Manuka honey is produced predominantly in New Zealand by European honey bees ( mellifera) feeding on the Manuka tree flower (Leptospermum ) nectars (Adams 2009). According to the New Zealand Ministry for Primary Industries, Manuka-type honey has the following, naturally produced, characteristics (NZMPI 2015):
A color greater than 62 mm .
A conductivity range of 347-867 µS/cm.
A flavor typical of Manuka-type honey (mineral, slightly bitter).
An aroma typical of Manuka-type honey (damp earth, heather, aromatic).
Presence of Manuka-type pollen.
Presence of dihydroxyacetone (DHA) and methylglyoxal (MG)
Manuka Honey Production
Manuka honey is mainly produced in New Zealand by approximately 3800 bee keepers and over 400,000 hives ( 2013). Figure 2 illustrates a typical Manuka honey apiary, found adjacent to heavily wooded areas. Some farmers use helicopters to find areas with dense Manuka bushes to aid in hive placement ( 2013). According to Unique Manuka Factor™ Honey Association (UMFHA) data, approximately 1,700 tons of Manuka honey are produced annually in New Zealand, representing almost all of the world's production ( 2013). However, approximately 10,000 tons are being sold internationally as Manuka honey, including 1,800 tons in the UK alone ( 2013). Counterfeit issues have become a significant concern with Manuka honey; in one publication, 41 of 73 Manuka honey samples tested from Britain, China and Singapore showed no non-peroxide activity, which is a key feature of Manuka honey ( 2013).
Assessing Manuka Honey’s Purity and Potency
There are various methods reported for determining and documenting the potency and purity of Manuka honey. Unfortunately, there is a lack of standardization in regards to labeling of Manuka honey, making interpretation and comparison very confusing. In order to better standardize labeling of Manuka honey, new interim guidelines have recently been released by New Zealand’s Ministry for Primary Industries (http://archive.mpi.govt.nz/food/food-safety/manuka-honey ; NZMPI 2015). Most Manuka honeys are currently labeled with a grading system that include a numerical value and a potency descriptor. Examples of potency descriptors include: active, bioactive, total activity, total peroxide activity, total non-peroxide activity, unique Manuka factor™ (UMF™), and methylglyoxal levels (NZMPI 2015). Third party test results to substantiate label claims are typically not readily available. Recent guidelines have suggested that terms such as “Non-Peroxide Activity”, “Total Peroxide Activity”, “Peroxide Activity”, “Total Activity” and “Active” should be removed from labels and advertising, as these terms involve a therapeutic claim that suggest an antimicrobial effect (NZPMI 2015). Methylglyoxal is thought to be the major contributor to Manuka honey’s non-peroxide antimicrobial activity (Adams 2009). Levels in honey are typically reported in mg/kg. References to methylglyoxal are permitted on honey labels provided they’re not used to imply antibacterial effects (NZPMI 2015).
One of the most well-known grading systems for Manuka honey is the Unique Manuka Factor® (UMF®) grade, which is a trademark of the Unique Manuka Factor Honey Association. The UMFHA is a group of certified licensees (currently 67) that can use the UMF trade mark on their products. To receive a UMF® grading, a honey must have the presence of DHA (dihydroxyacetone), methylglyoxal, and . Values typically range from UMF® 5+ to UMF® 28+ that vary with the methylglyoxal level in the honey (see Table 1, UMFHA 2015).