Fluorescence: A Novel Method for Determining Manuka Honey Floral Purity

Manuka honey, harvested from Leptospermum scoparium, is New Zealand\u27s most recognised honey type and commands a premium due to health‐related benefits. However, the plant\u27s distribution, relative to other species flowering simultaneously, allows honeybees to incorporate alternative nectars into the honey. Melissopalynological analysis in New Zealand is often unrepresentative due to the presence of many pollen‐bearing sources; consequently, alternative means of categorising manuka honey were examined. RP‐HPLC revealed that manuka honey contains distinct compounds, of which were relatively enriched and not present in the other New Zealand monofloral honeys. These main candidate compounds were isolated and have been described by mass spectrometry and nuclear magnetic resonance, synthesised to confirm structure, and as standards. These compounds, Leptosperin and Lepteridine, are a methyl syringate glycoside and pteridine derivative, respectively. Examination of these compounds revealed unique fluorescence signatures, this fluorescence could be detected in manuka honey samples the signal used to confirm that a honey was solely or predominantly consisted of L. scoparium nectar. Commercial manuka honeys were assessed by traditional analytical techniques, and comparisons were made with fluorescence signature; the fluorescence technique determined the authenticity of the honeys accurately

The rapid evaporative ionisation mass spectrometry metabolite fingerprint of Leptospermum honey is strongly associated with geographic origin

There is debate about whether the honey from Leptospermum scoparium nectar in New Zealand is substantially different to honey from Leptospermum spp nectar from Australia; many Leptospermum honeys have high amounts of the antibacterial compound methylglyoxal (MGO) but are known to differ in their amounts of other metabolites. Retail honey samples labelled as ‘mānuka’, manuka, or ‘tea tree’ honey sourced from New Zealand (n = 34) and Australia (n = 35), were measured using laser assisted-rapid evaporative ionisation mass spectrometry (REIMS) in positive and negative ionisation modes, with 1637 and 1744 molecular features detected, respectively. Country of origin was strongly reflected in the REIMS fingerprints irrespective of similarity of methylglyoxal, with >50% of detected features differing between New Zealand and Australian-sourced honey. Combined REIMS features in negative ionisation mode correlated strongly with current molecular markers of mānuka honey quality (r2 > 0.9). Leptospermum honey from New Zealand and Australia have distinct molecular fingerprints, potentially due to evolutionary and genomic differences between the predominant Leptospermum species, bees, environment and honey processing