Abstract
The phenolic acid profile of honey depends greatly on its botanical and geographical origin. In this study, we carried out a quantitative analysis of phenolic acids in the ethyl acetate extract of 12 honeys collected from various regions in Greece. Our findings indicate that protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid and p-coumaric acid are the major phenolic acids of the honeys examined. Conifer tree honey (from pine and fir) contained significantly higher concentrations of protocatechuic and caffeic acid (mean: 6640 and 397 µg/kg honey respectively) than thyme and citrus honey (mean of protocatechuic and caffeic acid: 437.6 and 116 µg/kg honey respectively). p-Hydroxybenzoic acid was the dominant compound in thyme honeys (mean: 1252.5 µg/kg honey). We further examined the antioxidant potential (ORAC assay) of the extracts, their ability to influence viability of prostate cancer (PC-3) and breast cancer (MCF-7) cells as well as their lowering effect on TNF- α-induced adhesion molecule expression in endothelial cells (HAEC). ORAC values of Greek honeys ranged from 415 to 2129 µmol Trolox equivalent/kg honey and correlated significantly with their content in protocatechuic acid (p<0.001), p-hydroxybenzoic acid (p<0.01), vanillic acid (p<0.05), caffeic acid (p<0.01), p-coumaric acid (p<0.001) and their total phenolic content (p<0.001). Honey extracts reduced significantly the viability of PC-3 and MCF-7 cells as well as the expression of adhesion molecules in HAEC. Importantly, vanillic acid content correlated significantly with anticancer activity in PC-3 and MCF-7 cells (p<0.01, p<0.05 respectively). Protocatechuic acid, vanillic acid and total phenolic content correlated significantly with the inhibition of VCAM-1 expression (p<0.05, p<0.05 and p<0.01 respectively). In conclusion, Greek honeys are rich in phenolic acids, in particular protocatechuic and p-hydroxybenzoic acid and exhibit significant antioxidant, anticancer and antiatherogenic activities which may be attributed, at least in part, to their phenolic acid content.