Investigation of Temporal Apparent C4 Sugar Change in Manuka Honey.

New Zealand manuka honeys are known for their propensity to increase apparent C4 sugar content during storage. Depending on the particular storage regime and the initial content of dihydroxyacetone (DHA) in honey, the ready-to-market product often fails the C4 sugar test because of the above phenomenon. We have used DHA labeled with a radioactive 14C isotope in a set of honeys subject to an incubation experiment. These honeys were analyzed for DHA, methylglyoxal (MG), hydroxymethylfurfural (HMF), apparent C4 sugars, and 14C scintillation counts over a period of 18 months. The major conclusion of this experiment is that neither DHA nor MG is responsible for the δ13C shift in the honey protein extract. There must be some other yet unknown substance of manuka honey, which binds to the protein and causes negative δ13C shift. One identified candidate for such a binding is carbon dioxide.

Leptosperin is a distinct and detectable fluorophore in Leptospermum honeys.

New Zealand manuka (Leptospermum scoparium) honey exhibits two unique fluorescence signatures that distinguish it from other honey types. One of these is the MM1 fluorescence marker (270-365nm excitation-emission) which we show is due to a Leptospermum nectar-derived compound, leptosperin. Synthetic or honey-purified leptosperin not only displayed an identical fluorescence spectrum, but supplementation of leptosperin into clover or artificial honeys generated the MM1 fluorescence signature. There was a quenching effect of the honey matrix on leptosperin fluorescence but otherwise leptosperin was chemically stable over prolonged storage at 37°C. Leptosperin was also present in the woody-fruited Australian Leptospermum species at elevated concentrations but virtually absent in Leptospermum subtenue suggesting its elevated expression developed following the mid-Miocene separation of the genus. These findings suggest that fluorescence spectroscopy could offer a rapid and high-throughput screening method for identification of Leptospermum honeys using the MM1 fluorescence marker.

Potential of solid phase microextraction and gas chromatography for quarantine-required detection of wood packaging in shipping containers.

Solid phase microextraction (SPME) coupled with gas chromatography (GC) was used to detect terpene hydrocarbons inside shipping containers entering New Zealand. The utility of this system for the rapid detection of undeclared wood packaging for quarantine purposes was demonstrated. A portable dynamic air-sampling device was built to house a SPME fibre and allow the air from shipping containers to be sampled. The effects of sample flow rate and sampling time were investigated and sampling conditions of 100 mL/min for 30 s were chosen to keep sampling within the linear range. A CV of less than 15% (n = 12) was obtained for all the compounds analysed under these conditions. To obtain an estimate for the limit of detection (LOD) for the terpene hydrocarbons of interest, small quantities of lime oil were placed in an empty shipping container and the air inside was analysed. LOD (S/N = 3) was estimated to be in the order of 50-100 ng/L of air using GC with flame ionisation detection (GC-FID). Finally, the device was tested in fully laden containers and was shown to be effective for trapping terpene hydrocarbons indicative of wood packaging.