Honey Research at GNS Science
GNS Science is New Zealand’s leading research group in honey adulteration and pollen verification of New Zealand’s monofloral honeys. Led by Dr Karyne Rogers and Dr Ian Raine, the team are addressing issues surrounding adulteration and honey verification, including differentiating between manuka (Leptsospermum scoparium) and kanuka (Kunzea ericoides) honey.
Dr Karyne Rogers leads the honey adulteration and verification research, and is currently a scientific representative to MPI’s Manuka Honey Science Work Group, responsible for providing Labelling guidelines for manuka honey [http://www.mpi.govt.nz/food/food-safety/manuka-honey]
Dr Ian Raine is New Zealand’s leading melissopalynologist (honey pollen expert) and is widely consulted for pollen and honey identification of New Zealand and overseas honey samples.
Publications on Verification and authentication of New Zealand honey
- Rogers, K. 2014. Why is New Zealand honey failing sugar adulteration tests? A final report for AGMARDT and co-funders. GNS Science Consultancy Report 2014/02. January 2014, pp 25.
- Rogers, K.M., Sim, M., Stewart, S., Phillips, A., Cooper, J., Douance, C., Pyne, R., Rogers, P. 2014. Investigating C-4 sugar contamination of manuka honey and other New Zealand honey varieties using carbon isotopes. Journal of agricultural and food chemistry, 62(12): 2605-2614; doi: 10.1021/jf404766f
- Rogers, K.M.; Grainger, M.; Manley-Harris, M. 2014. The unique manuka effect: why New Zealand manuka honey fails the AOAC 998.12 C-4 sugar method. Journal of agricultural and food chemistry, 62(12): 2615-2622; doi: 10.1021/jf404767b
- Spiteri, M., Jamin, E., Thomas, F., Rebours, A., Lees, M., Rogers, K.M., Rutledge, D.N. 2014. Fast and global authenticity screening of honey using 1H-NMR profiling. Food Chem. (submitted)
- Rogers, K.M, Manley-Harris, M. 2014. Adulterating mānuka honey: what are the risks? The New Zealand Beekeeper Journal, September 2014, V23, No 9, pg 13.
- Rogers, K.M. 2010. Sugar adulteration tests – what every good bee keeper should know. National Bee Keepers Magazine, June 2010, V18, No 5.
- Rogers, K.M., Somerton, K., Rogers, P., Cox, J. 2010. Eliminating false positive C4 sugar tests on New Zealand Manuka honey. Rapid Communications in Mass Spectrometry 24: 2370-2374.
- Rogers, K.M., Cook, J., Krueger, D., Beckmann, K. 2013. Report of an inter laboratory comparison exercise: Modification of AOAC Official Method 998.12 to add Filtration and/or Centrifugation. Journal of AOAC International, 96(3): 607-614; doi: 10.5740/jaoacint.12-386
Media stories on honey testing at GNS Science
- Boffins can spot if manuka is real deal. Wanganui Chronicle 27 June 2014
- The Grocer article – The great manuka honey swindle
- Rogers, K.M. 2010. Honey adulteration tests (article from the National Bee Keeper Magazine, June 2010, v. 18, n.5)
- Rogers, K.M. 2013. A sweet win for the honey industry. New Zealand beekeeper (April), 21(3): 21.
- Rogers, K.M. 2013. China Market Access update. New Zealand beekeeper (February), 21(1): 23-24.
Adulterating mānuka honey: what are the risks?
By Karyne Rogers, GNS Science and Merilyn Manley-Harris and Megan Grainger, Department of Chemistry, University of Waikato
The price of mānuka honey is indexed either to its biological activity or methyglyoxal content (MG) and trade continues to be extremely brisk, with mānuka honey containing MG 250mg/kg selling for up to $45/kg and more in some instances. Several research programs are underway to cultivate mānuka plants capable of producing honey with high MG content, some of which have multi-million dollar investments and plantations of such trees are becoming a reality. But what if it generating a high MG honey was as simple as taking synthetic dihydroxyacetone (DHA, the kinetic precursor of MG) and adding it to low MG mānuka honey? Or for that matter kānuka or even clover honey! Dr Karyne Rogers, GNS Science has teamed up with Associate Professor Merilyn Manley-Harris and PhD student Megan Grainger from the University of Waikato to explain the current state of play with adulteration detection and suggest some possibilities for further research in this area.
Synthetic MG versus natural MG – how can we tell?
It is possible to produce a high MG mānuka honey by adding synthetic methylglyoxal (MG) purchased from a chemical supplier; however authentic high MG mānuka honey has a DHA and MG content in an approximately 2:1 ratio when the honey is matured. A simple chromatographic profile will detect direct MG addition, as it would not have the correct DHA: MG ratio. However, addition of synthetic DHA cannot be detected by this method as it behaves in exactly the same way as the naturally-occurring DHA, converting to MG over time with a similar DHA: MG ratio upon maturation. An additional complication is that synthetic DHA, during the course of the reactions that give rise to MG, also changes some physical properties such as colour and viscosity that might be used for honey identification.
Can we differentiate between synthetic and natural DHA in honey?
In theory, it is possible to detect DHA artificially added to honey by analysing its carbon isotope signature since many commercially available products are made from petroleum products which have more negative carbon (around -30 ‰), compared to plant products which, for mānuka honey, lies between -25 to -26.5 ‰.
Dihydroxyacetone is manufactured by the oxidation or fermentation of glycerol; glycerol itself can be sourced either from the waste of biodiesel manufacture from fats and oils or synthetically from a petrochemical origin; DHA from these two sources would be expected to show different carbon isotope signatures.
Dr Karyne Rogers assessed the stable carbon isotope composition of a range of commercially available DHA products, which are used as standards in DHA and MG testing laboratories within New Zealand and China. Of the six synthetic DHA samples tested, only one synthetic sample was outside the naturally occurring honey isotope range (suggesting that this one was derived from petroleum products), while the other five synthetic products were isotopically indistinguishable from DHA found naturally in honey. This suggests that a methodology for detection of adulteration of the honey that involves the distinction either chemically or isotopically of naturally occurring DHA from that of DHA added deliberately would be unsuccessful.
However, it is still possible that an indirect chemical test could be developped since synthetically produced DHA may contain impurities resulting from manufacture which, if incorporated into honey, could be used to detect addition of this chemical.
Currently there are several research projects analysing honey samples from around New Zealand to characterise mānuka honey regions and their expected DHA and MG levels. They are documenting the ranges of plant DHA and honey DHA and MG contents, as well as looking at other microscopic, chemical and physical properties. Once these surveys are completed, deviations from expected values might be viewed with some suspicion by testing facilities and many buyers within the industry.
Is New Zealand mānuka honey under threat of adulteration?
There is always a significant risk in basing a pricing index or identification program for mānuka honey around the presence of DHA and/or methylglyoxal alone, as it may encourage adulteration. However, risks for New Zealand are extremely low, given the technology available to detect adulteration and the ongoing research around characterising mānuka honey. Although DHA and MG markers are critical for trading high value mānuka honey, other marker compounds and especially organoleptic, microscopic and physiochemical parameters will be included in any future mānuka honey authentication criteria. By using a combination of analytical parameters, unusual levels of DHA and/or MG will be evident when compared to normal background compounds. The biggest adulteration risks lie in overseas markets where there could be imitation of New Zealand’s mānuka honey by adulteration of other honey varieties with synthetic DHA or MG.
What still needs to be done?
- Completion and publication of comprehensive surveys of the range of DHA and MGO contents that can be expected from New Zealand mānuka honeys and DHA content of nectars of Leptospermum scoparium from different regions.
- Completion and publication of comprehensive surveys of the range of physical properties expected from mānuka honeys originating from New Zealand.
- Evaluation of the effect of the addition of synthetic DHA upon physical and chemical properties of mānuka honeys.
- Chemical investigation of the range of synthetic DHA products to attempt to identify potential marker compounds if these are used as adulterants.
- As far as the authors are aware some of this work is currently underway but not all.