The Study of the Antioxidant Activity of Phenolic Components of Manuka Honey

The phenolic compounds of honey have been known to pose significantly antioxidant activity, including iron-binding and free radical scavenging activity. Manuka honey has been widely used in wound treatment and the antioxidant activity of manuka honey is important in that. However, the antioxidant activity of phenolic compounds of manuka honey has been studied in a few of cases. The aim of this study was to identify the molecular structure of phenolic compounds of manuka honey mainly responsible for each type of antioxidant activity (iron-binding and free radical scavenging activity). The measurement of iron-binding type of activity was based on the inhibition of the Fenton reaction using the β-carotene-linoleic acid model system and the measurement of free radical scavenging activity was based on ABTS system. The phenolic extracts of manuka honey obtained off XAD column was run through Sephadex G-25 column. The elution was pooled to form fractions for assaying of antioxidant activity, so that the fractions with highest antioxidant activity can be detected. The fractions with highest antioxidant activity, including iron-binding and free radical scavenging activity, were re-run through Sephadex G-25 again, and the resulting fractions were assayed. After repeating fourth running through Sephadex G-25 column, 5 pools with highest antioxidant activity were obtained. The elution volumes of these 5 pools were mainly from 105.6 – 115.2 ml, indicating that this volume range had most of the antioxidant activity for phenolic extracts of manuka honey. Five pools were further separated by Superdex Peptide column on the FPLC system. The results showed that each pool was separated to have several main peaks. Each peak obtained from chromatography of all five pools was taken for activity assay. The peak with highest iron-binding activity was selected for structure identification by UV and mass spectra methods. The conclusion was made that the phenolic compound responsible for iron-binding type of antioxidant activity could be the molecule with molecular weight of 458