An universally calibrated microplate ferric reducing antioxidant power (FRAP) assay for foods and applications to Manuka honey

Amparo Angelica S. Bolanos de la Torre, Terence Henderson, Poonam Singh Nigam, Richard K. Owusu-Apenten

Research output: Contribution to journalArticle

59 Citations (Scopus)

Abstract

The 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 mFRAP assay was 141698 M-1 cm-1 for gallic acid, 49328 M-1cm-1 for ascorbic acid, and 21606 M-1cm-1 for ammonium ferrous sulphate. The significance of ε (M-1cm-1) is discussed in relation to mFRAP assay sensitivity, minimum detectable concentration, and the dimensionless FRAP-value. Gallic acid showed 6.6 moles of Fe2+ equivalents compared to 2.3 moles 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 100g 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 standardized 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 (199 words)
Original languageEnglish
Pages (from-to)119-123
Number of pages5
JournalFood Chemistry
Volume174
Issue number1
Early online date7 Nov 2014
DOIs
Publication statusPublished - 1 May 2015

Keywords

  • Antioxidant capacity
  • Microplate assay
  • Ferric reducing antioxidant power
  • FRAP
  • Manuka honey

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