Honey gives up healthy secret

Mature manuka honey. Photo / Martin Sykes

Waikato University researchers have discovered a compound in the nectar of manuka trees which converts to the antibacterial ingredient that active manuka honey is known for.

"We have known for some time that the unique antibacterial activity of manuka honey is associated with the presence of methylglyoxal, or MGO," Associate Professor Merilyn Manley-Harris said.

"But until now the origin of methylglyoxal was not known. It's well-known among beekeepers that the MGO increases with storage, but there was no research to underpin this belief."

A test to predict the potential for a drum of honey to develop antibacterial activity during storage has been patented by the university's commercialisation arm, WaikatoLink, and would be made available to industry.

"Storage is money for a lot of producers," Dr Manley-Harris said.

"With this test they can immediately tell if that batch of honey is going to mature into active manuka honey - if it's not going to become active, they may as well sell it as table honey."

The research from Waikato's chemistry department showed dihydroxyacetone, or DHA, is present in young honeys shortly after bees deposit it in the comb. As the honey ripens, the DHA converts to MGO, the component which gives the manuka honey its antibacterial activity.

During the research, young manuka honey was stored for 120 days and showed a strong correlation in the drop-off of DHA, and the increase in MGO. Because DHA is not antibacterial like the MGO is, the antibacterial activity increases as the honey matures.

Dr Manley-Harris said once researchers realised the DHA was the precursor to MGO they set about finding out where the DHA came from. They discovered it when they tested the nectar in manuka flowers from various trees around Hamilton and the Waikato.

By testing the nectar of the manuka flowers it was possible to identify which trees would produce highly active manuka honey when harvested by bees.

Those trees could then be bred and planted on marginal land where bees could do the hard work of harvesting.

Manuka is fast-growing and is tolerant of poor soils, exposure and waterlogged sites.

There are three species in New Zealand and a variety of cultivars often found in gardens.

Waikato's chemistry research has recently been published in the journal Carbohydrate Research.

- NZPA