Fe3+ Reducing Power as the Most Common Assay for Understanding the Biological Functions of Antioxidants

Antioxidants counteract the harmful effects of free radicals on metabolism and prevent fatty food degradation during processing and storage. The Fe3+-reducing assay, based on reduction of ferric ions (Fe3+) to ferrous ions (Fe2+) in the presence of antioxidants acting as reducing agents, is widely recognized and used to evaluate the antioxidant capacity of various biological samples, including plant extracts, food, beverages, and pharmaceuticals. Reduction of Fe3+ to Fe2+ is also crucial in biogeochemical cycling, microbial metabolism, and industrial applications. This review comprehensively describes the Fe3+-reducing assay, its adaptation to different analytes, identification of the most potent antioxidants, and optimization of measurement techniques. It outlines the chemical and fundamental principles of Fe3+ reducing ability, along with an in-depth analysis of Fe3+-reducing activity, covering biochemical mechanisms, microbial contributions, analytical methods, and practical applications along with recent advances and future perspectives in Fe3+ reduction research. The assay is straightforward, testing compounds or plant extracts are mixed with an Fe3+ solution, and their absorbance is measured after a specific incubation period. Despite significant advancements in analytical instrumentation and techniques, this method remains largely unchanged.