title: Evaluation of antioxidative activity of Croatian propolis samples using DPPH* and ABTS*+ stable free radical assays.
abstract: Propolis is one of the richest sources of plant phenolics (flavonoids and phenolic acids), which are widely recognized as rather strong antioxidants. The aim of our work was to use colored stable free radical (DPPH* and ABTS*+) spectrophotometric and thin-layer chromatographic (TLC) assays to study the antioxidative behavior of the phenolics (caffeic acid, galangin and pinocembrin) most commonly present in Croatian propolis samples obtained from different Croatian regions. We propose a mathematical model providing a more sophisticated interpretation of the obtained results and a new parameter named antioxidative efficiency (AOE) is introduced. The kinetic behaviour of chosen standards determined by spectrophotometric assays follows the exponential decrease of the absorption curve. Explained numerically, AOE represents the absolute value of the first derivative of an absorbance curve in the point A0/e (where A0 is the absorbance measured at t = 0 and e is the natural logarithm base). The advantage of this newly introduced parameter is that it provides an easy and accurate mutual comparison between the rates of antioxidative efficiency of different propolis samples. A TLC assay was only applicable in the case of the DPPH* radical. Dose-response curves were described using a linear function with AOE expressed as a coefficient of the slope. The chromatographic method was shown to be very rapid, reliable and easy-to-perform.
authors.affiliation: Department of Medicinal Chemistry, Faculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovacica 1, 10000 Zagreb, Croatia.
authors.forename: Ivona
authors.initials: I
authors.lastname: Jasprica
authors.forename: Mirza
authors.initials: M
authors.lastname: Bojic
authors.forename: Ana
authors.initials: A
authors.lastname: Mornar
authors.forename: Erim
authors.initials: E
authors.lastname: Besic
authors.forename: Kajo
authors.initials: K
authors.lastname: Bucan
authors.forename: Marica
authors.initials: M
authors.lastname: Medic-Saric
mesh_terms: D000975:Antioxidants / Q000494:pharmacology*; D052160:Benzothiazoles; D001713:Biphenyl Compounds / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D004353:Drug Evaluation, Preclinical; D005609:Free Radicals; D006834:Hydrazines / Q000737:chemistry*; D010851:Picrates; D011429:Propolis / Q000494:pharmacology*; D013056:Spectrophotometry, Ultraviolet; D013451:Sulfonic Acids / Q000737:chemistry*; D013844:Thiazoles / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D052160:Benzothiazoles; D001713:Biphenyl Compounds; D005609:Free Radicals; D006834:Hydrazines; D010851:Picrates; D013451:Sulfonic Acids; D013844:Thiazoles; C002502:2,2'-azino-di-(3-ethylbenzothiazoline)-6-sulfonic acid; D011429:Propolis; C004931:1,1-diphenyl-2-picrylhydrazyl