Cyclic voltammetry and UV/Vis spectroscopy in combination with multivariate data analysis for the assessment of authenticity of poplar type propolis

<p>Propolis, as a beneficial natural product, has found application in the food and pharmaceutical industries as a food preservative, active packaging material as well as a main component of propolis containing products. Quality control of propolis has thus gained in importance. We used simple, fast, and low-cost techniques such as UV/Vis spectrophotometry and cyclic voltammetry applied in combination with principal component analysis to confirm the presence of two botanical sub-types of propolis. Cyclic voltammetry, as a green, sensitive, and convenient technique suitable for investigation of chemical profile, together with multivariate chemometrics technique, was used for the first time for characterization and classification of propolis. UV/Vis spectroscopy was applied in two aspects, absorption at certain wavelength for the quantitative determination of analytes, i.e. determination of quality control parameters, and spectral profiles, for the confirmation of the existence of two botanically different poplar types. All investigated Serbian propolis samples were characterized with specific chemical patterns and were classified in two main botanical varieties, so-called orange and blue. The results confirmed that the applied methods have a potential to be used for the discrimination of complex natural products such as propolis.</p

Antimicrobial Activity of Serbian Propolis Evaluated by Means of MIC, HPTLC, Bioautography and Chemometrics

<div><p>New information has come to light about the biological activity of propolis and the quality of natural products which requires a rapid and reliable assessment method such as High Performance Thin-Layer Chromatography (HPTLC) fingerprinting. This study investigates chromatographic and chemometric approaches for determining the antimicrobial activity of propolis of Serbian origin against various bacterial species. A linear multivariate calibration technique, using Partial Least Squares, was used to extract the relevant information from the chromatographic fingerprints, <i>i</i>.<i>e</i>. to indicate peaks which represent phenolic compounds that are potentially responsible for the antimicrobial capacity of the samples. In addition, direct bioautography was performed to localize the antibacterial activity on chromatograms. The biological activity of the propolis samples against various bacterial species was determined by a minimum inhibitory concentration assay, confirming their affiliation with the European poplar type of propolis and revealing the existence of two types (blue and orange) according to botanical origin. The strongest antibacterial activity was exhibited by sample <b>26</b> against <i>Staphylococcus aureus</i>, with a MIC value of 0.5 mg/mL, and <i>Listeria monocytogenes</i>, with a MIC as low as 0.1 mg/mL, which was also the lowest effective concentration observed in our study. Generally, the orange type of propolis shows higher antimicrobial activity compared to the blue type. PLS modelling was performed on the HPTLC data set and the resulting models might qualitatively indicate compounds that play an important role in the activity exhibited by the propolis samples. The most relevant peaks influencing the antimicrobial activity of propolis against all bacterial strains were phenolic compounds at <i>R</i>_F values of 0.37, 0.40, 0.45, 0.51, 0.60 and 0.70. The knowledge gained through this study could be important for attributing the antimicrobial activity of propolis to specific chemical compounds, as well as the verification of HPTLC fingerprinting as a reliable method for the identification of compounds that are potentially responsible for antimicrobial activity. This is the first report on the activity of Serbian propolis as determined by several combined methods, including the modelling of antimicrobial activity by HPTLC fingerprinting.</p></div

Regression coefficients of PLS models obtained from six bacterial strains.

<p>Regression coefficients of PLS models obtained from six bacterial strains.</p

Bioautography assay of propolis samples against six bacterial strains.

<p>A) phenolic profile of propolis extract, B) <i>E</i>. <i>faecalis</i>, C) <i>B</i>. <i>subtilis</i>, D) <i>S</i>. <i>aureus</i>, E) <i>L</i>. <i>monocytogenes</i>, F) <i>A</i>. <i>hydrophila</i> and <i>G</i>) <i>S</i>. <i>flexneri</i>.</p

The Minimum Inhibitory Concentration (MIC) of Methanol Extracts of Serbian Propolis Samples in mg/mL.

<p>The Minimum Inhibitory Concentration (MIC) of Methanol Extracts of Serbian Propolis Samples in mg/mL.</p

Statistical parameters for the six PLS model.

<p>Statistical parameters for the six PLS model.</p