OR/15/070 Conclusion
| 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. |
A reliable method for the measurement of phytic acid in typical grain samples using UV/Vis spectroscopy and a commercially available assay kit from Megazyme® was verified. Phytic acid concentrations for a control sample of oat flour with a known concentration of 17 700 mg kg-1 produced a measured average of 17 862 mg kg-1, (within 1% of the known phytic acid concentration). Samples with concentrations approaching the LOQ of 1408 mg kg-1 demonstrated a lower precision than at higher concentrations. It is therefore recommended that all samples with a measured concentration below 2000 mg kg-1 phytic acid will be run in duplicate.
Standards at 7 and 80% of the top calibration concentration were found to show accuracies of 94 and 90%, respectively. Due to no commercially available certified reference material (CRM) being identified during validation, the oat powder sample provided by Megazyme® can be used as a quality control sample until a CRM can be sourced.
Reproducibility for wheat grain samples was demonstrated with a precision of 10% between separate runs, meeting the validation criteria outlined in Appendix 2. Rice samples were likely more homogenous and hence produced measurements within these limits, excluding the sample with concentrations below 2000 mg kg-1 phytic acid.
Spike recovery data for phytic acid were well within the limits set by the validation plan. Recovery was 94%, with an extremely high precision of 0.8%. The total spike concentration fell within the calibration concentration range of 45 to 55% with measured concentrations between 13 500 and 15 100 mg kg-1 of phytic acid. Using the Students T-Test, the null hypothesis for analyst variation was confirmed by a P-value of 0.91.
In summary, all validation tests passed the initial requirements of the validation plan with an exception of samples containing a phytic acid concentration below 2000 mg kg-1, close to the LOQ. The method described is fit-for-purpose for typical concentrations of phytic acid in common grain samples. In addition, the method through its simplicity is easily reproducible between operators, and could be transferred easily to labs with minimal infrastructure. The fast
throughput and low cost per sample will allow for large scale or routine analysis to better inform the impact of phytic acid mineral dietary intakes and enable improved mitigation approaches. The simplicity of the method will also allow for responsive analysis and is appropriate for small and large sample batches, due to the fast set-up of instrumentation compared to ion-chromatography.