Total Phenols, Antioxidant Capacity and Antibacterial Activity of Manuka Honey Extract

Aims: To evaluate total phenols content (TPC), antioxidant capacity (TAC) and antibacterial activity of Manuka honey extract (MHE) and to compare such properties with those for unfractionated Manuka honey.

Study Design: In vitro study.

Place and Duration of Study: School of Biomedical Sciences, Ulster University, Coleraine, UK. Between September 2016 and September 2017.

Methodology: MHE was prepared by solvent extraction using ethyl acetate. TPC was determined by Folin-Ciocalteu assay. The iron (III) reducing antioxidant capacity (IRAC) method was used to determine TAC. Antibacterial activity was evaluated using disc diffusion assay and 96-well microtiter plate methods with absorbance measured at 600 nm.

Results: The TPC for MHE was 30-fold higher than the value for Manuka honey (33420 ± 1685 mg vs. 1018 ± 78 mg GAE/kg) while TAC values were ~100-times greater (83,198 ± 7064 vs. 793 ± 104 TEAC, respectively). Antibacterial activity assessed by disc diffusion for Manuka honey (18.5mm on S. aureus and 20 mm on E. coli) was two times greater than for MHE (9mm for both S. aureus and E. coli). The 96-well microtiter plate assay confirmed the greater antibacterial activity for Manuka honey compared to equal concentrations MHE.

Conclusion: A polyphenol-rich Manuka honey extract with a high total antioxidant capacity, showed little or no antibacterial activity against E. coli and S. aureus in contrast with unfractionated Manuka honey.