From leaves, flowers, nectar, honeydew to linden honey: tracing the origin of numerous constituents

Honey has a complex composition derived from floral nectar and/or honeydew secreted by plant-sucking insects. This also applies to linden honey ( Tilia spp.), whose composition reflects multiple botanical and zoological sources, although the origin of several compounds remains unclear. This study aimed to identify the origin of specific compounds in linden honey. Two groups of honey samples differing in electrical conductivity, together with linden leaves, flowers, nectar, and honeydew, were analyzed for sugars, amino acids, inorganic ions, and organic acids using HPLC-based methods. Comparison of the chemical profiles enabled the origin of numerous compounds to be assigned. Sample types differed mainly in their sugar composition: nectar was characterized by glucose and fructose, whereas honeydew and honey contained various di- and oligosaccharides produced by aphids or honeybees. The amino acid composition of honey was strongly influenced by honeybees, particularly proline and phenylalanine. Inorganic ion contents in nectar and honey largely reflected plant tissue composition, while honeydew contained substantially higher concentrations, especially phosphate. Organic acid profiles also differed markedly: gluconic acid, mainly produced by honeybees, predominated in honey, whereas malic acid was characteristic of honeydew. PLS-DA clearly separated leaves, flowers, nectar, honeydew, and honey, although a complete discrimination of the two honey groups, which differed in their electrical conductivity, was not achieved. Nevertheless, honey with higher electrical conductivity contained significantly higher concentrations of several di- and oligosaccharides, inorganic ions, and malic acid than honey with lower conductivity.