Iodine-iodide Redox Assay
The iodine-iodide redox assay, also known as the Folin-Ciocalteu method, is a versatile and highly sensitive biochemical assay used to assay total reducing capacity in a given sample of amphiphilic compounds. Through the use of colorimetric detection reagents, it allows the measurement of antioxidant levels in a wide range of sample matrices such as food, drugs, and dietary supplements. The effectiveness of a sample is classified by its capacity to reduce the oxidized form of iodine (iodide) and thus, the ability of the sample to donate electrons.
The concept of an iodine-iodide redox assay can be broken down into two sections. The first section is the reduction (donation of electrons), and the second is oxidation (acceptance of electrons). In order to complete the redox reaction both an electron acceptor and an electron donor are required. The iodine-iodide redox assay is based upon the mechanism of iodide being reduced to iodine by the electron rich compounds found in food, drugs, and dietary supplements. To measure the reduction capacity of the sample, a chromogen (a chemical that becomes colored upon a reaction) such as the Folin-Ciocalteu reagent is used. The Folin-Ciocalteu reagent contains a chromophore, or a large molecule that absorbs light, which will absorb light, in this case blue light, and is then excited by the presence of iodine produced by the electron donor. If a sample has a high reducing capacity, it will result in an increased absorption of light at a wavelength of approximately 660nm when excited by the blue light source.
The Folin Ciocalteu reagent can be used in the iodine-iodide redox assay to measure both the total reducing capacity and total polyphenol content of a sample. To measure the total polyphenol content, a sample is diluted with a fixed volume of sodium carbonate and then is subsequently treated with the Folin Ciocalteu reagent. The polyphenols in the sample are then oxidized by the sodium carbonate and the reaction with the Folin Ciocalteu reagent results in a blue/purple color that is proportional to the polyphenol content in the sample.
To measure the total reducing capacity of a sample, the Folin Ciocalteu reagent is added to an iodide solution and then the sample is added. This results in the iodide in the solution being reduced to iodine and thus, a colored solution is produced that is proportional to the reducing capacity of the sample. The absorbance of the colored solution is then measured with a spectrophotometer at a specific wavelength.
The iodine-iodide redox assay is a powerful and widely used method of measuring the antioxidant potential of a sample. The assay is highly sensitive and is able to detect the amount of antioxidants in a sample even when the sample has reduced levels. Through the use of a chromogen and the Folin-Ciocalteu reagent, the assay is capable of measuring both the total reducing capacity and total polyphenol content of a sample. Furthermore, the assay is also widely used in the field of food science as it is able to detect the levels of antioxidants in a wide range of food and beverage matrices, including fruits, vegetables, grains, and even dairy products.
