ESI-MS fingerprinting of residues of green propolis, and evaluation of their antioxidant and antimicrobial activities

Abstract

In this study, we evaluated the composition of the residues of subsequent extractions of raw propolis compared to that of the first extraction (EEP) in order to determine the appropriate number of extractions that could be used. Three samples of green propolis, two of them from small apiaries and another from a larger apiary (all with similar composition) were analyzed. The chemical composition of the residues and the crude propolis was evaluated by direct insertion electrospray ionization mass spectrometry in the negative ion mode (ESI(-)-MS) using a TQD Acquity mass spectrometer. The antioxidant activity was assessed by DPPH and ORAC assays, and the antimicrobial activity was studied as well. A comparison of the ESI(-)-MS fingerprints showed that bioactive substances still remain in the residues after one or two extractions. Artepillin C was found to be present in green propolis extract (EEP) and also in the residues; however it was present in lower concentrations. Nevertheless, another important substance, dicaffeoylquinic acid, was only found in the propolis extract and in the first two residues. In the DPPH and ORAC assays, a sequential loss of antioxidant activity was observed. The antimicrobial activity of EEP and extract of the first two residues was investigated in vitro against gram-positive and gram-negative bacteria and EEP, and the first extract presented inhibition values of 1 mg ml−1 or less. Two sequential extractions of raw green propolis are appropriate to avoid the loss of important chemical components in the residue.