions of heart, liver, spleen, and kidney may contain very little iron yet cause much hemoglobin regeneration in anemic dogs. No investigator has reported any condition of copper deficiency in man or dog. In fact, in anemias copper is usually above normal concentration in the liver. It is unlikely, therefore, that in experimental anemia in dogs and in the various anemias of man, any significance attaches to the intake of copper.

Chemical composition, iron bioavailability, and antioxidant activity of Kappaphycus alvarezzi (Doty)

Kappaphycus alvarezzi, an edible seaweed from the west coast of India, was analyzed for its chemical composition. It was found that K. alvarezzi is rich in protein (16.24% w/w) and contains a high amount of fiber (29.40% w/w) and carbohydrates (27.4% w/w). K. alvarezzi showed vitamin A activity of 865 mug retinal equivalents/100 g of sample. It contained a higher quantity of unsaturated fatty acids (44.50% of the total), in which relative percentage of oleic acid was 11%, cis-heptadecanoic acid 13.50%, and linoleic acid 2.3% and 37.0% of saturated fatty acids (mainly heptadecanoic acid). K. alvarezziwas also found to be good source of minerals, viz 0.16% of calcium, 0.033% of iron, and 0.016% of zinc, which are essential for various vital biological activities. Bioavailability of iron by in vitro methods showed a higher efficiency in intestinal conditions than in stomach conditions. Ascorbic acid influenced higher bioavailability of iron. Successive extracts of n-hexane, acetone, ethyl acetate, ethanol, and direct extractables of chloroform/methanol (1:1 and 2:1) were screened for antioxidant activity using a beta-carotene linoleic acid model system (B-CLAMS), DPPH (alpha,alpha-diphenyl-beta-picrylhydrazyl) model system and hydroxyl radical scavenging activity. The chloroform/methanol (2:1) extract has shown 82.5% scavenging activity at 1000 ppm. Acetone fraction extracts at the 1000 ppm level showed 63.31% antioxidant activity in beta-carotene linoleic acid system. The acetone extract showed 46.04% scavenging activity at 1000 ppm concentration. In the case of hydroxyl radical scavenging activity, all the extracts showed better activity at the concentrations of 25 and 50 ppm, where at the 50 ppm level ethyl acetate extract showed 76.0%, acetone 75.12%, and hexane 71.15% activity, respectively. Results of this study suggest the utility of K. alvarezzi (Eucheuma) for various nutritional products, including antioxidant for use as health food or nutraceutical supplement.

Application of selective extraction to the study of iron species present in diet and rat gastrointestinal tract contents

Iron speciation in rodent diet and rat gastrointestinal tract lumen during dietary digestion and absorption was investigated with a novel selective extraction technique. Five Fe fractions were identified, namely exchangeable (soluble in 1 M-magnesium chloride), carbonate-bound (soluble in mild acid), oxide-bound (soluble in hydroxylamine-acetic acid), organic-bound (soluble after treatment with peroxide in nitric acid) and residual. Fe from the pelleted diet was mobilized by rat stomach to the exchangeable fraction, then redistributed to the carbonate- and oxide-bound fractions on passage through the proximal small intestine. In vitro incubation of diet with hydrochloric acid failed to mimic the in vivo effect of the stomach. In vitro neutralization of stomach contents with bicarbonate was found to produce a similar effect on Fe speciation to that seen when diet passed the proximal small intestine in vivo. Comparison of 59Fe speciation in extrinsically labelled diet with endogenous Fe speciation showed that extrinsic labelling does not uniformly label all endogenous species. The experiments suggest that selective extraction may provide a useful approach to the study of Fe species present in diets, in vitro digestions and gastrointestinal contents.

Forms of soluble iron in mouse stomach and duodenal lumen: significance for mucosal uptake

Stomach contents of mice fed on a standard rodent breeding diet contained 29-733 microM-soluble nonhaem-iron. A very variable percentage (3-100, mean 49.3 (SE 4.7), n 37) of this Fe was rapidly (half-life less than 1-2 s) available for chelation by the strong Fe(II) chelator ferrozine, with little or no further Fe being available on addition of ascorbate. Ferrozine-available Fe could be detected in the duodenal lumen at concentrations up to 60 microM in vivo and after in vitro neutralization of stomach contents. No significant changes in quantity of stomach ferrozine-available Fe or soluble non-haem-Fe occurred in mice with adaptive enhancement of Fe absorption induced by chronic hypoxia. Electron paramagnetic resonance (e.p.r.) spectroscopy of the soluble portion of mouse stomach contents demonstrated a g = 4.3 signal (rhombic Fe(III)) equivalent to up to 20% of soluble non-haem-Fe. The signal was unaffected by addition of excess ferrozine and increased on subsequent neutralization, suggesting redistribution of Fe from other e.p.r.-silent species. Solutions of Fe-nitrilotriacetate (NTA) (a synthetic Fe chelate used as a bioavailable, model Fe solution) were found to contain both rapidly and slowly ferrozine-available Fe (after addition of ascorbate) depending on pH, NTA:Fe ratio and the presence of Ca(II) ions. Fe-ascorbate mixtures (a model solution for Fe absorption studies) also contained ferrozine-available Fe. These results suggest the presence of Fe(II), rhombic Fe(III) and other e.p.r.-silent Fe species in the soluble fraction of mouse stomach contents. The ferrozine-available (Fe(II)) fraction is not limited by the reducing power in the diet, but by binding to ligands. Neutralization with bicarbonate leads to a loss of ferrozine-available Fe and increase in rhombic Fe(III) at the expense of both ferrozine-available and other e.p.r.-silent Fe species. The ferrozine-available Fe in mouse stomach and duodenal lumen can be related to Fe species present in model solutions used for in vitro studies of mucosal uptake mechanisms.

In vitro studies of iron bioavailability. Probing the concentration and oxidation-reduction of pinto bean iron with ferrous chromogens

The bioavailability of iron from foods is ultimately determined by interactions between iron and other components in the digestive milieu. Perhaps the most important factor is the concentration of Fe2+ during transit through the duodenum. During in vitro simulations of human digestion it is possible to probe the concentration of Fe2+, the rate of Fe2+ formation, and total iron concentration using ferrous chromogens. It is crucial, of course, that the chromogen not interfere with the redox reactions occurring during digestion. Accordingly, ferrozine was examined with regard to its ability to reduce complexes Fe3+, alter rates of Fe3+ production, detect Fe2+ present in the digestive mixture and differentiate the effects of chelating and reducing agents in the mobilization of iron from pinto beans. The chromogen was found to be free from apparent artefacts and to be a sensitive and reproducible probe of the state of iron in digestive mixtures.

In vitro estimation of iron availability from a range of plant foods: influence of phytate, ascorbate and citrate

Plant foods were digested in vitro and the proportion of iron which diffused across a semi-permeable membrane was used as an index of Fe availability. The mean (with SEM) Fe diffusibility from a group of eighteen cereals, legumes and nuts was very low, 2.1 (0.25)%, whereas from a group of sixteen fruits and vegetables it was high, 31.7 (1.09)%. The difference between the two food groups was highly significant (P less than 0.001). The results for Fe diffusibility correlated well with literature values for the in vivo absorption of Fe from similar foods (r0.84, P less than 0.01). When phytate, citrate and ascorbate were added to selected foods in amounts corresponding to endogenous levels, only phytate and citrate gave the expected effects on Fe diffusibility. Ascorbate only enhanced Fe diffusibility to the expected extent when it was added in much larger amounts, not normally found in foods. When added to cereal foods, orange juice was found to enhance greatly Fe diffusibility even when its content of ascorbate was completely destroyed by boiling followed by prolonged storage. When citrate and ascorbate were added to cereal foods in amounts equivalent to those found in fresh orange juice, both enhanced Fe diffusibility but citrate was far more effective. It is concluded that phytate is a major inhibitor of Fe diffusibility in cereals, legumes and nuts. However, citrate rather than ascorbate would appear to be the major enhancer of Fe diffusibility from many fruits and vegetables. The implications of the present results are discussed in relation to the relative influence of phytate, citrate and ascorbate on dietary Fe availability.

Availability of food iron

Iron has been extracted from 25 common foods under conditions resembling those prevailing in the stomach under physiological conditions. In most cases less than half the iron in the foods is released into solution. The soluble iron is mainly in ionizable form, except in the case of meat products and black pudding. The amount of food iron released is influenced by cooking and the presence of iron-binding substances in some foods. The total dietary iron probably does not represent the amount available for absorption.