Abstract
Mānuka honey is an internationally renowned and expensive honey variety produced in New Zealand from the nectar of the Leptospermum scoparium plant. Its distinctive non-peroxide activity (NPA) and a wide array of reputed health benefits have made Mānuka honey a highly sought-after product in both medicinal and cosmetic industries. However, its high price and limited availability make it subject to fraud; there is more Mānuka known to be traded than produced. This puts the reputation of the Mānuka industry in an insecure position by questioning the quality of the products. The value of Mānuka honey is closely linked to its methylglyoxal (MGO) content, which is responsible for its NPA activity. MGO is produced through the non-enzymatic conversion of dihydroxyacetone (DHA) during the storage period. A common method of honey adulteration involves introducing sugar syrup or mixing Mānuka honey with cheaper honey varieties. Recently, the emergence of synthetic chemicals in various industries has led to a new form of fraudulent practice, where some unscrupulous traders enhance low-quality Mānuka honey by adding synthetic DHA and MGO. This growing trend poses significant challenges to the authenticity and reputation of Mānuka honey products. This study aims to investigate techniques for detecting two forms of adulteration: 1) the addition of synthetic compounds and 2) the mixing with cheaper honey varieties.
For the detection of synthetic MGO and DHA, extraction methods were developed that utilize derivatization processes, employing pentafluorophenyl hydrazine (PFPH) and O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride (PFBHA) as derivatizing agents. These derivatized products were then analyzed using stable isotope techniques, facilitating the differentiation between exogenous and naturally occurring MGO and DHA. Specifically, MGO was examined through δ²H analysis conducted via Cr-EA/IRMS, while DHA was identified by evaluating its δ¹³C values through GC-C-IRMS. Additionally, the potential of ATR-FTIR spectroscopy for detecting synthetic MGO and DHA was explored using samples adulterated with DHA and MGO, in varying concentrations from three different synthetic brands. For this analysis, the spectral region ranging from 1700-600 cm⁻¹ was focused.
The preliminary investigations into detecting cheap honey additions to Mānuka honey were conducted using two approaches: 1) untargeted metabolomic profiling, and 2) ATR-FTIR fingerprinting. A variety of percentages (ranging from 2% to 40%) of Kānuka and Kamahi honey were mixed with three distinct brands of Mānuka honey and subsequently analyzed using UHPLC-Q-Orbitrap MS and ATR-FTIR spectroscopy, with data processed through latent
discriminant analysis. In the FTIR spectroscopy analysis, spectral regions of 1700-900 cm⁻¹ for Kānuka identification and 1700-600 cm⁻¹ for Kamahi identification were selected.
In conclusion, techniques such as stable isotope analysis and metabolomic profiling have shown potential in detecting Mānuka honey adulteration; however, they can be destructive, time-intensive, costly, and require skilled personnel for operation and analysis. In contrast, ATR-FTIR spectroscopy presented a user-friendly, rapid, and non-destructive method suitable for initial screening of both types of adulteration. While FTIR results should not be exclusively relied upon for confirmation, it can serve as an effective preliminary assessment tool. Further research is recommended to refine these methods and explore their full potential.