Antioxidant and radical-scavenging activities of Slovak honeys – An electron paramagnetic resonance study

The antioxidant properties of 15 honey samples from different floral sources and various Slovak regions were investigated by means of electron paramagnetic resonance spectroscopy. Cation radical of ABTS (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) diammonium salt), DPPH (1,1-diphenyl-2-picrylhydrazyl) and hydroxyl radicals generated by the photochemical decomposition of hydrogen peroxide were used as oxidants. The antioxidant activities found with ABTS+, expressed as trolox equivalent antioxidant capacity (TEAC), ranged from 0.15 to 1.14 mmol kg−1, and those determined with DPPH, from 0.04 to 0.32 mmol kg−1. TEAC values correlated well with results found by elimination of DPPH, and both values revealed a linear relationship with the concentration of phenolics obtained with the Folin–Ciocalteu phenol test (expressed as gallic acid equivalents, GAE). The colour coordinates (CIE L∗a∗b∗), as well as reflectance spectra determined for original honeys using a white background, demonstrated that the colour difference (ΔE∗) and coordinate b∗ interrelate with TEAC values. The radical-scavenging capacities (RSC) of the honey samples determined in the experiments with photochemically decomposed hydrogen peroxide, generating reactive OH radicals in the presence of spin trapping agent, differ from those found with ABTS+ and DPPH. Here, probably, the reactive OH radicals, having higher redox potential, are scavenged by a variety of compounds not effective with ABTS+ and DPPH (e.g., saccharides, proteins).