OR/15/070 Introduction

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Reason, D A, Watts, M J, and Devez, A. 2015. Quantification of phytic acid in grains. (Inorganic Geochemistry, Centre for Environmental Geochemistry). British Geological Survey Internal Report, OR/15/070.

Mineral micronutrient deficiencies (MNDs) are an important global health problem, affecting up to two billion people worldwide (WHO, 2009, 2015[1]). The common mineral MNDs include; iodine (Andersson et al. 2012[2]; Watts et al. 2015[3]; Zia et al. 2015[4]), iron (Siyame et al. 2014[5]; Gibson et al. 2015[6]), selenium (Hurst et al. 2013[7]) and zinc (Ahmad et al. 2012[8]; Joy et al. 2015[9]; Kumssa et al., 2015b[10]). Estimates of deficiency for some minerals (Fe, I, Se, Zn), are often based on direct measurement of mineral concentrations or indicators in blood, urine or other tissues (Ku et al. 2015; Fairweather-Tait et al. 2011[11]). Alternatively, for elements including Mg, food consumption or food supply data can be used to calculate dietary mineral intakes to estimate the risk of deficiency (Kumssa et al. 2015a[12]; Ecker and Qaim, 2011[13]) and national Food Balance Sheets (FBSs) available from the United Nations Food and Agriculture Organisation (FAO, 2014[14]; Broadley et al. 2012[15]; Joy et al. 2012[16]; 2014[17]). Local food composition data has improved estimates of mineral deficiencies, and for some MNs demonstrated a strong influence of soil type on dietary composition (Chilimba et al. 2011[18]; Hurst et al. 2013[7]; Joy et al. 2015[9]), resulting in significant spatial variation.

Mineral MNDs in developing countries, particularly in Sub-Saharan Africa are exacerbated by a lack of dietary diversity, with reliance on a limited range of staple foods for calorific intake (e.g. maize, rice). Developing countries most effected by MNDs often have a high reliance on a plant based diet, with the consumption of meat and dairy products limited in availability (Joy et al. 2012[16]; Joy et al. 2014[17]). This lack of dietary diversity can often lead to an insufficient intake of Fe and Zn, (Hunt et al. 2003[19]), whilst also increasing the intake of phytic acid (or phytate). Foods possessing large concentrations of phytic acid result in significant reductions to the bioavailability of Zn (Cakmak et al. 1998). Phytic acid is often present in seeds, serving as a storage for myo-inositol and phosphorus, which is utilised during seed germination and seedling growth (Bentley et al. 2015). Phytic acid is a strong chelator of Fe2+ and Zn2+ in-vivo and poses a major risk of anti-nutrient deficiency throughout Africa and worldwide (Hunt et al. 2003[19]; Kumssa et al., 2015b[10]), limiting the bioavailability of these essential minerals from an already deficient dietary intake. Measurement of phytic acid in foodstuffs is an important consideration to improve population estimates for mineral deficiency in combination with direct human biomonitoring, FBS, food composition data and better understanding of the spatial controls on their soil-to-crop transfer.

This report describes the analytical method used to quantify phytic acid in grain samples using simple and relatively low-cost UV/Vis spectroscopy, which could easily be applied in a developing world situation. Whilst measurement by Ion Chromatography provides very high sensitivity and specificity for phytate (Harlanda et al. 2004[20]), it requires expensive equipment and consumables, a high degree of technical competency and takes approximately 20–30 minutes per sample for analyses following a complex extraction process to measure phytic acid in solution. A commercially available kit (K-PHYT 12/12 Megazyme, Ireland) was reported by Xue et al. (2015)[21] to determine the distribution of stable Fe57 and Zn68 isotopes in tissues of wheat lines with respect to phytic acid content, with sufficient sensitivity suitable for phytic acid in the majority of common grains (e.g. maize, rice). There is also the potential for high throughput with analyses taking only 6 minutes per sample, whilst using relatively low cost equipment that requires little maintenance and effort for calibration for each analytical batch. This methodology employed a commercially available assay kit from Megazyme® for measuring phytic acid by enzymatic and redox chemistry.

This report describes the validation and implementation of this method recently completed at BGS, with the aim of undertaking cost effective measurements of phytic acid in a range of food grains to improve estimations for dietary mineral intake.

References

  1. ↑ World Health Organization, Micronutrient deficiencies, http://www.who.int/nutrition/topics/ida/en/ (accessed Oct 2015).
  2. ↑ Andersson M, Karumbunathan V, Zimmermann, M B. Global iodine status in (2011) and trends over the past decade. (2012). Journal of Nutrition, 142, 744–750.
  3. ↑ Watts, M J, Joy, E J M, Broadley, M R, Young, S D, Ander, E L, Chilimba, A D C, Gibson, R S, Siyame, E W P, Kalimbira, and Chilima, B. Iodine source apportionment in the Malawian diet. (2015). Scientific Reports, 5, 1521.
  4. ↑ Zia, M, Watts, M J, Gardner, A, Chenery, S R. Iodine content of agricultural soil and grain from Pakistan. (2015). Environmental Earth Sciences, 1–14.
  5. ↑ Siyame, E, Hurst, R, Wawer, A W, Young, S D, Broadley, M R, Chilimba, A D C, Ander, E L, Watts, M J, Chilima, B, Gondwe, J, Kang’ombe, D, Kalimbira, A, Fairweather-Tait, S J, Bailey, K B, and Gibson, R S. A high prevalence of zinc but not iron deficiency among Women in Rural Malawi: a cross-sectional study. (2014). International Journal for Vitamin and Nutrition Research, 83, 3, 176–187.
  6. ↑ Gibson RS, Wawer AA, Fairweather-Tait SJ, Hurst R, Young SD, Broadley MR, Chilimba ADC, Ander EL, Watts MJ, Kalimbira A, Bailey KB, Siyame EWP. Dietary iron intakes based on food composition data may underestimate the contribution of potentially exchangeable contaminant iron from soil. (2015). Journal of Analytical Food Research, 40, 19–23.
  7. ↑ 7.0 7.1 Hurst, R, Siyame, E, Young, S D, Chilimba, A D C, Joy, E J M, Black, C R, Ander, E L, Watts, M J, Chilima, B, Gondwe, J, Kang’ombe, D, Stein, A J, Fairweather-Tait, S J, Gibson, R, Kalimbira, A, and Broadley, M R. Soil type influences human selenium status and underlies widespread selenium deficiency risks in Malawi. (2013). Scientific Reports, 3, 1425.
  8. ↑ Ahmad, W, Watts, M J, Imtiaz, M, Ahmed, I, and Zia, M H. Zinc deficiency in soils, crops and humans. (2012). Agrochimica, 2, 65–97.
  9. ↑ 9.0 9.1 Joy, E J M, Black, C R, Young, S D, Broadley, M R, Ander, E L, Watts, M J, and Chilimba, A D C. Zinc enriched fertilisers as a potential public health intervention in Africa. (2015). Plant Soil, 389, 1–24.
  10. ↑ 10.0 10.1 Kumssa, D B, Joy, E J M, Ander, E L, Watts, M J, Young, S D, Walker, S, and Broadley, M R. Dietary calcium and zinc deficiency risks are decreasing but remain prevalent. (2015b). Scientific Reports, 5, 10974.
  11. ↑ Fairweather-Tait, S J, Bao, Y, Broadley, M R, Collings, R, Ford, D, and Hesketh, J E. (2011). Selenium in human health and disease, Antioxidant Redox Signal (2011). 14, 1337–1383.
  12. ↑ Kumssa, D B, Joy, E J M, Ander, E L, Watts, M J, Young, S D, Rosanoff, A, White, P J, Walker, S, and Broadley, M R. Global magnesium (Mg) supply in the food chain. (2015a). Crop and Pasture Science, 66, 1278–1289.
  13. ↑ Ecker, O, and Qaim, M. Analysing nutritional impacts of policies: am empirical study for Malawi, World dev (2011). 39, 412–428.
  14. ↑ FAO, Food Balance Sheets, http://faostat3.fao.org/browse/Q/*/E, (accessed 02/12/2015).
  15. ↑ Broadley, M R, Brown, P, Cakmak, I, Rengel, Z, Zhao, F. Function of Nutrients: Micronutrients. In Marschner’s Mineral Nutrition of Higher Plants 3rd edition. (2012). ed. P. Marschner, pp.191–243. Boston, MA: Academic Press.
  16. ↑ 16.0 16.1 Joy, E J M, Young, S D, Black, C R, Ander, E L, Watts, M J, and Broadley, M R. Risk of dietary magnesium deficiency is low in most African countries based on food supply data. (2012). Plant and Soil, 368. 129–137.
  17. ↑ 17.0 17.1 Joy, E J M, Ander, E L, Young, S D, Black, C R, Watts, M J, Chilimba, A D C, Chilima, B, Siyame, E W P, Kalimbira, A A, Hurst, R, Fairweather-Tait, S J, Stein, A J, Gibson, R S, White, P J, and Broadley, M R. Dietary mineral supplies in Africa. (2014). Physiologia Plantarum, 151, 208–229.
  18. ↑ Chilimba, A D C, Young, S D, Black, C R, Rogerson, K B, Ander, E L, Watts, M J, Lammel, J, and Broadley, M R. Maize grain and soil surveys reveal suboptimal dietary selenium intake is widespread in Malawi. (2011). Scientific Reports, 1, 72.
  19. ↑ 19.0 19.1 Hunt, J R. Bioavailability of iron, zinc, and other trace minerals from vegetation diets. (2003). The American Journal of Clinical Nutrition, 78, 633S–639S.
  20. ↑ Harlanda, B F, Smikle-Williams, S, Oberleas, D. High Performance Liquid Chromatography analusis of phytate (IP6) in Selected Foods. (2004). Journal of Food Composition Analysis. 17, 227–233.
  21. ↑ Xue, Y F, Xia, H Y, McGrath, S P, Shewry, P R, and Zhao, F J. Distribution of the stable isotopes 57Fe and 68Zn in grain tissues of various whear lines differing in their phytate content. (2015). Plant Soil, 396, 73–83.
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