Methods for determining the efficacy of radical-trapping antioxidants

Hydrocarbon autoxidation is the free radical chain reaction primarily responsible for the oxidative degradation of organic materials, including those that make up cells, tissues, and organs. The identification of compounds that slow this process (antioxidants) and the quantitation of their efficacies have long been goals of academic and industrial researchers. Antioxidants are generally divided into two types: preventive and radical-trapping (also commonly referred to as chain-breaking). Preventive antioxidants slow the rate of initiation of autoxidation, whereas radical-trapping antioxidants slow the rate of propagation by reacting with chain-propagating peroxyl radicals. The purpose of this review is to provide a comprehensive overview of different approaches to measure the kinetics of the reactions of radical-trapping antioxidants with peroxyl radicals, and their use to study the inhibition of hydrocarbon (lipid) autoxidation in homogeneous solution, as well as biphasic media (lipid bilayers) and cell culture. Direct and indirect approaches are presented and advantages and disadvantages of each are discussed in order to facilitate method selection for investigators seeking to address particular questions in this immensely popular field. •Radical-trapping antioxidants (RTAs) slow the rate of hydrocarbon (lipid) autoxidation by reacting with chain-carrying peroxyl radicals.•Excellent methods are available to determine the kinetics of RTAs with peroxyl radicals in solution and biphasic media, such as liposomes.•Data obtained in cell-based assays are difficult to interpret, and should be guided by consideration of the data in solution, and biphasic media.•Advantages and disadvantages of commonly used methods for determining “antioxidant activity” are presented and discussed.