Airborne Logo

Manuka Honey

Manuka honey is produced in New Zealand from two closely related plants, both of which are commonly referred to as manuka.

The most common honey source of these is Leptospermum scoparium. Other names for this plant include kahikatoa, red tea tree, and red manuka.

The other plant is Kunzea ericoides (reclassified from Leptospermum ericoides in 1983) and is called manuka and kanuka. Other names include white manuka, white tea tree and heath like manuka.

The Leptospermums are a genus comprising around 50 species that is widely spread throughout the South West corner of the Pacific. Hybridising and cross breeding occurs naturally between some of the species and this is also used as a tool by plant breaders to create ornamental varieties with a high variability of leaf and flower colours and multi petal variations.

For a further detailed discussion on "manuka" and common names, click here

Both the manuka and kanuka plants have historically been used by Maori and early European settlers for medicinal purposes. These include use of the bark as a poultice, for colds, for flu, and stomach aches. Both plants are called "tea tree" from the practice of making a tea from the leaves.

The physical identification between the two plants is often difficult even for experienced observers. In some cases there are easily identifiable Kanuka Flowers (Kunzea ericoides) commonly refered to as manuka characteristics e.g. the flowers and seed capsules for manuka can be up to twice the size of those of kanuka and mature kanuka is usually significantly larger than any manuka, but with the absence of these clues, a more detailed knowledge of the taxonomic differences is required to differentiate the two.

The honey is dark coloured, (around 84mm average colour ± 11.8mm SD - Pfund scale), strongly flavoured,with a herbal, woody characteristic, and is often highly "thixotropic" (jellied) like European Heather honey (Calluna vulgaris). Another Leptospermum in Australia (L. polygalifolium) also derives its name (Jellybush) from the thixotropic nature of its honey.

Manuka is classified as an over represented pollen type and has a higher than normal conductivity (about 4 times that of normal flower honeys.)

Manuka honey has an average glucose of 29.7%, fructose of 37.9%, maltose of 1.2% and sucrose of 0.5% (HPLC method, 775 samples)

Conductivity

Conductivity is an indirect measurement of the mineral content of a honey. Most flower honeys have low mineral content and a low conductivity. Manuka however has a conductivity that is approaching that of some honeydews. It has an average of 5.8 ± 1.54 standard deviation (SD). This may be due to manuka being a honeydew source, or it may be a feature of manuka honey.

Manuka as a Honeydew Source

Both manuka and kanuka are inhabited by a variety of scale insects, but particularly Eriococcus sp and Coelostomidia sp. These scale insects are producers of honeydew and the consequence of this is often observed as a black sooty mould on manuka and kanuka, and the plants exuding a sweet honeydew smell. Often this smell can be detected more than 200 metres away from the source. The sooty mould is seen as a blackness all over the plants but particularly on the branches and stems of the plants.

It is common for honeydew elements (fungal particles from the sooty mould) to be found in manuka honey. It is possible that some of the high conductivity for manuka honey is caused by it being a honeydew source.

Pollen Analysis

Pollen analysis of manuka honey is a reliable determinant of its floral origin in most cases. There are instances however where some other honey plants can provide a significant proportion of the nectar without contributing to the pollen spectrum. Two in particular are worth noting. These are Rewarewa and Beech honeydew. Both these honeys have a colour similar to manuka and both have stronger flavours that are not completely dissimilar to manuka.

In the case of Rewarewa, it has a low total pollen count. Any honey purporting to be manuka with a low total pollen count (less Manuka Pollen - electron microscope image than 200,000 pollen grains per 10 grams) and with the presence of Rewarewa pollen, should be carefully examined, even if it has more than 70% manuka.

The same applies to blends of manuka and Beech honeydew. This particular blend can be very difficult to assess due to the high conductivity and presence of honeydew elements of manuka. Local knowledge of the production location is helpful here.

Because of manuka honey's thixotropic nature, the honey extraction process requires a mechanical loosening or "pricking" prior to the frames being extracted. Some producers scrape the combs back to the mid rib rather than use a honey loosener. Being a valuable honey, producers may also take honey from around or close to the hive's brood nest where there is a high occurence of stored pollen. Both this and the extraction techniques peculiar to manuka honey may result in high total pollen counts of pollen species collected by bees foraging on pollen and not derived from the nectar source. For pollen analysis purposes these species are extraneous and cause the percentage of manuka pollen to be lower. Producers need to adjust their management to minimize this effect and buyers need to be aware of this effect when interpreting pollen data.

The pollen of both manuka and kanuka are indistinguishable from each other under a compound microscope. Any attempt to differentiate between the two honeys is thwarted by this and also the close proximity of both plants to each other, their close (often overlapping) time of flowering, and the fact that both plants are referred to by the common name "Manuka".

Antibacterial Activity in Manuka Honey - "Active" Manuka Honey

One area that is of particular interest regarding manuka honey is its antibacterial activity. Often this is just shortened to "Active" or "Active Manuka". Most honeys are in some way antibacterial (some quite highly so), but normally this antibacterial activity is almost exclusively derived from Hydrogen Peroxide (H2O2) and is referred to as Peroxide Activity or PA. This is created from the activity of the enzyme Glucose Oxidase in honey. Like many enzymes, Glucose Oxidase can become inactivated over time by light and heat. The stronger the light and/or heat, the faster it is inactivated. Room temperature and low light, given enough time, will in theory also reduce the Glucose Oxidase activity. It is claimed by some sellers that they pack their product in dark coloured jars to protect this enzyme from light. Another reason perhaps is their desire to hide the variable nature of the contents from the discerning consumer!

Honeybee collecting manuka nectar Non Peroxide Activity

Manuka honey also has this varying degree of antibacterial activity due to H2O2, but has been found to have a further amount of antibacterial activity that is present after the H2O2 has been neutralized with Catalase. This activity is referred to as the Non Peroxide Activity (NPA). The letters UMF ("Unique Manuka Factor") have been privately trademarked in New Zealand (UMF®) to represent a standard of NPA antibacterial activity that is compared to the disinfectant phenol. The UMF® letters are usually appended with a number. This number refers to the percentage of phenol in water. e.g. UMF12 equals an NPA activity equal to or greater than a 12% solution (%w/v) of phenol/water. Until 2006 only a small part of the NPA had been accounted for with the discovery of a number of naturally occurring compounds in manuka honey.

Methylglyoxal - MGO

In 2006 Methylglyoxal (MGO) was discovered to be the main substance in manuka honey responsible for NPA by professor Henle from Dresden University. This work was confirmed and elaborated on by Waikato University in 2007. MGO is found in numerous food Bee on Kanuka Flower substances but only at low levels (usually less than 10 ppm) compared to high NPA manuka honey.

MGO is a member of the dicarbonyl group (a group of toxic substances) and at the levels found in some manuka honeys, (up to 1,000 ppm) there is some concern regarding its food safety. MGO is the main precursor to Advanced Glycation End products (AGEs). AGEs are associated with a number of age related diseases including Alzheimer's disease, cardiovascular disease, stroke, eye cataracts, cancer and diabetes. The body has a specific enzyme system (the glyoxalase system) to detoxify this compound. This enzyme system has been found in the simplest life forms on earth as well as in mammals, indicating that its detoxification of MGO is universally important to most life on earth.

The main benefit of NPA / MGO active manuka is that it can be sterilized by irradiation for use as a wound dressing. Theoretically this same irradiation would neutralize any glucose oxidase due to the large molecule size and fragility of glucose oxidase but this is not borne out by this study.

As a topically applied wound dressing the MGO has little chance of entering the body to cause any significant negative effects. However, eating high NPA / UMF / MGO manuka honey is another story. Since manuka with MGO has no proven MGO related benefit once swallowed (see below for information on stomach ulcers), it should be noted that oral consumption of manuka with high NPA values may provide a significant health risk.

Further research at Waikato University in New Zealand has shown that MGO in manuka honey is derived from Manuka Flower (Leptospermum scoparium) dihydroxyacetone (DHA) that can be found in the flowers of some L. scoparium sub species. It is clear from this research (published April 2009) that this substance is found in differing quantities in various L. scoparium sub species.
To quote from the research:"All the manuka nectars contained dihydroxyacetone but in varying amounts"
and
"that there is variation in the amount of dihydroxyacetone in the nectar and that certain manuka trees have the potential to produce honeys with high nonperoxide antibacterial activity, whereas others do not."

Because of this variability it cannot therefore be used as a quantitative floral marker compound for manuka honey. i.e. the level of NPA activity of manuka is not an indicator of the purity of manuka honey, in contrast to some claims to the contrary. In fact honey with moderate levels (10-15 % phenol equivalent) of NPA activity may only have very small levels of manuka honey.

Not all manuka honey has PA and not all manuka honey has NPA. Some manuka honeys have both types of activity, and some have little or none. There is also a great deal of seasonal variation, with both types of activity being individually either present or absent in any particular honey season. To date, manuka has been tested in the laboratory against several strains of wound infecting bacteria and found to be effective in inhibiting the growth of most of them. It should be noted that action recorded in the laboratory does not automatically translate into the same action with topical application or particularly ingestion.

Glossary.

PA - Peroxide Activity. The antibacterial activity that is derived from Hydrogen Peroxide found in most honey in varying amounts.
TPA - Total Peroxide Activity. Same as PA above.
TAA - Total Antibacterial Activity - a measurement of all antibacterial activity. Sometimes also called TA
Glucose Oxidase - An enzyme in honey mostly responsible for the formation of Hydrogen Peroxide and also producing much of honey's acidity.
NPA - Non Peroxide Activity. ANY antibacterial activity found in any honey once it has been treated with Catalase to remove any hydrogen peroxide. Measured by microbial assay against a standard antiseptic (see Phenol below).
Catalase - An enzyme that breaks down Hydrogen Peroxide.
UMF® - A brand owned by the Active Manuka Honey Association (AMHA) that provides a measurement scale of the NPA in manuka honey relative to phenol. When used on honey products it is usually associated with a number being the equivalent of a percentage of phenol (see below)
AMHA - Active Manuka Honey Association. http://www.umf.org.nz. Now changed to UMFHA - see below.
UMFHA - UMF Honey Association. See AMHA above. The owner of the UMF® brand
MGO - Methylglyoxal the substance attributed with the NPA in some manuka honeys. Measured directly and levels usually reported in parts per million (same as milligrams per kilogram mg/kg).
DHA - Dihydroxyacetone, the manuka plant derived substance from which MGO is formed in manuka honey. Also is the key ingredient in most sunless tanning products - causes browning of the skin.
AGEs - Advanced Glycation End Products. Substances associated with causing age related diseases. MGO is the main precursor of AGEs
Phenol - A chemical with antiseptic properties. It is used as a comparative standard for the measurement of antibacterial activity in microbiological assays of some honey. An old and outdated method, but Numbers quoted usually refer to a percentage of Phenol in water. A higher number indicates a higher percentage of Phenol, thus theoretically higher antibacterial activity. In practise the use of this methodology and scale is problematic and has been the cause of much uncertainty and debate over activity ratings for manuka honey.

Additional References

Manuka Honey and Stomach Ulcers (Helicobacter pylori)

NPA Active Manuka honey has also been shown in vitro (in the test tube) to inhibit the growth of Helicobacter pylori -the bacteria considered the main cause of stomach ulcers. However clinical trials in New Zealand with manuka (and repeated by clinical trials in the UK) failed to show manuka to be effective against Helicobacter pylori in the stomach. Further research on this, particularly the ideal delivery system,including dosage rates, is needed before claims of a cure for stomach ulcers can be made. IMPORTANT! Anyone contemplating using manuka honey as a treatment for stomach ulcers should only do so under the guidance of a health professional.