Characterising honeys in situ by spectral methods : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Manawatu, New Zealand. EMBARGOED to 20 September 2024.

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New Zealand mānuka honey is derived mainly from Leptospermum scoparium nectar and is valuable through accumulation of antibacterial methyl glyoxal (MGO). Mānuka honey also has a strong polyphenolic profile. Some phenolics act as chemical markers aiding verification of botanical origin as Leptospermum scoparium. A total of eight key chemical markers (DHA, MGO, 3-PLA, 4-HPLA, 2’-MAP, 2-MBA, Leptosperin and LepteridineTM) are found at higher levels in mono-mānuka honey than in multi-mānuka honey, with little or none in other floral honeys. These key markers signify mānuka honey quality and purity (i.e., monoflorality of L. scoparium). The quality and purity of mānuka honeys depend on multiple factors, largely determined by botanical source, which define the value of the final honey product. Available nectar is, in turn, influenced by geographic district and season. Wild harvest honey is naturally a mixture from different nectars. Honey quality varies among apiaries, between beehives and even in a honey frame. Current industry practice lumps all frames of the same apiary together for extraction. Potentially, “good” quality frames of mānuka honey could be mixed with “bad” quality frames. This bulked process can limit the monetary value of mānuka honey. Quality assessment of honey while still in the frame before bulk extraction is of great of interest to the honey industry to preserve the value of mānuka honey at source and to ensure authenticity. The current study used rapid and non-destructive methods such as NIR and fluorescence combined with chemometrics, machine learning and deep learning to evaluate mānuka honey in the frame. The study focuses on assessment of mānuka honey quality in two ways: 1) direct measurement of levels of eight key chemical makers; 2) indirect measurement of potency (based on UMFTM score) and purity (verification of botanical origin as L. scoparium) that are built from key chemical markers. Honey samples (n ~ 1656) representing 200 L drums, each extracted from multiple frames, spanning eight geographic districts across New Zealand, were scanned with NIR non-imaging (350 - 2500 nm) and imaging (547 – 1701 nm) sensors. A sub-dataset of 100 honey samples was scanned in excitation-emission matrix mode (250 - 400/300 - 600 nm) under in-line geometry by a fluorescence sensor. Once techniques were verified, freshly uncapped seven honey frames were scanned and modelled to evaluate the current optical methods used. Overall, the research showed the capability of NIR methods for measurement of honey potency and purity in the frame, achieving 70 - 80 % accuracy. However, NIR methods showed limited ability to measure levels of individual key chemical markers, giving 60 - 70 % accuracy, due to the complexity of the honey matrix. This study has calculated the economic benefit of using NIR methods for sorting honey frames into different quality buckets (UMFTM buckets and MPI honey buckets) before lumped extraction. The greatest revenue increase is found for apiaries with large variation between frames and in seasons with high curvature in the price-quality curve. Later, this study employed fluorescence-based methods that further improved prediction of almost all key chemical markers, in particular two polyphenolic fluorescence markers, Leptosperin and LepteridineTM, to above 80 % accuracy. Moreover, the fusion of NIR and fluorescence data further enhanced predictability of chemical markers, potency and purity of mānuka honey to 90 - 100 % accuracy. In conclusion, this study confirms the fusion of NIR and fluorescence methods has great potential for at-line/on-line assessment of New Zealand mānuka honey while still in the frame. This research provides basic scientific guidance for future application of NIR and fluorescence methods for quality assessment of honey in general and has implications for other wild harvest foods.
Listed in 2023 Dean's List of Exceptional Theses
Honey, Quality, Analysis, New Zealand, Spectrum analysis, Dean's List of Exceptional Theses