Simultaneous determination of trigonelline and caffeine and its application in the identification of Chinese Citrus, Coffee and Rape honey

Honey is a popular healthy product, but the honey fraud is serious on the market, so the various characteristics of honey have been explored to identify its authenticity. In this study, a method of solid-phase extraction (SPE) combined with liquid chromatography-tandem mass spectrometry (LC–MS/MS) was developed for the simultaneous determination of trigonelline and caffeine in honey. Under the optimized conditions, both trigonelline and caffeine have good linearity (R 2 > 0.999), good accuracy (spiked recoveries ranged from 92.1 to 107.9%) and good precision (relative standard deviations < 8.1%), with the limits of detection of 6 μg/L. The developed method was applied to 330 Chinese honey samples of 23 botanical origins. The results indicated that caffeine was only detected in Citrus honey (5.8 mg/kg) and Coffee honey (90.7 mg/kg), and trigonelline was detected with high levels in Coffee honey (81.9 mg/kg) and in Rape honey (71.1 mg/kg), which were much higher than that in the honey samples from other botanical origins (ranged from 0.5 to 7.0 mg/kg). To our knowledge, the high level of trigonelline in Rape honey is a novel finding. Samples were classified by cluster analysis according to the contents of trigonelline and caffeine, and the result indicated that the samples could be divided into four cluster groups based on their botanical origins. Furthermore, a criterion was built based on the level of trigonelline and caffeine for the identification of Rape honey, Citrus honey and Coffee honey, and it provides some support for the identification of honey botanical origins.