Abstract
There is no systematic report about propolis chemical biodiversity from the Adriatic Sea islands affecting its antioxidant capacity. Therefore, the samples from the islands Krk, Rab, Pag, Biševo and Korčula were collected. Comprehensive methods were used to unlock their chemical biodiversity: headspace solid-phase microextraction (HS-SPME) and hydrodistillation (HD) followed by gas chromatography and mass spectrometry (GC-MS); Fourier transform mid-infrared spectroscopy (FT-MIR); ultra high performance liquid chromatography with diode array detector and quadrupole time-of-flight mass spectrometry (UHPLC-DAD-QqTOF-MS) and DPPH and FRAP assay. The volatiles variability enabled differentiation of the samples in 2 groups of Mediterranean propolis: non-poplar type (dominated by α-pinene) and polar type (characterized by cadinane type sesquiterpenes). Spectral variations (FT-MIR) associated with phenolics and other balsam-related components were significant among the samples. The UHPLC profiles allowed to track compounds related to the different botanical sources such as poplar (pinobanksin esters, esters and glycerides of phenolic acids, including prenyl derivatives), coniferous trees (labdane, abietane diterpenes) and Cistus spp. (clerodane and labdane diterpenes, methylated myricetin derivatives). The antioxidant potential determined by DPPH ranged 2.6–81.6 mg GAE/g and in FRAP assay 0.1–0.8 mmol Fe2+/g. The highest activity was observed for the samples of Populus spp. origin. The antioxidant potential and phenolic/flavonoid content was positively, significantly correlated.
Highlights
Apis mellifera L. propolis, known as the bee glue, combines resins collected by the honey bees from different plant organs, and with beeswax that honey bees incorporate
headspace solid-phase microextraction (HS-SPME) has been used in last decade for the analysis of propolis headspace (HS) volatile organic compounds (VOCs) as a simple and fast method
It is known that to produce propolis, bees collect various exudates including balsams, resins and waxes from the plants available in specific areas. It results in different typologies of the final product and the samples were divided into two groups depending on the probable plant sources
Summary
Apis mellifera L. propolis, known as the bee glue, combines resins collected by the honey bees from different plant organs, and with beeswax that honey bees incorporate. Since the 1960s, numerous studies have revealed propolis composition variability [2,6,7] with more than 300 natural organic compounds: flavonoids, phenolic acids and their esters, polyphenols, terpenes ( sesquiterpenes, diterpenes and triterpenes), lignans, steroids, hydrocarbons, amino acids and others. Their abundance has been influenced by botanical and geographical factors, as well as by the season [2,3]. According to the specific chemical composition, different types of propolis are referred in the literature [3]: (a) Poplar type (Populus spp.), (b) Birch type (Betula verrucosa Ehrh.), (c)
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