Abstract
Propolis is a gummy material produced by honey bees to protect their hives and currently has drawn the attention of researchers due to its broad clinical use. It has been reported, based only on observations, that honey bees also collect other non-vegetation substances such as paint or asphalt/tar to make propolis. Therefore, propolis samples were collected from bee hives in Riyadh and Al-Bahah, a natural area, Saudi Arabia to determine their compositional characteristics and possible sources of the neutral organic compounds. The samples were extracted with hexane and analyzed by gas chromatography-mass spectrometry. The results showed that the major compounds were n-alkanes, n-alkenes, methyl n-alkanoates, long chain wax esters, triterpenoids and hopanes. The n-alkanes (ranging from C17 to C40) were significant with relative concentrations varying from 23.8 to 56.8% (mean = 44.9+9.4%) of the total extracts. Their odd carbon preference index (CPI) ranged from 3.6 to 7.7, with a maximum concentration at heptacosane indicating inputs from higher plant vegetation wax. The relative concentrations of the n-alkenes varied from 23.8 to 41.19% (mean = 35.6+5.1%), with CPI = 12.4-31.4, range from C25 to C35 and maximum at tritriacontane. Methyl n-alkanoates, ranged from C12 to C26 as acids, with concentrations from 3.11 to 33.2% (mean = 9.6+9.5%). Long chain wax esters and triterpenoids were minor. The main triterpenoids were α- and β-amyrins, amyrones and amyryl acetates. The presence of hopanes in some total extracts (up to 12.5%) indicated that the bees also collected petroleum derivatives from vicinal asphalt and used that as an additional ingredient to make propolis. Therefore, caution should be taken when considering the chemical compositions of propolis as potential sources of natural products for biological and pharmacological applications. Moreover, beekeepers should be aware of the proper source of propolis in the flight range of their bee colonies.
Highlights
Honey bees collect waxy/resinous/gummy substances from different parts of plants, such as buds, leaves, stems and flowers, to make a sticky material known as propolis [1], which they utilize to protect their hives from invaders and infection by bacteria and fungi [2]
The general features of the GC-MS results for the total hexane extractable organic matter (EOM) from the propolis and asphalt samples are shown in Figs 2 and 3, respectively
Inputs of wax from vascular higher plants and asphalt residues, as well as compounds altered by bee metabolism are obvious in the propolis samples
Summary
Honey bees collect waxy/resinous/gummy substances from different parts of plants, such as buds, leaves, stems and flowers, to make a sticky material known as propolis [1], which they utilize to protect their hives from invaders and infection by bacteria and fungi [2]. Honey bees use the propolis to regulate nest temperature, light and humidity for optimum conditions [3,4]. Recent studies have shown that propolis has biological activities, which are related to its different chemical compositions [6]. The assorted chemical compositions and biological activities of propolis depend on the plant sources and collecting season [5]. The variations in chemical composition and biological activities of propolis gathered from different geographical locales are important for pharmaceutical purposes [9]
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