The type of plant species involved in honey production is significant, as some confer greater antibacterial properties than others. Currently, evidence suggests honey produced from the tea trees Leptospermum scoparium (New Zealand manuka) and LipolygalifoHum (Australian jelly bush) are the most effective, but batch testing is still required to verify the antibacterial activity of commercially produced preparations. However, other honeys, not specifically promoted for their anti-bacterial qualities, may still have antibacterial activity (Lusby et al 2005).
Several mechanisms of action account for the antibacterial effect of honey. Hydrogen peroxide content Hydrogen peroxide has antiseptic properties and is naturally produced in honey. The relative levels of two enzymes, glucose oxidase and catalase, within honey influence the amount of hydrogen peroxide produced. Additionally, diluting full-density honey encourages greater hydrogen peroxide and gluconic acid production from glucose (Aysan et al 2002). Differences in antimicrobial activity among honeys from various floral sources may, in part, be a reflection of these natural variations.
High osmolarity Honey has a high sugar and low water content, with sugar concentration reaching up to 80% in some seasons. Its high osmolarity is considered
important because sugar molecules bind existing water molecules, thereby reducing the amount of water available to bacteria.
Low pH Honey is an acidic substance and therefore unfavourable to the growth of certain bacteria. In vitro testing shows that Leptospermum honey can inhibit the growth of several important bacterial pathogens, including Escherichia coli, Salmonella typhimurium, Shigella sonnei, Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus and Streptococcus mutans (Steinberg etal 1996, Taormina etal 2001).
Honey has also been tested for efficacy against a range of drug-resistant bacteria, with positive results (Cooper et al 2002). Eighteen strains of methicillin-resistant Staphylococcus aureus and 27 strains of vancomycin-sensitive and resistant enterococci isolated from infected wounds and hospital surfaces were sensitive to concentrations below 10% w/v of manuka honey and pasture honey. Artificial honey was also effective, but concentrations three times greater were required to produce similar results.
Phenolic compounds The antioxidant activity of honey has been associated with the levels of phenolic compounds found in a range of floral honeys, with antioxidant activity varying between 43.0% and 95.7%. The responsible compounds suggested include p-coumaric acid, kaempferol, chrysin and apigenin (Baltrusaityte et al 2006). The variation in the concentration of the phenolic compounds between different floral honeys is further confirmed through another study, which found millefiori honey highest in polyphenols, flavonoids, and a corresponding high antioxidant activity, when compared with Acacia honey (Blasa et al 2006).
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