> Honey inhibited bacterial growth due to high sugar concentration (reduced
> water activity), hydrogen peroxide generation, and proteinaceous compounds
> present in the honey. Some antibacterial activity was due to other
> unidentified components. The ability of honey to inhibit the growth of
> microorganisms varies widely, and could not be attributed to a specific
> floral source or demographic region produced in this study.
>
That sounds like there has been little advancement since the section on
antimicrobial activity of honey in my copy of Hive and Honeybee from the
1950's. Back then they called the unknown components "inhibine".
But Peter has quoted a study from 2004. I know that in New Zealand they
rate the "unique manuka factor" or UMF of manuka honey. I wondered what
this factor was, and find that it is not a substance that they are
measuring, but just a measure of its anti-microbial activity (by some
standard of some group at Waikato University). Seems very much like hype
to me, especially when you read about it in the sales pitches for high
priced manuka honey.
But a 2008 paper (NOT from New Zealand) seems to indicate that
methylglyoxal is the active ingredient and now there is a new scale
measuring its concentration. Maybe that is the secret ingredient in
Juanse's ulmo honey as well.
In Molecular Nutrition and Food Research:
Identification and quantification of methylglyoxal as the dominant
antibacterial constituent of Manuka (*Leptospermum scoparium) *honeys from
New Zealand
1. Elvira Mavric1,
2. Silvia Wittmann1,
3. Gerold Barth2,
4. Thomas Henle
Article first published online: 21 JAN 2008
Abstract
The 1,2-dicarbonyl compounds 3-deoxyglucosulose (3-DG), glyoxal (GO), and
methylglyoxal (MGO) were measured as the corresponding quinoxalines after
derivatization with orthophenylendiamine using RP-HPLC and UV-detection in
commercially available honey samples. Whereas for most of the samples
values for 3-DG, MGO, and GO were comparable to previously published data,
for six samples of New Zealand Manuka (*Leptospermum scoparium*) honey very
high amounts of MGO were found, ranging from 38 to 761 mg/kg, which is up
to 100-fold higher compared to conventional honeys. MGO was unambigously
identified as the corresponding quinoxaline *via* photodiodearry detection
as well as by means of mass spectroscopy. Antibacterial activity of honey
and solutions of 1,2-dicarbonyl towards* Escherichia coli* (*E. coli*)
and*Staphylococcus aureus
* (*S. aureus*) were analyzed using an agar well diffusion assay. Minimum
concentrations needed for inhibition of bacterial growth (minimum
inhibitory concentration, MIC) of MGO were 1.1 mM for both types of
bacteria. MIC for GO was 6.9 mM (*E. coli*) or 4.3 mM (*S. aureus*),
respectively. 3-DG showed no inhibition in concentrations up to 60 mM.
Whereas most of the honey samples investigated showed no inhibition in
dilutions of 80% (v/v with water) or below, the samples of Manuka honey
exhibited antibacterial activity when diluted to 15–30%, which corresponded
to MGO concentrations of 1.1–1.8 mM. This clearly demonstrates that the
pronounced antibacterial activity of New Zealand Manuka honey directly
originates from MGO.
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