**5. Analytical techniques**

#### **5.1. Fluorescence spectroscopy**

Honey fluorescence was analysed by scanning fluorescence spectroscopy according to methods described previously [36]. Honey samples were diluted with distilled water to 2% w/v, and loaded as 100 μL aliquots into a flat‐bottom microplate (OptiplateTM‐384, black). Fluorescence measurements were carried out on a Gemini EM Dual‐Scanning Microplate Spectrofluorometer (Molecular Devices Inc., Sunnyvale, CA, USA) operated with the SoftMax® Pro software. A fluorescence top read setting with automatic calibration and sen‐ sitivity at an ambient temperature was adopted for analysis at both MM1 and MM2 marker wavelengths. Fluorescence intensity was expressed as arbitrary units, in this case relative fluorescence units (RFU).

#### **5.2. HPLC**

Leptosperin, Lepteridine, methyl syringate and 2‐methoxyacetophenone concentrations were quantified on a Dionex UltimateTM 3000 reverse‐phase HPLC system (Thermo Fisher Scientific, New Zealand) with diode‐array detection (DAD).

Honey samples were diluted 1 in 5 with 0.1% v/v formic acid. The injection volume was 3 μL. Separation was carried out on a Hypersil GOLD column (150 × 2.1 mm, 3μm particle size) by gradient elution at a constant flow rate of 0.200 mL>:in. The binary mobile phase consisted of 0.1% formic acid (Solvent A) and 80:20 acetonitrile:Solvent A (Solvent B). The gradient elution programme was as follow: initial (5% B, held 2 min), 7 min (25% B), 14 min (50% B), 16 min (100% B, held 3 min), 19 min (5% B, held 1 min) and 20 min (5% B, held 10 min). The column was thermostatically controlled at 25°C. Leptosperin, Lepteridine, methyl syringate and 2‐ methoxyacetophenone were monitored at 262, 320, 280 and 250 nm, respectively.

Data acquisition and peak integration were performed with Thermo Fisher ScientificTM Dionex™ Chromeleon™ 7.2 Chromatography Data System (CDS) software. The compounds of interests were quantified using external calibration curves of respective chemical standards based on integrated measurement of peak area.
