A universally calibrated microplate ferric reducing antioxidant power (FRAP) assay for foods and applications to Manuka honey
AuthorsBolanos de la Torre, Angelica A. S.
Nigam, Poonam S.
Owusu-Apenten, Richard K.
AffiliationONIRIS, Ecole Nationale Vétérinaire; Ulster University; University of Chester;
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AbstractThe ferric reducing antioxidant power (FRAP) assay was recently adapted to a microplate format. However, microplate-based FRAP (mFRAP) assays are affected by sample volume and composition. This work describes a calibration process for mFRAP assays which yields data free of volume effects. From the results, the molar absorptivity (ε) for the mFRAP assay was 141,698 M−1 cm−1 for gallic acid, 49,328 M−1 cm−1 for ascorbic acid, and 21,606 M−1 cm−1 for ammonium ferrous sulphate. The significance of ε (M−1 cm−1) is discussed in relation to mFRAP assay sensitivity, minimum detectable concentration, and the dimensionless FRAP-value. Gallic acid showed 6.6 mol of Fe2+ equivalents compared to 2.3 mol of Fe+2 equivalents for ascorbic acid. Application of the mFRAP assay to Manuka honey samples (rated 5+, 10+, 15+, and 18+ Unique Manuka Factor; UMF) showed that FRAP values (0.54–0.76 mmol Fe2+ per 100 g honey) were strongly correlated with UMF ratings (R2 = 0.977) and total phenols content (R2 = 0.982)whilst the UMF rating was correlated with the total phenols (R2 = 0.999). In conclusion, mFRAP assay results were successfully standardised to yield data corresponding to 1-cm spectrophotometer which is useful for quality assurance purposes. The antioxidant capacity of Manuka honey was found to be directly related to the UMF rating.
CitationBolanos de la Torre, A. A. S., Henderson, T., Nigam, P. S., & Owusu-Apenten, R. K. (2015). A universally calibrated microplate ferric reducing antioxidant power (FRAP) assay for foods and applications to Manuka honey. Food chemistry, 174, 119-123.
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