*2.7. Hydroxymethylfurfural (HMF)*

HPLC Dionex UltiMate 3000 Series (Thermo Scientific, Germering, Germany) equipped with UV detector was used to measure HMF. After dissolving 1 g of honey sample in 25 mL of water and filtered through a 0.45 μm nylon filter, 10 μL of sample was injected into the HPLC system. The HPLC column had a particle size of 3 μm and was a 150 × 3 mm Hypersil GOLD column (Thermo Scientific, Germany). Methanol and water (10:90, *v*/*v*) were used as the mobile phase at a flow rate of 1 mL/min. At 285 nm, HMF detection was carried out. Thermo Scientific's Chromeleon®7 software (Version 7.1, Dionex, Sunnyvale, CA, USA) was used to control the system. To calculate the amount of HMF in the samples, standard solutions' external calibration curves were employed.
