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Manuka Honey

Manuka honey is

produced in New Zealandfrom two closely relatedplants, both of which arecommonly referred to asmanuka.

The most common honeysource of these isLeptospermum scoparium.Other names for this plantinclude kahikatoa, red teatree, and red manuka.

The other plant is Kunzea ericoides (reclassifiedfrom Leptospermum ericoides in 1983) and iscalled manuka and kanuka. Other names includewhite manuka, white tea tree and heath likemanuka.

The Leptospermums are a genus comprisingaround 50 species that is widely spread throughoutthe South West corner of the Pacific. Hybridisingand cross breeding occurs naturally between someof the species and this is also used as a tool byplant breaders to create ornamental varieties with ahigh variability of leaf and flower colours and multipetal 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 medicinalpurposes. These include use of the bark as a poultice, for colds, for flu, and stomach aches. Both plants are called "teatree" 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 thereare easily identifiable characteristics e.g. the flowers and seed capsules for manuka can be up to twice the size of thoseof kanuka and mature kanuka is usually significantly larger than any manuka, but with the absence of these clues, amore 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). AnotherLeptospermum 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 higherthan 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 ahoney. Most flower honeys have low mineral content and a lowconductivity. Manuka however has a conductivity that is approaching thatof 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 maybe a feature of manuka honey.

Manuka asa

Honeydew

Source

Both manuka and kanuka are inhabited by a variety of scale insects, butparticularly Eriococcus sp and Coelostomidia sp. These scale insects

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are producers of honeydew and the consequence of this is oftenobserved as a black sooty mould on manuka and kanuka, andthe plants exuding a sweet honeydew smell. Often this smellcan be detected more than 200 metres away from the source.The sooty mould is seen as a blackness all over the plants butparticularly on the branches and stems of the plants.

It is common for honeydew elements (fungal particles from thesooty mould) to be found in manuka honey. It is possible thatsome of the high conductivity for manuka honey is caused by itbeing a honeydew source.

Pollen Analysis

Pollen analysis of manuka honey is a reliable determinant of itsfloral origin in most cases. There are instances however wheresome other honey plants can provide a significant proportion ofthe nectar without contributing to the pollen spectrum. Two inparticular are worth noting. These are Rewarewa and Beechhoneydew. Both these honeys have a colour similar to manukaand both have stronger flavours that are not completelydissimilar 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 than 200,000 pollen grains per 10 grams) and with thepresence 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 thehigh conductivity and presence of honeydew elements ofmanuka. Local knowledge of the production location is helpfulhere.

Because of manuka honey's thixotropic nature, the honeyextraction process requires a mechanical loosening or "pricking"prior to the frames being extracted. Some producers scrape thecombs back to the mid rib rather than use a honey loosener.Being a valuable honey, producers may also take honey fromaround or close to the hive's brood nest where there is a highoccurence of stored pollen. Both this and the extractiontechniques peculiar to manuka honey may result in high totalpollen counts of pollen species collected by bees foraging onpollen and not derived from the nectar source. For pollen analysispurposes these species are extraneous and cause thepercentage of manuka pollen to be lower. Producers need toadjust their management to minimize this effect and buyers needto be aware of this effect when interpreting pollen data.

The pollen of both manuka and kanuka are indistinguishable fromeach other under a compound microscope. Any attempt todifferentiate between the two honeys is thwarted by this and alsothe close proximity of both plants to each other, their close (oftenoverlapping) time of flowering, and the fact that both plants arereferred 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 thisantibacterial activity is almost exclusively derived from Hydrogen Peroxide (H2O2) and is referred to as Peroxide Activityor PA. This is created from the activity of the enzyme Glucose Oxidase in honey. Like many enzymes, GlucoseOxidase 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 claimedby some sellers that they pack their product in dark coloured jars to protect this enzyme from light. Another reasonperhaps is their desire to hide the variable nature of the contents from the discerning consumer!

Non Peroxide Activity

Manuka honey also has this varying degree of antibacterial activity due to H2O2, but has been found to have a furtheramount of antibacterial activity that is present after the H2O2 has been neutralized with Catalase. This activity is referredto as the Non Peroxide Activity (NPA). The letters UMF ("Unique Manuka Factor") have been privately trademarked inNew 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 smallpart of the NPA had been accounted for with the discovery of a number of naturally occurring compounds in manukahoney.

Methylglyoxal - MGO

In 2006 Methylglyoxal (MGO) (Wikipedia Link) was discovered to be the main substance in manuka honey responsible forNPA by professor Henle from Dresden University. This work was confirmed and elaborated on by Waikato University in2007. MGO is found in numerous food substances but only at low levels (usually less than 10 ppm) compared to highNPA manuka honey.

MGO is a member of the dicarbonyl group (a group of toxic substances) and at the levels found in some manuka

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honeys, (up to 1,000 ppm) there is some concernregarding its food safety. MGO is the mainprecursor to Advanced Glycation End products(AGEs). AGEs are associated with a number ofage related diseases including Alzheimer'sdisease, cardiovascular disease, stroke, eyecataracts, cancer and diabetes. The body has aspecific enzyme system (the glyoxalase system)to detoxify this compound. This enzyme systemhas been found in the simplest life forms on earthas well as in mammals, indicating that itsdetoxification of MGO is universally importantto most life on earth.

The main benefit of NPA / MGO active manuka isthat it can be sterilized by irradiation for use as awound dressing. Theoretically this sameirradiation would neutralize any glucose oxidasedue to the large molecule size and fragility ofglucose oxidase but this is not borne out by this

study.

As a topically applied wound dressing the MGOhas little chance of entering the body to cause anysignificant negative effects. However, eating highNPA / UMF / MGO manuka honey is anotherstory. Since manuka with MGO has no provenMGO related benefit once swallowed (see below forinformation on stomach ulcers), it should be notedthat oral consumption of manuka with high NPAvalues may provide a significant health risk.

Further research at Waikato University in NewZealand has shown that MGO in manuka honey isderived from dihydroxyacetone (DHA) that can befound in the flowers of some L. scoparium subspecies. It is clear from this research (publishedApril 2009) that this substance is found indiffering quantities in various L. scoparium subspecies. To quote from the research:"All the manukanectars contained dihydroxyacetone but invarying amounts"and

"that there is variation in theamount of dihydroxyacetone in thenectar and that certain manukatrees have the potential to producehoneys with high nonperoxideantibacterial activity, whereasothers do not."

Because of this variability it cannottherefore be used as a quantitativefloral marker compound for manukahoney. i.e. the level of NPA activity ofmanuka is not an indicator of thepurity of manuka honey, in contrast tosome claims to the contrary. In facthoney with moderate levels (10-15 %phenol equivalent) of NPA activitymay only have very small levels ofmanuka honey.

Not all manuka honey has PA and notall manuka honey has NPA. Somemanuka honeys have both types ofactivity, and some have little or none.There is also a great deal of seasonalvariation, with both types of activitybeing individually either present orabsent in any particular honeyseason. To date, manuka has beentested 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 benoted that action recorded in the laboratory does not automatically translate into the same action with topical applicationor particularly ingestion.

Glossary.

Active - A contraction of "antibacterial activity" meaning the property of to inhibit the growth of bacteria.PA - Peroxide Activity. The antibacterial activity that is derived from Hydrogen Peroxide found in most honey in varyingamounts.TPA - Total Peroxide Activity. Same as PA above.TAA - Total Antibacterial Activity - a measurement of all antibacterial activity. Sometimes also called TAGlucose Oxidase - An enzyme in honey mostly responsible for the formation of Hydrogen Peroxide and also producing

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much of honey's acidity.NPA - Non Peroxide Activity. ANY antibacterial activity found in any honey once it has been treated with Catalase toremove 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 theNPA in manuka honey relative to phenol. When used on honey products it is usually associated with a number being theequivalent 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 - a toxic substance attributed with most of the NPA in some manuka honeys. Measured directlyand levels usually reported in parts per million (same as milligrams per kilogram mg/kg). Hydrogen Peroxide - Formed in most honeys (including manuka) from the action of the enzyme Glucose Oxidase (seeabove). There is a large degree of variability between honeys. A highly effect antibacterial agent. Used by white bloodcells as a mechanism for killing bacteria.DHA - Dihydroxyacetone, the manuka plant derived substance from which MGO is formed in manuka honey. Also is thekey 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 mainprecursor of AGEsPhenol - A chemical with antiseptic properties. It is used as a comparative standard for the measurement of antibacterialactivity in microbiological assays of some honey. An old and outdated method, but Numbers quoted usually refer to apercentage of Phenol in water. A higher number indicates a higher percentage of Phenol, thus theoretically higherantibacterial activity. In practise the use of this methodology and scale is problematic and has been the cause of muchuncertainty 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 -thebacteria considered the main cause of stomach ulcers. However clinical trials in New Zealand with NPA manuka(and repeated by clinical trials in the UK) failed to show manuka to be effective against Helicobacter pylori inthe stomach. Further research on this, particularly the ideal delivery system,including dosage rates, is needed beforeclaims of a cure for stomach ulcers can be made. IMPORTANT! Anyone contemplating using manuka honey as atreatment for stomach ulcers should only do so under the guidance of a health professional.

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