Speciation and bioavailability of iron in plant foods

Lead Research Organisation: MRC Centre Cambridge
Department Name: MRC Elsie Widdowson Laboratory


Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

Technical Summary

We have selected common classes of plant-based foods that contribute significantly to the UK iron intake and are predicted to contain contrasting chemical forms of iron(cereals, pulses and vegetables). We will investigate the chemical form of iron-complexes in these crops, and the effect of processing and digestion on iron bio-availability and absorption.
To characterize abundant iron species, we will perform whole sample imaging of the plant tissues and of the processed and digested foods, using x-ray fluorescence (xrf) imaging and NanoSIMS. Soluble extracts from raw, processed and digested foods will be frationated by size exclusion chromatography. Iron-rich fractions will be identified by Inductively Coupled Plasma-Mass Spectrometry, and further analysed using advanced spectroscopy techniques (electron paramagnetic resonance, Mössbauer spectroscopy and x-ray based Extended x-ray Absorption Fine Structure). Nanoparticulate (<100 nm) iron will be observed using high resolution Transmission Electron Microscopy.
The bioavailability of different forms of iron will be determined using the Caco-2 cell model. The uptake of iron from digestates will be measured both before and after digestion. Chemical and siRNA-based inhibitory methods will be used to determine the contributions of the three uptake pathways in Caco-2 cells, namely (a) inhibitors of endocytosis, (b) an inhibitor of DMT1 and (c) an inhibitor of Dcyt-B. Endocytosis is the route by which all nanoparticulate (<100 nm) iron accesses the cell, whereas Dcyt-B is required to reduce soluble ferric iron so that it can be transported via DMT1.
The data on the chemical forms of iron in food, effects of processing and digestion, and the bio-availability of Fe, can be used by the food industry to improve nutritional quality of products. Th knowledge on iron speciation and bioavailability will also help in developing improved assays for predicting iron availability, and to state this information on food labels.

Planned Impact

Two billion people worldwide remain iron deficient with iron deficiency anaemia being one of WHO top 10 targets for cure and prevention. Children and women of child-bearing age, particularly pregnant women, have high iron requirements and are at increased risk of iron deficiency anaemia with consequent serious adverse effects on health. Traditionally iron deficiency has been tackled through fortification and supplementation programmes with little success. More recently, biofortification and the nutritional quality of food crops has become an important goal for the agricultural sector. Globally, we have to move to a more sustainable diet, taking into account climate change and nutritional (food) security, and therefore diets will contain lower intakes of meat, especially red meat which has the greatest greenhouse gas effect but which provides iron of the highest bioavailability. Alternative plant food sources, such as cereals and green vegetables, will be of growing importance for supplying iron in the diet. Diets consumed by vegetarians and low-income population groups are particularly low in bioavailable iron.
This project will provide information on the major forms of iron present in plant-based foods and how well they are absorbed by the body. It is anticipated that this will inform strategies for increasing the iron content of foods either by (i) controlling food processing or (ii) manipulating plant-food crops with the ultimate aim to improving the iron status of the UK population.
This project has great potential to bring benefit to (a) the health status of the UK population (b) food regulation and policy (c) UK competitiveness in the field.
(a) The understanding of how iron bioavailability in plant foods can be improved can help to inform plant breeders, growers and the food industry to take steps to ensure improved nutritional quality of their crops and food products produced using plant foods as raw materials. Furthermore, the findings from this project will be disseminated to health professionals (doctors, dieticians, nurses) so that they can offer personalised dietary advice for patients. This will in time help to improve the iron status of the population.
(b) The results of this project can be used for developing better food/nutrition policies for the UK (and internationally) and to develop food based dietary guidelines that ensure that the diet of all population groups meets their requirements.
(c) There are major gaps in our understanding of iron speciation in foods, particularly plant-based foods, and starting to fill these, as we propose, can inform on the development of food-like (and therefore safe) iron food fortificants/supplements and greatly enhance UK competitiveness in the field both academically and industrially.


10 25 50
Description The projected studied the content and bioavailability of iron in 3 food systems.

1. Wheat flour. iron on wheat is known to have low bioavailability due to its presence as insoluble phytates. We therefore compared the effects of three commercial breadmaking systems on the content of bioavailable Fe in bread, using the caCo2 cell system. These were sourdough, conventional long fermentation and the Chorleywood Breadmaking Process (CBP). Sourdough fermentation has been shown to reduce the content of phytates in dough, resulting in higher bioavailability of iron added as fortification. However, the endogenous iron remained unavailable, possibly due to binding to other components.

2. Peas. Using specific antibodies and in-gel iron staining, we show that ferritin loaded with iron accumulated gradually during seed development. Immunolocalization and high-resolution secondary ion mass spectrometry (NanoSIMS) revealed that iron-loaded ferritin was located at the surface of starch-containing plastids. Standard cooking procedures destabilized monomeric ferritin and the iron-loaded form. Iron uptake studies using Caco-2 cells showed that the iron in microwaved immature peas was more bioavailable than in boiled mature peas, despite similar levels of soluble iron in the digestates.

3. Green vegetables. We assessed iron bioavailability in five plant foods, using ferritin response in a simulated digestion/Caco-2 cell model. These were spinach (Spinacia oleracea), broccoli (Brassica oleracea var. italica), savoy cabbage (Brassica oleracea var. sabauda), kale (Brassica oleracea var. acephala) and green pepper (Capsicum annuum). Savoy cabbage gave the highest ferritin response. SEC-ICP-MS analysis of the digestate showed that the iron was present in low molecular weight fractions while 1H-NMR spectroscopy showed that these fractions also contained significant quantities of glucose and fructose, organic acids and amino acids. The addition of fructose 1,6,biphosphate, but not fructose, to Caco-2 cells increased iron uptake 2-fold compared with iron alone. These results demonstrated that cabbage was the best source of bioavailable iron and indicated that fructose complexes may have contributed to its higher iron bioavailability.
Exploitation Route To provide advice on iron availability and fortification in foods to processors, consumers and regulatory authorities.

To develop new processing technologies to increase iron bioavailability in plant foods.
Sectors Agriculture, Food and Drink,Government, Democracy and Justice,Manufacturing, including Industrial Biotechology

Description BBSRC DRINC2
Amount £43,724 (GBP)
Funding ID P1924503 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 08/2014 
End 08/2017