Two novel markers to discriminate poplar-type propolis from poplar bud extracts: 9-oxo-ODE and 9-oxo-ODA

Abstract This study aimed to distinguish poplar-type propolis from poplar bud extracts. Through HPLC-PDA-MS/MS, 9-oxo-10(E),12(E)-octadecadienoic acid (9-oxo-ODA) was firstly identified in propolis and poplar buds. We reveal that the contents of 9-oxo-ODE (9-oxo-10(E),12(Z)-octadecadienoic acid) and 9-oxo-ODA in the buds, resin-less buds, and bud resin keep much lower during the summer. Furthermore, we propose ratio D value, the ratio of the sum content of 9-oxo-ODE and 9-oxo-ODA to the content of pinobanksin. All ratio D values of 57 propolis samples were less than 0.7. Except summer, the ratio D value of poplar bud extracts was greater than 0.7. Thus, if the ratio D value exceeds 0.7, propolis products may be adulterated with poplar bud extracts. Finally, among 15 commercial propolis products, the ratio D values of the five products exceeded 0.7; these products may be counterfeit propolis. Therefore, we seem to provide a novel approach to discriminate poplar-type propolis from poplar bud extracts.