Extraction of honey polyphenols: Method development and evidence of cis isomerization

Honey polyphenols have been studied with the objective of relating honeys to their floral sources. Initially synthesized by plant, these polyphenols can be found in the plant’s nectar, where they are collected by bees which convert the nectar into honey. Consequently, polyphenols constitute minor honey components. The development of a solid phase extraction method for honey polyphenols is presented herein. The technique employs Amberlite XAD-2 adsorbent and was tested on monofloral honeys from six different plants: acacia, chestnut, eucalyptus, thyme, sunflower and wild carrot. Analyses were performed using high performance liquid chromatography coupled with UV detection and mass spectrometry. Several phenolic acids and flavonoids were identified: caffeic and p-coumaric acids, quercetin, kaempferol, naringenin, chrysin and pinocembrin. Generally, the quantity of a given polyphenol in the honey was around 0.2 mg/100g of honey, except for chestnut honey which contained around 3.0 mg of p-coumaric acid/100g of honey. Analyses highlighted significant formation of cis isomers for phenolic acids during the extraction despite protection from light.