Antimicrobial & antioxidant activity

Background

Evidence of “active” honey was discovered when a positive random test for antibiotic residue in honey samples from one of Western Australian (WA) packers proved to be false after honey samples were re-run using a more expensive test.

Khaira and Mee (2000) at the Department of Microbiology, The Queen Elizabeth II Medical Centre, University of Western Australia examined the minimum inhibitory concentrations (MIC) of various WA honey samples (from the August 1999 to January 2000 flowering season). Jarrah honey was a most active honey against microbes than all others tested. Its MIC for the most active Jarrah sample was 20% w/v (20 g honey in 100 mls water) for Candida albicans, 5% w/v for Pseudomonas aeruginosa and Escherichia coli, and 2.5% w/v for Staphylococcus aureus. S. aureus was the most sensitive microbe to Jarrah honey.

On the 26 February 2002, the then Department of Agriculture released a media statement about the results of research conducted by Rob Manning and Nola Mercer about WA honeys’ antimicrobial activity using an assay developed in New Zealand. The research showed that Western Australian honey had some of the highest activity levels in the world due to a naturally occurring enzyme in the honey. Upon dilution of honey, the enzyme glucose oxidase produces low concentrations of hydrogen peroxide which is the source of its antimicrobial activity. It is different to Manuka (Leptospermum scoparium) honey from New Zealand which is termed a ‘non-peroxide’ (Molan and Russell 1988) honey because it’s activity is derived from a chemical called methylglyoxal. The chemical, the “Unique Manuka Factor (UMF)” in Manuka is unique and so far it has only been discovered in honey from Leptospermum species (Allen et al. 1991; Anon 1998; Davis 2005) which includes a species found in Western Australia (Beeinformed 2008).

Since 2002, further research into WA honeys has been undertaken by researchers at the University of Sydney, Western Australian beekeepers and Wescobee Ltd. In 2009, Wescobee Ltd launched a new product that promoted a 100% honey product based on its antimicrobial activity into a health-care market for the first time and with it won an export award into Japan in 2010 (Wescobee 2011).

The Jarrah honey crop has been significantly affected by adverse environment conditions, particularly by drought for many of the years since 2002.

This bulletin provides a history of the discovery of active honeys in WA and more recently antioxidant activity.

Introduction

Honey is a highly complex mixture of at least 200 phytochemicals whose composition is strictly dependent on floral and geographical origin (Beretta et al. (2005). The antimicrobial activity of honey is due to its osmotic effect, acidity and the presence of hydrogen peroxide (Molan 1992) which can vary markedly between samples (Molan et al. 1988; Garcia et al. 2000; Brady et al. 2004). The hydrogen peroxide activity can be measured, and is now important in grading the activity of the honey in qualitative terms for the pharmaceutical-medical market, specifically in wound care and for skin infections.

Hydrogen peroxide presence in honey is derived from the enzymatic activity of glucose oxidase. The source of glucose oxidase found in honey can originate from the honey bees’ hypopharyngeal glands that are located within its head (Gauhe 1941, cited in Weston 2000) or from the nectar of the flower (Carter and Thornburg 2004).

Hydrogen peroxide is found in varying concentrations in honeys (Allen et al. 1991) and is produced optimally when honey is diluted to concentrations between 30 – 50% (v/v) (Bang et al. 2003). However, results from a number of surveys can show samples of honey with little or no antimicrobial activity (Allen et al. 1991; Brady et al. 2004).

Honeys with a high antimicrobial activity have achieved medical status as being important effective antiseptic alternatives when dressing wounds, burns and ulcers (Molan 2001).

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