Understanding the different ‘ratings’ on medicinal honey
Since the discovery that manuka and some other honeys have significant medicinal properties there have been a number of systems used by honey producers to describe and rate the activity.
There is currently an array of labels and terminology on different honeys, like UMF® (Unique Manuka Factor), NPA (Non-Peroxide Activity), MGO or MG (Methyglyoxal), Active + and TA (Total Activity). Unfortunately, this can be very confusing for people, but hopefully understanding what the different numbers mean will help.
Non peroxide activity (NPA) or Unique Manuka Factor (UMF®)
The NPA or UMF® ratings are used to describe the unique type of antimicrobial activity exhibited by certain Leptospermum honeys (a.k.a. manuka or jelly bush) from New Zealand and Australia. The lab tests used to generate these ratings are called “bioassays” because they test the honey directly against a biological organism (in this case, a germ related to Golden Staph). In the bioassays, the activity of honey is compared to a known antiseptic, phenol. So, the numbers generated from this assay are known as the ‘phenol equivalence’ rating, where a honey with NPA 10% is equivalent to the antibacterial activity we would see in a 10% phenol solution, honey with NPA 15% is equivalent to the antibacterial activity seen from a 15% phenol solution and so on.
The ‘Unique Manuka Factor’ (UMF®) rating system also uses a bioassay, as well as detection of key compounds that are characteristic of manuka honey: leptosperin, dihydroxyacetone (DHA) and methylglyoxal (MGO). UMF® is a trademark registered by the UMF honey Association in New Zealand and is only available for use under license by producers of manuka honey from New Zealand. Some other active Leptospermum honeys from New Zealand and Australia (with similar antimicrobial properties to New Zealand manuka) are sold with the NPA ratings.
Methylglyoxal – MGO (or MG)
Since it was discovered that methylgloxal (MGO) is responsible for much of the unique activity in manuka honey, a number of products on the market are labelled with a MGO (or MG) concentration. This is a direct measure of the amount of MGO in the honey and it is expressed as parts per million (ppm) or mg/kg. The numbers for this type of labelling are usually much higher than the NPA/UMF® ratings – although this doesn’t necessarily mean the honeys are more active.
There is a relationship between MGO concentration and the NPA/UMF® of a honey. However, it is important to remember that the numbers are derived from completely different types of tests, so they are not easily compared. Consumers should be aware that as the MGO scale is a completely different one, a “higher” MGO might not be as active as a honey with a “lower” NPA/UMF® rating.
As a rough guide:
NPA/UMF® 5+ = MGO 83
NPA/UMF® 10+ = MGO 263
NPA/UMF® 15+ = MGO 514
NPA/UMF® 20+ = MGO 829
But as there is more to the story of the medicinal activity of honey than the amount of MGO, just measuring this does not necessarily give the full picture of its medicinal potential.
Total activity generally refers to the activity of a honey in its entirety. That is, it includes all of the peroxide activity and any non-peroxide activity that might be present (but usually honeys marketed with “total” activity don’t have much of the unusual activity we see in manuka-type honeys).