The variability in the level of the antibacterial component (UMF) of Manuka honey produced in New Zealand has been examined. A field analysis conducted a study, which confirms a considerable variability exhibited by New Zealand produced Manuka honey, a number of reasoning hypotheses were proposed and examined. Honey derived from Leptospermum scoparium (Manuka), was indeed confirmed to be the source of UMF.
The dilution of Manuka honey with nectar derived from other floral sources was found to proportionally reduce the UMF in monofloral Manuka honey. The utilisation of the thixotropic properties of Manuka honey allowed the degree of dilution in the field samples to be distinguished, and after adjustments were made to the results to account for the dilution of UMF by other honey types, it was revealed that all monofloral Manuka honey contains UMF. Although, in the monofloral Manuka honey, there were significant variability in the level of UMF activity.
The cause of the variable levels of UMF activity found in Manuka honey would appear to be mainly due to the fact that honeybees harvest varying levels of L, scoparium, as well as environmental parameters influencing nectar production or another species interacting with L scoparium did not appear to have an influence over the UMF activity.
There were three methods adopted to establish genetic variability within specific regions of the North Island of New Zealand that gave rise to the various levels of UMF activity. Analyses of morphological characteristics, chemotaxonomic essential oil profiles, and population genetics of L. scoparium populations were all conducted, with the conclusions of each being very similar. There were two key divisions identified by the analysis, each being divided into two varieties. The northern division, which consisted mainly of the Northland and Waikato region, represented the previously described L. scoparium var. This division yielded Manuka honey and had high UMF activity results. The southern division, consisting largely of Central North Island and East Coast, represented the previously described L. scoparium var. Myrtifolium and an unnamed variety. The latter, growing chiefly on the East Coast, contains unique triketones essential oils;. However, the southern divisions UMF results were lower than that found in the northern region. Hybridisation between the varieties will occur, leading to a continuum of UMF activity among Manuka honey. The data indicated multiple dispersions of L. scoparium to New Zealand from the evolutionary centre of the persistent-capsule Leptospermum group in south-east Australia, and later regional dispersal in New Zealand.
The results from this study render two hypotheses acceptable: the variability in the UMF activity of Manuka honey is due to both the dilution by other honey types, and the diversity of L. scoparium harvested.