The effect of dairy products on iron availability.

Many researchers report substantial reductions in iron availability when dairy products are consumed with solutions of iron. Yet other studies indicate that dairy products have little effect on iron availability when added to complex meals. The conflicting data may be due to differences in the technique used to measure availability, species of animal used, form of iron in the diet, and meal composition. Human studies show superior bioavailability of iron in human milk when compared with cow's milk. Definitive causes for the differences between human and cow's milk have not been identified. Human milk contains lower amounts of casein, phosphate, and calcium, components thought to inhibit iron absorption. More work is needed to identify the factors that influence iron-dairy interactions. The nutritional benefits provided by dairy products outweigh the slight inhibitory effect they may have on iron availability.     

Comparison of the availability of iron in white bread, fortified with iron powder, with that of iron naturally present in wholemeal bread

The amounts of iron extracted from white bread and wholemeal bread by water and by simulated gastric juice (pepsin-hydrochloric acid)were estimated. Taking the ionisable iron content of the pepsin-hydrochloric acid extract as the standard by which the availability of iron was assessed, then the availability of iron in normally fortified white bread, expressed as a proportion of the total iron present, at least equalled, and possibly exceeded, that in wholemeal bread; in absolute terms the amount of available iron in wholemeal bread was greater than in white bread. Using the Same method, the availability of iron from white bread, fortified with iron powder to the same level as wholemeal was also estimated; approximately 24% more iron was available than from wholemeal. Results for the availability of iron obtained by this method were lower than those found by earlier workers using other methods of extraction which did not include pepsin.     

International collaborative study of an automated method for the determination of crude protein in fish-meals

An automated macro-Kjeldahl instrument (Kjel-Foss) determines protein at the rate of 20 samples in 1 h. The methodology is similar to the Kjeldahl method officially recommended by the IAFMM for fish-meal. The two methods were compared in a collaborative study. Six fish-meals, tryptophan and acetanilide were analysed by 15 participating laboratories. The results showed good agreement between the two methods. There was little difference between the two methods in terms of repeatability in the laboratory, but variability between laboratories was significantly less when the automated method was used.     

Biological availability of zinc from inorganic sources with excess dietary calcium

The effects of chemical form of supplemental zinc and elevated dietary calcium on intestinal absorption of zinc were measured. Calves and rats were fed diets low in zinc, and zinc availability was the percentage increase of zinc in plasma with dietary supplementation of zinc. Availabilities of zinc supplied as zinc chloride, zinc sulfate, zinc oxide, and zinc carbonate were comparable in both calves and rats. Elevated amounts of dietary calcium as ground limestone reduced absorption of zinc in rats fed soy-protein but had no effect on absorption of zinc in the lactating cow. Thus, for cows consuming large amounts of calcium, an increase in the concentration of zinc beyond 40 ppm of the diet appears unnecessary.     

Influence of food processing on iron availability in vitro from extruded maize-based snack foods

Samples of an extruded maize-based snack food taken at various points during manufacture were digested in vitro under simulated physiological conditions. The proportion of iron diffusing across a semi-permeable membrane was used as an index of bioavailability. Iron diffusibility increased from less than 3 % in raw whole maize to over 20 % in the finished product. Four processing stages were found to be responsible for this enhancement: (I) refining of raw maize, (2) product formulation, (3) extrusion cooking, (4) addition of flavourings. The extrusion cooking process itself was responsible for only a small part of the increase in iron diffusibility. There was a reduction in iron content due to refining, but a small increase in iron content due to product formulation and extrusion cooking. The various factors associated with each stage of snack food manufacture are discussed in relation to their potential influence on iron availability.     

Study on iron availability from prepared soybean sprouts using an iron-deficient rat model

During soya seeds germination in FeSO₄ solutions their phytoferritin content is multiplied. Prepared soybean sprouts have been proposed as a safe and easily available source of iron supplementation. The preparation was compared with FeSO₄ and ferritin isolates, using rats with induced iron deficiency anaemia. After the end of the 2-week supplementation experiment, it was observed that no statistically significant differences in haemoglobin concentration, mean corpuscular volume, mean corpuscular haemoglobin, and mean corpuscular haemoglobin concentration existed between those animals supplemented with sprouts enriched in ferritin, ferritin isolate and FeSO₄ and healthy animals forming the control group. Moreover, the examined preparation had a beneficial influence on the recreation of ferritin reserves in both the liver and the blood serum, and also did not induce negative alterations in general growth parameters of animals. Use of an easily obtainable ferritin iron source may be a profitable alternative in supplementation due to its wide availability and food preservative properties.     

Influence of different types of protein on in vitro availability of intrinsic and extrinsic iron and zinc

The influence of beef, pork and soy proteins on intrinsic and extrinsic iron and zinc in vitro availability was investigated, by measuring mineral dialysability. Intrinsic iron dialysability (percentage of iron dialysed) was similar in the animal proteins and higher than that from soy protein isolate (P<0·001). Intrinsic zinc dialysability from pork protein was statistically (P<0·001) higher than that from other proteins studied. Beef and soy proteins do not differ in their percentages of zinc availability. The effect on the extrinsic iron availability was different among the three proteins studied, but not on the extrinsic zinc availability. The composition of amino acids and/or the small peptides produced during the digestion process of the protein can modify the iron, and probably the zinc, availability. The inorganic zinc addition (10 μg ml⁻¹) reduced the non-haem and extrinsic iron availability, while it did not affect the haem iron availability. At the concentrations used in this study (10 μg ml⁻¹) a decrease of zinc dialysability caused by the inorganic iron addition was not observed. ©1997 SCI     

Counteracting the inhibitory effect of tea on the in-vitro availability of iron from cereal meals

Studies were carried out on the in-vitro availability of iron to determine the effect of addition of tea, milk and ascorbic acid to a standard cereal meal in all possible combinations. The availability of iron from the cereal meal was low (3.92%). Tea, when added to the meal, had a significant depressing effect on available iron (2.56%). Addition of 100 mg ascorbic acid or 200 g milk completely counteracted the inhibitory effect of tea, and addition of both ascorbic acid and milk brought about an even greater enhancement in the in-vitro availability of iron than when either was added alone. This investigation reveals that milk is as effective a factor as ascorbic acid in counteracting the depressing effect of tea on in-vitro iron availability.     

Effects of polyphenol oxidation on in vitro iron availability in faba bean (Vicia faba L.) flour

Tannic acid (TA) and green tea extract (GTE) were added to faba bean flour, before and after incubation with polyphenol oxidase (mushroom tyrosinase), and the effect on in vitro iron availability was investigated. The inhibitory effect of TA and GTE was dose dependent, and the in vitro iron availability decreased from 64.5% in the pure faba bean flour to 9.8% (P < 0.05) with the addition of 1 mg of TA 1 g^?1 to faba bean flour. The addition of 5 mg of GTE resulted in low in vitro iron availability as after the addition of 10 mg of TA (11.6% against 10.3% for 1 mg TA). Incubation of the polyphenols with tyrosinase before addition to the faba bean flour significantly increased the in vitro iron availability. The increase in iron availability was significant (P < 0.05) when amounts of 0.2, 0.5 or 1 mg g^?1 TA or GTE added to faba bean flour, respectively, were oxidised, even with the lowest amount of tyrosinase (150 u). Oxidation of 1 mg TA or GTE with 150 u tyrosinase increased the in vitro iron availability from 10.3% to 15.5% and from 19.2% to 26.1%, respectively. At the 300‐u level, the addition of higher amounts of enzyme (from 600 to 900 u) did not have any effect. The results from the study therefore suggest that the oxidation of polyphenols may be a promising way to increase the availability of iron in polyphenol‐containing legume foods.     

Non-haem iron availability from pork meat: Impact of heat treatments and meat protein dose

Pork meat heated at 60, 80, 100, and 120°C (1h), raw pork meat, BSA, casein and haemoglobin were examined for their effects on in vitro iron availability measured as Fe(2+)-dialysability, and on iron-reducing capacity following in vitro protein digestion (IVPD-dialysis). The pepsin-digested samples of meat heated at 80, 100, and 120°C resulted in increased in vitro iron availability. Generally, the capacity to reduce Fe(3+) to Fe(2+) was higher in the pepsin digests, whereas Fe(2+) decreased significantly after pepsin+pancreatin digestion and only part of the Fe(2+) was dialysable. Regardless of protein concentration, casein had no effect on in vitro iron availability, while pork meat protein treated at 120°C showed dose dependency reaching a plateau at 50mg protein/ml. In conclusion, the major effects on iron availability in vitro was shown in pepsin digests under conditions mimicking those in the duodenal lumen and heat-treatment of meat at 120°C showed the most pronounced effects.     

Biological reduction of nanoengineered iron(III) oxide sculptured thin films

Sculptured thin films (STFs) are assemblies of nominally identical, parallel nanowires with tailored shapes such as chevrons and spirals. A series of iron(lll) STFs were produced with varied crystallinity (from hematite toferrihydrite) and nanowire shapes (slanted columnar, clockwise helical, and counterclockwise helical). When the dissimilatory metal-reducing bacterium Shewanella putrefaciens CN32 was used to measure their bioreducibility, it was found that bioreduction was controlled primarily by oxide crystallinity. STFs were characterized by scanning electron microscopy, atomic force microscopy, and grazing incidence small-angle X-ray scattering. Postbioreduction characterizations determined that mineralogy of the film materials did not change, but surface roughness generally increased. Changes caused by bioreduction were assessed in terms of both transmittance and reflectance of light incident normal to the STFs. The greatest optical changes were obtained with crystalline hematite films. These results underscore the feasibility of an STF-based fiber optic iron(lll) reduction sensor for in situ subsurface deployment.     

Antinutrients and “in vitro” availability of iron in irradiated common beans (Phaseolus vulgaris)

Irradiation and cooking effects were investigated in beans. Determinations of iron and antinutrients and the “in vitro” dialysis of iron were carried out. Cooking caused a decrease in all parameters except for phytate and iron availability. Tannins were inversely correlated with applied irradiation doses. The same thing happened to the dialyzed iron. The 6-kGy-dose irradiation presented positive effects regarding the iron availability and its use is recommended.     

Effects of food processing and fruit juices on in-vitro estimated iron availability from cereals,vegetables and fruits

Selected processed foods were digested in vitro under simulated physiological conditions. The proportion of iron diffusing across a semi-permeable membrane was used as an index of bioavailability. Certain food processing procedures appeared to greatly enhance the proportion of diffusible iron. Many of the foods that were canned, dried, pickled, fermented, refined, or which contained certain additives, displayed enhanced iron diffusibility compared with unprocessed foods. Iron diffusibility from wheat flour was found to be enhanced by the addition of fruit juices. The constituent organic acids in the fruit juices, namely citric, ascorbic and malic, were found to be potentially responsible for this enhancement. These three compounds are also important examples of a sequestrant, an antioxidant, and an acidulant. These and similar compounds are added to many processed foods in order to improve their quality and preservation. All such additives have the potential to influence the chemical form, and probably the bioavailability, of food iron.     

Nutritive value of Middle Eastern foodstuffs. 3. Physiological availability of iron in selected foods common to the Middle East

The physiological availability of the iron in selected foods of the Middle East was studied from haemoglobin regeneration in anaemic rats fed on diets in which these foods were the sole source of iron. None of the foods studied was as efficient as ferrous sulphate in promoting haemoglobin regeneration. Taking iron in ferrous sulphate as being 100% available, iron availability values for okra, chard and parsley were low, namely, 25, 45 and 48% respectively; other relative percentage values were: kidney bean, 59; lentil, 67; broad bean, 63; decorticated sesame, 67; parboiled wheat, 62; and brown bread, 75. The values for whole wheat and chickpea were greater than 80%. The availability of iron in prepared dishes and meals reflected that in the component foods. Since the iron in many plant foods seems to be much less available than inorganic iron, it is suggested that requirements for this nutrient should be reconsidered for areas such as the Middle East where the population derives a high proportion of dietary iron from plant sources.     

Effects of reducing phytate content in sorghum through genetic modification and fermentation on in vitro iron availability in whole grain porridges

Improved iron availability from sorghum porridges will benefit many malnourished communities in rural Africa, where there is a high prevalence of iron deficiency. This research compared the efficacy of reducing sorghum phytate content by genetic modification (GM) and natural lactic acid fermentation on in vitro iron availability in porridges. GM low phytate, non-tannin (38% phytate reduction) and tannin (36% phytate reduction) sorghums and their null controls were processed into thick unfermented and fermented porridges. The inhibitory effect of the tannins seemed to prevent any increase in in vitro iron availability, regardless of the level of phytate reduction. Only the additive effect of GM in combination with fermentation in reducing the phytate content appeared to cause a substantial increase in in vitro iron availability in the GM fermented porridge (30%) made from the non-tannin line, compared to the GM unfermented porridge (8.9%) or the fermented porridge (17.6%) of the control sorghum. This could be of nutritional significance.