11
NEW ZEALAND BEEKEEPER, JUNE 2017
CHEMICAL CHANGES IN MATURING MANUKA HONEY RESEARCH Merilyn Manley-Harris, School of Science, University of Waikato The University of Waikato honey chemistry research group has recently published a fourth journal article in their series describing chemical changes in maturing mānuka honey; this article describes the development of 5-hydroxymethylfurfural (HMF) during maturation (Grainger, Owens, Manley-Harris, Lane, & Field, 2017).
Queen bee in a hive in Nelson. Photo: Elliott Kennedy.
Effect of temperature Probably the most important take-home message from this paper is the effect of temperature. At 4 o C, HMF remained at a very low level for 300 days; at 27 o C, the 40 mg/kg limit was reached at ~230 days; at 32 o C, the limit was reached at ~190 days and at 37 o C the same limit was reached at only ~90 days. Thus warming honey, in order to accelerate conversion of DHA to MG, can have the unwanted side effect of increasing the HMF. Warming can also reduce the final levels of MG, as shown in Parts I–III of this series. Research at Waikato and overseas indicate that different honeys can respond differently at the same temperature. This is undoubtedly due to the levels of components other than sugar for example amino acids, phenolic acids and water, which can have the effect both of accelerating production of MG or HMF but also consuming the product. Reference Grainger, M. N. C., Owens, A., Manley-Harris, M., Lane, J. R., & Field, R. J. (2017). Kinetics of conversion of dihydroxyacetone to methylglyoxal in New Zealand mānuka honey: Part IV – Formation of HMF. Food Chemistry, 232, 648–655. http://dx.doi. org/10.1016/j.foodchem.2017.04.066 [Editor’s note: a summary of the first three papers in the series was published in the May 2016 journal, pages 24–25.]
Because of its perceived toxicity, the international Codex Alimentarius , with certain exceptions, indicates a limit of 40 mg/kg of HMF in honeys and, although there is no legal domestic New Zealand limit, exporters usually try to ensure their product is below 40 mg/kg. HMF forms by a chemical reaction in maturing honey of any type: it is principally formed from fructose, which constitutes roughly half of the sugars present in the honey. Because it is a chemical reaction, it will continue for the entire life of the honey, processing, packaging, retail and domestic use. In mānuka honey the two reactions that form MG and HMF are unrelated but can impinge upon each other indirectly, because both reactions depend upon the presence of proton donor and acceptor molecules (amino acids, phenolic acids, etc.), and DHA, MG and HMF can all consume amino acids by reacting with them. Water, which can act as either a proton donor or acceptor, is very limited in honey and tied up by the sugar molecules. The research found that the increase of HMF versus time was first-order (logarithmic) during an induction period and zero-order (linear) thereafter; the duration of the induction period depended upon the temperature and was shorter at higher temperatures. A relatively simple computer model was able to simulate the formation of HMF in mānuka honeys at 37 o C and the behaviour of mānuka honey was mimicked by clover honey doped with DHA, or by artificial honey with DHA and appropriate amino acids added.
WE WANT YOUR PHOTOS! The Publications Committee welcomes photos for the journal. Pop a camera in the truck and snap away when you find something interesting. The safest way to supply a digital file is in a high-quality jpeg format. If you’re thinking big (such as a potential front cover photo), these need to be as large as possible (300 dots per square inch (dpi) at the size they are to be used, in portrait format (vertical rather than horizontal). Regular digital photos are only 72 dpi, so are not suitable for the front cover. Please provide a caption and the name of the photographer so we can credit them. Email photos and captions to editor@apinz.org.nz
Made with FlippingBook - Online catalogs