Location: Plant, Soil and Nutrition Research2012 Annual Report
1a. Objectives (from AD-416):
Objective 1. Determine the genes affecting iron level and bioavailability in edible portions of maize by utilizing quantitative trait loci (QTL) mapping and an in-vitro digestion/Caco-2 cell culture model system. Confirm this QTL information via in-vitro and in-vivo studies and transfer this information to plant breeders. Objective 2. Investigate the role and mechanisms of action of prebiotic compounds, beneficial bacteria, and plant phenolic constituents on the bioavailability of iron and zinc from the diet.
1b. Approach (from AD-416):
This project seeks to improve the bioavailability of iron (Fe) and zinc (Zn) in plant foods by two distinct strategies. First, a multidisciplinary, genomics-based approach will be used to identify the genes and chemical factors that modulate Fe bioavailability in maize grain, using maize as the model to demonstrate proof of concept for this work. The second approach defines how prebiotic (non-digestible carbohydrates) and polyphenolic compounds in plant foods influence Fe and Zn bioavailability and thereby enhance absorption of Fe and Zn from plant foods in the intestine. Maize Fe Bioavailability: The goal here is to improve the nutritional quality of maize with respect to Fe via identifying the genetic factors that contribute to improved seed-iron concentration and bioavailability. This will be accomplished by building on current genetic mapping of maize seed-Fe bioavailability using a simulated intestinal digestion/Caco-2 cell assay. Animal models will then be used to confirm the cell culture results before definitive testing in humans. By identifying the genes that contribute to seed-iron accumulation and bioavailability, plant breeders will be able to improve the nutritional quality of maize. Prebiotics, Beneficial Bacteria, Polyphenols and Fe/Zn Bioavailability: The gastrointestinal microflora is increasingly becoming recognized as a major factor in human health via systemic effects on gut health and nutrient absorption. Prebiotic compounds such as inulin dramatically alter the profile of intestinal microflora and this alteration may enhance absorption of Fe and Zn. Therefore, one of the goals here is to determine if prebiotics enhance Fe and Zn absorption via changes in gut microflora. The second subobjective is to determine if polyphenolic compounds play a significant role in Fe absorption in long term feeding trials. This will be accomplished via animal feeding trials and cell culture models, whereby foods will be compared that have low and high amounts of prebiotics (eg. inulin, raffinose, stachyose) and polyphenols (e.g., kaempferol, quercitin, chlorogenic acid, ferulic acid). In these studies Fe and Zn absorption from these foods will be measured, as well as their effect on the bacterial profile. By understanding the role of prebiotics and polyphenols in the absorption of these two essential minerals, plant foods and food products can be improved to provide more optimal nutrition.
3. Progress Report:
Successful progress was obtained in previous years as we identified regions of the maize genome that were associated with seed Fe bioavailability. Hence, we subsequently developed more targeted maize lines that we determined had either high and low seed Fe bioavailability. Subsequent reanalysis of these same lines after the seed is more than 1 year old indicate that the enhancing effect on Fe bioavailability is no longer present once the seed has been stored for 1 year or more. These results suggest that after about a year, the compounds that are present in the enhanced lines are no longer active in effect. Alternatively, other compounds may be generated in storage that result in a decrease in Fe bioavailability. Over the past two years, many additional crosses and plantings of the high and low bioavailable maize lines first developed in 2008-2009 by the ARS cooperative project 1907-21000-032-00D were evaluated. These lines, however, behaved inconsistently with regard to Fe bioavailability. The cooperative project is now conducting the studies to find reasons for those inconsistencies and to resolve the problem. Given the above mentioned results, we have begun screening maize samples from what is known as a “diversity panel” of maize samples. This is essentially a collection of samples that have been mapped for molecular markers and represents a major portion of the genetic diversity in maize worldwide. The previous mapping population we used to develop the lines we have studied to date was not as broad in diversity; hence, by analyzing the diversity panel, we are approaching this research from a different angle with the hope of reproducing the previous high and low maize seed available Fe lines.
1. ARS researchers at Ithaca, New York identified the polyphenolic compounds that influence Fe bioavailability in black beans. One of these is myricetin which is a major inhibitor of Fe bioavailability. However, caffeic acid and epicatechin were found to promote Fe bioavailability. These results are valuable to bean breeders allowing them to modify the concentration of these compounds to improve Fe bioavailability in black beans. The impact of these findings can be extended other crops such as lentils, peas, red beans and maize.
Tako, E.N., Blair, M., Glahn, R.P. 2011. Biofortified red mottled beans (phaseolus vulgaris L.) in a maize and bean diet provide more bioavailable iron than standard red mottled beans: studies in poultry (Gallus gallus) and an in vitro digestion/Caco-2 model. Nutrition Journal. 10:113.