Abstract
Soxhlet (SE), microwave-assisted (MAE) and ultrasound-assisted (UAE) extraction were compared using ten extraction solvents for their efficiency to extract phenolic and flavonoid antioxidants from Eastern Canada propolis. Extracts were compared for total phenolic (TPC) and total flavonoid (TFC) content, and radical scavenging activities. Anti-inflammatory activity through inhibition of 5-lipoxygenase (5-LO) products biosynthesis in HEK293 cells was also evaluated. The results showed that SE extracts using polar solvents had the highest TPC and TFC. Extracts obtained with ethanol, methanol and acetone were effective free radical scavengers, and showed 5-LO inhibition similar to zileuton. UAE was an effective extraction method since the extracts obtained were comparable to those using SE and the MAE while being done at room temperature. With UAE, extracts of less polar solvents showed similar free radical scavenging and 5-LO inhibition to extracts of much more polar solvents such as methanol or ethanol. Reversed-phase liquid chromatography tandem mass spectrometry confirmed the presence of 21 natural compounds in the propolis extracts based on the comparison of intact mass, chromatographic retention time and fragmentation patterns derived from commercial analytical standards. The current study is the first of its kind to concurrently investigate solvent polarity as well as extraction techniques of propolis.
Highlights
Propolis is a resinous material produced by bees upon the mixing of their saliva with substances originating from plant sources
Most of the substances found in propolis are lipophilic and unsurprisingly the best extraction yields for propolis, irrespective of the extraction method used, were obtained in polar organic solvents such as ethanol, methanol, acetone, ethyl acetate and dichloromethane (Table 1)
Results from our study have shown a consistent drop in total phenolic (TPC) and total flavonoid content (TFC) when comparing UAE
Summary
Propolis is a resinous material produced by bees upon the mixing of their saliva with substances originating from plant sources. Other current leads for therapeutic strategies using propolis include applications as diverse as a periodontal biomaterial for restorative oral surgery [12] or wound healing in ulcerative diabetic wound treatment [13] Most of those properties stem from the fact that a majority of the aforementioned pathologies have an oxidative nature characterized by the overproduction of reactive oxygen species (ROS) such as hydrogen peroxide, superoxide anion, hydroxyl ions and nitric oxide. Two groups of compounds, flavonoids and phenolic acids [14], are at the basis of the observed antioxidant properties and by extension of its beneficial therapeutic properties These 2 groups of antioxidant molecules are characterized by their ability to scavenge free radicals using the phenol groups present in their structure counteracting the oxidative stress common to many pathologies. Other non-phenolic substances found in propolis that exhibit an antioxidant activity include the amyrins with a triterpenoid structure [15]
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