FolinCiocalteu

Folin-Ciocalteu reagent, or Folin-Ciocalteu phenol reagent, is a mixture of phosphomolybdate and phosphotungstate used in a colorimetric assay to estimate total phenolic content in plant-derived samples, such as foods, beverages, and extracts. The reagent is named after Otto Folin and the Romanian chemist Ciocalteu. In the assay, reducing substances present in the sample reduce the reagent under alkaline conditions, producing a blue complex that absorbs light around 725 to 765 nm. The intensity of the blue color is proportional to the sample’s reducing capacity, and results are typically expressed as gallic acid equivalents (GAE) using a gallic acid standard curve.

Typical procedure involves extracting phenolics from the sample, reacting the extract with Folin-Ciocalteu reagent, adding sodium carbonate to alkalinize the mixture, incubating, and measuring absorbance with a spectrophotometer. The method is favored for its simplicity, speed, and broad applicability across diverse sample types. However, it is not specific to phenolics; any reducing agent—such as ascorbic acid, reducing sugars, certain organic acids, or some proteins—can contribute to the signal, potentially inflating estimates of phenolic content. Therefore, results reflect total reducing capacity rather than an absolute phenolic concentration, and extraction, standards, and blank corrections influence values.

History and usage: the assay was introduced in 1927 by Folin and Ciocalteu and has since become a standard technique in food chemistry and plant analysis for rapid assessment of phenolic content. Various modifications exist, including different reaction times, reagent formulations, and measurement wavelengths, but the underlying principle remains the same.