Characterization and classification of propolis extracts by HR-NMR

Propolis is a resinous substance collected by bees from exudates of different plants, rich in health-relevant phenolic compounds [1]. This study demonstrates that it is possible to use HR-NMR for the simultaneous recognition of 12 typical phenolic compounds (apigenin, chrysin, galangin, kaempferol, quercetin, naringenin, pinocembrin, pinostrobin, caffeic acid, cinnamic acid, p-coumaric acid and ferulic acid) [2] in propolis extracts, using appropriate tools for spectra pre-treatment [3] and analysis, and to verify if the same technique was able to classify propolis according to the harvesting method. A simple 1H-NMR sequence was used for phenolic compounds identification. Sixty-five propolis samples were used to test the proposed identification procedure. Ten out of 12 considered compounds were identified as statistically significant in most of the samples. For the propolis classification according to the harvesting method, the ethanolic extracts were initially analysed for quantification of the main bioactive substances, balsams and waxes. The 1H-NMR and heteronuclear multiple bond correlation spectra were then acquired and analysed by multivariate statistical techniques. The best model was obtained using the 1H-NMR by analysing the spectral region between 4.50 and 13.00 ppm (predictive capacity: 96.7%).