Antioxidant properties of BHT estimated by ABTS assay in systems differing in pH or metal ion or water concentration

Antioxidant activity (capacity or potential) is widely used as parameter to characterize different substances and mixtures, which is able to scavenge or neutralize free radicals. Recently, ABTS assay has been the most widely employed method for estimating antioxidant activity. The method is based on the spectrophotometric measurement of ABTS cation radical (ABTS•+) concentration changes resulting from the ABTS•+ reaction with antioxidants. Yet little is known about factors influencing the kinetics that reaction i.e., about factors affecting the estimation of antioxidant activity of examined compounds’. The paper shows that metal ion type and concentration, water content and pH of the measuring system all significantly influence the estimation of antioxidant activity in ABTS assay and thus make the estimation of correct antioxidant properties of plant and food extracts difficult. Butylhydroxytoluene (BHT) was used as standard antioxidant in the performed experiments. The relationships discussed in this paper indicate the necessity of standardizing the ABTS method and reveal the complexity of estimating adequate antioxidant activity of examined substances.