Chemical Characterization of Rare Unifloral Honeys of Ailanthus (Ailanthus altissima), Fennel (Foenicum vulgare), and Raspberry (Rubus idaeus) and their Antimicrobial and Antioxidant Activity

Characterization of unifloral honey is of great importance for the definition of quality standards and the confirmation of the authenticity of honey. In this study, standard physicochemical analyses, pollen analyses, determination of total phenolic and flavonoid content, analysis of antioxidant capacity and antimicrobial activity, and qualitative and quantitative analyses of phenolic compounds by LC–MS/MS method were performed in three rare uniofloral honeys—ailanthus (Ailanthus altissima), fennel (Foeniculum vulgare), and raspberry (Rubus idaeus) honeys. The results showed that each honey type has specific physicochemical properties and phenolic content, which consequently influence its biological activity. All honey samples showed good characteristics, according to the compositional and quality criteria of the standard codex for honey. Generally, the ailanthus honey samples had a higher total phenolic and flavonoid content, while the fennel samples showed greater variability. The ailanthus honey samples also showed higher DPPH antioxidant activity, and the ABTS and ORAC assays revealed no differences between the honey types analysed, with the exception of the raspberry honey. In ailanthus honey, the flavonoids chrysin, quercetin, and the phenolic acid 3,4-DHBA were the most abundant. Several quercetin derivatives, including quercetin-3-glucuronide, quercitrin, and quercetin methyl ether, were detected in the fennel honey. In addition, raspberry honey exhibited a distinct phenolic profile containing catechin, epicatechin, quercetin rhamnoside, sakuranetin, tectochrysin, quercetin dimethyl ether, rhamnetin, caffeic acid benzy ether, and pinobanksin-3-O-pentanoate. The strongest results for antibacterial activity came from ailanthus honey. The increased antimicrobial activity of ailanthus honey was found especially against S. aureus and E. coli and moderately against A. baumannii. This study is the first step towards a thorough characterization of ailanthus, fennel, and raspberry honeys and may contribute to the recognition of these rare honeys and provide a good basis for their use in the pharmaceutical industry.