Individual phenolic compounds comparison of rapeseed honey and floral source

Introduction. Honey’s nutritional, physicochemical, and bioactive properties depend largely on its floral origin. Differences in nectar composition ‑ such as sugar ratios, phenolics, and volatiles ‑ affect honey’s color, flavor, texture, and biological activity. Monofloral honeys reflect the traits of a single plant source, whereas polyfloral honeys display more complex profiles [1]. The aim of the study is to compare the phytochemical composition of rapeseed honey and its floral source. Materials and methods. Rapeseed honey samples were collected in 2023 from six different apiaries, and rapeseed flowers were obtained from two separate fields in Lithuania. Extracts were prepared by combining 1 g of each research material with 70% ethanol, followed by ultrasonication for 20 min. The resulting extracts were filtered through cotton wool with the help of a vacuum pump into 10 mL volumetric flasks. If necessary, the volume was adjusted to the mark with 70% ethanol. Prior to UHPLC-MS/MS analysis, the extracts were further filtered through a 0.22 μm membrane filter. Statistical analysis was performed using “MS Excel 2023” (“Microsoft”, Redmond, USA). Results and discussion. Both samples: honey and rapeseed flowers contained quercetin, p-coumaric acid, ferulic acid, isorhamnetin and kaempferol. The amounts of all detected phenolic compounds were higher in rapeseed flowers than in honey. Quercetin was found mainly in the flowers (14,81±0,93 µg/g), while its concentration in honey was significantly lower (1,83±0,52 µg/g). The concentration of p-coumaric acid reached 13,43±0,30 µg/g in rapeseed flowers and 4,16±1,62 µg/g in honey. Similarly, ferulic acid, isorhamnetin, and kaempferol were more abundant in rapeseed flowers (12,32±1,39 µg/g, 8,21±0,74 µg/g, and 2,67±1,11 µg/g, respectively) compared to honey (2,94±1,33 µg/g, 1,21±0,97 µg/g, and 2,50±0,55 µg/g, respectively). In addition to these compounds, several phenolics were detected exclusively in rapeseed flowers, including neochlorogenic acid, quercetin 3-arabinoside, chlorogenic acid, kaempferol-3-O-rutinoside, isorhamnetin-3-O-rutinoside, orientin, luteolin 7-rutinoside, vanillic acid, caffeic acid, rutin, sinapic acid, naringenin, 3,4-dihydroxybenzoic acid, and kaempferol-3-O-glucoside. Acacetin and apigenin were detected exclusively in honey samples (0,59±0,17 µg/g and 0,09±0,04 µg/g, respectively), which may be attributed to the presence of pollen originating from other plant species. Conclusions. The results demonstrated that rapeseed flowers contained higher concentrations and a greater diversity of phenolic compounds compared to rapeseed honey. The exclusive presence of acacetin and apigenin in honey suggests possible contributions from other floral sources and highlights the complex origin of its bioactive composition.