Rapid Colorimetric Determination of Methylglyoxal Equivalents for Manuka Honey
AuthorsKwok, T. H.
Yusof, H. I. Mohd
Nigam, Poonam S.
Owusu-Apenten, Richard K.
AffiliationUniversity of Chester, University of Ulster
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AbstractAims: Realization of a rapid colorimetric assay for monitoring levels of methylglyoxal and other dicarbonyl compounds from Manuka honey. Methods: N-acetyl cysteine (NAC) and 2, 4-dinitrophenylhydrazine (DNPH) were adopted as reagents for methylglyoxal colorimetric analysis of honey at 288 or 525 nm, respectively. Results and Discussion: NAC and DNPH produced linear responses for methylglyoxal with:(i) regression coefficient (R2) equal to 0.99 or 0.97, (ii) molar absorptivity (measure of sensitivity) equal to 287±11 or 14189±498 M-1 cm-1, (iii) a minimum detectable concentration (MDC) of 0.18 mM vs 7.3 µM, (iv) upper linearity limit of linearity (ULL) equal to 4mM or 83 µM, and (v) a day-to-day precision of 16.0 and 18.3%, respectively. Low interferences occurred with reducing sugars, glyoxal or 3-deoxy-D-glucosone. For honey with a unique manuka factor (UMF) rating 5+ to UMF18+, the net concentration of dicarbonyl compounds ranged from 1069 mg-methylglyoxal equivalence per kg (mg MeGEq /kg) to 2208 (mg MeGEq /kg) using the NAC assay. For the DNPH assay, the apparent dicarbonyl concentration was 350 to 1009-mg MeGEq /kg honey. Measures of methylglyoxal equivalences were strongly correlated with the UMF rating for honeys (R2=0.98-0.99). Conclusion: The proposed colorimetric analysis of methylglyoxal equivalence in Manuka honey is feasible proposition. Further work is needed for method validation.
CitationKwok, T. H., Kirkpatrick, G., Mohd Yusof, H. I., Portokalakis, I., Nigam, P., & Owusu-Apenten, R. (2016). Rapid colorimetric determination of methylglyoxal equivalents for Manuka honey. Journal of Advances in Biology & Biotechnology, 7(1), 1-6.
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