Farmers will now be able to select and grow
trees that will produce antibacterial honey.
Image: iStockphoto

Marginal New Zealand farmland could be mass-planted in "active" manuka trees following a breakthrough in the source of manuka honey's antibacterial activity.

Researchers at Waikato University's chemistry department have discovered a compound in the nectar of manuka trees which converts to the antibacterial ingredient that active manuka honey is known for. There is the potential for active manuka trees to be mass-planted and the resulting honey harvested.

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

The research from Waikato's chemistry department shows 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 over that time. Because DHA is not antibacterial like the MGO is, the antibacterial activity increases as the honey matures.

The honey was kept at 37 degrees Celsius, but storage at warmer temperatures is not better, Dr Manley-Harris says. Researchers tried to accelerate the conversion of DHA to MGO by heating the manuka honey. However, at higher temperatures, not only did both the DHA and MGO disappear, but it also created an undesirable hydroxymethylfurfural content. Hydroxymethylfurfural is formed by the breakdown of sugars, and many countries limit the amount of it allowed in foods.

Dr Manley-Harris says 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 from manuka flowers from various trees around Hamilton and the Waikato.

The chemistry research has recently been published in the journal Carbohydrate Research. Waikato University's chemistry department is ranked top in New Zealand under the government's Performance Based Research Fund. The university is also home to the Honey Research Unit, which researches honey for medicinal purposes.

A test to predict the potential for a drum of honey to develop antibacterial activity during storage has now been patented by the university's commercialisation arm, WaikatoLink, and will be available to industry within coming weeks. "Storage is money for a lot of producers," Dr Manley-Harris says. "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."

Through testing of the nectar of the manuka flowers it is possible to identify which trees will produce highly active manuka honey when harvested by bees. Those trees could then be bred and planted as a high value crop – a type of designer scrub, mass planted on marginal land where bees could do the hard work of harvesting.