This work describes a calibration process for mFRAP assays which yields data free of volume effects. From the
results, the molar absorptivity (e) for the mFRAP assay was 141,698 M1 cm1 for gallic acid,
49,328 M1 cm1 for ascorbic acid, and 21,606 M1 cm1 for ammonium ferrous sulphate. The significance
of e (M1 cm1) 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.
This work describes a calibration process for mFRAP assays which yields data free of volume effects. From the
results, the molar absorptivity (e) for the mFRAP assay was 141,698 M1 cm1 for gallic acid,
49,328 M1 cm1 for ascorbic acid, and 21,606 M1 cm1 for ammonium ferrous sulphate. The significance
of e (M1 cm1) 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.
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