Identification of Resveratrol as Bioactive Compound of Propolis from Western Romania and Characterization of Phenolic Profile and Antioxidant Activity of Ethanolic Extracts

The present study aimed to assess the phenolic content of eight ethanolic propolis samples (P1-P8) harvested from different regions of Western Romania and their antioxidant activity. The mean value of total phenolic content was 214 +/- 48 mg gallic acid equivalents (GAE)/g propolis. All extracts contained kaempferol (514.02 +/- 114.80 mu g/mL), quercetin (124.64 +/- 95.86 mu g/mL), rosmarinic acid (58.03 +/- 20.08 mu g/mL), and resveratrol (48.59 +/- 59.52 mu g/mL) assessed by LC-MS. The antioxidant activity was evaluated using 2 methods: (i) DPPH (2,2-diphenyl-1-picrylhydrazyl) assay using ascorbic acid as standard antioxidant and (ii) FOX (Ferrous iron xylenol orange OXidation) assay using catalase as hydrogen peroxide (H2O2) scavenger. The DPPH radical scavenging activity was determined for all samples applied in 6 concentrations (10, 5, 3, 1.5, 0.5 and 0.3 mg/mL). IC50 varied from 0.0700 to 0.9320 mg/mL (IC50 of ascorbic acid = 0.0757 mg/mL). The % of H2O2 inhibition in FOX assay was assessed for P1, P2, P3, P4 and P8 applied in 2 concentrations (5 and 0.5 mg/mL). A significant H2O2% inhibition was obtained for these samples for the lowest concentration. We firstly report the presence of resveratrol as bioactive compound in Western Romanian propolis. The principal component analysis revealed clustering of the propolis samples according to the polyphenolic profile similarity.