Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2004
Publication Date: 2/25/2005
Citation: Huang, D., Ou, B., Prior, R.L. 2005. The chemistry behind dietary antioxidant capacity assays. Journal of Agricultural and Food Chemistry. 3(6):1841-1856. Interpretive Summary: Clinical trials and epidemiological studies have established an inverse correlation between the intake of fruits/vegetables and occurrence of diseases such as cardiovascular diseases, cancer, and age related disorders. Dietary antioxidants are believed to be effective nutrients in prevention of these oxidative stress related diseases. Antioxidants have thus become a topic of increasing interest. A literature search on pubmed.gov revealed that the number of publications on antioxidants and oxidative stress has nearly quadrupled in the past ten years (857 in 1992, 2091 in 1998, 3148 in 2002). Due to the complexity of the composition of foods, separation and quantitation of each antioxidant compound to study them individually is costly and inefficient, notwithstanding the possible synergistic interactions among the antioxidant compounds in a food mixture. Therefore it is very appealing to researchers to have a convenient method of quantitation of total antioxidant capacity using one chemical reaction. As a result, there are numerous methods published claiming to measure total antioxidant capacity in vitro. Ironically, the biggest problem is the lack of a validated assay that can faithfully quantify antioxidant capacity of foods and biological samples. In this review we have summarized numerous methods and the advantages and disadvantages of each in order to help develop some consensus of opinion in the complex area of antioxidant chemistry.
Technical Abstract: In this review, we summarize the multi-faceted aspects of antioxidants and the basic kinetic models of inhibited autoxidation and analyze chemical principles of antioxidant capacity assays. Depending on the reactions involved, these assays can be classified into two types: assays based on hydrogen atom transfer (HAT) reactions and single electron transfer (SET) reaction based assays. The majority of HAT based assays involve a competition reaction scheme, where antioxidant and substrate compete for thermally generated peroxyl radicals. These assays include inhibition of induced-LDL autoxidation, oxygen radical absorbance capacity (ORAC), total radical trapping antioxidant parameter (TRAP), and crocin bleaching assays. SET based assays measure the capacity of an antioxidant to reduce a single electron oxidant, which changes color when reduced. The degree of color change is correlated with the sample antioxidant concentrations. SET based assays include Trolox equivalence antioxidant capacity (TEAC), ferric ion reducing antioxidant power (FRAP), and 'total antioxidant potential' assay using a Cu(II) complex as an oxidant. The pros and cons of these assays are analyzed based on respective reactions and quantitation approaches. In addition, we also briefly summarized other assays intended to measure a samples scavenging capacity of biologically relevant oxidants such as singlet oxygen, superoxide anion, peroxynitrite, and hydroxyl radical.