Total Phenols, Antioxidant Capacity and Antibacterial Activity of Manuka Honey Chemical Constituents

Abstract

Aims: To compare the total phenol content, antioxidant capacity and antibacterial activity of methyl syringate (MSY), methylglyoxal (MGO) and phenyllactic acid (PLA) as major components from Manuka honey Study Design: In-vitro study. Place and Duration of Study: Nutrition Innovation Centre for Food and Health (NICHE), School of Biomedical Sciences, University of Ulster, Coleraine Campus, between June 2016 and September 2017. Methodology: Total phenols content (TPC) was determined using the Folin-Ciocalteu assay. Antioxidant capacity was evaluated as 2,2′-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid (ABTS) radical quenching activity  or iron (III) reducing antioxidant capacity (IRAC).  Antibacterial activity was measured using the disc diffusion assay with, E.coli, Bacillus subtilis or Staphylococcus aureus. Results: The TPC for MSY was 60.8 % gallic acid equivalents (GAE) and significantly higher than 1.6-3.2% GAE observed for MGO or PLA. The antioxidant capacity for MSY (128% to 270% trolox equivalents (TE)) was significantly higher compared with -6% to 4.4%TE for MGO or PLA.  A disc diffusion assay for MGO and PLA showed antibacterial power but MSY had no antibacterial activity. Conclusion: Methylglyoxal and PLA from Manuka honey showed antibacterial activity but no detectable antioxidant and total phenol character. Methyl syringate, which shows high antioxidant capacity and TPC, had no detectable antibacterial activity. Total phenols content and antioxidant power of Manuka honey is unlikely to be related to its antibacterial activity.