An insight into quantitative, qualitative, and analytical methods for the measurement of antioxidant activity through various assays

In every cell, several redox reactions occur, leading to free radical formation like reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulphur species (RSS). These reactive species have a high affinity to bind with biomolecules like DNA, lipids, and proteins, and affect the usual functioning of the body, which leads to various ailments like inflammation, cancer, cardiovascular disease, and atherosclerosis. Oxidative stress occurs as a result of the excessive production of free radicals. These free radicals are neutralized by antioxidants and protect our body from disease. The antioxidants can be divided into synthetic antioxidants (butylated hydroxy anisole (BHA), tertiary butylhydroquinone (TBHQ), butylated hydroxytoluene (BHT), etc.) and natural antioxidants (flavonoids, ascorbic acid, polyphenols, carotenoids, and tocopherols, etc.). As compared to natural antioxidants, synthetic antioxidants have adverse effects on the human body. In the human body, enzymatic antioxidants are present, which fight with reactive oxygen species. There are three major classes of enzymatic antioxidants viz glutathione-S-transferase, superoxide dismutase, and catalase. Plants are the main source of natural antioxidants, and to determine antioxidant activities, different assays are used. In this review, we provide particulars of assays with quantitative, qualitative, and analytical methods to measure antioxidant activities. These assays provide a general diagnostic tool to test the antioxidant activity.