Melatonin and serotonin, products of tryptophan metabolism, are endogenous neurotransmitters and hormones. We have identified and quantified these metabolites in natural honey from Australia, USA, and Poland using a Xevo G2 XS qTof LC-MS. To help ensure correct product identification, some samples were prepurified by RP-HPLC based on the retention times of standards, prior to LC-MS. The concentrations of the metabolites of interest depended on the source of the honey. For Australian honey, levels for melatonin and 2-hydroxymelatonin were 0.91 and 0.68 ng/g, respectively. Melatonin was detected in one brand of US commercial honey at 0.48 ng/g, while a second brand contained serotonin at 88.2 ng/g. In Polish natural honey, 20.6 ng/g of serotonin and 40.8 ng/g of N-acetylserotonin (NAS) were detected, while in Polish commercial honey 25.9 ng/g of serotonin and 7.30 ng/g of NAS were present. We suggest that addictive and health-related properties of honey may be in part dependent on the presence of serotonin, melatonin, and their metabolites, and that these compounds may play a role in the colony activities of bees.
Keywords: 2-hydroxymelatonin; N-acetylserotonin; bees; honey; melatonin; serotonin.