Correlations between polyphenolic composition and antioxidant activity of Venetian propolis

https://doi.org/10.1016/j.fct.2009.09.018Get rights and content

Abstract

Four propolis samples have been picked up in the Venetian region, from different orography and habitative density areas with the purpose to: (i) evaluate propolis’ antioxidant activity, measured by inhibition of lipid peroxidation; (ii) determine the polyphenolic components – flavonoids and caffeic acid derivatives – which give antioxidant activity to propolis; (iii) verify the potential correlations between antioxidant activity, polyphenolic content, that has been determined by Folin–Ciocalteu, enzymatic, DPPH quenching, TEAC-like assays, and spectroscopic characteristics of propolis and (iv) correlate chemical structure and antioxidant efficacy of each of the major components. The possible localization of the lipophylic components of propolis into the phospholipidic bilayer by thermal analysis (DSC) and spin label EPR techniques has also been investigated.

Introduction

Propolis (bee glue, CAS N° 9009-62-5) is the generic name for an adhesive, resinous natural product, collected, transformed and used by bees to seal holes in their honeycombs, smooth out the internal walls, protect the entrance against intruders and prevent the decomposition of foreign living organisms killed by bees (Brumfitt et al., 1990, Burdock, 1998). Propolis has been used from ancient ages owing to its beneficial properties and for corps mummification in the ancient Aegipt (Grange and Davey, 1990); in the last century it has been employed in the popular medicine for the cure of many diseases (Castaldo and Capasso, 2002). Recent studies have confirmed its pharmacological activities as antiseptic, antimycotic, bacteriostatic, astringent, choleric, spasmolytic, anti-inflammatory, anaesthetic and antioxidant (Marcucci, 1995, Burdock, 1998, Banskota et al., 2001).

The composition of raw propolis depends on the source, bud exudates of different trees, generally populus in the temperate zones, betula in the northern and delchampia in the equatorial regions, clusia in Venezuela and xanthorrhoea in Australia (Burdock, 1998). Now it is generally accepted that in temperate zones the bud exudates of populus species and their hybrids are the main source of bee glue: the main components are pinocembrin, pinobanksin and 3-O-acetate, chrysin, galangin and caffeates (benzyl, phenylethyl, prenyl) (Bankova et al., 2000). Moreover, more than 200 different chemical components have been classified in propolis of different origins, belonging to various chemical classes (Marcucci, 1995, Bankova et al., 2000, Pietta et al., 2002, Kumazawa et al., 2004, Isla et al., 2005, Silici and Kutluca, 2005, Gomez-Caravaca et al., 2006, Mohammadzadeh et al., 2007, Jasprica et al., 2007, Alencar et al., 2007). Polyphenolic components, caffeic acid derivatives and flavonoids in particular, are matter of interest for their strong antioxidant properties. Several studies have been carried out in order to correlate polyphenolic composition of propolis with its antioxidant properties (Bors et al., 1990, Heim et al., 2002, Russo et al., 2002, Kumazawa et al., 2004), but further contributions are needed to better understand this complex phenomena. For this reason in the present work we have token account of four propolis samples picked up from apis mellifera hives located in different orography and habitative density areas, in the Venetian region. The purpose is: (i) to evaluate propolis’ antioxidant activity, measured by inhibition of lipid peroxidation; (ii) to determine the polyphenolic components – flavonoids and caffeic acid derivatives – that give antioxidant characteristics to propolis; (iii) to verify the possible correlations between antioxidant activity, polyphenolic content that has been determined by the Folin–Ciocalteu, enzymatic, DPPH quenching, TEAC-like assays and spectroscopic characteristics of propolis and (iv) to correlate chemical structure and antioxidant efficacy of each component.

Section snippets

Chemicals

All chemicals were reagent grade and were supplied from Sigma Chemical Co. (USA). ABIP was a kind gift of Wako Chemicals USA. The aqueous solutions were prepared with quality milliQ water.

Propolis

Raw native propolis samples come from different orography, natural environment and habitative density areas (Table 1). They were obtained directly from beekeepers and conserved in closed vessels at 3 °C to prevent natural oxidation. Ethanolic extract of propolis (EEP) at different alcohol concentrations, in the

Spectrophotometric characteristics of EEP samples

Overlapping the absorbance spectra of the different EEP samples (Fig. 1) a good similarity between samples becomes visible: spectra are all characterized by an absorption maximum at 290 nm. On average they have specific absorbance E1cm1% of 450, higher than those reported for propolis from other countries (Kumazawa et al., 2004). Furthermore, a shoulder at about 320 nm and significative absorbance values at higher wavelength (λ  350 nm) are also noticed.

Antioxidant capacity of propolis

Inhibition of lipid peroxidation (LPI) assay

On the antioxidant capacity of Venetian propolis

All examined ethanolic extracts of propolis show high antioxidant activity, expressed as capacity of inhibition of lipid peroxidation; the values are at least similar to that found for catechin at the same amount. Propolis’ antioxidant property is principally due to caffeic acid and its derivatives CAPE and DMAC. Galangin and, at less amount, kaempferol and quercetin, characterized by high antioxidant properties are present at low amounts; on the contrary chrysin and pinocembrin show high

Conflict of interest

The authors declare that there are no conflicts of interest.

Acknowledgements

The authors thank the beekeeper Piergiorgio Michieletto for the precious informations about bees and hives. Thanks are also due to Roberta Zangrando for the technical assistance in HPLC measurements.

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